The Study Of The Properties Of The Near-field Speckles And The Femtosecond Laser Pulses' Near-field Speckles Using Numerical Solutions Of Green's Integral Equation

Near-field optics is a new interdisciplinary subject which studies the optical phenomena within one wavelength, and it breaks free from the limitation of conventional optical resolution. 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 paper is concentrated on simulational and theoretical studies on the the properties of near-field speckles of the random surfaces and the femtosecond laser pulses. The whole paper is divided into four chapters.In chapter 1, we gives a summary and review of the description of random surfaces and its near-field speckles, the fundamental theories of light scattering, the properties of random light fields and near-field optics.In chapter 2, we present a method with Green functions and the boundary conditions for the simulational generation of light scattering from random surface with arbitrary parameters, and compare this method with the method of Kirchhoff approximation and near-field light scattering and speckle field. We simulate near-field speckles generated by the self-affine fractal surface samples with different surface parameters and different length, and then study in detail them and discover some properties of the near-field speckles. We also simulate the transmission of light scattering with different distance from the surface. When we compare the method of the Green's function with the method of Kirchhoff approximation, we find that the smaller the roughness of random surfaces is, the higher theprecision of the Kirchhoff approximation is. At the condition of the same roughness, smaller the roughness exponent of random surfaces is, the higher the precision of the Kirchhoff approximation is.In chapter 3, by use of a numerical calculation based on Green's integral equation, we study the near-field speckles produced by the random self-affine fractal surfaces of a dielectric medium. We computer and study the properties of the near-field speckles produced by random self-affine fractal surfaces with different surface parameter illuminated by the femtosecond laser pulses with the different temporal width, and find that the near-field speckles have a close relationship with the femtosecond laser pulses and the random self-affine fractal surfaces.In chapter 4, we calculate and study the diffraction of the femtosecond laser pulse propagating through a subwavelength aperture with the method of the Green functions. After the femtosecond laser pulse propagate through a subwavelength aperture they propagate along the interface, and in the propagating process the light wave, the nodes of the light intensity are produced at the interface and the region near the interface, the temporal width of the femtosecond laser pulses will be broadened, and the light intensity at the spatial points near the nodes will be splited into two pulses with respect to time.