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Custom Potassium Bromide

Potassium bromide (KBr) is a crystalline material that is widely used in spectroscopic applications. It’s wide transmission band means it has optical applications in the UV, visible, MWIR, and LWIR waveband regions.
Below is a brief summary of potassium bromide’s optical properties, a full data sheet is available here:

Transmission range

0.23 to 25µm

Refractive Index

1.527 @ 10µm


2.753 g/cm3

Melting Point



Knoop 7 <100> with 200g indenter

Operating temperature

< 300°C

Knight Optical can supply a variety of potassium bromide optical components including windows, lenses, prisms and sapphire ground blanks. We can also provide uncoated and coated optics, with broadband antireflective (BBAR) coatings. Our typical manufacturing specifications are listed below, however we are always expanding our capabilities so if your requirements are not mentioned below please contact our technical sales team who will guide you through your enquiry.


< 5mm to 200mm

Form error (@633nm)

< 0.25 waves

Centration /parallelism

< 1 arc minute


< 40/20

Typical coatings

BBAR @ 1-25µm

DLC @ 1-25µm

With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.

Additional Information

  • It is grown via the Kyropoulos method and cleaves easily.
  • Though it is extremely sensitive to moisture, it can still be highly polished under humidity controlled conditions.
  • KBr is relatively resistant to mechanical shock


  • Potassium bromide is very hygroscopic, so must be used in a moisture-free environment otherwise the surface of the optics will degrade.

Typical Applications

Fourier Transform Infrared (FTIR) Spectroscopy
  • IR grade KBr is widely used in FTIR spectroscopy, especially as the beamsplitter substrate. It enables an extended wavelength range of 4000-400cm-1 compared to, for example, sodium chloride’s 4000-650cm-1. It also shows no absorption in this region.
  • Potassium bromide can also be highly polished to achieve the high degree of flatness that is needed.


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