Equipment - PerkinElmer Spotlight 200 User Manual

74 . Spotlight 200 User's Guide
Inclusions in polymer films
Although they may appear identical when using non-polarized light, the film and inclusion
present in a polymer film may exhibit different degrees of birefringence when using polarized
light. If this is so, you can visibly identify the inclusion and collect an infrared spectrum to
determine its composition.
Rocks minerals and crystals
Most crystals are characteristically birefringent and thus are ideally suited to this technique.
Viewing a mixture consisting of crystals, such as an artificial sweetener, pharmaceutical
powder, or an illicit substance, enables you to visibly separate the components by their
relative size, shape and birefringence.
Fibers
Polarization may enable you to identify and separate fibers in a clump or to view a
bicomponent fiber. Most fibers in their natural state are optically thick and their cylindrical
shape can cause lensing effects. For these reasons, fibers are usually flattened in preparation
for infrared microspectroscopy. This flattening affects the birefringence of the structure and
may degrade the usefulness of this technique.
Biological substances
Birefringence can occur in some biological substances. You can collect infrared spectra of
thin sections of these materials. In some cases, polarized light can reveal structures or
chemical disparities in these structures, and infrared spectra can be collected of the different
regions of interest.

Equipment

The equipment for visible polarization studies consists of two parts: the polarizer and the
analyzer (Figure 25).
The polarizer polarizes the incoming beam from the illuminator and the analyzer contains a
polarizing element that you can rotate to any orientation. It is placed in front of the camera.
The polarizers for both transmittance and reflectance are built into the Spotlight 200, and are
automatically switched into the beam when the analyzer is inserted.
Figure 25 The Analyzer