二能级原子与复杂球壳相互作用系统的光谱特性
Spectroscopic properties of a two-level atom interacting with a complex spherical nanoshell
摘要：
频率偏移，辐射衰减率，欧姆损失贡献的非辐射衰减率，荧光产率，和光漂白的二能级原子辐射内或外的复杂的球形纳米壳，即分层球交替的二氧化硅和金同心球壳组成，进行了研究。与均匀电介质球相互作用的同一原子相比，与复杂纳米壳相互作用的原子的光谱性质的变化显著增强，通常超过两个数量级。检测到的荧光强度可以增强5个或更多个数量级。这些变化强烈依赖于纳米壳层参数和原子位置。当原子接近金属壳层时，衰变率强烈增强，但荧光表现出众所周知的淬灭。相反，当接近二氧化硅核-内部金壳界面时，较大纳米壳的二氧化硅核内的原子偶极的欧姆损耗对非辐射衰减速率的贡献可能会降低。准静态的结果，即在一个球壳界面附近的径向频移是切向频移的大约两倍大似乎也适用于复杂的纳米壳。显著改变的光谱特性（见计算机程序（待出版的手稿）免费提供的http://www.wave-scattering.com）可以在一个宽带包括所有（非共振）的光学和近红外波长。
英文摘要：
Frequency shifts, radiative decay rates, the Ohmic loss contribution to the nonradiative decay rates, fluorescence yields, and photobleaching of a two-level atom radiating anywhere inside or outside a complex spherical nanoshell, i.e. a stratified sphere consisting of alternating silica and gold concentric spherical shells, are studied. The changes in the spectroscopic properties of an atom interacting with complex nanoshells are significantly enhanced, often more than two orders of magnitude, compared to the same atom interacting with a homogeneous dielectric sphere. The detected fluorescence intensity can be enhanced by 5 or more orders of magnitude. The changes strongly depend on the nanoshell parameters and the atom position. When an atom approaches a metal shell, decay rates are strongly enhanced yet fluorescence exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss contribution to the nonradiative decay rates for an atomic dipole within the silica core of larger nanoshells may be decreasing when the silica core - inner gold shell interface is approached. The quasistatic result that the radial frequency shift in a close proximity of a spherical shell interface is approximately twice as large as the tangential frequency shift appears to apply also for complex nanoshells. Significantly modified spectroscopic properties (see computer program (pending publication of this manuscript) freely available at http://www.wave-scattering.com) can be observed in a broad band comprising all (nonresonant) optical and near-infrared wavelengths.
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