H6) at 3.34 μm using a widely tunable cw single-frequency optical parametric oscillator. The high frequency and power stability and the continuous tunability of the parametric oscillator make it ideally suited for this application. Detection sensitivities of 0.5 ppb for ethane are obtained, which is comparable to the best results previously obtained with intracavity detection using line-tunable CO overtone lasers. The flexibility and compact size of cw single-frequency parametric oscillators can lead to portable photoacoustic trace-gas detection systems for environmental monitoring and process control.

The simultaneous measurement of the C2H6 and C2H4 emission by plant material is known to be a good stress/damage indicator. A photoacoustic spectrometer, utilizing the CO-Overtone laser, has been used for such measurements for the first time. For the simultaneous online detection of C2H6 and C2H4 in plant physiological studies, a sensitivity was achieved of 370 ppt and 2 ppb, respectively. The performance of the system has been demonstrated measuring the stress/damage behaviour of rhododendron leaves after the application of freezing stress.

The ethylene evolution of germinating peas Pisum savitum L. exposed to elevated ozone levels is studied using a CO2 laser-driven photoacoustic detection system. For ozone fumigation experiments a specific flow system is developed resulting in adjustable, controlled ozone concentrations between 270 and 10 ppbv in air. Ozone fumigation enhances ethylene production, even before the onset of visible germination, and inhibits growth as compared to non-fumigated pea seedlings. The combination of ozone fumigation and application of the ACC-synthase inhibitor AVG still yields increased ethylene levels indicating an alternative pathway for enhanced ethylene production.