Photoacoustic measurements have been made at the 4.803 μm absorption line of carbon monoxide in a small nonresonant cell using a low power semiconductor laser source. A simple theoretical model correctly predicts the dependence of the CO signal on chopping frequency and concentration dependence but is inadequate in describing the pressure dependence. Concentrations as low as 50 ppmv were measured by operating the cell in a double pass mode.

The pulse velocity in a Ne absorption cell placed inside a self-locked He–Ne (6328 Å) laser has been found to exceed c, the free-space velocity of light, by about 3 parts in 104. Conversely, the pulse velocity in a He–Ne gain cell was less than c by about the same fraction. These results are consistent with the classical group velocity dω/dk, where the frequencies are confined to the central region of the resonant line.

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Infrared absorption by acetylene and diesel smoke particles was measured using a differential optoacoustic cell driven by a 3.4-W CO2 laser. Real-time particle mass concentration measurements are demonstrated. In addition we found the average particle extinction cross sections per unit mass of acetylene and diesel smoke were 0.94±0.1 m2/g and 0.83±0.2 m2/g, respectively, at the 10.6-μm wavelength.

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