Three-Dimensional\nVisualization of Chiral Nano-Optical\nField around Gold Nanoplates via Scanning Near-Field Optical Microscopy

In this study, we examine the three-dimensional chiral\noptical\nfield in the vicinity of a gold nanoplate using aperture-type scanning\nnear-field optical microscopy. Near-field imaging indicates that the\nchiral optical field shows a unique spatial distribution and depends\non the incident polarization. We also evaluate the modal dependence\nof chiral optical fields, which reveals that the plasmon mode with\nE symmetry contributes substantially to the chiral optical field while\nthat with A<sub>1</sub> symmetry contributes little because of the\nhigh spatial symmetry. Three-dimensional visualization of the chiral\nfield reveals that the field extends longer than that of the plasmonic\noptical field. The spatial extension difference between the chiral\nand optical fields originates from the unique spatial distribution\nof the electric and magnetic fields around the nanoplate. These findings\nprovide detailed insight into the plasmon-enhanced chiral field and\na fundamental basis for the highly sensitive detection of chiral molecules\nusing plasmon-based substrates.