Abstract

The selective and sensitive detection of trace gases in multicomponent gas mixtures by means of absorption spectroscopy requires narrowband continuously tunable laser sources. Newly available optical parametric oscillators (OPO) meet these requirements almost perfectly. Our commercial nanosecond OPO - system is pumped by the third harmonic of a Nd:YAG laser and offers a tuning range from 440 to 1800 nm. The linewidth of less than 0.2 cm^–1 at energy levels of several mJ per pulse is maintained over the whole tuning range. At standard pressure the absorption linewidths of most environmental relevant trace gases such as CO₂, CH₄ and volatile organic compounds (VOC's) match with the laser linewidth thus making the system particularly useful for the analysis of ambient air samples. First experiments with a specially designed nonresonant photoacoustic cell on CO₂ and CH₄ overtones in the idler range of the OPO (710 - 1800 nm) demonstrate the power of this approach. An example is shown in Fig. 1 for CO₂.

© 1996 IEEE