  Few-cycle lasers are essential for many research areas such as attosecond
physics that promises to address fundamental questions in science and
technology. Therefore, further advancements are connected to significant
progress in the underlying laser technology. Here, two-stage nonlinear
compression of a 660 W femtosecond fiber laser system is utilized to achieve
unprecedented average power levels of energetic ultrashort or even few-cycle
laser pulses. In a first compression step 408 W, 320 uJ, 30fs pulses are
achieved, which can be further compressed to 216 W, 170 uJ, 6.3 fs pulses in a
second compression stage. This is the highest average power few-cycle laser
system presented so far. It is expected to significantly advance the fields of
high harmonic generation and attosecond science.
