Three-Dimensional Visualization of Chiral Nano-Optical Field around Gold Nanoplates via Scanning Near-Field Optical Microscopy

In this study, we examine the three-dimensional chiral optical field in the vicinity of a gold nanoplate using aperture-type scanning near-field optical microscopy. Near-field imaging indicates that the chiral optical field shows a unique spatial distribution and depends on the incident polarization. We also evaluate the modal dependence of chiral optical fields, which reveals that the plasmon mode with E symmetry contributes substantially to the chiral optical field while that with A₁ symmetry contributes little because of the high spatial symmetry. Three-dimensional visualization of the chiral field reveals that the field extends longer than that of the plasmonic optical field. The spatial extension difference between the chiral and optical fields originates from the unique spatial distribution of the electric and magnetic fields around the nanoplate. These findings provide detailed insight into the plasmon-enhanced chiral field and a fundamental basis for the highly sensitive detection of chiral molecules using plasmon-based substrates.