Infrared Emission Spectroscopy with Transient Cooling

A new approach for collection of infrared spectral data from optically opaque materials is explored. This approach has previously been introduced in the literature and is known as transient infrared transmission spectroscopy (TIRTS). The front surface of a hot sample is transiently cooled with a jet of cold gas, and the ratio of the spectrum measured after cooling to that measured before cooling is shown to closely resemble a transmission spectrum. This report provides for a more theoretical understanding of the experiments than provided by previous workers, making use of unsteady-state heat flow calculations, harmonic oscillator modeling, and radiation transfer theory. Experimental data are collected from a solid polymer sample and two viscous liquid samples. The position of the spectral features for the emission measurements corresponds with transmission measurements, with some saturation of the more intense spectral features noted. Faster scanning instrumentation, proper pulse scan synchronization, or rotation of solid samples, as demonstrated by previous workers, may resolve the saturation problem.