Method for Determining the Response Function of a High-Resolution Infrared Spectrometer*

Abstract

A method has been developed for determining the response function of an infrared spectrometer under the usual running condition of partially coherent illumination from a thermal source. The method consists of deconvolving observed absorption lines of known Doppler shape. Only the sample-gas temperature, molecular weight, absorption-line frequency, and equivalent width are needed to construct the true absorptance profile. The response function of a high-resolution spectrometer has been determined by this method at several frequencies in the 3-μ region. It ranged from 0.014 cm⁻¹ to 0.020 cm⁻¹ in width and was typically 6%–20% narrower than the observed absorption line. The entire process was carried out automatically in the computer, with absorptance data in digital form. A procedure due to P. H. van Cittert, which is often used for resolution enhancement, is shown to be a special case of the more-general and efficient relaxation technique used in this study.