Basic Principles of Polarised Light Microscopy
Characteristics of Polarising Microscope
Polarising microscope is a kind of microscope to identify the optical properties of the fine structure of substances. Any substance with birefringence can be distinguished clearly under a polarising microscope, and of course these substances can be observed by staining, but some of them are impossible, and a polarising microscope must be used. The characteristic of polarising microscope is to change ordinary light into polarised light for microscopic examination, in order to identify a substance as monorefractive (isotropic) or birefractive (anisotropic). Birefringence is a fundamental characteristic of crystals. As a result, polarising microscopes are widely used in the fields of minerals and chemistry. In biology, many structures are also birefringent, which need to be distinguished using polarising microscopy. In botany, such as identifying fibres, chromosomes, spindle filaments, starch grains, cell walls and the presence of crystals in the cytoplasm and tissues. In plant pathology, the invasion of pathogens often causes changes in the chemical properties of the tissue, which can be identified by polarised light microscopy. In the human body and zoology, polarized light microscopy is often used to identify bone skeletons, teeth, cholesterol, nerve fibres, tumour cells, rhabdomyosarcoma and hair.
Basic principles of polarising microscopy:
(a) single refractive and birefringent: light through a substance, such as the nature of the light and the approach does not change due to the direction of irradiation, the substance is optically "isotropic", also known as a single refractor, such as ordinary gases, liquids, and non-crystalline solids; if the light passes through another substance, the speed of the light, the refractive index, the absorbance and light skin vibration, amplitude and so on due to the direction of irradiation and there are different, this material is optically "anisotropic", also known as birefringent, such as crystals, fibres and so on.
(ii) polarisation of light: light waves according to the characteristics of vibration, can be divided into natural light and polarised light. Natural light vibration is characterized by perpendicular to the light wave conduction axis with many vibrating surfaces, the vibration of the plane of the same amplitude, its frequency is the same; natural light after reflection, refraction, birefringence and absorption and other roles, it can become only in a direction of vibration of the light wave, this light wave is called "polarised" or "polarised light" or "polarised light". This kind of light wave is called "polarised light" or "polarised light".
The simplest is linearly polarised light that vibrates only in a straight line. When the light enters the birefringent body, as shown in the figure, is divided into A, B two kinds of linear plane polarised light, the vibration direction of the two perpendicular to each other, while the speed, refractive index and wavelength, etc. are different.
