Comparison of V:YAG and V:LuAG saturable absorbers for Nd:YAG 1338 nm microchip laser Q-switching

Abstract

Two saturable absorbers, V:YAG (V³⁺:Y₃Al₅O₁₂) and V:LuAG (V³⁺:Lu₃Al₅O₁₂), were compared as a passive Q-switches for microchip laser based on Nd:YAG gain medium. The emission wavelength of this laser was in 1.3 μm spectral range. Two Q-switched monolithic microchip laser devices were prepared: Nd:YAG/V:LuAG and Nd:YAG/V:YAG. Active Nd:YAG part of both microchip lasers was the same (4mm long, 1.1 at.% Nd/Y). The thickens of saturable absorbers ensured the same initial transmission (T₀ = 85%) of the passive Q-switch part (V:LuAG was 1.1mm long, V:YAG was 0.7mm long). The gain medium and the saturable absorber were diffusion bonded to form one monolithic crystal. The diameter of both crystals was 5 mm. Laser mirrors were deposited directly onto monolith faces. The output coupler with reflection 90% for the generated wavelength was placed on the V³⁺-doped part. The pump mirror (HT@808 nm, HR@1.3 μm) was placed on opposite monolith face. Lasers were tested under longitudinal continuous diode pumping and results were compared. Both lasers generated linearly polarized radiation at wavelength 1338nm with the lasing threshold 8W. Comparing the giant pulse parameters and the laser efficiency, the better results were obtained for Nd:YAG/V:YAG microchip laser. The pulse duration (FWHM) in this case was shorter (2.16±0.04 ns) and more stable than in Nd:YAG/V:LuAG case (3.3 ± 0.5 ns). The obtained average pulse energy was slightly higher for Nd:YAG/V:LuAG microchip laser (45 μJ) than for Nd:YAG/V:YAG (41 μJ) laser. However, due to shorter pulse length higher peak power (18.5 kW) was obtained with V:YAG saturable absorber than with V:LuAG (13.7 kW).