Abstract

Cavity ringdown spectroscopy is an efficient gas-sensing method, but improvement in measurement speed is required before this method can be applied to the analysis of fast phenomena. We present a new continuous-wave cavity ringdown design, involving fast tuning of the laser frequency and a rapidly swept optical cavity, to allow high-speed sensing with spectral resolution refinement. This approach, which provides a simple and versatile instrument, is investigated numerically and experimentally. By performing detection of a forbidden transition of molecular oxygen near 766 nm during a 2-ms single sweep of the laser frequency, we show that our system fulfils the requirements for probing rapid chemical processes.

© 2005 Optical Society of America

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References

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  1. G. Berden, R. Peeters, and G. Meijer, �??Cavity ring-down spectroscopy: experimental schemes and applications,�?? Int. Rev. Phys. Chem. 19, 565-607 (2000).
    [CrossRef]
  2. K. W. Busch and M. A. Busch, ed., �??Cavity-Ringdown Spectroscopy �?? An Ultratrace-Absorption Measurement Technique�?? (Oxford U. Press, Washington, D.C., 1999).
  3. A. O�??Keefe and D. A. G. Deacon, �??Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources,�?? Rev. Sci. Instrum. 59, 2544 (1988).
    [CrossRef]
  4. D. Romanini, A. A. Kachanov, N. Sadeghi, and F. Stoeckel, �??Cw cavity ring down spectroscopy,�?? Chem. Phys. Lett. 264, 316-322 (1997).
    [CrossRef]
  5. D. Romanini, A. A. Kachanov, and F. Stoeckel, �??Diode laser cavity ring down spectroscopy,�?? Chem. Phys. Lett. 270, 538-545 (1997).
    [CrossRef]
  6. D. Romanini, A. A. Kachanov, and F. Stoeckel, �??Cavity ringdown spectroscopy: broad band absolute absorption measurements,�?? Chem. Phys. Lett. 270, 546-550 (1997).
    [CrossRef]
  7. B. A. Paldus, C. C. Harb, T. G. Spence, B. Wilke, J. Xie, J. S. Harris, and R. N. Zare, �??Cavity-locked ring-down spectroscopy,�?? J. Appl. Phys. 83, 3991-3997 (1998).
    [CrossRef]
  8. K. J. Schulz and W. R. Simpson, �??Frequency-matched cavity ring-down spectroscopy,�?? Chem. Phys. Lett. 297, 523-529 (1998).
    [CrossRef]
  9. Y. He and B. J. Orr, �??Ringdown and cavity�??enhanced absorption spectroscopy using a continuous-wave tunable diode laser and a rapidly swept optical cavity,�?? Chem. Phys. Lett. 319, 131-137 (2000).
    [CrossRef]
  10. Y. He and B. J. Orr, �??Optical heterodyne signal generation and detection in cavity ringdown spectroscopy based on a rapidly swept cavity,�?? Chem. Phys. Lett. 335, 215-220 (2001).
    [CrossRef]
  11. Y. He and B. J. Orr, �??Rapid measurement of cavity ringdown absorption spectra with a swept-frequency laser,�?? Appl. Phys. B 79, 941-945 (2004).
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  14. J. Morville, D. Romanini, M. Chenevier, and A. A. Kachanov, �??Effects of laser phase noise on the injection of a high-finesse cavity,�?? Appl. Opt. 41, 6980-6990 (2002).
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  15. K. K. Lehmann and D. Romanini, �??The superposition principle and cavity ring-down spectroscopy,�?? J. Chem. Phys. 105, 10263-10277 (1996).
    [CrossRef]
  16. J. Y. Lee and J. W. Hahn, �??Theoretical investigation on the intracavity Doppler effect in continuous wave swept-cavity ringdown spectroscopy,�?? Appl. Phys. B 79, 371-378 (2004).
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Appl. Opt. (3)

Appl. Phys. B (3)

J. Y. Lee and J. W. Hahn, �??Theoretical investigation on the intracavity Doppler effect in continuous wave swept-cavity ringdown spectroscopy,�?? Appl. Phys. B 79, 371-378 (2004).
[CrossRef]

B. Bakowski, L. Corner, G. Hancock, R. Kotchie, R. Peverall, and G. A. D. Ritchie, �??Cavity-enhanced absorption spectroscopy with a rapidly swept diode laser,�?? Appl. Phys. B 75, 745-750 (2002).
[CrossRef]

Y. He and B. J. Orr, �??Rapid measurement of cavity ringdown absorption spectra with a swept-frequency laser,�?? Appl. Phys. B 79, 941-945 (2004).
[CrossRef]

Chem. Phys. Lett. (6)

D. Romanini, A. A. Kachanov, N. Sadeghi, and F. Stoeckel, �??Cw cavity ring down spectroscopy,�?? Chem. Phys. Lett. 264, 316-322 (1997).
[CrossRef]

D. Romanini, A. A. Kachanov, and F. Stoeckel, �??Diode laser cavity ring down spectroscopy,�?? Chem. Phys. Lett. 270, 538-545 (1997).
[CrossRef]

D. Romanini, A. A. Kachanov, and F. Stoeckel, �??Cavity ringdown spectroscopy: broad band absolute absorption measurements,�?? Chem. Phys. Lett. 270, 546-550 (1997).
[CrossRef]

K. J. Schulz and W. R. Simpson, �??Frequency-matched cavity ring-down spectroscopy,�?? Chem. Phys. Lett. 297, 523-529 (1998).
[CrossRef]

Y. He and B. J. Orr, �??Ringdown and cavity�??enhanced absorption spectroscopy using a continuous-wave tunable diode laser and a rapidly swept optical cavity,�?? Chem. Phys. Lett. 319, 131-137 (2000).
[CrossRef]

Y. He and B. J. Orr, �??Optical heterodyne signal generation and detection in cavity ringdown spectroscopy based on a rapidly swept cavity,�?? Chem. Phys. Lett. 335, 215-220 (2001).
[CrossRef]

Int. Rev. Phys. Chem. (1)

G. Berden, R. Peeters, and G. Meijer, �??Cavity ring-down spectroscopy: experimental schemes and applications,�?? Int. Rev. Phys. Chem. 19, 565-607 (2000).
[CrossRef]

J. Appl. Phys. (1)

B. A. Paldus, C. C. Harb, T. G. Spence, B. Wilke, J. Xie, J. S. Harris, and R. N. Zare, �??Cavity-locked ring-down spectroscopy,�?? J. Appl. Phys. 83, 3991-3997 (1998).
[CrossRef]

J. Chem. Phys. (1)

K. K. Lehmann and D. Romanini, �??The superposition principle and cavity ring-down spectroscopy,�?? J. Chem. Phys. 105, 10263-10277 (1996).
[CrossRef]

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

Rev. Sci. Instrum. (1)

A. O�??Keefe and D. A. G. Deacon, �??Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources,�?? Rev. Sci. Instrum. 59, 2544 (1988).
[CrossRef]

Other (1)

K. W. Busch and M. A. Busch, ed., �??Cavity-Ringdown Spectroscopy �?? An Ultratrace-Absorption Measurement Technique�?? (Oxford U. Press, Washington, D.C., 1999).

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Figures (8)

Fig. 1.
Fig. 1.

Schematic of a typical ringdown setup that produces an exponential decay of the transmitted light after termination of the laser coupling. An optional acousto- or electro-optic switch is generally used to interrupt injection by cw laser sources and prevent further entry of light. τ 0 and τ are, respectively, the ringdown time of the empty cavity and the ringdown time for when a sample is introduced between the mirrors.

Fig. 2.
Fig. 2.

Principle of light injection in a high-finesse cavity with a continuous pass through the successive moving cavity resonances (TEM00 modes). u las and u mode are the tuning speeds of the laser frequency ν las and the cavity frequencies ν i, respectively. They have to be of opposite signs for the number of resonance events to be increased.

Fig. 3.
Fig. 3.

(a) Simulated ringdown decays within 2 ms during a simple 0.4-cm-1 laser frequency sweep, with smoothed oscillations because of the beating between the progressively shifted intracavity field and the scanned incoming laser field. (b) Calculated intensity profiles that are transmitted during a 2-ms laser frequency tuning over 0.4 cm-1 and a synchronous sweep of the cavity length (L 0=50 cm) of total amplitudes 0, 5, and 10 µm, giving spectral resolutions of 0.01, 0.00753, and 0.00605 cm-1, respectively.

Fig. 4.
Fig. 4.

Theoretical investigations of reduction of the frequency space between ringdown events through (a) an increase of the cavity sweep amplitude or (b) a decrease of the laser tuning range, within 2 ms. The resolution enhancement factors are displayed as the dashed curves.

Fig. 5.
Fig. 5.

Experimental setup for high-speed CRDS. ECDL, external cavity diode laser; PBS, polarizing beam splitter; PD, silicon photodetector; APD, avalanche photodetector; PZT, piezoelectric translator.

Fig. 6.
Fig. 6.

Typical signals recorded during 2 ms at atmospheric pressure with the transmitted ringdown peaks in the upper curve, the PZT voltage ramp in green, the calibration signals from the potassium cell in red, and the Fabry-Perot etalon in blue. In (a), 65 ringdown events are recorded, whereas 77 events are recorded in (b), as the cavity is PZT scanned over 5 µm.

Fig. 7.
Fig. 7.

O2 absorption spectrum in air, at atmospheric pressure and room temperature (295 K). The ringdown times are shown in the upper part as a function of the recording time.

Fig. 8.
Fig. 8.

Absorption spectra for O2 in air, recorded during a single laser frequency sweep and a synchronous 5-µm cavity modulation, with a 280-Hz triangular scan pattern (a) at atmospheric pressure and (b) around 20 mbar (the residuals from the fitting are shifted for clarity).

Equations (7)

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

I ( t ) = I 0 exp ( t τ ) ,
1 c τ = 1 R + A L + α ,
u mode = d ν m d t = d ν m d L d L d t = ν m L u ν 0 L 0 u .
ν 0 + u las t 1 = ν m ( 0 ) + u mode t 1 ,
ν 0 + u las t 2 = ν m + 1 ( 0 ) + u mode t 2 .
u las ( t 2 t 1 ) = [ ν m + 1 ( 0 ) ν m ( 0 ) ] u las ( u las u mode ) .
Resolution = FSR u las ( u las u mode ) = FSR ( 1 u mode u las ) .

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