Over 400 W average power, sub-2-cycle, carrier envelope phase stable fiber laser system

We report on the development of a carrier-envelope phase (CEP) stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad RMS. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability, and sub-two-cycle pulse durations. Similarly to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS), this newly developed system is accessible to the international research community in peer-reviewed open user calls of Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC).