Polarization microscopy

A polarizing microscope is a combination of a light microscope and a polarimeter and is governed by Biot's laws (determining the property of rotational polarization). It uses linear polarized light that oscillates in one plane. Nowadays, it is mainly used in mineralogy and in the investigation of some anisotropic systems (striated muscle, cell walls, starch grains). However, with the introduction of the electron microscope, it lost its importance.

Construction of a microscope
Polarization is carried out by filters (polarizer, analyzer), which are placed in the optical axis of the microscope. If the polarization planes of these filters are perpendicular to each other (the filters are crossed), the field of view of the microscope is dark.
 * Polarizer - in the lighting system (under or in the condenser).
 * Analyzer – behind the objective (in the tube or above the eyepiece).

Principle

 * The method uses the interaction of light with optically anisotropic substances, during which the so-called birefringence occurs.
 * The beam passing through the sample is split into two new ones, whose vectors oscillate in mutually perpendicular planes: one oscillates perpendicular to the polarization plane of the analyzer and therefore does not pass further, the other parallel to it.
 * The parallel oscillating beam passes through the analyzer and manifests as light, or in color (when using white light due to interference).
 * Unirefringent substances - water, cytoplasm, cell nucleus:
 * Remain dark when cross-filtered (not shown).
 * Birefringent substances – crystals, cellulose cell walls:
 * create a regular and extraordinary beam and therefore appear bright on a dark background when cross-filtered.

Usage

 * Mineralogy (identification of crystalline substances).
 * To display linearly arranged cellular structures, e.g. tonofibrils.
 * In cases where it is necessary to exclude errors caused by birefringence (cytophotometric experiments, pathology).

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