In a new method of measuring diffuse reflectance in the infrared, the sample is irradiated from all directions with chopped light. The source and sample are placed at conjugate foci of a hemispherical mirror with the chopper between the source and mirror, making the component reflected by the sample distinguishable from the one emitted by it. Advantages are that reflectance may be measured over a very wide range of sample temperatures and that heating of the sample is relatively small. By adding another chopper after the sample, the emitted component may be recorded as an indication of sample temperature under the conditions of measurement. When calibrated against an aluminum mirror, the reflectance of a thin layer of MgO smoke on a mirror is measured as 99% at 2.5 μ. The performance of the system is illustrated with a number of spectra.
© 1964 Optical Society of AmericaFull Article | PDF Article
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