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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 46, Iss. 29 — Oct. 10, 2007
  • pp: 7083–7090

Highly sensitive electronically modulated photoacoustic spectrometer for ozone detection

M. A. Gondal and Z. H. Yamani  »View Author Affiliations


Applied Optics, Vol. 46, Issue 29, pp. 7083-7090 (2007)
http://dx.doi.org/10.1364/AO.46.007083


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Abstract

An ozone ( O 3 ) gas sensor with a sensitivity of parts per 10 9 (ppb) level and a high level of selectivity based on the resonant photoacoustic effect was developed using an electronically modulated cw CO 2 laser beam. Quite different from the standard chopper modulation of a laser beam, here the laser source was electronically modulated to overcome the inherent problem of frequency instability associated with chopper modulation. With electronic modulation, in conjunction with the fast Fourier transform (FFT) of transient signals, we were able to improve significantly the sensitivity of the photoacoustic (PA) system for the detection of O 3 . In addition to the improved sensitivity, our method proved that the FFT of a laser modulated PA signal could suppress the noise signal generated by spurious window diffused absorption, which in the case of most commonly used lock-in techniques is rather unavoidable. The dependence of the PA signal on various experimental parameters such as buffer gas, laser power, modulation frequency, and trace gas concentration was investigated. In the case of buffer gas, argon proved to be more suitable than nitrogen and helium in terms of enhancing the sensitivity of the system. The limits of detection of O 3 using the 9 P(14) CO 2 laser line in our PA system are 5 parts per 10 9 by volume (ppbv) and 14 ppbv with electronic and standard chopper modulation, respectively. This detection limit of O 3 is quite applicable for detection of safe levels of O 3 , at ground level.

© 2007 Optical Society of America

OCIS Codes
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(300.1030) Spectroscopy : Absorption
(300.6260) Spectroscopy : Spectroscopy, diode lasers
(300.6340) Spectroscopy : Spectroscopy, infrared
(300.6380) Spectroscopy : Spectroscopy, modulation
(300.6430) Spectroscopy : Spectroscopy, photothermal

ToC Category:
Spectroscopy

History
Original Manuscript: February 27, 2007
Revised Manuscript: July 31, 2007
Manuscript Accepted: August 6, 2007
Published: October 1, 2007

Citation
M. A. Gondal and Z. H. Yamani, "Highly sensitive electronically modulated photoacoustic spectrometer for ozone detection," Appl. Opt. 46, 7083-7090 (2007)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-46-29-7083

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