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Custom Sodium Chloride

Sodium chloride (NaCl), commonly known as rock salt, is a soft and highly soluble crystalline material. It has a very broad transmission range from 200nm to 15µm, with a transmission above 90%.
Below is a brief summary of sodium chloride’s optical properties, a full data sheet is available here.

Transmission range

0.2 to 16µm

Refractive Index

1.49065 @ 10.6µm


2.17 g/cm3

Melting Point



Knoop 18.2 in <100> with
200g indenter

Operating temperature

< 400°C in dry environment

Knight Optical can supply a variety of sodium chloride optical components including windows and sodium chloride 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


< 80/50

Typical coatings

BBAR @ 1-16µm

DLC @ 1-16µm

All optical components are tested in our state-of-the-art metrology lab and then visually inspected in our QA department, so you can be confident that your optics meet their specific requirements. You can find out more about our testing facilities here.

Additional Information

  • Sodium chloride is grown via the Kyropoulos method and, under humidity controlled conditions, can be highly polished.
  • It is a relatively low cost material.
  • NaCl is relatively resistant to mechanical and thermal shock.

Additional Information

  • Sodium chloride is hygroscopic, so requires protection from atmospheric conditions due to moisture degradation. A hydrophilic coating can help protect it from ‘fogging’ up when in contact with moisture.
  • It requires very careful handling as, with a hardness of HK18.2, it is extremely soft.
  • Do not clean NaCl optics with water.

Typical Applications

Fourier Transform Infrared (FTIR) Spectroscopy
  • NaCl optics, including cell windows, are used in FTIR spectrometers, due to its wide transmission range into the infrared region. They can be used to hold non-polar liquid samples, which will not degrade the material.
High-powered laser systems
  • Sodium chloride windows can be used in high-powered laser systems, such as CO2 lasers due to its low absorption. They are often used to protect other laser optics such as zinc selenide or YAG focussing lenses.


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