定义：
指向为布儒斯特角的透明盘。

有些情况下当一束光穿过一些透明窗口，在该窗口损耗必须非常小。一个典型的情况是由玻璃管密封和包含外置的谐振腔反射镜的氦氖激光器，如图1所示，其中玻璃窗口将激光器中的气体混合物与外界空气隔离开。假设增益很小，输出耦合器透射率也很小，那么每次通过表面产生的损耗需要远小于1%。这可以采用布儒斯特窗来实现，其中光束的入射角为布儒斯特角。在这种情况下，空气-玻璃界面处p偏振光的反射率非常小，也就是偏振方向平行于入射平面。 

  

图1：氦氖激光器示意图。玻璃窗口在谐振腔中，方向调节为布儒斯特角，对p偏振光产生的损耗很小。 

正入射到未镀膜玻璃盘上的反射率通常为百分之几。如果采用抗反射涂层，可以减小到0.2%。而布儒斯特窗的损耗则比它还要低至少10倍。另外，任何残余的反射都会离开谐振腔，而不会引起干涉效应（正入射窗口就会发生这一效应）。当然，上面装置中的两个布儒斯特窗必须具有严格具有相同的指向。 
由于p偏振和s偏振光损耗差别很大，激光辐射的偏振态通常为p偏振。在许多激光器中，这是唯一决定偏振方向的效应。 
激光器谐振腔中布儒斯特窗（或者其它偏振光元件）的一个缺点是当激光器晶体中的热效应影响偏振态时会引起较大的去极化损耗。在这种情况下，从布儒斯特窗口得到的反射光束的功率很大但是光束质量很差。 
布儒斯特窗还可以用于光学调制器和激光防护罩。
 

Definition: transparent plates which are oriented at Brewster's angle such that parasitic reflection losses are minimized.

There are situations where an optical beam must be sent through some transparent optical window, whereas the optical losses occurring at this window must be very small. A typical example is a helium–neon laser with a sealed glass tube and external resonator mirrors as shown in Figure 1, where glass windows separate the laser gas mixture from ambient air. Given the small gain and the small output coupler transmission, the losses at these interfaces need to be far below 1% per pass. This is achieved by using Brewster windows, where the angle of incidence is close to Brewster's angle. In that situation, the reflectivity at the air–glass interfaces becomes very small for p-polarized light, i.e., when the polarization direction (= direction of the electric field) is in the plane of incidence.

Figure 1: Setup of a helium–neon laser. Although two glass windows are within the laser resonator, these induce very little optical loss for p-polarized light, as they are oriented for Brewster-angled incidence.

An uncoated glass plate at normal incidence would normally have a reflectivity of several percent on each side. With an anti-reflection coating, this could be reduced to e.g. 0.2%. Brewster windows can have at least 10 times lower losses. In addition, any residual reflection will leave the resonator, rather than lead to interference effects (as can occur for windows with normal incidence). Of course, both Brewster windows in a setup as shown above must have exactly the same orientation.

Due to the significant loss difference between p and s polarization, the polarization of laser emission is usually forced to be in the p direction if a Brewster window or Brewster plate is within the laser resonator. In many lasers, this is the only effect determining the polarization direction.

A potential disadvantage of Brewster windows (or other polarizing optical elements) in a laser resonator is that large depolarization loss can arise if, e.g., thermal effects within a laser crystal affect the polarization. In that case, reflected beams with significant optical power and typically poor beam quality leave the Brewster windows.

Brewster windows are also often used for optical modulators and for laser housings.