Analysis on the surface-enhanced circular dichroism spectroscopy

Circular dichroism (CD), the difference in absorption of two opposite circularly polarized light by chiral molecules. Based on the generalized Poynting's theorem for chiral media, we reveal the origin of the CD in the chiral molecule/ nanostructure system. We find that CD enhancement arises through two distinct CD channels - inherent and induced. The inherent CD channel is direct molecular CD enhanced by strongly localized optical helicity density near the nanostructure. The induced CD channel, previously ignored, is asymmetric excitation and absorption of electromagnetic fields inside nanostructures surrounded by chiral molecules. We demonstrate that the induced CD channel can be significant in CD signals of entire system.