Infrared optical materials refer to a class of materials used in guidance technology and infrared imaging to manufacture filters, lenses, prisms, windows, fairings, etc. These materials have physical and chemical properties to meet the needs, that is, the main indicators are: good infrared transmittance 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 bond and energy level structure. For example, for crystalline materials, the short-wave absorption limit mainly depends on the band gap, while the long-wave limit depends on phonon absorption, that is, lattice vibration absorption. The frequency t of lattice vibration is related to the long-wave absorption limit, that is, the lower the vibration frequency t, The greater the long-wave limit, for the diamond crystal material, the infrared band has stronger primary lattice vibration harmonics and weaker sub-harmonic absorption, so the diamond structure crystal has better light transmittance and wider frequency band characteristics .
For crystalline materials, regardless of the library and defects (porosity, etc.), the infrared transparency of most single crystal materials is almost the same as that of polycrystalline materials. Since the properties of polycrystalline materials are the same as those of single crystals, there is no solid solution inside, and their mechanical strength, thermal shock resistance, and economic efficiency have been greatly improved. Because it is a single crystal, it can achieve large size and so on. In some areas, it has replaced single crystal materials.
The projection band and transmittance of glass and plastic are related to the structure of atoms and molecules. However, due to the long-term disorder of their structure, the relationship between the short-wave and long-wave absorption limits and the band gap and phonon absorption is relatively fuzzy. Application and research is an active field in recent years. Nowadays, infrared materials have developed into a big family, and its technology is complex and diverse and dazzling. This article only introduces the application and development of several important infrared materials in recent years.
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Crystal material
Crystal material is one of the first infrared optical materials used by people, and it is also the main optical material currently used. Crystal materials include ionic crystals and semiconductor crystals. Ionic crystals include alkali metal halide compound crystals, alkaline earth metals, halide compound crystals, and oxidation And some inorganic salt crystals, semiconductor crystals include o-group, o-group compound and o-group compound crystals of nitrogen element crystals. Ionic crystals usually have higher transmittance and lower refractive index, so the reflection loss is smaller. Generally, there is no need to apply anti-reflection coating. At the same time, compared with non-ionic crystals, the optical properties of ionic crystals are less affected by temperature. The crystals have a variety of physical and chemical properties, which can meet the needs of different applications. Some crystals also have optical technology, magneto-optical effect, acousto-optic effect and so on. Can be used as detector material.