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Title: Light-matter interaction in liquid crystal cells
Author: Daly, Keith Richard
ISNI:       0000 0004 2703 3654
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2011
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In this thesis we study the interactions between light and matter in photorefractive liquid crystal cells. To model the liquid crystal alignment we develop a fast and accurate approximation of the normally stiff equations which minimise the Landau-deGennes free energy of a nematic liquid crystal. The resulting equations are suitable for all configurations in which defects are not present, making them ideal for device simulation. Specifically, they offer an increase in computational efficiency by a factor of 100 while maintaining an error of order (10−4) when compared to the full stiff equations. As this approximation is based on aQ–tensor formalism, the sign reversal symmetry of the liquid crystal is respected. We consider both the simplified case, where the director is restricted to a plane, and the full three-dimensional case. An approximation of the error is also given. We use the liquid crystal model to understand two different optical effects. The first of these is optical coupling. This effect is observed in liquid crystals in both the Bragg and Raman–Nath regimes. To account for this behaviour we develop an extension to the coupled wave theory which is suitable for all regimes of coupling. The model assumes that the refractive index grating, generated by the liquid crystal, has an arbitrary profile in one direction and is periodic (but not necessarily sinusoidal) in the other. Higher order diffracted terms are considered and appropriate mismatch terms dealt with. It is shown that this model is analytically equivalent to both the Bragg and Raman–Nath regime coupling models under an appropriate set of assumptions. This model is also verified through comparison to finite element simulations of Maxwell’s equations. The second effect we model is the coupling of surface plasmon polaritons at the interface between a metal layer and a photorefractive liquid crystal cell. We implement existing numerical models to gain a thorough understanding of the system. These models are qualitatively compared with experimental observations. Analytic approximations to describe the coupling of surface plasmon polaritons at the surface of the liquid crystal cell are developed. These expressions provide a great deal of insight into the coupling mechanisms and will be of fundamental importance in optimising these systems.
Supervisor: D'alessandro, Giampaolo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA Mathematics ; QD Chemistry