Optical glass refers to glass that can change the direction of light propagation and can change the relative spectral distribution of ultraviolet, visible or infrared light. Optical glass can be used to manufacture lenses, prisms, mirrors and windows in optical instruments. Components made of optical glass are key elements in optical instruments. Amorphous (glassy) optical medium material that transmits light. It can be used to make various optical elements such as prisms, lenses, filters, etc. After the light passes through, it can change the propagation direction, phase and intensity. According to different requirements, optical glass can be divided into three categories: ① Colorless optical glass-it is almost completely transparent in the visible and near-infrared wide band, and it is the optical glass that is used in a large amount. According to the difference of refractive index and dispersion, there are hundreds of brands, which can be divided into two varieties, namely crown optical glass (represented by K) and flint optical glass (represented by F). Crown glass is borosilicate glass, which becomes flint glass after adding alumina. The main difference between the two is that the refractive index and dispersion of flint glass are relatively large, so spectroscopic components are mostly made of it. ②Radiation-resistant optical glass—has the properties of colorless optical glass, and can basically not change its performance under radiation exposure. For optical instruments irradiated by gamma, its variety and brand are the same as colorless optical glass. Its chemical composition is based on colorless optical glass, and a small amount of cerium oxide is added to eliminate the color center formed by high-energy radiation in the glass, so that the light absorption of this glass has little change after being irradiated. ③Colored optical glass-specific absorption or transmission properties for certain wavelengths of light. Also known as filter glass, there are more than one hundred varieties. The color filter can selectively absorb certain colors, and the neutral filter absorbs the light of all wavelengths the same, but it reduces the intensity of the beam without changing its color. The interference filter is based on the principle of light interference, reflecting off unwanted colors instead of absorbing them. The raw materials for the production of optical glass are some oxides, hydroxides, and carbonates, and phosphates or fluorides are introduced according to the requirements of the formulation. In order to ensure the transparency of glass, the content of colored impurities, such as iron, chromium, copper, manganese, cobalt, and nickel, must be strictly controlled. It requires accurate weighing and uniform mixing when batching. The main production processes are smelting, forming, annealing and inspection. There are single crucible batch smelting method and continuous smelting method in tank kiln (see kiln). Single crucible smelting method can be divided into clay crucible smelting method and platinum crucible smelting method. Regardless of the smelting method, it needs to be stirred with a stirrer, and the temperature and stirring are strictly controlled to make the glass liquid reach a high degree of uniformity. The molding methods of molding optical glass include classical crushing method, rolling method and pouring method. However, leakage molding (using a single crucible or continuous melt flow out) is more and more widely used, and it can be directly drawn or dripped. Large-size blanks are formed by molding or leaking materials, which improves the utilization rate of gobs and the rate of finished products. Annealing In order to eliminate the internal stress of the glass to a large extent and improve the optical uniformity, it is necessary to formulate a strict annealing system and perform precision annealing. The indicators tested and measured are: optical constant, optical uniformity, stress birefringence, fringes, bubbles, etc.