Terbium Aluminium Garnet Ceramics for Ultrahigh Power Laser Isolators

Summary form only given. Terbium gallium garnet (TGG) single-crystals and ceramics are widely used for high power laser isolators. The average laser power, however, limited by thermally-induced effects. For example, the thermal-birefringence-induced depolarization in TGG ceramics has been investigated experimentally. The extinction ratio and beam quality after passing through the Faraday isolator are degraded significantly by the thermal birefringence and the thermal wave front distortion of using a Faraday medium under kW-level high-average-power laser radiation. The magnitude of the thermal effects depends on the thermal properties of the Faraday materials. In particular, 1) Verdet constant, 2) thermal conductivity, 3) absorption coefficient at the laser wavelength, 4) thermo-optic coefficient (dn/dT), and 5) linear thermal expansion coefficient are essential characteristics of the thermal effect. Terbium aluminium garnet (TAG) single -crystals and ceramics are a new promising material for high power laser isolators, because it has high Verdet constant and thermal conductivity computed to TGG. In this paper, we report measurement results of the absorption coefficient at a wavelength of 1070 nm and the temperature dependence of Verdet constant and thermal conductivity of TAG ceramics. The sample of high quality TAG ceramics was fabricated by Konoshima Chemical Co., Ltd. From the measurements, we indicate that TAG ceramics can be used as 10 kW -level high -power isolator at a low temperature.