Optical glass cold processing technology and quality requirements

by:Crylight     2021-05-08

The difference between optical glass and other glasses is that as an integral part of the optical system, it must meet the requirements of optical imaging.

Its cold processing technology uses chemical vapor heat treatment and a single piece of soda lime silica glass to change its original molecular structure without affecting the original color and light transmittance of the glass, making it reach the ultra-hardness standard. Ultra-hard fire-resistant glass and its manufacturing method and special equipment that meet the fire-proof requirements under flame impact. It is made of the following weight ratio components: potassium salt vapor (72% to 83%), argon (7% to 10%), gaseous copper chloride (8% to 12%), nitrogen (2 %~6%).

It includes the following process: using soda lime silica glass as the substrate Cutting, cold processing of fine edge grinding → chemical vapor heat treatment of the cold processed soda lime silica glass → coating the surface of the soda lime silica glass with fire protection film treatment → special physical tempering treatment on the surface of the soda lime silica glass. A special thermal decomposition gasification equipment is composed of a cylinder body, a cylinder head fitted with it, and a reaction kettle integrally connected with the cylinder head.

There are the following requirements for the quality of optical glass:

First, the specific optical constants and the consistency of the optical constants of the same batch of glass

Each type of optical glass has a prescribed standard refractive index value for different wavelengths of light, which serves as the basis for optical designers to design optical systems. Therefore, the optical constants of the optical glass produced by the factory must be within a certain allowable deviation range of these values, otherwise the actual imaging quality will not match the expected result during the design and the quality of the optical instrument will be affected. At the same time, since the same batch of instruments are often made of the same batch of optical glass, in order to facilitate the unified calibration of the instruments, the allowable deviation of the refractive index of the same batch of glasses is more stringent than their deviation from the standard value.

Second, high transparency

The image brightness of the optical system is proportional to the glass transparency. 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 prisms and lenses, part of its energy is lost by the interface reflection of the 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 the surface with an 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 made less than 0.01 (that is, the light transmittance of the glass with a thickness of 1 cm is greater than 99%) .

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