Gaseous trace analysis using pulsed photoacoustic Raman spectroscopy.

A new method for trace analysis of gases, based on the pulsed photoacoustic Raman spectroscopy (PARS) technique, is described. The method has been applied to the analysis of mixtures of CH(4) in N(2), CO(2) in N(2), and N(2)O in N(2) at concentrations near 1 ppm. The apparatus used is described in some detail. Means of improving the method's sensitivity as well as sensitivity-limiting processes are evaluated. The analytical capabilities of this technique are compared with both direct (IR) absorption and other Raman techniques such as CARS and stimulated Raman gain spectroscopy (SRGS).