Abstract

The CO2 laser locked onto a saturated absorption resonance of OsO4 provides a secondary frequency standard in the 10 μm region, with an accuracy of 50 Hz to 1 kHz. For averaging times less than 100 s its stability performance is better than the Hydrogen maser. This paper deals with the present attempt to increase this performance by using a two-photon molecular resonance as a reference. We begin with some preliminary and promising results on a two-photon line of SF6 leading to characteristics similar to those obtained with a saturation line of OsO4. Then two alternative methods to increase the resolution are presented : optical detection of slow molecules and a new development of the well-known Ramsey fringes. Metrological features are analyzed for both methods.

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References

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  1. A. Clairon, C. Salomon, S. Guellati, and W. D. Phillips, "Ramsey resonance in a Zacharias fountain," Europhys. Lett. 16, 165-170 (1991).
    [CrossRef]
  2. E. Simon, P. Laurent, and A. Clairon, "Measurement of the Stark shift on the Cs hyperfine splitting in an atomic fountain," Phys.Rev. A 57, 436-439 (1998).
    [CrossRef]
  3. F. Riehle, H. Schnatz, G. Zinner, K. Zeiske, B. Lipphardt, and J. Helmcke, "Calcium optical frequency standard based on atom interferometry," Laser Phys. 6, 237-243 (1996).
  4. L. Hilico, R. Felder, D. Touahri, O. Acef, A. Clairon, and F. Biraben, "Metrological features of the Rubidium two-photon standards of the LPTF and the Kastler-Brossel Laboratories," Eur. Phys. J. AP 4, 219-225 (1998).
    [CrossRef]
  5. A. Huber, B. Gross, M. Weitz, and T. W. H„nsch, "Two-photon Ramsey spectroscopy of the 1S-2S transition in atomic Hydrogen," Phys. Rev. A 58, R2631-R2634 (1998).
    [CrossRef]
  6. P. E. Durand, G. Nogues, V. Bernard, A. Amy, and C. Chardonnet, "S‚lection des mol‚cules lentes en spectroscopie sans effet Doppler … deux photons," Ann. Phys. Fr. 20, 601-602 (1995).
    [CrossRef]
  7. P. E. Durand, G. Nogues, V. Bernard, A. Amy-Klein, and C. Chardonnet, "Slow-molecule detection in Doppler-free two-photon spectroscopy," Europhys. Lett. 37, 103-108 (1997).
    [CrossRef]
  8. S. N. Bagayev, A. E. Baklanov, V. P. Chebotayev, and A. S. Dychkov, "Superhigh resolution spectroscopy in methane with cold molecules," Rev. Roum. Phys. 33, 361-367 (1988).
  9. S. N. Bagayev, V. P. Chebotayev, A. K. Dmitriyev, A. E. Om, Y. V. Nekrasov, and B. N. Skvortsov, "Second-Order Doppler-Free Spectroscopy," App. Phys. B 52, 63-66 (1991).
    [CrossRef]
  10. C. Chardonnet, F. Guernet, G. Charton, and C. J. Bord‚, "Ultrahigh-resolution saturation spectroscopy using slow molecules in an external cell," Appl. Phys. B 59, 333-343 (1994).
    [CrossRef]
  11. V. Bernard, C. Daussy, G. Nogues, L. Constantin, P. E. Durand, A. Amy-Klein, A. van Lerberghe, and C. Chardonnet, "CO2 laser stabilization to 0.1-Hz level using external electrooptic modulation," QE-33, 1282 (1997).
  12. F. Herlemont, M. Khelkhal, J. Legrand, and G. Pierre, "Doppler-free two-photon spectrum of SF6 for metrological purposes," Opt. Lett. 23, 957-959 (1998).
    [CrossRef]
  13. A. Linskens, S. te Lintel Hekkert, and J. Reuss, "One and two photon spectra of SF6 molecular beam measurements," Infrared Phys. 32, 259-282 (1991).
    [CrossRef]
  14. Y. V. Baklanov, V. P. Chebotayev, and B. Y. Dubetsky, "The Resonance of Two-Photon Absorption in Separated Optical Fields," App. Phys. 11, 201-202 (1976).
    [CrossRef]
  15. C. J. Bord‚, "Sur les franges de Ramsey en spectroscopie sans ‚largissement Doppler," C. R. Acad. Sc. Paris 284B, 101-104 (1977).
  16. C. J. Bord‚, "Density matrix equations and diagrams for high resolution non-linear laser spectroscopy : application to Ramsey fringes in the optical domain," in Advances in laser spectroscopy, F. T. Arecchi, F. Strumia, and H. Walther, Editors, (1983).
  17. A. F. Linskens, W. L. Meerts, J. Reuss, and C. J. Bord‚, "Doppler-free two-photon Ramsey Fringes in the 10 mm region," in Laser controlled dynamics of molecular processes, A. F. Linskens, Ph. D. Thesis, University of Nijmegen, ISBN 90-9007146-6 (1994).
  18. C. J. Bord‚, Private communication
  19. O. Acef, "Metrological properties of CO2/OsO4 optical frequency standard," Opt. Comm. 134, 479-486 (1997).
    [CrossRef]
  20. M. P. Sassi and K. Stoll, "Investigation of anomalous Zeeman effect in OsO4 molecule," in Laser Spectroscopy XIII, 111-113 (1997).
  21. E. Giacobono, and B. Cagnac, "Doppler-free multiphoton spectroscopy," in Progress in Optics XVII, E. Wolf, Editor, 85-161 (1980).
  22. S. A. Lee, J. Helmcke, and J. L. Hall, "High Resolution two-Photon Spectroscopy of Rb Rydberg Levels," in Laser Spectroscopy IV, H.W.a.K.E. Rothe, Editor, 130-141 (1979).
  23. C. J. Bord‚, "D‚veloppements r‚cents en spectroscopie infrarouge … ultra-haute r‚solution," in Revue du Cethedec-Ondes et signal-NS 83-1, 1-118 (1982).
  24. F. Herlemont, M. Lyszyk, and J. Lemaire, "Doppler-Free Two-Photon Spectroscopy of the 2n3 band of SF6," Appl. Phys. 24, 369-374 (1981).
    [CrossRef]

Other

A. Clairon, C. Salomon, S. Guellati, and W. D. Phillips, "Ramsey resonance in a Zacharias fountain," Europhys. Lett. 16, 165-170 (1991).
[CrossRef]

E. Simon, P. Laurent, and A. Clairon, "Measurement of the Stark shift on the Cs hyperfine splitting in an atomic fountain," Phys.Rev. A 57, 436-439 (1998).
[CrossRef]

F. Riehle, H. Schnatz, G. Zinner, K. Zeiske, B. Lipphardt, and J. Helmcke, "Calcium optical frequency standard based on atom interferometry," Laser Phys. 6, 237-243 (1996).

L. Hilico, R. Felder, D. Touahri, O. Acef, A. Clairon, and F. Biraben, "Metrological features of the Rubidium two-photon standards of the LPTF and the Kastler-Brossel Laboratories," Eur. Phys. J. AP 4, 219-225 (1998).
[CrossRef]

A. Huber, B. Gross, M. Weitz, and T. W. H„nsch, "Two-photon Ramsey spectroscopy of the 1S-2S transition in atomic Hydrogen," Phys. Rev. A 58, R2631-R2634 (1998).
[CrossRef]

P. E. Durand, G. Nogues, V. Bernard, A. Amy, and C. Chardonnet, "S‚lection des mol‚cules lentes en spectroscopie sans effet Doppler … deux photons," Ann. Phys. Fr. 20, 601-602 (1995).
[CrossRef]

P. E. Durand, G. Nogues, V. Bernard, A. Amy-Klein, and C. Chardonnet, "Slow-molecule detection in Doppler-free two-photon spectroscopy," Europhys. Lett. 37, 103-108 (1997).
[CrossRef]

S. N. Bagayev, A. E. Baklanov, V. P. Chebotayev, and A. S. Dychkov, "Superhigh resolution spectroscopy in methane with cold molecules," Rev. Roum. Phys. 33, 361-367 (1988).

S. N. Bagayev, V. P. Chebotayev, A. K. Dmitriyev, A. E. Om, Y. V. Nekrasov, and B. N. Skvortsov, "Second-Order Doppler-Free Spectroscopy," App. Phys. B 52, 63-66 (1991).
[CrossRef]

C. Chardonnet, F. Guernet, G. Charton, and C. J. Bord‚, "Ultrahigh-resolution saturation spectroscopy using slow molecules in an external cell," Appl. Phys. B 59, 333-343 (1994).
[CrossRef]

V. Bernard, C. Daussy, G. Nogues, L. Constantin, P. E. Durand, A. Amy-Klein, A. van Lerberghe, and C. Chardonnet, "CO2 laser stabilization to 0.1-Hz level using external electrooptic modulation," QE-33, 1282 (1997).

F. Herlemont, M. Khelkhal, J. Legrand, and G. Pierre, "Doppler-free two-photon spectrum of SF6 for metrological purposes," Opt. Lett. 23, 957-959 (1998).
[CrossRef]

A. Linskens, S. te Lintel Hekkert, and J. Reuss, "One and two photon spectra of SF6 molecular beam measurements," Infrared Phys. 32, 259-282 (1991).
[CrossRef]

Y. V. Baklanov, V. P. Chebotayev, and B. Y. Dubetsky, "The Resonance of Two-Photon Absorption in Separated Optical Fields," App. Phys. 11, 201-202 (1976).
[CrossRef]

C. J. Bord‚, "Sur les franges de Ramsey en spectroscopie sans ‚largissement Doppler," C. R. Acad. Sc. Paris 284B, 101-104 (1977).

C. J. Bord‚, "Density matrix equations and diagrams for high resolution non-linear laser spectroscopy : application to Ramsey fringes in the optical domain," in Advances in laser spectroscopy, F. T. Arecchi, F. Strumia, and H. Walther, Editors, (1983).

A. F. Linskens, W. L. Meerts, J. Reuss, and C. J. Bord‚, "Doppler-free two-photon Ramsey Fringes in the 10 mm region," in Laser controlled dynamics of molecular processes, A. F. Linskens, Ph. D. Thesis, University of Nijmegen, ISBN 90-9007146-6 (1994).

C. J. Bord‚, Private communication

O. Acef, "Metrological properties of CO2/OsO4 optical frequency standard," Opt. Comm. 134, 479-486 (1997).
[CrossRef]

M. P. Sassi and K. Stoll, "Investigation of anomalous Zeeman effect in OsO4 molecule," in Laser Spectroscopy XIII, 111-113 (1997).

E. Giacobono, and B. Cagnac, "Doppler-free multiphoton spectroscopy," in Progress in Optics XVII, E. Wolf, Editor, 85-161 (1980).

S. A. Lee, J. Helmcke, and J. L. Hall, "High Resolution two-Photon Spectroscopy of Rb Rydberg Levels," in Laser Spectroscopy IV, H.W.a.K.E. Rothe, Editor, 130-141 (1979).

C. J. Bord‚, "D‚veloppements r‚cents en spectroscopie infrarouge … ultra-haute r‚solution," in Revue du Cethedec-Ondes et signal-NS 83-1, 1-118 (1982).

F. Herlemont, M. Lyszyk, and J. Lemaire, "Doppler-Free Two-Photon Spectroscopy of the 2n3 band of SF6," Appl. Phys. 24, 369-374 (1981).
[CrossRef]

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Figures (5)

Fig. 1.
Fig. 1.

Experimental apparatus. Frequency modulations at f1=90 kHz and f2=4.9 kHz are applied to the EOM. AOM : acoustooptic modulator, P : polarizer, OI : optical isolator.

Fig. 2.
Fig. 2.

a) Beat signal between the lasers, each stabilized onto the same two-photon R(47) resonance of the 2ν3 band of SF6 fitted with the best Lorentzian b) Square root of the Allan variance of the beat note frequency, divided by √2 in order to describe one of the two equivalent stabilized lasers.

Fig.3.
Fig.3.

Hyperfine structure of the P(4)E line in the 2ν3 3 band of SF6 a) Pressure P=10-2 Pa, power PW=60 mW, accumulation time t=3 s/point, modulation frequency f=2.2 kHz., depth 400 Hz, 2f-detection b) Central component. P=10-2 Pa, PW=12 mW, t=6 s/point, f= 120 Hz, depth 200 Hz.

Fig. 4
Fig. 4

a) Experimental scheme for two-photon Ramsey fringes ; AOM : acousto-optic modulator, b) Schematic of the 3 levels involved in the P(4) E resonance.

Fig. 5.
Fig. 5.

Two-photon absorption signal detected a) on the cavity transmission beam using a laser FM of 5 kHz (detection channel S1 on Fig. 4), b) on an auxiliary beam absorption (detection channel S2), tuned to the upper one-photon transition, using the molecular beam chopper at 550 Hz. Typical conditions : 15 mW in the cavity, 5 bars pure SF6 beam, accumulation time 4 s/point. Data are fitted to a) the derivative of a Gaussian and b) a Gaussian.

Tables (1)

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Table 1. Systematic shifts for slow molecule detection and Ramsey fringes.

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