Introduction to Infrared Optical Materials

Infrared optical materials refer to a type of material used in guidance technology and infrared imaging to manufacture filters, lenses, prisms, window panels, fairings, etc. These materials have physical and chemical properties that meet the requirements, namely good infrared transparency and wide projection band. Generally speaking, the transmittance and transmission of infrared optical materials are closely related to the internal structure of the material, especially the chemical bonds and energy level structure. For example, for crystal materials, the short wave absorption limit mainly depends on the band gap, while the long wave limit depends on phonon absorption, namely lattice vibration absorption. The frequency t of lattice vibration is related to the absorption long wave limit, that is, the lower the vibration frequency t, the larger the long wave limit. For diamond crystal materials, there are strong first-order lattice vibration harmonics and weak subharmonic absorption in the infrared band, so diamond structured crystals have good transmittance and wide frequency band characteristics.

For crystalline materials, without considering reservoirs and defects (porosity, etc.), the infrared transparency of most single crystal materials is almost the same as that of polycrystalline materials. Due to the similar properties of polycrystalline materials as single crystals and the absence of solid solutions inside, their mechanical strength, thermal shock resistance, and economy have been greatly improved. Due to being a single crystal, it is possible to achieve large sizes, etc. In some fields, it has replaced single crystal materials.

The projection band and transmittance of glass and plastic are related to their atomic and molecular structures, but due to the long-term disorder of their structures, the relationship between their short and long wave absorption limits and bandgap and phonon absorption is relatively vague. The application and research of glass and plastic have been an active field in recent years. Nowadays, infrared materials have developed into a big family, with complex and diverse technologies that are dazzling. This article only introduces the applications and developments of several important infrared materials in recent years.

Crystalline materials

Crystal materials are the first infrared optical materials used by people, and they are also the main optical materials currently in use. Crystal materials include ionic crystals and semiconductor crystals. Ionic crystals include alkali metal halide compound crystals, alkaline earth metals, halide compound crystals, oxides, and some inorganic salt crystals. Semiconductor crystals include nitrogen element crystals of O group, O group compounds, and O group compound crystals. Ionic crystals typically have higher transmittance and lower refractive index, resulting in lower reflection losses. Generally, it is not necessary to apply anti reflective film. Meanwhile, compared with non-ionic crystals, the optical properties of ionic crystals are less affected by temperature. This crystal has multiple physical and chemical properties, which can meet the needs of different applications. Some crystals also possess optical technology, magneto-optical effects, acousto-optic effects, and so on. Can be used as a detector material.