Ultrafast optical pulse studies of metallic layers and particles.
Item
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Title
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Ultrafast optical pulse studies of metallic layers and particles.
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Identifier
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AAI9510694
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identifier
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9510694
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Creator
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Mihailidi, Margarita.
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Contributor
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Adviser: R. R. Alfano
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Date
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1994
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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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Engineering, Electronics and Electrical
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Abstract
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In this thesis, time resolved measurements of the transmissivity change in niobium has been performed with 100-fs resolution, using the pump-probe technique. The temperature dependence of the electron-phonon relaxation time in a niobium film was obtained for a range of temperatures below the Debye temperature. The temperature dependence of the electron-phonon coupling parameter, g, that governs the electron-phonon relaxation time, has been derived for temperatures below the Debye temperature. The time dependence of g has been calculated and experimentally verified for temperatures below the Debye temperature. In the picosecond time domain, temporal measurements of the transmissivity change in niobium in the transition from the superconducting to the normal state have confirmed the existence of a postulated subnanosecond transient state. The effect of niobium particle absorption on the propagation of ultrashort light pulses in dense random media was also investigated.;The change in phonon temperature in the fs time scale has been measured for ambient (initial) temperatures ranging from 292 K to 7 K. From these results the time it takes for the electrons to thermalize with phonons was extracted and it was found to decrease from 370 fs at 292 K to 250 fs at 7 K. The time dependence of the electron-phonon coupling parameter governing the electron-phonon relaxation process was determined for temperatures ranging from 292 K to 7 K, showing a complex behavior in agreement with Allen's theory.;Measurements of the transient thermotransmittance decay in the ps time scale, for ambient temperatures ranging from room to superconducting temperatures, have been performed for a niobium film and have been attributed to cooling due to heat diffusion. A change in the transient decay dynamics of thermotransmittance in the visible has been detected in the transition from the normal to the superconducting phase and was related to the onset of nonequilibrium superconductivity.;The temporal profile of an ultrafast laser pulse incident on to a dense mixture of dielectric and niobium particles, has also been investigated. The pulse duration of the outgoing light was found to decrease as the concentration of metallic particles was increased. This process was modeled with diffusion theory taking into account the phase correlation among scattered waves.
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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.
