Alternative Window Materials
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BaF2 - Excellent Multispectral Material
BaF2 is easily cleaved and susceptible to thermal shock.
IR, UV, and VUV grades are available.
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GaAs - Broad transmission in infrared
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Ge - IR transmission to 23 microns.
The refractive index of Germanium changes rapidly with temperature. The material becomes opaque at all wavelengths above 75 degrees C as the band gap saturates with thermal electrons. The lowest-absorbing Ge optics are limited to a throughput power range of 50-100 watts before thermal lensing or thermal runaway.
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The data provided is for N-BK7. This is the most common Schott glass specified for visible applications.
There is an enormous variety of silica glasses available.
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SiO2 Infrared grade fused silica
Normal grades of Fused Silica contain water which gives it strong absorption in the IR. Infrasil is post processed to remove water.
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Sapphire Al2O3
Sapphire is very tough and strong. Sapphire is an optical window material for use in the ultraviolet, visible, and near infrared.
Higher quality Sapphire is manufactured by Kyropulos growth and has excellent UV transmission.
Sapphire is slightly birefringent. So-called zero degree exhibits the least birefringence.
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Si - Used as an optical window mainly in the 3 to 5 mm band.
Silicon additionally transmits between 30 to 100 microns.
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SiO2 xtal - Crystal quartz is isotropic. It is crystalline and birefringent.
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SiO2 Fused Silica is hard with very low expansion.
Fused silica is anisotropic (glass).
Strong absorption in the IR due to hydoxyl groups being present.
See Infrasil (or water-free) fused silica.
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SrF2 - Strontium Fluoride has optical properties between calcium fluoride and barium fluoride.
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ZnS - FLIR grade is harder than ZnS multispectral grade.
Zinc Sulfide windows should not be used above 250°C in air.
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ZnS - Multispectral is also known as Cleartran.
Zinc Sulfide sublimes under vacuum at 300°C and oxidizes in air.
ZnS windows should not be used above 250°C.
Material Data Source - Crystran Handbook 2020 https://www.crystran.co.uk
Contact sales@sealedoptics.com for alternative window quotation