Tóth Emese, Fekete Olivér A, Bánhelyi Balázs, Durach Maxim, Szabó Zsolt, Csete Mária
Department of Optics and Quantum Electronics, University of Szeged, Dóm tér 9, Szeged, 6720, Hungary.
Wigner Research Centre for Physics, Konkoly - Thege Miklós út 29-33., Budapest, 1121, Hungary.
Sci Rep. 2024 Nov 28;14(1):29568. doi: 10.1038/s41598-024-79629-z.
Azimuthal orientation and handedness dependence of the optical responses, accompanied by asymmetric transmission and asymmetric dichroism, were demonstrated on multilayers constructed with subwavelength periodic arrays of Babinet complementary miniarrays, illuminated by linearly and circularly polarized light. In case of single-sided illumination asymmetric optical responses were observed at the spectral location of maximal cross-polarization that is accompanied by radiative electric dipoles and weak, slowly-rotating in-plane magnetic dipoles on the nano-objects; where the outgoing waves are elliptically (almost circularly) polarized. The negative index material phenomenon was demonstrated, where the electric and magnetic dipoles overlap both spatially and spectrally. The negative index material (NIM) phenomenon is accompanied by electric multipoles that add up non-radiatively and correlates with the strong, pronouncedly-tilted, rotating magnetic dipoles characteristic on the nano-entities, where the outgoing waves are linearly (slightly elliptically) polarized. By illuminating the multilayer with two counter-propagating circularly polarized beams it was proven that asymmetrical normal component displacement currents at the bounding interfaces, arising along flat and tilted bands, accompany the asymmetric copolarized and cross-polarized transmission. The latter correlates with the asymmetric dichroism in the cross-polarized signal observed in case of single-sided circularly polarized light illumination. The dispersion maps in the single-sided asymmetrical co-polarized reflectance and absorptance indicate flat bands of analogous and complementary extrema, proving the partially dichroic nature of the observed asymmetric phenomena. The Tellegen (chirality) coefficients exhibit a maximum in a spectral region coincident with the asymmetric transmission (maximal polarization rotation in the 90° azimuthal orientation). The multilayer is proposed as an ultrathin NIM and nonreciprocal nanophotonic element.
在由巴比涅互补微阵列的亚波长周期阵列构成的多层结构上，通过线偏振光和圆偏振光照射，证明了光学响应的方位取向和手性依赖性，以及不对称透射和不对称二向色性。在单侧照明的情况下，在最大交叉偏振的光谱位置观察到不对称光学响应，这伴随着纳米物体上的辐射电偶极子和弱的、在平面内缓慢旋转的磁偶极子；在该位置，出射波是椭圆（几乎圆形）偏振的。证明了负折射率材料现象，其中电偶极子和磁偶极子在空间和光谱上都重叠。负折射率材料（NIM）现象伴随着非辐射相加的电多极子，并与纳米实体上强的、明显倾斜的旋转磁偶极子特征相关，在该位置，出射波是线性（轻微椭圆）偏振的。通过用两束反向传播的圆偏振光束照射多层结构，证明了在边界界面处沿平坦和倾斜能带产生的不对称法向分量位移电流伴随着不对称的同偏振和交叉偏振透射。后者与在单侧圆偏振光照射情况下观察到的交叉偏振信号中的不对称二向色性相关。单侧不对称同偏振反射率和吸收率中的色散图表明了类似和互补极值的平坦能带，证明了所观察到的不对称现象的部分二向色性本质。特勒根（手性）系数在与不对称透射（90°方位取向中的最大偏振旋转）一致的光谱区域中表现出最大值。该多层结构被提议作为一种超薄的负折射率材料和非互易纳米光子元件。
