Investigation of self-induced depolarization of laser radiation in terbiumgallium garnet

Absorption of laser radiation in magnetooptical materials results in a temp erature gradient which induces depolarization due to both the temperature d ependence of the Verdet constant and the photoelastic effect of thermal str ains. This results in a limitation of the isolation ratio of Faraday isolat ors in high average power lasers, Here, we derive expressions for the isola tion ratio as a function of beam power, beam radius, angle between incident polarization and crystal asis, and characteristics of the magnetooptical m aterial. The theoretical results are compared with experiments for a terbiu m gallium garnet crystal. Our results allow us to choose the optimal parame ters to maximize the isolation ratio and to compare different materials fro m this point of view.