PerkinElmer Spotlight 400 Series, User Manual

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Techniques for Collecting IR Images and Spectra . 71
Viewing a Sample with the Visible Polarizer
Polarized visible light can enable you to identify areas or structures that differ chemically and
to solve problems commonly found in infrared microspectroscopy applications.
The Theory of Light Polarization
Ordinary light and infrared radiation consists of waves vibrating in all possible planes
perpendicular to the direction of propagation. This is represented in the left side of Figure 24.
Conventionally the plane of the light is taken to be the plane of the continuously varying
electric vector.
If the light passes through a polarizer, the polarizer allows the passage of only those waves
that have their plane of vibration in one particular direction. The light that emerges is said to
be polarized, and is represented on the right side of Figure 24.
Figure 24 Representation of unpolarized light (left) and polarized light (right)
Because all components of the wave in the plane of polarization are transmitted, the ideal
polarizer allows 50% of the light through.
If a second polarizer is placed in the path of the polarized light two things may result:
• If the second polarizer is placed in the same direction as the first (as at the top of
Figure 25), the polarized light can pass straight through.
•
However, if the second is placed at a right angle to the first, a situation which is
referred to as crossed polarizers, the passage of the polarized light is blocked, that is,
extinction occurs (as at the bottom of Figure 25).