We have studied theoretically the depolarization thermally induced in an optical medium with disc or rectangular (slabs) geometry. Analytical dependences of the thermally induced depolarization in different Faraday devices on radiation power and on aspect ratio of slab or disc are obtained. Conditions at which the use of slabs or discs instead of rods allows creation of different Faraday devices operating at multikilowatt average power level are found. The emergence of high-quality TGG ceramics will help advance to even higher powers.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.