Cryogenic Faraday isolator with a disk-shaped magneto-optical element

A cryogenic Faraday isolator with disc-shaped magneto-optical element is described. Depolarization of laser radiation caused by transverse inhomogeneity of Verdet constant has been measured for the first time. The decrease of the thermally induced effects caused by heat removal from the face-end of the magneto-optical element of terbium gallium garnet with sapphire and aluminum-yttrium garnet discs is investigated. Characteristics of the cryogenic Faraday isolator at high laser power above 1 kW have been investigated experimentally and the possibility of its use at power as high as 6 kW is demonstrated. The reduction of thermo-optical constants Q and P by a factor of 5.7 and 6.8, respectively, with cooling from 300 K to 80 K has been measured for TGG crystal.