What is a polarizing microscope?
Polarizing microscope is a microscope that inserts a polarizer and a analyzer into the optical system of an optical microscope to examine the anisotropy and birefringence of a sample. Polarizing mirrors and polarization detectors are both made of Nicol prisms or polarizing plates. The former is installed between the light source and the sample, while the latter is installed between the objective lens and the eyepiece lens or above the eyepiece lens. In biological samples, muscle fibers, bones, and teeth exhibit anisotropy, while starch granules, chromosomes, and spindles exhibit birefringence and are therefore used for chemical studies of tissue cells. Easy to use single wavelength light source. Due to the significantly weaker birefringence of biological samples compared to metallography, rocks, or crystals, their interference colors are sometimes utilized through the addition and subtraction phenomena caused by sensitive polarizing plates
Natural light and polarized light
Light is an electromagnetic wave that belongs to transverse waves (vibration direction perpendicular to propagation direction). All actual light sources, such as sunlight, candlelight, fluorescent lamps, and tungsten filament lamps, are called natural light. These lights are the sum of a large number of atoms and molecules emitting light. Although the electromagnetic waves emitted by a certain atom or molecule vibrate in the same direction at a certain moment, the vibration directions emitted by each atom or molecule are also different, and the frequency of this change is extremely fast. Therefore, natural light is the sum of the luminescence of each atom or molecule, and it can be considered that the probability of its electromagnetic wave vibration in all directions is equal.
Linearly polarized light
Linear polarized light, also known as plane polarized light, has the same vibration direction as light in the same plane. When viewed from the direction of light propagation, the vibration direction of this light is a straight line, hence it is also called linear polarized light or linearly polarized light.
The birefringence phenomenon of light and the optical axis of crystals
When a beam of light enters an anisotropic crystal, it splits into two beams propagating in different directions, a phenomenon called birefringence. Both beams of light that undergo birefringence are polarized light. One of these two rays of light always follows the law of refraction of light, and the propagation speed does not change when the incident direction is changed. This ray is called a normal ray and is represented by o; The other beam of light does not follow the law of refraction. When the direction of the incident light changes, its propagation speed also changes. The refractive index of the light is different, and this beam of light is called extraordinary light, represented by e.
In anisotropic crystals, there are certain special directions in which birefringence does not occur. Ordinary and extraordinary rays propagate in the same direction and at the same speed, and these directions are called uniaxial crystals. Crystals with one optical axis are called uniaxial crystals, and crystals with two optical axes are called biaxial crystals. For a biaxial crystal, the two beams of light after birefringence are both extraordinary rays.
