Study Of Third Order Nonlinear Optical Property Of Two-dimensional Atomic Crystal

Third-order nonlinear optical effect and its application is a hot research spot in nonlinear optics.With the further investigation of third-order nonlinear optical effect,such as nonlinear optical absorption and optical Kerr effect,the third-order nonlinear optical materials are put forward higher requirements:ultra-wide bandwidth,large nonlinear refractive index and ultra-fast response.At present,the inorganic materials,organic materials and semiconductor optical materials have been proven to own good third-order nonlinear optical property,but few of them can simultaneously meet the demand of ultra-wide bandwidth,large nonlinear refractive index and fast response.In recent years,two-dimensional atomic crystal materials become a research focus in the area of condensed matter physics and materials.Among them,graphene is the most representative one.Special single atomic layer crystal structure and electronic band structure determine the excellent electrical,thermal and mechanical properties of graphene.Beyond that,graphene has excellent nonlinear optical characteristics:large nonlinear refractive index,broadband saturable absorption,broadband reverse saturable absorption and large two-photon absorption.In addition to graphene,the other two two-dimensional atomic crystal topological insulators and transition metal sulfides have been prepared.Due to the different composition and structure,they exhibit completely different physical and chemical properties,and provide a broad space for exploring new physical phenomena and application.In this paper,we investigate the third order nonlinearity of graphene and graphene-like two-dimensional atomic crystal material,and obtain the following results:(1)We experimentally investigate and qualitatively explain the broadband saturable absorption property of graphene.According to gapless Dirac cone band structure,graphene theoretically has saturable absorption property at ultra-violet,visible,near infrared,infrared,microwave,and even terahertz-wave band.Using lasers with different wavelengths,we measure the nonlinear absorption of graphene at 800 nm,1053 nm,1570 nm,1950 nm,and 0.1 THz band,respectively.The experimental data show that graphene has a broadband saturable absorption property,and the saturable absorption intensity is decrease with the increase of wavelength.The experimental results suggest that graphene can be used as a broadband material in the mode-locked pulse laser and optical filter.(2)For the first time,we experimentally measure the third-order nonlinear optical coefficient of topological insulator Bi2Se3 and analyze its nonlinear mechanism.Using auto Z-scan measurement system built by ourselves for the first time laser,we measure the third order nonlinear optical coefficient of few-layer Bi2Se3 at 800 nm,which is synthesized by chemical method.Measurement results show that the few-layer Bi2Se3 sample presents obvious saturable absorption property and self-focusing effect.By fitting data with theory model,the saturable intensity and normalized modulation depth of 50 nm thickness Bi2Se3 sample are about 10.12 GW/cm2 and 61.2%,respectively.The nonlinear refractive index is about 2.26×10-14 m/W,which is six orders of magnitude higher than that of bulk dielectric.Otherwise,the saturable absorption of Bi2Se3 nanosheet at optical communication band is also measured and demonstrated in optical fiber laser for mode locking.(3)We experimentally investigate the saturable absorption property of topological insulator Bi2Se3 and Bi2Te3 dispersions.With liquid phase exfoliation method,we prepare two kinds of few-layer typical topological insulators Bi2Se3 and Bi2Te3,and disperse them in DMF,IPA and NMP solutions.Using 800 nm femtosecond laser,we take the open Z-scan measurement of the different dispersions.The results show that both the Bi2Se3 and Bi2Te3 dispersions exhibit saturable absorption property and their saturable absorption performance correspond to the different solution's distribution effect.(4)For the first time,we investigate the broadband saturable absorption property of MOS2 and demonstrate its mode-locking application in 1 ?m optical fiber laser.Using Z-scan and P-scan technique,we measure the few-layer MoS2 dispersions and nanosheets,and reveal its broadband saturable absorption property at 400 nm,800 nm and 1064 nm band.Depositing the few-layer MOS2 to the fiber pigtail,we successfully achieve the mode-locking in fiber laser and output the pulse with 1054.3 nm wavelength and 0.8 nm pulse duration.