Enhanced Second-Harmonic Generation by S-shaped Toroidal Metasurfaces

Amir Hassanfiroozi^1*, Po-sheng Huang¹, Pin Chieh Wu¹

¹Department of Photonics, National Cheng Kung University, Tainan, Taiwan

* Presenter:Amir Hassanfiroozi, email:firoozi.01g@g2.nctu.edu.tw

Nonlinear optics plays a key role in various optical applications, such as high-resolution microscopy, information transfer, coherent light source, and nonlinear spectral imaging. Thus, it is of essential importance to boost nonlinear conversion efficiency. Confining light in the nano-structures that support nonlinearity is a promising way for efficient nonlinear generation. As a family of electromagnetic multipoles, toroidal dipolar response has the advantage of high energy confinement, which helps to augment the nonlinear conversion. In this work, an S-shaped plasmonic metasurface embedded in a thin film of titanium dioxide for the efficient second harmonic generation (SHG) is proposed. Our numerical as well as experimental analysis show that the strong second-order nonlinear response is attributed to the toroidal resonance associated with high field confinement. We also found that the toroidal dipolar resonance is polarization-independent, revealing the strong nonlinear response can be observed under different incident polarization states. This work paves a way for high-efficiency nonlinear photon conversion systems.

Keywords: Toroidal Metasurface, Nonlinear Optics, Second Harmonic Generation