Wavelength modulation photoacoustic spectroscopy using a near-infrared DFB diode laser

Photoacoustic spectroscopy (PAS) has been a powerful tool in terms of sensitivity, selectivity and simplicity. In this paper, a resonant PAS sensor system based on a distributed feed-back (DFB) diode laser near 1653 nm for methane (CH₄) detection is introduced. Wavelength modulation spectroscopy (WMS) with second harmonic (2f) method is combined with the PAS detection strategy for further sensitivity improvement. A PA cell working in the second-order longitudinal resonant mode was fabricated and used for experimental test of CH₄ spectroscopy measurement. Photoacoustic signal dependence on gas pressure and modulation parameters were studied to optimize the sensor performance. In addition, potential approaches and detection schemes on improving sensor performance are also discussed.