Abstract

By using lead-salt tunable diode lasers (TDLs) it is possible to detect individual rovibrational lines and measure their intensity in order to determine gas concentration and isotopic ratio. The 2300 cm⁻¹ spectral region is especially interesting because the ¹²CO₂ and ¹³CO₂ bands overlap in such a way that their rotational lines have almost equal absorbances at the anticipated isotopic ratio of carbon. Using sweep integration and signal averaging techniques, we have measured ³C/¹²C in CO₂ to an accuracy of better than 0.4%. To improve accuracy we have used various techniques to measure, and incorporate into the data analysis programs, the Gaussian and Lorentzian parts of the instrument response function (IRF). A technique to minimize the Gaussian part of the IRF has been developed to remove spectral drift prior to spectrum coadding.

© 1992 Optical Society of America