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Simultaneous dual gas QEPAS sensing of water and methane/nitrous oxide

Simultaneous detection of different trace gases is an important topic in many applications, such as breath analysis, environmental monitoring and oil exploration. Quartz-enhanced photoacoustic spectroscopy offers a good solution of this problem, due to the possibility to operate the quartz resonators at the fundamental and overtone resonance frequencies by simultaneously exciting two different antinodes with two different laser sources. In this work we employed a custom spectrophone coupled with a diode laser and a quantum cascade laser for simultaneous detection of water vapor and methane/nitrous oxide with minimum detection limits in the ppb range.