Lunnemann Per, Koenderink A Femius
DTU Fotonik, Department of Photonics Engineering, Østedsplads 343, DK-2800, Denmark.
Center for Nanophotonics, FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
Sci Rep. 2016 Feb 12;6:20655. doi: 10.1038/srep20655.
While metamaterials are often desirable for near-field functions, such as perfect lensing, or cloaking, they are often quantified by their response to plane waves from the far field. Here, we present a theoretical analysis of the local density of states near lattices of discrete magnetic scatterers, i.e., the response to near field excitation by a point source. Based on a pointdipole theory using Ewald summation and an array scanning method, we can swiftly and semi-analytically evaluate the local density of states (LDOS) for magnetoelectric point sources in front of an infinite two-dimensional (2D) lattice composed of arbitrary magnetoelectric dipole scatterers. The method takes into account radiation damping as well as all retarded electrodynamic interactions in a self-consistent manner. We show that a lattice of magnetic scatterers evidences characteristic Drexhage oscillations. However, the oscillations are phase shifted relative to the electrically scattering lattice consistent with the difference expected for reflection off homogeneous magnetic respectively electric mirrors. Furthermore, we identify in which source-surface separation regimes the metasurface may be treated as a homogeneous interface, and in which homogenization fails. A strong frequency and in-plane position dependence of the LDOS close to the lattice reveals coupling to guided modes supported by the lattice.
虽然超材料通常适用于近场功能，如完美透镜或隐形，但它们通常是通过其对来自远场的平面波的响应来量化的。在这里，我们对离散磁散射体晶格附近的局域态密度进行了理论分析，即对由点源进行近场激发的响应。基于使用埃瓦尔德求和的点偶极子理论和阵列扫描方法，我们可以快速且半解析地评估由任意磁电偶极子散射体组成的无限二维（2D）晶格前的磁电点源的局域态密度（LDOS）。该方法以自洽的方式考虑了辐射阻尼以及所有延迟的电动力学相互作用。我们表明，磁散射体晶格呈现出特征性的德雷夏格振荡。然而，这些振荡相对于电散射晶格发生了相移，这与分别从均匀磁镜和电镜反射所预期的差异一致。此外，我们确定了在哪些源 - 表面分离区域中，超表面可以被视为均匀界面，以及在哪些区域均匀化失效。靠近晶格处LDOS的强烈频率和面内位置依赖性揭示了与晶格所支持的导模的耦合。
