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Refroidissement laser sub-recul par résonances noires:-exp. avec des atomes d'hélium métastables,-approches Monte-Carlo quantique et vols de Lévy

Abstract : This thesis presents new experimental and theoretical approaches of laser cooling by dark resonances. The recoil energy is the kinetic energy communicated to an atom initially at rest by the absorption or by the emission of a single photon. This important milestone in laser cooling has been overcome for the first time in 1988 by the method of velocity selective dark resonances. This work deals with extensions of this method to the long interaction time regime and to several dimensions. The new experimental setup is based on the development of a laser trap of ultracold metastable helium atoms. The atoms are released in free fall and their small velocities allow the interaction time to be increased by 2 orders of magnitude. Stray magnetic fields are compensated to one milligauss by mechanical Hanle effect experiments. The first experiments with this new setup reached one fortieth of the recoil energy (100 nanokelvins) in one dimension. The recoil limit has been passed for the first time in two dimensions, reaching one twentieth of the recoil energy, i e. 200 nanokelvins. Theoretically, a new type of quantum Monte-Carlo simulations much more efficient than the resolution of optical Bloch equations. The long interaction time behaviour has been explored. These simulations suggested another new approach, based on the Lévy statistics recently introduced to study anomalous diffusion. With this approach, we proved a conjecture predicting a decrease of the temperature as the inverse of the interaction time. We also give new analytical results, for example about the proportion of cooled atoms or about the role of dimensionality.
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https://tel.archives-ouvertes.fr/tel-00011898
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Submitted on : Thursday, March 9, 2006 - 5:38:08 PM
Last modification on : Thursday, October 29, 2020 - 3:01:51 PM
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  • HAL Id : tel-00011898, version 1

Citation

François Bardou. Refroidissement laser sub-recul par résonances noires:-exp. avec des atomes d'hélium métastables,-approches Monte-Carlo quantique et vols de Lévy. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 1995. Français. ⟨tel-00011898⟩

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