26.4

Polarization and the Reflection and Refraction of Light

For incident angles other than 0°, unpolarized light becomes partially polarized in reflecting from a nonmetallic surface, such as water. To demonstrate this fact, rotate a pair of Polaroid sunglasses in the sunlight reflected from a lake. You will see that the light intensity transmitted through the glasses is a minimum when the glasses are oriented as they are normally worn. Since the transmission axis of the glasses is aligned vertically, it follows that the light reflected from the lake is partially polarized in the horizontal direction.
There is one special angle of incidence at which the reflected light is completely polarized parallel to the surface, the refracted ray being only partially polarized. This angle is called the Brewster angle . Figure 26-17 summarizes what happens when unpolarized light strikes a nonmetallic surface at the Brewster angle. The value of is given by Brewster’s law, in which n1 and n2 are, respectively, the refractive indices of the materials in which the incident and refracted rays propagate:

| (26.5)

This relation is named after the Scotsman David Brewster (1781–1868), who discovered it. Figure 26-17 also indicates that the reflected and refracted rays are perpendicular to each other when light strikes the surface at the Brewster angle (see problem 37 at the end of the chapter).

Figure 26-17 When unpolarized light is incident on a nonmetallic surface at the Brewster angle , the reflected light is 100% polarized in a direction parallel to the surface. The angle between the reflected and refracted rays is 90°.

Copyright © 2007 John Wiley & Sons, Inc. All rights reserved.