Preparation And Nonlinear Optical Properties Of Surface Functional Graphene Films

With the rapid development of ultrafast optics,ultrafast nonlinear optical materials have become an important development direction in the field of nonlinear optics.As a two-dimensional material with excellent performance,graphene not only has linear optical properties such as wide band response and high transmittance,but also exhibits many special non-linear optical properties such as saturable absorption,optical Kerr and photothermal effects.However,the ultra-thin structural properties also inhibit the nonlinear optical effects of graphene films,limiting their practical applications.The functionalization of graphene surfaces can introduce new optical enhancement effects to graphene and expand its non-linear optical applications.Therefore,this thesis presents a series of studies on the preparation,structural characterization and non-linear optical properties and applications of functionalized graphene films.The main studies are as follows:（1）Preparation of carboxy-functionalized graphene oxide saturable absorbers and their pulsed laser mode-locking applications.To address the limitation that pure graphene powder is insoluble in water,the graphene oxide was carboxy-functionalized and ultra-flat graphene-based saturable absorbers were prepared by using the Langmuir-Blodgett film technique.The prepared graphene films were characterized to demonstrate that the method can be used to obtain large-area,high optical quality de graphene saturable absorber mirrors with carboxyl functionalization.The results of the non-linear optical characterization show that the films have a modulation depth of 2.3%and a saturable absorption intensity of 24.7KW/cm².The saturable absorber was inserted into Nd:Gd VO₄ solid-state lasers with different laser cavity types and was able to achieve stable output of both passively Q-modulated and Q-locked pulse sequences with an average output power of more than 1W.（2）High harmonic properties of quantum dot functionalized twisted bilayer graphene.To enhance the nonlinear optical properties of twisted bilayer graphene,quantum dots were used to modify the graphene surface to obtain quantum dot modified twisted bilayer graphene films.Firstly,high quality bilayer torsional graphene with regular shape was prepared by low pressure chemical vapor deposition method.The torsion angles of the prepared bilayer graphene were measured by various characterization methods.The existence of van Hove singularities in the bilayer twisted graphene structure was indirectly confirmed using Raman spectroscopy to reveal its variation with the twisting angle of the bilayer twisted graphene.Based on the quantum dot functionalized bilayer torsion graphene structure,the nonlinear optical properties such as the third harmonic were initially investigated and the nonlinear linear enhancement mechanism was analyzed.