[15p-B12-1~19] 3.12 Nanoscale optical science and near-field optics

[15p-B12-7] Local Circular Dichroism Measurements of Two-Dimensional Metallic Nanostructures

〇Tetsuya Narushima^1,2, Hiromi Okamoto¹ (1.Inst. for Mol. Sci. and The Graduate Univ. for Advanced Studies, 2.JST-PRESTO)

Keywords:Circular dichroism, Chirality, Optical near-field

In this work, we developed a microscope specialized for imaging with circular dichroism (CD), with a device to avoid commingling of linear birefringence (LB) and linear dichroism (LD) signals. The CD signal is in principle free from commingling influence of LD and LB, if the sample is illuminated only with highly pure circularly polarized light (CPL). We propose a novel polarization modulation method based on this idea, which enables us to achieve high-sensitivity CD detection (10^-4 level in optical density unit or mdeg level in ellipticity) for microscopic imaging at a nearly diffraction limited spatial resolution (sub-μm level). Near-field optical CD imaging is also realized with the polarization modulation method of CPL. Because local CD distribution is sensitively observed with high spatial resolution, we can conduct, for example, direct analyses of chiral structures in materials with the spatial scale of μm to tens of nanometers, and spatial mappings of optical activity in metallic nanostructures, polymer thin films and liquid crystals. The CD microscope proposed here may yield many potential applications as a unique optical imaging method.