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Innovation et optimisation d'une méthode de polarimétrie pompe-sonde avec des faisceaux laser impulsionnels en vue d'une mesure précise de violation de la parité dans l'atome de césium

Abstract : While Parity Violation (PV) experiments on highly forbidden transitions have been using detection of fluorescence signals; our experiment uses a pump-probe scheme to detect the PV signal directly on a transmitted probe beam. A pulsed laser beam of linear polarisation linéaire ε_1 excites the atoms on the 6S-7S cesium transition in a colinear electric field E parallèle à k_ex. The probe beam (k_pr parallèle à k_ex) of linear polarisation ε_2 tuned to the transition 7S-6P3/2 is amplified. The small asymmetry ( ~ 10^-6) in the gain that depends on the handedness of the trihedron (E, ε_1, ε_2) is the manifestation of the PV effect This is measured as an E-odd apparent rotation of the plane of polarization of the probe beam; using balanced mode polarimetry. New criteria of selection have been devised, that allow us to distinguish the true PV-signal against fake rotations due to electromagnetic interferences, geometrical effects, polarization imperfections, or stray transverse electric and magnetic fields. These selection critena exploit the symmetry of the PV-rotation - linear dichroism - and the revolution symmetry of the experiment. Using these criteria it is not only possible to reject fake signals, but also to elucidate the underlying physical mechanisms and to measure the relevant defects of the apparatus. The present signal-to-noise ratio allows embarking in PV measurements to reach the 10% statistical precision. A 1% measurement still requires improvements. Two methods have been demonstrated. The first one exploits the amplification of the asymmetry at high gain - one major advantage provided by our detection method based on stimulated emission. The second method uses both a much higher incident intensity and a special dichroic component which magnifies tiny polarization rotations.
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Submitted on : Friday, March 10, 2006 - 9:08:06 AM
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  • HAL Id : tel-00011914, version 1

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Dominique Chauvat. Innovation et optimisation d'une méthode de polarimétrie pompe-sonde avec des faisceaux laser impulsionnels en vue d'une mesure précise de violation de la parité dans l'atome de césium. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 1997. Français. ⟨tel-00011914⟩

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