亚波长金属扫描探针的场型结构及其透射特性

Fields configurations and transmission characteristics of sub-wavelength metallic scanning probe

利用时谐电磁场理论和时域有限差分数值方法分析了亚波长金属扫描探针电磁场模式的场型结构和空间分布及透射特性等主要的传输性质,导出了亚波长金属探针内球横电模和球横磁模各电磁场分量的解析表达,运用数值求解获得的精确本征值,得到了金属探针内几个低阶模在球横截面内的场型结构.时域有限差分数值模拟研究结果表明,时谐电磁场的空间分布在亚波长金属探针内呈现准周期性振荡变化,并且在传输径向坐标上会出现一个最大值,最大值的位置随光波波长发生改变,研究结果还表明,在亚波长探针内刻蚀可以更好地激发和引导表面等离子体激元波到达出射孔径端口,提高亚波长空心锥的透射率和增强光学仪器的空间分辨率.

Based on the time-harmonic electromagnetic field theory and finite-difference time-domain （FDTD） method, the main propagation properties including the electromagnetic fields confignrations, the spatial distributions of field components and the transmission of a metallic scanning probe with a sub-wave- length-sized exit hole are analyzed. The analytical expressions for the field components of the spherical transverse-magnetic （TM） and transverse-electric （TE） modes inside the sub-wavelength metallic probe are derived. By using the accurate eigenvalues obtained numerically, some low order modal fields＇ config- urations are plotted. The numerical simulation results by FDTD show that the spatial distributions of time- harmonic electromagnetic field inside the probe vary quasi-periodically. The quasi-period has relation with the light wavelength, and there is a clearly pronounced maximum in the radial dependence. The position of an appreciable maximum for the time-averaged energy density varies rapidly with the light wavelength. It is also shown that corrugations inside the sub-wavelength probe can excite and guide the surface plasma polariton wave to exit hole better, which resulting in enhancing transmission of the sub-wavelength probe and spatial resolution of optical instrument.