Sodium chloride (NaCl) is a material with a high transmission in the wavelength range between 0.25 µm and 16 µm and is therefore used for optical windows, lenses and prisms for the UV and IR range. Due to its low absorption, sodium chloride is mainly used in high-power laser systems.

Sodium chloride is hygroscopic and highly soluble in water. It therefore requires a dry environment or a special protective layer against moisture when used. Sodium chloride can be used at temperatures of over 400 °C, but is sensitive to thermal shock.