Vector Diffraction Of A Subwavelength Metal Plate And Array Structures

With the progress of precision machining technology,the structure size of optical components has been able to reach the micro-nano level.Optical microstructures contain many unique optical properties,which have attracted the attention of more and more researchers,resulting in many new interdisciplinary disciplines,such as near-field optics,atomic optics,surface plasma photonics,optical lattice,etc.Diffraction,as a basic and important optical phenomenon,is ubiquitous in the field of optics.In this paper,the vector diffraction of a subwavelength metal circular plate and its array structure is studied.This article summarized optical properties of vector optical fields,the research and application of vector optical fields and vector beams.The basic principle of vector diffraction theory is intruduced.The characteristics and excitation modes of surface plasmons have been reviewed.The vector diffraction of linearly polarized plane wave passing through a thin circular plate with a sub-wavelength radius is investigated by the finite element method.The transverse distribution and propagating evolution of the diffracted field with different intensity expressions are analyzed and compared.It is found that there are not only the component of the incident polarization,but also those of other two vertical directions in the near-field diffracted region.Regardless of the relationship between the wavelength and the radius of the circular plate,the diffracted field could evolve into a steady annular diffracted pattern,in which there is a central bright spot(so-called Poisson spot).There is an obvious difference of the diffracted properties between two intensity expressions from the square of electric field and the average magnitude of the Poynting vector as the propagation distance is very small,while they can be considered same with a large propagation distance(e.g.more than a wavelength).Based on the vector plane angular spectrum method,the analytical expression of a linearly polarized gaussian beam passing through a subwavelength circular plate is derived.Mathematic numerical calculation software was used to study the evolution of evanescence field and propagation field in near field.The magnetic field characteristics of circular plate diffraction are studied.It isfound that the two-dimensional distribution pattern of magnetic field is similar to that of electric field.The evolution of magnetic field is obviously different from that of electric field.A hybrid system of a thin metal disk coupled with atoms is proposed.A sub-wavelength well is formed within 100 nanometre of the thin metal disk,in which the small number of cold atoms could be trapped.The trapped distance and volume of the potential well could be controlled by changing the parameters of the disk.The results provide a new hybrid system for nano-micro optical devices and atomic physics.On the basis of single circular plate diffraction in the first two chapters,the 3×3metal circular plate array is discussed.In Comsol simulation calculation.The optical field distribution near the circular plate array at different incident wavelengths has been discussed.The distribution of localized surface plasmon on circular plates,the effect of local field enhancement and the variation of absorption spectra under different parameters are analyzed.The similarities and differences between the near-field coupling of the diffraction field and the coupling of the localized surface plasmon are studied.Finally,the effect of the silica substrate on the intensity is discussed.