Pitch-dependent resonances and near-field coupling in infrared nanoantenna arrays.
Pitch-dependent resonances and near-field coupling in infrared nanoantenna arrays.
复制标题
红外纳米天线阵列中的节距相关共振和近场耦合。
作者：
B. Simpkins;J. Long;O. Glembocki;J. Guo;J. Caldwell;J. Owrutsky
我们研究了在硅和蓝宝石上作为半波天线共振的纳米粒子阵列中的耦合，并发现了当天线长度和衬底折射率变化时的普遍行为。通过严格的时域有限差分模拟，识别和表征了三种不同的耦合区域。当粒子间距降低到通常描述的辐射到消逝转变以下时，共振发生蓝移和变窄，并显示出与Fano线型一致的不对称带。在进一步降低音调后，观察到了到第三个区域的转变，这里称为近场耦合，其中共振红移，变得更对称，并显著展宽。当谐振模式在物理天线端之外的延伸与其邻居的延伸重叠时，就会出现后一种情况。模拟发现伴随这一区域的场强有明显的重排，说明纵向模式场位于气隙而不是较高折射率衬底中，其间距与实验观察到的相变一致。
We investigate coupling in arrays of nanoparticles resonating as half-wave antennas on both silicon and sapphire, and find a universal behavior when scaled by antenna length and substrate index. Three distinct coupling regimes are identified and characterized by rigorous finite-difference time domain simulations. As interparticle pitch is reduced below the oft-described radiative to evanescent transition, resonances blue shift and narrow and exhibit an asymmetric band consistent with a Fano lineshape. Upon further pitch reduction, a transition to a third regime, termed here as near-field coupling, is observed in which the resonance shifts red, becomes more symmetric, and broadens dramatically. This latter regime occurs when the extension of the resonant mode beyond the physical antenna end overlaps that of its neighbor. Simulations identify a clear rearrangement of field intensity accompanying this regime, illustrating that longitudinal modal fields localize in the air gap rather than in the higher index substrate at a pitch consistent with the experimentally observed transition.