[54] LASER-BASED PHOTOACOUSTIC SENSOR AND METHOD FOR TRACE DETECTION AND DIFFERENTIATION OF ATMOSPHERIC NO AND N02
[75] Inventor: Rosario C. Sausa, Bel Air, Md.
[73] Assignee: The United States of America as
represented by the Secretary of the Army, Washington, D.C.
[21] Appl. No.: 09/168,340 [22] Filed: Oct. 5, 1998
[51] Int. C I. G02B 6/26
[52] U.S. CI 250/227.24; 250/338.5;
436/159; 340/632
[58] Field of Search 250/227.14, 338.5,
250/339.12, 573, 227.25, 227.24, 227.23, 339.13, 341.1; 436/159, 164; 340/632, 633; 356/437
[56] References Cited
U.S. PATENT DOCUMENTS
3,553,461 1/1971 Siano 436/159
OTHER PUBLICATIONS
Temperature Dependent Quenching of the A22+ and B2|
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 A22+ and -X2||(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 N02 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 laser-based photoacoustic sensor performs trace detection and differentiation of atmospheric NO and N02 in order to obtain respective concentrations for NO and N02 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 N02 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 N02 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.
24 Claims, 6 Drawing Sheets
