Compact sensor for methane detection in the mid infrared region based on Quartz Enhanced Photoacoustic Spectroscopy

• A compact QEPAS sensor is presented.
• Two setups are studied.
• Methane measurements are discussed.
• The setup is adapted to any laser source.

A compact system for methane sensing based on the Quartz-Enhanced Photoacoustic Spectroscopy technique has been developed. This development has been taken through two versions which were based respectively on a Fabry Perot quantum wells diode laser emitting at 2.3 μm, and on a quantum wells distributed feedback diode laser emitting at 3.26 μm. These lasers emit near room temperature in the continuous wave regime. A spectrophone consisting of a quartz tuning fork and one steel microresonator was used. Second derivative wavelength modulation detection was used to perform low methane concentration measurements. The sensitivity and the linearity of the QEPAS sensor were studied. A normalized noise equivalent absorption coefficient of 7.26 × 10−6 cm−1 W/Hz1/2 was achieved. This corresponds to a detection limit of 15 ppmv for 12 s acquisition time.