Automatically tunable continuous-wave optical parametric oscillator for high-resolution spectroscopy and sensitive trace-gas detection

We present a high-power (2.75 W), broadly tunable (2.75-3.83 mu m) continuous-wave optical parametric oscillator based on MgO-doped periodically poled lithium niobate. Automated tuning of the pump laser, etalon and crystal temperature results in a continuous wavelength coverage up to 450 cm(-1) per poling period at < 5x10(-4) cm(-1)upercript stop resolution. The versatility of the optical parametric oscillator as a coherent light source in trace-gas detection is demonstrated with photoacoustic and cavity ring-down spectroscopy. A 17-cm(-1)-wide CO2 spectrum at 2.8 mu m and multi-component gas mixtures of methane, ethane and water in human breath were measured using photoacoustics. Methane (at 3.2 mu m) and ethane (at 3.3 mu m) were detected using cavity ring-down spectroscopy with detection limits of 0.16 and 0.07 parts per billion by volume, respectively. A recording of (CH4)-C-12 and (CH4)-C-13 isotopes of methane shows the ability to detect both species simultaneously at similar sensitivities.