Research On Yb-doped Mode-locked Fiber Laser And Its Power Amplification

In recent years,the high power short pulse fiber laser has attracted more and more attention in the fields of scientific research,industrial processing and biomedicine.This kind of fiber laser is extremely valuable because of its advantages such as simple structure,low cost and easy to be used.This thesis focuses on the research of the Yb-doped mode locking fiber laser and its power amplification.Firstly,three kinds of mode-locked fiber lasers with different cavity structures are researched.The core pumped all-PM "figure-of-eight" cavity mode locking fiber laser operates in the dissipative soliton resonance(DSR)regime and delivers square pulses with a central wavelength of 1064nm and a repetition rate of 4.302MHz,in which the pulse duration ranges from 82ps to 1.33ns with an average power from 3.3mW to 27.1mW.The cladding pumped all-PM "figure-of-eight" cavity mode locking fiber laser also gives DSR square pulses output,but with a central wavelength of 1064nm,a repetition rate of 4.683MHz,a tunable pulse duration from 0.8ns to 5ns,corresponding to an average power from 74.8mW to 429.7mW.With such an all-PM structure,the mode locking state of these two kinds of fiber lasers can be self-started and keep stable for a long time even under violent vibration.In order to simplify the "figure-of-eight" cavity,the cladding pumped "figure-of-nine" cavity mode-locking fiber laser is built,which delivers square pulses with a central wavelength of 1065nm and a repetition rate of 9MHz,in which the pulse duration ranges from 0.677ns to 2.103ns,with an average power from 0.761W to 2.2W.The pulse energy can be as high as 244nJ while the peak power is basically stable at 120W.Based on the consideration of the stability and the output power,the cladding pumped all-PM "figure-of-eight" cavity mode locking fiber laser is chosen to be the seed source.A duration tunable Yb-doped mode-locked fiber laser is built via a two-stage MOPA configuration.In order to suppress the amplified spontaneous emission(ASE)generated by the subsequent amplification,the power of seed source is raised to 2W by a stage of preamplification.A 5m Large mode area(LMA)Yb-doped double clad fiber is utilized as gain medium in the second stage of main power amplifier,which ultimately put the average power up to 100W when the pump power is 150W,corresponding to an optical-to-optical conversion efficiency of 65.53%.The repetition rate is still 4.683MHz and the duration tunable range still from 0.8ns to 5ns.The peak power can be as high as 26Kw.No evidence of significant stimulated Raman scattering(SRS)effect is observed from laser spectrum.