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The difference between optical glass and others and polishing precautions
Optical glass is used to manufacture glass materials such as lenses, prisms, mirrors, windows, etc. of optical instruments or mechanical systems. Including colorless optical glass (usually referred to as optical glass), colored optical glass, radiation resistant optical glass, radiation protection glass and optical quartz glass. Optical glass has a high degree of transparency, a high degree of uniformity in chemistry and physics (structure and performance), and has specific and precise optical constants.
The difference between optical glass and other glasses is that as a component of the optical system, it must meet the requirements of optical imaging. Therefore, the judgment of the quality of optical glass also includes some special and stricter indicators. The image brightness of the optical system is proportional to the transparency of the glass. The transparency of optical glass to light of a certain wavelength is expressed by the light absorption coefficient Kλ.
After the light passes through a series of laser focusing mirror prisms and lenses, part of its energy is lost to the interface reflection of optical parts and the other part is absorbed by the medium (glass) itself. The former increases with the increase of the refractive index of the glass. For high-refractive-index glass, the value is very large. For example, the light reflection loss of one surface of the counterweight flint glass is about 6%.
Therefore, for an optical system containing multiple thin lenses, the main way to increase the transmittance is to reduce the reflection loss on the lens surface, such as coating a surface antireflection coating. For large-size optical parts such as the objective lens of an astronomical telescope, the transmittance of the optical system is mainly determined by the light absorption coefficient of the glass itself due to its large thickness. By improving the purity of the glass raw materials and preventing any coloring impurities from mixing in the entire process from batching to smelting, the light absorption coefficient of the glass can generally be less than 0.01 (that is, the light transmittance of the glass laser protective glass with a thickness of 1 cm). Greater than 99%).
Optical lens is a lens made of optical glass, generally refers to a lens that can transmit and adjust visible light. Optical lenses must be measured by optical instruments to check purity, transparency, and uniformity Whether the degree, refractive index and dispersion rate meet the specifications, the qualified glass block is heated and forged to form an optical lens blank. After the optical lens is finely ground by the abrasive liquid, there is still a thick cracked layer on the surface. The method to eliminate this cracked layer is polishing.
After the optical lens is finely ground with a grinding fluid, there is still a crack layer about 2–3m thick on the surface. The method to eliminate this crack layer is polishing. The mechanism of polishing and grinding is the same, except that the tool material used is different from the slurry. The materials used for polishing include cloth, polishing leather (polyuret laser collimator hane) and pitch (pitch). To achieve a high-precision polished surface, the most commonly used material is high-grade polished asphalt.
Using asphalt to polish, the fine surface of asphalt drives the polishing liquid to grind the surface of the lens to generate heat, which makes the glass melt and flow, melt away rough vertices and fill up cracks At the bottom of the valley, the crack layer is gradually removed.
Currently, the polishing powder used for polishing glass lenses is mainly cerium oxide (CeO2). The proportion of the polishing liquid varies according to the polishing period of the lens. Generally, the initial stage of polishing Use a high-concentration polishing liquid when combining with the polishing mold. After the lens surface is bright, use a thinner polishing liquid to avoid orange peel on the mirror surface (fogging of the lens surface).
The movement mechanism used for polishing and grinding is the same. In addition to the polishing tools and working fluids are not the same as optical lenses, the environmental conditions required for polishing are also stricter than those for polishing. The general things to pay attention to when polishing are as follows: There should be no impurities in the surface of the polishing asphalt and the polishing liquid, otherwise it will cause scratches on the mirror.
The polished asphalt surface must match the surface of the lens, otherwise it will be bounced during polishing, which will bite the polishing powder and scratch the surface of the lens. Before polishing, it must be determined whether there are scratches or punctures on the surface of the lens after polishing. Whether the size and material of the polishing tool are appropriate. Whether the hardness and thickness of the asphalt are appropriate.
During the polishing process, you must always pay attention to the condition and accuracy of the lens surface. In the inspection of lens surface defects, because the inspection process is judged by personal vision and methods, the inspector should have a deep understanding of the specifications of scratches and sand holes, and often compare the standard samples of scratches and sand holes. To ensure the correctness of the inspection.