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Polariton optics of spherical nanostructures

This thesis describes the completely coherent polariton optics of a spherical semiconductor photonic dot (PD). Our theoretical model solves the eigen-modes of the system to produce the polariton frequencies as a function of the PD radius, o (a), where the photonic modes with A = 2a are resonant with the sphere. Dispersion curves are classified into the weak and strong coupling regimes according to crossing/anti-crossing of the polariton branches, in analogy with polaritons in bulk materials. We assume the coherent distribution of energy between the photonic and excitonic branches in order to calculate the total radiative linewidth. The effect of spatial dispersion of excitons is considered using the dispersion equations developed by Ruppin and the Pekar Additional Boundary Condition. The asymptotic values of the resulting dispersion curves are described, and plots of the dispersion curves for a CuCl PD show low-order modes (n = 1 and 2) to be in the weak coupling regime, whilst n = 3 and 4 are in the strong regime. Our analysis of the radiative linewidth, both including and excluding spatial dispersion, produces a 1/a dependence for Tn for large radii, corresponding the "ballistic escape" of optically-dressed excitons from the PD. The low-radius behaviour, usually described as an a3 volume-dependent increase of the oscillator strength, is shown to be more complex with powers from a1 - a7 depending on the mode polarisation and the presence/absence of spatial dispersion. The transition between weak and strong coupling regimes is identified as a discrete point at which the two polariton branches meet, characterised by critical values of the Rabi frequency, dielectric permittivities of the PD and surrounding material, and the PD radius, which have been obtained analytically and numerically. We propose the observation of the transition point via derivatives of the radiative linewidth, using high-precision modulation techniques.
Date January 2005
CreatorsSmith, Andrew
PublisherCardiff University
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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