Ultrafast Science & Technology Spain 2026 − USTS 2026

18 Nov 2026, 09:00 → 20 Nov 2026, 19:00 Europe/Madrid

📍 IGFAE, Santiago de Compostela

Aaron Alejo Alonso (Universidade de Santiago de Compostela)

Welcome to the VI Edition of the Ultrafast Science and Technology 2026, a three-day event which aims to bring together researchers, partners and companies whose development, innovation and research areas are linked to the field of ultrafast laser and their applicability in Physics, Chemistry, Medicine, or Material Science.

Organised by the Specialised Group in Ultrafast Lasers (GELUR) from the Spanish Physics Royal Society (RSEF), USTS 2026 aims to interconnect and increase Spanish activity around ultra-fast and ultra-intense laser applications and to promote collaborations in the fields of ultra-fast materials processing, chemistry and molecular dynamics, biophysics, particle acceleration, plasma physics, and quantum science and technology.

The event will be held at the Galician Institute of High Energy Physics (IGFAE) of the Universidade de Santiago de Compostela in Santiago de Compostela on November 18^th-20^th 2026.

 

The organisation encourages all researchers and their teams to submit their applications:

Regular registration is currently open.

 

Satellite event: Matter in Action! Fall School

For the first time, the USTS conference will have a satellite event: the Fall School "Matter in Action", co-organised in conjunction with the MATRIX-CM (Matter in Action with UlTRafast OptIcal and X-ray Lasers – Comunidad de Madrid) network. The school will take place at the IGFAE premises on the 16^th and 17^th of November, and will include tutorial lectures by prestigious international researchers, as well as a session where students will be encouraged to present their work.

 

Registration to the Fall school is now closed.

 

---

Organised by

              

 

With collaboration from

   

 

 

USTS2026_AbstractTemplate.docx

Wednesday 18 November

09:30 → 11:00 Registration

11:00 → 13:25 Oral: Session 1

11:00 Opening

11:30 Ultrafast Molecular Science with Soft X-ray Free-Electron Lasers

Many molecular light-energy conversion processes in nature occur on an ultrafast (sub-picosecond) timescale, such as retinal light harvesting, optical switching of green and yellow fluorescent proteins, and nucleobase photoprotection. The conversion process often occurs at conical intersections, which are regions in molecular phase space characterized by degenerate potential energy surfaces and a linear lifting of energy degeneracy.

To fully monitor and understand the ultrafast dynamics of a molecule, a combined knowledge of two subsystems—nuclear geometry and electronic structure—is required. Specifically, this involves understanding the molecular geometry changes that drive the molecule toward regions of strong coupling among electronic states, as well as the resulting changes in these states.

In this talk, I will show how time-resolved soft X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) of isolated molecules at free-electron lasers are used to obtain information on the changes in the molecular electronic structure during photoexcited molecular dynamics. The element- and site-selective nature of this method allows us to gather information about valence charge dynamics with angstrom precision in space and on a femtosecond timescale. I will highlight the power of these methods with a couple of molecular processes from internal conversion and photoinduced isomerization[1,2].

To investigate the light-induced changes in molecular geometry, we employ Coulomb-Explosion Imaging, a method that utilizes an intense and short X-ray pulse to highly ionize the molecules and subsequently resolve the momenta of the exploding molecular fragments. We use hydrogen atoms as messengers and discover the deplanarization of the molecular geometry on its path toward the conical intersection. The combination of both methods provides unprecedented experimental insight into the light-energy conversion dynamics in molecules[3].

In the last part of the talk, I will give an overview of the free-electron laser FLASH at DESY in Hamburg and its current upgrade process to highlight new opportunities for the ultrafast molecular and materials community at FLASH.

References
[1] Mayer D, Lever F, Picconi D et al., 2022 Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy Nat. Commun. 13 198
[2] Lever F, Picconi D, Mayer D et al., 2025 Direct Observation of the ππ to nπ Transition in 2-Thiouracil via Time-Resolved NEXAFS Spectroscopy J. Phys. Chem. Lett. 16 4038–46
[3] Jahnke T, Mai S et al., 2025 Direct observation of ultrafast symmetry reduction during internal conversion of 2-thiouracil using Coulomb explosion imaging Nat. Commun. 16 2074

Speaker: Markus Guehr (Deutsches Elektronen-Synchrotron (DESY))

12:15 Disruptive Probing: Revealing Hidden Reaction Pathways in Molecular Ions and Clusters

Disruptive probing reveals reaction pathways that are hidden in conventional mass spectra by following how a delayed laser pulse redirects evolving molecular ions and clusters into specific fragment channels [1]. Here we combine femtosecond strong-field ionization, time-resolved mass spectrometry, and ab initio molecular dynamics simulations to investigate H3+ formation in methylamine, methanol, and ethanol. This comparison shows that H3+ production is strongly influenced by the hydrogen bound to the heteroatom, whose role changes across the amine and alcohol series as molecular structure controls hydrogen migration, H2 roaming, and proton-abstraction pathways. We then extend the approach to methanol and ethanol clusters, where hydrogen bonding opens intermolecular proton-transfer and relaxation pathways not available in isolated molecules. In ethanol clusters, disruptive probing also identifies channels in which ethanol undergoes demethylation, revealing additional fragmentation pathways enabled by clustering. Together, these results show that disruptive probing provides a general strategy for uncovering hidden ultrafast reaction pathways in molecular ions and clusters.

Speaker: Marcos Dantus (Michigan State University)

12:40 Femtosecond Resonant Coulomb Explosion Imaging of Methyl Iodide Dimers

Evidence of resonant Coulomb explosion imaging induced by low-intensity femtosecond UV-pump UV-probe pulses is presented and applied to the investigation of the methyl iodide molecular dimer, (CH$_3$)$_2$. Since the UV-pump leads to excitation and dissociation of both monomers, and the UV-probe is configured to resonantly enhance ionization of a specic fragment, iodine or methyl, Coulomb repulsion between the two fragment ions takes place, which is detected by velocity map imaging (VMI). The time dependent fragment translational energy distributions are shown to provide relevant information on the initial geometry of the dimer. The experimental results are complemented by electronic structure calculations followed by semiclassical trajectories to further support the proposed approach. The direct correlation between the time-resolved Coulomb explosion trajectories of the nascent fragments and the original dimer geometry exploits a novel methodology for the investigation of cluster dynamics and structural characterization.

Speaker: Ignacio M. Casasús (Universidad Complutense de Madrid)

12:55 Photoinduced charge transfer in rylene diimide monomers, oligomers and polymers

Three examples of charge transfer processes in rylene diimide molecules and macromolecules will be discussed using ultrafast transient absorption spectroscopy (TAS) results. First, the photoinduced charge transfer dynamics in luminescent donor-acceptor polymers and copolymers1 that use a single naphthalene diimide (NDI) as acceptor, polystyrene chains as primary donor, and secondary stronger-donor chains, will be presented. Here, TAS shows that electron transfer (ET) process occurs mostly intrachain when in solution, while in the spin-coated films the ET occurs mostly interchain. Our results also show that excitation at the red-edge of the NDI absorption band prompts the population of highly coupled pairs. This is the first study on this type of polymers.

In the second part, we will examine charge-transfer processes within three perylene diimide (PDI) chromophores forming a cage that undergoes photoinduced symmetry-breaking charge separation (SB-CS) i.e., ET occurs between two PDIs yielding the PDI•- and PDI•+ radicals2. We will show how a six-parameter kinetic model allows us to successfully interpret the femtosecond to microsecond TAS data while ensuring a single solution for the time constants using the biexponential fluorescence lifetimes and amplitudes as constraints. This approach can be extended to the analysis of similar systems that also display thermally-activated delayed fluorescence (TADF).

Finally, we will dive into the quenching of PDI•- in the excited state, which can be used as a photocatalyst for the reduction of aryl halides in the controversial con-PET (consecutive-photoinduced electron transfer) mechanism. Our TAS results were obtained using a combination of pump-probe and pump-pump probe3,4 strategies. They demonstrate that static quenching between PDI•- and the aryl halide 4-bromoacetophenone (BAP) is operative and plays a major role in this system, yielding a small (1%) quantum yield of this mechanism. Our molecular dynamics simulations show that preassociation is not necessary for static quenching, and rather, a high probability of finding a BAP molecule in the vicinity of PDI•- (a condition fulfilled at high concentrations of this quencher) is sufficient to have electron transfer without the need for diffusion. This study brings into question the challenges faced using radical species as photocatalysts.

Speaker: Estefania Sucre-Rosales (University of Geneva)

13:10 Ultrafast mapping of magnetic-field generation in laser-solid interactions using LWFA electron beams

The generation of strong, transient magnetic fields is a defining characteristic of relativistic laser-solid interactions, playing a pivotal role in phenomena ranging from Target Normal Sheath Acceleration (TNSA) to micro-turbulent plasma instabilities. When high-intensity laser pulses irradiate overdense plasma targets, they drive complex, high-current electron dynamics that rapidly manifest as strong volumetric magnetic fields. Because these fields evolve on femtosecond timescales and at submicron spatial dimensions, capturing their detailed spatiotemporal dynamics has long posed a significant diagnostic challenge. Understanding these field generation mechanisms is essential, as they profoundly influence fast-electron transport, particle acceleration efficiency, and can provide a controlled platform for exploring laboratory astrophysics.

To resolve these ultrafast structures, we carried out a series of experimental campaigns at the Laboratoire d'Optique Appliquée (LOA) using a 100-TW, 1-Hz laser system1,2. We implemented a pump-probe scheme where laser-wakefield-accelerated (LWFA) electron beams were utilized as synchronized, low-emittance relativistic probes. By passing these high-energy electron bunches through the interaction zone, the strong magnetic fields deflected the probe particles, mapping the volumetric field profile directly onto the beam’s angular distribution. This deflectometry technique successfully captured the femtosecond-scale evolution of strong magnetic-field fluctuations. Complementary, fully relativistic particle-in-cell (PIC) simulations confirmed that these fluctuations grow to amplitudes capable of significantly broadening the probe bunch distribution just tens of femtoseconds after the laser pulse peak.

These results demonstrate the power of synchronized LWFA electron beams as a high-resolution, ultrafast diagnostic tool for extreme high-field plasma environments. By showing that relativistic electron probes can faithfully resolve transient field structures, these campaigns establish a robust framework for investigating the real-time dynamics of laser-driven plasma instabilities and particle acceleration mechanisms. Ultimately, these capabilities open new pathways for optimizing laser-driven ion sources, mitigating detrimental transport effects in fusion-relevant schemes, and deeping our understanding of cosmic magnetic field generation through scaled laboratory experiments.

Speaker: PABLO SAN MIGUEL CLAVERIA (Universidad Politécnica de Madrid)

13:25 → 15:00 Lunch break

15:00 → 16:30 Oral: Session 2

15:00 Nanoscale probing of ultrafast optical phenomena using free electrons

Ultrafast electron microscopy has emerged as a research frontier, enabling the investigation of material excitations with an unparalleled combination of spatial and temporal resolution. Beyond their role as classical probes, free electrons have unique quantum properties that make them attractive resources for quantum nanophotonics and open fundamentally new avenues for quantum technologies. In this talk, we will discuss the fundamental principles governing the interactions among free electrons, light, and photonic nanostructures, with an emphasis on quantum phenomena such as electron decoherence induced by coupling to radiative modes and the generation and manipulation of quantum states of light. We will show how radiative decoherence can be harnessed for quantum sensing applications, including the interaction-free detection of distant objects and the measurement of vacuum temperature. We will also demonstrate how quantum correlations between electrons and waveguided polaritons enable the generation of single and entangled photons heralded by measurements of electron energy loss and angular deflection. Finally, we will discuss emerging opportunities for quantum sensing and metrology based on free electrons, as well as prospects for generating zeptosecond electron pulses to probe material excitations at unprecedented spatiotemporal scales.

Speaker: Prof. F. Javier García de Abajo (ICFO-Institut de Ciencies Fotoniques)

16:00 3D multiscale modelling of the interaction of HOH carrying OAM with inhomogeneous plasmas: applications to plasma diagnosis

This work presents recent results on the interaction of structured light with plasmas. Experimental and modelling results unveil its potential applications in plasma diagnosis, especially in the fields of Inertial Confinement Fusion (ICF), plasma based soft X-ray lasers and Laboratory Astrophysics. The full propagation + interaction with plasma process can be modelled using our multiscale, multiphysics computational framework [1]. This framework takes into account plasma creation and its posterior hydrodynamic expansion; the related collisional and radiative processes; and the propagation and amplification of UV/XUV beams.

The interaction of structured IR beams (taking advantage of spatio-temporal couplings to implement a flying focus) [2] and the posterior interaction of High Order Harmonics carrying Orbital Angular Momentum will be presented, stressing applications towards diagnosing hot, dense plasmas [3,4,5], by measuring the perturbation of the HOH wavefront after propagation through the plasma and relating this perturbation to the electron density and its gradient. Finally, we will present the generation of Stokes skyrmions from second harmonic generation in nitrogen plasmas [6].

Figure 1: (left) 3D intensity distribution of an amplified XUV seed carrying OAM along with ASE. (right) Initial (upper figure) wavefront of a l=25 Laguerre-Gauss HOH and perturbed wavefront (lower figure) of the same HOH after amplification through a plasma.

Notes and References
1 E. Oliva, et al, “3D multi-scale modelling of plasma-based seeded soft X-ray lasers”, The European Physical Journal D, 75, 11 (2021)
2 A. Kabacinski, et al, “Spatio-temporal couplings for controlling group velocity in longitudinally pumped seeded soft X-ray lasers”, Nat. Phot. 17, 345-359 (2023)
3 F. Tuitje, et al, “Nonlinear ionization dynamics of hot dense plasma observed in a laser-plasma amplifier”, Light: Sci Appl, 9, 1 (2020)
4 S. López, et al, “Conservation of Orbital Angular Momentum throughout amplification of high order harmonics in Ni-like krypton and silver plasmas”, Opt. Exp., 31, 5, 8465-8478 (2023)
5 S. López, et al, “Diagnosing the electron density of plasma amplifiers using XUV vortex beams”, Opt. Exp., 33, 22, 46285-46303 (2025)
6 M. G. Barriopedro, E. Oliva and M. A. Porras, “Spontaneous optical skyrmion generation by frequency doubling in underdense plasmas”, arXiv preprint arXiv:2605.03145 (2026)

Speaker: Eduardo Oliva Gonzalo (Universidad Politécnica de Madrid)

16:15 Probing Surface Light Localization in Topological Multilayers via Surface Second-Harmonic Generation

In this work we design and study a dielectric multilayer with a geometry implementing the topological Su-Schrieffer-Heeger (SSH) model1,2 supporting a strong electromagnetic field localization at the surface, which enhances linear and nonlinear optical interactions. We study second harmonic generation (SHG) from the multilayer and use it as an indirect measurement of the localized surface mode.

The studied structure consists of alternating SiO2 and Ta2O5 layers arranged following the SSH geometry, as schematically shown in Fig. 1. The multilayer is deposited on a prism in order to excite the surface modes using the Kretschmann configuration3. By selecting different truncations of the multilayer, the structure can have either a topologically non-trivial (Type 1) or trivial (Type 2) phase, which gives two structures with identical periodicity but different surface properties2.

Numerical calculations, using the transfer matrix method, reveal a highly confined surface mode in the Type 1 structure, while no localized mode is supported by the Type 2 multilayer (Fig. 1 Left). The surface mode shows strong field localization at the last layer for a wavelength of 800 nm and incident angle of 68.1º, achieving 300-fold field enhancement. In the Type 2 structure, on the other hand, there is no localization at the surface.

The increase of the confined field at the surface strengthens light-matter interactions, producing an enhancement of the nonlinear (NL) processes. In particular, since TaO2 and SiO2 are centrosymmetric materials, the expected SHG originates primarily from surface contributions and magnetic-field-induced mechanisms. In the present configuration we use the measurement of the SHG as a tool to sense the field localization on the superficial layer of the structure of Type 1. SHG measurements were performed in reflection using a tunable femtosecond laser source, with a pulse duration of 180 fs and peak intensity of 9 GW/cm2. As seen in figure 1, SHG efficiency shows a clear enhancement for the Type 1 sample compared to the Type 2 one, which has a nearly negligible signal. Moreover, Type 1 NL spectrum shows chromatic sensibility: the maximum efficiency is achieved around the resonance wavelength of the mode, 800 nm. Meanwhile, Type 2 SH signal remains flat along the measured wavelength. Experimental results show good agreement with simulations of the NL response. In addition, simulations show that the efficiencies are sensible to pulse duration, showing that the pulse bandwidth also matters.

These results show a direct link between topological field localization and enhanced harmonic generation, proving that the SHG comes only from the excitation of the surface mode in Type 1 structure.

Speaker: Eva Otero Picon (Universitat Politècnica de Catalunya)

16:30 → 17:30 Poster + Coffee: Poster session 1

16:30 Bimolecular process in bidimensional NiPS3

NiPS₃, a member of the metal phosphotrichalcogenide family, consists of crystalline layers strongly bonded within planes that are held together by weaker van der Waals forces. Quantum confinement effects promote the formation of tightly bound excitons, endowing NiPS₃ with properties of interest for applications in electrocatalysis and optoelectronic devices – such as transistors, photodetectors, and energy conversion systems – due to its tunable bandgap around 1.4 eV. Below its Néel temperature (150 K), the antiparallel alignment of nickel magnetic moments leads to antiferromagnetic ordering, opening opportunities for spintronic, magneto-optical, and magnetic storage applications, as well as for exploring two-dimensional magnetism. Notably, many-body phenomena such as collective excitonic states have also been observed below 150 K.

In this work, we employ time-resolved absorption spectroscopy (TAS) to investigate the ultrafast dynamics of charge carriers in NiPS₃. The transient response reveals a bimolecular relaxation process followed by a slower exponential decay, providing insights into carrier recombination pathways in this layered antiferromagnetic semiconductor. Temperature-dependent excitonic emission was also studied to gain insight into NiPS₃ photophysics.

Speaker: Sebastián Mesa Apestegui (IMDEA Nanoscience)

16:30 Chirp-Dependent Control of Low-Frequency Vibronic Dynamics in High-Performance Donor Polymers for Organic Solar Cells

Understanding and controlling ultrafast vibronic dynamics of conjugated donor polymers is crucial for further advancing exciton transport and charge separation in organic solar cells (OSCs). In this contribution, we demonstrate the first application of the chirp-dependent time-resolved (CDTR) photoluminescence double-pump technique to relevant donor materials: PM6, PBDB-T, and PBDB-T thin films with added Chloronaphthalene (CN) [1].
By employing programmable pulse shaping with a pair of phase-locked femtosecond pulses with one transform-limited (TL) and one linearly chirped pulse, we are able to record two-dimensional CDTR photoluminescence maps under near-resonant excitation of the (intra-molecular) charge-transfer state. This approach enables us to selectively prepare and investigate vibronic coherences within the excited state of the material under investigation.
In all materials investigated here, pronounced delay-dependent oscillations with periods of 60–80 fs are found to be related to low-frequency vibrational modes of 0.05–0.08 eV associated with torsional and collective motions of the polymer backbone. The oscillation amplitude and phase are found to be strongly dependent on the chirp value and sign. This indicates that the temporal order of spectral components determines the generation of the initial wavepacket. In contrast to this finding, the contribution of high-frequency C=C stretching modes to the CDTR signal is found to be negligible despite being prominent features of the linear absorption spectrum. This underlines the intrinsic selectivity of this technique for low-frequency modes.
In addition to these common features of the investigated materials, material-dependent differences are found for PM6 with a more pronounced and longer-lived coherence related to its higher structural order compared to PBDB-T. Pristine PBDB-T shows faster dephasing of the oscillation, which improves upon CN doping with enhanced contrast and coherence lifetime due to improved π–π stacking and reduced disorder [2].
The results are supported by simulations of the CDTR signal with a two-level excitonic model coupled to an effective vibrational coordinate and clearly show the interference between the chirped pulse phases and the generation of the wavepacket to be responsible for the population of the excited state. This contribution establishes chirp-dependent double-pump spectroscopy as a powerful tool for tailoring low-frequency vibronic coherence in state-of-the-art OSC donor polymers.

References
[1] Xu, Xin-peng, Richard Hildner, and Elisa Palacino-González. "Selective manipulation of low-frequency modes in conjugated polymers via chirped pulses." The Journal of Chemical Physics 163.17 (2025).
[2] Kroh, Daniel, et al. "Identifying the signatures of intermolecular interactions in blends of PM6 with Y6 and N4 using absorption spectroscopy." Advanced Functional Materials 32.44 (2022): 2205711.
[3] Wang, Xinkang, et al. "High‐efficiency (16.93%) pseudo‐planar heterojunction organic solar cells enabled by binary additives strategy." Advanced Functional Materials 31.33 (2021): 2102291.

Speaker: Shahriar Mohammadi (Zernike Institute for Advanced Materials, University of Groningen)

16:30 Coherent Bound-State Wavepacket Dynamics in Anisole Revealed by UV–XUV Time-Resolved Photoelectron Spectroscopy

Understanding how photoexcited aromatic molecules redistribute energy is central to determining whether excitation leads to photostable relaxation or bond-selective chemistry. Anisole is a model methoxy-substituted aromatic in which bound ππ^states coexist with dissociative πσ^states along the O-CH3 coordinate. Its structured near-ultraviolet absorption band supports bound vibronic levels,¹ whereas methyl elimination is known at higher excitation energies.²˒³ Here, we investigate the early-time dynamics of gas-phase anisole using ultraviolet-extreme-ultraviolet time-resolved photoelectron spectroscopy (UV–XUV TRPES), with excitation at 258, 265, and 278 nm and an approximately 24 eV probe pulse.⁴ At all three wavelengths, the photoelectron signal appears promptly and evolves without abrupt spectral reshaping, delayed continua, or rapid signal loss indicative of prompt transfer to a strongly dissociative state. The response is instrument-response limited at 258 and 265 nm, while excitation at 278 nm shows an additional buildup on an approximately 55 fs timescale. The centre-of-mass of the photoelectron binding-energy distribution exhibits oscillatory modulations arising from coherent vibrational wavepacket motion. Fourier and time–frequency analyses reveal a reproducible component at 930-1030cm-1 across all excitation wavelengths, together with wavelength-dependent contributions at 730-760 cm-1 and weaker features at 1100-1250 cm-1. These coherences decay within approximately 120-160 fs and are assigned predominantly to coupled ring–methoxy motion. Complementary multiconfigurational electronic-structure calculations and surface-hopping simulations indicate confined nuclear motion near the Franck–Condon region or shallow excited-state minima and reproduce vibrational activity in the experimentally observed range. Together, the experimental and theoretical results show that selective excitation between 258 and 278 nm launches coherent vibrational wavepackets within a bound excited-state manifold. Within the temporal window and sensitivity of the measurements, no clear evidence is found for rapid access to the dissociative πσ^*pathway leading to O-CH3 bond cleavage.

Speaker: Kushal Shaw (Universidad Complutense Madrid)

16:30 Coherent propagation of Laser Induced Periodic Surface Structures (LIPSS) by ad-hoc doping of ZnO films

ZnO is a multifunctional transparent conductive oxide (TCO) with many scientific and technologic uses. They include, among others, applications in biomedicine, photonics, sensing or photocatalysis. These applications could benefit in many cases from the use of large-area, electrically anisotropic surfaces (i.e. optically transparent surfaces with alternating highly conductive and highly resistive regions). It has recently been shown that such anisotropies can be induced in other TCO´s, particularly ITO1 and FTO2, by structuring the material surface with fs-laser pulses leading to the formation and of coherently-propagated low spatial frequency (LSF) Laser Induced Periodic Structures (LIPSS).

We have analyzed the role of the carrier density of the material (ne) in the formation and coherent propagation of LIPSS in ZnO films grown by Pulsed Laser Deposition (PLD) ad-hoc doped with small amounts of Yb2O3 (below 5 at. %). This induces n-type conductivity but enables preserving the functional properties of pure ZnO. For ne > 1019 cm-3 coherent propagation of LSF-LIPSS can be successfully achieved upon irradiation with 350 fs and longer pulses at 1030 nm, and laser scan speeds well above 1 m/s.

The ablation mechanism (ZnO sublimation at the LIPSS valleys), and the large melting temperature of ZnO make though the thermal conductivity of the substrate, the film thickness and the irradiation pulse duration to play a determining role in configuring the resulting morphology of the LIPPS propagated over large areas, very especially in avoiding film cracking to preserve the film conductivity along the LIPSS.

Processed surfaces can show conductivities along the LIPSS about hundred times larger than transversally. This enables the development large area applications based on LIPSS-structured surfaces, like gas sensing, or electrothermal transparent devices

Notes and References
1 Lopez-Santos, C., et al, Anisotropic Resistivity Surfaces Produced in ITO Films by Laser-Induced Nanoscale Self-Organization. Adv. Opt. Mater. 2021, 9 202001086. https://doi.org/10.1002/adom.202001086
2 Gomez-Munoz, G., et al., Formation and Coherent Propagation of Laser Induced Periodic Surface Structures (LIPSS) upon Fs-Laser-Irradiation of Fluorine-Doped Tin Oxide: Control, Potential Applications and Challenges. https://doi.org/10.1021/acsami.6c06535

Speaker: Mr Gonzalo Gomez-Munoz (Instituto de Optica-CSIC, Madrid, ES)

16:30 Design of helical structures for the manipulation of laser-accelerated ion beams

Currently, conventional particle accelerators, such as cyclotrons or linear accelerators, can accelerate charged particles to extremely high energies, and are therefore fundamental in applications including hadron therapy, and radioisotope production for medical diagnostics. However, the acceleration gradients in these systems are typically limited to values on the order of tens of MV/m, requiring the construction of large-scale facilities to achieve the energy levels needed for these applications. Laser-based accelerators can reach electric fields of up to $10^{12}$ V/m, orders of magnitude above conventional accelerators, reducing the acceleration distance to the μm scale, which enables the development of more compact and cost-effective alternatives.

Proton acceleration is typically achieved via the Target Normal Sheath Acceleration (TNSA) mechanism, based on the irradiation of a solid target by an ultra-intense laser pulse. Hot electrons generated in this interaction propagate through the target and escape from its rear surface, establishing an intense electrostatic sheath field that accelerates ions from the target's surface impurities. However, the generated ion beams exhibit significant limitations, such as high divergence and broad energy spread. In this work, the use of metallic helical structures coupled to thin solid targets is studied as an alternative to improve the quality of proton beams. The transient electromagnetic pulse guided by the coil enables the focusing, collimation, post-acceleration, and energy selection of protons synchronized with the pulse. The performed analysis demonstrates an effective reduction of the angular divergence of 3-5 MeV protons below 1º and post-acceleration gradients up to 1.5 GeV/m at higher energies. Furthermore, a Monte Carlo particle-tracing code was developed to reproduce the experimental results, yielding beam profiles and energy distributions consistent with the experimental measurements. The simulations are also used to predict the behavior of the helical targets fabricated for our laboratory (Laser Laboratory of Acceleration and Applications, L2A2), showing efficient collimation, energy gains of 2 to 3 MeV, and the formation of narrow, quasi-monoenergetic spectral peaks controllable through the coil pitch.

Speaker: Judith Reyes Martín (Instituto Galego de Física de Altas Enerxías)

16:30 Direct Observation of Ultrafast Charge Transfer and Relaxation in exTTF-Based Dyads

At the heart of any light-harvesting technology, such as artificial photosynthesis or photovoltaics, lie the fundamental steps of photoinduced charge transfer and separation, which are best optimized by combining electron donor and acceptor materials into molecular dyads. In these architectures, the donor and acceptor units are integrated into a single molecule and linked by a π-conjugated moiety that facilitates intramolecular charge transfer (ICT) [1], where achieving high efficiency requires fast and efficient charge transfer with slow charge recombination to maintain the charge-separated state. Our approach focuses on the study of organic dyads based on the π-extended tetrathiafulvalene (exTTF) donor [2], a remarkable unit widely recognized for its applications in molecular electronics and solar energy conversion [3,4], linked to various nitrogen-containing acceptor groups to modulate the system's electronic dynamics. Our primary interest lies in fundamentally understanding how this charge separation occurs, and we therefore aim to track this phenomenon directly. We selected exTTF-based dyads due to their excellent electron-donating properties, as well as the presence of sulfur atoms within the exTTF core. The sulfur K-edfe can be easily probed using X-Ray Free electron Lasers (XFELs), enabling us to monitor the charge transfer process in real time. By employing X-ray Transient Absorption Spectroscopy (XTAS) at the SwissFEL facility of the Paul Scherrer Institut, we demonstrate the ability to track simultaneous oxidation and reduction processes with atomic-level precision by specifically monitoring the electronic environment of the sulfur centers. This element-specific approach provides a direct, real-time report on the electronic evolution of the system, showcasing the viability of tracking ultrafast redox dynamics in complex functional materials.

Speaker: Alejandro Serrano Capote (IMDEA Nanociencia)

16:30 Femtosecond imaging of the CH2Cl radical photodissociation

Femtosecond velocity map imaging is employed here to investigate the time-resolved formation of CH2 and Cl (2P3/2,1/2) following from the photodissociation of the CH2Cl radical at 298 nm, in combination with a 800 nm probe to monitor its temporal evolution. The CH2Cl species was generated through photolysis of the a precursor precursor, chloroiodomethane (CH2ICl), by excitation at 268 nm. The I (2P3/2,1/2) fragments resulting from the 268 nm photodissociation of the CH2ICl precursor were detected using resonance-enhanced multiphoton ionization (REMPI) coupled with velocity map imaging (VMI), enabling the determination of the initial internal energy distribution of the CH2Cl radicals. The lifetimes of the excited CH2Cl radical upon excitation at 298 nm were determined by analyzing the temporal evolution of CH2Cl+ ions produced by 800 nm multiphoton ionization as a function of the pump-probe time delay. The transients obtained show an average lifetime of 266 fs for this photodissociation channel. Furthermore, a more detailed analysis demonstrated the existence of multi-dynamic dissociation, since the high internal energy with which the CH₂Cl⁺ radicals were created allows to accessexcitation into the first three excited states. Finally, , oscillations in lifetimes were observed in the experimental transients as reflecting the evolution of the population across the different potential energy surfaces, due to vibrational coherence processes during excitation.

Speaker: Mr Alberto Sanz Verdejo (Universidad Complutense de Madrid (UCM))

16:30 Femtosecond Laser Engineering of Tunable Structural and Interferential Colouring in Ag-Based Nanocomposites

Localized surface plasmon resonance (LSPR) in novel metal embedded nanocomposites have attracted considerable interest due to their tunable optical properties with applications in photonics and sensing [1]. The light induced coupling between photons and oscillating conduction electrons (SPR) governs the optical response in nanoparticles (NPs) embedded in dielectrics. Furthermore, light-matter interaction transforms the NPs (size, shape, volume concentration) leading to localized effect on structural coloration. In this context, femtosecond laser irradiation has emerged as a versatile technique for tailoring metal nanocomposites through high peak intensity enabling energy coupling via non-linear effects, resulting in reorganizing or reshaping nanoparticles [2].

In this work, we present a dual laser-based strategy which combines nanocomposite synthesis optimization along with fs laser processing. As a first step, Ag based nanocomposite samples were fabricated by the technique of alternate pulsed laser deposition (a-PLD) with an excimer laser (λ= 193 nm, = 20 ns) [3]. By systematically tuning deposition parameters, we obtain near-coalescent Ag-thin films of less than 6 nm thickness on soda lime glass, as characterized by Rutherford backscattering Spectrometry (RBS) measurements. Variation in the dielectric (Al2O3) top cover-layer thickness (from 35 to 240 nm) is introduced to obtain different spectral responses (so different colour response), as shown in the spectra and insets in Figure 1(a)).

Femtosecond laser processing (λ= 515 nm, = 300 fs) of large areas (1.5 × 1.5 mm2) on the nanocomposite samples by varying fluence at constant repetition rate (500 kHz) shows the possibility to tune colours both in reflectivity and in transmission. In Figure 1(b-d) we show the results obtained in the sample with 240 nm dielectric cover layer. In reflectivity (Figure 1(b)), we obtained both yellow and turquoise colours, indicating respectively a red-shift and blue-shift with respect to the original greenish colour. In transmission (Figure 1(c-d)), colour changes are obtained when exceeding a fluence threshold, (F ≥ 55 mJ/cm2, beyond the bleaching limit). Noteworthy, the colouring shows an anisotropic behaviour depending on the direction of the while light illumination polarization with respect to the laser polarization (either parallel or perpendicular), which is consistent with a laser-induced reorganization and shaping of the nanoparticles. Complementary TEM measurements provide additional information about the underlying processes.

Speaker: Alka Philip (Instituto de Óptica 'Daza de Valdés' (IO), CSIC)

16:30 Femtosecond laser processing of biopolymers to foster cell-substrate cues

Among the different techniques to modify materials at the surface level, laser micromachining offers a versatile working route to alter the topography of a target in the micrometric scale. Femtosecond pulsed laser ablation (fs PLA) leads to minimal debris outcomes in comparison to longer pulse technologies, such as pico or nanosecond PLA. The briefness of the interaction conferred by fs PLA avoids heat transfer to the phonon network in the lattice, enabling a highly localised material removal [1]. This heat-hindered workflow is suitable for samples with low melting points such as biopolymers, with a great application in fields such as tissue engineering and personalised medicine [2]. Essentially, an increasing interest is being set to systems where surface modification could lead to novel cell responses in terms of adhesion, proliferation and mechanotransduction [3].

The need of precisely modify the surface of biopolymers lead us to employ fs PLA as an interesting approach avoiding the melting of the sample. This work motivates an exploration of ultrashort-pulse laser-matter interaction in polycaprolactone (PCL) scaffolds with the aim of analysing cell-substrate interactions.

Specifically, 4-layer PCL scaffolds were processed by laser with the STELA femtosecond laser, located at the L2A2 facilities in University of Santiago de Compostela. This laser supplies pulses of 35 fs duration, 1 kHz repetition rate and 1 mJ energy, with a central wavelength of 800 nm and a bandwidth of 80 nm. Microgrooves of two different widths were processed by modifying the power reaching the sample: 30 μm and 10 μm width (powers of 15 and 4.3 mW, respectively). Then, human dermal fibroblasts (HDF) and murine macrophages were seeded on the laser-ablated scaffolds and analysed after a 72-hour culture. It was seen that both cell lines were responsive to these micropatterns, resulting in a strong alignment of their cytoplasm and nucleus in the groove direction (Figure 1), as well as strongly increasing their adhesion compared to the control case.

Next steps are envisioned to relate the alignment of the cells with their mechanotransduction mechanisms (proregenerative macrophage M2 polarisation and HDF activation).

1. Chichkov, B.N., Momma, C., Nolte, S. et al. Femtosecond, picosecond and nanosecond laser ablation of solids. Appl. Phys. A 63, 109–115 (1996). https://doi.org/10.1007/BF01567637
2. Aboal‐Castro L, Radziunas‐Salinas Y, Pita‐Vilar M, et al.. Advanced Healthcare Materials. 2025;14(3). doi:10.1002/adhm.202403992
3. Xing Lei, Sheng Miao, Xiuli Wang, Yi Gao, Hao Wu, Pengzhen Cheng, Yue Song, Long Bi, Guoxian Pei; Microgroove Cues Guiding Fibrogenesis of Stem Cells via Intracellular Force. ACS Appl. Mater. Interfaces 5 April 2023; 15 (13): 16380–16393. https://doi.org/10.1021/acsami.2c20903

Speaker: Yago Radziunas Salinas (Photonics4Life, Universidade de Santiago de Compostela)

16:30 Laser fabrication of vibrating microcavities on silicon: dynamic and static study

Silicon’s exceptional optical and electrical properties, combined with its high purity, crystal quality, abundance and low price makes it the main standard for developing new micro- and nanoscale technologies in electronics and photonics [1]. In this work, we present a novel application: the formation of vibrating microcavities by irradiating a Si (111)-oriented wafer covered with a micrometer-thick layer of SiO2, using single femtosecond laser pulses (120 fs, 800 nm) (Fig. 1(a)).

By using pulse fluences above the evaporation threshold of silicon, which causes a bulging of the SiO2 layer, microcavities of varying heights can be fabricated, giving rise to optical interference (Fig. 1(b)). To study the early stages of their formation, we employed time-resolved Femtosecond Microscopy. This pump–probe method enables the acquisition of reflectivity snapshots of the sample surface at different time delays of an illumination probe pulse (λprobe = 400 nm) after arrival of the pump, allowing the study of microcavity formation with sub-picosecond temporal resolution (Fig. 1(c)). The results reveal the presence of material melting and surface evaporation between layers at the Si/SiO2 interface, leading to a transient strong surface bulging, followed by subsequent cooling and contraction of the SiO2 layer to its final size.
Using other time-resolved optical probing techniques, such as Real-Time Reflectivity (RTR) measurements, the slower dynamics of microcavity formation can be studied, featuring complex long-lasting reflectivity oscillations (Fig. 1(d,e)). For delay times > 1 microsecond, periodic oscillations associated with membrane vibrations at well-defined resonance frequencies are observed. The microcavities have been re-excited using laser fluences below the modification threshold, demonstrating that the structures vibrate at specific frequencies in the MHz range (Fig. 1(f)). The oscillation frequency can be tuned smoothly by changing the laser fluence, demonstrating a high degree of control over the cavity dynamics, and results have been compared with theoretical predictions, yielding good agreement. These unique structures might find applications as acoustic resonators.

Speaker: Belén Valiente Pascual (Instituto de Óptica, CSIC)

16:30 Laser-induced dynamics with newly extended multiple spawning approaches on CO2

With the advent of coherent light sources featuring attosecond resolution and sub-femtosecond UV/VIS pulses generated via high-order harmonic generation, observing pure, laser-induced electronic coherences before nuclear response has become possible.\textsuperscript{1,2} Accurately tracking these nonlinear dynamics and non-adiabatic transitions requires computational methods capable of providing a full quantum mechanical description of vibronic wave packets. While full quantum mechanical approaches, e.g., the Multi-Configuration Time-Dependent Hartree (MCTDH) method, provide exact solutions to the time-dependent Schr\"odinger equation, they face exponential scaling constraints in higher dimensions, becoming computationally prohibitive already for a few-center molecular targets. Conversely, classical trajectory-based approaches such as Trajectory Surface Hopping, while demonstrating wide applicability to compute excitation probabilities, tracking the appearance of non-adiabatic couplings or determining branching ratios, lack essential relative phase information to fully characterize the molecular wave packets. Critically, they rely on ad hoc decoherence corrections, whereas Multiple Spawning approaches smoothly split wave functions using adaptive Gaussian trajectories to preserve phase-sensitive observables while offering scalable, on-the-fly quantum calculations.\textsuperscript{3--5} To bridge methodological gaps in tracking these dynamics, the Coherent external Field Full Multiple Spawning approach incorporating First Order Corrections (XFFMS-SPA1) releases the Independent First Generation Approximation to start with a set of fully coupled initial trajectories and adds first-order saddle-point corrections to the potential energy evaluation. Applied to the benchmark LiH molecule, this method accurately reproduced complex time-dependent wave packet evolutions, population dynamics, and wave packet overlaps/revivals using a significantly low number of initial trajectories, matching MCTDH accuracy while successfully modeling non-perturbative phenomena like two-photon Rabi oscillations.\textsuperscript{6} Looking forward, this efficient framework holds strong potential for designing, simulating, and steering ultrafast, phase-controlled photochemical reaction pathways in small-to-medium molecules using tailored, few-femtosecond laser pulses. We here now present our ongoing progress on novel applications for multi-state excited states dynamics in triatomic systems. We explore the sub-fs UV/VIS induced dynamics in CO$_2$ molecule, that presents degeneracies in its molecular landscape and for which scarce reliable data is available, even for single-state scenarios.
\par}

Speaker: Rodrigo González Fuentes (Dpto de Química, Universidad Autónoma de Madrid)

16:30 Millijoule laser source delivering few-cycle, 3 µm pulses driven by an industrial Yb system

Ultrafast mid-infrared lasers provide access to molecular vibrational and rotational modes that play a crucial role in science. New-generation high-energy ultrafast sources have enabled significant advances in fields such as harmonic generation and attosecond pulse generation. Optical Parametric Chirped Pulse Amplification (OPCPA) is one of the most well-established methods of producing mJ-level mid-infrared radiation.
We present the current developments of such a system driven by an industrial Yb source. A fraction of our Yb driver seeds a commercial OPCPA enclosure, down-converting it to 3 µm, 65 µJ, 40 fs pulses with active CEP stabilization. To enable amplification of these pulses to the multi-mJ level, the remaining output of the Yb driver is amplified in a Chirped Pulse Amplification (CPA) system developed in-house, serving as the pump for a custom 3 µm OPCPA system. The OPCPA was designed and numerically validated to amplify the 65 µm pulses up to 5 mJ with a duration of 85 fs and a repetition rate of 10 Hz. This design allows the implementation of a pre-existing Yb:YAG-based amplifier, which operates at 10 Hz. Nevertheless, repetition rates > kHz would be feasible with thin-disk laser technologies.
We discuss the architecture of this system and the capabilities for driving next applications such as high harmonic generation, attosecond science, and particle acceleration.

Speaker: Gonçalo Vaz (GoLP-IPFN)

16:30 Nanosecond-Laser Photoacoustic Generation of Ultrasound for Probing Periodic Stainless-Steel Cylinder Arrays

In this work, a nanosecond pulsed laser was used to photoacoustically generate ultrasonic waves in an unsaturated polyester resin plate. The generated waves propagated through periodic arrays of stainless-steel cylinders immersed in water. The objective was to investigate how the center-to-center spacing between cylinders modifies the propagation of ultrasonic waves.

Three periodic configurations with spacings of 1.4, 1.5, and 1.6 mm were analyzed, while keeping the cylinder diameter, the number of rows, and all other experimental conditions constant. The transmitted ultrasonic signals were recorded using a 0.5 mm PVDF needle hydrophone. During the measurements, the periodic array was translated over 50 positions with a spatial step of 0.1 mm, while both the photoacoustic excitation point and the detector remained fixed. From these measurements, two-dimensional B-scan maps and their corresponding frequency-domain representations were obtained.

The results show that ultrasonic wave propagation is modified by the center-to-center spacing between cylinders. The arrival time of the photoacoustic signal depends on its propagation path through the periodic array. Owing to the periodicity of the array, these temporal variations repeat spatially, giving rise to well-defined curved patterns. For the arrays with 1.5 and 1.6 mm spacing, these curved patterns are clearly distinguished, whereas for the 1.4 mm configuration they become less distinguishable. Likewise, the spectral distribution exhibits differences among the three periodic configurations studied.

The analysis includes two-dimensional frequency-wavenumber (FFT2D) maps, which allow for the investigation of the spatial redistribution of acoustic energy and the identification of possible preferential propagation directions associated with each periodic configuration.

Speaker: ILIANA HERNANDEZ CRUZ (CENTRO DE INVESTIGACIONES EN ÓPTICA)

16:30 Passive detector-based X-ray spectromete

Laser-based accelerators offer a compact and cost-effective alternative to conventional accelerators for X-ray production, enabling applications in medicine and industry. However, their ultrashort radiation pulses can lead to pile-up effects in conventional spectrometers, motivating the use of passive detectors such as Image Plates (IPs) which integrate the X-ray energy over the exposure time. In this work, we present the characterization and absolute calibration of a system of reusable IPs and a scanner designed for dental applications using an X-ray tube source. The study includes IP reproducibility, signal linearity, resolution dependence, and temporal fading. Results show a reproducible and linear response, with rapid signal fading within the first 30 min, requiring a correction curve to be applied to the measurements. The scanner does not normalize the IP signal, and the output is expressed in instrument-specific units rather than PSL, as commonly used for passive detectors, making an absolute calibration necessary. An X-ray fluorescence-based setup is employed to establish the signal-photon energy relationship using nine elemental targets to generate well-defined characteristic lines while avoiding contributions from the continuous X-ray tube spectrum. We present a calibration curve in the 8-30 keV range, showing good agreement with published results at low energies. Finally, an iterative algorithm for spectral reconstruction is developed using the energy-dependent transmission functions obtained from the measurements of the IP irradiated after a stack of 13 um Al filters, and the number of incident photons. The X-ray tube spectrum is accurately reconstructed by this model at two operating energies, 30 and 50 keV. Future work will focus on recovering the laser-driven X-ray spectrum available at our laboratory (Laser Laboratory for Acceleration and Applications) using the developed algorithm.

Speaker: Judah Amir Rentería Lampaya (Galician Institute of High Energy Physics (IGFAE))

16:30 Plasmon-Exciton Interaction Induced Efficient Charge Separation in Cu2-xS-CsPbBr3 Heterostructure

Non-stoichiometric plasmonic semiconductors such as Cu2-xS have emerged as promising materials for energy conversion applications owing to their tunable band gaps, cost-effectiveness, and ability to harvest near infrared (NIR) energy. Integrating these plasmonic semiconductors with lead halide perovskites in heterostructures enables strong plasmon-exciton coupling, resulting in enhanced light absorption and efficient interfacial charge transfer. This work presents synthesis and investigation of the spectroscopic behavior of non-stoichiometric Cu2-xS, CsPbBr3 nanocrystals (NCs) and their heterostructure. Femtosecond transient absorption (TA) measurements are performed at two different excitations (400 and 800 nm) to develop a fundamental understanding of the hot carrier dynamics and their extraction in the heterostructure system. The TA results confirm plasmon-induced hot-hole transfer from Cu2-xS to the valence band of CsPbBr3 at both excitations, while 400 nm excitation additionally promotes hot-electron transfer from CsPbBr3 to Cu2-xS conduction band, leading to efficient charge separation and retarded exciton recombination. The efficient charge separation results in enhanced photocurrent response for the heterostructure. These synergistic charge transfer processes establish the Cu2-xS-CsPbBr3 heterosystem as a strong candidate for high performance optoelectronic devices.

Speaker: Nitika * (Institute of Nano Science and Technology, Mohali)

16:30 Protein–Chromophore Biohybrids for Tunable Delayed Emission

Protein–Chromophore Biohybrids for Tunable Delayed Emission

Adhil Kabeer^a, Juan Cabanillas^a, and Sara Hernández^a,*

^a IMDEA Nanoscience, Madrid, Spain

Presenting Author: adhil.kabeer@imdea.org

---

Proteins possess three-dimensional structures that confer upon them a cardinal role in a plethora of natural processes, viz. photosynthesis. Biohybrids are novel systems that harness the synergy between de novo proteins and chromophores for next-generation applications in light-emitting devices.¹ Yet, precise control over how the protein environment influences chromophore relaxation remains elusive in these systems.

We use Thermally Activated Delayed Fluorescence Chromophores (TADF-Cs), known for their high quantum efficiency and widespread use in OLEDs. However, non-radiative energy transfer to the host materials remains a major bottleneck, limiting their versatility and large-scale applications.² We advocate a novel approach to augment TADF properties through a conformationally rigid, chiral de novo protein environment³ (Figure 1). Within the protein cavity, the chromophore is confined, enabling nuanced control over its photophysical properties.

Herein, we employ Eosin Y (Ey) as a model molecule. Owing to its relatively small size, Ey can fit within the protein cavity.^4,5 Based on this model, we investigate the possibility of fine-tuning the singlet–triplet energy gap through the protein environment. We rely on a Michael addition reaction to label the protein with Ey molecules within the cavity.

Our results indicate the successful expression of proteins containing the desired mutations, along with efficient labeling by Ey. Temperature-dependent studies reveal that the motion of Ey couples with the dynamics of the protein, thereby enhancing the phosphorescence decay rate. Taken together, this work provides molecular-level insights into how the protein environment influences the photophysics of these chromophores and lays the foundation for the development of next-generation protein-based photonic materials.

---

References

1. M. Marques dos Santos et al. Chem. Rev. 2024, 124, 13736–14110.

2. H. Yersin; T. Monkowius. Adv. Photonics Res. 2024, 2400111, 1–44.

3. C. Karas; M. Hecht. Life 2020, 10, 1–15.

4. G. Serrano; C. Echavarría; S. Mejias. Protein Sci. 2024, 33, e5164.

5. M. Arbeloa; V. Porcal; G. Bertolotti; M. Previtali. J. Photochem. Photobiol., A 2013, 252, 31–36.

---

Figure 1. Schematic illustration of the de novo protein cavity encapsulating a chromophore, enabling modulation of its photophysical properties and tunable delayed emission.

Speaker: Mr Adhil Kabeer K (PhD student, IMDEA Nanoscience)

16:30 Resonance-enhanced above-threshold ionization of ammonia under strong fields

Molecules exposed to intense femtosecond laser fields display a complex interplay of multiphoton ionization, resonances, and tunneling dynamics. Although above-threshold ionization (ATI) has been extensively characterized in atoms, its resonance-enhanced counterpart in polyatomic molecules has remained elusive. Here we investigate the strong-field ionization of ammonia (NH$_3$) by 800 nm femtosecond pulses coupled with photoelectron velocity map imaging, exploiting its distinctive vibrational fingerprint in the umbrella bending mode. We uncover a weak Stark-induced Freeman resonance whose ATI replicas are shown to dominate over the parent channel. A strong resonance-enhanced above-threshold ionization (REATI) phenomenon is thus demonstrated here in a polyatomic molecule. Moreover, our results connect non-resonant and resonant multiphoton ionization, Freeman resonances, ATI, and REATI, into a unified roadmap, establishing ammonia as a benchmark system for exploring vibrationally resolved strong-field ionization. Beyond unveiling a distinct regime of molecular ionization, our findings highlight how the vibrational structure governs strong-field phenomena in complex molecules.

Speaker: Ignacio M. Casasús (Universidad Complutense de Madrid)

16:30 Role of A-Site Cation Size on Carrier Dynamics and Bulk-Phase Formation in Quasi-2D Halide Perovskites

Quasi-2D perovskites (L₂Aₙ₋₁PbₙI₃ₙ₊₁) are naturally forming quantum wells with highly tunable optoelectronic properties¹. While extensive research has explored the roles of spacer cation chemistry and halide substitution in governing carrier dynamics, the influence of A-site cation variation remains comparatively understudied¹⁻³. Here, we employ a fixed 4-fluorobenzylammonium (4-FBA) spacer paired with four representative A-site cations — methylammonium (MA), formamidinium (FA), cesium (Cs), and guanidinium (Gua) spanning a range of ionic sizes and organic/inorganic character, to systematically probe their effect on the optical properties and carrier dynamics of the resulting n=2 quasi-2D perovskite films.
Transient absorption (TA) measurements under 480 nm excitation reveal pronounced bleach features at 520 nm and 572 nm, assigned to the n = 1 and n = 2 phases, respectively, along with an additional bulk-like-phase bleach in the Cs- (700 nm), FA- (760 nm), and MA- (760 nm) based films (Figure 1). The presence of this bulk-phase signature and its apparent absence in Gua-based films, together with the extracted TA kinetics, points to clear A-site-dependent differences in carrier dynamics: the smaller Cs, MA, and FA cations favor 3D-like domain formation and efficient carrier funneling toward the bulk phase, whereas the bulkier Gua cation appears to suppress this process. Among the bulk-phase-forming compositions, the FA-based film shows the shortest n = 1 lifetime, indicating the most rapid and efficient downhill energy funneling, while Cs-, Gua-, and MA-based films exhibit longer n = 1 lifetimes, consistent with comparatively slower funneling. At the bulk phase, MA- and Cs-based films show the longest lifetimes, suggesting stronger carrier localization attributable to the formation of MAPbI₃-like domains and the lattice rigidity of the CsPbI₃-like framework, which promotes carrier self-trapping and thereby prolongs the observed lifetimes. These results identify A-site cation size and rigidity as a practical, spacer-independent lever for tuning carrier localization and emission energy in layered perovskite optoelectronics.

Speaker: AKANSHA VERMA (INDIAN INSTITUTE OF TECHNOLOGY MANDI)

16:30 Solution-State Assembly Dictates Excitonic Coupling and Function in Semiconducting Polymer Nanoparticles

Understanding how molecular organization in solution governs excitonic coupling and structure in conjugated polymer nanostructures remains a central challenge in soft condensed matter physics. Here, we show that controlled solution-state pre-assembly of poly(3-hexylthiophene) (P3HT) prior to nanoparticle (NP) formation enables tuning of intrachain and interchain interactions, with direct consequences for the excitonic landscape. Progressive pre-assembly in chloroform promotes chain planarization and the emergence of intrachain-dominated (J-like) interactions, evidenced by red-shifted absorption, enhanced 0-0 vibronic intensity, a reduced optical bandgap, and increased near-infrared absorption associated with sub-gap electronic states. These signatures are preserved in NPs produced by miniemulsion, indicating that solution-state correlations are imprinted into the solid-state morphology.
By combining optical spectroscopy and structure characterization, we establish a direct relationship between pre-assembly time, π–π stacking and crystalline coherence length, revealing a non-monotonic evolution of electronic order. An optimal pre-assembly regime maximizes backbone planarization and excitonic delocalization while maintaining finite structural disorder at the nanoscale.
These results highlight solution-state pre-organization as an effective route to control excitonic coupling and electronic disorder in conjugated polymer nanostructures, providing general design principles for soft semiconducting systems with tunable optical and electronic properties. These principles are finally illustrated through visible-light photocatalysis, used here as a functional probe of the tuned excitonic landscape.

Speaker: Aitana Hurtado Mendoza (Instituto de Química Física Blas Cabrera, CSIC)

16:30 Thermodynamic approach to ultrafast phase transitions

Controlling phase transitions in correlated quantum materials [1] with ultrafast light pulses offers a powerful route to creating and probing non-equilibrium states of matter. However, identifying the microscopic mechanisms that drive these transformations remains a major challenge. Vanadium dioxide (VO2) provides a particularly compelling example. It undergoes a first-order insulator-to-metal transition from a monoclinic (M1) insulating phase to a rutile (R) metallic phase when heated above 343 K or when excited by an ultrafast optical pulse [2] above a critical fluence. Although this photoinduced transition has been studied extensively, its underlying origin remains controversial, with competing interpretations emphasizing electronic correlations [3], coherent structural dynamics [4], or thermally driven processes [5].
In this work, we demonstrate that temperature-dependent ultrafast pump–probe spectroscopy provides a model-agnostic means to unequivocally distinguish the proposed mechanisms governing the photoinduced insulator-to-metal transition in VO2. We introduce an analytical method based on the dimensionality and statistical properties of the ultrafast heat capacity, extracted from the fluence- and temperature-dependent photoinduced reflectivity dynamics. By examining the associated statistical scaling and dimensionality, we establish a general framework capable of distinguishing between different driving mechanisms, including purely electronic excitation, selective coherent-phonon coupling, and excitation of the full phonon bath through their distinct temperature dependence of the critical fluence.
Our results indicate that a persistent metallic state emerges only when energy is distributed across the complete phonon spectrum, including high-energy oxygen vibrations, highlighting the fundamentally thermal character of the transition. At the same time, we identify that it is possible to trigger an electronic-only transition at short times that disappears rapidly when the lattice is not sufficiently stabilized. These results provide a clearer picture of the interplay between electronic excitation and lattice dynamics in VO2, while establishing ultrafast heat-capacity analysis as a versatile framework for identifying the microscopic origin of light-induced phase transitions. More broadly, this approach can be readily extended to other photoinduced transitions without requiring complex multimodal experimental techniques, providing a versatile framework for understanding and controlling non-equilibrium phase transformations, including those driven by incoherent processes.

References

[1] A. de la Torre et al., “Colloquium: Nonthermal pathways to ultrafast control in quantum materials,” Rev. Mod. Phys. 93, 041002 (2021).
[2] A. Cavalleri et al., “Femtosecond Structural Dynamics in VO2 during an Ultrafast Solid-Solid Phase Transition,” Phys. Rev. Lett. 87, 237401 (2001).
[3] T. V. Slusar et al., “Mott transition in chain structure of strained VO2 films revealed by coherent phonons,” Sci. Rep. 7, 16038 (2017).
[4] S. Wall et al., “Tracking the evolution of electronic and structural properties of VO2 during the ultrafast photoinduced insulator-metal transition,” Phys. Rev. B 87, 115126 (2013).
[5] S. Wall et al., “Ultrafast disordering of vanadium dimers in photoexcited VO2,” Science 362, 572–576 (2018).

Speaker: Shreya Bagchi (IMDEA Nanociencia)

17:30 → 18:30 Oral: Session 3

17:30 Watching femtochemistry with nonadiabatic dynamics

Femtochemistry explores the ultrafast structural and electronic changes that occur in molecules following light absorption. The relaxation of photoexcited molecules often involves nonadiabatic effects, where coupled electronic and nuclear motion drives processes such as photodissociation, isomerization, ring-opening reactions, and internal conversion. Understanding these mechanisms is crucial in fields ranging from atmospheric chemistry and photobiology to materials science.

In this work, we employ nonadiabatic molecular dynamics simulations to investigate the excited-state relaxation mechanisms of molecular systems in the gas phase, with particular emphasis on atmospherically relevant pollutants.1 Photodissociation represents the primary light-induced reaction pathway in the troposphere, while ring-opening processes contribute significantly for certain aromatic and heterocyclic compounds. Among these, furan derivatives, chlorofluorocarbons (CFCs), and bromocarbons are notable atmospheric contaminants involved in air pollution and ozone depletion.

When feasible, the Multi-Configuration Time-Dependent Hartree (MCTDH) quantum method is applied; for more demanding problems, mixed quantum-classical propagation methods are used.2 These studies also contribute to the ongoing effort to establish reliable benchmarks in nonadiabatic molecular dynamics (NAMD),3 addressing a recognized gap in theoretical photochemistry research.

Speaker: Sandra Gómez (Universidad Autonoma de Madrid)

17:55 Femtosecond pulsed laser ablation in liquids upscale of nanoparticle production by beam shaping

Femtosecond laser ablation in liquids enables advanced control over nanoparticle (NP) structure, but efficient energy delivery remains a key challenge that can be addressed through beam-shaping strategies [1]. While conventional PLAL setups rely on spherical focusing optics, advanced spatial beam engineering offers new degrees of freedom to control energy distribution and ablation dynamics [2]. In this work, we explore a beam-shaping strategy based on an optical system composed of two cylindrical lenses, enabling independent control of the beam propagation along orthogonal transverse directions. Unlike single cylindrical lens configurations [3], the double cylindrical lens system allows tailored focal conditions and extended flexibility in defining the irradiation geometry at the target surface. Moreover, additive manufacturing by fused deposition modeling (FDM) was employed to fabricate custom-designed ablation chambers with precisely controlled liquid-layer geometries. This approach results in a controlled elliptical or quasi-line focus, increasing the effective ablation area and influencing NP generation mechanisms, shown in Figure 1a).

Experimentally, NPs were synthesised by PLAL using a Ti-Sapphire laser with 800 nm central wavelength, 35 fs and 5 kHz repetition rate. By adjusting the relative position between the two cylindrical lenses, the focal shape and fluence at the target were tuned without modifying the optical path length, enabling controlled energy deposition at the ablation plane. NP productivity was found to strongly depend on the delivered fluence, with maximum yields obtained at intermediate fluence values, indicating an optimal energy density regime. The highest productivity reached 77.1 ± 2.8 mg/h at 4.89 W, corresponding to a maximum efficiency of 15.8 ± 0.6 mg/hW, while total production of 88.9 ± 2.7 mg/h was achieved at 9.61 W, shown in Figure 1b). At lower fluence, ablation was inefficient, whereas excessive fluence promoted nonlinear effects in the liquid, reducing effective energy delivery.
Structural and optical characterization revealed spherical Au NPs with narrow size distribution (10–20 nm), depicted in Figure 1c), showing that the dual cylindrical lens configuration is an effective and flexible approach for optimizing laser ablation synthesis in liquids.

Figure 1: a) Optical setup composed of two cylindrical lenses used to generate an elliptical focus on the target surface. b) NP production rate as a function of laser fluence, which varies by adjusting D. c) Characterization of Au NPs synthesized using the dual cylindrical lens configuration.

Notes and References
[1] I. Y. Khairani, G. Mínguez-Vega, C. Doñate-Buendía, and B. Gökce, “Green nanoparticle synthesis at scale: a perspective on overcoming the limits of pulsed laser ablation in liquids for high-throughput production,” Jul. 06, 2023, Royal Society of Chemistry. doi: 10.1039/d3cp01214j.
[2] S. Molina-Prados, et al., “Beam shaping techniques for pulsed laser ablation in liquids: Unlocking tunable control of nanoparticle synthesis in liquids” Beilstein J. Nanotechnol., 2026.
[3] H. Marrapu, R. Avasarala, V. R. Soma, S. K. Balivada, and G. K. Podagatlapalli, “Silver nanoribbons achieved by picosecond ablation using cylindrical focusing and SERS-based trace detection of TNT,” RSC Adv, vol. 10, no. 67, 2020, doi: 10.1039/d0ra05942k.

Speaker: Carlos Doñate Buendia (University Jaume I, GROC-UJI)

18:10 Four Synchronized Laser Pumped CEP-Stable 2.1 μm OPCPA with Broadband 2.5–10 μm Generation

Optical parametric chirped-pulse amplification (OPCPA) enables simultaneous generation of few-cycle pulses, high peak power, and high average power required for advanced strong-field and ultrafast mid-infrared applications [1]. We present a fully integrated OPCPA platform developed entirely using Light Conversion technologies, combining an ORPHEUS-OPCPA frontend with four synchronized 5 mJ PHAROS femtosecond amplifiers to generate carrier-envelope phase (CEP)-stable 2.1 μm pulses and broadband tunable mid-infrared radiation extending to 10 μm.

Speaker: Robertas Grigutis

19:30 → 21:00 Social: Reception at City Hall (Cocktail)

Thursday 19 November

09:00 → 11:00 Oral: Session 4

09:00 Ultrafast physics of nanoplasma rods in dielectrics

The generation of very dense plasmas with ultrafast lasers is key to applications such as tabletop warm dense matter generation—the state of matter found in planetary cores or inertial confinement fusion paths—and laser-induced synthesis of new material phases. For these applications, generating dense plasma inside materials is highly desirable to benefit from large volumes and confined geometries, unlike at solid/vacuum interfaces where plasma expands. A longstanding, challenging issue was that, inside the bulk of transparent materials, the plasma defocuses the intense laser pulse. This drastically limits the peak plasma density well below the critical density.

With ultrafast Bessel beams we have overcome this limitation and demonstrated the creation of subwavelength diameter plasma channels with lengths scalable from tens of micrometers to centimeters. This enables energy density on the order of MJ/cm3, even at modest input pulse energies.
The physical mechanisms underpinning this process have been elucidated through a combination of experimental diagnostics and Particle-In-Cell (PIC) simulations.1 Collisionless resonance absorption dominates energy deposition. The ability of PIC codes to reproduce these results, where hydrodynamic models fail, highlights the importance of capturing the non-Maxwellian electron distributions, such as Landau damping2. Additionally, the extreme confinement of energy deposition explains the efficiency of nano-drilling with Bessel beams, as well as the formation of voids and high-aspect-ratio nanochannels in materials such as sapphire and fused silica.3
These findings open new avenues for both fundamental and applied research. Not only the High-Energy Density regime becomes accessible with tabletop lasers, but nanoplasma rods also enable novel applications in nonlinear optics since the critical surface of the plasma is a surface at epsilon-near-zero, where a number of nonlinear wave conversion can be excited: we have observed second harmonic generation on the nanoplasma rod by the pump pulse itself.4 Our PIC simulations also predict THz emission.5 Ultrafast Bessel beams therefore offer a new, scalable platform for exploring laser-matter interaction in a number of different extreme regimes.

Notes and References
1 K. Ardaneh et al, Physical Review Letters (2026), in print, DOI 10.1103/k23j-c9y7
2 B. Morel, et al, Physical Review B (2022), 106, 035207
3 L. Rapp, et al, Scientific Reports (2016), 6, 34286
4 K. Ardaneh et al, Physics of Plasmas (2022) 29, 072716
5 K. Ardaneh et al, The European Physical Journal Special Topics (2023) 232, 2247–2252

Speaker: Francois COURVOISIER (Marie and Louis Pasteur University, CNRS, FEMTO-ST institute, F-25000 Besancon, France)

09:45 Ultrafast linear and non-linear spectroscopies

Ultrafast X-ray spectroscopies (absorption, emission and resonant inelastic X-ray scattering or RIXS) are powerful tools to monitor the photoinduced electronic, spin and structural changes in matter, with element-selectivity. They were developed over the past 25 years and are now firmly established to probe dynamics in (bio)molecular systems and in Materials, either using Synchrotron radiation sources and more frequently since about 25 years, X-ray Free Electron Lasers (XFELs).
Indeed, the advent of XFELs has not only boosted the capabilities of photon-in/photon-out X-ray spectroscopies such as emission or RIXS, but is also enabling the advent of non-linear X-ray spectroscopy and optics. This revolution is akin to what happened in the optical domain with the birth of the laser in the early 1960s.
In this talk, I will present applications of linear and non-linear X-ray spectroscopy to the study of photoinduced phenomena in molecules and proteins, as well as solid materials. In addition, I will present recent work in X-ray natural circular dichroism (XNCD) of molecular systems in solutions and prospects for probing chirality using non-linear X-ray methods.

Speaker: Prof. Majed Chergui (Elettra Sincrotrone)

10:10 Ultrafast laser fabrication and modelling of functional microstructures for biomedical applications

Ultrafast laser fabrication offers a flexible way to produce three-dimensional microstructures with well-defined geometries and functionalities. Our work focuses on hybrid organic-inorganic photoresists as materials for biomedical microdevices, particularly for localized drug delivery1.

Dexamethasone is incorporated into the photoresist as a model drug, allowing its inclusion directly within the polymeric matrix during fabrication. The structures obtained are characterized by optical and confocal microscopy to evaluate their morphology, structural fidelity, and response to different development conditions. Our preliminary observations show that both drug loading and post-processing have a strong influence on the final structures. Development conditions must therefore be carefully selected: overly aggressive treatments can damage the microstructures, whereas milder conditions may not completely remove the unpolymerized material.

In parallel, we are starting to explore the design of microneedle-based systems for ocular drug administration2. This work combines preliminary numerical models of microneedle insertion into the cornea with drug-diffusion simulations for timolol and dexamethasone. The aim is to study how parameters such as tip angle, cross-section, and insertion depth affect mechanical penetration and drug release into the corneal tissue.

By combining laser fabrication, material functionalization, structural characterization, and numerical modelling, this work seeks to contribute to the development of customized microdevices for localized therapies.

References
1 Jing, X.; Mi, H.-Y.; Salick, M. R.; et al. Two-photon polymerization for 3D biomedical scaffolds: Overview and updates. Frontiers in Bioengineering and Biotechnology 2022, 10, 994355. https://doi.org/10.3389/fbioe.2022.994355
2 Thakur, R. R. S.; Tekko, I. A.; Al-Shamkhi, A.; et al. Rapidly dissolving polymeric microneedles for minimally invasive intraocular drug delivery. Drug Delivery and Translational Research 2016, 6, 800–815. https://doi.org/10.1007/s13346-016-0332-9

Speaker: Dr Ana I. Gómez-Varela (Universidade de Santiago de Compostela)

10:35 Versatile metrology of ultrashort pulses using amplitude swing technique

Versatile metrology of ultrashort pulses using amplitude swing technique

Íñigo Sola, a,b Cristian Barbero, a,b Miguel López-Ripa, a,b and Benjamín Alonso a,b
a Grupo de Investigación en Aplicaciones del Láser y Fotónica (ALF), Universidad de Salamanca, 37008 Salamanca, Spain.
b Unidad de Excelencia en Luz y Materia Estructuradas (LUMES), Universidad de Salamanca, 37008 Salamanca, Spain.
E-mail Presenting Author: ijsola@usal.es

In ultrafast optics, accurately measuring the temporal profile of ultrashort pulses is crucial, as the control of light-matter interactions relies on knowing the pulse phase, spectrum, temporal structure, and duration. Despite the availability of various characterization methods, there remains a demand for techniques that merge high precision with operational simplicity to handle complex setups. Our group has developed the amplitude swing (a-swing) technique [1] to meet this demand, offering a simpler, highly robust alternative. This versatile diagnostics tool is tailored for diverse ultrafast optics applications, e.g., nonlinear optics, and fiber laser applications, featuring a design that minimizes alignment errors for highly reliable performance.
The a-swing method works by interfering two temporally delayed replicas of a pulse, using the modulation of their relative amplitude [1] as the phase-encoding control parameter to record a 2D trace (Fig. 1). Experimentally, this is achieved via a compact in-line setup utilizing birefringent crystals (multi-order waveplates) and a linear polarizer. This configuration acts as a common-path interferometer, providing exceptional inherent stability [2]. The framework has also been generalized to alternative amplitude modulation patterns, allowing flexible adaptation to different experimental configurations [3].
Several algorithmic methods have been developed to retrieve pulse profiles from the second-harmonic traces, evolving from global optimization routines to a ptychographic iterative algorithm [4–6]. This ptychographic approach enables the rapid, simultaneous reconstruction of both the spectral phase and temporal intensity of the electric field, significantly improving the retrieval process.
The versatility of a-swing is demonstrated by its broad operating capabilities. It operates across a multi-octave spectral range from the visible to the near-infrared [6], and can characterize pulses down to the few-cycle regime [7]. Beyond scalar fields, a-swing is specially sensitive to vector pulses (i.e., pulses with time-evolving polarization), allowing researchers to determine the temporal evolution of ellipticity and orientation from just a single trace [5]. Furthermore, its robustness enables the simultaneous retrieval of the pulse and the spectral response of the nonlinear stage through the marginale [2].
Applications of a-swing range from fundamental studies to the diagnostics of commercial laser platforms. It has been successfully used to optimize Chirped Pulse Amplifier (CPA) compressors, analyze post-compression systems, study time-evolving polarization sources, and characterize tunable Optical Parametric Amplifiers (OPAs), as well as diagnostics of unstable sources. Additionally, it has been applied to industrial-grade high-power lasers and commercial Erbium-doped fiber lasers, establishing a-swing as a comprehensive metrology tool for process control in diverse ultrafast technology applications.

Figure 1. Measured and retrieved a-swing traces (left panel) and spectral and temporal amplitude (black) and phase (red) retrievals (right panel).

Notes and References

1 Alonso, B.; Holgado, W.; Sola, Í. J. Opt. Express 2020, 28, 15625
2 Sola, Í. J.; Alonso, B. Sci. Rep. 2020, 10, 18364
3 López-Ripa, M.; Sola, Í. J.; Alonso, B. Opt. Express 2023, 31, 34428
4 Barbero, C.; Sola, Í. J.; Alonso, B. Opt. Laser Technol. 2025, 188, 112939
5 Barbero, C.; Alonso, B.; Sola, Í. J. Opt. Express 2024, 32, 10862
6 López-Ripa, M.; Sola, Í. J.; Alonso, B. Opt. Laser Technol. 2023, 164, 109492
7 López-Ripa, M.; Pérez-Benito, Ó.; Alonso, B.; Weigand, R.; Sola, Í. Opt. Express 2024, 32, 21149

Speaker: Íñigo Sola (Universidad de Salamanca)

11:00 → 11:35 Coffee break

11:35 → 13:40 Oral: Session 5

11:35 High-power ultrafast moves into the Terahertz

Ultrafast laser-driven broadband Terahertz light sources are nowadays ubiquitous tools in many scientific fields, enabling researchers to control and probe an immense variety of low energy phenomena in condensed matter and other systems. They are also being increasingly deployed in industrial settings for inspection and non destructive testing: THz waves "see through" optically opaque objects, and can provide rich spectroscopic information at a glance. While techniques to generate short, broadband THz pulses using ultrafast laser pulses and nonlinear conversion techniques have seen continuous performance progress in the last few years, their average power has traditionally moved comparatively slowly, which has prevented many of these fields from blooming. On the other hand, the increasing availability and enormous performance progress of ultrafast Ytterbium-based lasers providing multi-100-W to kilowatt average-power levels has opened up the area of high average power, laser-driven THz sources: recent results reaching average power levels in the THz domain approaching the watt-level, opening the door to a multiplicity of new and old research areas to be re-visited. We review recent progress in the generation of high-average power THz-pulses, including how novel high-power lasers are supporting progress in this area, current technological challenges in scaling THz average power, and applications areas that could potentially benefit from these novel sources.

Speaker: Clara Saraceno (Ruhr University Bochum)

12:10 Attosecond Transient Absorption Spectroscopy

Abstract
Attosecond transient absorption spectroscopy (ATAS) serves as a paramount technique for tracking real-time electronic motion and coherence in matter with unprecedented temporal resolution. Extending this technique towards higher photon energies adds an element sensitive probe as it allows to access core electrons. Apply to many body physics it allows to resolve both electron and lattice dynamics and therefore bringing new insights on the interaction among them.

In this work we present an overview of the recent developments in the field including our latest result on solid samples and also an overview on the generation and characterization of pulses down to 19 attoseconds.

References

1. F. Ardana-Lamas et Al. Brilliant Source of 19.2-Attosecond Soft
   X-ray Pulses below the Atomic Unit of Time. Ultrafast Sci. 2025;5:
   Article 0128. https://doi.org/10.34133/ultrafastscience.0128
2. S Severino et Al, Attosecond core-level absorption spectroscopy
   reveals the electronic and nuclear dynamics of molecular ring
   opening. Nat. Photon. 18, 731–737 (2024).
   https://doi.org/10.1038/s41566-024-01436-9
3. K Zinchenko et Al, Sub-7-femtosecond conical-intersection dynamics
   probed at the carbon K-edge.
   Science371,489-494(2021).DOI:10.1126/science.abf1656

Speaker: Fernando Ardana Lamas (ICFO – The Institute of Photonic Sciences)

12:35 Femtosecond Lasers for the Design and Modification of Niobium-Based Materials

Niobium and niobium-based oxides are attracting increasing interest because of their chemical and thermal stability, superconducting properties, and potential applications in catalysis, photocatalysis [1,2], and energy storage [3]. Niobium oxides and mixed titanium-niobium oxides exhibit rich structural chemistry, defect-driven electronic behaviour, and tunable optical and electrochemical properties. Nevertheless, their functional performance is often limited by low electronic conductivity, wide band gaps, and the large diversity of possible compositions and crystal structures. Non-stoichiometric oxygen-deficient phases may enhance electrical conductivity and solar-light absorption, while also creating new surface-active sites for electrochemical processes. In this context, femtosecond laser processing offers a versatile approach to the synthesis and modification of niobium-based materials, enabling localized energy deposition, non-equilibrium phase formation, controlled oxidation, and surface micro- and nanostructuring.

This work presents results on the design and modification of niobium-based materials using femtosecond lasers. First, ultrafast laser powder-bed processing is employed to produce layers of niobium oxides and titanium niobates directly from high-purity precursor powders [4]. By adjusting the laser irradiation parameters, the microstructure, oxygen deficiency, and crystalline phase composition of the resulting layers can be controlled (Figure 1a). This energy-efficient approach promotes the formation of functional niobium-based oxides, including oxygen-deficient Wadsley-Roth-type crystal structures relevant to photocatalytic and energy-storage applications.

Second, the femtosecond-laser modification of metallic niobium surfaces is investigated through the formation of laser-induced periodic surface structures (LIPSS) [5,6]. Under ambient conditions, periodic nanostructures are generated by controlling the laser fluence, pulse overlap, and number of accumulated pulses. In addition to surface texturing, laser irradiation induces localized oxidation, producing niobium oxide layers with different oxidation states, morphologies, and crystal structures (Figure 1b). Subsequent thermal treatments show that the initial laser-induced oxidation state affects the oxidation kinetics and oxide growth. These findings suggest that ultrafast laser irradiation may promote the formation of less common crystal structures. Overall, the results demonstrate the potential of femtosecond laser processing as a flexible tool for both the synthesis and surface modification of niobium-based materials.

FIGURE 1. (a) Real-colour optical microscopy images of femtosecond-laser-irradiated niobium oxide powders. (b) SEM image of a laser-processed region on a metallic niobium surface, showing the formation of cone-like structures.

Notes and References
[1] A. Calvo-Villoslada et al., Accepted in Ceramics International 2026, DOI: 10.1016/j.ceramint.2026.06.221
[2] A. Calvo-Villoslada et al., Nanomaterials 15, 846, 2025.
[3] A. Calvo-Villoslada et al., Materials Today Chemistry 47, 102860, 2025.
[4] B. Sotillo et al., Materials & Design 224, 111346, 2022.
[5] I. Gnilitskyi et al., Scientific Reports 7, 8485, 2017.
[6] A. Cubero et al., Applied Surface Science 508, 145140, 2020.

Speaker: Belén Sotillo Buzarra (Department of Material Physics, Faculty of Physics, Complutense University of Madrid)

13:00 Ultrashort laser-induced micro- and nanostructuring for the functionalisation of photopolymer surfaces

This work investigates the influence of laser repetition rate, pulse number, and fluence on surface-structure formation in PVA/AA and Biophotopol photopolymers under femtosecond laser irradiation [1]. By analyzing the dependence of structure height on the irradiation parameters, different growth efficiencies associated with monomer diffusion are identified, providing further insight into repetition-rate effects during ultrafast laser-induced photopolymerization [2]. These results demonstrate that micro- and nanostructures can be fabricated in these materials more rapidly and with greater control than in other dielectrics, metals, or semiconductors, making them promising candidates for functional and biomimetic surfaces.
Experiments were performed using a 120, 220 and 450 fs laser at (800, 1030 and 515 nm, respectively) operating from single-pulse to 1 MHz repetition rates by varying the fluence. The photopolymer films (~110 µm thick) were prepared following the standard formulation reported in Ref. [3]. Laser irradiation induces radical generation, monomer polymerization, and diffusion-driven formation of surface relief structures.

Figure 1. (a) 3D representation of the structure generated on the surface of PVA/AA after irradiating with N = 1 pulse and F = 1.25 J/cm2. (b) Measured heights of the structures induced on the surface of PVA/AA irradiations as a function of the fluence for N = 1 (blue), N = 2; 1 kHz (orange) and N = 2; 60 kHz (yellow).

Figure 1a shows a 3D confocal microscopy image (N = 1; F = 1.25 J/cm²) revealing a Gaussian-like surface profile characteristic of diffusion-driven monomer redistribution. Figure 1b presents the dependence of the structure height on fluence for three irradiation conditions: N = 1, N = 2 at 1 kHz, and N = 2 at 60 kHz. The results demonstrate that structure height increases with both pulse number and fluence. However, for the same number of pulses, structures produced at 1 kHz are significantly higher than those obtained at 60 kHz, indicating that repetition rate strongly affects monomer diffusion. The longer interval between pulses at lower repetition rates promotes more efficient monomer transport towards the irradiated region, enhancing structure growth. These findings highlight the interplay between photopolymerization and monomer diffusion, showing that repetition rate governs the balance between polymer formation and monomer transport, thereby determining the final surface morphology.

Acknowledgements
This work was supported by the Spanish MCIN/AEI and ERDF/EU through projects PID2024-161610OB-I00 and+ PID2023-148178OB-C22; by the Generalitat Valenciana (CIPROM/2024/90); the EU Horizon Europe programme (NFFA-Europe, Grant No. 101007417, Access Proposal ID894); and the Provence-Alpes-Côte d’Azur Regional Council (INTENSITY 2022). A.P.B. and I.S. acknowledges a predoctoral fellowships (PRE2022-105016 and FPU23/01300) from the Spanish MCIU. This work was carried out using the LaMP facilities at LP3.

Notes and References
1 M. Malinauskas, A. Žukauskas, S. Hasegawa, Y. Hayasaki, V. Mizeikis, R Buividas, S. Juodkazis, Light-Sci. Appl., 5 (2016).
2 T. Babeva, I. Naydenova, S. Martin, V. Toal, Opt. Express 26, 8487–8497 (2008)
3 A. P. Bernabeu, J. C. Bravo, J. J. Sirvent-Verdú, B. Nieto-Rodríguez, D. Puerto, S. Gallego, Polymers 18, 46 (2025)

Speaker: DANIEL PUERTO GARCIA (Universidad de Alicante)

13:25 Ultrafast Relaxation Dynamics of Pyrroles in Solution: the Role of Specific Interactions

Pyrrole is a common aromatic motif present in many biological chromophores that can be electronically photoexcited by solar radiation. In isolated conditions, its relaxation dynamics takes place in tens of femtoseconds (fs), involving the coupling of πσ reactive states to the bright ππ states that mediate the photoexcitation.1 This behavior is thought to have important consequences in the response exhibited by biomolecules to radiation exposure.2 However, the relaxation mechanisms observed in isolated conditions are fully conditioned by the environment, in particular, by the specific interactions established by the surrounding molecules.3 In this work, we have tracked the relaxation dynamics of pyrrole in the protic water and methanol solvents, by fs transient absorption methods. The only species found after excitation, at different wavelengths from the onset of the electronic absorption, are solvated pyrrole cations and electrons. The study aims to unravel the photoionization route, characterize the intermediate species and understand the role played by the specific interactions established between the pyrrole N-H group and the water and methanol solvent molecules.

Speaker: Dr Asier Longarte (Euskal Herriko Unibertsitatea (EHU))

13:40 → 15:00 Lunch break

15:00 → 16:30 Oral: Session 6

15:00 Intramolecular electron transfer reactions: accelerated or decreased by the medium?

Electron transfer reactions are arguably the simplest chemical reactions but they have not yet ceased to intrigue researchers. Charge-separation and charge-recombination reactions are at the core of life-sustaining processes, molecular electronics and solar cells. Intramolecular electron donor-acceptor systems capture the essential features of these reactions and enable their fundamental understanding. We investigated intramolecular electron transfers in weakly polar solvents covering a range of 100 kcal mol–1 in exothermicities and showed that their rates increase, then decrease, and finally increase again with the driving force of the reactions [1]. Concomitantly, apparent activation energies change from positive, to negative and finally to positive. Reactions with positive activation energies are found to be faster than analogous reactions with negative effective activation energies. More recently, we investigate the same reactions in polar solvents and in a series of alcohols with dielectric constants ranging from 10 to 33. Both charge-separation and charge recombination reactions revealed a strong dependence on the driving-force of the reaction, in contrast with the observations published for weakly polar solvents (Figure 1). Interestingly, charge recombinations in 1-octanol and dichloromethane differ by one order of magnitude although their dielectric constants and exothermicities are very similar. These reactions occur in the Marcus inverted region. The medium effect is very strong in these reactions but it is not simply related to the solvent polarity and exothermicity of the reaction. A revision of the existing theories of electron transfer is proposed.

Speaker: Luis Arnaut (University of Coimbra)

15:35 Structured light for new regimes of laser–plasma interaction

The increasing ability to control the spatial, temporal and polarization structure of ultrashort laser pulses opens new possibilities for tailoring light–matter interactions beyond the conventional Gaussian pulse. Orbital angular momentum, vector beams and spatio-temporal couplings can be used not simply to modify the focal intensity distribution, but to control the topology, velocity and angular momentum of the fields that drive a plasma. These developments are beginning to provide new handles on phenomena ranging from high-harmonic generation to plasma waves, particle acceleration and kinetic plasma dynamics.

In this talk I will review our recent work at the VOXEL laboratory at Instituto Superior Técnico on the generation, characterization and application of structured ultrashort light. I will discuss the control of high-harmonic wavefronts and orbital angular momentum, including the use of diffractive optics to structure EUV radiation, and our first experiments with spatio-temporal “light springs”, where orbital angular momentum is encoded across the spectrum of an ultrashort pulse.
Finally, I will give some perspectives on the ongoing evolution of the VOXEL laboratory and the new experimental capabilities it will enable.

Speaker: Marta Fajardo (Instituto Superior Técnico, Instituto de Plasmas e Fusão Nuclear)

16:00 Excited State Dynamics of Congested Cu(I) Complexes.

Transition metal complexes play a central role in modern photophysics and photochemistry due to their ability to harvest light and mediate charge transfer processes [1,2] . However, many of the most efficient photoactive systems are based on scarce and expensive noble metals such as Ru, Ir, or Pt, which limits their large-scale application in photocatalysis, light-emitting devices, and solar energy conversion. In this context, first-row transition metals such as Cu have emerged as sustainable alternatives thanks to their earth abundance and tunable electronic properties [3,4].
In this work, we investigate the ultrafast excited-state dynamics of Cu(I) complexes bearing N-heterocyclic carbene (NHC) ligands. The Cu(I) systems are heteroleptic, containing bulky diphosphine co-ligands to stabilize the photoactive metal-to-ligand charge transfer (MLCT) state and hinder flattening distortion in the excited state [5].
Femtosecond transient absorption spectroscopy and time resolved optical emission provides direct insight into the temporal evolution of the MLCT states, revealing their formation, nonradiative pathways, and decay on the tens of femtosecond up to milisecond timescales. Complementary time-dependent density functional theory (TD-DFT) calculations aid in interpreting the steady-state absorption spectra and assigning the nature of the excited states involved.
By combining experimental and theoretical approaches, this study elucidates the lifetimes of the involved excited states and the structural processes along the deactivation mechanism, thereby contributing to the rational design of efficient, earth-abundant photoactive coordination compounds for sustainable photochemical applications

Speaker: Marcos de Lucas Medina (IMDEA-Nanociencia)

16:15 Ultrafast imaging at sunlight fluence to track optimal energy transport in photosynthetic membranes

Ultrafast pump-probe spectroscopy generally involves fluences above J/cm2. Inside a microscope with diffraction limited spots fluences can be even higher. In contrast, natural light harvesting systems operate at sun-light conditions: ~100 mw/cm2, corresponding to around 1 nJ/cm2 for typical pulsed laser, rendering conventional transient pump-probe experiments unfeasible. Here we present a novel approach StrEET - Structured Excitation Energy Transfer microscopy, combining the tracking of ultrafast transients with super-resolved spatial information, to study energy materials, such as TMDs, organic photovoltaics and especially the ultrafast dynamics and transport in light-harvesting membranes at natural light level.
Optimizing bio-inspired light-harvesting systems requires understanding how natural architectures govern energy transport. In this study, we investigate the optimal exciton diffusion in a monolayer of bacterial LH2 antenna complexes by controlling their packing density. Using novel StrEET microscopy, we track exciton diffusion at ultralow illumination conditions, below solar light level, free of any annihilation, while maintaining picosecond temporal and nanometer spatial resolution. Using fluorescence lifetime as an indicator for intermolecular coupling, we measured exciton diffusivity from the close packing to the single molecule limits. Interestingly, we observe a bell-shaped curve, where an ideal antenna concentration for optimal transport is identified. This maximum corresponds to a diffusion length close to 50 nm and a lifetime of 300 ps, consistent with Forster transport models and conditions in natural systems. Our findings show Nature’s design follows natural laws of coupling and energy transfer and provide critical design principles for the development of efficient, biologically inspired nanoscale platforms for sustainable energy conversion.

Speaker: Niek van Hulst (ICFO - Institute of Photonic Sciences)

16:30 → 17:00 Coffee break

17:00 → 18:20 Oral: Session 7

17:50 Latest achievements and developments in high repetition rate ultrashort femtosecond lasers for secondary sources

Key words: High Average Power, High Peak Power, High Energy, Ultrashort Pulse, OPA/OPCPA, Ti:Sapphire, Ytterbium

Amplitude provides the broadest portfolio of ultrafast lasers based on diverse existing technologies: Ytterbium, Ti:Sapphire, Neodymium, OPCPA based systems... We report here the latest achievements in the development of high energy ultrafast femtosecond lasers along with our roadmap aimed at ramping up the repetition rate, to address in particular the need for compact, lab-based secondary sources.

We will first report our recent achievements in high energy, high peak power Ti:Sapphire laser systems together with our roadmap towards 100Hz operation rate at hundreds of TW level. This evolution is enabled by the development of our last-generation diode-pumped high energy nanosecond Nd:YAG pump lasers at 100Hz.

For lower peak power applications, high repetition rate and high average power are currently better addressed by Ytterbium technology. After a brief introduction of Yb-based lasers available at Amplitude, we will show how applications like secondary sources and related facilities can benefit from this mature technology, including the flexibility added by technologies such as post compression to reach even higher peak powers, or Optical Parametric Amplification (OPA) for wavelength tunability.

We will finally conclude by presenting one recent achievement at the LRCS in Amiens (France) consisting in a compact kHz laser-plasma X-ray source1 at 17.4 keV integrated in an all-laser-driven pump-probe architecture for the time-resolved study of perovskites degradation, based on the above-mentioned technologies available at Amplitude.

Notes and References
1 Barbrel, B; Barjou, E.; Courjaud, A.; Dorchies, F.; Lehoux, P.; Mastropietro, F.; Song, P.; Bakkali, A. “Demonstration of a robust laser-driven X-ray source for CT”. e-Journal of Nondestructive Testing. 29. 10.58286/29239 (2024)

Speaker: Olivier ZABIOLLE (Amplitude)

18:05 Solvent-Controlled Ultrafast Relaxation and Long-Lived State Formation in para-Nitroaniline

Photoexcitation of donor–acceptor chromophores initiates coupled electronic, structural, vibrational, and solvent dynamics. Here, we investigate the solvent-dependent photophysics of para-nitroaniline (PNA), a prototypical push–pull chromophore, using femtosecond broadband transient absorption spectroscopy following excitation at 400 nm.¹˒² Measurements were performed in water, methanol, dimethyl sulfoxide, acetonitrile, and tetrahydrofuran. In every solvent, photoexcitation produces a prompt ground-state bleach below approximately 400 nm together with a broad positive transient absorption across the visible region. These features are consistent with formation of a charge-transfer-like excited-state population followed by rapid electronic, nuclear, and solvent reorganization. ¹˒² Despite the similar initial response, the subsequent dynamics are strongly solvent dependent. Global analysis reveals a rapid sub-picosecond contribution followed by dominant recovery components of approximately 1.44 ps in water, 4.89 ps in methanol, 5.03 ps in dimethyl sulfoxide, 6.77 ps in tetrahydrofuran, and 7.77 ps in acetonitrile. These timescales describe the coupled evolution of excited-state relaxation, hot-ground-state formation, vibrational redistribution, and solvent-mediated energy dissipation.¹˒³ The long-delay response follows a different solvent trend. No pronounced persistent signal is observed in water or dimethyl sulfoxide, whereas absorption remains beyond the available 7.4 ns window in methanol. In acetonitrile and tetrahydrofuran, long-lived components are resolved with effective decay constants of approximately 187 and 114 ns, respectively, and are predominantly assigned to triplet-state absorption.²˒⁴ Methanol and dimethyl sulfoxide exhibit nearly identical picosecond recovery times but markedly different long-delay behaviour, showing that broadband recovery does not uniquely determine persistent-state formation. These results demonstrate that picosecond recovery and long-lived-state population are related but non-equivalent aspects of PNA relaxation. Their solvent dependence reflects the combined influence of charge-transfer-state stabilization, specific solvation, vibrational-energy dissipation, and branching between internal conversion and the triplet manifold.¹˒²˒⁵

Speaker: Kushal Shaw (Universidad Complutense Madrid)

18:20 → 20:00 Poster + Beer: Poster Session 2

18:20 Charge migration timescales are pre-determined by molecular dipoles, not correlations

Quantum coherence naturally arises from the many-body quantum nature of molecules. Upon strong-field ionization, a molecule can undergo a periodic oscillation of its charge density owing to coherent superposition of ionic states known as charge migration (CM) [1]. Since CM primarily arises from fundamental quantum effects such as electron correlations, it offers novel routes for probing many-body quantum coherence [2-4], chemical reactivity, photosynthesis, femto-astrochemistry and coherences in quantum science applications [1-6]. As CM is dominantly an electronic process [1-4], an appropriate theoretical treatment of the correlations is required at all levels [5-8]. The effect of molecular geometry and its electronic structure on CM has not been systematically explored. Being very crucial elements, such pathways open up novel control mechanisms to affect electronic degrees of freedom. Ultimately, control over CM could pave the way for tuning molecular response and chemical reactions by utilizing ultrashort laser pulses. However, to enable such control we first need to resolve big open questions in the field, starting with what physical mechanisms dominate CM, and especially, which determine the timescales of oscillations in the attosecond regime.
Here we perform an extensive ab initio analysis [5-8] of CM dynamics using time-dependent density functional theory (TDDFT) in a model system- BrC4H. We explore the role of electronic correlations at different levels of approximations in the CM dynamics by various exchange correlation (XC) functionals. We explore molecular attributes by artificially changing Bond Length (BL) and Bond Angle (BA) and the ionized molecular orbitals (MOs).

FIGURE 1: (I). Top: Original optimized geometry and its angular varied profiles. Bottom: MOs from which electron ionization is initiated.
(II). The hole moment evolution along the molecular backbone under various molecular attributes and levels of electronic correlations.
(III). Spectral profiles of the hole moment (from II) elucidate the presence of a universal dominant frequency beyond molecular attributes
and level of electronic correlations.

From FIGURE 1, it is evident that upon considering different levels of electronic correlations and molecular attributes, CM dynamics changes significantly in the oscillation profiles of the hole moment across the temporal scale (changing the evolution of the hole density). However, interestingly, a universal dominant frequency is seen arising in their respective spectral profiles for the average hole position and its velocity (the main frequency associated with attosecond CM). We directly reconstruct the dynamics in the cationic basis by a coherent superposition of cationic states, showing that a dominant universal frequency is retrieved in the spectral profile due to molecular dipole selection rules, akin to harmonic oscillator systems. Our results directly impact experimental observations of CM that dominantly probe the hole moments rather than the direct density evolution.

References

1. Cederbaum L. S.; Zobeley J. Chem. Phys. Lett. 1999, 307, 205-210.
2. Matselyukh D. T. et al. Nat. Phys. 2022, 18, 1206–1213.
3. Wanie V. et al. Nature 2024, 630, 109-115.
4. Calegari F. et al. Science 2014, 346, 336–339.
5. Folorunso A. S. et al. J. Phys. Chem. A 2023, 127, 1894−1900.
6. Lara-Astiaso M. et al. Faraday Discuss. 2016, 194, 41-59.
7. Despré V.; Kuleff A. I. Phys. Rev. A 2022, 106, L021501.
8. Neufeld O.; Tancogne-Dejean N.; Rubio A. JPCL 2024, 15, 7254-7264.

Speaker: Dr KM AKANKSHA DUBEY (Technion- Israel Institute of Technology Israel)

18:20 Conformational switch of 1,4-bis(4-vinylpyridyl)benzene adsorbed on a nanostructured silver surface: A synergetic study of femtosecond transient absorption, electrochemical SERS and DFT calculations

The electrochemical surface-enhanced Raman spectra (SERS) of 1,4-bis(4-vinylpyridyl)benzene (bvpb) recorded on silver electrodes at different potentials, using three excitation wavelengths (785, 532, and 473 nm), reveal the presence of a resonance process at negative potentials under 785 nm excitation. This process leads to the appearance of two strongly enhanced SERS bands at ca. 1500 and 1150 cm⁻¹. These findings are consistent with the VIS–NIR transient absorption spectrum, which displays a prominent band at 607 nm and a weaker band at 1163 nm, assigned to the first singlet (S₁) and triplet (T₁) excited electronic states, respectively.
Density functional theory (DFT) calculations of the potential energy profiles for the trans–cis (E–Z) isomerization indicate that, in the S₁ state, the energy barrier is significantly lower than in the ground state (S₀). Moreover, a conical intersection between S₁ and S₀ is identified at a geometry characterized by a 90° twisting of the vinyl double bond. Time-dependent DFT (TD-DFT) simulations of resonance Raman spectra, based on a simplified surface complex model (Ag₂₀–bvpb), show that the twisted conformation accurately reproduces the selective enhancement of the two observed SERS bands.
These results suggest that bvpb may function as an electroactive conformational molecular switch under suitable laser excitation conditions, with potential applications in nanoelectronic devices.

Speaker: Juan Carlos Otero Fdez. de Molina (Departamento de Química Física, Facultad de Ciencias, 29071, Málaga; España)

18:20 Decoding Intersystem Crossing: Molecular Design, Vibrational Control and Environmental Modulation

Intersystem crossing (ISC) is a photophysical process which is essential for triplet-state formation, with profound implications for photocatalysis, photodynamic therapy, and optoelectronic devices. Our research combines ultrafast and steady state spectroscopy, and quantum chemical calculations to unravel how molecular structure, vibrational dynamics, and environmental factors govern ISC efficiency. Across diverse systems including aromatic carbonyls, nitroaromatic compounds, thiocarbonyls, heavy atom substituted organoboron compounds we have demonstrated that ISC is not dictated solely by static spin-orbit coupling (SOC) strength. Our findings suggest that specific bond associated vibrational modes can modulate the singlet-triplet conversion in all these compounds. For example, ISC in positional isomers in heavy-atom-substituted chromophores reveals that vibrational mixing and heavy-atom participation in key orbital transitions can influence or take precedence over SOC magnitude. Intermolecular interactions, such as hydrogen bonding, and medium viscosity further modulate ISC by reshaping nuclear motion and altering access to the singlet-triplet crossing. Collectively, these findings establish a detailed mechanistic understanding in which ISC efficiency emerges from a synergy of electronic structure, nuclear coordinates, and environmental constraints offering actionable design principles for next-generation triplet photosensitizers and photochemical systems.

Speaker: Suman Bhowmik (IIT Kanpur)

18:20 Full temporal characterization of the polarization state of few-cycle laser pulses: D-TURTLE

The polarization state of few-cycle laser pulses plays a fundamental role in light–matter interactions, governing phenomena such as optomagnetic effects, high-harmonic generation, and coherent control. Accurate characterization of the time-dependent polarization of ultrashort pulses is therefore essential for both optimizing these applications and gaining insight into the underlying physical processes. Diverse techniques for the characterization of the polarization state of ultrashort laser pulses have been developed, such as single-channel 1 or dual-channel spectral interferometry [2], tomographic ultrafast retrieval of transverse light E-fields (TURTLE) [3], V-FROG [4] or a recently reported extension of the dispersion-scan (d-scan) technique in which a polarization gate is temporally characterized [5].

Here, we present D-TURTLE [6], a novel technique for the complete characterization of the time-resolved polarization state of few-femtosecond laser pulses. The method combines dispersion scan (d-scan) with the Tomographic Ultrafast Retrieval of Transverse Light E-fields (TURTLE) approach in a robust, self-referenced, and inline configuration. D-TURTLE retrieves the full temporal polarization dynamics, the relative temporal delay between polarization components, and the handedness of the polarization vector.

D-TURTLE is based on recording four d-scan traces corresponding to four different projections of the electric field onto the fixed axis of a nonlinear crystal optimized for second-harmonic generation of linearly polarized light. Two orthogonal projections are first independently retrieved using conventional d-scan algorithms to obtain the two polarization components. A dedicated retrieval algorithm, specifically developed for D-TURTLE, then exploits the remaining projections and simultaneously minimizes two error functions to unambiguously determine the relative phase and temporal ordering of the polarization components. Unlike conventional FROG, d-scan, or FROG-based TURTLE approaches, this strategy uniquely resolves the complete polarization state.

Numerical simulations and experimental measurements demonstrate that D-TURTLE unambiguously reconstructs the time-resolved polarization state of few-cycle pulses, including the relative temporal position of the polarization components (even if the polarization components do not overlap in time) and the instantaneous handedness of the polarization vector. The combination of robustness, self-referencing operation, and inline implementation makes D-TURTLE a powerful and practical tool for the complete characterization of ultrafast vector laser pulses, specially in the few-cycle regime.

Notes and References
1 Alonso, B.; Sola, Í. IEEE J. Sel. Top. Quantum Electron. 2019, 25, 1-7
2 Walecki, W. J.; Fittinghoff D. N.; Smirl A. L.; Trebino R. Opt. Lett. 1997, 22, 81-83
3 Schlup P.; Masihzadeh, O; Xu L.; Trebino R.; Bartels R. A. Opt. Lett. 2008, 33, 267-269
4 Haham G. I.; Levin A.; Sidorenko P.; Lerner G.; Cohen O. J. Phys: Photonics 2021, 3, 034017
5 Rivas, D. D.; Raab A. K.; Guo C.; Viotti A. L.; Sytcevich I.; L´Huillier A.; Arnold C. J. Phys: Photonics 2024, 6, 015003
6 Pérez-Benito Ó.; Weigand R. Opt. Laser Technol. 2024, 179, 111273

Speaker: Prof. ROSA MARIA WEIGAND TALAVERA (UNIVERSIDAD COMPLUTENSE DE MADRID)

18:20 Methyl iodine fast photodissociation revisited using few fs UV pulses

Photodissociation of methyl iodine in its A band is a classical example of a fast reaction mediated with by a conical intersection. The arrival time to this conical intersection was first estimated using theoretical simulations using semiclassical [1, 2, 3] and quantum [4, 5, 6, 7, 8, 9, 10] dynamics over pre-existent potential energy surfaces [1, 2, 5]. From the experimental point of view, the confirmation of the arrival time of the system at the conical intersection was first measured by means of Coulomb explosion [3] and afterwards using Attosecond Transient Absorption [11]. In both cases, combining the measurement with theoretical models based on semiclassical dynamics using the SHARC method [12]. However, the duration of the pump pulse in these
experiments is longer than the estimated arrival time, and the conical pass would be affected. In
fact, in similar experimental setups and for this type of molecules, dumping of the population was
observed [13].

In this work [14], we are going to use a few fs (4.2) pump laser so that during the pass through the conical intersection the laser pulse is not acting. From the theoretical side (where this presentation will focus), this implies the consideration of a broad range of excitation energies and the propagation of a large number of trajectories using state-of-the-art electronic structures methods in combination with surface hopping methodology. In this scheme, strong spin-orbit coupling and fast photodissociation dynamics, is where the combination of the SHARC method [12] with high level ab initio methodology (XMS-CASPT2) brights giving a very good accuracy that agrees with the experimental results.

Notes and References
1 Amatatsu, Y. et al. J. Chem. Phys. 1991, 94, 4858
2 Amatatsu, Y. et al. J. Chem. Phys. 1996, 104, 9783
3 Corrales, M. E. et al. J. Phys. Chem. Lett. 2019, 10, 138
4 Guo, H. et al. J. Chem. Phys. 1992, 96, 6629
5 Xie, D. et al. J. Phys. Chem. A 2000, 104, 1009
6 de Nalda, R. et al. J. Chem. Phys. 2008, 128, 244309
7 Rubio-Lago, L. et al. J. Chem. Phys. 2009, 131, 174309
8 Evenhuis, C. R.; Manthe, U. J. Phys. Chem. A 2011, 115, 5992
9 Garcı́a-Vela, A. et al. J. Chem. Phys. 2011, 135, 154306
10 Corrales M. E. et al. Nat. Chem. 2014, 6, 785
11 Chang K. F. et al. J. Chem. Phys. 2021, 154, 234301
12 Richter M. et al. J. Chem. Theory Comput. 2011, 7, 1253
13 Chang K. F. et al. J. Chem. Phys. 2022, 156, 114304
14 Colaizzi L. et al. Nat. Commun. 2024, 15, 9196

Speaker: Jesus Gonzalez Vazquez (Universidad Autónoma de Madrid)

18:20 Reactive Pulsed Laser Deposition of TiN Thin Films: Influence of Deposition Temperature on Structure and Mechanical Performance

Titanium nitride (TiN) thin films are widely used as protective coatings and functional materials because of their high hardness, excellent wear resistance, chemical stability, and compatibility with silicon-based electronic devices. In this study, TiN thin films were deposited on Si (100) substrates by reactive pulsed laser deposition using a titanium target in a nitrogen atmosphere at a background pressure of 10 mTorr. The influence of substrate temperature (200–600 °C) on the structural, mechanical, and tribological properties of the films was systematically investigated. Surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), while nanoindentation, residual stress measurements, and pin-on-disk testing were employed to evaluate the mechanical and tribological performance of the coatings. The deposited TiN films exhibited dense and uniform microstructures with near-stoichiometric composition. Increasing the substrate temperature significantly enhanced the hardness of the coatings, indicating improved film quality and densification. The residual stress evolved from compressive to tensile with increasing deposition temperature, reflecting changes in the film growth mechanism. The tribological behavior was also found to be strongly dependent on the deposition conditions. These findings demonstrate that substrate temperature is a critical processing parameter for tailoring the microstructure and performance of TiN thin films deposited by reactive pulsed laser deposition, providing useful guidelines for the development of high-performance protective coatings and silicon-compatible functional thin films.

Speaker: Faisal Alresheedi (Department of Physics, College of Science, Qassim University, Saudi Arabia)

18:20 Repetition Rate Dependent Thermal and Ablative Regimes in Ultrafast Processing of PVC

Ultrafast laser processing enables highly localized material modification, although the final morphology and the extent of the collateral thermal effects strongly depend on the temporal distribution of the delivered energy. In polymers, their low thermal diffusivity and relatively low phase transition temperatures promote heat accumulation even at repetition rates in the kHz regime. Although this accumulation can assist material removal, it may also induce swelling and extended thermally modified regions around the processed area.

In this work, the transition between thermally dominated and ablation regimes was investigated in poly(vinyl chloride) (PVC) under femtosecond laser irradiation. Experiments were performed at 1030 nm using 220 fs pulses. The fluence was fixed at 0.40 J/cm2, with a focused beam radius of 118 μm, remaining below the single-pulse ablation threshold. Repetition rates ranging between 100 Hz and 60 kHz were investigated for different numbers of delivered pulses.

As shown in Fig.1, irradiation at 1 kHz produced a pronounced thermal halo surrounding the ablation crater, indicating that a significant fraction of the deposited energy was diffused into the surrounding material. In contrast, irradiation at 60 kHz resulted in larger and more clearly defined ablation crater together with a reduced thermally affected region. Quantitative measurements confirmed that increasing the repetition rate promoted more efficient material removal while limiting lateral extent of thermal modification.

This behavior is consistent with the concept of ablation cooling1. At higher repetition rates, the shorter time between pulses enhances heat accumulation and facilitates an earlier onset of ablation. Once efficient material removal is established, part of the deposited energy is carried away by the ejected material, reducing the fraction available for heat diffusion.

These results provide experimental evidence that ablation cooling effects can occur in PVC at repetition rates considerably lower than the GHz regime commonly employed in ultrafast burst processing. The low thermal diffusivity of this material allows the balance between material removal and heat diffusion to be reached in the kHz range2, where shielding effects are expected to be less significant3.

Acknowledgements
This work was supported by PID2024-161610OB-I00 (funded by MCIN/AEI/10.13039/501100011033 and by ERDF/EU, Spain) and by the Generalitat Valenciana, Spain (CIPROM/2024/90). A.P.B. gratefully acknowledges the “Ministerio de Ciencia, Innovación y Universidades” of Spain for the grant PRE2022-105016. The research leading to these results has received funding from the French PACA (Provence-Alpes-Cote d’Azur) Regional Council (2022 Grants: INTENSITY). It has been conducted using LaMP facilities at LP3.

Speaker: Prof. Daniel Puerto (Universidad de Alicante)

18:20 Second Harmonic Generation induced by Ultrashort pulses in ITO/Au Bilayers

We present an experimental and theoretical study of second harmonic generation (SHG) in an ITO/gold bilayer with emphasis on the role of interfacial effective mass and charge discontinuities. First, we measure the SHG response of individual components- ITO and gold nanolayers- separately, and as expected, the SH signal is triggered by Coulomb, magnetic Lorentz and convective sources. In ITO the response is strongest near the epsilon near zero (ENZ) regime. The linear transmission through the ITO layer displays a minimum near the ENZ crossing point, (fig. 1a) while gold (fig. 1b, red curve) reflects like a mirror. However, the bilayer behaves in an unusual manner, by showing a resonance in linear reflection at a shifted ENZ wavelength (fig. 1b, blue curve). The nonlinear response of the bilayer is also unsual. The measured reflected SHG spectrum (fig. 1c, markers only curve) shows two distinct features: a small wavelength bump and plateau region, and a pronounced peak at longer wavelengths for a fixed incidence angle. To explain this behavior,- we use a hydrodynamic-Maxwell model for the coupled bilayer system. The model suggests that at shorter wavelengths the response is dominated by gold-related surface (Coulomb and convective) and Lorentz contributions, while at longer wavelengths the identification of SH sources is more subtle: near the ENZ crossing point a discontinuity in both effective mass and free electron density at ITO-gold interface triggers nonlinear convective sources that enhance the overall efficiency. Mass and density discontinuities are pivotal and establish angle-resolved SHG as a sensitive probe of interface-driven nonlinearities in conductive-oxide and metal-based nanophotonic systems.

Speaker: Jyoti Arya (Universitat Politecnica de Catalunya)

18:20 Terahertz emission from Bi/GaAs heterostructures

Two-dimensional (2D) materials exhibit unique properties due to quantum confinement and large surface-to-volume ratios. Thin bismuth (Bi) layers are promising for topological insulators, thermoelectric devices, sensors, and ultrafast optoelectronics. While bulk Bi is a semimetal, ultrathin films become semiconducting. Femtosecond excitation of Bi films can generate terahertz (THz) radiation through photocurrent and nonlinear optical effects, while THz excitation spectroscopy (TES) provides insight into carrier dynamics and band structure. In this work, Bi layers were grown by molecular beam epitaxy on (100)-oriented GaAs, a previously unexplored substrate orientation. THz emission was investigated using wavelength-tunable femtosecond excitation from an OPA seeded by a Yb:KGW laser.

Heterostructures containing 9 nm Bi layers were fabricated on semi-insulating, n-type, and p-type GaAs substrates. TES measurements were performed in reflection geometry using p-polarized femtosecond pulses incident at 45°, with constant average excitation power of 20 mW. Strong THz emission appeared only when photon energy exceeded the GaAs bandgap (1.42 eV), indicating that emission mainly originates from processes in the GaAs substrate. Below the bandgap, THz emission was observed only for Bi/n-GaAs structures.
Opposite THz pulse polarities from n- and p-type substrates were attributed to reversed internal electric fields at the Bi/GaAs interface. The Bi optical absorption coefficient was estimated as 3×10⁵–4×10⁵ cm⁻¹ in the 1.5–1.7 eV range, exceeding that of GaAs by more than an order of magnitude. Bi/SI-GaAs structures showed polarity reversal near 1.7 eV, suggesting an additional interface-related THz generation mechanism. Enhanced THz emission from Bi/p-GaAs heterostructures was linked to hole drift velocity overshoot in strong internal electric fields, demonstrating the potential of Bi/GaAs heterostructures as efficient THz emitters.
[1] Reis, F., Li, G., Dudy, L., Bauernfeind, M., Glass, S., Hanke, W., Thomale, R., Schaefer, J. and Claessen, R., 2017. Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material. Science, 357(6348), pp.287-290.
[2] Inbar, H.S., Zubair, M., Dong, J.T., Engel, A.N., Dempsey, C.P., Chang, Y.H., Nishihaya, S., Khalid, S., Fedorov, A.V., Janotti, A. and Palmstrøm, C.J., 2023. Inversion symmetry breaking in epitaxial ultrathin bi (111) films. arXiv preprint arXiv:2302.00803.
[3] Jalil, A.R., Hou, X., Schüffelgen, P., Bae, J.H., Neumann, E., Mussler, G., Plucinski, L. and Grützmacher, D., 2023. Phase-Selective Epitaxy of Trigonal and Orthorhombic Bismuth Thin Films on Si (111). Nanomaterials, 13(14), p.2143.
[4] Liu, Y., Benter, S., Ong, C.S., Maciel, R.P., Bjork, L., Irish, A., Eriksson, O., Mikkelsen, A. and Timm, R., 2023. A 2D bismuth-induced honeycomb surface structure on GaAs (111). ACS nano, 17(5), pp.5047-5058.
[5] Aspens, D.E., Kelso, S.M., Logan, R.A. and Bhat, R., 1986. Optical properties of Al x Ga 1-x As. J. Appl. Phys, 60, pp.754-767.

Speaker: Benas Stanionis (Center for Physical Sciences and Technology)

18:20 Towards table-top ultrafast soft X-ray absorption spectroscopy at K and L edges

In condensed matter systems, many dynamical processes driven by strong correlations and non-equilibrium effects occur on ultrashort timescales, ranging from femtoseconds to nanoseconds. The objective of this work is to establish a table-top setup capable of extracting detailed information about these processes in complex materials at ultrafast timescales. X-ray absorption spectroscopy (XAS) has proven to be a powerful technique for obtaining element-specific information of electronic and structural properties of such systems. Here, we present a table-top soft X-ray source based on high-harmonic generation (HHG) in noble gases, which serves as an ideal tool for performing time-resolved XAS experiments. A four-stage optical parametric chirped pulse amplifier (OPCPA) has been developed to deliver intense mid-infrared pulses at 1.5 µm and 3 µm, with broad spectral bandwidths supporting with ~35 fs pulse durations. By employing the 1.5 µm driving laser with ~50 fs duration and 1 mJ pulse energy, and helium as the high-harmonic generation (HHG) medium, photon energies extending up to 350 eV have been achieved. Complementary to this, a thin-disk multipass amplifier capable of producing 100 mJ output pulses is currently under development. Integration of this amplifier with the existing OPCPA setup will enable HHG driven by the 3 µm beam, thereby extending the accessible X-ray photon energy range upto 1 keV. Furthermore, a pump-probe configuration has been realized, utilizing optical pump pulses at 1.2 eV and 2.4 eV to excite materials, followed by ultrafast X-ray to probe the dynamic electronic and structural changes.
Our earlier XAS study at the B K-edge in hexagonal boron nitride (h-BN) revealed well-resolved spectral features attributed to electronic transitions into σ⋆ and π⋆ molecular orbitals [1]. Current work is focused on probing ultrafast electron-phonon coupling and energy relaxation dynamics in borophane (HB) and its different polymorphs [2]. Furthermore, the extented photon energy range will enable access to transition metal L-edges and the oxygen K-edge, significantly broadening the applicability of table-top pump-probe XAS to a wider class of condensed matter systems.

We acknowledge the financial support by the DFG through SFB 1242 (Project No. 278162697) and BO 1823/14–1.

Speaker: Mr Rajdwip Bhar (University of Duisburg-Essen)

18:20 Ultrafast Photodissociation of Allyl Iodide: The Role of Resonance Stabilization in Excited-State Dynamics

The photodissociation of alkyl iodides has long served as a benchmark for understanding nonadiabatic molecular dynamics following ultraviolet excitation1. Allyl iodide provides an interesting extension to this family owing to the resonance stabilization of the allyl radical, which is expected to modify the excited-state potential energy landscape and influence the dissociation mechanism.
Here, we investigate the femtosecond photodissociation dynamics of allyl iodide at 200 nm using pump–probe velocity map imaging. Time-resolved detection of the iodine photofragments is achieved through state-selective Resonance Enhanced Multiphoton Ionization (REMPI) of both I and I*. Complementary measurements were carried out employing an intense 800 nm probe induce Coulomb explosion, providing complementary information on the structural evolution of the molecule during fragmentation. The combination of state-selective fragment detection and Coulomb explosion imaging provides a comprehensive picture of the competing ultrafast pathways following photoexcitation.
In contrast to the typical picosecond predissociation characterizing the dynamics induced at 200 nm in saturated alkyl iodides2, a fast dissociation occurring within 200 fs is observed. Complementary ab initio calculations indicate that the dissociation proceeds predominantly through the ion-pair state, providing a mechanistic explanation for the remarkably short dissociation timescale. These results demonstrate how resonance stabilization dramatically reshapes the excited-state dynamics of allyl iodide and reveal a distinct photodissociation pathway compared with other alkyl iodides.

Speaker: Sonia MarggiPoullain (Universidad Complutense de Madrid)

18:20 Vibronic Coupling Effects in the Photoelectron Spectra of LiB$_6^-$

The present article exhibits a theoretical exploration of vibronic coupling effects in the 193 nm experimental photoelectron spectra of the LiB$_6^-$, focusing on its six lowest-lying electronic states. Based on adiabatic potential energy curves derived from ab initio calculations, we construct a diabatic vibronic Hamiltonian and perform nuclear dynamics by adopting TD and TI formulations of quantum mechanics, treating in adiabatic (uncoupled) and non-adiabatic (coupled) scenarios. In this study, Poisson statistics provided vibronic intensity progressions from an adiabatic perspective, and the rapid transfer of electronic population confirmed the magnitude of the non-adiabatic coupling. Our final simulated spectrum reproduces the peaks of the experimental spectra in good agreement, providing the detailed vibronic interpretation of the photoelectron spectrum of LiB$_6^-$.

Speaker: Rishabh Kumar Pandey (The Chinese University of Hong Kong Shenzhen)

18:20 Visualizing Thermally Activated Conical Intersections Governing Non-Radiative Triplet Decay in Ni(II) Porphyrin-Nanographene Conjugates

Metalloporphyrins based on open-shell transition metals, such as Ni(II), exhibit typically fast excited-state relaxation. In this work, we shed light into the non radiative relaxation mechanism in a panchromatic nanographene-Ni(II) porphyrin conjugate. Variable temperature transient absorption spectroscopy (VTTAS) and global fit analysis are combined to produce a picture of the relaxation pathways.[1,2] The deciphered photophysical scenario comprises an intramolecular fast vibrational relaxation in 1.6 ps and subsequent intersystem crossing in 16 ps, bearing a short temporal window wherein singlets relax to the ground state, as confirmed by a short-lived NIR PL spanning from 850 to 1200 nm. Following intersystem crossing, fast relaxation of the triplet to the ground state proceeds in only 40 ps, almost an order of magnitude faster compared to Ni-based porphyrins. VTTAS combined with global analysis provide further information into this terminal relaxation stage. The results are interpreted in terms of a thermally induced population transfer from the lowest triplet energy level (a T(d,d) state according to DFT calculations) to a vibrationally excited ground state, enabled through a conical intersection of the respective ground and triplet potential energy surfaces. The findings presented herein showcase the remarkable potential of VTTAS in deciphering and quantifying rapid thermally activated relaxation phenomena.

Speaker: Prof. Juan Cabanillas Gonzalez (IMDEA Nanociencia)

19:00 → 20:00 Other: GELUR + LaserLab Spain - General Meeting

21:00 → 22:30 Social: Conference Dinner at Hostal Reyes Católicos

Friday 20 November

09:00 → 11:05 Oral: Session 8

09:00 Laser cavity solitons in microcombs: dynamics, robustness, and perspectives

Optical frequency combs in microresonators, often termed 'microcombs', are optical sources made up of a series of equally spaced frequency lines. These lines are typically produced in nonlinear microcavities through the Kerr nonlinearity. The discovery of dissipative temporal cavity solitons marked a significant breakthrough in the field, enabling the generation of broad and smooth spectra particularly suited to metrological frequency-comb applications[1].
We demonstrated the ability to generate localized pulses when a nonlinear microresonator is integrated within a fibre laser loop [2]. This led to our observation of laser cavity solitons. By combining the attributes of microresonators and multimode laser systems, this scheme provides an approach for the generation, stabilization and control of solitary optical pulses in microcavities. A distinctive feature of this architecture is the decoupling of the optical path in the gain medium from that of the parametric resonator [5]. Consequently, while the gain limits the pulse circulating in the amplifying cavity, the bandwidth generated within the nonlinear Kerr cavity is ultimately determined by its energy, dispersion and nonlinear interaction. This architecture can therefore overcome the gain-bandwidth limitation and has demonstrated high spectral efficiency, with parametric conversion efficiencies exceeding 50% [6].
Within this context, it is crucial to highlight the primary physical characteristics of these waves. These include their energy efficiency and dynamic properties, both of which are essential for initiating and restoring the system. We have shown that these states can emerge spontaneously and recover with resilience [3], including when interacting with other states within the system [4].
Lasing spontaneously emerges within the resonant lines of the nonlinear microresonator and leverages intrinsic stabilising feedback effects enabled by slow, energy-dependent nonlinearities, such as thermal effects and gain-induced refractive-index changes, in both the amplifying and nonlinear cavities [3,7,8]. This provides distinctive self-starting and self-recovery features to the architecture without external control. Similar stabilisation mechanisms are well explored in continuous-wave configurations, for example through thermal and self-injection locking [9,10], but here they act on the full pulse. The balance of these nonlinearities can be controlled through external global parameters, such as pump power and cavity length, allowing the system to naturally evolve into soliton, Turing or crystal states without resonance scanning or complex 'writing' procedures. The result is a highly versatile and robust system that can switch between different nonlinear states, including single-soliton operation, simply by tuning static global parameters [3]. The coexistence of different nonlinear states does not disrupt soliton formation; on the contrary, it can provide further robustness mediated by nonlocal nonlinearities [4].
Finally, the multi-modal nature of microresonator-filtered lasers fundamentally allows the lasing modes, and therefore the accessible nonlinear states, to be controlled with some degree of independence. In particular, the ability to select which modes reach threshold is enabled by the microresonator acting simultaneously as a nonlinear element and as a spectral filter. Very recent results show the capability to independently control the lasing threshold of different soliton families and access molecules and topological states [11], opening perspectives for topologically enabled robustness, ultra-low-phase-noise metrological sources and new regimes of photonic dynamics.
Microcombs are also increasingly considered as key sources for millimetre-wave and terahertz systems. The combination of favourable noise properties and high spectral efficiency can enable the direct driving of broadband emitters for communications, positioning and time-domain spectroscopy. We have recently demonstrated direct photoconductive conversion of a 50 GHz laser-cavity-soliton microcomb into a millimetre-wave baseband comb covering the sub-THz region [12]. The microresonator-filtered source combines low free-running phase noise and high spectral efficiency, enabling coherent conversion.
Notes and References
1 Herr, T. et al. Nature Photonics 2014, 8, 145-152.
2 Bao, H. et al. Nature Photonics 2019, 13, 384-389.
3 Rowley, M. et al. Nature 2022, 608, 303-309.
4 Cutrona, A. et al. Communications Physics 2023, 6, 259.
5 Peccianti, M. et al. Nature Communications 2012, 3, 765.
6 Cutrona, A. et al. Optics Express 2022, 30, 39816-39825.
7 Carmon, T.; Yang, L.; Vahala, K. J. Optics Express 2004, 12, 4742-4750.
8 Rowley, M. et al. Optics Express 2019, 27, 19242-19256.
9 Liang, W. et al. Nature Communications 2015, 6, 7957.
10 Shen, B. et al. Nature 2020, 582, 365-369.
11 Das, D. et al. Quenching of Noise in a Free-Running Möbius Microcomb, arXiv:2505.18911 (2025).
12 Peters, L. et al. Millimetre-wave comb generated by an optical microcomb. Nature Communications 2026. DOI: 10.1038/s41467-026-76747-2.

Speaker: Alessia Pasquazi (Loughborough University)

09:45 VEGA laser facility at CLPU: Infraestructure expansion and performance upgrades

The Spanish Center for Pulsed Lasers (CLPU) [1] is one of the Spanish Singular Scientific and Technical Infrastructures (ICTS), hosting the VEGA laser facility as its user-oriented experimental target area.
VEGA system is a Ti:Sapphire Chirped Pulse Amplification (CPA)-based laser chain comprising three beamlines called VEGA-1,2 and 3 delivering up to 20 TW, 200 TW and 1 PW peak power respectively. These three outputs share a common front-end and operate at a central wavelength of 800 nm with pulse durations of 30 fs. VEGA1-2 operate at a repetition rate of up to 10 Hz, while VEGA-3 operates at 1 Hz. The facility also provides the so called AREX1 experimental area, which is open to the national and international scientific community for laser–matter interaction experiments through competitive access calls. Since the beginning of user operations in 2018, the facility has supported laser-plasma acceleration experiments and related research activities [2], [3].
Throughout 2025-2026, the facility has undergone a significant upgrade aiming the expansion of its experimental capabilities as well as the improvement of its operational performance. Within this framework, a new building has been constructed adjacent to the existing infrastructure, providing a second experimental area (AREX2) together with additional space for a future upgrade of the VEGA laser system. In parallel, several technological projects have been initiated in order to improve the overall facility performance under operating conditions approaching the nominal repetition rates of the different beamlines, while also enabling parallel experimental activities by exploiting the availability of two independent target áreas. These developments are intended to increase the overall efficiency of the facility.
The ongoing projects include studies of the high-repetition-rate behaviour of pulse-compressor diffraction gratings, upgrades to enable robust simultaneous operation of VEGA-2 and VEGA-3 beamlines as well as the development of advanced targe-handling solutions to support operation at the nominal repetition rates during future experimental campaigns.
This contribution reviews the progress achieved in these developments, presents the new infrastructure and experimental capabilities enabled by the facility expansion, and provides an overview of the upcoming user-access calls, including their expected schedule and main characteristics, marking the beginning of a new operational stage for the CLPU user facility.

Speaker: Cruz Mendez (Centro de Láseres Pulsados)

10:10 Structured laser pulses: a tool to study chirality

Laser light can be tailored in a broad variety of ways. From standard temporal and spectral shaping, which led to the generation of ultrashort laser pulses, to harnessing light’s polarization or creating beams with properties associated to their spatial structure. Interestingly, the capability of shaping light’s symmetries and structure can be used to investigate matter’s symmetries and structure. Chirality, a universal property of objects that are not superimposable to their mirror image, is specially relevant in this context. Tailored fields allow us to probe chiral matter and ultrafast chiral dynamics in unprecendent ways. The merging of these two ingredients, tailored light and chirality, has led to new methods for studying chiral molecules [1].

On the one hand, microscopic tailoring includes shaping the electric field’s polarization by mixing frequencies, which results in a collection of Lissajous curves. A relevant polarization shaping in the context of chiral discrimination is locally chiral light, which presents a 3-dimensional polarization at each point of space [2]. On the other hand, macroscopic tailoring includes topological light, such as vortex beams, which carry orbital angular momentum associated to its azimuthally varying phase, and which have already proven to be a valuable tool for obtaining enantio-sensitity observables [3]. Another noteworthy type of topological light are vector beams, which possess a Poincaré index associated to its azimuthally-rotating polarization, being the most typical type of a vector beam radially polarized [4] (Fig. 1A). Vector beams have demonstrated to enhance super-resolution imaging and nonlinear interactions due to their improved focusing capabilities, and they offer promising applications in optical trapping, communications or laser manufacturing [5].

We propose a robust, ultrafast and highly efficient setup for distinguishing molecular enantiomers by combining ultrafast techniques with vector beams. Here, an infrared, elliptically polarized and tightly focused vector beam generates high-order harmonics in a sample of randomly oriented chiral molecules. High-order harmonic generation (HHG) results from the highly nonlinear interaction of the intense driving laser field with the target [6]. In our work, HHG leads to the emission of an ultraviolet vector beam whose intensity profile carries information about the handedness of the chiral molecules [7] (Fig. 1B-C). In particular, the handedness of the chiral molecules is imprinted in the divergence of the emitted light, leading to topological chiral rings. Our approach allows for spatial discrimination of molecular enantiomers, opening a new route for studying chirality in ultrafast time scales.

Figure 1. (A) Intensity and polarization of a radially polarized vector beam, which carries a topological charge linked to its spatial structure. (B,C) Total intensity profile of harmonic 6th after propagating to the far-field plane, emitted from the L-handed enantiomer (B) and R-handed enantiomer (C).

Notes and References
1. Habibović, D., Hamilton, K.R., Neufeld, O. and Rego, L. Nat. Rev. Phys. Emerging tailored light sources for studying chirality and symmetry. 2024, 6, 663–675.
2. Ayuso, D., Neufeld, O., Ordonez, A.F. et al. Nat. Photonics. Synthetic chiral light for efficient control of chiral light–matter interaction. 2019, 13, 866–871.
3. Mayer, N., Ayuso, D., Decleva, P. et al. Nat. Photonics. Chiral topological light for detection of robust enantiosensitive observables. 2024 18, 1155–1160.
4. Zhan, Q. Adv. Opt. Photonics. Cylindrical vector beams: from mathematical concepts to applications. 2009, 1, 1, 1-57.
5. Rosales-Guzmán, C., Ndagano, B., and Forbes, A. J. Opt. A review of complex vector light fields and their applications. 2018, 20, 123001.
6. Ferray, M., L’Huillier, A., Li, X. F., et al., J. Phys. B: At. Mol. Opt. Phys. Multiple-harmonic conversion of 1064 nm radiation in rare gases. 1988, 21, L31.
7. Rodriguez, A. and Rego, L. Ultrafast chiral sensing with an ultraviolet vector beam. 2026, arXiv:2606.13402.

Speaker: Laura Rego Cabezas (Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC))

10:35 Ultrafast nanoscale phase imaging at the tabletop

We present progress towards the realization of a coherent extreme ultraviolet (XUV) beamline at IMDEA Nanociencia that images nanoscale phase textures in quantum materials with femtosecond temporal resolution. This is achieved by combining high-harmonic generation (HHG)¹ with coherent imaging methods². The beamline will deliver monochromatized, polarization-controlled XUV radiation for coherent imaging experiments, overcoming the time restrictions of large-scale facility beamtimes and enabling a great control over the experimental conditions, as well as providing a test platform for optimization prior to synchrotron or XFEL experiments.

The driving laser is an Astrella HE amplifier delivering 30 fs pulses at 800 nm with 10 W average power at 1 kHz. These pulses are spectrally broadened in a gas-filled hollow-core fiber (HCF)³ and compressed down to 5 fs, leading to an HHG XUV supercontinuum. This generated supercontinuum, in combination with subsequent stages of the beamline, leads to a fully tunable XUV source. Polarization control of the XUV is achieved by generating circularly polarized HHG via a counter-rotating circularly polarized crossed-beam geometry⁴. To maximize harmonic efficiency in the non-collinear geometry, opposite-sign pulse-front tilts are introduced to the crossing beams to compensate temporal walk-off and improve the spatiotemporal overlap on the HHG target⁵. To this end, we designed a four-wedge compressor combining highly dispersive and birefringent low-dispersive media, allowing us to obtain angular dispersion that remains linear across the full bandwidth, while improving polarization purity. As a result, this approach produces the required spatial chirp for walk-off compensation without compromising few-cycle post-compression using commercially available double-chirped mirrors (DCMs), and avoids the significant energy losses associated with grating-based schemes.

In the next stage, the generated harmonics will be monochromatized using a time-and-polarization-preserving monochromator⁶, delivering tunable XUV radiation with ~250 meV bandwidth, targeting X-ray absorption fine-structure resonances, primarily at the Mn M-edge (~50 eV, ~25 nm) and Fe M-edge (~55 eV, ~22.5 nm). Finally, the beam will be delivered to a scattering chamber equipped with a cryogenically cooled sample manipulator, enabling temperature-controlled resonant scattering and imaging with in situ alignment and external field compatibility. A final spatial resolution of 25 nm and temporal resolution of 50 fs are targeted.

Our beamline will provide a tabletop source of tunable, narrowband (250 meV), polarization-controlled coherent XUV radiation with ultrafast temporal resolution (~50 fs), enabling resonant imaging of a wide variety of quantum materials.

1 Corkum, P. B. et al. Nature Physics, 2007, 3, 381–387.
2 Johnson, A. S. et al. Science Advances, 2021, 7, eabf1386.
3 Travers, J. C. et al. Nature Photonics. 2019, 13, 547–554.
4 Hickstein, D. et al. Nature Photonics, 2015, 9, 743–750.
5 Hernández-García, C. et al. Physical Review A, 2016, 93.4, 043855.
6 Poletto, L. et al. Applied Optics, 2010, 49, 5465–5473.

Speaker: Óscar Pérez Benito (IMDEA Nanociencia)

10:50 RESEARCH ON ULTRAFAST PHOTONICS SYSTEMS AT FYLA LABS

The Spanish company FYLA designs and manufactures ultrafast lasers and photonics systems. This talk presents the activities of the FYLA Ultrafast Photonics R&D Lab, whose research supports the company's different business units:

1. LASER Business Unit:
   Research on supercontinuum sources, focused on achieving ultra-broad, ultra-flat spectra and temporally coherent pulses.

2. INSPECTION Business Unit:
   Research on non-invasive inspection systems based on ultra-flat laser illumination and advanced photonic elements for beam management, detection, and signal analysis.

RAINBOW™: In-line industrial inspection of color, thickness, and defects during production processes.

PULSAT™: Non-invasive 3D inspection of semiconductor devices based on the Two-Photon Absorption Transient Current Technique (TPA-TCT).

1. NETWORKS Business Unit:
   Research on wireless laser communication systems. Based on ultrashort-pulse lasers with repetition rates in the GHz range, these systems provide longer reach and greater resilience to adverse atmospheric conditions than current state-of-the-art solutions.

Speaker: Dr Pere Peréz-Millán

11:05 → 11:35 Coffee break

11:35 → 13:50 Oral: Session 9

11:35 Ultrafast OPCPA for fundamental physics

As the generation and amplification of ultrafast laser pulses have also become widespread, multidisciplinary applications ranging from fundamental physics to the biomolecular fields have proliferated.
Recently, femtosecond technologies have been extended to high repetition rates (and high average powers) and scaled to high peak powers (high energy and short pulse duration) by using new generation of Yb-doped Diode-pumped solid-state lasers (DPSSLs) to pump ultrashort Optical Parametric Chirped Pulse Amplifiers (OPCPAs) [1]. This approach relies on the use of high (wall-plug) efficiency diodes to pump low quantum defect Yb based solid state amplifiers acting as drivers for ultrafast OPCPA. Allowing for spectral tunability while preserving large amplification bandwidth for ultrashort pulses. This is enabled by careful design and operation of the OPCPA stages, which also provides intrinsic Carrier Envelope Phase (CEP) stability, which is crucial for many applications of few-cycle pulses.
Using such a system we recently demonstrated for the first time second-harmonic generation (SHG) mediated by a fifth-rank nonlinear susceptibility tensor in Si(111). This was done by looking at the power scaling at each rotation angle of the sample - i.e. to study the intensity scaling of the rotational anisotropy dependence of the SHG emission (RA-SHG).
Nonlinear optical phenomena have long been a powerful tool to investigate the structural and electronic properties of materials. In particular, SHG is used for probing surfaces and interfaces of centrosymmetric materials, where bulk contributions are forbidden due to inversion symmetry, revealing surface-specific interactions by leveraging symmetry-breaking effects at the interface; and providing insight into the atomic-scale structure and bonding at interfaces, including chemically modified surfaces and oxide layers.
Additionally, we discuss recent developments and future prospects for ultrafast laser science and highlight some of the multidisciplinary applications that can be driven with ultrafast laser systems operating in the mid-Infrared (mid-IR) spectral region [3,4].
Mid-IR lasers are of great interest due to the high efficiency interaction with atmospheric and biological molecules, and due to the ability to enter strong field regimes while suppressing multi-photon ionization [2]. Due to the lack of suitable solid-state lasing materials for direct operation in the mid-IR, OPCPA based lasers are the undisputed approach towards few-cycle mid-IR laser systems.
[1] H. Fattahi et al, "Third-generation femtosecond technology," Optica 1, 45-63 (2014).
[2] Pires, H. et al “Ultrashort pulse generation in the mid-IR” Progress in Quantum Electronics, 43, 2015,
[3] Pires, H. et al “Ultrabroadband OPA in YCOB with a sub-ps Pump Source” Photonics 2023, 10, 253
[4] Alves, J. et al, “Multi-mJ Scaling of 5-Optical Cycle, 3 µm OPCPA”. Photonics 2021, 8, 503.

Speaker: Hugo Pires (Group of Lasers and Plasmas, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico de Lisboa)

12:25 Laser Isolation of Circulating Tumoral Cells in Liquid Biopsy

The isolation of circulating tumor cells (CTCs) with high cell viability for further multi-omic analysis and organoid generation is a turning point in modern oncology. In recent years, CTCs and CTC cluster research have completely changed the roadmap of disruptive translational technologies in oncology, mainly because if adequate CTC isolation without cell modification could be achieved in liquid biopsies, this would mean a paradigm shift in clinical and preclinical oncology. In this work, we present a proof of concept of CTCs isolation using Blister Actuated Laser Induced Forward Transfer (BA-LIFT) and demonstrate that the technique is not only valid for isolation and further single cell sequencing for multiomic analysis, but also for CTCs cell culture, which opens the possibility of using them to study tumor biology and generate new patient-derived models.

Speaker: Carlos Molpeceres (Universidad Politecnica de Madrid)

12:50 Inter-pulse memory and surface morphology formation in ultrafast-laser-modified fused silica for selective laser-induced etching

Selective laser-induced etching (SLE) relies on ultrafast laser modification of glass followed by selective chemical removal, yet the transient mechanisms that connect laser exposure to the final etched surface morphology remain insufficiently understood. A key open question is to what extent the periodic and quasi-periodic surface patterns frequently observed after etching originate from the ultrafast laser–matter interaction itself, from cumulative inter-pulse or inter-line dynamics, or from subsequent etching-driven roughness evolution.
In this work, we investigate surface topography formation in SLE-processed fused silica by combining systematic laser-parameter studies, controlled chemical etching, surface characterization, and time-resolved pump–probe microscopy. Laser writing strategies are varied to modify the spatial and temporal overlap of subsequent pulses and lines. The resulting surfaces are analyzed after etching to quantify roughness evolution, micro- and sub-micrometer feature formation, and the possible existence of an asymptotic roughness limit. A central part of the study is a pump–probe investigation of transient optical responses in fused silica after ultrafast excitation. The dynamics from ps to µs time scales are correlated with the etched surface morphology to identify which transient processes are likely to survive into permanent, etch-revealed structures.
This combined ultrafast-diagnostics and surface-metrology approach provides a route toward understanding how pulse-to-pulse material response governs morphology formation in SLE. Ultimately, the goal is to move from empirical laser-etching parameter selection toward predictive control of surface topography in three-dimensional glass microfabrication.

Speaker: Henry Axt

13:05 Surface passivation effects on the optical and excitonic properties of Ag₂S nanocrystals for NIR-II applications

Ag₂S-based nanocrystals (NCs) emerged in the recent years as highly promising emitters for deep-tissue imaging and luminescence nanothermometry. Their assets combine efficient NIR luminescence in the second biological window (1000 – 1350 nm), low cytotoxicity and large absorption cross-section. In this contribution we will focus on the light emission and photophysics properties of Ag2S NCs with different surface passivation. We will show how the nature of surface passivation plays an important role on their temperature-dependent photoluminescence properties and ultrafast excited-state dynamics.[1,2] By comparing plain Ag₂S NCs, Ag/Ag₂S NCs, and highly emissive surface-passivated Ag₂S NCs with graded Se/Zn shells, we show that surface chemistry critically determines their optical performance. Temperature-dependent measurements reveal strong thermal quenching of the infrared emission, enabling thermal sensing with high sensitivity, while also showing that the thermal stability of the photoluminescence quantum yield is crucial for practical imaging performance under physiological conditions. In particular, surface-passivated nanocrystals exhibit improved robustness against temperature-induced emission losses in aqueous media. Femtosecond transient absorption spectroscopy further shows that passivation sharpens excitonic resonances and suppresses defect-assisted recombination.[3] At low excitation densities, the dynamics are governed by trapping and exciton recombination, whereas at higher fluences biexciton and Auger recombination become significant. Faster multi-exciton recombination in passivated samples highlights the strong impact of surface engineering on many-body interactions.
Keywords: nanocrystals, luminescence, imaging, photophysics
[1] D. Ruiz et al., Adv. Funct. Mater. 2017, 1604629.
[2] P. Wang et al., Mater. Horiz. 2024,11, 6158-6168.
[3] V. Vega-Mayoral et al., Nanoscale, 2025, 17, 15697

Speaker: Victor Vega Mayoral (Madrid Institute for Advanced Studies in Nanoscience, IMDEA Nanociencia)

13:20 Photoinduced Charge-Transfer Suppresses Triplet Formation Efficiency in Thiocoumarins: Evidence from Ultrafast Spectroscopy and Theoretical Calculations

Thiocarbonyl-containing compounds are known for their distinctive photophysical properties, particularly for their rapid intersystem crossing (ISC) and high triplet yield facilitated by enhanced spin–orbit coupling (SOC). However, the ISC efficiency and resulting triplet yields can vary significantly depending on molecular properties. This study explores the role of intramolecular charge transfer (CT) in modulating triplet state generation in thiocoumarins. Specifically, the introduction of a diethylamino group at the 7-position of the thiocoumarin ring (Thiocoumarin 1 or TC1) induces CT character, yielding a moderate singlet oxygen generation efficiency (0.5-0.6) and solvent polarity-dependent fluorescence property. In contrast, the 7-acetoxy-substituted derivative (Acetoxy-TC) achieves remarkably high singlet oxygen yields (0.8-0.9) that are independent of the solvent environment. Time-resolved spectroscopic measurements reveal an ultrashort fluorescence lifetime and concomitant ultrafast triplet state generation in acetoxy-TC across solvents, indicating highly efficient ISC. On the other hand, TC1 having CT behavior has relatively stable singlet excited states and slower ISC dynamics, consistent with its steady state photophysical behavior. Complementary theoretical calculations further support these observations: Acetoxy-TC exhibits solvent-independent high SOC values and a small singlet–triplet energy gap, both conducive to efficient ISC. In contrast, TC1 has less favorable ISC promoting parameters. These findings underscore the importance of molecular design, specifically avoiding CT states, in achieving efficient triplet generation in thiocarbonyl systems.

Speaker: Abhijit Dutta (IIT Kanpur)

13:35 Closure