Брюстер бұрышы және жарық поляризациясы

Angle of incidence for which all reflected light will be polarized

Brewster's angle (also known as the polarization angle) is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized. The angle is named after the Scottish physicist Sir David Brewster (1781–1868).

While at the Brewster angle there is no reflection of the p polarization, at yet greater angles the reflection coefficient of the p polarization is always less than that of the s polarization, almost up to 90° incidence where the reflectivity of each rises towards unity. Thus reflected light from horizontal surfaces (such as the surface of a road) at a distance much greater than one's height (so that the incidence angle of specularly reflected light is near, or usually well beyond the Brewster angle) is strongly s polarized. Polarized sunglasses use a sheet of polarizing material to block horizontally polarized light and thus reduce glare in such situations. These are most effective with smooth surfaces where specular reflection (thus from light whose angle of incidence is the same as the angle of reflection defined by the angle observed from) is dominant, but even diffuse reflections from roads for instance, are also significantly reduced. Photographers also use polarizing filters to remove reflections from water so that they can photograph objects beneath the surface. Using a polarizing camera attachment which can be rotated, such a filter can be adjusted to reduce reflections from objects other than horizontal surfaces, such as seen in the accompanying photograph (right) where the s polarization (approximately vertical) has been eliminated using such a filter. When recording a classical hologram, the bright reference beam is typically arranged to strike the film in the p polarization at Brewster's angle. By thus eliminating reflection of the reference beam at the transparent back surface of the holographic film, unwanted interference effects in the resulting hologram are avoided. Entrance windows or prisms with their surfaces at the Brewster angle are commonly used in optics and laser physics in particular. The polarized laser light enters the prism at Brewster's angle without any reflective losses. In surface science, Brewster angle microscopes are used to image layers of particles or molecules at air liquid interfaces. Using illumination by a laser at Brewster's angle to the interface and observation at the angle of reflection, the uniform liquid does not reflect, appearing black in the image. However any molecular layers or artifacts at the surface, whose refractive index or physical structure contrasts with the liquid, allows for some reflection against that black background which is captured by a camera.

Gas lasers using an external cavity (reflection by one or both mirrors outside the gain medium) generally seal the tube using windows tilted at Brewster's angle. This prevents light in the intended polarization from being lost through reflection (and reducing the round trip gain of the laser) which is critical in lasers having a low round trip gain. On the other hand, it does remove s polarized light, increasing the round trip loss for that polarization, and ensuring the laser only oscillates in one linear polarization, as is usually desired. And many sealed tube lasers (which do not even need windows) have a glass plate inserted within the tube at the Brewster angle, simply for the purpose of allowing lasing in only one polarization.

When the reflecting surface is absorbing, reflectivity at parallel polarization (p) goes through a non zero minimum at the so called pseudo Brewster's angle.