Hesari-Shermeh Maryam, Abbasi-Arand Bijan, Yazdi Mohammad
Opt Express. 2021 Jan 18;29(2):647-662. doi: 10.1364/OE.411110.
The polarizability tensors of a particle are its characteristic parameters, which once obtained, can be applied as equivalent representations of the particle in any problems involving plane wave illuminations. In this paper, the generalized Kerker's conditions for unidirectional scattering are derived, in the case of normal and oblique incidence, in terms of the polarizability tensors of any arbitrary nanostructures in homogeneous media and located on dielectric substrates. In order to present structures that corroborate the conditions derived from such polarizabilities, first, the effect of constituent material on the frequency response of the nanoparticle is investigated. Then, the dimensions of nanostructures that satisfy the first and second Kerker's conditions are evaluated, while it is also ascertained that by varying the excitation wavelengths in an individual nanoparticle, switching between forward and backward unidirectional scattering can be achieved. This creates numerous attractive possibilities for the manipulation of optical pressure forces. Moreover, the influence of impinging direction upon the forward-to-backward scattering ratio is studied. Since, in many applications, nanoparticles are situated on dielectric substrates to make the structures more practically feasible, in this work, the effect of substrates on the Kerker's conditions are evaluated. It is shown that the presence of a substrate adds new dimensions of polarizability to the structure. Despite this new polarizability, two structures are engineered, here, which create strong asymmetrical scattering over a wide frequency range and wide angle of incidence.
粒子的极化率张量是其特征参数，一旦获得，在任何涉及平面波照射的问题中，都可作为粒子的等效表示。本文根据均匀介质中位于电介质基底上的任意纳米结构的极化率张量，推导了垂直入射和斜入射情况下单向散射的广义克尔克条件。为了给出符合由这种极化率导出的条件的结构，首先研究了组成材料对纳米粒子频率响应的影响。然后，评估了满足第一和第二克尔克条件的纳米结构尺寸，同时还确定了通过改变单个纳米粒子中的激发波长，可以实现向前和向后单向散射之间的切换。这为光压力的操纵创造了许多有吸引力的可能性。此外，研究了入射方向对向前散射与向后散射比率的影响。由于在许多应用中，纳米粒子位于电介质基底上以使结构更具实际可行性，在这项工作中，评估了基底对克尔克条件的影响。结果表明，基底的存在为结构增加了极化率的新维度。尽管有这种新的极化率，本文设计了两种结构，它们在很宽的频率范围和入射角上产生强烈的不对称散射。
