  We present nonlinear pulse compression of a high-power SESAM-modelocked
thin-disk laser (TDL) using an Ar-filled hypocycloid-core Kagome Hollow-Core
Photonic Crystal Fiber (HC-PCF). The output of the modelocked Yb:YAG TDL with
127 W average power, a pulse repetition rate of 7 MHz, and a pulse duration of
740 fs was spectrally broadened 16-fold while propagating in a Kagome HC-PCF
containing 13 bar of static Argon gas. Subsequent compression tests performed
using 8.4% of the full available power resulted in a pulse duration as short as
88 fs using the spectrally broadened output from the fiber. Compressing the
full transmitted power through the fiber (118 W) could lead to a compressed
output of >100 W of average power and >100 MW of peak power with an average
power compression efficiency of 88%. This simple laser system with only one
ultrafast laser oscillator and a simple single-pass fiber pulse compressor,
generating both high peak power >100 MW and sub-100-fs pulses at megahertz
repetition rate, is very interesting for many applications such as high
harmonic generation and attosecond science with improved signal-to-noise
performance.
