A New Metastable Helium Machine : An Investigation into the Attributes of Trapping, Cooling and Detecting Metastable Helium

Lynn Hoendervanger 1
1 Laboratoire Charles Fabry / Optique atomique
LCF - Laboratoire Charles Fabry
Abstract : This thesis describes the work done over the past three and a half years on the new metastable helium experiment at the Institut d'Optique in Palaiseau. In the first chapter it describes a study to improve both the efficiency and the accuracy of the Microchannel Plate (MCP) detection system. We have experimented with adding a gold layer on the top of the input plate, something that we have found increases the efficiency but also decreases the accuracy. The addition of a voltage between the two stacked plates has been shown to both raise the efficiency and improve the accuracy in non-coated MCPs.The second chapter is devoted to the construction of the experimental apparatus. Here the excitation of ground state helium to its metastable state is described, as well as the subsequent collimation and cooling by Zeeman slower of the resulting hot atomic beam. The slowed beam is then captured in a Magneto-Optical Trap, in which we have captured 8x108 atoms.In the third chapter an original study on three-dimensional Doppler cooling in a red-detuned molasses and in the Magneto-Optical trap is presented. The metastable helium system is unique as there is no multiple scattering of photons and there are no sub-Doppler effects. This allows for a never before seen experimental realisation of pure Doppler cooling theory. The fourth chapter describes a study on collisions in a magneto-optical trap of metastable helium. Light-induced Penning collisions are responsible for high trap losses at high intensities and at frequencies close to the transition frequency. We measure the constant rate coefficient to Ksp = 2.8 ± 0.4 x 10-7cm3/s.
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Lynn Hoendervanger. A New Metastable Helium Machine : An Investigation into the Attributes of Trapping, Cooling and Detecting Metastable Helium. Optics [physics.optics]. Institut d’Optique Graduate School, 2014. English. ⟨NNT : 2014IOTA0006⟩. ⟨tel-01124010⟩

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