Advances in differential photoacoustic spectroscopy for trace gas detection.

Photoacoustic spectroscopy (PAS), as a nondestructive method, permits high sensitivity and selectivity in trace gas detection fields. Advances in differential PAS configurations have dramatically suppressed the background noise and triggered the detectivity improvement. A detailed review on the development of differential photoacoustic gas sensors is presented: using two identical cavity differential cells and optical path types provides good performance for coherent noise suppression, and differential mode excitation technique, which evaluates the signal ratios with two frequency excitations, suppresses the common mode noise and signal drifts generated by the light power or the responsivity of the PA system. An overview of the latest developments of the differential PAS sensors is reported. Distinguished results in terms of sensitivity, selectivity, and miniaturization are presented. The advantages and limitations of differential sensors with different photoacoustic sensing technologies are discussed. [ABSTRACT FROM AUTHOR]