Effect of Internal Radiation Heat Transfer on the Thermal Stress in Growing Ti:Sapphire Crystal by Heat Exchanger Method
Titanium-doped sapphire crystal(Ti∶Al2O3,Ti∶sapphire)is the core material for the development of ultra-fast ultra-high-power laser systems.During the high-quality large-size Ti∶sapphire crystal growth process by heat exchanger method(HEM),internal radiation heat transfer has a significant impact on the heat transport,temperature and thermal stress distributions,and ultimately affects the crystal quality.Therefore,in this paper,the finite volume method is employed to simulate the internal radiation heat transfer within the Ti∶sapphire crystal and melt,while a displacement-based thermoelastic stress model is used to calculate the thermal stress in the crystal.The effects of internal radiation heat transfer on the temperature and thermal stress distributions were investigated in detail.The results show that internal radiation heat transfer significantly enhances the heat transport in the crystal and melt,resulting in dense distribution of isotherms at the bottom of the crystal and a significant increase of temperature gradient and thermal stress in this region.In addition,the thermal stress at the bottom of the crystal first increases and then decreases with the increase of the crystal absorption coefficient(doping concentration).As the absorption coefficient of the melt increases,the temperature gradient and thermal stress at the bottom of the crystal decrease slightly.As the scattering coefficient of the crystal increases,the temperature gradient and thermal stress at the bottom of the crystal gradually decrease.However,this influence is only important after the scattering coefficient is larger than the absorption coefficient.
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