Modulation Spectroscopy is a sensitive, convenient, versatile and cost-effective method for monitoring gaseous species and for obtaining quantitative information about molecular collision dynamics through precise measurements of the absorption lineshape function. Even slight perturbations in the lineprofile can be measured precisely, and because these perturbations are directly linked to changes in physical conditions of the sampled target, one obtains very precise non-intrusive measurements of these parameters. Over the last few years, we have extended this technique to the regime of higher harmonic detection and demonstrated that, in many cases, one obtains a higher precision by using an optimal harmonic detection order higher than the commonly used second harmonic. Experimental and theoretical results have been presented. In this paper we use the principles of Information Theory developed by Shannon to describe the information content in modulation spectroscopic signals. A simple argument is used to show that information that may otherwise be lost because of distortion can be recovered by derivative like techniques, such as those used in low frequency modulation spectroscopy. Experimental results obtained for the resolution of overlapping lines of disparate strength are discussed.

Date Published: 28 March 2002
PDF: 9 pages
Proc. SPIE 4634, Methods for Ultrasensitive Detection II, (28 March 2002); doi: 10.1117/12.463826

Published in SPIE Proceedings Vol. 4634:
Methods for Ultrasensitive Detection II
Charles W. Wilkerson Jr., Editor(s)