Compensation of thermally induced birefringence in active medium made of polycrystalline ceramics

摘要

The essential difference of ceramics from a single crystal is that crystal axes in each grain comprising ceramics are arbitrarily oriented. We apply quaternion formation (instead of traditional Jones matrix formalism) to describe depolarization of laser beam. This allows us to derive analytical expressions for depolarization ratio for uncompensated case and for all known compensation techniques as well. The analytic results, we have got, are in good agreement with numerical ones. It has been shown, that ceramic is almost equivalent to [111] crystal if the ratio of the rod length to grain length is about 300 or more. In particular, uncompensated depolarization is inversely proportional to this ratio. The latter is an important consequence of the random nature of thermally induced birefringence in ceramics.