The measurement of the infrared energy emitted from materials has been of interest since at least the time of Coblentz. Applications for Space, Solar Energy, etc. have increased the interest in the field in the last twenty-five years. The emittance of a sample at any given wavelength is one minus the sum of the reflectance and transmittance (E=1.-(R+T)). The instrument described here illuminates the sample at near normal incidence and collects all of the reflected or transmitted flux with an integrating sphere. Since the flux on the detector in this case is orders of magnitude less than if it could be focused, it is necessary to use a Fourier Transform spectrophotometer to get adequate signal to noise. To obtain good photometric accuracy, a true double beam system is used which simultaneously observes the sample and a reference. This eliminates the effects of drift in the source, detector, interferometer, etc. This system also has an advantage over hohlraum and ellipsoidal reflector systems in that very little energy irradiates the sample and therefore no heating occurs. This system uses an IBM-PC for the data processing. The transmittance of lenses and irregular samples can also be measured. Representative sample spectra are shown for a variety of applications.
Ronald R. Willey,
"An Instrument To Measure Spectral Emittance From 2 to 20 Micrometers", Proc. SPIE 0590, Infrared Technology and Applications, (1 May 1986); doi: 10.1117/12.951991; https://doi.org/10.1117/12.951991