Refractive Index of Potassium Bromide for Infrared Radiant Energy*†

The index of refraction of potassium bromide at 22°C has been measured for the infrared region from 1 micron to 25 microns by means of two methods on two different instruments. The two resulting sets of indexes agree to within the probable error of either one except at the two longest wavelengths. A five constant expression has been found that represents the index as a function of wavelength over the region from 0.4047 microns to 25 microns. Indexes were measured at several of the wavelengths at temperatures higher and lower than 22°C and thermal coefficients of index were computed.