定义：插入到以布儒斯特角入射的光束中的共面盘。

布儒斯特盘具有表面是共面的由光学材料做成的盘，插入到以布儒斯特角入射的偏振激光光束中是为了使p偏振的反射损耗最小。 
布儒斯特角是入射角（与法线之间的夹角），根据盘的折射率得到： 

图1：布儒斯特盘，插入到入射角为布儒斯特角的入射光束中。P偏振光的反射损耗最小。 
图2表明在盘的表明p偏振和s偏振光的反射损耗随入射角度的变化曲线。 
布儒斯特盘通常插入到体激光器的激光器谐振腔中，用来产生依赖于偏振的损耗。这样辐射光是稳定的线偏振光，而偏振方向对应于布儒斯特盘的p偏振。在这一偏振态工作时，如果偏振态没有发生旋转或者其他腔内成分产生畸变，布儒斯特盘产生的损耗非常低。 
谐振腔中的去极化（例如，由增益介质的热效应引起，参阅热透镜）会将一部分功率耦合到s偏振光中，这时布儒斯特盘会产生很大的反射损耗。因此，尽管布儒斯特盘对p偏振光的损耗非常小，但是插入布儒斯特盘还是会降低激光器效率。反射光的空间形状很复杂，从中可以得出去极化机制的信息。 

图2：熔融二氧化硅表面对1064nm光的菲涅尔反射率随入射角的变化曲线。对于p偏振，当入射角为布儒斯特角时，反射率为0，而s偏振的反射率则随着入射角度增加而增加。反射损耗发生在布儒斯特盘的两个表面。 
除了依赖于偏振状态的损耗，布儒斯特盘用于高功率激光器中时还会存在热透镜效应，在锁模激光器中，其非线性和色散效应也都是有影响的。

Definition: coplanar plates inserted into beams at Brewster's angle

A Brewster plate is a plate of an optical material with coplanar surfaces, which is inserted into a polarized laser beam under Brewster's angle so that minimum reflection losses occur for p polarization.

Brewster's angle is the angle of incidence (measured against the direction of normal incidence), calculated from the refractive index of the plate according to

Figure 2 shows how the reflection losses of p-polarized and s-polarized light at each surface of the plate depend on the angle of incidence.

Figure 1: A Brewster plate, inserted into a laser beam at Brewster's angle. The reflection loss becomes minimal for p-polarized light.

A Brewster plate causes a parallel shift of the beam position, which is proportional to its thickness.

Brewster plates are often inserted into laser resonators of bulk lasers, often with the purpose of introducing polarization-dependent losses. This can force the laser to emit light with a stable linear polarization, the direction of which corresponds to p polarization at the Brewster plate. In this state of operation, the losses caused by a Brewster plate can be very low, if the polarization state is not rotated or distorted by the other intracavity components.

Figure 2: Fresnel reflectivity of a fused-silica surface at 1064 nm versus angle of incidence from air. For p polarization, the reflectivity vanishes at the Brewster's angle of incidence (55.4°), whereas for s polarization the reflectivity increases monotonously with increasing incidence angle. Note that the resulting reflection losses occur at both surfaces of a Brewster plate.Insertion of a Brewster plate in a laser can substantially reduce the laser power even if the Brewster plate is of high quality!

Depolarization within the resonator (e.g. caused by thermal effects in the gain medium) (→ thermal lensing) can couple some of the power into s polarization, which then experiences high reflection losses at the Brewster plate. Therefore, insertion of a Brewster plate can significantly decrease the laser efficiency even if the losses of the Brewster plate for p polarization are very small. The spatial shape of the reflected light can be complicated and reveal information on the depolarization mechanism.

Apart from polarization-dependent loss, a Brewster plate can exhibit thermal lensing when used in a high-power laser, and its nonlinearity and chromatic dispersion can be relevant in a mode-locked laser.