There are many kinds of glass. Optical glass is one of them. It can change the direction of light transmission. It is widely used in optical instruments such as lenses and prisms. Optical glass must satisfy the imaging requirement of light. It is not better than ordinary glass and has high quality requirement for optical glass. Qualified optical glass needs to meet the following requirements.
Firstly, the optical constants of optical glasses and the optical constants of the same batch of glasses should be consistent. The first kind of optical glasses has standard refractive index values for different wavelength light, which can be used as the basis for optical designers to design optical systems.
Therefore, the optical constants of optical glasses manufactured in factories must be within a certain allowable deviation range of these values, otherwise the actual imaging quality will be inconsistent with the expected results at design time and the quality of optical instruments will be affected. At the same time, because the same batch of glasses are often manufactured with the same batch of optical glasses, the tolerance of refractive index of the same batch of glasses is more stringent than that of their standard values in order to facilitate the uniform calibration of the instrument.
Secondly, it needs a high degree of transparency. The brightness of optical system imaging is proportional to the transparency of glass. The transparency of optical glass to a certain wavelength of light is expressed by the optical absorption coefficient K_ lambda. When light passes through a series of prisms and lenses, part of its energy is dissipated by the reflection of the interface of the optical parts and the other part is absorbed by the medium (glass). The former increases with the increase of refractive index of glass, and the value of high refractive index glass is very high. For example, the light reflection loss on a surface of heavy flint glass is about 6%.