Preparation, Characterization And Ultrafast Optical Properties Of Large Bandgap Materials

With the improvement of production and living requirements in material society,people have higher and higher requirements for tools,which also promotes the further development of science and technology.As far as laser is concerned,compared with other lasers,fiber laser has the advantages of compact structure,low price,high beam quality,compatibility and so on.It is considered to be the most promising pulse laser carrier.On the one hand,it also promotes the vigorous development of ultra short pulse direction in fiber laser.At present,the realization of ultrashort pulse is mainly in two main forms:Q-switching and mode locking of fiber laser.As one of the core devices of short pulse fiber laser,saturable absorber can modulate the laser phase with appropriate materials.We used ZnS with large band gap and MOF-NiO with metal organic framework respectively to study the influence of materials in modulator on laser output.As a wide direct band gap semiconductor material,ZnS has potential special application prospects(such as luminescence,fluorescence,sensor,infrared)by changing its morphology,size and crystal structure window materials,photocatalysis,etc.);In recent years,MOFs,as one of the good coordination polymers,has made great achievements in the research of energy,luminescence and biological applications.Under the background that two-dimensional materials are famous for their excellent nonlinear optical properties in the near infrared(NIR)and mid infrared regions,people have gradually begun to use MOFs with special structure(especially molecular symmetry and intramolecular interaction)to realize multiphoton absorption,upconversion and nonlinear refractive index change based on the materials;although the relevant reports of these two materials are currently available There are not many channels.We have also realized the corresponding Q-switching,traditional mode-locked and harmonic mode-locked in the fiber laser,which not only provides a new method for realizing ultrashort pulse,but also marks an important step in the optical research and device application of chemical materials.In this paper,we mainly study the passively Q-switched and mode-locked fiber lasers based on zinc sulfide and MOF-NiO materials.We focus on their nonlinear saturable absorption effect and the analysis of the evolution results in the field of ultrafast optics.The main content of the paper is divided into seven chapters,as follows:In the first chapter,the basic principles and advantages of fiber lasers are introduced,and the types of mainstream fiber lasers and their development in recent years are analyzed.The second chapter introduces the principle of Q-switched and mode-locked fiber laser,and summarizes the principle of Q-switched and mode-locked fiber laser.In the third chapter,the basic characterization and nonlinear optical properties of ZnS nanospheres are introduced,and the principle of saturable absorption based on materials is further explained,and the saturable absorption parameters of materials are measured in a double arm pump balance device.In Chapter 4,the passive Q-switching and mode-locked fiber laser based on ZnS are studied.The ZnS nanospheres were prepared by hydrothermal method.The ZnS was transferred to the fiber end face and the tapered fiber area respectively,and then the optical fiber integrated saturable absorption device was fabricated,which was embedded in the resonant cavity for laser experiment.In the experiment of Q-switching,the repetition frequency can reach 29.1 MHz and the pulse interval is 34.36 ns.The nonlinear effect process in the interaction between light and ZnS material provides a new method for the power and frequency control of all-optical modulation of ZnS.In the mode-locked experiment,the output of the soliton pulse with the center wavelength of 1564 nm and 3-dB bandwidth of 2.96 nm is obtained,and the pulse width is 1.048 ps after hyperbolic secant fitting.From these experimental results,we can see that the ZnS nanospheres and the interaction of dispersion and nonlinearity in the fiber can effectively modulate the laser and realize the pulse of the fiber laser.In Chapter 5 and 6,we use the same method to study the metal organic framework nickel oxide material,adjust the polarization controller,and realize the harmonic mode locking of the fiber laser at 288.2 mW pump power.Among them,the repetition frequency of 416.7 MHz is reached,which is equivalent to 109 harmonics of basic repetition frequency.The central wavelength is 1555 nm,the spectral bandwidth of 3 dB is 3.2 nm,and the pulse duration is 766 fs.The seventh chapter is the summary and discussion of the whole paper,which explains the research content and shortcomings of this paper,and prospects the future development of this research direction.