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Abstract

Spectral broadening of sub-200 fs near-infrared frequency comb pulses is carried out using the process of self-phase modulation (SPM) in a Herriott-type multi-pass cell. This geometry involves periodic focusing of the beam by curved mirrors to accumulate a small nonlinear phase at each pass through a Kerr medium. The multi-plate approach towards spectral broadening with fused silica crystals is followed by temporal post-compression to sub-100 fs using chirped mirrors. In addition, the case of self-compression is numerically simulated, where the anomalous dispersion of a KDP crystal is utilized to compensate for the SPM-induced positive chirp. The cell is distinctly designed to allow dispersion tunability using pressurized gases even during bulk-plate operation. Furthermore, external access to the optics is facilitated by home-built rotary feedthroughs. With an enhanced peak intensity, these shorter pulses promise a better yield of extreme ultraviolet light, which is generated using intra-cavity high-harmonic generation that will be employed for the spectroscopy of highly charged ions, and improved temporal resolution of multi-photon ionization studies.