We demonstrate a scheme for nonlinear pulse compression at high average powers based on self-phase modulation in a multi-pass cell using fused silica as the nonlinear medium. The scheme is suitable for compression of pulses with peak powers exceeding the threshold for critical self-focusing. At >400  W of input power, the pulses of a Yb:YAG-Innoslab laser system (10 MHz repetition rate, 850 fs pulse duration) are spectrally broadened from 1.6 to >13.5  nm bandwidth while maintaining almost diffraction-limited beam quality. The chirp is removed with a dispersive mirror compressor, and pulse durations of 170 fs at an output power of 375 W are achieved. The compression unit reaches an overall transmission of >90%.

We demonstrate nonlinear pulse compression by multi-pass cell spectral broadening (MPCSB) from 860 fs to 115 fs with compressed pulse energy of 7.5 µJ, average power of 300 W and close to diffraction-limited beam quality. The transmission of the compression unit is >90%. The results show that this recently introduced compression scheme for peak powers above the threshold for catastrophic self-focusing can be scaled to smaller pulse energies and can achieve a larger compression factor than previously reported. Good homogeneity of the spectral broadening across the beam profile is verified, which distinguishes MPCSB among other bulk compression schemes.

We report on single-pass high-harmonic generation (HHG) with amplified driving laser pulses at a repetition rate of 20.8 MHz. An Yb:YAG Innoslab amplifier system provides 35 fs pulses with 20 W average power at 1030 nm after external pulse compression. Following tight focusing into a xenon gas jet, we observe the generation of high-harmonic radiation of up to the seventeenth order. Our results show that state-of-the-art amplifier systems have become a promising alternative to cavity-assisted HHG for applications that require high repetition rates, such as frequency comb spectroscopy in the extreme UV.

We present first experimental results of our investigation of non-collinear high harmonic generation (NCHHG) with a chirped pulse amplification system. Collimated high harmonic radiation of higher than 9th order is observed along the bisector of two fundamental beams crossing in a xenon gas target. The obtained results show that cavity-assisted non-collinear high harmonic generation is a promising candidate for efficient generation and outcoupling of extreme ultraviolet (XUV) radiation.