Polarized Light The wave model of light depicts light waves vibrating at right angles to the way of travel of light with all vibration directions being evenly possible. This is “common” light. In plane-polarized light there is only one vibration direction. The human eye-brain system has no sensitivity to the vibration directions of light, and plane-polarized light can only be noticed by an intensity or color effect, for example, by abridged glare when wearing polarized sun glasses. The most broadly used material is Polaroid film. Invented by Land in 1932, Polaroid film consists of long chain polymers, treated with light absorbing dyes, and stretched so that the chains are lined up. Light vibrating parallel with the chains is absorbed while light perpendicular to the chains is conveyed.
There are two polarizing filters in a polarizing microscope - the polarizer and analyzer. The polarizer is located below the specimen stage typically with its tolerable vibration direction set in the left-to-right, East-West direction, though this is frequently rotatable through 360 degrees. The analyzer, typically aligned North-South but again rotatable on some microscopes, is sited above the objectives and can be enthused in and out of the light path as necessary. When both the analyzer and polarizer are in the optical path, their allowable vibration directions are positioned at right angles to each other. In this configuration, the polarizer and analyzer are said to be crossed, with no light passing through the system and a dark field of view present in the eyepieces.
The polarizer and analyzer are the vital components of the polarizing microscope ( darkfield polarized light microscope ,brightfield polarized light microscope and etc ) but other pleasing features consist of: • A rotating specimen stage to assist orientation studies with centration of the objectives and stage with the microscope optical axis to make the midpoint of rotation correspond with the center of the field of view. • Strain free objectives – stress in assemblage can create optical effects under polarized light, a factor that could complicate observations. • An eyepiece fitted with a cross wire graticule to mark the center of the field of view. Frequently, the cross wire graticule is alternated for a photomicrography graticule that assists in focusing the specimen and composing images with a set of frames bounding the area of the viewfield to be captured either digitally or onto film. • A Bertrand lens – to allow simple examination of the objective rear focal plane, to agree to precise adjustment of the illuminating aperture diaphragm and to view interference figures. • A slot to permit the placing of compensators/retardation plates between the polarizers, which are used to enhance optical path dissimilarity in the specimen. In most modern microscope designs with different techniques (darkfield polarized light microscope ,brightfield polarized light microscope and etc ), this slot is located also in the microscope nosepiece or an intermediate tube located between the body and eyepiece tubes. Compensation plates inserted into the slot are then located between the specimen and the analyzer. Polarizing microscopy (such as darkfield polarized light microscope ,brightfield polarized light microscope and etc ) be used both with reflected as well as transmitted light. Reflected light is helpful for the study of opaque materials such as mineral oxides and sulphides, metals and silicon wafers. Reflected light methods entail a dedicated set of objectives that have not been corrected for viewing through the coverslip, and those for polarizing work should, once more, be stress free.
