Investigations of solids, especially of powders, are of great interest in infrared spectroscopy. The applicability of transmission or attenuated total reflectance (ATR) techniques is often limited by the scattering of the radiation. This scattering can be spectrally analyzed, if the diffuse reflected radiation can be collected and transfered to the infrared detector.
Hans Maulhardt and Dietmar Kunath, "A Simple Device for Diffuse Reflectance Fourier Transform Infrared Spectroscopy," Appl. Spectrosc. 34, 383-385 (1980)