High-repetition-rate few-cycle green source generation for sub-optical-cycle two-color Yb laser synthesizers

High-repetition-rate sub-optical-cycle synthesis based on two-color Yb lasers requires few-cycle pulses from both the fundamental wave (FW) and its second harmonic (SH). Yet generating few-cycle SH pulses remains challenging. Here, we demonstrate a 3.1 W few-cycle green source at 50 kHz using a strategy that first compresses the FW pulses, followed by frequency doubling and subsequent post-compression of the SH pulses in an argon-filled gas cell. The system derived pulses of 6.3 fs with 62-µJ pulse energy with 0.3% RMS power stability over 6 h, enabling strong-field electron dynamics control within sub-cycle regime and its applications at high signal-to-noise ratio.