Abstract

An electronic noise-cancellation scheme has been developed and tested for second-harmonic (2f) detection with short-external-cavity and distributed-feedback InGaAsP diode lasers and wavelength modulation. The 2f background signal and noise from, e.g., optical feedback, optical fringes, and power-supply pickup are effectively reduced by subtraction of a measure of the signal-beam photocurrent from a measure of the reference-beam photocurrent. The dynamic range required for the lock-in amplifier is also reduced because the signal owing to modulation of the laser output at the first harmonic is canceled. Reduction of the 2f background and dynamic range are important for atmospheric-pressure detection where a large wavelength modulation is necessary. The detector noise was minimized by the use of zero-biased detectors in the subtraction circuit. A beam-noise level (defined as 2× the rms value) equivalent to a line-center absorption of 1.6 × 10−6 was achieved with an equivalent-noise bandwidth of 1.25 Hz for 2f detection at 10 kHz. The electronic circuit is easy to construct and low cost.

© 1995 Optical Society of America

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References

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  1. R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).
  2. C. E. Wieman, L. Hollberg, “Using diode lasers for atomic physics,” Rev. Sci. Instrum. 62, 1–20 (1991).
    [Crossref]
  3. K. Uehara, H. Tai, “Remote detection of methane with a 1.66-μm diode laser,” Appl. Opt. 31, 809–814 (1992).
    [Crossref] [PubMed]
  4. D. T. Cassidy, “Trace gas detection using 1.3-μm InGaAsP diode laser transmitter modules,” Appl. Opt. 27, 610–614 (1988).
    [Crossref] [PubMed]
  5. M. P. Arroyo, R. K. Hanson, “Absorption measurements of water-vapor concentration, temperature, and line-shape parameters using a tunable InGaAsP diode laser,” Appl. Opt. 32, 6104–6116 (1993).
    [Crossref] [PubMed]
  6. W. Lenth, M. Gehrtz, “Sensitive detection of NO2 using high-frequency heterodyne spectroscopy with a GaAlAs diode laser,” Appl. Phys. Lett. 47, 1263–1265 (1985).
    [Crossref]
  7. H. Sasada, “1.5-μm DFB semiconductor laser spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
    [Crossref]
  8. D. T. Cassidy, D. M. Bruce, B. F. Ventrudo, “Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers,” Rev. Sci. Instrum. 62, 2385–2388 (1991).
    [Crossref]
  9. G. C. Bjorkland, “Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions,” Opt. Lett. 5, 15–17 (1980).
    [Crossref]
  10. J. Reid, D. Labrie, “Second-harmonic detection with tunable diode lasers—comparison of experiment and theory,” Appl. Phys. B 26, 203–210 (1981).
    [Crossref]
  11. D. E. Jennings, “Absolute line strengths in ν4, 12CH4: a dual-beam diode laser spectrometer with sweep integration,” Appl. Opt. 19, 2695–2700 (1980).
    [Crossref] [PubMed]
  12. D. T. Cassidy, J. Reid, “Harmonic detection with tunable diode lasers: two-tone modulation,” Appl. Phys. B 29, 279–285 (1982).
    [Crossref]
  13. J. A. Silver, “Frequency-modulation spectroscopy for trace species detection: theory and comparison among experimental methods,” Appl. Opt. 31, 707–717 (1992).
    [Crossref] [PubMed]
  14. D. E. Cooper, R. E. Warren, “Two-tone heterodyne spectroscopy with diode lasers: theory of line shapes and experimental results,” J. Opt. Soc. Am. B 4, 470–480 (1987).
    [Crossref]
  15. C. B. Carlisle, D. E. Cooper, H. Prier, “Quantum noise-limited FM spectroscopy with a lead-salt diode laser,” Appl. Opt. 28, 2567–2576 (1989).
    [Crossref] [PubMed]
  16. P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
    [Crossref]
  17. D. S. Bomse, A. C. Stanton, J. A. Silver, “Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser,” Appl. Opt. 31, 718–731 (1992).
    [Crossref] [PubMed]
  18. T. J. Johnson, F. G. Wienhold, J. P. Burrows, G. W. Harris, “Frequency modulation spectroscopy at 1.3 μm using InGaAsP lasers: a prototype field instrument for atmospheric chemistry research,” Appl. Opt. 30, 407–413 (1991).
    [Crossref] [PubMed]
  19. 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]
  20. J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
    [Crossref]
  21. C. R. Webster, R. D. May, C. A. Trimble, R. G. Chave, J. Kendall, “Aircraft (ER-2) laser infrared absorption spectrometer (ALIAS) for in-situ stratospheric measurements of HCl, N2O, CH4, NO2, and HNO3,” Appl. Opt. 33, 454–472 (1994).
    [Crossref] [PubMed]
  22. D. T. Cassidy, J. Reid, “Atmospheric pressure monitoring of trace gases using tunable diode laser,” Appl. Opt. 21, 1185–1190 (1982).
    [Crossref] [PubMed]
  23. B. F. Ventrudo, D. T. Cassidy, “Operating characteristics of a tunable diode laser absorption spectrometer using short-external-cavity and DFB laser diodes,” Appl. Opt. 29, 5007–5013 (1990).
    [Crossref] [PubMed]
  24. 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]
  25. N. Goldstein, S. M. Adler-Golden, “Long-atmospheric-path measurements of near-visible absorption lines of O2 isotopes and H2O with a prototype AlGaAs laser transceiver system,” Appl. Opt. 32, 5849–5855 (1993).
    [Crossref] [PubMed]
  26. M. Gehrtz, G. C. Bjorklund, “Quantum-limited laser frequency-modulation spectroscopy,” J. Opt. Soc. Am. B 2, 1510–1525 (1985).
    [Crossref]
  27. C. B. Carlisle, D. E. Cooper, “Tunable diode laser frequency modulation spectroscopy through an optical fibre: high-sensitivity detection of water vapor,” Appl. Phys. Lett. 56, 805–807 (1990).
    [Crossref]
  28. K. L. Haller, P. C. D. Hobbs, “Double beam absorption spectroscopy: shot noise-limited performance at baseband with a novel electronic noise canceller,” in Optical Methods for Ultrasensitive Detection and Analysis: Techniques and Applications, B. L. Feary, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 1435, 298–309 (1991).
  29. P. C. D. Hobbs, in Laser Noise, R. Roy, ed., “Shot noise limited optical measurement at baseband with noisy lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 1376, 216–221 (1990).
  30. H. W. Ott, Noise Reduction Techniques in Electronic Systems (Wiley, New York, 1988).
  31. M. L. Meade, Lock-In Amplifiers: Principles and Applications (Peregrinus, London, 1982).
  32. R. T. Menzies, “Laser heterodyne detection techniques,” in Laser Monitoring of the Atmosphere, E. D. Hinkley, ed. (Springer, New York, 1976).
    [Crossref]
  33. C. R. Webster, “Brewster plate spoiler: a novel method for reducing the amplitude of interference fringes that limit tunable-laser absorption sensitivities,” J. Opt. Soc. Am. B 2, 1464–1470 (1985).
    [Crossref]
  34. J. A. Silver, A. C. Stanton, “Optical interference fringe reduction in laser absorption experiments,” Appl. Opt. 27, 1994–1996 (1988).
    [Crossref]

1994 (1)

1993 (3)

1992 (3)

1991 (3)

T. J. Johnson, F. G. Wienhold, J. P. Burrows, G. W. Harris, “Frequency modulation spectroscopy at 1.3 μm using InGaAsP lasers: a prototype field instrument for atmospheric chemistry research,” Appl. Opt. 30, 407–413 (1991).
[Crossref] [PubMed]

C. E. Wieman, L. Hollberg, “Using diode lasers for atomic physics,” Rev. Sci. Instrum. 62, 1–20 (1991).
[Crossref]

D. T. Cassidy, D. M. Bruce, B. F. Ventrudo, “Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers,” Rev. Sci. Instrum. 62, 2385–2388 (1991).
[Crossref]

1990 (3)

1989 (3)

1988 (3)

H. Sasada, “1.5-μm DFB semiconductor laser spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
[Crossref]

D. T. Cassidy, “Trace gas detection using 1.3-μm InGaAsP diode laser transmitter modules,” Appl. Opt. 27, 610–614 (1988).
[Crossref] [PubMed]

J. A. Silver, A. C. Stanton, “Optical interference fringe reduction in laser absorption experiments,” Appl. Opt. 27, 1994–1996 (1988).
[Crossref]

1987 (1)

1985 (4)

W. Lenth, M. Gehrtz, “Sensitive detection of NO2 using high-frequency heterodyne spectroscopy with a GaAlAs diode laser,” Appl. Phys. Lett. 47, 1263–1265 (1985).
[Crossref]

C. R. Webster, “Brewster plate spoiler: a novel method for reducing the amplitude of interference fringes that limit tunable-laser absorption sensitivities,” J. Opt. Soc. Am. B 2, 1464–1470 (1985).
[Crossref]

M. Gehrtz, G. C. Bjorklund, “Quantum-limited laser frequency-modulation spectroscopy,” J. Opt. Soc. Am. B 2, 1510–1525 (1985).
[Crossref]

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

1982 (2)

D. T. Cassidy, J. Reid, “Atmospheric pressure monitoring of trace gases using tunable diode laser,” 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]

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]

1980 (2)

Adler-Golden, S. M.

Arroyo, M. P.

Bjorkland, G. C.

Bjorklund, G. C.

Bomse, D. S.

Bräuchle, C.

P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
[Crossref]

Bruce, D. M.

D. T. Cassidy, D. M. Bruce, B. F. Ventrudo, “Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers,” Rev. Sci. Instrum. 62, 2385–2388 (1991).
[Crossref]

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]

Burrows, J. P.

Carlisle, C. B.

C. B. Carlisle, D. E. Cooper, “Tunable diode laser frequency modulation spectroscopy through an optical fibre: high-sensitivity detection of water vapor,” Appl. Phys. Lett. 56, 805–807 (1990).
[Crossref]

C. B. Carlisle, D. E. Cooper, H. Prier, “Quantum noise-limited FM spectroscopy with a lead-salt diode laser,” Appl. Opt. 28, 2567–2576 (1989).
[Crossref] [PubMed]

Cassidy, D. T.

Chave, R. G.

Cooper, D. E.

Fox, R. W.

R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).

Gallagher, T. F.

Gehrtz, M.

P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
[Crossref]

W. Lenth, M. Gehrtz, “Sensitive detection of NO2 using high-frequency heterodyne spectroscopy with a GaAlAs diode laser,” Appl. Phys. Lett. 47, 1263–1265 (1985).
[Crossref]

M. Gehrtz, G. C. Bjorklund, “Quantum-limited laser frequency-modulation spectroscopy,” J. Opt. Soc. Am. B 2, 1510–1525 (1985).
[Crossref]

Goldstein, N.

Grant, W. B.

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

Haller, K. L.

K. L. Haller, P. C. D. Hobbs, “Double beam absorption spectroscopy: shot noise-limited performance at baseband with a novel electronic noise canceller,” in Optical Methods for Ultrasensitive Detection and Analysis: Techniques and Applications, B. L. Feary, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 1435, 298–309 (1991).

Hanson, R. K.

Harris, G. W.

Hobbs, P. C. D.

K. L. Haller, P. C. D. Hobbs, “Double beam absorption spectroscopy: shot noise-limited performance at baseband with a novel electronic noise canceller,” in Optical Methods for Ultrasensitive Detection and Analysis: Techniques and Applications, B. L. Feary, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 1435, 298–309 (1991).

P. C. D. Hobbs, in Laser Noise, R. Roy, ed., “Shot noise limited optical measurement at baseband with noisy lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 1376, 216–221 (1990).

Hollberg, L.

R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).

C. E. Wieman, L. Hollberg, “Using diode lasers for atomic physics,” Rev. Sci. Instrum. 62, 1–20 (1991).
[Crossref]

Jennings, D. E.

Johnson, T. J.

Kendall, J.

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]

Lenth, W.

W. Lenth, M. Gehrtz, “Sensitive detection of NO2 using high-frequency heterodyne spectroscopy with a GaAlAs diode laser,” Appl. Phys. Lett. 47, 1263–1265 (1985).
[Crossref]

May, R. D.

Meade, M. L.

M. L. Meade, Lock-In Amplifiers: Principles and Applications (Peregrinus, London, 1982).

Menzies, R. T.

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

R. T. Menzies, “Laser heterodyne detection techniques,” in Laser Monitoring of the Atmosphere, E. D. Hinkley, ed. (Springer, New York, 1976).
[Crossref]

Ott, H. W.

H. W. Ott, Noise Reduction Techniques in Electronic Systems (Wiley, New York, 1988).

Prier, H.

Reid, J.

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

D. T. Cassidy, J. Reid, “Atmospheric pressure monitoring of trace gases using tunable diode laser,” 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]

Riris, H.

Sasada, H.

H. Sasada, “1.5-μm DFB semiconductor laser spectroscopy of HCN,” J. Chem. Phys. 88, 767–777 (1988).
[Crossref]

Silver, J. A.

Sinclair, R. L.

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

Slemr, F.

P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
[Crossref]

Stanton, A. C.

Tai, H.

Tate, D. A.

Trimble, C. A.

Turk, G. C.

R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).

Uehara, K.

Ventrudo, B. F.

D. T. Cassidy, D. M. Bruce, B. F. Ventrudo, “Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers,” Rev. Sci. Instrum. 62, 2385–2388 (1991).
[Crossref]

B. F. Ventrudo, D. T. Cassidy, “Operating characteristics of a tunable diode laser absorption spectrometer using short-external-cavity and DFB laser diodes,” Appl. Opt. 29, 5007–5013 (1990).
[Crossref] [PubMed]

Wang, L.-G.

Warren, R. E.

Webster, C. R.

Weimer, C. S.

R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).

Werle, P.

P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
[Crossref]

Wieman, C. E.

C. E. Wieman, L. Hollberg, “Using diode lasers for atomic physics,” Rev. Sci. Instrum. 62, 1–20 (1991).
[Crossref]

Wienhold, F. G.

Appl. Opt. (14)

K. Uehara, H. Tai, “Remote detection of methane with a 1.66-μm diode laser,” Appl. Opt. 31, 809–814 (1992).
[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]

M. P. Arroyo, R. K. Hanson, “Absorption measurements of water-vapor concentration, temperature, and line-shape parameters using a tunable InGaAsP diode laser,” Appl. Opt. 32, 6104–6116 (1993).
[Crossref] [PubMed]

D. E. Jennings, “Absolute line strengths in ν4, 12CH4: a dual-beam diode laser spectrometer with sweep integration,” Appl. Opt. 19, 2695–2700 (1980).
[Crossref] [PubMed]

J. A. Silver, “Frequency-modulation spectroscopy for trace species detection: theory and comparison among experimental methods,” Appl. Opt. 31, 707–717 (1992).
[Crossref] [PubMed]

D. S. Bomse, A. C. Stanton, J. A. Silver, “Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser,” Appl. Opt. 31, 718–731 (1992).
[Crossref] [PubMed]

T. J. Johnson, F. G. Wienhold, J. P. Burrows, G. W. Harris, “Frequency modulation spectroscopy at 1.3 μm using InGaAsP lasers: a prototype field instrument for atmospheric chemistry research,” Appl. Opt. 30, 407–413 (1991).
[Crossref] [PubMed]

C. R. Webster, R. D. May, C. A. Trimble, R. G. Chave, J. Kendall, “Aircraft (ER-2) laser infrared absorption spectrometer (ALIAS) for in-situ stratospheric measurements of HCl, N2O, CH4, NO2, and HNO3,” Appl. Opt. 33, 454–472 (1994).
[Crossref] [PubMed]

D. T. Cassidy, J. Reid, “Atmospheric pressure monitoring of trace gases using tunable diode laser,” Appl. Opt. 21, 1185–1190 (1982).
[Crossref] [PubMed]

B. F. Ventrudo, D. T. Cassidy, “Operating characteristics of a tunable diode laser absorption spectrometer using short-external-cavity and DFB laser diodes,” Appl. Opt. 29, 5007–5013 (1990).
[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]

N. Goldstein, S. M. Adler-Golden, “Long-atmospheric-path measurements of near-visible absorption lines of O2 isotopes and H2O with a prototype AlGaAs laser transceiver system,” Appl. Opt. 32, 5849–5855 (1993).
[Crossref] [PubMed]

C. B. Carlisle, D. E. Cooper, H. Prier, “Quantum noise-limited FM spectroscopy with a lead-salt diode laser,” Appl. Opt. 28, 2567–2576 (1989).
[Crossref] [PubMed]

J. A. Silver, A. C. Stanton, “Optical interference fringe reduction in laser absorption experiments,” Appl. Opt. 27, 1994–1996 (1988).
[Crossref]

Appl. Phys. B (3)

P. Werle, F. Slemr, M. Gehrtz, C. Bräuchle, “Quantum-limited FM-spectroscopy with a lead-salt diode laser,” Appl. Phys. B 49, 99–108 (1989).
[Crossref]

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]

Appl. Phys. Lett. (2)

W. Lenth, M. Gehrtz, “Sensitive detection of NO2 using high-frequency heterodyne spectroscopy with a GaAlAs diode laser,” Appl. Phys. Lett. 47, 1263–1265 (1985).
[Crossref]

C. B. Carlisle, D. E. Cooper, “Tunable diode laser frequency modulation spectroscopy through an optical fibre: high-sensitivity detection of water vapor,” Appl. Phys. Lett. 56, 805–807 (1990).
[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 (4)

Opt. Lett. (1)

Opt. Quantum Electron. (1)

J. Reid, R. L. Sinclair, W. B. Grant, R. T. Menzies, “High sensitivity detection of trace gases at atmospheric pressure using tunable diode lasers,” Opt. Quantum Electron. 17, 31–39 (1985).
[Crossref]

Rev. Sci. Instrum. (2)

C. E. Wieman, L. Hollberg, “Using diode lasers for atomic physics,” Rev. Sci. Instrum. 62, 1–20 (1991).
[Crossref]

D. T. Cassidy, D. M. Bruce, B. F. Ventrudo, “Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers,” Rev. Sci. Instrum. 62, 2385–2388 (1991).
[Crossref]

Spectrochim. Acta Rev. (1)

R. W. Fox, C. S. Weimer, L. Hollberg, G. C. Turk, “The diode laser as a spectroscopic tool,” Spectrochim. Acta Rev. 15, 291–299 (1993).

Other (5)

K. L. Haller, P. C. D. Hobbs, “Double beam absorption spectroscopy: shot noise-limited performance at baseband with a novel electronic noise canceller,” in Optical Methods for Ultrasensitive Detection and Analysis: Techniques and Applications, B. L. Feary, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 1435, 298–309 (1991).

P. C. D. Hobbs, in Laser Noise, R. Roy, ed., “Shot noise limited optical measurement at baseband with noisy lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 1376, 216–221 (1990).

H. W. Ott, Noise Reduction Techniques in Electronic Systems (Wiley, New York, 1988).

M. L. Meade, Lock-In Amplifiers: Principles and Applications (Peregrinus, London, 1982).

R. T. Menzies, “Laser heterodyne detection techniques,” in Laser Monitoring of the Atmosphere, E. D. Hinkley, ed. (Springer, New York, 1976).
[Crossref]

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Figures (6)

Fig. 1
Fig. 1

Schematic of the noise subtracter. Amplifier A3 controls the light level of the LED and thus the resistance of the photoresistor, Rp, by feedback of the DC level in the summing point, S. This ensures that the signal current and the scaled reference current are equal at S and thus that the common signals cancel with the DC level.

Fig. 2
Fig. 2

Schematic of the apparatus used for second-harmonic (2f) detection. The output from either the signal detector or the noise subtracter could be directed to the lock-in amplifier. This permits results with and without the noise subtracter to be compared. ADC, analog–digital converter; DAC, digital–analog converter.

Fig. 3
Fig. 3

Performance of the noise subtracter. Trace a is the noise spectral density from the signal detector. Trace b is from the noise subtracter. The noise level at 10 kHz is 0.2 μV/Hz1/2, 1.4 dB above the theoretical shot-noise value. 9 dB noise suppression is obtained for the laser excess-noise floor, and 30 dB suppression is obtained for the 15.8 kHz pickup. Trace c is from the signal detector when the beam is blocked.

Fig. 4
Fig. 4

Spectral baseline scan with and without noise cancellation. The scans were obtained for 10 Torr water vapor in 200 Torr air. 17-dB noise reduction was achieved.

Fig. 5
Fig. 5

Second-harmonic (2f) scan obtained for an atmospheric-pressure-broadened weak line. The upper trace shows the absorption signal riding on a 2f background caused by the nonlinear L–I curve of the laser. The background and noise are reduced by subtraction, as shown in the lower trace.

Fig. 6
Fig. 6

Sensitivity of 2f detection when the subtraction circuit is used. a, b, 2f scans of the water-vapor lines at a total pressure of 35 Torr. The three traces in the inset, top to bottom, are modulation noise, beam noise, and detector noise (beam blocked). Two times the rms value of the beam noise is equivalent to an absorbance of 1.6 × 10−6 and is limited by the shot noise after noise cancellation.

Equations (3)

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V o = K V s K + 1 ,
V nt = [ ( e nA 2 + i nA 2 R f 2 + 4 k T R f B ) ( K 2 + 1 ) / ( K + 1 ) 2 + ( 2 q i s B R f 2 ) K / ( K + 1 ) ] 1 / 2 ,
V o V nt = V s i ns R f ( K K + 1 ) 1 / 2 = ( i 2 q B K K + 1 ) 1 / 2 .

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