Investigation Of Spatial Self-phase Modulation Effect In Two-dimensional Dirac Material

In recent years,Dirac material has become a hot spot in the field of condensed matter physics and materials,such as graphene and topological insulator,have zero-effective-mass carrier,and linear relationship between energy and momentum,which can be described by the relativistic Dirac equation.Because of its unique structure,rich scientific connotation and broad application prospects,Dirac material has become the focus of international scientific research.In recent years,researchers have reported on the nonlinear optical properties and applications of graphene and topological insulators,but there are few reports on the study of the nonlinear coherent scattering of these two materials.Based on the previous research,this thesis studies the broadband nonlinear optical properties of graphene and topological insulator.And the major research contents and result are summarized as follow:1.The characteristic of broadband spatial self-phase modulation of graphene dispersion was studied,and the nonlinear optical parameters were obtained.By investigating experiment data of 632.8 nm,we calculate the nonlinear refractive index(n2)and third-order nonlinear susceptibility(?(3))of grapheme nanosheets.2.The broadband spatial self-phase modulation characteristics of topological insulator dispersion have been studied,and the nonlinear optical parameters and the evolution characteristics have been obtained.It found that Bi2Te3 dispersions would exihibit spatial self-phase modulation patterns for every wavelength as the incident intensity greater than the threshold.For 632.8 nm laser experiment,by calculating nonlinear refractive index(n2)and third-order nonlinear susceptibility(?(3))of one unit cell Bi2Te3 nanosheets in different effective sample length,we found the effective sample length would do not make a difference to n2 or ?(3)of nanosheets.By investigating the data of 1070 nm pulse source and CW source,it found that for pulse source has less thermal effect than for the CW source.Thus,using ultrafast pulse laser,the value of nonlinear index is more approximate to the nonlinear index by Kerr effect.The SSPM method is a quick and efficient NLO measurement technique.