Optical crystal is used as the crystal material of optical medium material. It is mainly used for making windows, lenses and prisms in ultraviolet and infrared regions. According to the crystal structure, it can be divided into single crystal and polycrystalline. Because single crystal materials have high crystal integrity and light transmittance, as well as low input loss, the commonly used optical crystals are single crystal.
Types of optical single crystals
Halide single crystal
Halide single crystals are divided into fluoride single crystals, compound single crystals of bromine, chlorine and iodine, and halide single crystals of thallium. Fluoride single crystal has high transmittance, low refractive index and low light reflection coefficient in the ultraviolet, visible and infrared bands, but its disadvantages are high expansion coefficient, low thermal conductivity and poor impact resistance. The single crystal of bromine, chlorine and iodine compounds can pass through a wide infrared band, and its melting point is low, so it is easy to make large-size single crystal; the disadvantages are easy deliquescence, low hardness and poor mechanical properties. The halide single crystal of thallium also has a wide infrared spectral transmission band and is slightly soluble in water. It is a kind of detector window and lens material used at low temperature. Its disadvantages are cold fluidity, easy to be corroded by heat and toxic.
Oxide single crystal
The main oxide single crystals are sapphire (Al2O3), crystal (SiO2), magnesium oxide (MgO) and rutile (TiO2). Compared with halide single crystal, it has high melting point, good chemical stability, and good transmittance in visible and near infrared spectrum. It is used to manufacture all kinds of optical elements from ultraviolet to infrared spectrum.
Semiconductor single crystal
Semiconductor single crystals include single crystal (such as germanium single crystal, silicon single crystal), group II - VI semiconductor single crystal, group III - V semiconductor single crystal and diamond. Diamond is a crystal with long spectral transmission band, which can be extended to far infrared region, and has high melting point, high hardness, excellent physical properties and chemical stability. Semiconductor single crystals can be used as infrared window materials, infrared filters and other optical elements.
Optical polycrystalline materials
Optical polycrystalline materials are mainly hot pressed optical polycrystalline materials, which are obtained by hot pressing sintering process. There are oxide hot pressed polycrystalline, fluoride hot pressed polycrystalline, semiconductor hot pressed polycrystalline. Hot pressed optical polycrystals not only have excellent light transmittance, but also have excellent mechanical and physical properties such as high strength, high temperature resistance, corrosion resistance and impact resistance. They can be used as optical elements and window materials for various special needs.