Fig. 1

Excitation model of a chiral particle chain-film system and the optical properties. a Oblique view: The chiral particle chain is consisted of closely spaced Ag nanospheres with different radius of 20 nm (smallest), 30, 40, and 50 nm (largest) and is placed on a 100-nm-thick gold film with 1 nm gap. The circularly polarized light with left-hand circular polarization (LCP) or right-hand circular polarization (RCP) illuminates from the chiral particle chain side normal to the Au film. The surrounding medium of the Ag nanospheres is air. b Top view: The center of every particle of the chiral particle chain is on a same circle with radius R in the x-y plane (as shown with blue dotted line). The radius of every particle is shown with Arabic numbers in the figure and the unit is nanometer. The smallest spaces of each two adjacent particles are 2 nm. c Optical properties of chiral particle chain-film system. The blue and red solid lines represent the absorption spectra for RCP and LCP light, respectively (labeled as LCP and RCP). Lower panel: the corresponding circular dichroism (CD) spectrum is shown with black solid line. The vertical dashed lines from left to right correspond to the peaks at 590, 635, 710, and 785 nm, respectively