Broadband Ultrafast Third-order Nonlinear Optical Properties And Application Of Two-dimensional Layered Materials

Two-dimensional layered materials represented by graphene is a kind of new material,which has diverse and unique structure with novel physical and chemical properties and rich application in many fields,such as electronics,information and energy.It is one of the most rapid and active research frontier during Materials Science and Condensed Matter Physics areas.The optical properties associated with the light intensity of two-dimensional materials enriched the field of scientific development.In addition,the nonlinear optics is closely related to the laser physics:on the one hand,the coherent light source is needed to study the basic principle of light and matter,and on the other hand,it needs excellent optical properties materials to improve the performance of the laser system.With the development of low-dimensional micro-nano photoelectric functional devices,nanomaterials and structures will become the cornerstone of future nanotechnology applications,especially in the low-dimensional materials due to quantum confinement caused by the new physical phenomena and material properties.With graphene as an example,its excellent carrier mobility,mechanical properties in Condensed Matter Physics and Materials Science has aroused a wide range of research interests and has made great progress.Dirac cone exists to give graphene many novel physical phenomena and electronic properties.The graphene has the characteristics of broadband saturable absorption and adjustable modulation depth,high damage threshold and short recovery time,and its nonlinear response is enhanced with wavelength.While topological insulator has a similar band structure of graphene,and its unique surface electronic and electronic structures bring a series of new physical phenomena,which have aroused widespread concern in the fields of physics and materials.Similar to graphene,graphene-like two-dimensional layered materials,such as transition metal sulfides,topological insulators,black phosphorus,etc.,also has unique broadband ultrafast nonlinear optical properties,and huge potential for application in ultrafast optical and photonics devices.In this thesis,the ultrafast nonlinear optical properties of two-dimensional layered materials represented by graphene are studied based on the application of broadband ultrafast optical and optoelectronic devices.Meanwhile,the potential of application of two-dimensional materials is explored in special band laser,such as two-dimensional graphene and molybdenum sulfide.The main results are as follows:?1?The nonlinear refractive index of graphene in the mid-infrared band was obtained for the first time via Z-scan technique based on the ultrafast nonlinear optical response characteristics.Variation of nonlinear response with laser wavelength were obtained.Z-scan measurement setup was constructed and optimized to characterize the real and imaginary parts of the third-order nonlinearity of graphene.The Z-scan technique was used to measure the mid-infrared saturable absorption and the large refractive properties of graphene.Time-resolved pump probe technique was employed to characterize the ultrafast carrier dynamics of conduction band and valance band.Experiments show that graphene has a large figure of merit and is expected to be an efficient mid-infrared nonlinear optical material.?2?The third-order nonlinear optical properties of topological insulator bismuth telluride nanosheets were studied systematically for the first time.The nonlinear optical response characteristics and the variation law from near infrared to mid-infrared were obtained.The nanocrystalline bismuth telluride nanosheets were obtained by hydrothermal method.The linear absorption,XRD,transmission electron microscopy,atomic force microscopy and scanning electron microscopy were systematically characterized.The experimental results show that the prepared bismuth telluride nanosheets have a perfect hexagonal structure with a single nanosheet size of about 400-600 nm and a sample thickness of about 20 nm,respectively.The nonlinear optical response of the bismuth telluride nanosheets was characterized by Ti:sapphire femtosecond,communication band picosecond and the mid-infrared band picosecond laser source.The results show that bismuth telluride nanosheets are not only a broadband saturable absorption material,but also a broadband nonlinear Kerr material,and the nonlinear response increases with wavelength.?3?The ultrafast spatial self-phase modulation of black phosphorus solution was studied,and the nonlinear optical response characteristics and regulation were obtained.The nonlinear parameters of black phosphorus solution were systematically studied by using spatial self-phase modulation.Ultrafast nonlinear response and coherent diffraction can be attributed to the larger third-order polarizability of the black phosphorus sample.The change of diffraction rings under different irradiation conditions of 1061 nm pulsed laser are gradually increasing,then collapse and finally reach stable process.The larger the concentration,the smaller the time required to form the diffraction ring.The effective refraction coefficient of monolayer black phosphorus is estimated to be 10-19 m2/V2.The fast relaxation time and slow relaxation time of the black phosphorus samples were 0.13 ps and 1.15 ps,respectively by the pump probe technique.Because black phosphorus has a thickness dependent band gap,the number of layers has a great influence on the nonlinear response.?4?The broadband laser output of two-dimensional materials at 1170 nm,1330 nm and 1680 nm is realized,and the broadband nonlinear optical properties of graphene and MoS₂ are further verified.The broadband pulsed laser of 1170nm to 1700 nm was studied by using graphene and transitional metal sulfide MoS₂ as a saturated absorber.Using 15 m BiO8 as the gain fiber and graphene as the saturated absorber,the Q-Switched pulse with the center wavelength of 1332 nm,the repetition frequency of 2.8 MHz and the pulse width of about 100 ns was obtained.With 10 m BiO4 as the gain fiber and MoS₂ as the saturated absorber,we obtain the pulse with the central wavelength of 1170 nm and the repetition frequency of 6 MHz.Finally,employing the linear cavity design and 1 m thulium doped fiber as the gain medium,and MoS₂ as the saturated absorber,we obtain the pulse with center wavelength of 1680 nm,pulse interval of 4.5 ?s.In addition,we studied broadband nonlinear mode-locked laser,which is attribute to nonlinear phase shift in the fiber and the equivalent saturation absorption for passive mode-locked.