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Currently available infrared transparent materials typically exhibit a trade-off between optical performance, mechanical strength and price. For example, sapphire (crystalline alumina) is very strong, but it is expensive and lacks full transparency throughout the 3–5 μm mid-infrared range.
Transparent spinel (MgAl 2 O 4) ceramic is used traditionally for applications such as high-energy laser windows because of its excellent transmission in visible wavelengths and mid-wavelength infrared (0.2–5.0 μm) when combined with selected materials – source: U.S. Naval Research Laboratory [citation needed]
Aluminium oxynitride (marketed under the name ALON by Surmet Corporation [3]) is a transparent ceramic composed of aluminium, oxygen and nitrogen.Aluminium oxynitride is optically transparent (≥80% for 2 mm thickness) in the near-ultraviolet, visible, and mid-wave-infrared regions of the electromagnetic spectrum.
Indium tin oxide (ITO) is a conducting material with the unusual property that it is transparent, so it is widely used in the flat panel display industry. Reflectance and transmittance measurements of the uncoated glass substrate were needed in order to determine the previously unknown n ( λ ) and k ( λ ) spectra of the glass.
Doped metal oxides for use as transparent conducting layers in photovoltaic devices are typically grown on a glass substrate. This glass substrate, apart from providing a support that the oxide can grow on, has the additional benefit of blocking most infrared wavelengths greater than 2 μm for most silicates, and converting it to heat in the glass layer.
Silicon is transparent to infrared light with wavelengths above about 1.1 micrometres. [58] Silicon also has a very high refractive index, of about 3.5. [58] The tight optical confinement provided by this high index allows for microscopic optical waveguides, which may have cross-sectional dimensions of only a few hundred nanometers. [10]
The most commonly used material is an oxide of a composition of ca. In 4 Sn. The material is a n-type semiconductor with a large bandgap of around 4 eV. ITO is both transparent to visible light and relatively conductive. It has a low electrical resistivity of ~10 −4 Ω·cm, and a thin film can have an optical transmittance of greater than 80% ...
For infrared light refractive indices can be considerably higher. Germanium is transparent in the wavelength region from 2 to 14 μm and has a refractive index of about 4. [18] A type of new materials termed "topological insulators", was recently found which have high refractive index of up to 6 in the near to mid infrared frequency range ...