High-resolution photoacoustic and direct absorption spectroscopy of main greenhouse gases by use of a pulsed entangled cavity doubly resonant OPO

An entangled cavity doubly resonant optical parametric oscillator (ECOPO) has been developed to provide tunable narrow line width (<100 MHz) pulsed (8 ns) radiation over the 3.8–4.3 μm spectral range at a multi-kilohertz repetition rate with up to 100-W peak power. We demonstrate that coarse single mode tuning is obtained over the full spectral range of oscillation (300 cm−1), while automated mode-hop-free fine tuning is carried out over more than 100 GHz. High-resolution spectra of main greenhouse gases (CO2, N2O, SO2 and CH4) have been obtained in good agreement with calculated spectra from the HITRAN database. These experiments outline the unique capabilities of the ECOPO for multi-gas sensing based on direct absorption as well as photoacoustic spectroscopy.