K9 glass is a glass product made from K9 material, which is used in optical coating and other fields. K9 material belongs to optical glass, and K9 is its domestic grade designation. Its corresponding foreign glass grades are as follows: BK7 is the grade of Schott AG in Germany, N-BK7 is also a glass grade of Schott AG in Germany, BSC7 is the grade of HOYA Corporation in Japan, and the domestic equivalent is H-K9L, a glass grade produced by CDGM (Chengdu Guangming Optical Glass Co., Ltd.).
BK7 has been used in the production of lenses and prisms for a long time. Although alternative grades such as BSC7 and BSL7 are available from different manufacturers, they are essentially identical in chemical composition, optical properties, physical properties and chemical properties. This glass features excellent transmittance in the visible spectral range and contains few bubbles or impurities; striae and refractive index inhomogeneities, which would adversely affect optical systems, are reduced to a level that has almost no impact on performance. In addition to lenses and prisms, BK7 is also used in the majority of optical components, such as substrates for mirrors, beam splitters, and various coated optical filters.