Resonance photoacoustic spectroscopy and gas analysis of gaseous flow at reduced pressure

The results of theoretical and experimental studies of sensitivity of a resonant photoacoustic Helmholtz resonator detector for gas flowing through a photoacoustic cell under reduced pressure are presented. The measurements of the sensitivity and ultimate sensitivity of the differential photoacoustic cell were performed with a near-IR room-temperature diode laser using the well-known H2O absorption line (12496.1056 cm(-1)) as a reference. The measured value of the sensitivity (6-17 Pa W m(-1)) is in satisfactory agreement with the calculated one, which equals 6-35 Pa W m(-1). The obtained value of the ultimate sensitivity ((3-5) x 10(-7) W m(-1) Hz(-1/2)) provides measurements of the concentration of molecules at the ppb-ppm level.