Study On The Nonlinear Characteristics Of The New Type Two-dimensional Material In Fiber Lasers

As typical two-dimensional(2D)materials,Au nanoparticles(Au-NPs)have attracted much attention in the applications of medical diagnostics and therapy,biosensing imaging,and near-field super-resolution imaging.These applications are enabled by the outstanding saturable absorption properties of Au-NPs,which arise mainly from the local SPR.SPR is an optical phenomenon attributed to the collective oscillation of conduction electrons resulting in strong plasmonic electromagnetic field at the surface of plasmonic nanoparticles,which is the major cause of optical properties like strong optical absorption and Surface Enhanced Raman Scattering(SERS).Moreover,many kinds of Au-NPs have promising anisotropic nanoparticles,which are ascribed to their structure-and environment-dependent optical features,their anisotropic surface energetics,and the emergence of reliable synthetic methods for producing them with control the ratio of their edge lengths and thickness.For different size of the Au-NPs,the aspect ratio is varied at different ranges.The longitudinal surface plasmon resonance(LSPR)band can be flexibly tuned from the visible to the near-infrared region by changing the aspect ratio.These properties make Au-NPs promising saturable absorbers(SAs)for Q-switched or mode-locked lasers.And with the change of the symmetry of nanoparticle structure,the material will produce some new optical physical properties,so that it has great potential in optical region.In this paper,based on the properties of large third-order nonlinearity,broadband absorption,and fast response time of the gold nanotriangles?Au nanocages?Au Nanocages/SiO2,we applied them as saturable absorber to the optical field for the first time,and made a further study of their optical propertiesWith the Gold nanotriangles(GNTs-SA)film,a generated pulse with 1.149 ?s duration and a 118.2 kHz repetition rate was obtained at 1064.9 nm.Under a pump power of 158.4 mW,the average output power of 10.56 mW was obtained,which led to a high slope efficiency of 9.9%.These results indicate that GNTs exhibits excellent saturable absorption properties with the potential for important applications in the field of pulse lasers.Then,we demonstrate a passively Q-switched Yb-doped fiber laser based on gold nanocages saturable absorber(GNCs-SA).The localized surface plasmon resonance(LSPR)absorption peak of GNCs is located in the emission range of the Yb-doped fiber laser,so that it can be used to induce Q-switching.A minimum pulse width of 2.09 ?s with a repetition rate of 134.9 kHz and a maximum average output power of 6.03 mW with a maximum pulse energy of 44.7 nJ are obtained at a pump power of 385 mW.GNCs have high thermal tolerance,high photo-thermal stability,and fast thermal diffusion time of tens picoseconds,which can support them for stable operation without thermal damage even at high pump power.Au Nanocages/SiO2(Au-NCs/SiO2)with surface plasmon resonance(SPR)peak at 1060 nm were fabricated and experimentally exploited as the saturable absorber(SA)in an all-fiber passively Q-switched ytterbium-doped fiber(YDF)laser for the first time.By inserting the Au-NCs/SiO2 SA film,a generated pulse with 1.405 ?s duration and a 126.9 kHz repetition rate was obtained at 1060.5 nm.Under a pump power of 440 mW,the average output power of 10.6 mW was obtained.In other types of fiber lasers based on Au-NPs SA,the maximum allowable single pulse energy was limited mostly because of the low damage threshold.However in our experimental,optical damage was not observed.Au-NCs/SiO2 SA has higher damage threshold,which comes from the characterization that the Au-NCs/SiO2 don't have thermal accumulation effect.Benefitted by this character,the higher the pump power is,the more obvious effect will be,and the narrower the output pulse width will be obtained.If the pump power was increased continuously,the output power would also increase as a function of the pump power.These results indicate that Au-NCs/SiO2 exhibits excellent saturable absorption properties with the potential for important applications in the field of pulse lasers.Finally,based on the extra wide absorption line of WS2,I demonstrated successfully mode locked experiments in EDF and YDF lasers respectively;Dissipative soliton pulses with the fundamental frequency of 35 MHz were achieved in 1?m and stable bright-dark soliton pulses were obtained in 1.5?m with the corresponding pulse width of about 258.8 fs.