Polarizing Microscopes: Basic Principles & Characteristics
1, Characteristics of polarizing microscope: Polarization microscope is a type of microscope used to identify the optical properties of fine structures of substances. Any substance with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed using staining methods, but some are impossible and must be observed using a polarizing microscope. The characteristic of polarizing microscope is the method of changing ordinary light into polarized light for mirror inspection, in order to distinguish whether a substance is birefringent (isotropic) or birefringent (anisotropic). Birefringence is a fundamental characteristic of crystals. Therefore, polarizing microscopes are widely used in fields such as minerals and chemistry. In biology, many structures also have birefringence, which requires the use of polarizing microscopes to distinguish them. In botany, such as identifying fibers, chromosomes, spindles, starch granules, cell walls, and whether crystals are present in cytoplasm and tissues. In plant pathology, the invasion of pathogens often causes changes in the chemical properties of tissues, which can be identified by polarized light microscopy. Polarized microscopy is commonly used in human and animal studies to identify bones, teeth, cholesterol, nerve fibers, tumor cells, striated muscles, and hair.
2, The basic principle of polarizing microscope: (1) Monorefractive and birefringence: When light passes through a substance, if the properties and path of light do not change due to the direction of irradiation, this substance has "isotropy" in optics, also known as a single refractive body, such as ordinary gases, liquids, and amorphous solids; If light passes through another substance, its velocity, refractive index, absorption, and the vibration and amplitude of the optical skin vary depending on the direction of irradiation, this substance has "anisotropy" in optics, also known as a birefringent body, such as crystals, fibers, etc. (2) Polarization phenomenon of light: According to the characteristics of vibration, light waves can be divided into natural light and polarization. The vibration characteristic of natural light is that it has many vibration surfaces on the vertical axis of light wave propagation, and the amplitude and frequency of vibration on each plane are the same; Natural light can become light waves that vibrate only in one direction through reflection, refraction, birefringence, and absorption, and this type of light wave is called "polarized light" or "polarized light". *Simply put, it is linearly polarized light that vibrates only in a straight line. When light enters a birefringent body, it is divided into two types of linearly polarized light, A and B, as shown in the figure. The vibration directions of the two are perpendicular to each other, but the velocity, refractive index, and wavelength are different.
