Sensitive intracavity photoacoustic measurements with a CO2 waveguide laser

A photoacoustic intracavity configuration is presented; a resonant photoacoustic cell excited in its first longitudinal mode is placed inside the cavity of a CO₂ waveguide laser. Due to the high laser power and the sharp intracavity focus, saturation effects occur in the excitation and relaxation process of absorbing C₂H₄ molecules. A more optimal configuration is applied to measure the C₂H₄ emission of several Rumex species. A detection sensitivity of 6 ppt (parts per trillion) C₂H₄ is reached, equivalent to a minimal detectable absorption of 1.8×10^–10 cm^–1.