Diffuse reflectance infrared spectrometry: characteristics of the diffuse and specular components

Regular and polarized diffuse reflectance IR spectra of powdered samples of Ottawa sand were measured at grain sizes ranging from 1.5 to 26 microm with concentrations ranging from 0.5 to 4 wt% in KCl using three conceptually different diffuse reflectance accessories. The characteristics of the specularly and diffusely reflected radiation are discussed in terms of the state of polarization of the incident beam relative to that of the reflected beam and as a function of the angle between the detector fore-optics and the sample fore-optics. It was found that the specularly reflected radiation and the diffusely reflected radiation coexist in the measured diffuse reflectance spectrum. The specular component, which is primarily sample dependent, is not necessarily the same as the front-surface reflection.