The Research On Ultra-large-mode-area Ytterbium-doped Fiber And High Power Pulsed Ytterbium-doped Fiber Laser

High power Yb-doped fiber laser has attracted much attentions due to the high efficiency,flexibility,reliability and high beam quality.Pulsed fiber laser plays an essential role in military,medical and industrial because of the high peak power and pulse energy.Focused on the key technology of the high-power pulsed fiber laser realization,we design the ultra-large-mode-area doubling-cladding Yb-doped fiber and built the ps-pulsed seed resource,the ns-pulsed seed resource and the ns-high-power pulsed amplifier while paying attention on the large-mode-area fiber,laser structure and features.The bottleneck problems of high average power realization were solved and a record of average power of more than kilowatt depending a single fiber was set.Firstly,the fabrication of fiber based on Modified Chemical Vapor Deposition and solution doping technique was described in the article,in which the challenges and solutions of ultra-large-mode fiber fabrication were mainly focused.The extra-large-mode-area fiber fitted in high power laser was fabricated by simulating the relationship of fiber profile and mode distribution as well as pattern distortion induced by fiber bend.And then,the actual fiber profile and absorption character were measured.Then,the pulsed fiber laser was built by two different means,in which the characteristics of output pulses were studied,respectively.The evolution process and the phenomenon of spectrum modulation induced by nonlinearity were observed in mode-locking fiber laser.In the particular condition,the vector solitons with special characteristics were obtained and researched.What's more,the tunable repetition rate all-fiber passive mode-locked fiber laser was built based on the polarization rotation of vector soliton.At the condition of half fundamental repetition operating,comparing with the pulsed laser with single pulse energy of 4.3 n J,peak power of 111 W operated at fundamental repetition,the pulsed laser could output with single pulse energy of 7.8 n J with about 2 times of 4.3 n J,peak power of 161 with about 1.5 times of 111 W.Otherwise,as the Q-switching technique which could be used to generate the pulse has been widely developed,the performances of the acousto-optic modulation based Q-switched pulse and whose relative factors of system and fiber were investigated.To explain the following phenomenon,the Q-switched oscillator model was studied.It's found that with the ratio of inverted population density increases,the peak power of pulse tends to higher and the pulse width tends to narrower.Finally,the seed resource was picked by analyzing the results from the amplifier model and the threshold of stimulated raman scattering,and the maximum extracted energy of ultra-large-mode 100/400-?m fiber was calculated.Then,the high power experiment was conducted and the heat effect and parasitic oscillation which are the two limited factors of high power was studied utilizing the 100/400-?m fiber based high-power amplifier.By utilizing the 915-nm pumping source and increasing the fiber coiling,the heating effect was efficiently mitigated.By increasing the injection,pulse width,fiber length,repetition rate and change the doping ions of the fiber,the threshold of parasitic oscillation was promoted in some degree.Eventually,the power of 1050 W and the energy of 24.6 m J were reached,respectively,in the optimizing system which is the highest target report in field of average power and pulse energy in domestic.