Abstract

Second harmonic detection at audio frequencies of isolated absorption lines with a laser absorption spectrometer employing AlGaAs and InGaAsP diode lasers, short external cavity (SXC) AlGaAs and InGaAsP diode lasers, and InGaAsP distributed feedback (DFB) diode lasers was investigated and compared. Noise levels equivalent to line center absorptions of ~3 × 10−6 were achieved with each source. Single mode tuning ranges of 20–50 cm−1 were obtained with both the SXC and DFB sources. The contamination of absorption spectra by suppressed laser side modes was identified and investigated as it relates to the identification of weak lines in the presence of strong lines.

© 1990 Optical Society of America

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  1. H. Sasada, “Stark Modulation Spectroscopy of NH3 with a 1.23-μm Semiconductor Laser,” Opt. Lett. 9, 448–450 (1984).
    [CrossRef] [PubMed]
  2. D. T. Cassidy, “Trace Gas Detection Using 1.3-μm InGaAsP Diode Laser Transmitter Modules,” Appl. Opt. 27, 610–614 (1988).
    [CrossRef] [PubMed]
  3. H. Sasada, “1.5-μm DFB Semiconductor Laser Spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
    [CrossRef]
  4. T. Yanagawa, S. Saito, Y. Yamamoto, “Frequency Stabilization of a 1.5-μm InGaAsP DFB Laser to NH3 Absorption Lines,” Appl. Phys. Lett. 45, 826–828 (1984).
    [CrossRef]
  5. H. Sasada, K. Yamada, “The Calibration Lines of HCN in the 1.5-μm Region,” Appl. Opt. 29, 3535–3547 (1990), 10Aug.?
    [CrossRef] [PubMed]
  6. D. T. Cassidy, L. J. Bonnell, “Trace Gas Detection with Short-External-Cavity InGaAsP Diode Laser Transmitter Modules Operating at 1.58 μm,” Appl. Opt. 27, 2688–2693 (1988).
    [CrossRef] [PubMed]
  7. L. J. Bonnell, D. T. Cassidy, “Alignment Tolerances of Short-External-Cavity InGaAsP Diode Lasers For Use as Tunable Single-Mode Sources,” Appl. Opt. 28, 4622–4628 (1989).
    [CrossRef] [PubMed]
  8. D. M. Bruce, D. T. Cassidy, “Detection of Oxygen Using Short External Cavity GaAs Semiconductor Diode Lasers,” Appl. Opt. 29, 1327–1332 (1990).
    [CrossRef] [PubMed]
  9. J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
    [CrossRef] [PubMed]
  10. D. T. Cassidy, J. Reid, “Atmospheric Pressure Monitoring of Trace Gases Using Tunable Diode Lasers,” Appl. Opt. 21, 1185–1190 (1982).
    [CrossRef] [PubMed]
  11. J. Reid, D. Labrie, “Second-Harmonic Detection with Tunable Diode Lasers—Comparison of Experiment and Theory,” Appl. Phys. B 26, 203–210 (1981).
    [CrossRef]
  12. P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
    [CrossRef]
  13. P. Werle, F. Slemr, M. Gehrtz, C. Brauchle, “Wideband Noise Characteristics of a Lead-Salt Diode Laser: Possibility of Quantum Noise Limited TDLAS Performance,” Appl. Opt. 28, 1638–1642 (1989).
    [CrossRef] [PubMed]
  14. P. Werle, F. Slemr, M. Gehrtz, C. Brauchle, “Quantum-Limited FM-Spectroscopy with a Lead-Salt Diode Laser,” Appl. Phys. B 49, 99–108 (1989).
    [CrossRef]
  15. A. C. Stanton, J. A. Silver, “Measurements in the HCl 3–0 Band Using a Near IR InGaAsP Diode Laser,” Appl. Opt. 27, 5009–5015 (1988).
    [CrossRef] [PubMed]
  16. L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
    [CrossRef]
  17. N. C. Wong, J. L. Hall, “High-Resolution Measurement of Water-Vapor Overtone Absorption in the Visible by Frequency-Modulation Spectroscopy,” J. Opt. Soc. Am. B 6, 2300–2308 (1989).
    [CrossRef]
  18. C. B. Carlisle, D. E. Cooper, “Tunable-Diode-Laser Frequency Modulation Spectroscopy Using Balanced Homodyne Detection,” Opt. Lett. 14, 1306–1308 (1989).
    [CrossRef] [PubMed]
  19. L. S. Rothman et al., “The HITRAN Database: 1986 Edition,” Appl. Opt. 26, 4058–4097 (1987).
    [CrossRef] [PubMed]
  20. D. T. Cassidy, J. Reid, “Harmonic Detection with Tunable Diode Lasers—Two-Tone Modulation,” Appl. Phys. B 29, 279–285 (1982).
    [CrossRef]
  21. D. T. Cassidy, “Influence on the Steady-State Oscillation Spectrum of a Diode Laser for Light Interacting Coherently and Incoherently with the Field Established in the Laser Cavity,” Appl. Opt. 23, 2070–2077 (1984).
    [CrossRef] [PubMed]
  22. Harmonic detection can be performed if, instead of the laser wavelength, some property is modulated that influences the wavelength of absorption of a particular molecular species. Stark modulation of neutral molecules or velocity modulation of molecular ions are examples of such techniques. If the laser wavelength is not modulated, the weak fringes caused by accidental etalons (of finesse ≈ 10−4) in the optical path should not be observed. In such cases, the laser beam noise will limit the sensitivity of the TDLAS.
  23. The modulation required for atmospheric pressure detection will sweep over a greater number of fringes than the modulation required for low pressure detection. The maximum fringe signal should reduce as the modulation depth is increased. However, the difference in the modulation noise between detection of atmospheric pressure absorptions with AlGaAs lasers and detection of low pressure absorptions with InGaAsP lasers is greater than predicted theoretically. See Ref. 20.
  24. H. Sasada, Keio U., Japan; private communication.

1990 (2)

1989 (6)

1988 (4)

A. C. Stanton, J. A. Silver, “Measurements in the HCl 3–0 Band Using a Near IR InGaAsP Diode Laser,” Appl. Opt. 27, 5009–5015 (1988).
[CrossRef] [PubMed]

D. T. Cassidy, L. J. Bonnell, “Trace Gas Detection with Short-External-Cavity InGaAsP Diode Laser Transmitter Modules Operating at 1.58 μm,” Appl. Opt. 27, 2688–2693 (1988).
[CrossRef] [PubMed]

D. T. Cassidy, “Trace Gas Detection Using 1.3-μm InGaAsP Diode Laser Transmitter Modules,” Appl. Opt. 27, 610–614 (1988).
[CrossRef] [PubMed]

H. Sasada, “1.5-μm DFB Semiconductor Laser Spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
[CrossRef]

1987 (1)

1984 (3)

1983 (1)

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

1982 (2)

D. T. Cassidy, J. Reid, “Harmonic Detection with Tunable Diode Lasers—Two-Tone Modulation,” Appl. Phys. B 29, 279–285 (1982).
[CrossRef]

D. T. Cassidy, J. Reid, “Atmospheric Pressure Monitoring of Trace Gases Using Tunable Diode Lasers,” Appl. Opt. 21, 1185–1190 (1982).
[CrossRef] [PubMed]

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]

1978 (1)

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

Ballik, E. A.

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

Bjorklund, G. C.

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

Bonnell, L. J.

L. J. Bonnell, D. T. Cassidy, “Alignment Tolerances of Short-External-Cavity InGaAsP Diode Lasers For Use as Tunable Single-Mode Sources,” Appl. Opt. 28, 4622–4628 (1989).
[CrossRef] [PubMed]

D. T. Cassidy, L. J. Bonnell, “Trace Gas Detection with Short-External-Cavity InGaAsP Diode Laser Transmitter Modules Operating at 1.58 μm,” Appl. Opt. 27, 2688–2693 (1988).
[CrossRef] [PubMed]

Brauchle, C.

Bruce, D. M.

Carlisle, C. B.

Cassidy, D. T.

Chu, F.

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

Cooper, D. E.

Gallagher, T. F.

L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
[CrossRef]

Garside, B. K.

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

Gehrtz, M.

Hall, J. L.

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]

Pokrowsky, P.

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

Reid, J.

D. T. Cassidy, J. Reid, “Atmospheric Pressure Monitoring of Trace Gases Using Tunable Diode Lasers,” Appl. Opt. 21, 1185–1190 (1982).
[CrossRef] [PubMed]

D. T. Cassidy, J. Reid, “Harmonic Detection with Tunable Diode Lasers—Two-Tone Modulation,” Appl. Phys. B 29, 279–285 (1982).
[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]

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

Riris, H.

L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
[CrossRef]

Rothman, L. S.

Saito, S.

T. Yanagawa, S. Saito, Y. Yamamoto, “Frequency Stabilization of a 1.5-μm InGaAsP DFB Laser to NH3 Absorption Lines,” Appl. Phys. Lett. 45, 826–828 (1984).
[CrossRef]

Sasada, H.

Shewchun, J.

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

Silver, J. A.

Slemr, F.

Stanton, A. C.

Tate, D. A.

L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
[CrossRef]

Wang, L.-G.

L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
[CrossRef]

Werle, P.

Wong, N. C.

Yamada, K.

Yamamoto, Y.

T. Yanagawa, S. Saito, Y. Yamamoto, “Frequency Stabilization of a 1.5-μm InGaAsP DFB Laser to NH3 Absorption Lines,” Appl. Phys. Lett. 45, 826–828 (1984).
[CrossRef]

Yanagawa, T.

T. Yanagawa, S. Saito, Y. Yamamoto, “Frequency Stabilization of a 1.5-μm InGaAsP DFB Laser to NH3 Absorption Lines,” Appl. Phys. Lett. 45, 826–828 (1984).
[CrossRef]

Zapka, W.

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

Appl. Opt. (2)

J. Reid, J. Shewchun, B. K. Garside, E. A. Ballik, “High Sensitivity Pollution Detection Employing Tunable Diode Lasers,” Appl. Opt. 17, 300–307 (1978).
[CrossRef] [PubMed]

D. T. Cassidy, L. J. Bonnell, “Trace Gas Detection with Short-External-Cavity InGaAsP Diode Laser Transmitter Modules Operating at 1.58 μm,” Appl. Opt. 27, 2688–2693 (1988).
[CrossRef] [PubMed]

Appl. Phys. B (1)

D. T. Cassidy, J. Reid, “Harmonic Detection with Tunable Diode Lasers—Two-Tone Modulation,” Appl. Phys. B 29, 279–285 (1982).
[CrossRef]

Appl. Opt. (9)

D. T. Cassidy, “Influence on the Steady-State Oscillation Spectrum of a Diode Laser for Light Interacting Coherently and Incoherently with the Field Established in the Laser Cavity,” Appl. Opt. 23, 2070–2077 (1984).
[CrossRef] [PubMed]

H. Sasada, K. Yamada, “The Calibration Lines of HCN in the 1.5-μm Region,” Appl. Opt. 29, 3535–3547 (1990), 10Aug.?
[CrossRef] [PubMed]

L. S. Rothman et al., “The HITRAN Database: 1986 Edition,” Appl. Opt. 26, 4058–4097 (1987).
[CrossRef] [PubMed]

L. J. Bonnell, D. T. Cassidy, “Alignment Tolerances of Short-External-Cavity InGaAsP Diode Lasers For Use as Tunable Single-Mode Sources,” Appl. Opt. 28, 4622–4628 (1989).
[CrossRef] [PubMed]

D. M. Bruce, D. T. Cassidy, “Detection of Oxygen Using Short External Cavity GaAs Semiconductor Diode Lasers,” Appl. Opt. 29, 1327–1332 (1990).
[CrossRef] [PubMed]

P. Werle, F. Slemr, M. Gehrtz, C. Brauchle, “Wideband Noise Characteristics of a Lead-Salt Diode Laser: Possibility of Quantum Noise Limited TDLAS Performance,” Appl. Opt. 28, 1638–1642 (1989).
[CrossRef] [PubMed]

A. C. Stanton, J. A. Silver, “Measurements in the HCl 3–0 Band Using a Near IR InGaAsP Diode Laser,” Appl. Opt. 27, 5009–5015 (1988).
[CrossRef] [PubMed]

D. T. Cassidy, J. Reid, “Atmospheric Pressure Monitoring of Trace Gases Using Tunable Diode Lasers,” Appl. Opt. 21, 1185–1190 (1982).
[CrossRef] [PubMed]

D. T. Cassidy, “Trace Gas Detection Using 1.3-μm InGaAsP Diode Laser Transmitter Modules,” Appl. Opt. 27, 610–614 (1988).
[CrossRef] [PubMed]

Appl. Phys. B (1)

P. Werle, F. Slemr, M. Gehrtz, C. Brauchle, “Quantum-Limited FM-Spectroscopy with a Lead-Salt Diode Laser,” Appl. Phys. B 49, 99–108 (1989).
[CrossRef]

Appl. Phys. Lett. (1)

T. Yanagawa, S. Saito, Y. Yamamoto, “Frequency Stabilization of a 1.5-μm InGaAsP DFB Laser to NH3 Absorption Lines,” Appl. Phys. Lett. 45, 826–828 (1984).
[CrossRef]

Appl. Phys. B (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]

J. Chem. Phys. (1)

H. Sasada, “1.5-μm DFB Semiconductor Laser Spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
[CrossRef]

J. Opt. Soc. Am. B (1)

L.-G. Wang, D. A. Tate, H. Riris, T. F. Gallagher, “High-Sensitivity Frequency-Modulation Spectroscopy with a GaAlAs Diode Laser,” J. Opt. Soc. Am. B 6, 871–876 (1989).
[CrossRef]

J. Opt. Soc. Am. B (1)

Opt. Commun. (1)

P. Pokrowsky, W. Zapka, F. Chu, G. C. Bjorklund, “High-Frequency Wavelength Modulation Spectroscopy with Diode Lasers,” Opt. Commun. 44, 175–179 (1983).
[CrossRef]

Opt. Lett. (2)

Other (3)

Harmonic detection can be performed if, instead of the laser wavelength, some property is modulated that influences the wavelength of absorption of a particular molecular species. Stark modulation of neutral molecules or velocity modulation of molecular ions are examples of such techniques. If the laser wavelength is not modulated, the weak fringes caused by accidental etalons (of finesse ≈ 10−4) in the optical path should not be observed. In such cases, the laser beam noise will limit the sensitivity of the TDLAS.

The modulation required for atmospheric pressure detection will sweep over a greater number of fringes than the modulation required for low pressure detection. The maximum fringe signal should reduce as the modulation depth is increased. However, the difference in the modulation noise between detection of atmospheric pressure absorptions with AlGaAs lasers and detection of low pressure absorptions with InGaAsP lasers is greater than predicted theoretically. See Ref. 20.

H. Sasada, Keio U., Japan; private communication.

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Figures (6)

Fig. 1
Fig. 1

The signal indicated by the arrow is caused by a weak side mode passing through an 16O-16O absorption profile; the other signal is caused by the desired laser mode passing through an 16O-18O absorption profile. Since the ratio of the main laser mode to side mode is approximately the same as the ratio of 16O-16O to 16O-18O (i.e., ≈ 500:1), the signals are of roughly the same magnitude. This scan was done with an SXC AlGaAs laser at a modulation frequency of 10 kHz and detection bandwidth of 5.5 Hz and shows a modulation noise of ~5 × 10−6.

Fig. 2
Fig. 2

Three adjacent AlGaAs laser modes were selected with the SXC and a scan was made in each mode over the identical range of laser injection current. The main mode in one scan becomes a suppressed side mode in another scan. However, the side mode still has sufficient power to cause a signal at the exactly the same laser current as it passes through the same strong absorption profile as it did when it was the main mode. The resulting contamination of the spectra is clear.

Fig. 3
Fig. 3

Scans through the same spectral region. For one scan the SMSR was adjusted to alter the fraction of energy in the side modes and yet have a negligible effect on the energy in the main mode. This causes the absorption signal due to the side mode passing through a strong line to change relative to the absorption due to the main mode.

Fig. 4
Fig. 4

(a) Typical second-harmonic absorption signal obtained with a 1.3-μm InGaAsP laser with a SXC. (b)–(d) Scans of beam noise (no laser modulation) in three different laser modes selected with the SXC, normalized to the power in each mode. (e) Detector noise. All scans are with a detection frequency of 20 kHz with a 1.25-Hz ENBW.

Fig. 5
Fig. 5

Profiles of H2O absorption obtained using an SXC InGaAsP laser and 2f detection with an optimum depth of modulation. The absorption in the upper trace is atmospheric-pressure broadened, while the lower trace shows the same absorption at a total gas pressure of 100 Torr. The depth of laser current modulation required for optimum second-harmonic detection is directly proportional to the linewidth of the absorption. The 2f background obvious in the 760-Torr scan is caused the increased depth of current modulation that sweeps over a greater range of the slightly nonlinear LI curve of the laser.

Fig. 6
Fig. 6

Plot of 2f signals as a function of optical frequency for operation of the LAS with: (a) SXC AlGaAs diode laser; (b) SXC InGaAsP diode laser; and (c) a DFB laser.

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