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Cadmium telluride is a medium refractive index material (2.67 @ 10 microns) with excellent long wavelength transmission in the infrared. It is non-hygroscopic with very good chemical resistance. Since it is a multiple crystalline material, some lots of material can exhibit large Mie scattering at the shorter wavelengths. It has been marketed in the past as IRTRAN-6.
Windows, including those used for cooled infrared detectors, must be thicker than those made from other materials because of the low tensile strength.
Far-IR Transmission – 1 mm thick CdTe Window
Far-IR Transmission – 4 mm thick CdTe Window
CdTe also transmits at wavelengths longer than 80 microns at very low temperatures. However the transmission is temperature dependent and Si is generally a better choice for a window for this spectral region.
Melting Point: 1092 °C
Density: 6.2 g/cm3
Solubility in H2O: Insoluble
Hardness: 56 kg/mm2
Appearance: Black, cubic crystalline material, either polished or satin finish
Short Wavelength Limit: 17,000 cm-1 (1 mm)
Long Wavelength Limit: 313 cm-1 (1 mm), 340 cm-1 (4 mm)
CdTe can be coated with a BBAR (Broad Band Antireflection) coating. However, this coating will not improve transmission at wavelengths longer than about 16 microns.
Short and Long Wavelength Ranges for which transmissivity is greater than 50% of stated crystal thickness.