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|Title:||I. Resonant Two-Photon Reabsorption by Exciton-Polaritons in Cuprous Chloride Films. Ii. Heat Pulse Propagation Across Metal/sapphire Interfaces. Iii. Phonon Focusing in Piezoelectric Crystals|
|Author(s):||Koos, Gregory Lee|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||The work described in this thesis involves the study of optical and thermal properties of semiconductors and consists of three separate topics.
I. Resonant two-photon absorption by exciton polaritons in CuCl films. A study of the lineshape and intensity of the biexciton decay luminescence reveals a two-photon reabsorption process in which the longitudinal exciton and the transverse polariton act as resonant intermediate states. Dispersion information on these states at large momentum is produced and a simplified theory of the resonant resonant reabsorption process is described.
II. Heat pulse propagation across metal/sapphire interfaces. The angular dependence of ballistic phonon propagation in sapphire is found to exhibit three distinct types of features. The first corresponds to mathematical singularities in the bulk phonon focusing. The second type of feature observed corresponds directions in which the phonon flux exhibits a local but nonsingular maximum. These features are termed "precursors" because they will transform into normal singularities if the elastic constants are modified slightly. These two types of features are readily predicted by classical elasticity theory. The third type of feature is a surface effect in which a consentration of transverse phonons near the critical cone for mode conversion from bulk transverse waves to longitudinal waves along the surface. It is found to be dependent on surface orientation and is very sensitive to surface quality. A theory by A. Every is described in which this feature is due to a longitudinal pseudo-surface wave on free or weakly bonded surfaces.
III. Phonon Focusing in Piezoelectric Crystals. The calculation of phonon focusing patterns through classical elasticity theory is extended to include the piezoelectric effect in the quasistatic limit through the use of "stiffened" elastic constants. Good agreement between experimental and theoretical predictions is obtained. While the effect is small for (alpha)-quartz it is dramatic for lithium niobate.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2015-05-13|