Transient grating measurements of refractive-index changes in intensively pumped Yb-doped laser crystals

摘要

Mechanisms of transient light-induced refractive-index changes in Yb-doped crystals Yb:KYW, Yb:KGW and Yb:YVO_4 were studied. Relative amplitudes and lifetimes of the electronic component of phase gratings caused by the po-larizability difference of the excited and unexcited Yb~(3+) ions and the thermal component arising from thermalization of the pump energy were measured. Polarizability difference values of the ground ~2F_(7/2) and the excited metastable ~2F_(5/2) levels at the testing wavelength of 633 nm were determined for all crystals. The thermal diffusivity of the samples was estimated for selected directions of the thermal gradient. An athermal direction, along which the thermal component of refraction disappears, was found in Yb:KYW. crystal under specific experimental conditions.