Generation of High Energy Sub-10fs Pulses at MHz Repetition Rate

Pump-probe experiments at the cutting-edge x-ray free-electron laser facility European XFEL [1] require ultrashort laser pulses at high repetition rates and with high pulse energy. However, mJ-class, sub-10 fs, MHz repetition rate lasers are not readily available, hence must be developed. In particular, an extension towards the ultraviolet wavelengths through resonant dispersive wave emission [2] would enable novel applications at EuXFEL. Here, we demonstrate the first steps towards reaching this goal, namely spectral broadening of MHz repetition rate milli-Joule ps-pulses in a gas filled Herriott cell, followed by compression, further broadening in a gas filled hollow core fiber [3] and final compression.