Barium Fluoride (BaF2)

Barium fluoride (BaF2) is a general-purpose optical window material that offers a wide range of transparency, from the ultraviolet to the long-wave infrared, with low reflectance loss and low dispersion. It is noted that this combination of broad transparency and low dispersion is rare in optical window materials used in infrared systems. Thus, it allows experimenters to conveniently perform initial system alignment in the visible and then switch to the infrared with only minor correction of the optical components. BaF2 exhibits good surface hardness and it is not attacked by the water vapors. It is very brittle and generally requires careful handling. BaF2 is essentially a cubic crystal with the fluorite structure, space group Fm3m, with four formula units per unit cell. The atomic arrangement is barium atoms occupy the 4(a) sites and the fluorine atoms occupy the 8(c) sites. Ultraviolet reflectance of bulk BaF2 is measured by Ganin et al up to 20 eV at the room temperature and liquid-helium temperature.