Improvement of The Sensitivity of Optoacoustic Trace Gas Analysis by Condensation*

The optoacoustic effect has been used to detect atmospheric pollutants at concentration levels as low as ~ 10−10 volume/volume. Both nonresonant [1] and resonant [2] cells have been used to achieve these detectivity limits. The limiting acoustic noise was about an order of magnitude above the Brownian noise of the ideal membrane inserted in the optoacoustic cell. The optoacoustic effect has also been used in liquids to measure low concentration traces [3] as well as ultralow absorption of visible radiation by pure water [4]. The noise equivalent concentration in liquids approached the ~ 10−11 limit.