Knowledge points about optical glass
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-equivalent in visible and near infrared It is almost completely transparent in a wide band, and it is an optical glass that is used very much. 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 very large, so spectroscopic components are mostly made of it.
2. Radiation 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 clean the color center formed by high-energy radiation in the glass, so that the light absorption of this glass is small after being irradiated.
3. Colored 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, 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.
Smelting has a single crucible batch smelting method and a tank kiln (see kiln) continuous smelting method. 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 for molding optical glass include the classical crucible method, the rolling method and the pouring method. However, leakage molding (using a single crucible or continuous melting liquid) is more and more widely used. Directly draw the rod or drop material to press or leak the material to form a large-size blank, which improves the utilization rate of the drop and the yield rate.
Annealing In order to clean the internal stress of the glass to a very large extent and improve the optical uniformity, it is necessary to formulate a strict annealing system for accurate annealing.
Inspection and measurement indicators include: optical constant, optical uniformity, stress birefringence, streaks, bubbles, etc.