Bibliography: p. 153-170. / The nature of optical whispering-gallery-mode resonances in a layered microcylinder is investigated numerically by studying the scattering characteristics and the internal electromagnetic fields of a normally-illuminated cladded dielectric fiber calculated using the boundary-value method. Computed resonant mode configurations are compared to the better-known results for homogeneous spheres and cylinders and coated spheres. It is shown that high-Q whispering-gallery-mode resonances can be supported by the curved interface between the core and cladding regions of a layered fiber if the core refractive index is sufficiently greater than that of the outer layer, and that these modes can be directly related to the so-called morphology-dependent resonances of a homogeneous cylinder of the same size and relative refractive index as the fiber core. The implications of these resonant modes for inelastic optical processes are made clear by developing a model for optical emissions from a molecule in the core of a capillary fiber. The results of the model show that the transition rates of molecules in the fiber core and near to the core/cladding interface are enhanced at frequencies corresponding to cavity resonances. It is shown experimentally that these high-Q cavity modes can be excited to above the threshold for laser emission by providing gain in the fiber core material. We have used a refractive dye-doped solvent as a gain medium and a fused-silica capillary to form the resonant cavity. Upon optical excitation of the dye by illuminating the fiber normally with the green beam from a frequency-doubled Nd:YAG laser, laser emission is emitted from the fiber core in the plane perpendicular to the fiber axis. We explain the novel spatial and spectral dependences of the laser emission in terms of the calculated frequencies and Q-values of the resonant cavity modes and the bulk properties of the cavity medium. We show that the thresholds observed in the laser system can be explained using a simplified rate-equation approach, and that this also explains some of the other observed features of the emissions. The heating of the dye solvent during a laser pulse has an observable effect on the resonance mode locations due to the temperature dependence of the refractive index. We demonstrate the use of observed laser spectra to determine the size and taper of the capillary fiber core.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/17386 |
| Date | January 1993 |
| Creators | Knight, Jonathan Cave |
| Contributors | Robertson, G N, Driver, H S T |
| Publisher | University of Cape Town, Faculty of Science, Department of Physics |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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