A Study Of Nonlinear Brillouin Scattering Properties In Metamaterials

The metamaterials can be used to control the characteristics of nonlinear Brillouin scattering.Based on this,this thesis constructs metamaterials with a simple cubic lattice structure,the basic unit of which is a cubic matrix inlaid with a small sphere,and then conducts theoretical researches on Brillouin scattering parameters and characteristics regulations in the metamaterials.The main contents are as follows:Firstly,the basic theories of Brillouin scattering and metamaterials are introduced.Including introducing the stimulated Brillouin scattering acousto-optic coupling equation and its gain factor;and introducing that the wave in metamaterials is Bloch wave.Then the effective medium theories are utilized for numerical calculation and analysis of the peak value of the Brillouin gain factor in the metamaterials.The COMSOL Multiphysics software is employed for simulating and screening the appropriate effective medium theory,which verifies the correction of Maxwell Garnett(MG)theory.The calculations of mass density and Brillouin linewidth of the metamaterials based on the volume average method.Then the effective medium theory is adopted to convert the longitudinal sound velocity in the metamaterials into an analytical expression related to the volume ratio,bulk modulus and shear modulus of the constituent materials.Finally,the acousto-optic coupling parameter expression of metamaterials is derived based on the MG theory.By comparing with the existing research results,the rationality and accuracy of the theories in this thesis are verified.Finally,using the theoretical basis of this thesis,several new metamaterials are designed and constructed,which can respectively enhance or suppress nonlinear Brillouin scattering,and then new metamaterials that can theoretically achieve zero Brillouin scattering are designed.This thesis finds that,firstly,the regulation of the metamaterial structure itself on the electrostriction constant plays a key role in suppressing Brillouin scattering;secondly,by studying the influence of synthetic acousto-optic coupling parameter on the metamaterial's electrostriction constant,it is found the combination of two materials with the same sign of the electrostriction constant can also acquire a metamaterial with zero or opposite sign of electrostriction constant,which may provide a new idea for the study of the characteristics regulations of nonlinear Brillouin scattering in metamaterials.