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Journal of the Optical Society of America B

Journal of the Optical Society of America B


  • Vol. 16, Iss. 5 — May. 1, 1999
  • pp: 702–709

Compression of a cold atomic cloud by on-resonance laser light

Lev Khaykovich and Nir Davidson  »View Author Affiliations

JOSA B, Vol. 16, Issue 5, pp. 702-709 (1999)

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We analyze the light-induced atom–atom interactions in optically thick atomic clouds and show that, when the laser frequency is on-resonance with the atomic transition, they become attractive. On the basis of this analysis we propose and demonstrate a novel scheme to compress a cold and dense atomic cloud with a short on-resonance laser pulse. The compression force arises from attenuation of the laser light by the atomic cloud. The following free propagation of the atoms shows a lenslike behavior that yields a transient density increase at the focal time, where neither laser nor magnetic field perturbations exist. A cooling pulse, which is applied at the focal time of this lens, restores the initial temperature of atoms, and hence the phase space density is increased. Finally, we adopt our compression scheme to a quasi-steady-state mode by temporally chopping it with the cooling and trapping beams of a magnet-optical trap.

© 1999 Optical Society of America

OCIS Codes
(140.3320) Lasers and laser optics : Laser cooling
(140.7010) Lasers and laser optics : Laser trapping

Lev Khaykovich and Nir Davidson, "Compression of a cold atomic cloud by on-resonance laser light," J. Opt. Soc. Am. B 16, 702-709 (1999)

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  15. We assume a uniform spatial distribution of the atoms over the period of the standing wave. This is applicable to the on-resonance case (δ=0), whereas at δ≠0 some localization of the atoms toward the nodes (δ>0) and the antinodes (δ<0) of the standing wave is expected owing to the dipole force. We neglect this localization here.
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  17. At low intensities the neglect of the repulsive inter-atomic forces by our simplified model is not justified anyway.
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  20. We observed nearly identical dependence on laser detuning in one-beam and six-beam configurations.
  21. Note that for the pulsed compression the optimal compression was obtained for detuning of 1–2 MHz above resonance (see inset of Fig. 7). This frequency shift can be explained by the fact that when the atoms are accelerated during the ~100-μs compression pulses they acquire a negative Doppler shift of a few megahertz, so their average detuning is close to zero when their initial detuning is somewhat posi-tive. This does not apply for the quasi steady state of Fig. 9, as is confirmed by the exact zero location of the optimal detuning.
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  23. L. Khaykovich, N. Friedman, and N. Davidson, “Saturation of the weak probe amplification in a strongly driven cold and dense atomic cloud,” Europhys. J. (to be published).

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