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Jet lent d’atomes d’argon métastable pour l’étude de la diffraction au travers de nanoréseaux et de l’interaction avec des champs magnétiques co-mobiles

Abstract : We present a new set-up producing a slow beam of metastable argon atoms pulsed at 10 Hz maximum, which velocity can be tuned from 10 to 150 m.s-¹. The atomic velocity was measured with an uncertainty of one thousandth by use of an original technique of laser double-chopping. Longitudinal and transverse velocity dispersions have been retrieved by a Monte Carlo method. Metastable argon atoms in the 3p⁵4s, ³P₂ state interact by means of their magnetic moment with periodic magnetic co-mobile potentials pulsed in time with a wide frequency spectrum. Time-of-flight measurements allowed us to observe slowing down or acceleration processes as predicted by both classical and semi-classical theories. We obtain velocity variations of the order of 10 % of the initial velocity value. The typical de Broglie wavelength of an atom in the beam is 1 nm, thus well suited to the study of attractive atom-surface interactions of Casimir-Polder type (potential in the form –C₃/z³, z being the distance to the surface). We have got silicon nitride transmission gratings of pitch a = 100 nm, opening window e = 50 nm and depth L = 130 nm. Diffraction profiles show an envelope with a large angular width which is significantly broadened at low velocity, much more than the one given by a simple geometrical model like in optics. It emphasizes the importance of the effect of long atom-surface interaction times. The set of data we collected should permit to get the C₃ van der Waals dispersion coefficient with a relative uncertainty smaller than 5 %.
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Franck Correia. Jet lent d’atomes d’argon métastable pour l’étude de la diffraction au travers de nanoréseaux et de l’interaction avec des champs magnétiques co-mobiles. Physique Atomique [physics.atom-ph]. Université Sorbonne Paris Cité, 2018. Français. ⟨NNT : 2018USPCD074⟩. ⟨tel-02613294⟩

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