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Description
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.