定义：
激光器谐振腔中，由于去极化效应而引起的光功率损耗。

如果采用的增益介质没有双折射效应，且激光谐振腔中的某一元件对于一个偏振方向会产生很高的损耗，那么高功率激光器中增益介质的热效应会通过去极化而引起很强的损耗。原因是增益介质中的温度梯度会产生机械应力和一些双折射，因此轴向在光束横截面上发生变化。
（双折射轴也指向轴向和切线方向。）因此，最初的线偏振态发生畸变，在腔内偏振器件会产生损耗。 
如果增益介质本身具有很强的双折射，那么热效应引起的去极化效应就会受到抑制，双折射轴不会由于热效应而旋转很多。Nd:YVO4激光器就是这种情形。对于各向同性增益介质，例如Nd:YAG，在激光器谐振腔中采用一个法拉第旋转器和一个四分之一波片，就可以使去极化损耗最小化，或者调整激光器谐振腔，得到合适的古衣相移。这种补偿方式的基本原理就是通过增益介质的不同的去极化之间相互抵消或者部分抵消。采用一个YAG晶体也可以优化切割方向，从而降低去极化损耗。

Definition: losses of optical power in a laser resonator, caused by depolarization e.g. in a laser crystal

Thermal effects in a laser gain medium of a high-power laser can cause significant power losses through depolarization, if a gain medium without intrinsic birefringence is used and the laser resonator contains an element with high losses for one of the polarization directions (e.g. a Brewster plate). The reason for this is that the temperature gradients in the gain medium induce mechanical stress and thus some amount of birefringence, with the direction of the local birefringence axis varying over the beam cross-section. (The birefringence axes are those directions of polarization with the maximum and minimum refractive index; they are often oriented in the radial and tangential direction.) As a result, an originally linear polarization state is distorted, so that losses can occur at a polarizing intracavity element.

Thermally induced depolarization is suppressed if the gain medium has a sufficiently strong natural birefringence, so that the birefringent axis can not be significantly rotated by thermal effects. This is the case, e.g., in Nd:YVO₄ lasers. For optically isotropic gain media such as Nd:YAG, thermal depolarization loss can be minimized, e.g. by using a Faraday rotator [1], a λ/4 plate in the laser resonator [4], or by arranging the laser resonator for a Gouy phase shift of suitable magnitude [7]. The basic idea behind such compensation methods is to create a situation where depolarization from different passes through a gain medium cancel each other at least partially. Depolarization losses can also be reduced by using a YAG crystal with optimized cut direction [6, 8].

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