Transportable, highly sensitive photoacoustic spectrometer based on a continuous-wave dual-cavity optical parametric oscillator

We present an all solid state, transportable photoacoustic spectrometer for highly sensitive mid-infrared trace gas detection. A complete spectral coverage between 3.1 and 3.9 mum is obtained using a PPLN-based continuous-wave optical parametric oscillator pumped by a Nd: YAG laser at 1064 nm. A low threshold is achieved by resonating the pump, and spectral agility by employing a dual-cavity setup. An etalon suppresses mode-hops. Active signal cavity stabilization yields a frequency stability better than +/- 30 MHz over 45 minutes. Output idler power is 2 x 100 mW. The frequency tuning qualities of the OPO allow reliable scan over gas absorption structures. A detection limit of 110 ppt for ethane is achieved. (C) 2003 Optical Society of America.