The Studies Of The Amplitude And The Phase Distributions Of The Metal-coated Probe In Near-field Region Based On The Finite-difference Time-domain Method

Near-field optics is a new interdisciplinary subject which studies the optical phenomena within the region of one wavelength near the medium interfaces. In this region, there exists abundant nanometric optical information unobtainable by the conventional means. With the rapid development of near-field optical microscopy in recent years, considerable advancement has been achieved in the studies of near-field optics. The metal-coated optical fibre probe plays an important role in the studies of the light wave propagations and in the design of near-field microscopy. By using the finite-difference time-domain (FDTD) method, this paper studies the optical near-field light field distribution of the nanometric metal-coated probe, and obtains for the first time the amplitude and phase distributions of the light field near the probe. The whole paper includes five chapters.In chapter 1, we give a summary and review of the development, the properties and the applications of the FDTD method.In chapter 2, we give a present the fundamental theories of the finite-difference time-domain (FDTD) method. Based on the Maxwell's equations, we obtain the finite-difference equations, and discuss the stability of the FDTD numerical solution and its dependence on the time and space steps. We finally discuss the numerical dispersion problems.In chapter 3, the fundamental theories of Perfectly Matched Layer (PML) absorbing boundary conditions in FDTD method are presented in detail. By setting particular medium layers on the boundary of the computational space, we give the numeration method of the light field components located on the edges of problem space, and in limited space, we modulate the light field propagation in boundless space.In chapter 4, the optical near-field distribution of a subwavelength aperture is investigated using the finite-difference time-domain (FDTD) method. The result reveals that the polarized incident wave becomes depolarized after passing through the aperture because of the discontinuousness of the medium. By using the finite-difference time-domain (FDTD) numerical solutions of the metal-coated probe tip, this paper treats the amplitude and the phase distributions of the light field in the near-field region of the tip, instead of the instantaneous light field as given in most of the literature. Taking the advantage of FDTD computation with its direct numerical realization of Maxwell equations, we study the physical essentials of the dynamic mutual inductions of electric and magnetic fields behind these characteristics of amplitude and phase distributions.In chapter 5, we give a summary of this paper, and put forward the following work plan about the study on the light field properties of silver-coated probe in the near-field region.