Abstract

We describe the development and characterization of a near-infrared diode-laser-based sensor to measure the vapor from trace gases having unstructured absorption spectra. The technique uses two equal amplitude-modulated laser beams, with the modulation of the two lasers differing in phase by 180 deg. One of the laser beams is at a wavelength absorbed by the gas [for these experiments, vapor is from pyridine (C5H5N)], and the second laser beam is at a wavelength at which no absorption occurs. The two laser beams are launched onto near-coincident paths by graded-index lens-tipped optical fibers. The mixed laser beam signal is detected by use of a single photodiode and is demodulated with standard phase-sensitive detection. Data are presented for the detection and measurement of vapor from pyridine (C5H5N) by use of the mixed laser technique. The discussion focuses on experimental determination of whether a compound exhibits unstructured absorption spectra (referred to here as a broadband absorber) and methods used to maximize sensitivity.

© 2000 Optical Society of America

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References

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  1. I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
    [CrossRef]
  2. J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
    [CrossRef]
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  4. D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
    [CrossRef]
  5. P. C. D. Hobbs, “Ultrasensitive laser measurements without tears,” Appl. Opt. 36, 903–921 (1997).
    [CrossRef] [PubMed]
  6. D. B. Oh, D. C. Hovde, “Wavelength modulation detection of acetylene with a near-infrared external cavity diode laser,” Appl. Opt. 34, 7002–7005 (1995).
    [CrossRef] [PubMed]
  7. K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
    [CrossRef]
  8. G. Hertzberg, Infrared and Raman Spectra (Van Nostrand Rheinhold, New York, 1945).
  9. M. Allen, Physical Sciences, Inc., 20 New England Business Center, Andover, Mass. 01810 (personal communication, 1999).
  10. J. H. Miller, S. Elreedy, B. Ahvazi, F. Woldu, P. Hassanzadeh, “Tunable diode-laser measurement of carbon monoxide concentration and temperature in a laminar methane–air diffusion flame,” Appl. Opt. 32, 6082–6089 (1993).
    [CrossRef]

1998 (3)

I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
[CrossRef]

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

1997 (1)

1995 (1)

1993 (1)

1992 (1)

1981 (1)

J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
[CrossRef]

Ahvazi, B.

Allen, M.

M. Allen, Physical Sciences, Inc., 20 New England Business Center, Andover, Mass. 01810 (personal communication, 1999).

Allen, M. G.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

Barrick, J. D. W.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

Bomse, D. S.

Clay, M.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Elreedy, S.

Hassanzadeh, P.

Hertzberg, G.

G. Hertzberg, Infrared and Raman Spectra (Van Nostrand Rheinhold, New York, 1945).

Hobbs, P. C. D.

Hoke, S. H.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Hovde, D. C.

Jaeger, T.

I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
[CrossRef]

Kaspersen, P.

I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
[CrossRef]

Kessler, W. J.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

Labrie, D.

J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
[CrossRef]

Linnerud, I.

I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
[CrossRef]

Magill, J. C.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

McNesby, K. L.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Miller, J. H.

Miser, C. S.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Miziolek, A. W.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Oh, D. B.

Reid, J.

J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
[CrossRef]

Silver, J. A.

Skaggs, R. R.

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Sonnenfroh, D. M.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

Stanton, A. C.

Upschulte, B. L.

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

Woldu, F.

Appl. Opt. (4)

Appl. Phys. B (4)

I. Linnerud, P. Kaspersen, T. Jaeger, “Gas monitoring in the process industry using diode laser spectroscopy,” Appl. Phys. B 67, 297–305 (1998).
[CrossRef]

J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
[CrossRef]

D. M. Sonnenfroh, W. J. Kessler, J. C. Magill, B. L. Upschulte, M. G. Allen, J. D. W. Barrick, “In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer,” Appl. Phys. B 67, 275–282 (1998).
[CrossRef]

K. L. McNesby, R. R. Skaggs, A. W. Miziolek, M. Clay, S. H. Hoke, C. S. Miser, “Diode laser-based measurements of hydrogen fluoride gas during chemical suppression of fires,” Appl. Phys. B 67, 443–447 (1998).
[CrossRef]

Other (2)

G. Hertzberg, Infrared and Raman Spectra (Van Nostrand Rheinhold, New York, 1945).

M. Allen, Physical Sciences, Inc., 20 New England Business Center, Andover, Mass. 01810 (personal communication, 1999).

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Figures (5)

Fig. 1
Fig. 1

Percentage of the transmittance spectrum of pyridine (C5H5N; P T = 4 Torr, 225-cm path length), together with the percentage of the transmittance spectrum of methane (CH4; P T = 10.5 Torr, 15-cm path length), measured with a Fourier transform spectrometer. The inset shows the wavelength modulation spectrum of a mixture of pyridine and methane (P T = 13.5 Torr, 400-cm path length) measured with a TDL with detection at 2f near 1.653-µm wavelength. The breadth of the 2f scan is approximately 0.4 cm-1. The absorption coefficient of pyridine at a wavelength of 1.653 µm was found to be 3.6 × 10-22 cm2/molecule.

Fig. 2
Fig. 2

Value of the integral in Eq. (4) (calculated signal) for a moderately strong absorbing gas as a function of absorbance (A = αcl). For this calculation, as for the measurements, the modulation frequency is 100 kHz, p and m are set equal to unity, and the number of periods per measurement (C) is 1000, corresponding to a measurement time of 10 ms. For a trace gas in a bath of air at 1 atm, the signal measured with the mixed laser method described here is predicted to vary linearly with partial pressure.

Fig. 3
Fig. 3

Schematic of the experimental apparatus that we used for our experiments.

Fig. 4
Fig. 4

Absorption spectrum of pyridine (C5H5N; 4 Torr, 225-cm path length, 1-cm-1 resolution, measured with a FTIR spectrometer) superimposed on the spectrum of the mixed laser probe beam (1-cm-1 resolution, also measured with a FTIR spectrometer). The decrease in signal-to-noise ratio in the percentage of transmittance spectrum at lower wavelengths is due to a decrease in sensitivity of the InSb detector that was used with the FTIR and to an increase in scatter in the multipass gas cell.

Fig. 5
Fig. 5

Measured signal for pyridine (C5H5N) vapor obtained with the mixed laser technique. The path length was 400 cm. The inset shows the signal response at the lowest pressures that we used in our experiments.

Tables (1)

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Table 1 Absorption Coefficients for Pyridine and Selected Atmospheric Gases

Equations (4)

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

S1a, n, t+S2a, m, t=n sinat+m sinat+π.
2C0π  S1a, n, t+S2a, m, tp sinatdt=Cpπn-m.
2C0π  S1a, n, t+S2a, m, texp-αclp sinatdt=Cpπn-mexp-αcl.
2C0π  S1a, n, t+S2a, m, texp-αclp sinatdt=CpπmA.

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