Application of a widely electrically tunable diode laser to chemical gas sensing with quartz-enhanced photoacoustic spectroscopy

A near-infrared diode laser with sample-grating distributed Bragg reflectors was used as a widely tunable spectroscopic source for multispecies chemical sensing. Quartz-enhanced photoacoustic spectroscopy was utilized to obtain high absorption sensitivity in a compact gas cell. CO2, H2O C2H2, and NH3 were monitored. A noise equivalent sensitivity of 8 x 10(-9) cm(-1) W(-1) Hz(-1/2)for NH3 detection was achieved, which corresponds to a NH3 mixing ratio of 4.4 parts in 10(6) by volume (ppmv) with a 1-s time constant and available 5.2-mW optical power in the gas cell.