Highly-efficient Q-switched Yb:YLF laser at 995 nm with a second harmonic conversion

We report on a high-average power, pulsed source at 497.5 nm based on the frequency doubling of an acousto-optically Q-switched, cryogenically-cooled Yb:YLiF4 (Yb:YLF) laser. The Yb:YLF was resonantly pumped by a laser diode module into the 960 nm absorption band and generated a diffraction limited output beam at 995 nm. At this wavelength, the laser delivered up to 50 W of average Q-switched output power at a pulse repetition frequency (PRF) of 10 kHz with a pulse duration of 60 ns and a slope efficiency of 69%. At a PRF of 500 Hz, this laser yielded 14 ns long, 31 mJ pulses with the slope efficiency of ~40%. Frequency doubling was achieved using an LBO crystal with a conversion efficiency approaching 50% at both 500 and 1000 Hz PRF. The maximum achieved pulse energy at 497.5 nm was 14.3 mJ at 500 Hz PRF (average power over 7 W). To the best of our knowledge, this is the highest reported pulse energy and average power for an all-solid-state laser operating under 500 nm.