Polarization characteristics of a diode pumped Yb:GdCa 4 O(BO 3 ) 3 laser

Abstract

GdCa4O(BO3)3 (GdCOB) is a promising host material for the trivalent Yb-ion with large splitting (>1000 cm-1) of the ground state (2F7/2) which facilitates efficient laser operation at room temperature. There have been a number of investigations in the continuous-wave (cw) regime, however, most of the previous studies ignored the issue of crystal orientation. GdCOB is a low symmetry biaxial crystal (point group m) and the absorption and emission spectra of Yb exhibit strong anisotropy. Here we report our experimental results with Yb:GdCOB crystals cut along the three principal optical axes under high-power unpolarized diode pumping in a simple plano-concave cavity. Our study reveals clearly significant anisotropy of the laser performance of Yb:GdCOB. For the y-cut crystal, polarized laser oscillation along the x- or z-axes is feasible, depending on the output coupling (T) utilized; with a specific T = 3% the two orthogonal polarization states exist simultaneously at different emission wavelengths. The laser oscillation obtained with the x- and z-cut crystals is polarized along the z- and x-axes, respectively, independent of T and the power level. Despite its complex output-coupling-dependent nature of laser oscillation, the y-cut crystal turns out to be the most promising for efficient high-power operation. A cw output power of 7.35 W at 1083-1085 nm polarized along the x-axis is obtained at room temperature, with an optical-to-optical efficiency of 63% and slope efficiency as high as 84%.