The Polarization of Balmer-Alpha Radiation Emitted by Beam-Tilted Excited Hydrogen Atoms.

One of the most fundamental electronic particle -surface interactions is the electron-exchange that occurs between an ion and the electrons from a nearby surface, such as the interaction following the transmission of ions through a very thin foil. The work presented in this dissertation is an investigation of the beam-foil electron-exchange interaction using 20- to 50-keV protons as projectiles incident on very thin amorphous carbon foils. Measurements of the properties of the final excited states and their dependence on the state of the surface are used (1) to characterize the state of the excited atom at the instant of electron-capture and (2) to determine the influence of surface electric fields on such states. Measurements of the intensity and polarization of the Balmer-alpha radiation emitted by excited hydrogen atoms following the transmission of 20- to 50-keV protons through thin amorphous carbon foils have been made. The polarization measurements show a strong beam-fluence dependence which has been correlated to an ion-beam induced change in the structure of the foil. Raman measurements of the foil samples before and after irradiation by the proton beam indicate that the proton bombardment modifies the original amorphous structure of the foil into a structure which is more graphitic in character. The tilt-angle dependence of the polarization of the Balmer-alpha radiation emitted by the foil excited hydrogen atoms also changes with proton dose. Specifically the alignment enhanced with increasing beam dose and the orientation at small tilt angles changes to the opposite sign from what one would expect from simple anisotropic electron-capture arguments. In addition, measurements of the polarization of Balmer-alpha radiation emitted by beam-foil excited hydrogen atoms which have traversed an applied electric field have been made. These measurements, as a function of the strength of the applied field, show strong oscillations which are often called quantum beats. The field-induced, quantum-beat measurements have been compared to model calculations which predict the polarization of Balmer-alpha radiation emitted by beam-foil excited states. The calculations are based on the quantum-mechanical time evolution of an initial hydrogen density matrix through the applied electric field.