The Properties Of Non-uniform Amplitude, Partially Coherent And Partially Polarized Beams On Weak Scattering

When light is incident on an inhomogeneous object, it will deviate from its own path and is scattered in other directions. The phenomenon of light deviated from its original path to other directions, which is caused by the inhomogeneity of the media, is referred to as light wave scattering. The light wave scattering may cover a wide range of phenomena associated with the interaction of light waves with material media. For example, the scatterer may be determinate or random, isotropic or anisotropic, continuous media or particle collections, and the incident light may be monochromatic or polychromatic, scalar or vector. But until recently, the researches for the light scattering have been mainly devoted to the scattering of plane waves. On the other hand, the development of the first ruby laser in the 1960s makes it possible to produce a laser beam, which has good directivity, monochromaticity, coherency and high brightness. After that, the investigations for the propagation and scattering properties of various laser beams through different optical systems and media have attracted lots of researchers’interests, due to the potential practical applications in optical communications, remote sensing, detection, medical diagnosis and so on. In this situation, the optical properties of non-uniform amplitude, partially coherent and partially polarized beams scattered from a deterministic or a random medium are detailed investigated in this dissertation within the accuracy of the first-order Born approximation, and the influences of different source parameters (i.e., the beam width, the source correlation width, the two spectral amplitudes and the value of beam profile) and scatterer parameters (i.e., the effective radius and the correlation length) on the spectral density, spectral degree of coherence, spectral degree of polarization, correlation of intensity fluctuations and spectral shifts of the far-zone scattered field are discussed carefully. The dissertation is arranged as follows:Chapter 1 is the introduction, which has two parts. Firstly, the research background and status of light wave scattering are given. By analyzing the actuality and trend at home and abroad, the motivation and significance of the dissertation can be presented clearly. Then the methods and theoretical bases used in the content are stated as follows:weak scattering theory of scalar light waves; weak scattering theory of vector light waves; angular spectrum representation of light fields.In Chapter 2, the weak scattering properties of a non-uniform amplitude beam and a partially coherent beam are investigated. A Hermite-Gaussian beam and a multi-Gaussian Schell-mdel beam are took as examples in the process of numerical simulations, respectively, and the method of angular spectrum representation of plane waves is used to describe the incident beam. When a plane wave is scattered by a deterministic or a random medium, the scattered field is derived by the integral equation of potential scattering, and by the superposition of all the scattered fields, the total scattered field is obtained. After that, by use of the cross-spectral density function of the total scattered field, the statistical properties, including the spectral density and spectral degree of coherence can be discussed.In Chapter 3, the weak scattering properties of stochastic electromagnetic beams are studied carefully. Firstly, the recently introduced scalar rectangular Gaussian Schell-model source is extended to its electromagnetic form and the statistical properties, including the spectral density, spectral degree of coherence and spectral degree of polarization are discussed when the electromagnetic form of the source is scattered from a deterministic medium. Then the correlation of intensity fluctuations of the far-zone scattered field is also considered when an electromagnetic Gaussian Schell-model source is scattered by a random medium. The investigation for the weak scattering theory of stochastic electromagnetic beams needs a vector treatment to deal with the polarization of the incident beam, and the cross-spectral density matrix is introduced to describe the statistical properties of the scattered fieldIn Chapter 4, the spectral shifts of partially coherent light waves on scattering are discussed. In the process of numerical simulation the rectangular Gaussian Schell-model sources are used as examples, and the influences of different source parameters (i.e., the source width, the correlation widths and the value of beam profile), scatterer parameter (i.e., the effective radius of the media) and the scattering direction on the spectral shifts are illustrated carefully.In Chapter 5, the main conclusions and innovations of the dissertation are given, and the plans for future work are also presented.