Why do infrared thermometers have to use germanium glass?

Silicon plano convex lens
The general infrared thermal imager is equipped with germanium glass as the window of the instrument to protect the subsequent optical system and infrared detection devices. However, since the refractive index of germanium material is 4, direct use will cause great loss to the incident signal. In order to improve the transmission ability of infrared signals, appropriate thin films need to be plated on the germanium glass to improve the transmission rate and protect the surface of the germanium lens.

Germanium laminated glass has very good light transmittance at 2-16um, and its physical properties are relatively stable. It is not easy to react with hydroxide, acid gas and water. The infrared temperature measuring instrument and thermal imager must use the medium and far infrared color filter. The wavelength band of the infrared temperature measuring instrument and thermal imager is generally 2-13um, while the germanium laminated glass just has a very good transmittance in the far infrared. The transmittance of ordinary optical lenses in this wavelength band is extremely low, so it can not be completed.

In addition, the transmittance of the germanium laminated glass can be greatly increased and the transmittance of the surface layer of the germanium laminated glass can be reduced by inlaying a light film on the germanium laminated glass. Germanium laminated glass does not pass in the invisible light band. In some thermal imagers, people can also use silicon crystal to replace germanium laminated glass. The wavelength band of silicon crystal is not as far as that of germanium laminated glass.

Silicon (polysilicon is a kind of organic chemical plastic raw material with high strength and insoluble water. It is in the range of 1 – π μ M-band has very good transmittance energy, and it is 300-30o in the far infrared band μ I also has very good light transmittance, which is a characteristic that other light and infrared raw materials do not have

Silicon (polysilicon is generally used for 35 μ Because of its good heat transfer performance and low relative density, it is also a common raw material for making laser mirrors, infrared thermometers and infrared optical laser lenses.

Germanium glass is used on the windows of infrared thermal imaging and infrared thermometer. The wavelength band of 8-14um is mainly considered. The transmittance of germanium glass is only 40-50% without coating, and the transmittance can reach 90% after coating. In addition, most customers also require DLC diamond-like carbon film on germanium glass to strengthen the hardness of germanium glass and achieve certain explosion-proof effect.


Hanzhong Brisun Optics Co., Ltd. Is the high precision optical element manufacturer provides customized production of Various optical lenses, including spherical lens, cylindrical lens, optical window, mirror, prism, filter, metal base mirror and other high-precision optical elements. The base materials include various optical glass, fused quartz, calcium fluoride (CaF2), zinc selenide (ZnSe), germanium (GE), silicon (SI), sapphire, metal and other materials. And provide antireflective film, high reflection film, spectroscopic film, metal film and other optical coatings.

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