A polarizing microscope is a microscope used to study so-called transparent and opaque anisotropic materials. Any substance with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed by dyeing, but some are impossible, and a polarizing microscope must be used. Reflective polarized light microscope is an indispensable instrument for research and identification of birefringent materials by utilizing the polarization characteristics of light. It can be used for the majority of users to observe single polarized light, orthogonal polarized light observation and cone light observation.
main feature
A method of microscopically changing ordinary light to polarized light to identify whether a substance is monorefracted (isotropic) or birefringent (anisotropic). Birefringence is a fundamental property of crystals. Therefore, polarized light microscopes are widely used in the fields of minerals, chemistry, etc., and are also used in biology and botany. Polarized microscopy is a microscope that identifies the optical properties of a subtle structure. Any substance with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed by dyeing, but some are impossible, and a polarizing microscope must be used. The characteristic of a polarizing microscope is to change the ordinary light into polarized light for microscopic examination to identify whether a substance is monorefractory (isotropic) or birefringent (anisotropic). Birefringence is a fundamental feature of crystals. Therefore, polarized light microscopes are widely used in the fields of minerals, polymers, fibers, glass, semiconductors, and chemistry. In biology, many structures also have birefringence, which requires differentiation using a polarizing microscope. In botany, such as identification of fibers, chromosomes, spindles, starch granules, cell walls, and whether cells and tissues contain crystals. In plant pathology, the invasion of pathogens often causes changes in the chemical properties of tissues, which can be identified by polarized light microscopy.
Fundamental
(1) Single refraction and birefringence: When light passes through a substance, such as the nature of light and the way the light does not change due to the direction of illumination, this substance is optically "isootropic", also known as single refraction. Body, such as ordinary gases, liquids, and amorphous solids; if light passes through another substance, the speed, refractive index, absorbance, and polarization, amplitude, etc. of the light vary depending on the direction of illumination, and the substance is optically "Anisotropic", also known as birefringent, such as crystals, fibers, and the like.
(2) Polarization of light: Light waves can be classified into natural light and polarized light according to the characteristics of vibration. The vibration characteristic of natural light is that there are many vibration planes on the vertical light wave transmission axis, and the amplitude distribution of vibration on each plane is the same; natural light undergoes reflection, refraction, birefringence, and absorption to obtain light waves that vibrate in only one direction. Light waves are called "polarized light" or "polarized light".
(3) The generation and effect of polarized light: The most important components of polarized light microscopes are polarizing devices - polarizers and analyzers. In the past, both were made up of Nicola prisms, which were made of natural calcite. However, due to the large size of the crystal, it is difficult to obtain a large area of ​​polarization. Polarized microscopes use artificial polarizers. Instead of the Nicole shuttle. The artificial polarizer is made of crystals of quinoline sulfate, also known as Herapathite, which is green olive. When ordinary light passes through it, linearly polarized light that vibrates only in a straight line can be obtained. The polarizing microscope has two polarizers, one called the “polarizer†between the light source and the object to be inspected; the other device is called the “analyzer†between the objective lens and the eyepiece, and the handle extends into the lens barrel or the middle. The outside of the attachment is operated for a scale with a rotation angle. When the light emitted from the light source passes through the two polarizers, if the vibration directions of the polarizer and the analyzer are parallel to each other, that is, in the case of "parallel detection position", the field of view is the brightest. Conversely, if the two are perpendicular to each other, that is, in the case of "orthogonal misalignment," the field of view is completely dark, and if the two are tilted, the field of view indicates a moderate degree of brightness. It can be seen that the linearly polarized light formed by the polarizer can pass completely if its vibration direction is parallel to the vibration direction of the analyzer; if it is skewed, it passes only a part; if it is vertical, it cannot pass at all. Therefore, in the case of using a polarized light microscope, in principle, the polarizer and the analyzer are in a state of being orthogonally detected.
(4) Birefringent body under quadrature detection: In the case of orthogonality, the field of view is dark, if the object to be inspected is optically isotropic (single refractor), no matter how the object is rotated At the stage, the field of view is still dark, because the direction of vibration of the linearly polarized light formed by the polarizer does not change, and is still perpendicular to the direction of vibration of the analyzer. If the object to be inspected has birefringence characteristics or contains a material having birefringence characteristics, the field of view with birefringence characteristics becomes brighter because the linearly polarized light emitted from the polarizer enters the birefringent body and generates a vibration direction. Different kinds of linearly polarized light, when the two kinds of light pass through the analyzer, because the other beam is not orthogonal to the polarization direction of the analyzer, it can pass through the analyzer, so that the human eye can see the bright Elephant. When the light passes through the birefringent body, the vibration directions of the two polarized lights are different depending on the type of the object.
In the case of the birefringent, when the stage is rotated, the image of the birefringer changes four times in the 360° rotation, and dims every 90°. The darkened position is the position where the two vibration directions of the birefringent coincide with the vibration directions of the two polarizers, and the "extinction position" is rotated by 45° from the extinction position, and the object to be inspected becomes the brightest, which is " Diagonal position", because when the polarized light reaches the object when it deviates from 45°, part of the light is decomposed and can pass through the analyzer, so it is bright. According to the above basic principle, it is possible to judge isotropic (single-refractive) and anisotropic (double-refractive) substances by polarized light microscopy.
(5) Interference color: In the case of orthogonal detection, the mixed light of different wavelengths is used as the light source to observe the birefringent body. When rotating the stage, not only the brightest diagonal position appears in the field of view, but also You will also see the color. The reason for the appearance of color is mainly caused by the interference color (of course, the object to be inspected may not be colorless and transparent). The distribution characteristics of the interference color are determined by the type of the birefringer and its thickness, which is due to the corresponding delay in the dependence on the wavelength of the light of different colors. If the delay of one region of the object to be inspected is different from the delay of the other region, then The color of the light passing through the analyzer is different.
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