| Ultrafast laser sources with high peak power and high energy are important tools for promoting the development of modern science and technology.The ultrafast laser sources have been widely used in many fields such as precision machining,information communication,biomedicine,military defense,and frontier scientific research.Oscillations in fiber lasers can be used in the direct generation of ultrashort laser pulses.Based on the mode-locking technology,the pulse duration can be achieved to the picosecond or femtosecond level.However,the direct output energies and average powers of the oscillators are generally low,making it difficult to meet the requirements for high-power laser applications.To solve this problem,laser amplification technologies were proposed.Currently,the mainstream laser amplification technologies mainly include the chirped pulse amplification technology and a series of nonlinear amplification technologies.In comparison,the chirped pulse amplification technology can realize higher pulse energy by suppressing the self-phase modulation effect,however,due to the gain narrowing effect,the pulse duration is typically above 100 fs.Nonlinear amplification technologies can realize broader spectral bandwidth and narrower pulse duration by enhancing the self-phase modulation effect,however,due to the stimulated Raman scattering and the self-focusing effects,the pulse energies are limited at μJ level.Integrating the characteristics of the two amplification technologies based on raising the threshold of the stimulated Raman scattering and the self-focusing effects,and fully utilizing the self-phase modulation effect to achieve the maximum spectral broadening,and ultimately obtaining high-energy,narrow pulse duration femtosecond laser pulses,are of great research significance for breaking through the bottleneck of the current amplification technologies.Aiming at the technical bottleneck of linear and nonlinear amplification,this dissertation studied the evolution law of ultrafast fiber laser oscillation and laser amplification and broke through the technical problems of double-pass pre-chirp management amplification and confined-chirp nonlinear amplification(CNA).High-energy 1-μm and 1.1-μm ultrafast laser systems from oscillators to amplifiers were successfully developed,which provided important research ideas for breaking through the bottleneck of current amplification technology.The main research work of this dissertation is summarized as follows:(1)Based on the NPR and NALM mode-locking technologies,the output characteristics of various mode-locked fiber oscillators doped with Yb3+and Er3+ions were studied in detail.The development scheme of oscillators with high stability was summarized,which provided a reliable seed source for the subsequent fiber laser amplification system.(2)Based on the self-developed 1.1-μm NALM mode-locked fiber oscillator,the design and construction of a double-pass pre-chirp managed amplification system was carried out.The output characteristics of the system under different structures were thoroughly studied.1.1-μm ultrashort pulses with pulse energy>20nJ and pulse duration<50fs were finally realized.The research results filled the research gap of the high-energy 1.1-μm ultrafast laser source.(3)The confined-chirp nonlinear amplification technology was proposed,of which the technical principle was clearly defined.Then,the theoretical modeling simulation was carried out.Under the guidance of the simulation results,the proof-of-principle experiment was carried out,and the results fully proved the feasibility of the CNA technology.Based on the theoretical simulation,the output pulse characteristics of the high-energy fiber amplification system based on the CNA technology were analyzed in detail,and the simulation results provided important theoretical guidance for the design of a high-energy femtosecond fiber laser system. |
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