Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1998-10-05
2000-12-12
Le, Que T.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
2503385, 436159, 340632, G02B 626
Patent
active
061602558
ABSTRACT:
A laser-based photoacoustic sensor performs trace detection and differentiation of atmospheric NO and NO.sub.2 in order to obtain respective concentrations for NO and NO.sub.2 using photoacoustic spectroscopy. The device of the invention employs a single, pulsed laser having two outputs near 454 nm and 227 nm, respectively, to irradiate a sample vapor, the sample vapor being collected by a hand-held wand. A photoacoustic response from both NO and NO.sub.2 is detected using microphone detectors, is converted into electrical signals, and is analyzed using a microcomputer. The results of the analysis--the respective concentrations of NO and NO.sub.2 in the sample vapor--are displayed on a digital oscilloscope. Preferably, the electrical signals are amplified prior to analysis, and a boxcar integrator is used to sample and average the electrical signals during the analysis operation.
REFERENCES:
patent: 3553461 (1971-01-01), Siano
Temperature Dependent Quenching of the A.sup.2 .SIGMA.+ and B.sup.2 .paral. States of NO, George A. Raiche and David R. Crosley,J. Chem. Phys 92(9), May 1, 1990, pp. 5211-5217.
Detection of Ambient NO by Laser-Induced Photoacoustic Spectrometry Using A.sup.2 .SIGMA.+ and -X.sup.2 .parallel.(0,0) Transistions Near 226nm, C.K. Williamson, *R.L. Pastel, and R.C. Sausa, vol. 50, Num 2, 1996, Applied Spectrometry, pp. 205-210 (Month Unknown).
Trace Analysis of NO.sub.2 in the Presence of NO by Laser Photofragmentation Fragment Photoionization Spectrometry at Visible Wavelengths, J.B. Simeonsson and R.C. Sausa, vol. 50, Num 10, 1996, Applied Spectroscopy, pp. 1277-1282.
A Study of Measurement Interference in the Optoacoustic Detection of NO.sub.2 by Argon-Ion Laser Excitation, Alan Fried, vol. 36, Num 5, 1982, Applied Spectrocopy, pp. 562-565. (Month Unknown).
Ozone, NO, and NO.sub.2 : Oxidant Air Pollutants and More, Jerold A. Last, .sup.1 and Hanspeter Witschi.sup.2, Dec. 1994, pp. 179-184.
Radiative Lifetimes and Electronics Quenching Rate Constants for Single-Photon-Excited Rotational Levels of NO (A.sup.2 .SIGMA..sup.+, v.sup.1 =0), I. Stuart McCermid and James B. Laudenslager, vol. 27, 1982, pp. 483-492. (Month Unknown).
Biffoni U. John
Clohan Paul S.
Le Que T.
The United States of America as represented by the Secretary of
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