Whispering Gallery Modes: Impact of resonator shape on lasing properties

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Whispering gallery modes (WGM) are the dominating optical modes in prismatic micro- and nano-wires. Using ZnO as a model system, the correlation of real geometry and the optical properties in the transparency regime and lasing regime (close to the band edge) will be investigated. Optical modes shall be determined experimentally, polarisation and angularly resolved and under optical pumping. At the positions of optical investigation, the real geometry shall be determined using scanning electron microscopy in plan-view and for cross-sections, prepared by cleaving and focussed ion beam etching. Through comparison with theoretical models, the theory of WGM in realistic geometry shall be verified. Using the boundary element method WGM theory shall be extended with aspects which so far have been neglected but seem essential for real cavities: (i) dispersion of WGM (for wave-vector along the wire) and (ii) modes in hexagonal cavities with round corners and irregular cross-section, various aspect ratios and surface roughness. The close correlation of experiments and theory allows to draw general conclusions for the effect of real geometry on optical properties of polygonal cavities beyond the used ZnO model system.