Spectral properties and modes of surface microcavities

Abstract

This thesis describes the experimental investigations into the transverse mode structure of nearly hemispherical microcavities. The nearly hemispherical microcavity structures are fabricated electrocemically through a template of self assembled latex spheres. Controlling the electrochemical parameters, such as the electrochemical solution and electrode potential. allows a wide range of nearly hemispherical microcavities to be realised.
The spatial intensity profiles arid resonant frequencies of the transverse modes of nearly hemispherical microcavities are measured experimentally for a wide range of cavity lengths amid mirror curvatures. The experimental mode profiles are radially symmetric Gauss-Laguerre modes, but do not display the frequency degeneracies typical of large scale optical cavities. The nearly hemispherical microcavity samples are compared to investigate how the cavity parameters. such as cavity length and mirror curvature, affect the experimental spatial intensity profiles and resonant frequencies of the transverse modes. Higher order modes are observed despite the fact that they are forbidden due to the symmetrical coupling geometry. the symmetry breaking is shown to be produced by the surface roughness of the curved mirror.
The frequency degeneracy lifting which occurs in the nearly hemispherical microcavity structures can he explained and modelled by considering non-parabolic elements in the cavity. A number of mathematical models for the cavity propagation are developed based on paraxial theory. these models are analysed and the predictions made from the models are compared with the experimental profiles and frequencies. The basic agreement between theory and experiment shows that the paraxial theory is able to model the cavity modes. However, the spectrum and the mode profiles are quite sensitive functions of the geometry of the cavity amid the surface roughness of the cavity mirrors.
The nearly hemispherical microcavities are structures which offer a new fabrication technique allowing inexpensive and a uncomplicated method of fabrication. An important feature of the nearly hemispherical microcavities is the tunability, and the ease in which this can be achieved. The structures are also empty, and this will allow them, in the future, to be easily filled with functional optical materials such as liquid crystals.

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