Study On Light Scattering Characteristics And Inverse Problem Of Micro - Nano Particles

Scattering is the most common form of interactions between light and matter. Scattered light field can be used as an important information source for collecting the structural information of microscopic particles or macroscopic objects. Scattering processes can be divided into weak or strong scattering regimes, and near or far zone of the scattered field should also be distinguished. Different divisions of the scattered field carry completely different information which has been widely used in fields such as optical data storage, nano-optics, nonlinear high resolution microscopy, nano-plasmoics and advanced fluorescence imaging. This paper systematically studies two typical problems which are the cross-spectral purity of the weakly scattered field in the far zone and the near field of particle scattering and the concomitant reconstruction techniques.The research of the cross -spectral purity of weakly scattered field in the far zone, which is based on the first-order Born approximation and statistical optics, analyzes the second-order correlation property of light field in both time and frequency domain and then deeply explores a special phenomenon of spectral reconstruction, i.e., cross-spectral purity. We also extend the scalar treatment by further analyzing vector light field and derived some constraint conditions for the incident field, the scattering media as well as the observation region. The results can provide theoretical supports for practical applications of cross-spectrally pure property of scattered light. The study on particle scattering in the near field and its inverse problem is based on quasi-static approximation and researches the near field particle surface modes and its radiation patterns in a dielectric substrate. In this technique, to effectively simplify the derivations, spherical harmonic expansion and its angular spectrum representation as well as scattering amplitude T matrix method are used to analyze the optical field. This technique comes up with a dipole coefficient method for numerical calculation. The effectiveness of the proposed method is verified through the example of reconstructing a tightly focused light field and its comparison with exact theoretical results. Our methods are expected to find uses in the practical applications involving microscopic particle scattering.