An electrically and optically cooperated QEPAS device for highly integrated gas sensors

A QEPAS device is demonstrated where the quartz tuning fork (QTF) is not only excited by a laser-induced acoustic wave but also driven electrically by a CMOS circuit at the same time. The gas absorption is measured as the sum of the optically and electrically generated QTF amplitudes. For this design, no accurate and expensive frequency generators are needed since the QTF acts as a photo-acoustic transducer and frequency reference at the same time. Furthermore, simultaneous or alternate electrical and photo-acoustic driving allows for new techniques in combination with QEPAS, such as the analysis of the QTF decay time or the demodulation at the beat frequency if electrical and optical excitation is applied at slightly different frequencies.