Superchiral Light Emerging from Bound States in the Continuum in Metasurfaces of Si Nanorod Dimers,ACS Photonics

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Superchiral Light Emerging from Bound States in the Continuum in Metasurfaces of Si Nanorod Dimers
ACS Photonics ( IF 6.5 ) Pub Date : 2024-09-03 , DOI: 10.1021/acsphotonics.4c00938
Jose Luis Pura _{1,

2} , Beatriz Castillo López de Larrinzar ₃ , Minpeng Liang _{4,

5} , Antonio García-Martín ₃ , Jaime Gómez Rivas _{4,

5} , José A. Sánchez-Gil ₁

Affiliation

Bound states in the continuum (BICs) in all-dielectric metasurfaces enhance light–matter interaction at the nanoscale due to their infinite Q factors and strong field confinement. Among a variety of phenomena already reported, their impact on chiral light has recently attracted great interest. Here we investigate the emergence of intrinsic and extrinsic optical chirality associated with the excitation of BICs in various metasurfaces made of Si nanorod dimers on a quartz substrate, comparing three cases: parallel nanorods (neutral) and shifted and slanted dimers, with/without index-matching superstrate. We analyze both the circular dichroism (CD) of the far-field (FF) interaction and the helicity of the near-field (NF) distribution. We show that the best approach to achieve chiral response in the FF based on extrinsic chirality is to exploit quasi-BICs (q-BICs) appearing in the case of slanted nanorod dimers. By contrast, the helicity density is largely enhanced in the case of shifted dimers, as it presents intrinsic chirality, with values 2 orders of magnitude larger than those of circularly polarized plane waves. These so-called superchiral electromagnetic fields concentrated at the nanoscale within the metasurface hold promise of appealing implications in phenomena such as strong-coupling, photoluminescence emission, or other local light–matter interactions.

中文翻译：

从 Si 纳米棒二聚体超表面连续体中的束缚态出现的超手性光

全介电超表面中的连续体束缚态（BIC）由于其无限的 Q 因子和强场限制而增强了纳米尺度的光-物质相互作用。在已经报道的各种现象中，它们对手性光的影响最近引起了极大的兴趣。在这里，我们研究了在石英衬底上由 Si 纳米棒二聚体制成的各种超表面中与 BIC 激发相关的本征和外源性光学手性，比较了三种情况：平行纳米棒（中性）和移位和倾斜二聚体，带/不带折射率匹配超层。我们分析了远场（FF）相互作用的圆二色性（CD）和近场（NF）分布的螺旋度。我们表明，在基于外源性手性的 FF 中实现手性响应的最佳方法是利用出现在倾斜纳米棒二聚体情况下的准 BIC （Q-BIC）。相比之下，在移位二聚体的情况下，螺旋度密度在很大程度上增强，因为它呈现本征手性，其值比圆偏振平面波的值大 2 个数量级。这些集中在超表面内纳米尺度的所谓超手性电磁场有望在强耦合、光致发光发射或其他局部光-物质相互作用等现象中具有吸引人的意义。

更新日期：2024-09-03

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