Intracavity quartz-enhanced photoacoustic spectroscopy for CO/N2O detection in the part-per-trillion concentration range

A mid-infrared gas sensor based on intracavity quartz-enhanced photoacoustic spectroscopy (I-QEPAS) and a custom quartz tuning fork is here reported. A 4.59 μm distributed feedback quantum cascade laser was optically coupled into a high-finesse Brewster window linear optical cavity. A power enhancement factor of ~ 250 has been achieved. A spectrophone composed of a custom tuning fork having 1.5 mm prong spacing, acoustically coupled with a pair of micro-resonator tubes, was placed in the focal point of the high-finesse cavity. The sensor was calibrated for humidified carbon monoxide and nitrous oxide detection. Gas concentration sensitivities in the part-per-trillion range were achieved for both gas species.