Photoacoustic trace gas detection of ethane using a continuously tunable, continuous-wave optical parametric oscillator based on periodically poled lithium niobate

A 1.2 W, continuous-wave, continuously-tunable, singly-resonant optical parametric oscillator (OPO) (idler tuning range 3.0-3.8 mum), pumped by a 10 W continuous-wave Nd:YAG laser, is used in combination with a photoacoustic cell for the detection of ethane. An intracavity solid-state etalon (thickness 400 mum) was used to stabilize the OPO cavity and could be used to mode-hop tune the idler wavelength over 10 cm(-1). The usefulness of the system was demonstrated by determining a detection limit for ethane down to 10 parts per trillion. The selectivity was achieved by making a 24 GHz wide pump laser scan over the ethane absorption line at 2996.9 cm(-1), after which a Lorentzian fit determined the total area of the absorption signal. Both area value and peak value proved to be linearly depending on the ethane concentration. (C) 2002 American Institute of Physics.