Resonant photoacoustic measurements of optical absorption in gases

Abstract

The use of the photoacoustic (or optoacoustic) effect in spectroscopy gives a valuable tool for examining weak optical absorption features of gases. It is inherently a more sensitive detector of light absorption than other techniques, which attempt to measure a small attenuation of an intense beam. Instead, absorption by the gas of periodically interrupted optical energy, from either a tunable or fixed-wavelength laser, results in the production of sound at the same frequency. Device optimization has followed a number of different paths. The particular approach emphasized here uses a cylindrical gas cell, driven at its 1st azimuthal acoustic resonance, to increase signal amplitude. Experimental concerns include enhancement of the signal relative to acoustic and electronic noise. Examples are presented of what can be learned through application of this technique. These include results for the absorption of visible light by nitrogen dioxide and aerosol particles, as well as from a study of the profiles of oxygen absorption lines in the infrared region.