BaF2 windows is a low refractive index (1.40 @ 10 microns) material with low solubility in water. Since it has a good refractive index match to water, in liquid cell applications sampling aqueous solutions it shows minimal interference fringing. As result it has become the preferred window material for infrared biological samples. These applications are in the medical area, both research and clinical and the food and beverage area, both QC and process control.
BaF2 windows has a similar refractive index to KBr. Therefore, the broad band beamsplitter coatings developed for KBr can be slightly modified to use on BaF2 substrates. The longer wavelength range of KBr can be sacrificed to optimize near-IR performance.