There are many types of glass, optical glass is one of them, it can change the direction of light propagation. It is widely used in lenses and prisms of optical instruments. Optical glass must meet the requirements of the imaging of light. It is no different from ordinary glass and has high requirements for the quality of optical glass. Qualified optical glass needs to meet the following requirements.
First, the optical constants of the optical glass and the optical constants of the same batch of glass need to be consistent. The first variety of optical glass has a prescribed standard refractive index value for different wavelengths of light, as the basis for the optical designer to design the optical system.
Therefore, the optical constant of the optical glass produced by the factory must be within a certain tolerance range of these values, otherwise the actual imaging quality will not match the expected result at the time of design and affect the quality of the optical instrument. At the same time, because the same batch of instruments are often made of the same batch of optical glass, in order to facilitate the uniform calibration of the instruments, the allowable deviation of the refractive index of the same batch of glass is more strict than their deviation from the standard value.
Secondly, it needs a high degree of transparency, the brightness of the imaging 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 prisms and lenses, part of its energy is lost at the interface reflection of the optical parts and the other part is absorbed by the medium (glass) itself. The former increases with the refractive index of the glass. This value is very large for high refractive index glass, such as about 6% of the light reflection loss of a surface of heavy flint glass.