Generation Of High-energy Ultrashort Pulses Directly From Fiber Oscillators

High-energy ultrashort pulse laser sources are playing an increasing role in various scientific and industrial applications.Ultrashort pulse generation from rare-earth-doped fibers is particularly widely recognized as a promising approach.The main limitation of fibers is the accumulation of excessive nonlinearity,which hinders the directly achievable pulse energy from an oscillator.Typically,rather complex multi-stage amplifier systems are required for further power/energy scaling.Hence,the development of advanced modelocked oscillator designs with enhanced performance has attracted great research attention.This dissertation is mainly aimed at the generation of high-energy ultrashort pulses from a simple oscillator.Different mode-locking mechanisms are developed to increase the laser performance to achieve an oscillator with simple structure,stable operation and flexibility.The main contents of this dissertation are as follows:1.Large-mode-area fiber lasers mode-locked by nonlinear polarization evolution are further developed.To increase the reconfigurability of the oscillator,programmable control over the pulse dynamics and flexible output are achieved by incorporating an intracavity pulse shaper based on the digital micromirror device.Meanwhile,the mechanism and method to further increase single-pulse energy are investigated.With the introduction of excessive normal dispersion within the all-normal-dispersion fiber laser,the intracavity pulses are further broadened to support higher energy.In the simulation,up to microjoule single pulse energy are obtained through this laser configuration model.In the experiment,with a Martinez-type stretcher to provide additional normal-dispersion,the laser delivers 230 n J pulses with a dechirped duration of 69 fs.2.Large-mode-area fiber lasers mode-locked by nonlinear amplifying loop mirror are developed.With numerical simulation and experimental study,the operation of the laser in different mode-locking states are investigated.The laser support ～100 fs pulses with a maximum average power of 2 W,corresponding to ～28 n J pulse energy.Compared to state-of-the-art PM-fiber ultrafast lasers based on NALM technique,significant advances in both the output pulse energy and average power are achieved.3.Mamyshev oscillators with single-polarization large-mode-area fiber are developed.Based on cascaded spectral broadening and offset spectral filtering,the oscillator exhibits excellent performance with high pulse energy(μJ-class),extremely short pulse duration(sub-50fs)and environmental stability,which can directly compete with the state-of-the-art complex laser amplifying systems.To the best of our knowledge,this is the highest pulse energy and peak power generated by a mode-locked fiber oscillator.