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Etude expérimentale des collisions de redistribution et d'échange dans le niveau 23P de l'hélium

Abstract : This work consisted in an experimental investigation of the effect of collisions in the 23P state, and between the 23P and the fundamental 11S states, on the populations of the 23P magnetic sublevels. The 23P, 23S, and 11S states are involved in metastability exchange optical pumping in helium and these collisions are currently suspected to limit its efficiency. Accurate characterization of the collisional redistribution of atoms has been achieved by a laser absorption spectroscopy technique on the 23P - 33S transition using a double-resonance ladder scheme and two tunable monochromatic lasers. A laser diode at 1083 nm selectively populates sublevels of the 23P state, while all populations are probed by a laser diode at 706.5 nm scanned over the entire 23P - 33S transition. We present a theoretical calculation of the relevant level structure of helium as well as simple models with the rate equations for the populations, suitable for interpretation of the experimental observations by considering various processes such as changes of sublevel mJ or mF, of level J or F, with or without change of atoms velocity. From scans of the probe laser frequency, we identify the populations of pumped levels as well as those resulting from the transfer of atoms from other levels. A first set of experimental results from the study of the absorption line profiles is in excellent agreement with the previously calculated values for the Zeeman structures, the hyperfine structure of the 33S state of 3He and the 3He - 4He isotopic shift. The shapes of the absorption spectra were studied as a function of the pump intensity used. Finally, we present the study of the effects of collisions in 4He, at different pressures, ranging from 0.13 to 4.27 mbar. It was also applied to isotopic mixtures, at different pressures, where the excitation transfer can be directly observed. The values of integrated absorption of the spectral lines yields populations in each level in the 23P state from which collisional transfer rates can be inferred. These rates are compared with those reported in the literature and discussed from the point of view of the limits of metastability exchange optical pumping technique.
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Contributor : Pierre-Jean Nacher Connect in order to contact the contributor
Submitted on : Thursday, September 2, 2021 - 5:27:45 PM
Last modification on : Thursday, March 17, 2022 - 10:08:59 AM


  • HAL Id : tel-03332480, version 1


Ali Dia. Etude expérimentale des collisions de redistribution et d'échange dans le niveau 23P de l'hélium. Physique Atomique [physics.atom-ph]. Université Paris Sciences et Lettres; Université Saint-Joseph de Beyrouth, 2021. Français. ⟨tel-03332480⟩



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