Nonlinear Optical Properties Of Graphene And Gold Nanorod Composites And The Application Of Indium Tin Oxide In Ultrafast Laser

In the past two decades,many efforts have been payed to the study of different kinds of saturable absorbers?SAs?forlasersto get better ultrafast pulse output.Such as semiconductor saturable absorption mirror?SESAM?,carbon nano-tube?CNT?,graphene,transition-metal dichalcogenides?TMDs?,topological insulator?TI?and black phosphorous?BP?.Among them,SESAM is the most widely used because of its high flexibility and stability.But,SESAM has the drawbacks of expensive price,complex fabrication and narrowband wavelength operation range,which greatly limits its application.For graphene based SAs,it attracted a great deal of interest duo to their broadband saturable absorption and ultrafast recovery time.However,when the strong light-matter interaction is required,the low absorption coefficient and the absence of band-gap of graphene also restraint its applications.Besides,TMDs?MoS₂,WS₂?has unique absorption property and thickness dependent band-gap.It has also been extensively studied and successfully applied to lasers as SAs.Although it is possible to introduce TMDs into infrared or mid infrared optoelectronics by introducing some suitable defects,the fabrication process is complex.TI based SAs have also attracted much attention of researches due to their gap-less surface states and indirect band-gap of 0.35 eV.In addition to the above mentioned graphene,TMDs and TI,BP as a new type of two-dimensional material,its excellent photoelectric properties also promote the development of optoelectronics.However,the inefficient light-matter interaction due to the intrinsic property of these materials is a bottleneck for optical nonlinearity that limits their applications in ultrafast lasers.Thus,researchers are still making some efforts even now to seek for new SAs which are expected to have the ideal characteristics of ultrafast recovery time,broad saturable absorption region,strong light-matter interaction,low cost and uncomplicated preparation process.In this paper,we are committed to discovering and researching new nanomaterials.By studying their nonlinear optical properties,we can evaluate whether they can be used as SAs to ultrafast lasers,and finally get excellent laser pulse output through a series of experiments.The main contents of this paper are as follows:1.The structure,properties and preparation methods of graphene and indium tin oxide?ITO?are briefly introduced.The nonlinear optical properties of graphene and the potential of ITO as SAs are briefly analyzed.In addition,the Q-switched fiber lasers and the dark soliton fiber laser are briefly introduced.2.The nonlinear optical properties of graphene,gold nanorods and graphene@gold nanorods nanocomposites were studied by using open-aperture Z-scan technique.It is found that the composites possess better nonlinear optical response,which proves that graphene@gold nanorods nanocomposites havegreat potential as SAs.3.ITO nanocrystals with uniform particle size and high quality were prepared by coprecipitation method.By inserting the ITO SAs into the erbium-doped fiber?EDF?laser,we obtain a stableQ-switched pulse output.The results show that the ITO nanocrystals have shown great potential in the application of ultrafast lasers.4.By optimizing the preparation process,we have prepared a more excellent ITO SAs.The stable dark soliton pulse output is obtained by using the ITO SAs at 1.5?m.The experiment proved that the SAs based on ITO can be applied to other types of fibers and solid-state lasers to obtain ultrafast laser output,thus promoting the further development of ultrafast laser.