近场光学显微镜的广义谱方法
Generalized spectral method for near-field optical microscopy
摘要：
从理论上研究了亚波长粒子（探针）与物质表面（样品）之间的电磁相互作用。示出的相互作用是由一系列的共振相对应的表面极化激元模式本地化附近的探头。共振参数取决于介电函数和探头的几何形状，以及材料的表面反射率。这种共振的计算进行了几种类型的轴对称探头：球形，椭球形，梨形。对于椭球体的一个有效的数值方法，能够处理的情况下，大或强烈的动量依赖的表面反射率。将该方法应用于高度共振的材料，例如氧化铝（本身或覆盖有石墨烯），揭示了多峰光谱和非单调接近曲线的丰富结构，即，探针-样品距离依赖性。这些特征还很大程度上取决于探针形状和模型的光学常数。对于较少共振的材料，例如氧化硅，依赖性较弱，因此球体模型是可靠的。计算是在准静态近似下进行的，辐射阻尼包括微扰。
英文摘要：
Electromagnetic interaction between a sub-wavelength particle (the `probe') and a material surface (the `sample') is studied theoretically. The interaction is shown to be governed by a series of resonances corresponding to surface polariton modes localized near the probe. The resonance parameters depend on the dielectric function and geometry of the probe, as well as the surface reflectivity of the material. Calculation of such resonances is carried out for several types of axisymmetric probes: spherical, spheroidal, and pear-shaped. For spheroids an efficient numerical method is developed, capable of handling cases of large or strongly momentum-dependent surface reflectivity. Application of the method to highly resonant materials such as aluminum oxide (by itself or covered with graphene) reveals a rich structure of multi-peak spectra and nonmonotonic approach curves, i.e., the probe-sample distance dependence. These features also strongly depend on the probe shape and optical constants of the model. For less resonant materials such as silicon oxide, the dependence is weak, so that the spheroidal model is reliable. The calculations are done within the quasistatic approximation with the radiative damping included perturbatively.
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