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Infrared Windows

Knight Optical can manufacture custom IR windows to meet your requirements.

The following materials all have properties that make them beneficial as IR windows:



Custom fluoride windows – fluoride materials excel in applications that use UV-VIS-IR applications, with transmission wavebands ranging from 0.12-12µm.

  • Calcium fluoride, CaF2, transmits from 0.13-10µm with a high refractive index homogeneity.
    • CaF2 windows are often used in Excimer laser optics due to its high damage threshold, low absorption and high transmission band ranging from UV to MWIR.
    • These properties also make them a popular choice for thermal imaging systems.
    • Calcium fluoride also comes in Raman grade which are designed to be fluorescence free IR windows and used, as the name suggests, in Raman spectroscopy.
  • Barium fluoride, BaF2, transmits from 0.12-12µm, so has a slightly extended transmission band in comparison the calcium fluoride, transmission is above 90% from 0.2-10µm. However BaF2 windows will cost more to manufacture as the material must be synthesised chemically. However, their transmission is above 90%
  • Magnesium fluoride, MgF2, is the hardest of the optical fluoride windows and transmits from 0.1-7µm, making it ideal for UV to IR applications. It is a water stable IR window which means it can be used for outer surfaces in an optical system, compared to both calcium fluoride and barium fluoride which both start degrading when in contact with moisture.

Custom potassium bromide (KBr) windows are often used as Fourier Transform Infrared (FTIR) windows due to their exceptional average transmission of 90% between 0.3-20µm. They are crystalline IR windows with applications in UV, VIS, MWIR and LWIR due to its impressive waveband range. However, it must be used in a moisture-free environment as the polished surfaces will degrade in a moist atmosphere.

Custom sodium chloride (NaCl) windows are ideal for UV to IR transmitting applications, such as FTIR spectroscopy, due to its high transmission from 0.2-15µm. The material is very soft, highly soluble and hygroscopic and therefore requires protection from normal atmospheric conditions otherwise it will rapidly degrade. Under humidity controlled conditions, NaCl can be a highly polished and a protective coating can be applied if the window will be exposed.

Custom Zinc Selenide (ZnSe) windows are ideal as CO2 laser resonator windows. It transmits from 0.5-15µm before dropping off to zero transmission, it also has low absorbance in the IR range which is what makes it ideal for CO2 lasers operating at 10.6µm. Zinc selenide windows are generally available in 5mm to 100+mm diameters, with a thickness of 0.5mm up to 50mm.

Another material to consider is JGS3 which is an IR grade fused quartz which transmits from 0.26-3.5µm. It also has low bubble, striae and inclusion content. These can be AR coated to increase their transmission performance in their useful range.

Germanium (Ge) is an ideal for applications where the UV and VIS regions are blocked and you only get the transmission into the LWIR region. Germanium transmits from 1.8-23µm, however uncoated germanium only offers about 45% transmission between 2-14µm so an AR is recommended for increased transmission. A DLC (diamond-like carbon) coating can also be applied to increase the durability of the surface it is applied to, this is especially useful if that surface is on the outside of an optical system and exposed to harsher environments. A typical AR/DLC coating will operate at 7-12µm, so covering the thermal imaging wavelengths, making precision IR coated germanium an ideal candidate as a thermal camera window, including as a front window to a FLIR camera.

Knight Optical supply high quality IR Optical Window components made to your specific bespoke custom specification.  Every component is individually tested by our highly skilled technicians in our state of art metrology lab to ensure all components meet our high quality standards. We also hold a large range of stock not listed on our website, so please enquire.

Contact our multilingual technical sales team and discover how Knight Optical’s high quality IR Optical Windows and service can improve your instrumentation and supply chain experience.

Our 2021/2022 Catalogue

Inside Knight Optical’s catalogue you’ll find details of the industries we serve as well as the many other services we can offer. It also showcases hundreds of our most popular products, supported by useful technical information, to help you choose the right part for your application.
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