Light scattering studies of two systems. I.~Surface plasmon enhanced Brillouin scattering in silver films: Double resonance effect. II.~Relation of anomalous Raman spectra of gallium-arsenide to metastable transitions of EL2 defects
Abstract
Light scattering studies of two different phenomena, Surface Plasmon enhanced Brillouin scattering and anomalous forbidden optical Raman scattering in GaAs, are presented in this work. The enhancement of surface non-linear optical phenomena by the high surface electromagnetic fields associated with surface plasmons has been extensively explored. In particular much interest has been generated by the phenomenon of Surface Enhanced Raman Scattering in which the Raman scattering cross-section of molecules adsorbed to roughened metal surfaces is found to be increased by a factor $\sim$10$\sp6$ over the cross-section in solution. The mechanism for this process, although not completely understood, is generally agreed to be a combination of a chemical mechanism and an electromagnetic mechanism. The electromagnetic enhancement is associated with the amplification in the incident light field by the excitation of electromagnetic resonances, surface plasmons, in the small metal features of the roughened surface. The very high enhancements are achieved because both the incident field and the Raman scattered field due to the adsorbed molecule are resonant with the surface plasmon excitation of the metal feature. In this work we show that a similar double resonance is achievable for surface-plasmon mediated Brillouin scattering from surface acoustic waves and measure the attendant increase in the scattering cross-section over the cases where surface plasmons are not involved, or are involved as the incident but not as the scattered radiation. For Brillouin scattering the localized plasmons associated with roughened metal surfaces are not able to give sharp line Brillouin spectra thus we used extended, propagating surface plasmons generated in a prism configuration. The second project explores the origin of the anomalous forbidden optical phonon Raman signals observed in the Nd:YAlG laser Raman spectra of GaAs. The appearance of the anomalous Raman signal was found to coincide with the quench of a band of sub-bandgap absorption associated with the EL2 defect. Our experiments showed that the anomalous signal arose as a consequence of the quench in the sample absorption.
Degree
Ph.D.
Advisors
Bray, Purdue University.
Subject Area
Condensation
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