About using polarized light with Optem® Optical Systems:
Many Optem® optical systems have the ability to include polarization components in their optical paths. The polarizing accessories have two applications: 1. Reduction of internally reflected stray light for brightfield viewing of low to medium reflectivity specimens.
2. Polarized light viewing of optically active specimens.
Polarized light is useful in extinguishing unwanted reflections that may exist or in extracting weak polarized signals from a strong background. If the specimen has features that effect the polarization of incident light, the use of polarized illumination and possibly other polarization components in the system will aid in seeing these features on the specimen.
Three polarization components can be added as standard options of many Optem® systems. The first is a polarizer to polarize the incoming light from the coaxial port. The second is an analyzer to selectively block the light returning from the specimen. These components are always used together, and usually used to enhance contrast in optically active specimens. The optional third component is a quarter wave plate which is positioned below, or outside, any objective and supplementary lenses. Its function is explained below:
For simple brightfield illumination, the addition of the quarter wave plate is required. While reflected light from the lenses (noise) is nearly eliminated by the polarizer/analyzer components, the plane of polarization is effectively rotated 90 degrees by the quarter wave plate, so that the light reflected from the specimen (signal) is not eliminated by the analyzer, but passes through. The result is an increase in the optical signal to noise ratio when the reflectivity of the specimen is low to moderate.
In a coaxial illumination system, the incoming Illuminator light is polarized before it reaches the coaxial beam splitter. An analyzer is inserted into the optical path above the beam splitter. The above combination effectively cancels any reflections off lens surfaces below the beam splitter when the polarizers are crossed. A quarter wave plate can then be added below the objective to allow a reflective specimen to be seen. If the features of the specimen that are being viewed effect the polarization of the incident light, the quarter wave plate will not be needed.
Typical systems are illustrated here:
®Optem Z70XL Modular .pdf (25KB)
®Optem Z70XL Non-Modular .pdf (25KB)
®Optem Z70XL with Zoom 12/Lower Modules .pdf (30KB)
®Optem Z12/ pdf (40KB)
®Optem Z160 .pdf (40KB)
