Infrared (IR) emission spectroscopy is an ideal candidate for in situ process monitoring. Infrared spectra contain a wealth of information, and measurement of an IR emission spectrum requires only that a sufficient temperature difference exist between the radiating sample and the detector. A probe beam, such as required for absorbance or reflectance measurements, is not needed, and the sample need not be transparent. The lack of constraints on sample type and relatively simple instrumentation required to make infrared emission measurements are the major reasons that infrared emission spectroscopy has potential as a process-monitoring technique.
J. A. McGuire, B. Wangmaneerat, T. M. Niemczyk, and D. M. Haaland, "Modifications to a Commercial Infrared Emission Apparatus to Permit Quantitative Applications," Appl. Spectrosc. 46, 178-180 (1992)