Research on high sensitivity of resonant enhancement laser intracavity photoacoustic spectroscopy technology

Abstract

Laser intracavity photoacoustic spectroscopy (ICPAS), in combination laser intracavity absorption (ICAS) with photoacoustic spectroscopy(PAS) technology is presented. It can effectively enhance the photoacoustic signal intensity by means of increasing the laser power and overlapping in phase when the laser beam passed through the acoustic wave detector every time. Two sets of experimental results were obtained when probing the water vapor with the effective absorption coefficient, keff, 1.06×10−6cm−1×ppm−1 in the air using a tunable distributed feedback laser diode (DFB-LD) and validate the relevance of the reported mathematical model. It can be found that for a quartz-enhanced photoacoustic spectroscopy(QEPAS) sensor system, the relationship between the second harmonic current amplitude I2f and the laser power WL is linear, and the slope of the fitting results is 285.0809pA/mW compared to that of theoretical calculation 278.7025pA/mW, with the fitting constant of 17.1318 pA, which was corresponding to the laser power less than 0.0601 mW and for a resonant photoacoustic(PA) cell sensor system, the relationship between the second harmonic voltage amplitude U2f and the laser power WL is also linear, and the slope of the fitting results is 108.8463mV/mW compared to that of theoretical calculation 111.26mV/mW, with the fitting constant of 0.4875mV, which was corresponding to the laser power less than 0.0045 mW.