8.8 GHz Q-switched mode-locked waveguide lasers modulated by PtSe2 saturable absorber.

We demonstrate high-repetition-rate fundamentally Q-switched mode-locked Nd:YAG waveguide laser modulated by platinum diselenide (PtSe2) saturable absorber. The laser operation platform is a femtosecond laser-written monolithic Nd:YAG waveguide, and the saturable absorber is large-area few-layer PtSe2 that possesses relatively lower saturation intensity and higher modulation depth in comparison with graphene. With the superb ultrafast nonlinear saturable absorption properties of as-synthesized PtSe2, the waveguide laser could operate at ~8.8 GHz repetition rate and ~27 ps pulse duration, while maintaining a relatively high slope efficiency of 26% and high stability with signal-to-noise ratio (SNR) up to 54 dB. Our work indicates the promising applications of laser-written Nd:YAG waveguides and atomically thin PtSe2 for on-chip integration of GHz laser sources toward higher repetition rates and shorter pulse duration.