Passively Q-switched high-repetition-rate Yb:LuGG channel waveguide laser

We report on a compact, passively Q-switched waveguide laser fabricated via femtosecond direct laser writing (fs-DLW) in an Yb:LuGG crystal. Prior to Q-switching experiments, continuous-wave operation was systematically characterized under various cavity configurations, achieving a maximum output power of 678 mW and a slope efficiency of 53.6% using a 70% output coupler. Passive Q-switching was implemented by incorporating single-walled carbon nanotubes (SWCNTs) as a saturable absorber, enabling stable laser operation over several hours. The 7.39-mm-long waveguide laser operated near 1030 nm, and its Q-switched performance was investigated using three output couplers with different transmissions. The best performance was obtained with a 50% output coupler, yielding pulses as short as 35 ns, a maximum output power of 478 mW, and a highest repetition rate of 2.51 MHz. These results demonstrate the excellent compatibility between fs-DLW-fabricated Yb:LuGG waveguides and SWCNT-based saturable absorbers, offering a promising route toward robust and highly efficient compact pulsed laser sources.