Page 137 - Fundamentals of Light Microscopy and Electronic Imaging

120 PROPERTIES OF POLARIZED LIGHT

Filter
Polarized
transmitted
Random light
incident light

(a)

(b) (c)

Figure 8-3
A Polaroid sheet generates linearly polarized light. (a) Only rays whose E vectors
vibrate in a plane parallel with the transmission axis of the sheet are transmitted as a
linearly polarized beam; other rays are partially transmitted or blocked. (b) A second
overlapping polar transmits light of the first polar if its transmission axis is parallel to
that of the first polar. (c) Transmission is completely blocked if the transmission axes of
the two polars are crossed.

the second. The removal of light at the unique crossed position is called
extinction. Here, polarized light from the first filter vibrates in a plane that is
perpendicular to the transmission axis of the second filter and is substantially
blocked by the second filter.
• Examine a beam of light reflected off a flat nonconducting surface (glass or
plastic) with a polar while rotating it through 360°. The reflected beam is
minimized at two azimuths, indicating that it is partially linearly polarized.
Used this way, the Polaroid sheet is called an analyzer. If the transmission
axis of the polar is known beforehand, you should be able to observe that the
plane of vibration of the reflected rays is parallel to the plane of the reflect-
ing surface. If the transmission axis of a polar is not known, inspection of a
reflected beam can be used to determine the approximate orientation of its
transmission axis.