Speaker
Description
Angle-resolved photoelectron spectroscopy with subcycle temporal resolution has emerged as a powerful technique for visualizing ultrafast carrier dynamics in the band structure of crystalline solids [1,2]. Yet, low probe photon energies limited these experiments to one-dimensional cuts through the center of the Brillouin zone. For orbital reconstruction via photoemission orbital tomography (POT), however, access to the entire two-dimensional momentum distribution is essential to capture all relevant signatures of molecular orbitals, which typically appear at large momentum values corresponding to the inverse of characteristic bond lengths [3].
Recently, we succeeded in combining phase-stable mid-infrared (MIR) pulses with MV/cm field strengths and an extreme-ultraviolet beamline generating few-femtosecond probe pulses. In combination with a time-of-flight momentum microscope, this enables the direct observation of strong-field effects on subcycle time scales across the entire first Brillouin zone of most quantum materials. The MIR field strength is even enough to directly alter inner molecular bonds and drive them on subcycle time scales. Additionally, a noncolinear optical-parametric amplifier provides wavelength-tunable excitation pulses. Therefore, the setup is also ideally suited to investigate phenomena like high-harmonic and high-order sideband generation, Floquet engineering, or Landau-Zener-Majorana transitions directly in the band structure [4].
In molecules, the energy differences between highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) typically occur on the eV scale. A dedicated POT setup providing visible pump and isolated attosecond probe pulses at a repetition rate of up to 1 MHz may soon resolve the associated attosecond electron dynamics.
References
[1] Reimann et al., Nature 562, 396 (2018)
[2] Ito et al., Nature 616, 696 (2023)
[3] Wallauer et al., Science 371, 1056 (2021)
[4] Eggers et al., arXiv:2602.12844 (2026)