Quantitatively extracting the contribution of asymmetric local-field to χ(2) in cross-shaped Ag nanoholes.

Jiawei Chen,Hongbo Hu,Peixiang Lu,Bing Wang,Hua Long,Kai Wang,Xiaobo Han

doi:10.1364/oe.25.001296

Abstract

We systematically study the contribution of local-field distribution to second-harmonic generation (SHG) in cross-shaped Ag nanohole arrays, which is usually covered by resonance enhancement effect. By increasing one arm-length of the centrosymmetric cross-shaped Ag nanohole, the local-field distribution varies from centrosymmetric to non-centrosymmetric, while the localized surface plasmon resonance peak is red-shifted to the wavelength of the pumping laser accordingly. Both experimental and stimulated results indicate that the contribution of the asymmetric local-field distribution to SHG is quantitatively separated from a strong resonance enhancement effect. It shows that the pure effective second-order nonlinear susceptibility increases as the asymmetric degree of local-field distribution increases, and the largest effective second-order nonlinear susceptibility is ~2.5 times to that in a centrosymmetric local-field distribution. Our results provide evidence for optimizing the design of nonlinear plasmonic nanoantennas and metasurfaces.

Highlights

Localized surface plasmon resonances (LSPRs), arising from the interaction of light with noble metal nanostructures, can be described as the collective oscillations of free conduction electrons [1]
Since the resonance enhancement effect is usually prominent, this relatively small contribution from the asymmetric local-field distribution is neglected or covered by the strong resonance enhancement factors [31,32]. It is a complicated and crucial question to distinguish the influence of the asymmetric local-field distributions from the resonance enhancement effect and make a compromise between these two effects, which is essential in optimizing the designs of nonlinear plasmonic nanoantennas and metasurfaces
By increasing one arm-length of the centrosymmetric cross-shaped Ag nanohole, the local-field distribution varies from centrosymmetric to non-centrosymmetric

Summary

Introduction

Localized surface plasmon resonances (LSPRs), arising from the interaction of light with noble metal nanostructures, can be described as the collective oscillations of free conduction electrons [1] It sensitively depends on the size and shape of nanostructures [2,3,4] and leads to a strong enhancement of local electromagnetic fields, which shows potential applications in super-resolution imaging [5], single molecule detection [6] and light harvesting [7]. The experimental results show that the contribution of asymmetric local-field can be quantitatively extracted from the strong resonance enhancement effect by a white-light supercontinuum signal, which is supported by a theoretical calculation based on nonlinear scattering theory.

Results and discussions

Findings

Conclusions