Thesis defense of Anahita OMOUMI

Thesis defense of Anahita OMOUMI, PhD student in the Lasers group of the LCF, on Friday 15 December 2023 at 2pm in the Auditorium of the Institut d'Optique Graduate School in Palaiseau, on the topic: "Development of an ultrafast VUV source for TR-ARPES applications."

Abstract: "Time and angle-resolved photoemission spectroscopy (TR-ARPES) stands as one of the most powerful techniques in condensed matter physics that enables us to obtain information about the energy and momentum of electrons in materials simultaneously. Among the array of light sources suitable for this technique, table-top laser-based sources have gained considerable attention in recent years. In this context, this manuscript reports on the development of a high flux high, repetition rate VUV source featuring a switchable pulsewidth. One of the key factors of concern in this category of sources is the frequency conversion method employed to adapt the laser pulse frequency to the required photon frequency in photoemission spectroscopy. In this work, we opted for two stages of third harmonic generation (THG), first in BBO crystals and then in xenon gas. Starting from an Ytterbium-doped industrial laser delivering 500 fs-pulses at 1030 nm and operating at 100kHz, nonlinear compression and broadening of laser pulses through a single multipass cell (MPC) geometry is carried out. This results in two near Fourier transformed (FT) beamlines with spectrally/temporally compressed and broadened pulsewidths. These beamlines along with 500 fs laser pulses form three FT beamlines with the pulse durations of 100 fs, 500 fs and 3ps and each of them can be used as fundamental pulse for THG stages.

The first THG stage results in 343 nm pulses which are served as driver pulse for the THG in xenon resulting in 114 nm. This versatility in pulsewidth selection within our setup has broadened the scope of TR-ARPES applications and allowed us to explore perturbative THG with different spectral and temporal pulsewidths revealing the important role of ionization in phase-matching conditions and efficiency of generation."