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Choa’s lab







Research Areas

MOCVD Growth

NIR Lasers and Detectors

MIR Lasers

Photo-Acoustic Sensing

Neural Circuitry

Undergrad Researches


Current Projects

Previous Project







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)



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.



Computer Science and Electrical Engineering Department

University of Maryland, Baltimore County
1000 Hilltop Circle, Baltimore, MD 21250