What is Brewster's Angle?

Brewster’s angle, or the polarizing angle, is defined as an angle at which an incident beam of unpolarized light is reflected after complete polarization.

The incident light with an electric field parallel to the plane of incidence usually has a zero reflection coefficient at a particular angle between 0 and 90°. As a result, the reflected light at the polarizing angle is linearly polarized by having its electric field vectors parallel to the plane of reflecting surface and perpendicular to the plane of incidence. The reflected light is partially polarized at other angles.

Brewster’s angle can be calculated using the following equation:

      n = sin(q_i)/sin(q_r) = sin(q_i)/sin(q_90-i) = tan(q_i)

where n is the refractive index of the medium of light reflection, q_i is the angle of incidence, and q_r is the angle of refraction.

This equation is also useful when determining the refractive index of an unknown specimen, such as opaque materials with high absorption coefficients for light transmission.

The critical Brewster’s angles for diamond, glass and water are 67.5°, 57° and 53°, respectively.

It has been observed that light reflected from the surface at the Brewster’s angle produces glare effects. Brewster’s angle is an important concept applied in modern lasers for producing linearly polarized light by reflections at the mirror surfaces of the laser cavity.

References

• Polarization by Reflection – Georgia State University
• Polarization by Reflection – Davidson College
• Brewster's Angle – Florida State University