Study On Mode Locking Of New Materials And 2μm All Fiber Laser Amplification

Ultrashort pulse fiber laser has the advantages of high average power,high peak power,high conversion efficiency and so on.2μm band laser has become a research hotspot because of its great application value in medicine,military,scientific research and other fields.In order to obtain stable output of high power 2μm band pulse laser,chirped pulse amplification（CPA）is usually used.The 2μm band pulse laser can further expand the spectrum and realize the pulse output of wide spectrum.In this thesis,we focus on the study of high-power all fiber thulium doped fiber amplifier and supercontinuum generation.The main work of the thesis is as follows:In the first part,the research background and significance of the subject are described.The research progress of passive mode-locked fiber laser with new materials,ultrashort pulse thulium doped fiber amplifier and mid infrared supercontinuum light source at home and abroad are investigated,and the research direction of this paper is clarified.In the second part,the passive mode-locked fiber laser oscillator is studied.In this paper,the passive mode-locked fiber oscillator is analyzed theoretically.The pulse dynamic process in the cavity is analyzed by using the nonlinear Schrodinger equation.The pulse working mechanism in the mode-locked fiber oscillator is introduced.The passive mode-locked technology of saturable absorber is described.The energy level structure and spectral characteristics of thulium and ytterbium ions are studied respectively.Thulium doped fiber oscillators based on SESAM mode-locked are constructed.The repetition frequency is 44.31 MHz,the spectral width is 0.3 nm,and the pulse width is 63 ps.The average power of the laser output is 4 m W.The ytterbium doped fiber oscillator based on KP₁₅ mode-locked is constructed.The output of 978 nm mode-locked laser with repetition frequency of 15.65 MHz,spectrum width of 5.6 nm and pulse width of 30 ps is realized.The average output power is 7.24 m W.In the third part,high power ultrashort pulse fiber amplifier is studied.Firstly,the basic theory of thulium doped fiber amplifier is summarized and analyzed,including the rate equation of thulium ion and the dispersion and nonlinear effect of pulse in fiber amplifier.On this basis,the SESAM mode-locked thulium doped fiber oscillator is used as the seed source,and CPA technology is used to amplify the power of the seed source.The average power of 2μm picosecond pulse laser output is 125.8 W.Furthermore,the amplification path and gain fiber are designed and optimized to achieve 58.39%optical conversion efficiency.In the fourth part,the supercontinuum generation of ZBLAN fiber pumped by 2μm picosecond laser is studied.The generation process of supercontinuum in ZBLAN fiber is simulated by nonlinear Schrodinger equation.A 2μm picosecond laser source was used for the experiment of nonlinear spectrum broadening in the mid infrared band.The SC output with wavelength of more than 2.75μm was obtained.The whole experimental system is all fiber structure.