High-sensitivity detection of methane-combining photoacoustic spectroscopy and optical parametric oscillator

摘要

Abstract: We have combined a LiNbO$-3$/ optical parametric oscillator (OPO) and a photoacoustic (PA) open cell to perform air pollution measurements. THe OPO is pumped by a Nd:YAG laser working at 10 Hz. It is tunable between 1.55 $mu@m and 4.5 $mu@m. The PA cell is designed to be isolated from outside acoustic noise. The OPO output wavelength is tuned between 3.39 $mu@m and 3.44 $mu@m to monitor absorption lines of methane. The characteristics of the pulses are E $EQ 2 mJ, $tau $EQ 15 ns, $Delta $nu $EQ 2 cm$+$MIN@1$/. The minimum detected concentration is 1 ppm. Decreasing the background noise, detection of concentrations as low as 20 ppb is expected. !5