Publication: Sub-ppm-level ammonia detection using photoacoustic spectroscopy with an optical microphone based on a phase interferometer
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2019-07-01
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MDPI
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Abstract
A sensitive optical microphone for photoacoustic spectroscopy based on the common path topology of a fibre laser Doppler vibrometer (FLDV) using phase-generated carrier demodulation and a slim diaphragm as an acoustic wave transducer was demonstrated. A resonant gas cell was adapted to enhance gas-detection performance and simultaneously provide efficient cancellation of the window background acoustic signal. Ammonia (NH3) was selected as the target gas. The absorption line was experimentally identified using a distributed feedback laser diode emitting at 1530 nm. The linearity and sensitivity of the gas sensor were measured using wavelength modulation spectroscopy with second harmonic detection. A Teflon diaphragm was used to implement the optical microphone, along with the FLDV, showing a minimum detectable pressure of 79.5 mu Pa/Hz(1/2). The noise-equivalent absorption sensitivity for NH3 detection at the absorption line at 1531.7 nm was 1.85 x 10(-8) W cm(-1) Hz(-1/2), and the limit of detection was 785 ppbv.
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Photoacoustic spectroscopy, Gas detection, Optical microphone, Resonant cell, Membrane
Bibliographic citation
Sensors 2019, 19(13), 2890, 14 p.