Compensation of Thermally Induced Distortions in a GGG-Based Cryogenic Faraday Isolator

We describe a cryogenic Faraday isolator with a gadolinium gallium garnet (GGG) crystal used for the first time as a magneto-optic element. Simultaneous compensation of thermally induced depolarization and thermal lensing using FK51 glass is demonstrated theoretically and experimentally. The temperature dependence of the ratio of thermo-optical constants P/Q is measured in the temperature range of 300-80 K for the GGG crystal and FK51 glass. The possibility of using this device at laser powers of ~20 kW is shown.