Polarized light microscopy is a contrast-enhancing technique that may be utilized for both quantitative and qualitative analysis of optically anisotropic specimens. In order for polarized light microscopes to reveal details that are poorly observed using traditional microscopy techniques, they must be equipped with a polarizer positioned in the light path before the specimen and an analyzer in the optical pathway between the observation tubes or camera port and the objective rear aperture. It is then the interaction of plane-polarized light with a birefringent specimen that results in image contrast. More specifically, this interaction produces two individual wave components with different velocities that fluctuate with the propagation direction through the specimen and that are each polarized in mutually perpendicular planes. When the light components pass through the specimen, they undergo phase alterations, but are eventually recombined with constructive and destructive interference when they pass through the analyzer.

Chemical Crystals - Chemical compounds can exist in three basic phases: gaseous, liquid, or solid. In gaseous form, chemicals are comprised of weakly bonded atoms that are able to expand to fill any available space. Liquids, however, are slightly more structured than gases, the component parts that comprise them moving freely among themselves, but tending not to disperse and separate from one another. Solid compounds, which exhibit strong atomic bonding, are the most structured type of chemicals, featuring a rigid shape and a definite volume. Furthermore, many solids exist naturally as crystals, their atoms displaying distinct three-dimensional geometrical patterns. Advances in science and technology have also made it possible to create a tremendous array of artificial crystals in the laboratory, a feat that has many important commercial and industrial applications.

Fibers - Natural fibers may be derived from many sources, including animals, vegetables, and minerals. The use of such fibers extends back beyond recorded history, archaeological evidence indicating that wool and flax had begun being woven into fabrics by the sixth century BC. Man-made fibers, however, which are fibers chemically and structurally altered to an appreciable extent during their production, were not developed until after the Industrial Revolution. The earliest of these fibers, including rayon and acetate, were comprised of the same cellulose polymers found in many natural fibers, though in a drastically modified form. Later man-made fibers, such as nylon and polypropylene, were created through purely artificial means and came to be classed in a separate category of fibers known as synthetics.

Hairs - Hair is a characteristic attribute of mammals. The primary purpose of the epidermal outgrowth is to provide insulation from the cold. Thus, animals inhabiting colder climes typically are covered in thicker masses of hair, often referred to as a coat or wool, than those native to warmer regions. Humans, who have little need for extra protection from the cold due to the development of clothing, are among the least hairy mammals. Indeed, humans have been intricately involved in increasing the hair growth of certain other animals in order to make them more productive contributors to the fur and textiles industries, further decreasing the necessity of human hair. Through selective breeding efforts, the output and quality of hair produced by sheep, goats, rabbits, and a wide array of other animals has been drastically improved for human purposes.

Rocks and Minerals - Minerals are naturally occurring substances of inorganic origin that have a definite chemical composition and usually exhibit a crystalline structure. Plants and animals require a wide variety of minerals in order to survive on a daily basis. Minerals are also important, however, as the basic building blocks of rocks, which comprise the solid portion of the Earth and other planets. Rocks are formed through various means and are usually broadly categorized based on this fundamental characteristic. More precisely, igneous rocks are those that have solidified from magma, sedimentary rocks are those that have formed from fragments, or sediments, of other rocks, and metamorphic rocks are produced via the alteration of igneous or sedimentary rocks.

Miscellaneous Polarized Light Specimens - In addition to chemical crystals, fibers, hairs, rocks, and minerals, a number of other types of specimen may benefit from observation through polarized light microscopy. The technique, for instance, readily reveals the striations present in many fish scales and samples of human muscle tissue, as well as the structural details of fossilized dinosaur bones. Utilization of polarized light microscopy can also reveal important information regarding harmful insects and parasites that afflict humans and other animals, such as the biting louse and the whipworm.

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