Properties of a thermal lens in laser ceramics

A model of thermal optical effects in laser ceramics was constructed, which takes into account random orientations of crystallographic axes in ceramics grains. Analytic expressions for the thermally induced phase, its average value and dispersion were derived. The effect of the beam-phase modulation with the characteristic transverse size of the order of the grain size was predicted. It was shown that deterioration of the parameters of the beam quality caused by this effect is inversely proportional to the ratio of the length of the ceramic element to the grain size.