Multi-physics simulation for thermal lensing suppression in high-power TGG crystals with power-dependent light-to-heat conversion coefficient

High-power laser induces severe photothermal effects in terbium gallium garnet (TGG), including high heat, thermal lensing, and thermal-stress distortion, thereby severely degrading device performance. Conventional simulations for TGG thermal effect generally adopt an estimated constant light-to-heat conversion coefficient (η), ignoring its power-dependent behavior revealed by recent experiments. This work constructs a light–heat–mechanics coupled finite element model based on this power-dependent η. Using measured absorption and η coefficients, the effects of pump power, cooling conditions, and beam waist on temperature gradient, refractive index distribution, thermal stress, and thermal focal length are quantitatively investigated. Results show that high-convection cooling reduces overall crystal temperature yet weakly suppresses thermal lensing. Expanding beam waist can efficiently lower temperature gradients and weaken thermal lensing. Thermal stress introduces a focal length one order of magnitude larger than the temperature gradient, indicating that the thermal-stress contribution to the total thermal lensing can be neglected. Those qualitative trends agree with physical intuition. Our corrected quantitative predictions provide practical references for high-power Faraday isolator design.