Abstract

The pulsed excitation of acoustic resonances was studied with a continuously monitoring photoacoustic detector system. Acoustic waves were generated in C2H4/N2 gas mixtures by light absorption of the pulses from a transversely excited atmospheric CO2 laser. The photoacoustic part consisted of high-Q cylindrical resonators (Q factor 820 for the first radial mode in N2) and two adjoining variable acoustic filter systems. The time-resolved signal was Fourier transformed to a frequency spectrum of high resolution. For the first radial mode a Lorentzian profile was fitted to the measured data. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the averaging of the photoacoustic signal in the time domain suppressed the outside noise by a factor of 4500 (73 dB). The detection limit for trace gas analysis of ethylene in pure N2 was 2.0 parts in 109 by volume (ppbV) (minimal absorption coefficient αmin = 6.1 × 10−8 cm−1, pulse energy 20 mJ, 1-bar N2), and in environmental air, in which the absorption of other gas components produces a high background signal, we can detect C2H4 to ~180 ppbV. In addition, an alternative experimental technique, in which the maximum signal of the second azimuthal mode was monitored, was tested. To synchronize the sampling rate at the resonance frequency, a resonance tracking system was applied. The detection limit for ethylene measurements was αmin = 9.1 × 10−8 cm−1 for this system.

© 1995 Optical Society of America

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References

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  1. L. B. Kreuzer, “Ultralow gas concentration infrared absorption spectroscopy,” J. Appl. Phys. 42, 2934–2943 (1971).
    [CrossRef]
  2. C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
    [CrossRef]
  3. M. W. Sigrist, S. Bernegger, P. L. Meyer, “Atmospheric and exhaust air monitoring by laser photoacoustic spectroscopy,” in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, Heidelberg, 1989), pp. 173–211.
    [CrossRef]
  4. M. W. Sigrist, “Air monitoring by laser photoacoustic spectroscopy,” in Air Monitoring by Spectroscopic Techniques, M. W. Sigrist, ed., Vol. 127 of Chemical Analysis (Wiley, New York, 1994), pp. 163–238.
  5. S. Bernegger, M. W. Sigrist, “CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis,” Infrared Phys. 30, 375–429 (1990).
    [CrossRef]
  6. P. L. Meyer, M. W. Sigrist, “Atmospheric pollution monitoring using CO2-laser photoacoustic spectroscopy and other techniques,” Rev. Sci. Instrum. 61, 1779–1807 (1990).
    [CrossRef]
  7. G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
    [CrossRef]
  8. A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
    [CrossRef]
  9. P. C. Claspy, C. Ha, Y.-H. Pao, “Optoacoustic detection of NO2 using a pulsed dye laser,” Appl. Opt. 16, 2972–2973 (1977).
    [CrossRef] [PubMed]
  10. M. A. Leugers, G. H. Atkinson, “Quantitative determination of acetaldehyde by pulsed laser photoacoustic spectroscopy,” Anal. Chem. 56, 925–929 (1984).
    [CrossRef]
  11. M. Fiedler, P. Hess, “Frequency domain analysis of acoustic resonances excited with single laser pulses,” in Photoacoustic and Photothermal Phenomena, J. C. Murphy, J. W. Maclachlan Spicer, L. C. Aamodt, B. S. H. Royce, eds., Vol. 62 of Springer Series in Optical Sciences (Springer-Verlag, Berlin, Heidelberg, 1990), pp. 344–346.
  12. R. Gerlach, N. M. Amer, “Brewster window and windowless resonant spectrophones for intracavity operation,” Appl. Phys. 23, 319–326 (1980).
    [CrossRef]
  13. A. Miklós, A. Lörincz, “Windowless resonant acoustic chamber for laser-photoacoustic applications,” Appl. Phys. B 48, 213–218 (1989).
    [CrossRef]
  14. A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).
  15. J. P. M. Trusler, Physical Acoustics and Metrology of Fluids (Hilger, Bristol, 1991), pp. 68–72.
  16. P. M. Morse, K. U. Ingard, Theoretical Acoustics (Princeton U. Press, Princeton, N.J., 1968), pp. 490–492.
  17. R. J. Brewer, C. W. Bruce, J. L. Mater, “Optoacoustic spectroscopy of C2H4 at the 9- and 10-μm C12O2 laser wavelengths,” Appl. Opt. 21, 4092–4100 (1982).
    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  19. L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
    [CrossRef]
  20. F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
    [CrossRef]

1994

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

1992

1990

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

S. Bernegger, M. W. Sigrist, “CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis,” Infrared Phys. 30, 375–429 (1990).
[CrossRef]

P. L. Meyer, M. W. Sigrist, “Atmospheric pollution monitoring using CO2-laser photoacoustic spectroscopy and other techniques,” Rev. Sci. Instrum. 61, 1779–1807 (1990).
[CrossRef]

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

1989

A. Miklós, A. Lörincz, “Windowless resonant acoustic chamber for laser-photoacoustic applications,” Appl. Phys. B 48, 213–218 (1989).
[CrossRef]

L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
[CrossRef]

1984

A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
[CrossRef]

M. A. Leugers, G. H. Atkinson, “Quantitative determination of acetaldehyde by pulsed laser photoacoustic spectroscopy,” Anal. Chem. 56, 925–929 (1984).
[CrossRef]

1982

1980

R. Gerlach, N. M. Amer, “Brewster window and windowless resonant spectrophones for intracavity operation,” Appl. Phys. 23, 319–326 (1980).
[CrossRef]

1977

1973

C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
[CrossRef]

1971

L. B. Kreuzer, “Ultralow gas concentration infrared absorption spectroscopy,” J. Appl. Phys. 42, 2934–2943 (1971).
[CrossRef]

Amer, N. M.

R. Gerlach, N. M. Amer, “Brewster window and windowless resonant spectrophones for intracavity operation,” Appl. Phys. 23, 319–326 (1980).
[CrossRef]

Angeli, G. Z.

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

Atkinson, G. H.

M. A. Leugers, G. H. Atkinson, “Quantitative determination of acetaldehyde by pulsed laser photoacoustic spectroscopy,” Anal. Chem. 56, 925–929 (1984).
[CrossRef]

Back, M. H.

L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
[CrossRef]

Back, R. A.

L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
[CrossRef]

Bernegger, S.

S. Bernegger, M. W. Sigrist, “CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis,” Infrared Phys. 30, 375–429 (1990).
[CrossRef]

M. W. Sigrist, S. Bernegger, P. L. Meyer, “Atmospheric and exhaust air monitoring by laser photoacoustic spectroscopy,” in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, Heidelberg, 1989), pp. 173–211.
[CrossRef]

Bijnen, F. G.

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Blom, C. W. P. M.

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Bozóki, Z.

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

Brand, C.

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

Brewer, R. J.

Bruce, C. W.

Claspy, P. C.

Dewey, C. F.

C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
[CrossRef]

Fiedler, M.

M. Fiedler, P. Hess, “Frequency domain analysis of acoustic resonances excited with single laser pulses,” in Photoacoustic and Photothermal Phenomena, J. C. Murphy, J. W. Maclachlan Spicer, L. C. Aamodt, B. S. H. Royce, eds., Vol. 62 of Springer Series in Optical Sciences (Springer-Verlag, Berlin, Heidelberg, 1990), pp. 344–346.

Gerlach, R.

R. Gerlach, N. M. Amer, “Brewster window and windowless resonant spectrophones for intracavity operation,” Appl. Phys. 23, 319–326 (1980).
[CrossRef]

Giroux, L.

L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
[CrossRef]

Ha, C.

Hackett, C. E.

C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
[CrossRef]

Hammerich, M.

Harren, F. J. M.

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Henningsen, J.

Hess, P.

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
[CrossRef]

M. Fiedler, P. Hess, “Frequency domain analysis of acoustic resonances excited with single laser pulses,” in Photoacoustic and Photothermal Phenomena, J. C. Murphy, J. W. Maclachlan Spicer, L. C. Aamodt, B. S. H. Royce, eds., Vol. 62 of Springer Series in Optical Sciences (Springer-Verlag, Berlin, Heidelberg, 1990), pp. 344–346.

Ingard, K. U.

P. M. Morse, K. U. Ingard, Theoretical Acoustics (Princeton U. Press, Princeton, N.J., 1968), pp. 490–492.

Kamm, R. D.

C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
[CrossRef]

Karbach, A.

A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
[CrossRef]

Kreuzer, L. B.

L. B. Kreuzer, “Ultralow gas concentration infrared absorption spectroscopy,” J. Appl. Phys. 42, 2934–2943 (1971).
[CrossRef]

Leugers, M. A.

M. A. Leugers, G. H. Atkinson, “Quantitative determination of acetaldehyde by pulsed laser photoacoustic spectroscopy,” Anal. Chem. 56, 925–929 (1984).
[CrossRef]

Lörincz, A.

A. Miklós, A. Lörincz, “Windowless resonant acoustic chamber for laser-photoacoustic applications,” Appl. Phys. B 48, 213–218 (1989).
[CrossRef]

Lörincz, András

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

Mater, J. L.

Meyer, P. L.

P. L. Meyer, M. W. Sigrist, “Atmospheric pollution monitoring using CO2-laser photoacoustic spectroscopy and other techniques,” Rev. Sci. Instrum. 61, 1779–1807 (1990).
[CrossRef]

M. W. Sigrist, S. Bernegger, P. L. Meyer, “Atmospheric and exhaust air monitoring by laser photoacoustic spectroscopy,” in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, Heidelberg, 1989), pp. 173–211.
[CrossRef]

Miklós, A.

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

A. Miklós, A. Lörincz, “Windowless resonant acoustic chamber for laser-photoacoustic applications,” Appl. Phys. B 48, 213–218 (1989).
[CrossRef]

Miklós, András

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

Morse, P. M.

P. M. Morse, K. U. Ingard, Theoretical Acoustics (Princeton U. Press, Princeton, N.J., 1968), pp. 490–492.

Olafsson, A.

Pao, Y.-H.

Reuss, J.

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Röper, J.

A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
[CrossRef]

Sigrist, M. W.

P. L. Meyer, M. W. Sigrist, “Atmospheric pollution monitoring using CO2-laser photoacoustic spectroscopy and other techniques,” Rev. Sci. Instrum. 61, 1779–1807 (1990).
[CrossRef]

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

S. Bernegger, M. W. Sigrist, “CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis,” Infrared Phys. 30, 375–429 (1990).
[CrossRef]

M. W. Sigrist, “Air monitoring by laser photoacoustic spectroscopy,” in Air Monitoring by Spectroscopic Techniques, M. W. Sigrist, ed., Vol. 127 of Chemical Analysis (Wiley, New York, 1994), pp. 163–238.

M. W. Sigrist, S. Bernegger, P. L. Meyer, “Atmospheric and exhaust air monitoring by laser photoacoustic spectroscopy,” in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, Heidelberg, 1989), pp. 173–211.
[CrossRef]

Thöny, A.

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

Trusler, J. P. M.

J. P. M. Trusler, Physical Acoustics and Metrology of Fluids (Hilger, Bristol, 1991), pp. 68–72.

Voesenek, L. A. C. J.

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Winkler, A.

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

Anal. Chem.

M. A. Leugers, G. H. Atkinson, “Quantitative determination of acetaldehyde by pulsed laser photoacoustic spectroscopy,” Anal. Chem. 56, 925–929 (1984).
[CrossRef]

Appl. Opt.

Appl. Phys.

R. Gerlach, N. M. Amer, “Brewster window and windowless resonant spectrophones for intracavity operation,” Appl. Phys. 23, 319–326 (1980).
[CrossRef]

Appl. Phys. B

A. Miklós, A. Lörincz, “Windowless resonant acoustic chamber for laser-photoacoustic applications,” Appl. Phys. B 48, 213–218 (1989).
[CrossRef]

L. Giroux, M. H. Back, R. A. Back, “The absorption of pulsed CO2-laser radiation by ethylene at total pressures from 25 to 3000 Torr,” Appl. Phys. B 49, 307–313 (1989).
[CrossRef]

F. J. M. Harren, F. G. Bijnen, J. Reuss, L. A. C. J. Voesenek, C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurement with a CO2 waveguide laser,” Appl. Phys. B 50, 137–144 (1990).
[CrossRef]

Appl. Phys. Lett.

C. F. Dewey, R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants,” Appl. Phys. Lett. 23, 633–635 (1973).
[CrossRef]

Infrared Phys.

S. Bernegger, M. W. Sigrist, “CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis,” Infrared Phys. 30, 375–429 (1990).
[CrossRef]

J. Appl. Phys.

L. B. Kreuzer, “Ultralow gas concentration infrared absorption spectroscopy,” J. Appl. Phys. 42, 2934–2943 (1971).
[CrossRef]

J. Phys. IV (Colloque C7)

A. Miklós, C. Brand, A. Winkler, P. Hess, “Effective noise reduction on pulsed laser excitation of modes in a high-Q photoacoustic resonator,” J. Phys. IV (Colloque C7) 4, 781–784 (1994).

Rev. Sci. Instrum.

P. L. Meyer, M. W. Sigrist, “Atmospheric pollution monitoring using CO2-laser photoacoustic spectroscopy and other techniques,” Rev. Sci. Instrum. 61, 1779–1807 (1990).
[CrossRef]

G. Z. Angeli, Z. Bozóki, András Miklós, András Lörincz, A. Thöny, M. W. Sigrist, “Design and characterization of a windowless resonant photoacoustic chamber equipped with resonance locking circuitry,” Rev. Sci. Instrum. 62, 810–813 (1990).
[CrossRef]

A. Karbach, J. Röper, P. Hess, “Computer-controlled performance of photoacoustic resonance experiments,” Rev. Sci. Instrum. 55, 892–895 (1984).
[CrossRef]

Other

M. W. Sigrist, S. Bernegger, P. L. Meyer, “Atmospheric and exhaust air monitoring by laser photoacoustic spectroscopy,” in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, Heidelberg, 1989), pp. 173–211.
[CrossRef]

M. W. Sigrist, “Air monitoring by laser photoacoustic spectroscopy,” in Air Monitoring by Spectroscopic Techniques, M. W. Sigrist, ed., Vol. 127 of Chemical Analysis (Wiley, New York, 1994), pp. 163–238.

J. P. M. Trusler, Physical Acoustics and Metrology of Fluids (Hilger, Bristol, 1991), pp. 68–72.

P. M. Morse, K. U. Ingard, Theoretical Acoustics (Princeton U. Press, Princeton, N.J., 1968), pp. 490–492.

M. Fiedler, P. Hess, “Frequency domain analysis of acoustic resonances excited with single laser pulses,” in Photoacoustic and Photothermal Phenomena, J. C. Murphy, J. W. Maclachlan Spicer, L. C. Aamodt, B. S. H. Royce, eds., Vol. 62 of Springer Series in Optical Sciences (Springer-Verlag, Berlin, Heidelberg, 1990), pp. 344–346.

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Figures (8)

Fig. 1
Fig. 1

Schematic of the experimental setup of the high-Q system: M, microphone; A/F, amplifier and bandpass filter; D, light detector.

Fig. 2
Fig. 2

Schematic of the experimental setup with the resonance tracking system: 1–4: microphones; A/F, amplifier and bandpass filter; RTS, resonance tracking system; A/D, 16-bit A/D card; D, light detector.

Fig. 3
Fig. 3

Comparison of the calculated (lower spectrum) with the measured (upper spectrum) PA Fourier spectrum of the signal in the high-Q system for 20 ppmV C2H4 in 1-bar N2. For a better comparison, the lower spectrum is shifted down 4 orders of magnitude. In both spectra the first radial (100), the adjoining second longitudinal (002), and the combination (102) modes are excited. The second azimuthal mode (020) does not appear in the calculated spectrum.

Fig. 4
Fig. 4

PA Fourier spectrum for the high-Q system with 20 ppmV C2H4 in N2 (upper spectrum) and for pure N2 (background, lower spectrum). The 10P14 line of the TEA CO2 laser with an average pulse energy of 20 mJ was used. The frequency resolution is 2 Hz.

Fig. 5
Fig. 5

Measured Lorentzian profile of the first radial mode (100) for 20 ppmV C2H4 in N2. The 10P14 line was used with an averaged and normalized pulse energy of 20 mJ. The filled circles represent the measured values, and the curve indicates the fitted Lorentzian profile. The resonance frequency is ν100 = 4164.9 Hz, and the full-width at half-maximum is Δν100 = 5.08 Hz. This corresponds to a Q value of 820.

Fig. 6
Fig. 6

Calibration curves for the two PA setups. The filled circles and the filled squares represent the measurements on the 10P14 and 10P10 lines, respectively, with the high-Q system. The open circles (10P14) and open squares (10P10) were recorded with the resonance tracking system. Because of saturation, the calibration curve of the two laser lines have a parallel distance in this log–log plot corresponding to a ratio of ~3 instead of the theoretical value of ~10.

Fig. 7
Fig. 7

PA Fourier spectrum for the high-Q system with 20-ppmV C2H4 in N2 (upper spectrum) and in air (background, lower spectrum). The 10P14 line of the TEA CO2 laser with an average pulse energy of 20 mJ was used. The shift of the resonance frequencies between the two spectra is caused by the change of the mean molar mass. The background signal in air that is due to H2O or CO2 absorption corresponds to a C2H4 concentration of 180 ppbV.

Fig. 8
Fig. 8

PA Fourier spectrum for the resonance tracking system for 20-ppmV C2H4 in N2 (filled circles) and for the electronic background (filled squares). The 10P14 line of the TEA CO2 laser with an average pulse energy of 2.7 mJ was used. The frequency resolution is 200 Hz.

Tables (2)

Tables Icon

Table 1 Characteristics of the Two PA Systems

Tables Icon

Table 2 Overview of the S/N Ratios, Estimated Detection Limits, and Minimum Absorption Coefficients of the High-Q Setup (hQ) and the Resonance Tracking System (RT)

Equations (17)

Equations on this page are rendered with MathJax. Learn more.

t 2 p ( r , t ) - c 2 2 p ( r , t ) = ( γ - 1 ) t H ( r , t ) ,
H ( r , t ) = α I ( r , t ) ,
p ( r , t ) = j A j ( t ) p j ( r ) exp ( i ω j t ) ,
p j ( r ) = J m ( k r r ) cos ( k z z ) [ sin ( m φ ) cos ( m φ ) ] .
ω j = c ( k r 2 + k z 2 ) 1 / 2 .
ω j f j + i g j = k j c .
j ( t 2 A j + 2 i ω j t A j ) p j exp ( i ω j t ) = ( γ - 1 ) t H ( r , t ) .
t 2 A j + 2 i ω j t A j = γ - 1 V j exp ( - i ω j t ) × V Cell t H ( r , t ) p j * d V .
t A j + 2 i ω j A j = γ - 1 V j - t V Cell exp ( - i ω j t ) t H ( r , t ) p j * d V d t .
H ( r , t ) = H ( r ) exp ( - t / τ )
t A j + 2 i ω j A j = - γ - 1 V j V Cell H ( r ) p j * d V × - t exp ( - t / τ ) τ × exp ( - i ω j t ) d t
lim τ 0 - a + a exp ( - t / τ ) τ f ( t ) d t = - a + a δ ( t ) f ( t ) d t = f ( 0 ) ,             a > 0.
t A j + 2 i ω j A j = S j ,
S j - γ - 1 V j V Cell H ( r ) p j * d V .
A j ( t ) = A 0 j exp ( - 2 i ω j t ) + S j 2 i ω j .
p ( r M , t ) = j p j ( r M ) exp ( i ω j t ) S j 2 i ω j .
p ( r M , ω ) = 1 2 π j p j ( r M ) S j ω j ( ω - ω j ) ,

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