The spectroscopic methods of circular dichroism (CD) is commonly used in analysing the chirality of molecules, which plays an important role in pharmaceutical compounds. However, the current methods require high sample density due to the weak CD effect of natural material, making it challenging to detect the signal of individual chiral molecule. In this work, we propose a technique to enhance CD signal of individual chiral molecule with the use of superchiral optical field, which is acquired by focusing a twisted radially polarized vortex onto a one-dimensional photonic band gap structure. Through adjusting the topological charge and the focusing angle of the illumination, a deep subwavelength optical field with full width at half maxima (FWHM) of 0.02λ and 22.4-fold superchirality factor enhancement can be generated. In addition, we demonstrate that up to 20-fold CD enhancement can be obtained by introducing 2 nm on-resonant chiral molecule into the superchiral optical field. This finding will have widely potential applications in CD spectroscopy and superresolution imaging for sparse subdiffraction chiral objects.

圆二色性 (CD) 光谱方法常用于分析分子的手性，这在药物化合物中起着重要作用。然而，由于天然材料的弱 CD 效应，目前的方法需要高样品密度，这使得检测单个手性分子的信号具有挑战性。在这项工作中，我们提出了一种利用超手性光场增强单个手性分子的 CD 信号的技术，该技术是通过将扭曲的径向偏振涡旋聚焦到一维光子带隙结构上而获得的。通过调整照明的拓扑电荷和聚焦角，得到半峰全宽（FWHM）为0.02 λ的深亚波长光场并且可以产生22.4倍的超手性因子增强。此外，我们证明了通过将 2 nm 共振手性分子引入超手性光场可以获得高达 20 倍的 CD 增强。这一发现将在 CD 光谱和稀疏亚衍射手征物体的超分辨率成像中具有广泛的潜在应用。