The Study Of The Near-field Of Metallic Nanostructure Based On The Finite-difference Time-domain Method

The study about the surface plasmons (SPs) in metal with nanostructure has been attracted lots of attentions in recent years. Recurring to the excitation of SPs, the power of the beam can be concentrated and released so as to control the wave within the sub-wavelength. This is important for the design of the nano-optics devices, such as nano-antennas, sub-wavelength imaging and super-resolution lenses. Therefore, the study about SPs is a hot subject in optical field, and a fundamental branch of optics, i.e., the surface Plasmon sub-wavelength optics, is formed. The propagation rule of the wave through the metal nano-slit or the periodical structure is a basis question in the study of SPs. The near-field discussion about the nano-slit has important significance for the foundational study of SPs.In this paper, using the two dimensional dispersive finite-difference time-domain (2D-Dispersive FDTD) method, we study the continuity of the electromagnetic wave on the metallic sliver boundary and contrast the transmissions of the perfect conductor and the metallic sliver. We calculate numerically the transmission field and transmission spectra of a single-slit and give the physical explanation about the abnormal transmission phenomenon. The whole paper includes five chapters.In chapter 1, we introduce the topic of the research background, and give a brief overview of the near-field optical with the surface plasmons (SPs) applications.In chapter 2, we describe the finite-difference time-domain (FDTD) method. We discuss the stability of the numerical solution about FDTD and its relationship of the temporal step and spatial step. The fundamental theories of Perfectly Matched Layer (PML) absorbing boundary conditions in FDTD method is presented too.In chapter 3, for the metal with the negative refractive index, we introduce the model of Lorentz dispersion, and write the calculation program in Fortran language. Through the modulation of the program on the boundary of the metal and the vacuum, the continuation conditions of the electromagnetic fields on the boundary are also satisfied. In chapter 4, the transmission characteristics of silver nano-slit have been calculated on the basis of the two dimensional dispersive finite-difference time-domain method. The continuation conditions of electromagnetic field on the boundary of the sliver and the vacuum are verified. Finally, the physical explanation about the unusual transmission phenomenon has been presented.In chapter 5, we give a summary of this paper, and put forward the following work.