Random Surface And Its Light Scattering And Speckle Field Characteristics

This paper is concentrated on theoretical, experimental and simulational studies on the properties of light scattering and speckle field of random surfaces and their applications in the characterization of surfaces. The whole paper is divided into seven chapters. Chapter 1 gives a summary and review of the properties of random surfaces, the fundamental theories of light scattering, theories of non-Gaussian speckle field and the basic algorithm for the phase retrieval of light field. Chaptcr 2 gives the theoretical analysis of the central 8 -peak intensity of random rough surface and proposes an experimental method for measuring the roughness w. This method is based on the linear relationship between the logarithm of normalized central 5 -peak intensity and the square of the perpendicular component of wave vector whose variation is induced by changing the wavelength of Ar laser. In chapter 3, the morphology of random screens with different surface roughness is studied with AFM and it is found that their height distributions have very obvious fractal characteristics in short range regions. For screens with larger and smaller roughness, the fractaLs exist respectively in forms of random height fluctuations and small grains without characteristic size. The self-affine fractal surface model is introduced to the quantitative descriptions of random screens. The light scattering measurements show that: there is a halo ring in the scattered fields in the paraxial region; the scattered intensity inoff-axis region descends in negative power functions and the theoretical analysis based on self-affine fractal model indicates it is originated from the short-range fractal of the screens. Chapter 4 proposes the method for the simulational generation of self- affine random surfaces with arbitrary parameters, and simulates the light scattering intensity profiles of such surfaces and the relationships between their full-width at half-maximum (FWHM) and surface parameters. These relationships are the basis for measuring surface parameters by light scattering. Chapter 5 proposes a method for the simulational generation of Gaussian correlation random surfaces and performed the computational simulation of the speckle ld produced by this kind of surfaces on the Fraunhofer plane. 10000 speckle field samples at each spatial point produced by 10000 surface samples are taken as an ensemble and the probability density distributions of such speckle intensity ensembles are examined. We find that the Gaussian and non-Gaussian characteristics of the speckle fields are space-dependent, andthat Gaussian speckles can also be formed when the scattering surfaces contains only a few scatterers. Chapter 6 reports the flake structure in the speckle field produced by a few scattercrs by experimental observations and computer simulations. This structure appears in the off-axis region and its size is much larger than that of the normal speckles. The one-dimensional simulations show that as the roughness of the random surface sample increases or its lateral correlation length decreases, the flakes go father away from the axis, their relative intensities increase, their sizes become larger and the fluctuations in them decrease. A sub-scatterer model that we call isoclinic element is proposed to explain the formation and properties of flakes. Flake structure is a typical non- Gaussian phenomenon. In chapter 7, the light scattering microscopy is proposed...