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Ultrafast spectroscopy of semiconducting and multiferroic materials
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Title
Ultrafast spectroscopy of semiconducting and multiferroic materials
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Lou
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Shitao
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Shitao Lou
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author
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Zimmermann
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Frank
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Advisory Committee
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Frank M Zimmermann
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chair
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Bartynski
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Robert
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Advisory Committee
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Robert A Bartynski
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co-chair
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David Vanderbilt
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David
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Advisory Committee
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David David Vanderbilt
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internal member
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Murnick
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Daniel
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Advisory Committee
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Daniel E Murnick
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internal member
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Mitrofanov
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Oleg
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Advisory Committee
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Oleg Mitrofanov
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outside member
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Rutgers University
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degree grantor
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Graduate School - New Brunswick
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Text
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theses
OriginInfo
DateCreated
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2007
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2007
Language
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English
PhysicalDescription
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electronic
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application/pdf
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text/xml
Extent
xii, 114 pages
Abstract
In this thesis, we have used ultrafast spectroscopy to study the optical properties of two semiconductors, GaAs and Ge, and one hexagonal multiferroic material, LuMnO3. Both semiconductor and multiferroic materials are of great importance technologically and economically. By using ultrafast spectroscopy, we obtained time resolved electron and phonon dynamics directly, which is unavailable by conventional optical methods.
Electron-hole pairs, coherent phonon oscillations and an optical coherence response are excited when femtosecond laser pulses interact with either GaAs or Ge crystals. The coherent phonon mode excited in GaAs/Ge is of T2/T2g symmetry as determined by probe beam polarization analysis. The pump polarization dependence of the phonon oscillation is consistent with the transient stimulated Raman scattering (TSRS) mechanism. From the pump polarization dependence of the phonon oscillation, we have identified two excitation mechanisms contributing to the coherent phonon in GaAs,one is consistent with TSRS, and the other is consistent with screening effect of photoexcited electrons.
The femtosecond laser pulse, with 800 nm center wavelength and polarized perpendicular to the c axis of LuMnO3, excites a narrow intra-atomic dxy, x2-y2 to d3z2-r2 transition in Mn. This excitation results in a transient reflectivity change for light of the same wavelength and polarization, by partial saturation of the transition. The relaxation time of this electronic excitation is about 1 ps. Furthermore, the electronic excitation resonantly excites a coherent optical phonon with A1 symmetry (TO: 118 cm-1 and LO: 120 cm-1), involving Lu ions motion along the c-axis, which is identified to be the soft mode driving the ferroelectric transition. A remarkable reversal of the sign of the oscillation amplitude ([pi sign] phase shift) of the reflectivity curve was observed upon comparing longitudinal optical (LO) with transverse optical (TO) mode geometries. The phase reversal is attributed to the macroscopic electric depolarization field accompanying IR active longitudinal phonon modes, but absent in TO modes, or to coupling of LO phonon coordinate to a change in ferroelectric polarization upon to excitation via a macroscopic electric field.
Electron-hole pairs, coherent phonon oscillations and an optical coherence response are excited when femtosecond laser pulses interact with either GaAs or Ge crystals. The coherent phonon mode excited in GaAs/Ge is of T2/T2g symmetry as determined by probe beam polarization analysis. The pump polarization dependence of the phonon oscillation is consistent with the transient stimulated Raman scattering (TSRS) mechanism. From the pump polarization dependence of the phonon oscillation, we have identified two excitation mechanisms contributing to the coherent phonon in GaAs,one is consistent with TSRS, and the other is consistent with screening effect of photoexcited electrons.
The femtosecond laser pulse, with 800 nm center wavelength and polarized perpendicular to the c axis of LuMnO3, excites a narrow intra-atomic dxy, x2-y2 to d3z2-r2 transition in Mn. This excitation results in a transient reflectivity change for light of the same wavelength and polarization, by partial saturation of the transition. The relaxation time of this electronic excitation is about 1 ps. Furthermore, the electronic excitation resonantly excites a coherent optical phonon with A1 symmetry (TO: 118 cm-1 and LO: 120 cm-1), involving Lu ions motion along the c-axis, which is identified to be the soft mode driving the ferroelectric transition. A remarkable reversal of the sign of the oscillation amplitude ([pi sign] phase shift) of the reflectivity curve was observed upon comparing longitudinal optical (LO) with transverse optical (TO) mode geometries. The phase reversal is attributed to the macroscopic electric depolarization field accompanying IR active longitudinal phonon modes, but absent in TO modes, or to coupling of LO phonon coordinate to a change in ferroelectric polarization upon to excitation via a macroscopic electric field.
Note
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Ph.D.
Note
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Includes bibliographical references (p. 103-112).
Subject
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Topic
Physics and Astronomy
Subject
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Topic
Semiconductors
Subject
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Topic
Ferroelectric devices
Subject
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Topic
Nanotechnology
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Graduate School - New Brunswick Electronic Theses and Dissertations
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rucore19991600001
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http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.16732
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ETD_466
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Identifier
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doi:10.7282/T3KH0NR8
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ETD doctoral
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The author owns the copyright to this work.
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Copyright protected
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Open
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Shitao Lou
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Rutgers University. Graduate School - New Brunswick
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Non-exclusive ETD license
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Author Agreement License
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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