Calcium Fluoride is good choice for optical windows in the 0.15 μm - 9 μm range,which is relatively soft and somewhat hygroscopic so polishing, coating and handling are more critical than UV Fused Silica windows. In addition, The quality of a UV window can be extremely critical, it should be of high purity and polish in order not to affect the optical system.
Calcium Fluoride Windows are also applicable for a wide range of spectrum. It is particularly useful for wavelength at 2980nm laser application.
Due to its low refractive index, Calcium Fluoride can be used without anti-reflection coating