title: Multipolar Effects in the Optical Active Second Harmonic Generation from Sawtooth Chiral Metamaterials.
abstract: Based on the facts that chiral molecules response differently to left- and right-handed circular polarized light, chiroptical effects are widely employed for determining structure chirality, detecting enantiomeric excess, or controlling chemical reactions of molecules. Compared to those in natural materials, chiroptical behaviors can be significantly amplified in chiral plasmonic metamaterials due to the concentrated local fields in the structure. The on-going research towards giant chiroptical effects in metamaterial generally focus on optimizing the field-enhancement effects. However, the observed chiroptical effects in metamaterials rely on more complicated factors and various possibilities towards giant chiroptical effects remains unexplored. Here we study the optical-active second harmonic generation (SHG) behaviors in a pair of planar sawtooth gratings with mirror-imaged patterns. Significant multipolar effects were observed in the polarization-dependent SHG curves. We show that the chirality of the nanostructure not only give rise to nonzero chiral susceptibility tensor components within the electric-dipole approximation, but also lead to different levels of multipolar interactions for the two orthogonal circular polarizations that further enhance the nonlinear optical activity of the material. Our results thus indicate novel ways to optimize nonlinear plasmonic structures and achieve giant chiroptical response via multipolar interactions.
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.|Department of Physics, The South University of Science and Technology of China, Shenzhen 518055, P. R. China.
authors.forename: Huimin
authors.initials: H
authors.lastname: Su
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.
authors.forename: Wensheng
authors.initials: W
authors.lastname: Gao
authors.affiliation: Key Laboratory of Optoelectronic Information and Sensing Technologies of Guangdong Higher Education Institutes, Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, P. R. China.
authors.forename: Jie
authors.initials: J
authors.lastname: Ma
authors.affiliation: Key Laboratory of Optoelectronic Information and Sensing Technologies of Guangdong Higher Education Institutes, Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, P. R. China.
authors.forename: Yongchun
authors.initials: Y
authors.lastname: Zhong
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.
authors.forename: Wing Yim
authors.initials: WY
authors.lastname: Tam
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.
authors.forename: C T
authors.initials: CT
authors.lastname: Chan
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, P. R. China.
authors.forename: Kam Sing
authors.initials: KS
authors.lastname: Wong