Double multiphotoionization of helium.
Item
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Title
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Double multiphotoionization of helium.
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Identifier
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AAI9807900
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identifier
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9807900
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Creator
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Altzman, Jerry B.
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Contributor
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Adviser: Marvin H. Mittleman
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Atomic | Physics, General
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Abstract
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In this thesis we consider the problem of formulating a general theory of multiphoton double-ionization and use this theory to make predictions about the photoionization rates of helium.;We begin by creating a macroscopic picture of the double-ionization processes in terms of transition rates between the ground, ground-singly-ionized, and doubly-ionized states. We divide these processes into sequential and direct ionization paths. We form a microscopic description of the problem using scattering theory and use an S-matrix formalism to describe the ionization process. We make the approximation of expanding in powers of the correlation interaction to perform the calculation. We also approximate our uncorrelated initial and final states by requiring them to satisfy the Hartree-Fock equations. We shall also assume that our initial state is a pure singlet {dollar}(L=0){dollar} state and we will ignore relativistic (spin) effects as being much smaller than the other effects we measure. We represent the electron-laser field interaction by the minimal-coupling gauge in the dipole approximation. We find that there is an additional, induced state representing a third non-direct path. These three paths interfere. Finally, we connect our microscopic description to our macroscopic events. The connection comes via the structure of energy singularities of the S-matrices describing the ionization dynamics, which we connect to the rates by expanding the latter in a Taylor series in time.;Second, we find analytic expressions for the ionization rates in terms of the laser intensity for the specific case of a linearly-polarized laser with bounds on intensity and frequency, where we can get analytic results. We can then make a connection between experimental observations of ionization yields and our theory. We find that the experimentalists' hypothesis, that the sudden change in the shape of the yield curve is due to the dominance of the sequential process over the direct one, is not supported by our theory in the region of its applicability.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
