Reflection measurements in the infrared are useful in the determination of optical constants of materials, reststrahlen peaks, efficiency of black paints, and attenuated total reflection studies. While many papers have dealt with reflection, few have investigated the effect of the angle of incidence upon the reflection spectra. Besides angle of incidence, another important factor is the use of a collimated beam. Both of these parameters must be known and controlled for best results. Some results illustrating the effect of varying the incident angle on samples are discussed, as well as the relationship between angle of incidence and polarization.
Donald E. McCarthy, "Variable-Angle Reflectance Measurements in the Infrared," Appl. Spectrosc. 22, 460-463 (1968)