Formation de molécules froides par photoassociation d'atomes froids de césium. Mise en évidence de forces à longue portée entre atomes froids excités de césium.

Abstract : This thesis deals with the experimental study and the theoretical interpretation of the processes involved in photoassociation and the formation of cold caesium molecules. It also presents a study of the dipolar forces between a pair of cold excited caesium atoms. We present here the first photoassociation experiment on cold caesium atoms : two cold atoms absorb a photon to form an excited electronically excited molecules in a rotation-vibration level. The first production of cold molecules which was realised experimentally, after the spontaneous desexcitation of the photoassociated molecules, is described, stressing the role of the potential well of the molecular states $0_g^- (6s+6p_(3/2))$ or $1_u (6s+6p_(3/2))$ of caesium. The detection of the formed caesium molecules is based on a two-photons resonant ionisation that creates Cs$_2^+$ ions, afterwards selectively detected. Temperatures arround $20-200\,\mu$K have been measured. The photoassociative spectroscopy is described on the theoretical point of view : a detailed theoretical study allows to calculate precisely the asymptotic parts of the potential curves. On the experimental point of view, we present the spectroscopy of the extern potential well of the caesium state $0_g^- (6s+6p_(3/2))$ and the construction of an effective potential curve of the RKR type. A unified theory of photoassociation in weak field, considered as a collision assisted by laser, is developed. The cold atoms experiments allow to study and control the collision between two atoms whose mutual interaction is of the dipole-dipole type. Two different physical systems are studied : a sample of Rydberg atoms, and the photoassociation process which is a laser-assisted collision. A modification of the motion of one pair of atoms makes it possible to control the bipolar forces and to choose the atoms relative speeds.
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Submitted on : Thursday, November 13, 2003 - 5:11:49 PM
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• HAL Id : tel-00002752, version 1

Citation

Daniel Comparat. Formation de molécules froides par photoassociation d'atomes froids de césium. Mise en évidence de forces à longue portée entre atomes froids excités de césium.. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 1999. Français. ⟨tel-00002752⟩

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