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Custom Potassium Chloride

Potassium chloride (KCl) is a crystalline material that is often used as a sputter window in CO2 lasers. It’s wide transmission band means it also has optical applications in the UV, visible, mid-wave and far-IR regions.

Below is a brief summary of potassium chloride’s optical properties, a full data sheet is available here.

Transmission range

0.21 to 20µm

Refractive Index

1.45644 @ 10µm


1.99 g/cm3

Melting Point



Knoop 7.2 <110>, 9.3 <100> with 200g indenter

Knight Optical can supply a variety of potassium chloride optical components including windows and 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 80mm

Form error (@633nm)

< 0.25 waves

Centration /parallelism

< 1 arc minute


< 40/20

Typical coatings

BBAR @ 1-20µm

DLC @ 1-20µm

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

  • Potassium chloride is grown via the Kyropoulos method , and cleaves easily.
  • It is slightly more durable than potassium bromide but its transmission does not extend as far in the IR region.


  • KCl is extremely soft so care needs to be taken when handling. It is also very hygroscopic so needs to be kept in a moisture-free environment., or a protective coating should be applied to the exposed surface.

Typical Applications

Laser windows
  • KCl is often used as a disposable protective window in CO2 laser systems due to its low refractive index, low absorption, and high damage threshold.


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