Sodium Chloride is the most common infrared transmission crystal window for gas and liquid sample cells used with infrared and FTIR spectrophotometers. It is also useful for CO₂ lasers, although KCl is normally preferable due to its lower refractive index at 10.6 microns. NaCl windows are soft and hygroscopic.

 

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Optical Properties---Sodium Chloride (NaCl) Optical Crystals

Transmission Range: 0.2 to 20 microns
Refractive Index: 1.494 at 10 microns
Reflection Loss: 7.5% at 10 microns ( 2 surfaces)
dN/dT: -36.2 x 10^-6/°C at 0.7 microns

Physical Properties---Sodium Chloride (NaCl) Optical Crystals

Melting Point: 801° C
Young's Modulus: 39.98 GPa
Apparent Elastic Limit: 350 psi
Structure: Cubic-(100) cleavage plane

Chemical Properties---Sodium Chloride (NaCl) Optical Crystals

Solubility: 35.7gm/100gm H₂O at 0° C