Page 139 - Fundamentals of Light Microscopy and Electronic Imaging

122 PROPERTIES OF POLARIZED LIGHT

Normal

Brewster Reflected ray
Incident
ray

90°

Refracted
ray

(a)

Blocked

(b)

Figure 8-4
Reflection polarization and Brewster’s critical angle. (a) The drawing shows an incident ray of
random light (E vectors at random orientations) being reflected off a horizontal surface
(glass or other dielectric material) as a linearly polarized beam to the eye. At a certain critical
angle (Brewster’s angle ), the degree of polarization of the reflected ray is 100% and the E
vectors of reflected rays vibrate in a plane that is perpendicular to the plane of incidence (the
plane defined by the incident, reflected and refracted rays). The refracted ray, oriented at a
90° angle with respect to the reflected ray, is only partially polarized. (Note: Brewster’s angle
is defined by the condition that exists when the reflected wave is at 90° to the refracted
wave; the phenomenon occurs because in the second medium the electric vector of the
component in the plane of incidence is pointing in the direction of propagation of the
reflected wave and consequently has no resultant wave in that direction.) (b) A Polaroid
sheet can be used to demonstrate the polarized nature of the reflected ray. If the
transmission axis of the Polaroid is oriented at 90° with respect to the vibrational plane of the
reflected ray, transmission is blocked. This principle is used to advantage in the design of
Polaroid sunglasses to reduce or eliminate reflective glare.