Saturation anisotropy in V:YAG passive Q-switch at 1338 nm

Abstract

Yttrium aluminum garnet YAG doped by Vanadium ions V3+ is a saturable absorber useful for passive Q-switching of lasers operating at wavelengths around 1.3 µm [1]. The topic of our present work was investigation of nonlinear transmission polarization anisotropy. The goal was to estimate V:YAG saturable absorber orientation in respect to cavity mode polarization to improve Q-switched laser output. The saturable absorber transmission in dependence on incident energy/power density was measured using the z-scan method. A diode pumped Nd:YAG/V:YAG microchip laser [2], operating at wavelength 1338 nm, was used as a polarized radiation source (pulse length 6.2 ns, energy 0.08 mJ). Measured data were fitted using a numerical model of a “thick“ saturable absorber transmission for Q-switched Gaussian laser beam [3]. Following parameters were estimated: saturable absorber initial transmission T 0 , saturation energy density w s , ground-state absorption cross-section σ GSA , saturated absorber transmission T s , excited-state absorption cross-section σ ESA , ratio γ = σ GSA /σ ESA , and absorbing ions density. The saturable absorber nonlinear transmission curve was measured repetitively for absorber turning around longitudinal crystal axis. For each angle, measured data were processed and absorber parameters were obtained. This measurement was done for two various cuts of V:YAG crystal - [111] and [100].