QEPAS with electrical co-excitation for photoacoustic measurements in fluctuating background gases

Quartz-enhanced photoacoustic spectroscopy is a photoacoustic spectroscopy technique which substitutes the conventional microphone by a quartz tuning fork which enables very sensitive detection in small volumes. The piezo-electric properties are used to transfer the oscillation amplitude into an electric signal. However, the opposite is also possible and the tuning fork can be driven electrically. By alternate electric and photoacoustic driving, it is possible to extract information about the background gas and to determine decay times rather than amplitudes which result presently in a comparable limit of detection as conventional QEPAS but still shows potential for improvement.