Abstract

We report the laboratory demonstration of two-tone frequency-modulation spectroscopy with a continuous-wave (cw) CO2 laser. Using a resonant-cavity electro-optic phase modulator operating at 1 GHz, we obtained sensitivities to absorptions of 2 × 10−5 in a 1-Hz bandwidth from an étalon resonance and from calibrated mixtures of NH3. This sensitivity was within a factor of 3 of the quantum noise limit for our apparatus and was limited by baseline drift and fluctuations due to residual amplitude modulation and optical fringes.

© 1990 Optical Society of America

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References

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  1. G. C. Bjorklund, “Frequency modulation spectroscopy,” Opt. Lett. 5, 15 (1980).
    [CrossRef]
  2. W. Lenth, “High frequency heterodyne spectroscopy with current modulated diode lasers,” IEEE J. Quantum Electron. QE-20, 1045 (1984).
    [CrossRef]
  3. M. Gehrtz, W. Lenth, A. T. Young, H. S. Johnston, “High-frequency modulation spectroscopy with a lead-salt diode laser,” Opt. Lett. 11, 132 (1986).
    [CrossRef]
  4. D. E. Cooper, J. P. Watjen, “Two-tone optical heterodyne spectroscopy with a tunable lead-salt diode laser,” Opt. Lett. 11, 606 (1986).
    [CrossRef] [PubMed]
  5. L. Wang, H. Riris, C. B. Carlisle, T. F. Gallagher, “Comparison of approaches to modulation spectroscopy with GaAlAs semiconductor lasers: application to water vapor,” Appl. Opt. 27, 2071 (1988).
    [CrossRef] [PubMed]
  6. J. A. Silver, A. C. Stanton, “Two-tone optical heterodyne spectroscopy using buried double heterostructure lead-salt diode lasers,” Appl. Opt. 27, 4438 (1988).
    [CrossRef] [PubMed]
  7. D. E. Cooper, T. F. Gallagher, “Frequency modulation spectroscopy with a CO2 laser: results and implications for ultrasensitive point monitoring of the atmosphere,” Appl. Opt. 24, 710 (1985).
    [CrossRef]
  8. G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
    [CrossRef]
  9. G. R. Janik, C. B. Carlisle, T. F. Gallagher, “Two-tone frequency modulation spectroscopy,” J. Opt. Soc. Am. B 3, 1074 (1986).
    [CrossRef]
  10. 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 (1987).
    [CrossRef]
  11. D. E. Cooper, R. E. Warren, “Frequency modulation spectroscopy with lead-salt diode lasers: a comparison of single-tone and two-tone techniques,” Appl. Opt. 26, 3726 (1987).
    [CrossRef] [PubMed]
  12. E. A. Whittaker, M. Gehrtz, G. C. Bjorklund, “Residual amplitude modulation in laser electro-optic phase modulation,” J. Opt. Soc. Am. B 2, 1320 (1985).
    [CrossRef]
  13. D. E. Cooper, “Frequency modulation spectroscopy with infrared lasers,” in Digest of Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C.1986), paper FE4.
  14. M. Gehrtz, G. C. Bjorklund, E. A. Whittaker, “Quantum-limited frequency modulation spectroscopy,” J. Opt. Soc. Am. B 2, 1510 (1985).
    [CrossRef]
  15. M. Gehrtz, W. Length, IBM Tech. Discl. Bull. 29, 1237 (1986).
  16. C. B. Carlisle, D. E. Cooper, “Tunable diode laser FM spectroscopy using balanced homodyne detection,” submitted to Opt. Lett.
  17. E. R. Murray, “Remote measurement of gases using discretely tunable infrared lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 95, 96 (1976).
  18. T. F. Gallagher, N. H. Tran, J. P. Watjen, “Principles of a resonant cavity optical modulator,” Appl. Opt. 25, 510 (1986).
    [CrossRef] [PubMed]
  19. P. K. Cheo, “Frequency synthesized and continuously tunable IR laser sources in 9–11 μ m,” IEEE J. Quantum Electron. QE-20, 700 (1984).
    [CrossRef]

1988 (2)

1987 (2)

1986 (5)

1985 (3)

1984 (2)

W. Lenth, “High frequency heterodyne spectroscopy with current modulated diode lasers,” IEEE J. Quantum Electron. QE-20, 1045 (1984).
[CrossRef]

P. K. Cheo, “Frequency synthesized and continuously tunable IR laser sources in 9–11 μ m,” IEEE J. Quantum Electron. QE-20, 700 (1984).
[CrossRef]

1983 (1)

G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
[CrossRef]

1980 (1)

1976 (1)

E. R. Murray, “Remote measurement of gases using discretely tunable infrared lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 95, 96 (1976).

Bjorklund, G. C.

Carlisle, C. B.

L. Wang, H. Riris, C. B. Carlisle, T. F. Gallagher, “Comparison of approaches to modulation spectroscopy with GaAlAs semiconductor lasers: application to water vapor,” Appl. Opt. 27, 2071 (1988).
[CrossRef] [PubMed]

G. R. Janik, C. B. Carlisle, T. F. Gallagher, “Two-tone frequency modulation spectroscopy,” J. Opt. Soc. Am. B 3, 1074 (1986).
[CrossRef]

C. B. Carlisle, D. E. Cooper, “Tunable diode laser FM spectroscopy using balanced homodyne detection,” submitted to Opt. Lett.

Cheo, P. K.

P. K. Cheo, “Frequency synthesized and continuously tunable IR laser sources in 9–11 μ m,” IEEE J. Quantum Electron. QE-20, 700 (1984).
[CrossRef]

Cooper, D. E.

Gallagher, T. F.

Gehrtz, M.

Janik, G. R.

G. R. Janik, C. B. Carlisle, T. F. Gallagher, “Two-tone frequency modulation spectroscopy,” J. Opt. Soc. Am. B 3, 1074 (1986).
[CrossRef]

Johnston, H. S.

Length, W.

M. Gehrtz, W. Length, IBM Tech. Discl. Bull. 29, 1237 (1986).

Lenth, W.

M. Gehrtz, W. Lenth, A. T. Young, H. S. Johnston, “High-frequency modulation spectroscopy with a lead-salt diode laser,” Opt. Lett. 11, 132 (1986).
[CrossRef]

W. Lenth, “High frequency heterodyne spectroscopy with current modulated diode lasers,” IEEE J. Quantum Electron. QE-20, 1045 (1984).
[CrossRef]

G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
[CrossRef]

Levinson, M. D.

G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
[CrossRef]

Murray, E. R.

E. R. Murray, “Remote measurement of gases using discretely tunable infrared lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 95, 96 (1976).

Ortiz, C.

G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
[CrossRef]

Riris, H.

Silver, J. A.

Stanton, A. C.

Tran, N. H.

Wang, L.

Warren, R. E.

Watjen, J. P.

Whittaker, E. A.

Young, A. T.

Appl. Opt. (5)

Appl. Phys. B (1)

G. C. Bjorklund, M. D. Levinson, W. Lenth, C. Ortiz, “Frequency modulation spectroscopy: theory of lineshapes and signal-to-noise analysis,” Appl. Phys. B 32, 145 (1983).
[CrossRef]

IBM Tech. Discl. Bull. (1)

M. Gehrtz, W. Length, IBM Tech. Discl. Bull. 29, 1237 (1986).

IEEE J. Quantum Electron. (2)

P. K. Cheo, “Frequency synthesized and continuously tunable IR laser sources in 9–11 μ m,” IEEE J. Quantum Electron. QE-20, 700 (1984).
[CrossRef]

W. Lenth, “High frequency heterodyne spectroscopy with current modulated diode lasers,” IEEE J. Quantum Electron. QE-20, 1045 (1984).
[CrossRef]

J. Opt. Soc. Am. B (4)

Opt. Lett. (3)

Proc. Soc. Photo-Opt. Instrum. Eng. (1)

E. R. Murray, “Remote measurement of gases using discretely tunable infrared lasers,” Proc. Soc. Photo-Opt. Instrum. Eng. 95, 96 (1976).

Other (2)

D. E. Cooper, “Frequency modulation spectroscopy with infrared lasers,” in Digest of Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C.1986), paper FE4.

C. B. Carlisle, D. E. Cooper, “Tunable diode laser FM spectroscopy using balanced homodyne detection,” submitted to Opt. Lett.

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Figures (8)

Fig. 1
Fig. 1

Schematic diagram of the CO2 laser two-tone frequency-modulation spectrometer. The associated rf detection electronics are shown in the inset.

Fig. 2
Fig. 2

Schematic illustration of the optical electric field components of the CO2 laser 10R(8) emission line after two-tone modulation at 1.0162 and 1.0202 GHz.

Fig. 3
Fig. 3

Two-tone frequency-modulation signal (TTFMS) from an étalon resonance equivalent to an absorption of 0.6.

Fig. 4
Fig. 4

Plot of sensitivity as a function of bandwidth for the two-tone heterodyne signal from an étalon resonance.

Fig. 5
Fig. 5

Oscilloscope traces of a two-tone signal from a tunable étalon resonance with a NH3 absorption cell inserted in the optical path. The corresponding NH3 pressures are (a) 0 μm, (b) 100 μm, (c) 180 μm, and (d) 600 μm.

Fig. 6
Fig. 6

Plot of two-tone signal as a function of White cell pressure.

Fig. 7
Fig. 7

Strip chart recording of absorptions of 1.5 × 10−2 and 7.6 × 10−3 made using two-tone FMS with phase-sensitive detection.

Fig. 8
Fig. 8

Strip chart recordings of the two-tone signal from NH3 in a 22-cm path-length cell with the cell pressure reduced in discrete steps. The step from 0.857 to 0 Torr is shown on an expanded scale in the inset.

Tables (2)

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Table 1 Experimental Parameters

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Table 2 Molecules Detectable with a CO2 Laser Two-Tone FM Spectrometer

Equations (2)

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α min = 4.2 ( 1 CNR 0 + M 4 σ 2 P 0 2 ) 1 / 2 ,
CNR 0 = ( η e h ν ) 2 2 P 0 2 2 e Δ f [ ( η e h ν ) P 0 ( 1 + M 2 2 ) 2 + 2 k T N e R L ] .

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