The absorptive and dispersive properties of a Doppler-broadened vapour of rubidium atoms is investigated. A detailed model of the atom-light interaction is developed and found to be in excellent agreement with experiment in the regime where the interacting light field is sufficiently weak such that it does not significantly alter the medium through which it propagates. The importance of using a weak beam to probe atomic systems is discussed, and a method of characterising how weak such a beam has to be is provided. The theoretical model is applied to both situations of illumination by continuous-wave and pulsed light, the latter situation providing a demonstration of the slow light effect. This phenomenon is a manifestation of the dispersive properties of the medium and is shown to exist over a particularly large frequency range, compared to the absorption spectrum, in thermal vapours. Off-resonant interactions are studied, in which incident laser-light is detuned from resonance to such a degree that Doppler-broadening can be neglected. We quantify the extent to which the light needs to be detuned to be in this regime, and provide approximations to the line-shape function developed in earlier parts of the thesis. The approximate line-shapes are much easier to manipulate and allow a more intuitive understanding of the atom-light interaction. In the second part of the thesis we study the Faraday effect and related phenomena which are an expression of the birefringent properties of the atom-light system. Beginning with a theoretical and experimental investigation of the Faraday rotation of a weak continuous-wave beam, we move on to the consideration of pulsed light. Optically-induced birefringence via the application of an intense continuous-wave pumping field is demonstrated experimentally, and the theoretical plausibility of controlling the polarisation state of a weak pulsed field mediated via intense pulsed light is shown.

A computational approach is taken to studying a range of light-matter interactions which are interesting in terms of their potential applications as well as from a fundamental point of view. Two different types of polariton, part-light, part-matter quasiparticles, namely exciton-polaritons and Tamm plasmon-polaritons (a type of surface plasmon-polariton) are considered. The conditions required for the strong coupling of optical whispering gallery modes and bulk excitons in submicron spheres are ascertained for the materials gallium arsenide, gallium nitride and zinc oxide. It is shown that the strong coupling regime may be accessed by optical modes with a low decay constant, typically exhibited by those modes with higher angular momentum quantum numbers. Tamm plasmon-polaritons have previously been shown to exist at the boundary between a metal and a planar Bragg reflector structure. The conditions required for the formation of Tamm plasmon-polaritons in cylindrical multilayer structures with a metal core, cladding or metal in both of these locations are determined. The cylindrical Tamm plasmon-polaritons are shown to have low effective masses and low group velocities. It is also shown that it is possible to obtain split polariton modes in structures containing metal in both the core and the cladding. The effect of disorder on a two-dimensional photonic crystal structure consisting of air holes in a slab of dielectric material is studied. It is shown that the defined threshold disorder is not signicantly affected by the dierent relative band widths of the ideal crystal structures considered.

Surface Plasmon Resonance (SPR) has been utilised in various forms in sensors for many years. It is usually based on angular or wavelength interrogation of the reflectivity minimum found with Transverse Magnetic (TM) light. However, as the SPR is traversed there is also a very rapid change in the phase of the reflected TM light there being no such change in the Transverse Electric (TE) light. Presented in the thesis a new SPR sensor has been developed that exploits this rapid change in optical phase. Linearly polarised light of mixed TM/TE polarisation is passed through a polarization modulator, which adds a small amplitude modulation to the polarisation. This modulated light is incident on a gold film 40 nm thick evaporated onto the base of a SF2 prism in the Kretschmann-Raether, configuration. The coupling of the TM polarised light to the SPR is dependant on the properties of the dielectric medium adjacent to the gold film. The SPR shifts when this sensed medium undergoes a change in refractive index (or index or thickness if it is a bound analyte layer). This in turn causes a change in the reflected elliptically polarised light. The change of the resultant modulated polarisation dither is interrogated through the use of a phase sensitive detectors. Initially a simple photo diode coupled with a lock-in amplifier was used to monitor the modulated signal. This was expanded into an imaging technique by using two cameras (64 by 64 pixels) fabricated with the equivalent of a lock-in amplifier on each of the 4096 pixels. The spatial map of the modulation amplitude gives an optical phase differential image. By imaging in this way it is possible to produce a multi channel differential sensor

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