Date of Award

2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

A. R. P. Rau

Second Advisor

Kenneth J. Schafer

Abstract

We study the dynamics of highly excited (Rydberg) atoms in laboratory-scale magnetic fields via their ionization by THz half-cycle pulses (HCPs). A half-cycle pulse is a unipolar electromagnetic pulse that can probe an atomic electron at all points along its orbit around the atomic core. The dynamical evolution of diamagnetic Zeeman states subjected to an ultrashort (picosecond) HCP is calculated for both hydrogen and sodium atoms. Diamagnetic Zeeman states are localized parallel and perpendicular to the magnetic field. We use a grid-based pseudo-potential method to determine these eigenstates of the combined Coulomb-diamagnetic potential. We study states with principal quantum number n between 15--30 in the ℓ-mixing regime at magnetic fields of 1--6T. These initial states are subjected to the electric field of an HCP and their subsequent time evolution is calculated by solving the time-dependent Schrodinger equation. The HCP width is varied between the short pulse (impulsive) and the long pulse limit, keeping the total momentum transferred a constant. We calculate the total ionized fraction, and also the spectrum of the ionized photoelectrons. We find that, in the impulsive limit, where the width of the pulse is much smaller than typical time scales in the system, the calculated amount of ionization and the photoelectron spectra are different depending on the localization of the initial state. These differences are shown to be due to the different initial momentum distributions of the parallel and perpendicular states. As the duration of the HCP is made longer, we find that ionization is suppressed as compared with the impulsive limit. The states localized perpendicular to the magnetic field are found to be much more sensitive to the HCP width than the parallel states, reflecting the fact that the two classes of states interact with different parts of the Coulomb-diamagnetic potential during the HCP. The ionization characteristics are shown to scale classically with the principal quantum number. The results are presented in such a manner that they can be verified by experiment.

ISBN

9780599853461

Pages

119

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