| In recent years,two-dimensional materials have attracted more and more researchers'attention.Due to their unique physical properties,two-dimensional materials have shown great application potential in various high-tech fields.The application of two-dimensional materials has very high requirements for crystal quality.Accurate assessment of the crystal quality of two-dimensional materials is essential.Although diverse characterization methods provide us with research tools,the problem is that each method has its own advantages and disadvantages,and the exploration of the nature of materials requires multiple means to complete,the process is cumbersome.Nonlinear optics provides us with an idea to simplify this problem.As a branch of modern optics,nonlinear optics has now developed into a key technology.From the most widely used second harmonic generation(SHG)to third harmonic generation(THG),four-wave mixing(FWM),and some new nonlinear methods such as coherent anti-Stokes Raman Scattering(CARS),the nonlinear optical characterization of two-dimensional materials has shown great potential.Therefore,we built a broadband multi-modal nonlinear optical system to meet our needs for the characterization of a variety of two-dimensional materials as much as possible.On this basis,the characterization of the crystal orientation of Ti S3 and the nonlinear optical response of heterojunction was realized.At the same time,broadband CARS spectra were collected for graphene using the broadband function.The main innovations of this paper are as follows:(1)We have built a multi-modal nonlinear optical imaging system,and realized nonlinear detection such as second harmonic generation,sum frequency generation,four-wave mixing,and coherent anti-Stokes Raman scattering(CARS).The system has the characteristics of fast,in-situ and non-destructive,and also has the functions of spectrum acquisition and scanning imaging.Based on the system we built,the nonlinear spectra of WS2,Mo S2 and its heterojunctions were detected,and the surface morphology defects of a large area of the sample were analyzed using multi-modal spectral imaging.In addition,the system was used to collect and image the CARS spectrum of graphene,and the two-photon excitation fluorescence imaging detection of the microvascular structure processed by the two-photon polymerization technology.(2)Based on the polarization four-wave mixing technology(P-FWM),we have realized the determination of the crystal orientation of the new two-dimensional material Ti S3.Through experiments,it is found that when the polarization state of the incident light is parallel to the b-axis direction of Ti S3,the four-wave mixing signal has the maximum signal strength.At the same time,it was found that the polarization four-wave mixing response along the a-axis of Ti S3 will be limited to some extent,and will not increase or decrease in proportion to the signal intensity along the b-axis.In addition,we conducted a four-wave mixing characterization of the graphene Ti S3 heterojunction and found that the graphene,which had a strong four-wave mixing response,had an annihilation signal on Ti S3.(3)We designed and built a supercontinuum generation device,which converts the pump light into a supercontinuum to realize the system's broadband CARS detection function.The characterization of graphene layers depends on the determination of multiple CARS peak positions.When a single-frequency CARS detects multiple CARS peak positions,it will introduce a large number of errors due to laser power,pulse period and spectral fluctuations.The broadband CARS technology is used to achieve the function of acquiring multiple CARS peaks at one time.In the experiment,the CARS spectrum information of two characteristic peaks of the G?peak(2450(88)-1)and 2D peak(2700(88)-1)of the graphene sample was obtained at the same time.It solves the problem of graphene CARS signal acquisition,and can more comprehensively detect the relevant characteristic information of the sample. |
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