Polarisation and Alignment Studies in Electron Scattering From Rubidium
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Measurements have been made of the A2 spin asymmetry in the scattering of polarised electrons from rubidium atoms. Results have been taken at an incident energy of 15, 20, 30, 50 and 80eV for elastic scattering, and at 15, 20, 30 and 50eV for 5S to 5P excitation where the fine structure has not been resolved. The measurements covered the angular range 30° to 110°. Results were taken using a crossed beam type experiment, with a hemispherical electrostatic detector. Polarised electrons were provided by a conventional gallium arsenide spin-polarised electron source. The Rmatrix and relativistic distorted wave calculations available demonstrate good agreement with the experimental results, though there are some clear discrepancies between the magnitudes and positions of the extrema as predicted by theory. These A2 results follow on from those taken by Went (2003). A study of the autoionisation resonances of rubidium has also been undertaken. This consisted of first measuring the angular variation of the autoionisation resonances in the angular range 30° to 130°, at an incident energy of 1keV. A crossed beam method was also used for these results, though electrons were provided by a conventional electron gun. Significant relative angular variation between sets of autoionisation resonances was observed. The results taken represent the first experimentally determined values of the alignment parameter, A20 and R0, the isotropic distribution ratio for the leading autoionisation doublet of rubidium. The experimentally determined values of A20 and R0 were not inconsistent with the theoretical values available for comparison. Finally an attempt was made to measure a circular dichroism in the angular distribution of autoionised electrons due to stepwise laser/electron impact excitation (CPDAD). The experimental detection of such a circular dichroism would be the very first of its kind. Such a measurement would also help validate the theoretical approach that predicted its existence. Preliminary investigation requires identification of an autoionisation resonance that is enhanced with the stepwise excitation procedure. A crossed beam experiment identical to the procedure immediately above was undertaken using a conventional electron gun. Laser light resonant with the D2 line of rubidium was provided by a titanium-sapphire laser, while a diode laser was used to repump the dark state. Measurements were taken at incident energies of 250, 450, 700 and 1000eV at ejected electron angles of 75°, 75°, 90° and 90° respectively. No enhancement was visible with the stepwise process for any of the observed autoionisation resonances, so it was not possible to study CPDAD.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical sciences
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Materials identified by the author for which third party copyright has not been obtained have been retained in the published version. This fulfills our policy of "Take down". The materials which the author indentified are; Fig 1.1 p. 18; Table 1.5 p. 18; Table 1.6 p. 18; Fig. 1.2 p. 23; Fig. 1.3 p. 25; Fig. 1.4 p. 25; Fig. 1.5 p. 26; Fig. 1.6 p. 27; Fig 1.7 p. 29; Fig. 1.8 p. 29; Fig. 2.2 p. 55; Fig. 3.1 p. 70; Fig. 3.4 p. 81; Fig. 3.6 p. 88; Fig. 3.7 p. 92; Fig. 3.11 p. 102; Fig. 3.1 p. 103; Fig. 4.1 p. 131; Fig. 4.2 p. 132; Fig.4.3 p. 133; Fig. 4.4 p. 134; Fig. 4.5 p. 135; Fig. 4.6 p. 136; Fig. 4.7 p. 137; Fig. 4.8 p. 138; Fig. 4.9 p. 139; Table B1 p. 185.