Stabilization of positronium by laser fields.
Item
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Title
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Stabilization of positronium by laser fields.
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Identifier
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AAI9605610
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identifier
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9605610
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Creator
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Karlson, Antonella V.
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Contributor
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Adviser: M. H. Mittleman
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Date
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1995
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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
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Abstract
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We consider the problem of a positronium atom interacting with laser fields with the goal to extend its lifetime. Ps is an unstable system. Singlet Ps annihilates mainly by emission of two {dollar}\gamma{dollar} quanta and the triplet state-- mainly by 3{dollar}\gamma{dollar} emission. The lifetimes are respectively {dollar}\tau\sbsp{lcub}an{rcub}{lcub}s{rcub}{dollar} = 1.25 10{dollar}\sp{lcub}-10{rcub}{dollar} sec and {dollar}\tau\sbsp{lcub}an{rcub}{lcub}tr{rcub}{dollar} = 1.4 10{dollar}\sp{lcub}-7{rcub}{dollar} sec. The annihilation reaction is caused by an interaction term in the Hamiltonian, which on the scale of the Ps atom is essentially a zero range operator. Thus, the annihilation rate is proportional to the absolute value squared of the Ps wave function at the origin. Since the wave function of Ps vanishes at the origin for all but states with angular momentum zero, Ps annihilates for all practical purposes only from S states. If lasers are used to keep Ps out of them, the annihilation lifetime can be increased. Singlet and triplet Ps are not coupled by the lasers and they are discussed separately. A Ps atom interacting with laser fields is in a dressed state. Its wave function can be represented as a linear superposition of the bare states and under certain conditions it does not contain the ground state. This is the phenomenon of coherent population trapping. The latter can be used to extend the lifetime of Ps when the atom is driven by two semiclassical lasers.;We consider a two and three state Ps atom interacting respectively with one and two near-resonant circularly polarized lasers with spontaneous radiative transitions, annihilation from the ground state and photoionization from the excited states. The last two processes lead to the destruction of Ps and they are included via an antihermitian (absorptive) term in the Hamiltonian. The new annihilation rate depends on the initial Ps state, on the choice of bare states coupled by the laser(s) and on the laser parameters (intensity and detuning).;We obtain that the lifetime of triplet Ps in the field of two lasers cannot be extended more than two times its value without the interaction with the lasers. This is due to spontaneous radiative transitions, which are fast and the atom fluoresces many times before annihilation. Therefore the effect of coherent population trapping is eliminated. The lifetime of singlet Ps can be extended with a small probability. If the initial state was 1S, up to 45 times its value outside of the lasers. If the initial state was 2P, almost twice the lifetime of this state outside of the lasers.
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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.
