Basic principles and characteristics of polarizing microscopes
Characteristics of polarizing microscope: Polarizing microscope is a microscope used to identify the optical properties of the fine structure of substances. Any substance with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed by staining, but for some it is impossible and a polarizing microscope must be used. The characteristic of polarizing microscopy is to change ordinary light into polarized light for microscopic examination to identify whether a certain substance is monorefractive (isotropic) or birefringent (anisotropic). Birefringence is a basic characteristic of crystals. Therefore, polarizing microscopes are widely used in minerals, chemistry and other fields. In biology, many structures are also birefringent, which requires the use of polarizing microscopy to distinguish them. In botany, such as identifying whether fibers, chromosomes, spindles, starch granules, cell walls, and cytoplasm and tissues contain crystals, etc. In plant pathology, the invasion of pathogenic bacteria often causes changes in the chemical properties of tissues, which can be identified by polarized light microscopy. In human and zoology, polarized light microscopy is often used to identify bones, teeth, cholesterol, nerve fibers, tumor cells, striated muscle and hair.
The basic principles of polarizing microscopy: (1) Single refraction and birefringence: When light passes through a certain substance, if the nature and path of the light do not change depending on the direction of illumination, the substance is optically "isotropic" ", also known as a single refractive body, such as ordinary gases, liquids and non-crystalline solids; if light passes through another substance, the speed, refractive index, absorptivity of the light and the vibration and amplitude of the light skin will be different depending on the direction of illumination. , this kind of material is optically "anisotropic" and is also called birefringent body, such as crystals, fibers, etc. (2) Polarization phenomenon of light: Light waves can be divided into natural light and polarized light according to the characteristics of vibration. The vibration characteristic of natural light is that it has many vibration planes on the vertical light wave transmission axis. The amplitude of vibration on each plane is the same and its frequency is also the same. Natural light can vibrate in only one direction through reflection, refraction, birefringence and absorption. The light wave is called "polarized light" or "polarized light". The simplest is linearly polarized light that vibrates only in a straight line. When light enters a birefringent body, it is divided into two linear plane polarized lights, A and B, as shown in the figure. The vibration directions of the two are perpendicular to each other, but the speed, refractive index, and wavelength are different.
