Here are the fundamentals of what you want from a polarizing microscope
Polarizing microscope is a kind of microscope used to study so-called transparent and opaque anisotropic materials, and has important applications in geology and other science and engineering majors. All substances with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed by staining, but some of them cannot be used, and a polarizing microscope must be used. Reflective polarizing microscope is an essential instrument for the research and identification of birefringent substances by using the polarization characteristics of light.
The basic principle of polarizing microscope:
1. Single refraction and double refraction: When light passes through a certain substance, if the nature and path of light do not change due to the direction of irradiation, this substance is optically "isotropic", also known as single refraction , such as ordinary gases, liquids, and non-crystalline solids; if light passes through another substance, the speed, refractive index, absorption, polarization, and amplitude of the light are different due to the direction of irradiation, and this substance has optically " Anisotropy", also known as birefringent bodies, such as crystals, fibers, etc.
2. Light polarization phenomenon: 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 there are many vibration planes on the vertical light wave transmission axis, and the vibration amplitude distribution on each plane is the same; natural light can obtain light waves vibrating in only one direction after reflection, refraction, birefringence and absorption, etc. This kind of light wave is called "polarized light" or "polarized light".
3. The generation and function of polarized light: The most important components of a polarizing microscope are polarizing devices - polarizers and analyzers. In the past, both were composed of Nicola prisms, which are made of natural calcite, but due to the limitation of large crystal volume, it is difficult to obtain large-area polarization, and polarizing microscopes use artificial polarizers to Replaces the Nicholas mirror. Artificial polarizers are made of quinoline sulfate, also known as Herapathite crystals, which are green olive in color. When ordinary light passes through it, linearly polarized light that only vibrates in a straight line can be obtained. Polarizing microscopes have two polarizers, one device is called "polarizer" between the light source and the object to be examined; The outside of the accessory is easy to operate, and there is a scale for the rotation angle on it. When the light emitted from the light source passes through two polarizers, if the vibration directions of the polarizer and the analyzer are parallel to each other, that is, under the condition of "parallel analyzer position", the field of view will be the brightest. Conversely, if the two are perpendicular to each other, that is, in the "orthogonal correction position", the field of view is completely dark, and if the two are inclined, the field of view shows a moderate degree of brightness. It can be seen from this that the linearly polarized light formed by the polarizer, if its vibration direction is parallel to the vibration direction of the analyzer, can pass through completely; if it is skewed, it can only pass through a part; if it is vertical, it cannot pass through at all. Therefore, when using a polarizing microscope, in principle, the polarizer and the analyzer should be in the state of the orthogonal analyzer.
4. Birefringent body under orthogonal analysis position: In the case of orthogonality, the field of view is dark. If the object under inspection is optically isotropic (single refractor), no matter how you rotate the stage , the field of view is still dark, this is because the vibration direction of the linearly polarized light formed by the polarizer does not change, and is still perpendicular to the vibration direction of the analyzer. If the object to be inspected has birefringence characteristics or contains substances with birefringence characteristics, the field of view of the place with birefringence characteristics will become brighter. This is because the linearly polarized light emitted from the polarizer enters the birefringence body and produces a vibration direction. Two different linearly polarized lights, when the two kinds of light pass through the analyzer, because the other beam of light is not perpendicular to the polarization direction of the analyzer, it can pass through the analyzer, and the human eye can see bright elephant. When light passes through a birefringent body, the vibration directions of the two polarized lights are different depending on the type of object.
When the birefringent body is orthogonal, when the stage is rotated, the image of the birefringent body has four light and dark changes in the 360° rotation, and darkens once every 90°. The darkened position is the position where the two vibration directions of the birefringent body coincide with the vibration directions of the two polarizers, which is called the "extinction position". Rotating 45° from the extinction position, the object under inspection becomes the brightest, which is " Diagonal position", this is because when the polarized light reaches the object when it deviates from 45°, part of the decomposed light can pass through the analyzer, so it is bright. Based on the above basic principles, it is possible to judge isotropic (single refractor) and anisotropic (birefringent) substances by polarizing microscopy.
5. Interference color: In the case of orthogonal analysis, use mixed light of various wavelengths as the light source to observe the birefringent body. When the stage is rotated, not only the brightest diagonal position appears in the field of view, but also the will see the color. The reason for the appearance of color is mainly caused by interference color (of course, it is also possible that the object to be inspected is not colorless and transparent). The distribution characteristics of interference color are determined by the type of birefringent body and its thickness, which is due to the dependence of the corresponding delay on the wavelength of light of different colors. If the delay of a certain area of the object under inspection is different from that of another area, then The color of the light passing through the analyzer is also different.
