Research On Artificial Second Harmonic Generation Based On Magnetic Lorentz Effect Of Metasurface

For lasers with very strong light intensity,such as when light waves of electric field intensity can be compared with the coulomb field of the atom fitting,the interaction of light and medium will produce nonlinear effect.The polarization strength of the medium is not only related to the first power of the electric field strength,but also depends on the higher power term of the electric field strength,resulting in many new phenomena that are not obvious in linear optics.In the past few decades,the researchers looked for new nonlinear materials,trying to uncover the physical mechanism of nonlinear optical.However,the current study is still not enough to provide a clear physical model to completely describe the mechanism of nonlinear.Due to the weak magnetic field of electromagnetic wave and low electron drift rate,the second order nonlinear phenomena caused by Lorenz effect tend to be ignored.Inspired by the physical model of the classic electron movement in the magnetic field forced by the Lorentz force,the researchers established a second-order optical nonlinear physical model based on the magnetic Lorentz effect.This paper designed an artificial second-order nonlinear metasurface based on magnetic Lorentz force,and the optimized design realizes the artificial second-order nonlinear strength enhancement,frequency adjustment and efficiency improvement.The specific contents are as follows:?1?Studied the enhancement of artificial non-linear intensity result from near-field bright-dark mode coupling.An electric dipole mode is provided near the metal ring,which can excite the dark mode in the metal ring to form a bright-dark mode coupling so that the local energy in the near field improves significantly.Simulation results demonstrate that a smaller gap between the near-field electric dipole and the gold U-shaped resonant ring can not only increase the electromagnetic coupling between the electric dipole and the gold U-shaped resonant ring,but also enhance the second harmonic signal of metasurface.Through reasonable optimization,we finally increased the second harmonic signal intensity by more than 3.4 times.In addition,the longer the near-field electric dipole resonator,the stronger the second harmonic signal.?2?Studied the control of the frequency of artificial nonlinear effect from graphene's electrically adjustable characteristics.We embed a single layer of graphene into the metasurface structure,and use the electrically adjustable characteristics of graphene to change the graphene Fermi level so that can affect the frequency response of the entire metasurface.Simulation results demonstrate that by varying the Fermi energy of graphene from 0.2 e V to 1.0 e V,the frequency control range of the second harmonic is 17.2 THz.In addition,by increasing the number of graphene layers,the frequency control range of the second-order harmonics can be further expanded.?3?Studied the mode matching is used to improve the efficiency of artificial nonlinearity.According to the idea of mode matching,we designed a double resonance metasurface,in which strong magnetic resonance at the fundamental frequency to realize the second-order nonlinear effect based on the magnetic lorentz force and provides strong electric dipole resonance at the second frequency to realize the radiation enhancement of the second harmonic.The simulation results show that the second harmonic efficiency of the designed mode matching plasma metasurface can reach to1.4×10^-9and the second harmonic intensity is 5.17 times of that in the case of non-pattern matching.Furthermore,we discuss the frequency matching and the polarization matching of fundamental and second harmonic frequency resonance.