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Proceedings Paper

Photoacoustic detection by means of a differential double resonator cell applied to security and defence
Author(s): Arturo Vallespi; Verónica Slezak; Alejandro Peuriot; Francisco González; Andrea Pereyra; Guillermo Santiago
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Paper Abstract

The purpose of this article is to present a sensitive optical system for immediate detection of traces of ammonia by means of photoacoustic spectroscopy and study some properties with both a pulsed CO2 laser (TEA) and a CW CO2 laser. The laser beam is aimed to an innovative dual resonator differential cell, which lowest resonant frequency is the first longitudinal mode at 1205 Hz, filled with a flowing NH3 and N2 mixture. The chosen cell’s material is polypropylene, suitable for reducing the effects of adsorption. As a result of physical adsorption-desorption studies, based on a pulsed CO2 laser, 5 % PA signal decay from an enclosed sample of 248 ppmV of NH3 in N2 is recorded within 1 hour. The setup for CW CO2 laser excitation takes advantage of a differential microphone connected to both resonators by picking up out of phase signals. For this purpose, the beam is modulated at the cell’s resonance by means of a chopper with a special blade which allows both reflection and transmission of the laser beam; the direct and the reflected beam are alternatively aimed to one resonator and the other. The measurements show that for the double resonator configuration a signal increase is achieved, as expected from the study of the sensitivity of both resonators separately, which have been previously characterized. Measurements with this system indicate a limit of detection of 13ppbV at the 10P(32) laser line, deduced from one standard deviation of the PA signal from pure N2.

Paper Details

Date Published: 16 October 2013
PDF: 8 pages
Proc. SPIE 8901, Optics and Photonics for Counterterrorism, Crime Fighting and Defence IX; and Optical Materials and Biomaterials in Security and Defence Systems Technology X, 89010Q (16 October 2013); doi: 10.1117/12.2034482
Show Author Affiliations
Arturo Vallespi, Instituto de Investigaciones Científicas y Técnicas para la Defensa (Argentina)
Verónica Slezak, Instituto de Investigaciones Científicas y Técnicas para la Defensa (Argentina)
Alejandro Peuriot, Instituto de Investigaciones Científicas y Técnicas para la Defensa (Argentina)
Francisco González, Instituto de Investigaciones Científicas y Técnicas para la Defensa (Argentina)
Andrea Pereyra, Instituto de Investigaciones Científicas y Técnicas para la Defensa (Argentina)
Guillermo Santiago, Univ. de Buenos Aires (Argentina)


Published in SPIE Proceedings Vol. 8901:
Optics and Photonics for Counterterrorism, Crime Fighting and Defence IX; and Optical Materials and Biomaterials in Security and Defence Systems Technology X
Roberto Zamboni; Douglas Burgess; Gari Owen; Francois Kajzar; Attila A. Szep, Editor(s)

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