The Characterization Of The Random Surfaces By Speckles And The Properties Of The Near-field Speckles

Great attention has been paid on the study of random surfaces in many scientific and technological fields such as the growth fronts of thin films, surfaces of fabricated optical devices, and the fractured cross-section of materials, etc.. With the rapid development of near-field optical microscopy in recent years, considerable advancement has been achieved theoretically and experimentally in the studies of near-field optics. This dissertation is concentrated on theoretical, experimental and simulational studies on the characterizations of random surface by speckle methods and the properties of speckles in near-field. The whole dissertation is divided into four chapters.In chaper 1, we give a summary and an overall review for the descriptions and measurements of random surfaces , the light scattering theory and its applications in the characterization of random surfaces, and the near-field optics and the near-field speckles.In chaper 2, we present a method for the extraction of the height-height correlation function of random rough surfaces from the data of average intensity of image speckles. Based on the theoretical expression of the average intensity in the Fourier transforming and imaging optical system with variable aperture, an algorithm is developed to change the intensity data versus the aperture radius into the Bessel-Fourier-transform-and-the-inversion of a function of the height-height correlation function. Three samples of Gaussian correlation are used for the experimental demonstration. The extracted height-height correlation function and the random surface parameters obtained ever since conform with those obtained by the measurement of AFMIn chaper 3, based on the light scattering theory of Kirchoff approximation, we propose the method for the extraction of surfaces parameters from the correlation functionsof speckles intensity produced by light scattering in the region near the random surfaces. The quantitative expression for speckle correlation function is formulated, in which the scattered intensity profile reciprocated on the surface plane acts as the aperture function in Van Cittert-Zernike theorem. By least-squares fit of the measured data of speckle correlation function to the obtained quantitative expression, parameters of random surfaces can be extracted. The theory and the method are validated by the simulational experiments, in which the scattering from random self-affme fractal surface are simulated and the speckle intensity correlation function are calculated. The extracted values of 3 surface parameters i.e., the roughness w, lateral correlation length ξ, and roughnessexponent a are in good accordance with the set values.Chaper 4, we put forward the concept of the near-field speckles and study their properties by the numerical solution of the integral equation based on the Green's theorem. We study the near-field speckles produced the by random self-affine fractal surfaces of dielectric medium. The speckle intensities evolve considerably in the near-field region and the local fluctuations in them disappear in the distance of a wavelength. The transition of the speckle contrast either on the surface or in the near-field and the neighborhood non-near-field regions depends on lateral correlation length ξ and the roughnessexponent a of the random surfaces. Preliminary qualitative explanations are given to the computation results based on the analogy of the integral equation to the point spread function in the conventional diffraction theory.