Abstract

A pulsed quantum-cascade distributed feedback laser operating at near room temperature was used for sensitive high-resolution IR absorption spectroscopy of ambient air at a wavelength of ∼8 µm. Near-transform-limited laser pulses were obtained owing to short (∼5-ns) current pulse excitation and optimized electrical coupling. Fast and slow computer-controlled frequency scanning techniques were implemented and characterized. Fast computer-controlled laser wavelength switching was used to acquire second-derivative absorption spectra. The minimum detectable absorption was found to be 3 × 10-4 with 105 laser pulses (20-kHz repetition rate), and 1.7 × 10-4 for 5 × 105 pulses, based on the standard deviation of the linear regression analysis.

© 2000 Optical Society of America

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References

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  1. F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).
  2. B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
    [CrossRef]
  3. A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
    [CrossRef]
  4. B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
    [CrossRef]
  5. S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
    [CrossRef]
  6. K. Namjou, S. Cai, E. A. Whittaker, J. Faist, C. Gmachl, F. Capasso, D. L. Sivco, A. Y. Cho, “Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser,” Opt. Lett. 23, 219–221 (1998).
    [CrossRef]
  7. D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.
  8. A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
    [CrossRef]
  9. D. Richter, D. G. Lancaster, F. K. Tittel, “Development of an automated diode laser based multicomponent gas sensor,” Appl. Opt. 39, 4444–4450 (2000).
    [CrossRef]
  10. International Atomic Energy Agency/World Meteorological Organisation (Geneva) (1998), Global Network for Isotopes in Precipitation (The GNIP Database. Release 3, October1999), http://www.iaea.org/programs/ri/gnip/gnipmain.htm .

2000 (2)

1999 (3)

1998 (2)

1997 (1)

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Allen, M.

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Baillargeon, J. N.

B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
[CrossRef]

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
[CrossRef]

B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
[CrossRef]

S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
[CrossRef]

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Cai, S.

Capasso, F.

B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
[CrossRef]

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
[CrossRef]

B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
[CrossRef]

F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).

S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
[CrossRef]

K. Namjou, S. Cai, E. A. Whittaker, J. Faist, C. Gmachl, F. Capasso, D. L. Sivco, A. Y. Cho, “Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser,” Opt. Lett. 23, 219–221 (1998).
[CrossRef]

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Cho, A. Y.

B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
[CrossRef]

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
[CrossRef]

F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).

B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
[CrossRef]

S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
[CrossRef]

K. Namjou, S. Cai, E. A. Whittaker, J. Faist, C. Gmachl, F. Capasso, D. L. Sivco, A. Y. Cho, “Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser,” Opt. Lett. 23, 219–221 (1998).
[CrossRef]

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Curl, R. F.

Drummond, James R.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Faist, J.

Fried, A.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Gilpin, T.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Gmachl, C.

B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
[CrossRef]

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
[CrossRef]

B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
[CrossRef]

F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).

S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
[CrossRef]

K. Namjou, S. Cai, E. A. Whittaker, J. Faist, C. Gmachl, F. Capasso, D. L. Sivco, A. Y. Cho, “Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser,” Opt. Lett. 23, 219–221 (1998).
[CrossRef]

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Harb, C. C.

Harren, F. J. M.

Hartman, J. S.

Henry, B.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Hutchinson, A. L.

Kelly, J. F.

Kosterev, A. A.

Lancaster, D. G.

Miller, M.

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Namjou, K.

Oomens, J.

Paldus, B. A.

Parker, D. H.

Richter, D.

Sewell, S.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Sharpe, S. W.

Sivco, D. L.

B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers,” Opt. Lett. 25, 666–668 (2000).
[CrossRef]

A. A. Kosterev, R. F. Curl, F. K. Tittel, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser,” Opt. Lett. 24, 1762–1764 (1999).
[CrossRef]

B. A. Paldus, T. G. Spence, R. N. Zare, J. Oomens, F. J. M. Harren, D. H. Parker, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, “Photoacoustic spectroscopy using quantum-cascade lasers,” Opt. Lett. 24, 178–180 (1999).
[CrossRef]

F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).

S. W. Sharpe, J. F. Kelly, J. S. Hartman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers,” Opt. Lett. 23, 1396–1398 (1998).
[CrossRef]

K. Namjou, S. Cai, E. A. Whittaker, J. Faist, C. Gmachl, F. Capasso, D. L. Sivco, A. Y. Cho, “Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser,” Opt. Lett. 23, 219–221 (1998).
[CrossRef]

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Sonnenfroh, D.

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Spence, T. G.

Tittel, F. K.

Wert, B. P.

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Wetjen, E.

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

Whittaker, E. A.

Zare, R. N.

Appl. Opt. (1)

J. Geophys. Res. (1)

A. Fried, S. Sewell, B. Henry, B. P. Wert, T. Gilpin, James R. Drummond, “Tunable diode laser absorption spectrometer for ground-based measurements of formaldehyde,” J. Geophys. Res. 102, 6253–6266 (1997).
[CrossRef]

Opt. Lett. (5)

Phys. World (1)

F. Capasso, C. Gmachl, D. L. Sivco, A. Y. Cho, “Quantum cascade lasers,” Phys. World 12, 27–33 (1999); also F. Capasso, C. Gmachl, A. Tredicucci, A. L. Hutchinson, D. L. Sivco, A. Y. Cho, “High performance quantum cascade lasers,” Opt. Photon. News 10, 32–37 (1999).

Other (2)

D. Sonnenfroh, E. Wetjen, M. Miller, M. Allen, C. Gmachl, F. Capasso, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho, “Application of balanced detection to absorption measurements with quasi-cw QC lasers,” OSA Trends in Optics and Photonics Series, Vol. 36, Laser Applications to Chemical and Environmental Analysis, Technical Digest, Postconference Edition (Optical Society of America, Washington, D.C., 2000), pp. 60–62.

International Atomic Energy Agency/World Meteorological Organisation (Geneva) (1998), Global Network for Isotopes in Precipitation (The GNIP Database. Release 3, October1999), http://www.iaea.org/programs/ri/gnip/gnipmain.htm .

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Figures (7)

Fig. 1
Fig. 1

Experimental arrangement for absorption spectroscopy with a pulsed QC-DFB laser. The laser is mounted on a thermoelectric cooler in an evacuated housing.

Fig. 2
Fig. 2

Laser frequency: tuning (a) with temperature and (b) with a computer-controlled voltage applied to the resistor R 1 (shown in Fig. 1). The circles show the positions of the etalon fringes used for calibration.

Fig. 3
Fig. 3

Solid line, acquired envelope of the CH4 absorption line at 1256.602 cm-1; dashed line, simulated envelope computed as a convolution of the Doppler-limited absorption line with a Fourier transform of a 3.1-ns-long rectangular pulse. The experimental data were obtained with a 3-cm-long gas cell filled with 1.25 Torr of CH4.

Fig. 4
Fig. 4

Absorption spectra of ambient air in a 100-m path-length multipass cell obtained with a linearized fast frequency scanning technique: (a) laser temperature set to -8.5 °C; (b) laser temperature set to -6.0 °C. The pressure in the cell is 85 Torr.

Fig. 5
Fig. 5

CH4 and HDO concentrations obtained from fast-scan measurements: (a) Solid line, simulated first-derivative spectrum of standard air, with the laser line shape taken into account; dotted line, acquired data after calculation of a numerical derivative. (b) Linear regression analysis of the data above for the CH4 line. (c) Same analysis for the HDO line.

Fig. 6
Fig. 6

Schematic of computer-controlled wavelength cycling for a pulsed QC-DFB laser. The steps show a subthreshold current (controlled by the computer-synthesized voltage U i ) added to the short laser excitation pulses represented as spikes. The laser wavelength cycles through three temperature-dependent values λ i .

Fig. 7
Fig. 7

Modified wavelength modulation spectroscopy: (a) IR detector signal simultaneously acquired at three laser wavelengths; (b) resulting second-derivative signal. Inset shows (left to right) weak H2O, CH4, and HDO absorption lines. The two lines to the right on the main plot correspond to N2O and HDO absorption. The second-derivative signal is not normalized for changing laser power. The data are acquired at 50 Torr of air in the multipass cell.

Tables (1)

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Table 1 Measurements of Trace-Gas Concentrations by Linear Regression Analysis of Fast-Scan Data

Equations (2)

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ν=fU=fgN=νmax×N/Nmax,
U=gN=f-1νmax×N/Nmax.

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