Abstract

The feasibility of the application of harmonic saturated spectroscopy to molecular detection in the infrared regime was investigated. Experimental measurements using SF6 as a model gas were performed with a CO2 laser photoacoustic molecular vapor detector operating in the 9–11-μm portion of the infrared regime. These experiments demonstrated the negligible loss of absolute sensitivity, the maintenance of a characteristic readily identifiable absorption profile, and the ability to scale with laser intensity in the proper conditions. Our work demonstrates the importance of a laser modulation waveform that is completely devoid of spatial asymmetries for the realization of the full potential of this method.

© 1985 Optical Society of America

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References

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  1. C. K. N. Patel, R. J. Kerl, “A New Optoacoustic Cell with Improved Performance,” Appl. Phys. Lett. 30, 578 (1977).
    [CrossRef]
  2. R. P. Frueholz, J. A. Gelbwachs, “Harmonic Saturated Spectroscopy for Improved Atomic Detection,” Appl. Opt. 19, 2735 (1980).
    [CrossRef] [PubMed]
  3. L. B. Kreuzer, “Ultraflow Gas Concentration IR Absorption Spectroscopy,” J. Appl. Phys. 42, 2934 (1971).
    [CrossRef]
  4. A. Yariv, Quantum Electronics (Wiley, New York, 1975), p. 170.
  5. J. C. Peterson, M. E. Thomas, R. J. Nordstrom, E. K. Damon, R. K. Long, “Water Vapor-Nitrogen Absorption at CO2 Laser Frequencies,” Appl. Opt. 18, 834 (1979);S. H. Suck, J. L. Kassner, Y. Yamaguchi, “Water Cluster Interpretation of IR Absorption Spectra in the 8–14-μm Wavelength Region,” Appl. Opt. 18, 2609 (1979);H. R. Carlon, “Phase Transition Changes in the Molecular Absorption Coefficient of Water in the Infrared: Evidence for Clusters,” Appl. Opt. 17, 3192 (1978);S. A. Clough, F. X. Kneizys, R. Davies, R. Gamache, R. Tipping, “Theoretical Line Shape for H2O Vapor; Application to the Continuum,” in Atmospheric Water Vapor, A. Deepak, T. D. Wilkerson, L. H. Ruhnke, Eds. (Academic, New York, 1980);G. L. Loper, M. A. O'Neill, J. A. Gelbwachs, “Water-Vapor Continuum CO2 Laser Absorption Spectra Between 27°C and −10°C,” Appl. Opt. 22, 3701 (1983).
    [CrossRef] [PubMed]
  6. A. R. Calloway, Aerospace Corp.;unpublished results.
  7. J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
    [CrossRef]

1980

1979

1977

C. K. N. Patel, R. J. Kerl, “A New Optoacoustic Cell with Improved Performance,” Appl. Phys. Lett. 30, 578 (1977).
[CrossRef]

1971

L. B. Kreuzer, “Ultraflow Gas Concentration IR Absorption Spectroscopy,” J. Appl. Phys. 42, 2934 (1971).
[CrossRef]

1969

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Burak, I.

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Calloway, A. R.

A. R. Calloway, Aerospace Corp.;unpublished results.

Damon, E. K.

Frueholz, R. P.

Gelbwachs, J. A.

Kerl, R. J.

C. K. N. Patel, R. J. Kerl, “A New Optoacoustic Cell with Improved Performance,” Appl. Phys. Lett. 30, 578 (1977).
[CrossRef]

Kreuzer, L. B.

L. B. Kreuzer, “Ultraflow Gas Concentration IR Absorption Spectroscopy,” J. Appl. Phys. 42, 2934 (1971).
[CrossRef]

Long, R. K.

Nordstrom, R. J.

Nowak, A. V.

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Patel, C. K. N.

C. K. N. Patel, R. J. Kerl, “A New Optoacoustic Cell with Improved Performance,” Appl. Phys. Lett. 30, 578 (1977).
[CrossRef]

Peterson, J. C.

Steinfeld, J. I.

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Sutton, D. G.

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Thomas, M. E.

Yariv, A.

A. Yariv, Quantum Electronics (Wiley, New York, 1975), p. 170.

Appl. Opt.

Appl. Phys. Lett.

C. K. N. Patel, R. J. Kerl, “A New Optoacoustic Cell with Improved Performance,” Appl. Phys. Lett. 30, 578 (1977).
[CrossRef]

J. Appl. Phys.

L. B. Kreuzer, “Ultraflow Gas Concentration IR Absorption Spectroscopy,” J. Appl. Phys. 42, 2934 (1971).
[CrossRef]

J. Chem. Phys.

J. I. Steinfeld, I. Burak, D. G. Sutton, A. V. Nowak, “IR Double Resonance in Sulfur Hexafluoride,” J. Chem. Phys. 52, 5421 (1969).
[CrossRef]

Other

A. Yariv, Quantum Electronics (Wiley, New York, 1975), p. 170.

A. R. Calloway, Aerospace Corp.;unpublished results.

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Figures (3)

Fig. 1
Fig. 1

Schematic diagram of the experimental apparatus. The vapor absorption cell contained SF6 at a continuously adjustable pressure. It was used to attenuate the laser to the desired intensity. The infrared sensor was used to measure the second harmonic content of the modulated laser light. The sensor detected scattered laser light originating at the entrance slit of the spectrum analyzer.

Fig. 2
Fig. 2

Fundamental, harmonic, and predicted harmonic spectra of SF6. The fundamental spectrum (solid line) was measured at the modulation frequency. The harmonic spectrum (dashed line) was measured at the second harmonic of the modulation frequency, corrected for harmonic background distortion, and then normalized to the peak value of the fundamental spectrum. The predicted harmonic spectrum (dot-dash line) is the square of the measured fundamental spectrum. It too has been normalized to the peak intensity of the fundamental spectrum.

Fig. 3
Fig. 3

Dependence of the fundamental and harmonic photoacoustic responses on the laser intensity at f0 and 2f0.

Equations (17)

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a n = ( 1 α ) ( 1 α 2 ) 1 / 2 [ ( 1 α 2 ) 1 / 2 1 α ] n ( n 1 ) ,
a 1 = ¼ ( I I 0 ) ; a 2 = 1 / 16 ( I I 0 ) 2 , ( α 1 ) ,
r ω = N a 1 N a 1 ; r 2 ω = N a 2 N a 2 ,
r 2 ω r ω = α [ ( 1 α 2 ) 1 / 2 1 ] α [ ( 1 α 2 ) 1 / 2 1 ] α α .
r 2 ω r ω 0.6 α α .
ϕ ( ν ν 0 ) = δ ν L 2 π [ ( ν ν 0 ) 2 + ( δ ν L / 2 ) 2 ] ,
I 0 ( ν ) = N a h ν 2 α ϕ ( ν ν 0 ) τ ,
r 2 ω r ω = I 0 I 0 = α ϕ ( ν ν 0 ) α ϕ ( ν ν 0 ) .
S 2 ω υ ( υ ) d ν = υ ɛ f ( ν ɛ ) [ L ( ν ν ɛ ) ] 2 I 2 ( d ν ) 2 ,
S 2 ω υ ( ν ) d ν f ( ν ) I 2 ( d ν ) 2 [ L ( ν ν ɛ ) ] 2 d ν ɛ .
S 2 ω υ ( ν ) d ν = π f ( ν ) Γ σ υ 2 I 2 ( d ν ) 2 ,
S 2 ω ( ν ) d ν = π Γ I 2 ( d ν ) 2 all υ N υ f υ ( ν ) σ υ 2 ,
S ω ( ν ) d ν = π Γ I ( d ν ) all υ N υ f υ ( ν ) σ υ .
r 2 ω r ω σ υ ( υ ) σ υ ( υ ) ,
r 2 ω r ω = α ϕ ( ν ν 0 ) α H 2 O ( ν ) ,
r 2 ω r ω α ( ν ) α cont ( ν ) ,
| S 2 ω ( true ) | = | S 2 ω ( meas ) k S ω ( meas ) | ,

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