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Molécules Exotiques d'Hélium

Abstract : We study the photoassociation of an ultracold cloud of magnetically trapped helium atoms : pairs of colliding atoms interact with one or two laser fields to produce a purely long range 4He2(23S1-23P0) molecule, or a 4He2(23S1-23S1) long range molecule.
Light shifts in one photon photoassociation spectra are measured and studied as a function of the laser polarization and intensity, and the vibrational state of the excited molecule. They result from the light-induced coupling between the excited molecule, and bound and scattering states of the interaction between two metastable atoms. Their analysis leads to the determination of the scattering length a=7.2 ± 0.6 ruling collisions between spin polarized atoms.
The two photon photoassociation spectra show evidence of the production of polarized, long-range 4He2(23S1-23S1) molecules. They are said to be exotic as they are made of two metastable atoms, each one carrying a enough energy to ionize the other . The corresponding lineshapes are calculated and decomposed in sums and products of Breit-Wigner and Fano profiles associated to one and two photon processes. The experimental spectra are fit, and an intrinsic lifetime τ=1.4±0.3 μs is deduced.
It is checked wether this lifetime could be limited by spin-dipole induced Penning autoionization. This interpretation requires that there is a quasi-bound state close to the dissociation threshold in the singlet interaction potential between metastable helium atoms for the theory to match the experiment.
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Contributor : Maximilien Portier <>
Submitted on : Thursday, February 21, 2008 - 8:59:16 PM
Last modification on : Thursday, December 10, 2020 - 12:36:57 PM
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  • HAL Id : tel-00258383, version 1

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Maximlien Portier. Molécules Exotiques d'Hélium. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2007. Français. ⟨tel-00258383⟩

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