Near-field Optical Microscopy Imaging Numerical Simulation Study

Near- field optical microscope is a new type of super-resolution optical microscope developed for the recent twenty years. It obtains the various optical images of the sample's nanometer surface, transcended the diffraction limit of conventional optical microscope, by using a fine optical-fiber tip probing ultra-high frequency optical information on the sample surface. And it has extensively been applied on life science, chemistry and material science fields.This thesis concentrates on the mesoscopic sample's electromagnetic field distributions and numerical simulations of scanning imaging process of near-field optics. That aims at clarifying near-field imaging process theoretically, providing the scientific basis for correctly interpretation of near-field optical images and developing new class instruments.The thesis mainly includes the following three parts:1. The finite-difference time-domain method is applied to imaging system of near-field optics, in order to solve the complicated problem about theoretical calculation of near-field optics. The three-wave method under the total internal reflection in PSTM was proposed and developed firstly, resolving the incident source technique problem. The application of Perfectly Matched Layer absorption boundary condition is researched and carried out. It is realized that FDTD method is applied to metal thin film and the dynamics equations for plasma and Maxwell's discretized formulas are presented. Here the scattered field formulas applied to Photon Scanning Tunneling Microscope are perfected. Numerical simulations of the imaging of system of realistic near-field optics are resolved well.2. The imaging mechanism of PSTM is explored deeply. The perturbation approach method and Finite-Difference Time-Domain method are applied to PSTM system respectively. The perturbation approach method combined eliminating spurious images theory is extended to the multiplayer system of PSTM. We simulated the imaging of a periodic sample for correcting the shift of the images of the sample. The perturbation approach method applied to PSTM is further perfected. The thesis studied and discussed the near-field distribution depending on scale and the thickness of the sample for p-polarized incident light. The photon tunneling effects are showed firstly. We simulated the scanning imaging process in the realistic experimentalconditions for using a bare probe tip and a metallic probe tip respectively. The scanning modes influenced on the images and the resolutions are discussed. The numerical results are consistent with the published articles and the experimental results. The high-resolution PSTM images can be qualitatively understood using dipole model of the classical electromagnetic field.The samples are limited for conventional PSTM imaging. The surface topographical images and the refractive index images can only be obtained for the samples of uniformity of the refractive index and topographical surface or flat surface and varied refractive index. The images of the samples of either varied refractive index or topographical surface show their mix images. In order to solve the problem, this paper introduces the principle of a new generation of AF/PSTM and theoretical basis of separated topography and refractive index images, which a bent optical fiber tip does a dither on constant amplitude and scans in constant mean gap mode in AF/PSTM. The diagram of AF/PSTM system is presented. The formula of refractive index imaging is proved by FDTD method. We simulated the images of MgF2 film with holes on optical glass and the results are consistent with the experimental results. Moreover, the images of separated topography and refractive index are presented for one scanning.3. The key element of scanning near-field optical microscopy (SNOM) breaking the diffraction limit to realize super resolution is the light source of sub-wavelength scale. The most challenge work is the design of optical probe in SNOM to realize two contrary demands: higher throughput and smaller light spot siz...