Year: 2014
Type: dissertation
Abstract: The theory of quantum electrodynamics is employed in the description of linear and \nnonlinear optical effects. We study the effects of using a two energy level \napproximation in simplifying expressions obtained from perturbation theory, \nequivalent to truncating the completeness relation. However, applying a two-level \nmodel with a lack of regard for its domain of validity may deliver misleading results. \nA new theorem on the expectation values of analytical operator functions imposes \nadditional constraints on any atom or molecule modelled as a two-level system. We \nintroduce measures designed to indicate occasions when the two-level approximation \nmay be valid. \nAnalysis of the optical angular momentum operator delivers a division into spin \nand orbital parts satisfying electric-magnetic democracy, and determine a new \ncompartmentalisation of the optical angular momentum. An analysis is performed on \nthe recently rediscovered optical chirality, and its corresponding flux, delivering \nresults proportional to the helicity and spin angular momentum in monochromatic \nbeams. A new polarisation basis is introduced to determine the maximum values that \nan infinite family of optical helicity- and spin- type measures may take, and disproves \nrecent claims of ‘superchiral light’. A theoretical description of recent experiments \nrelate helicity- and spin- type measures to the circular differential response of \nmolecules, and show that nodal enhancements to circular dichroism relate only to \nphoton number-phase uncertainty relation and do not signify ‘superchiral’ regions. \nThe six-wave mixing of optical vortex input, in nonlinear media, demonstrates the \nquantum entanglement of pairs of optical vortex modes. The probability for each \npossible output pair displays a combinatorial weighting, associated with Pascal’s \ntriangle. \nA quantum electrodynamic analysis of the effect of a second body on absorption \ncan be extended by integrating over all possible positions of the mediator molecules, \nmodelling a continuous medium. This provides links with both the molecular and \nbulk properties of materials.
Author: M.E. Coles
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W241982220