What is the Brewster's angle?

The Brewster's angle is the angle of incidence at which light is polarised.

When light is incident on a surface, it can be reflected, refracted or absorbed. When light is reflected, it can be polarised in a specific direction. The Brewster's angle is the angle of incidence at which light is reflected and polarised in a direction perpendicular to the plane of incidence. This means that the reflected light is completely polarised and there is no reflection in the other direction.

The Brewster's angle can be calculated using the formula tanθB = n2/n1, where θB is the Brewster's angle, n1 is the refractive index of the medium in which the incident light is travelling and n2 is the refractive index of the medium in which the reflected light is travelling. The Brewster's angle is dependent on the refractive indices of the two media.

The Brewster's angle has many applications in optics, including in polarising filters, anti-reflection coatings and laser cavities. Polarising filters are used to block out light that is polarised in a specific direction, while anti-reflection coatings are used to reduce unwanted reflections. Laser cavities use Brewster's windows, which are windows that are placed at the Brewster's angle, to allow the laser light to pass through without being reflected.