Yb:YAG/Cr:YAG composite crystal with external and microchip resonator

Abstract

A compact diode pumped Q-switched lasers, operating at wavelength 1031 nm, were based on the composite crystal Yb:YAG/Cr:YAG. This composite crystal (diameter 3mm) consisted of diffusion bounded 3mm long Yb:YAG (10 at.% Yb/Y) and 1.6mm long Cr:YAG crystal (initial transmission 85% @ 1031 nm). External resonator allowing to tune generated Q-switched pulse parameters or microchip configuration offering the shortest pulses and highest peak power were tested for this device. For longitudinal pumping of Yb:YAG gain medium, fibre coupled (core diameter 200 μm, NA= 0.22) laser diode, operating at wavelength 968 nm, was used. In the first case, Yb:YAG/Cr:YAG composite crystal was AR-coated and placed inside the 150mm long semihemispherical resonator consisted of a flat pumping mirror (HR @ 1.01 − 1.09 μm, HT @ 0.97 μm) and curved output coupler (r = 150mm) with reflectivity 70% @ 1031 nm. Generated pulses with the peak power 23 kW were 17 ns long (FWHM). The highest generated pulse energy was 0.38 mJ. In the second case, the resonator mirrors were deposited directly on the crystal faces. The output coupler reflectivity was 85% @ 1031 nm. In this compact microchip configuration, 140 ps long (FWHM) pulses with energy 0.13mJ and peak power 0.92MW were generated at wavelength 1031 nm.