Compensation for Thermally Induced Depolarization in Magneto-Optical Media Made of Materials With a Negative Optical Anisotropy Parameter

Abstract

Thermally induced depolarization of radiation is the principal limiting factor of using Faraday devices in laser radiation with a high average power. In this work thermally induced depolarization is analyzed in a system of two optical elements made of cubic magneto-optical materials with a negative optical anisotropy parameter separated by a quartz rotator. The parameters of the optical scheme of a Faraday isolator (FI) based on single crystals cut in the [C] orientation, at which effective compensation of thermally induced depolarization is realized, are found. These parameters are universal and do not depend on the material of the magneto-optical element. Analytical expressions for the integral thermally induced depolarization are derived and the contributions of thermally induced linear birefringence and of the temperature dependence of the Verdet constant are analyzed. The parameter that allows assessing the contributions to depolarization of each of the thermal effects and predicting the efficiency of using the compensation scheme for a specific magneto-optical material is introduced. The proposed FI scheme with compensation is investigated for a number of known magneto-optical materials possessing a negative optical anisotropy parameter. The results obtained will significantly reduce thermally induced polarization distortion of radiation, and will allow developing FIs providing a high isolation ratio in powerful laser radiation.