Abstract

It is shown that the optoacoustic effect in gases can be used for radiometric remote trace-gas analysis. The relevant physical principles involved are outlined and practical limitations are discussed and shown to be rather severe.

© 1980 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. P. Perlmutter, S. Shtrikman, and M. Slatkine, “Optoacoustic detection of ethylene in the presence of interfering pollutants,” Appl. Opt. 18, 2267–2274 (1979).
    [Crossref] [PubMed]
  3. E. Kritchman, S. Shtrikman, and M. Slatkine, “Resonant optoacoustic cells for trace gas analysis,” J. Opt. Soc. Am. 68, 1257–1271 (1978).
    [Crossref]
  4. Smith, Jones, and Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University, New York, 1968).
  5. P. L. Hanst, “Spectroscopic Methods for Air Pollution Measurements,” in Advances in Environmental Science and Technology, edited by Pitts and Calf (Wiley, New York, 1971), Vol. 2.
  6. Notice the lack of need to calculate the optoacoustic pressure response for the S/N analysis. This is so for an ultimate Brownian noise-limited optoacoustic cell. However, in practical cases when electronic noise from the microphone limits detectivity, the pressure signal should obviously be calculated.
  7. The method follows the same identification principles applied in former “Luft” spectrophones used prior to the introduction of laser optoacoustic spectroscopy.See, for example, P. Powell and W. Hill, Non Dispersive Infrared Analysis in Science and Industry, (Plenum, New York, 1968).See also A. Girard and J. Laurent “Selective Radiometer for Remote Sensing of Gases Pollutants,” in Physics in Industry, edited by E. O’Mongain and C. P. O’Tool (Pergamon, Oxford, 1976).
  8. We assumed a 5-km standard air path.See W. L. Wolfe, Handbook of Military Infrared Technology (ONR, Washington, D.C., 1965), Chap. 6.

1979 (1)

1978 (1)

1971 (1)

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

Chasmar,

Smith, Jones, and Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University, New York, 1968).

Hanst, P. L.

P. L. Hanst, “Spectroscopic Methods for Air Pollution Measurements,” in Advances in Environmental Science and Technology, edited by Pitts and Calf (Wiley, New York, 1971), Vol. 2.

Hill, W.

The method follows the same identification principles applied in former “Luft” spectrophones used prior to the introduction of laser optoacoustic spectroscopy.See, for example, P. Powell and W. Hill, Non Dispersive Infrared Analysis in Science and Industry, (Plenum, New York, 1968).See also A. Girard and J. Laurent “Selective Radiometer for Remote Sensing of Gases Pollutants,” in Physics in Industry, edited by E. O’Mongain and C. P. O’Tool (Pergamon, Oxford, 1976).

Jones,

Smith, Jones, and Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University, New York, 1968).

Kreuzer, L. B.

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

Kritchman, E.

Perlmutter, P.

Powell, P.

The method follows the same identification principles applied in former “Luft” spectrophones used prior to the introduction of laser optoacoustic spectroscopy.See, for example, P. Powell and W. Hill, Non Dispersive Infrared Analysis in Science and Industry, (Plenum, New York, 1968).See also A. Girard and J. Laurent “Selective Radiometer for Remote Sensing of Gases Pollutants,” in Physics in Industry, edited by E. O’Mongain and C. P. O’Tool (Pergamon, Oxford, 1976).

Shtrikman, S.

Slatkine, M.

Smith,

Smith, Jones, and Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University, New York, 1968).

Wolfe, W. L.

We assumed a 5-km standard air path.See W. L. Wolfe, Handbook of Military Infrared Technology (ONR, Washington, D.C., 1965), Chap. 6.

Appl. Opt. (1)

J. Appl. Phys. (1)

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

J. Opt. Soc. Am. (1)

Other (5)

Smith, Jones, and Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University, New York, 1968).

P. L. Hanst, “Spectroscopic Methods for Air Pollution Measurements,” in Advances in Environmental Science and Technology, edited by Pitts and Calf (Wiley, New York, 1971), Vol. 2.

Notice the lack of need to calculate the optoacoustic pressure response for the S/N analysis. This is so for an ultimate Brownian noise-limited optoacoustic cell. However, in practical cases when electronic noise from the microphone limits detectivity, the pressure signal should obviously be calculated.

The method follows the same identification principles applied in former “Luft” spectrophones used prior to the introduction of laser optoacoustic spectroscopy.See, for example, P. Powell and W. Hill, Non Dispersive Infrared Analysis in Science and Industry, (Plenum, New York, 1968).See also A. Girard and J. Laurent “Selective Radiometer for Remote Sensing of Gases Pollutants,” in Physics in Industry, edited by E. O’Mongain and C. P. O’Tool (Pergamon, Oxford, 1976).

We assumed a 5-km standard air path.See W. L. Wolfe, Handbook of Military Infrared Technology (ONR, Washington, D.C., 1965), Chap. 6.

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Figures (2)

FIG. 1
FIG. 1

Schematics of an optoacoustic remote-trace-gas analyzer. The window area of the cell is Σ. Its subtended field-of-view vertex angle α is approximately Σ / f rad. The walls are IR reflecting in order to minimize emission from the wall material, thereby enhancing spectral selectivity associated with the IR-absorbing gas, which then dominates the radiation absorption characteristics of the cell.

FIG. 2
FIG. 2

Computer simulation of detection and identification of remote ethylene traces: r1 = Ps,C2H4/Ps,NH3; r2 = Ps,C2H4/Ps,air. Ps is calculated according to Eqs. (3), (7), and (8). The ethylene concentration c1 in cell 1 is varied for a constant ethylene concentration c2 in cell 2. For c2 = c1, Ps = 0 [Eq. (8)] thus rendering r1 and r2 indeterminable. Notice that the infrared spectral signatures of NH3 and air give different signs of r1 and r2. For a practical radiometric cell, a criterion for ethylene identification would be|r1|,|r2| > 1.

Equations (9)

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P e = E λ 1 λ 2 ( 1 e α ( λ ) c A l ) F λ d λ ,
P abs = E λ 1 λ 2 ( 1 e α ( λ ) c A l ) ( 1 e β ( λ ) c B L ) F ( λ ) d λ ,
P rad = P e P abs = E λ 1 λ 2 [ ( 1 e α ( λ ) c A l ) ( 1 e α ( λ ) c A l ) ( 1 e β ( λ ) c B L ) ] F ( λ ) d λ .
( S / N ) voltage = P abs / NEP ,
NEP = ( 4 k T 2 Δ 0 ( 1 e α ( λ ) c a l ) F ( λ ) T d λ + 4 k T 2 Δ f K ) 1 / 2 ,
( S / N ) max E σ T 4 β c B L / ( 16 k σ T 5 Δ f ) 1 / 2 = 2 δ f N 2 ( β c B L ) ( 4 σ T 4 / k T Δ f ) 1 / 2 .
P abs / P e β ( λ ) c B L 10 3 ( for c B = 10 ppb , L = 1 km ) .
G = ( λ 1 λ 2 1 e α ( λ ) c 2 l ) F ( λ ) d λ λ 1 λ 2 ( 1 e α ( λ ) c 2 l ) F ( λ ) d λ .
P s P rad ( c 2 ) G P rad ( c 1 ) ,