| The photorefractive surface waves (PR SWs) are a kind of waves which can propagate along the surface of the photorefractive materials. The most attractive feature of PR SWs is that the concentration of beam energy with high intensity in the narrow surface layer, which ensures various nonlinear surface optical phenomena to be enhanced. So PR SWs are potentially useful for waveguide fabrication, harmonic generation, integrated optics technique and so on.Although some elementary research about PR SWs has been done, there are still many problems, such as the formation mechanism, mode modulation, and stability of PR SWs, need to be studied further. In addition, with the development of new photorefractive materials, such as two-photon photorefractive crystal, photorefractive polymer and liquid crystal, the photorefractive performance has been improved dramatically. In this dissertation, the PR SWs are studied systematically. The main contents are shown as follows:(1) The formation mechanism of PR SWs is studied. The influences of diffusion, drift, and photovoltaic effect on the PR SWs are analyzed. The analytical results show that:diffusion nonlinearity is the essential cause for the formation of PR SWs. The drift and photovoltaic nonlinearity are not necessary in the formation of PR SWs；but they can be used to modulate the modes of PR SWs.(2) The generation and mode characteristics of PR SWs are analyzed; the relationship between the modes of PR SWs and the incident angles or propagating constants was presented:the large angles of incidence correspond to the large propagating constants and low-frequency modes, while the small angles of incidence correspond to the small propagating constants and high-frequency modes.(3) The stability of PR SWs is analyzed. The equivalent oscillator model is presented and used to do quantitative analysis of the PR SWs'stability. The analytical results show that:the electrical field has a threshold as Eth=(k02n2-β2)/k02n4reff, above which the PR SWs will be destructed. The spatial-partition fast Fourier transform beam propagation theory is used to test the stability of PR SWs.(4) The formation and properties of PR SWs in two-photon photorefractive medium are studied. The surface waveguides induced by single-photon PR SWs can be erased and recorded easily. However, the recording reversibility also makes them volatile and can not be stored for long period. Due to the two step photorefractive mechanism, the two-photon PR SWs can induce surface waveguides with no erasure problem, which supplies a feasible method for creating permanent surface waveguides. (5) The PR SWs in photorefractive polymer and liquid crystal are studied systematically. Organic photorefractive materials can provide many advantages over the traditional inorganic crystals, which include cheapness, flexibility of fabrication, wide working wavelength range, ease of processing, and improvement of PR effect. In this dissertation, the theoretic models for PR SWs in polymer and liquid crystal are presented, the analytical results show that:the applied external electric field can change not only the spatial frequency but also the penetration depth of the polymeric and liquid crystal PR SWs. Moreover, the properties of PR SWs in polymer and liquid crystal are polarization-dependent. Additionly, the PR SWs in liquid crystal can be excitated and modulated with much low electric field. These properties make the PR SWs in polymer and liquid crystal more controllable than that in inorganic photorefractive crystals. By taking advantage of the above characteristics, the performance of PR SWs can be improved dramatically and used widely.In this dissertation, the PR SWs are studied systematically. The innovative points are as follows:1. The equivalent oscillator model is presented for the first time. It is shown theoretically that the diffusion nonlinearity is necessary in the formation of PR SWs, while the drift and photovoltaic nonlinearity are not essential causes for the formation of PR SWs；but they can be used to modulate the modes of PR SWs. The relationship between the modes of PR SWs and the incident angles or propagating constants was presented. The method based on equivalent oscillator model to anlyze the stability is presented and can used to analyze quantitatively the influence of the applied external electric field on PR SWs.2. We predict that the PR SWs can be supported by two-photon photorefractive medium. The two-photon PR SWs can induce surface waveguides that can be stored for long period.3. The theoretical framework for PR SWs in polymer and liquid crystal is presented. It is shown theoretically that PR SWs can form in photorefractive liquid crystal. Due to the orientationally enhanced photorefractive effect, the applied external electric field can change not only the spatial frequency but also the penetration depth of the PR SWs in polymer and liquid crystal.
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