激光振荡器和激光放大器中激光晶体的热效应对光束特性有着重要的影响，不仅改变了光束的波前，还影响了光束的偏振态。基于激光晶体内的弹光效应，通过对光率体的主轴化，研究了自然双折射晶体中的热致双折射效应。结果表明，弹光效应对自然双折射晶体光率体的影响主要表现为横截面内椭圆主轴的偏转，主轴偏转角度小于0.01°。在激光振荡器和放大器中，一束线偏振激光经过具有热效应的自然双折射晶体之后退偏率小于1.8×10-8，这种条件下热致双折射效应的影响可以忽略，这与光学各项同性晶体完全不同。

The thermal effects in laser crystals have important influences on the properties of laser beams in a laser resonator and an amplifier. They not only change the beam wave fronts, but also affect the polarization states of the beams. Based on the elasto-optic effect of laser crystal, the thermally induced birefringence effect in natural birefringent crystals is investigated. It is showed that the effect of the elasto- optic effect on optical indicatrix in natural birefringent crystals is characterized by elliptical principal axis deflection in the cross section. The deflection angle of the principal axis is less than 0.01°. If a linearly polarized beam passes through a natural birefringent crystal with thermal effects in a laser resonator or an amplifier, the depolarization ratio is less than 1.8 × 10- 8. In this condition, the effect of the thermally induced birefringence effect can be ignored. This characteristic is quite different with that in the optically isotropic crystals.