“Polars” or “polarizers” are devices that permit passage of light with vibrations in only one direction. In an optical “polarizing microscope”, two polarizers (the lower device is often referred to as the “polarizer” and the upper device is the “analyzer”) are oriented such that light vibrations are at 90 degrees from each other (and the two polarizers are said to be “crossed”). If nothing is present in the optical path between the two devices to change the light vibrations, all light is prevented from passing and the image is black. Material placed in the optical path changes the behavior of the light rays, with the behavior dependent on the crystallography of the material (e.g., crystal structure, crystallinity), the chemical composition, the thickness of the material, and refractive indices. If the analyzer is removed from the optical path, then the devices are not considered “crossed”.
Syn., crossed nicols, crossed polars