Potassium chloride (KCl) has a high transmission in the wavelength range between 0.3 µm and 20 µm. The material has a low refractive index and a high optical damage threshold. Potassium chloride is hygroscopic and highly soluble in water, so it must be stored in a dry environment or protected against moisture by means of a protective layer. Thermally, the use of KCl is limited to 400 °C.

KCl optics are used in IR spectroscopy and as protective windows for_CO2 lasers.