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

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 ;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.