Second-harmonic Generation From Sandwich Optical Magnetic Metamaterials

Recent years, the studies about magnetic metamaterial in the field of optical nonlin-earcauseworld-wideconcern, it’simportanttofigureoutthegeneratingmechanismofthemagnetic resonance and how to utilize efficiently. We present a numerical investigationof efficient generation of second harmonic from a kind of nonlinear magnetic metama-terial composite. The analysis is focused on a structure consisting of periodic arrays ofpaired thin silver strips with second-order nonlinear material filled in the gap. The sand-wich shaped periodic structure exhibits remarkable advantage in the generation of secondharmonic signal.Firstly, we make an introduction to this sandwich structure, summarize the linearresonant properties and the impact of the geometry parameters. Then we investigate ofthe wavelength dependence of the field enhancement in the gap, which gives birth to theconclusion that the magnetic resonance lead to strong electrostatic energy concentratinginside the gap.Next, the electromagnetic parameters of this magnetic metamaterial is obtained byapplying the S-parameter retrieval method. Furthermore, we get the dispersions of ef-fective permittivity and permeability of the sandwich structure, which provide the directevidence of the magnetic properties of this kind of metamaterial.Finally, a study is made about the instrinsic nonlinearity of metals, and the nonlinearoptical response of metal is described by a hydrodynamic model. Some numerical simula-tions have also been made. We mainly analyze second-harmonic generation (SHG) fromcomposite structure doping with isotropic nonlinear material by comparing with that fromsingle layer nonlinear material and several other conditions. The results figure out thatthe magnetic resonance property of this nonlinear metamaterial composite makes a greatcontribution to the energy localization and gives rise to strong inhomogeneous field insidethe gap. As a result, the strength of SHG is almost two orders larger than that of a purenonlinear layer with comparable dimensions. Then we change the material property fromisotropic to anisotropic, and investigate the impact combining with field enhancement,field profiles and linear and nonlinear polarization considerations, showing that most ofthe fundamental-harmonic electric field in the gap polarize along y direction, which is thepower giving rise to the second-harmonic generation of the composite.