Thermo-optic effects of ceramic TGG in the 300–500 K temperature range

The thermal expansion coefficient α and the thermo-optic coefficient dn/dT were measured using a He-Ne laser (λ = 632.8 nm) between 300 K and 500 K for ceramic and single-crystal terbium gallium garnet (TGG). For ceramic TGG, the experimental values of α and dn/dT at 300 K were 7.0×10−6 K−1 and 17.5×10−6 K−1, respectively. We proposed fitting relations regarding the temperature dependence of α and dn/dT. Both α and dn/dT increased with temperature, and the temperature dependencies for ceramic TGG were in agreement with those of single-crystal TGG with orientation. We then evaluated thermally induced depolarization for an average laser power of 1 kW. The depolarization was evaluated to be larger than 0.01 at room temperature. Moreover, we simulated the thermal lens focal length and found that the temperature dependence is very slight compared to its dependence on the beam radius.