Response of semiconductors to intense laser pulses, including time-dependent susceptibilities /
Motivated in part by experiments at Harvard, the University of Essen, and other laboratories, we have performed simulations of the response of GaAs and Si to ultrafast and ultra-intense laser pulses. These simulations employ tight-binding electron-ion dynamics (TED), a nonadiabatic technique which i...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=727726191&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Motivated in part by experiments at Harvard, the University of Essen, and other laboratories, we have performed simulations of the response of GaAs and Si to ultrafast and ultra-intense laser pulses. These simulations employ tight-binding electron-ion dynamics (TED), a nonadiabatic technique which is fully described in the text. Using a formalism that modifies a tight-binding Hamiltonian to include interaction with a time-dependent electromagnetic field, we have also obtained an analytical expression for the second-order susceptibility. This expression was then used to calculate the energy dependence of [](²)[()] for GaAs. The results are in agreement with the best previous calculations and with available experimental data for GaAs subjected to low intensity light. Comparison of our simulations with experiments involving ultra-intense laser pulses shows good agreement in all important respects. There is a nonthermal phase transition as the intensity is varied at fixed pulse duration. For both GaAs and Si, we find that the transition threshold corresponds to excitation of about 17% of the valence electrons to the conduction bands. In experimental pump-probe observations, the dielectric function [][] and the second-order susceptibility [](²) can be measured. ([](²) is nonzero for noncentrosymmetric materials like GaAs; [] is, of course, nonzero for both Si and GaAs.) These same quantities can be calculated during a TED simulation, and there is good agreement in the behavior with respect to both time and frequency. We find that above the threshold intensity, the imaginary part of the dielectric function exhibits metallic behavior, and in addition the second-order susceptibility goes to nearly zero, indicating a change of symmetry. Our simulations provide much additional microscopic information which is experimentally inaccessible: for example, the time dependence of the atomic pair-correlation function, electronic energy bands, occupancies of excited states, kinetic energy of the atoms, and excursions of atoms from their initial positions. |
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| Item Description: | Vita. "Major Subject: Physics". |
| Physical Description: | xiii, 105 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 89-96). |