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Photo-acoustic
sensing
Photoacoustic
(PA) effect is a light-matter interaction effect which involves acoustic
wave generations from materials that absorb energy of light. It has
been known as a sensitive spectroscopic technique for material
studies including solids, liquids, and gases. PA spectroscopy has
been applied to a wide range of applications such as chemical
detections, material study, biomedical imaging and so on. The
following picture shows a standoff chemical detection system operated
outdoors.
Standoff
chemical detection system for outdoor field operation
(1) standoff
detection of gas vapor (IPA vapor)
Standoff
photoacoustic chemical detection of gas
vapor at distance ~41 feet
Dependence
of PA signal on detection distance. Detection sensitivity is 1/r
dependence.
(2) standoff detection
of explosives
Standoff
photoacoustic detection of TNT using
ultra-sensitive microphone and sound reflector.
Detected
signal and FFT spectrum of microphone signal.
Detected
photoacoustic signal at different
distances. Both amplitude decay and phase shift present.
(3) standoff
detection of nerve gas agent
Standoff
photoacoustic detection of nerve agent
stimulant (calibrated at 14ppm)
Detected
photoacoustic signal at distance over 13
feet and signal FFT spectrum (2 feet for 2ppm calibration)
Ref:
Xing Chen, Liwei
Cheng, Dingkai Guo,
Yordan Kostov,
and Fow-Sen Choa,“Quantum
cascade laser based standoff photoacoustic
chemical detection”, Optical Express, Vol. 19, No. 21, pp. 20251-
20257, October 2011.
Xing Chen, Dingkai Guo, Fow-Sen Choa, Chen-Chia Wang, Sudhir Trivedi, Jenyu Fan, “Quantum
cascade laser based standoff photoacoustic
detection of explosives using ultra-sensitive microphone and sound
reflector”, SPIE Photonic West, San Francisco, California, 2-7 Feb. 2013.
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