Numerical analysis for lacarized and ehnhaneed surface plasmon polariton of near field of dumbbell-Shaped aperture in the metallic screen.

金属屏亚波长孔径附近的光学近场特性是近场光学技术研究的重要内容。孔径扫描近场光学显微镜（孔径SNOM）是该技术最显著的应用，其分辨率近似相当于亚波长孔径的尺寸。在这些应用中，孔径小于在探头中传播的模式的截止半径，其结果是所有模式都进入截止，孔径只发射极小部分的输入功率。孔径不能任意减小，因为必须保证最小的发射水平。因此，低透射率，即孔径处的光强较低，成为限制孔径SNOM分辨率的主要因素。因此，光学探头的优化对SNOM技术的发展具有重要意义。到目前为止，增加亚波长孔径的近场强度被认为是与较小光斑尺寸相权衡的。然而，本文作者最近在金属屏上提出了一个i形（哑铃形）孔径，它同时提供高发射强度和小光斑尺寸，并表明这种有趣的特性是由于在孔径内激发的表面等离子激元（SPP）。本课题详细研究了厚金属屏中i型孔径近场强度对各参数的依赖关系，优化了i型孔径的设计，以获得高近场强度和小光斑尺寸。对i型孔径散射光波的散射进行了数值求解，并计算了孔径的近场强度和散射截面。采用广义共轭残差（CGR）迭代和快速傅立叶变换（FTT），采用体积积分方程（VIE）进行数值求解。少

The characteristics of optical near-fields around subwavelength apertures in metallic screens are important in research on near-field optical (NFO) technology. The aperture-scanning near-field optical microscope (aperture SNOM) is the most notable application of this technology, and offers resolution approximately equivalent to the dimensions of the subwavelength aperture. The aperture in these applications is smaller than the cutoff radius of the modes propagating in the probe, with the result that all modes run into cutoff and the aperture emits only an extremely small fraction of the input power. The aperture diameter cannot be reduced arbitrarily because a minimum level of emission must be ensured. Low transmission, observed as low light intensity at the aperture, therefore becomes the primary factor limiting the resolution of aperture SNOM. Optimization of the optical probe is therefore of great importance for advancement of the SNOM technique.Increasing the near-field intensity o … More f a subwavelength aperture has thus far been considered to be a trade off with smaller spot size. However, the present authors have recently proposed an I-shaped (dumbbell-shaped) aperture in a metallic screen that provides both high emission intensity and small spot size simultaneously, and have shown that this interesting characteristic is due to the surface plasmon polariton (SPP) excited inside the aperture.In this project, the dependence of the near-field intensities of the I-shaped aperture in a thick metallic screen on various parameters are investigated in detail, and the design of the I-shaped aperture is optimized so as to obtain high near-field intensity and small spot size. The scattering of optical waves scattered by the I-shaped aperture is solved numerically and the near-field intensities and scattering cross-sections of the aperture are calculated. The solutions are obtained numerically using a volume integral equation (VIE) by generalized conjugate residual (CGR) iteration and fast Fourier transformation (FTT). Less