■在经典电动力学中,使用麦克斯韦方程对光质相互作用进行建模。麦克斯韦方程组的解,这通常是通过电场和磁场给出的,本质上是矢量。然而,众所周知,对于许多光学应用,可以以标量(偏振无关)方式近似地描述光-物质相互作用。虽然标量近似的精度可以在理论上计算,据我们所知,它从未被实验确定。这里,我们介绍涡旋圆二色性(VCD),具有评估衍射矢量所需特征的光学测量。
■VCD被测量为左右圆偏振涡旋光束的差分透射(或吸收)。我们用两种不同的系统测试VCD测量:i)在直径范围为150至1950纳米的金膜中钻出的单个圆形纳米孔的实验组;和ii)具有与纳米孔相同直径的金色球体的理论组。
■我们观察到,在这两个系统中,VCD>0对于较小的直径,VCD0表示中间值,VCD≈0表示较大的直径值。此外,模拟表明,以VCD≈0(VCDΦ0)为特征的衍射过程与偏振无关(与偏振相关)。因此,我们将VCD辛0与矢量衍射联系起来,和VCD≈0到标量1。
■总的来说,我们的结果显示了令人信服的证据,可以通过实验评估衍射过程的标量/矢量机制,并且VCD技术具有测量涉及等离子体圆柱对称结构的衍射过程的矢量性所需的特征。
UNASSIGNED: In classical electrodynamics, light-matter interactions are modelled using Maxwell equations. The solution of Maxwell equations, which is typically given by means of the electric and magnetic field, is vectorial in nature. Yet it is well known that light-matter interactions can be approximately described in a scalar (polarization independent) way for many optical applications. While the accuracy of the scalar approximation can be theoretically computed, to the best of our knowledge, it has never been determined experimentally. Here, we introduce Vortex Circular Dichroism ( VCD), an optical measurement that has the required features to assess the vectoriality of diffraction.
UNASSIGNED: VCD is measured as the differential transmission (or absorption) of left and right circularly polarized vortex beams. We test the VCD measurement with two different systems: i) an experimental set of single circular nano-apertures drilled in a gold film with diameters ranging from 150 to 1950 nm; and ii) a theoretical set of golden spheres with the same diameters as the nano-apertures.
UNASSIGNED: We observe that in both systems, VCD > 0 for smaller diameters, VCD ≲ 0 for intermediate values and VCD ≈ 0 for larger values of the diameter. Furthermore, the simulations show that a diffraction process characterized by a VCD ≈ 0 ( VCD ≠ 0) is polarization-independent (polarization-dependent). As a result, we relate VCD ≠ 0 to a vectorial diffraction, and VCD ≈ 0 to a scalar one.
UNASSIGNED: Overall, our results show compelling evidence that it is possible to experimentally assess the scalar/vectorial regime of a diffraction process, and that the VCD technique possesses the required features to measure the vectoriality of diffraction processes involving plasmonic cylindrically symmetric structures.