Study On The Novel Fiber Laser Oscillator And Amplifier

Fiber laser and fiber amplifier developed dramatically fast in the past ten years. The pulse duration, average power and pulse energy were improved every year. The advantages of fiber laser are the ideal pulse quality, the compact size, the light weight, the flexibility and the low cost. In scientific research, high power near-infrared lasers could generate ultraviolet and mid-infrared lasers via nonlinear processes. In industry, it can be used in laser making, cutting, drilling and trimming. To study fiber lasers, the dissertation was focused on stable all fiber oscillator and high power high pulse energy amplifier.The detailed works in this dissertation include:1. All fiber laser oscillators were established with output pulse duration ranging from femtosecond to nanosecond, which would be employed as stable seed lasers for high power all fiber amplifiers.1) Ultra-short pulses with a duration of181fs and spectral width of95nm were produced by a mode-locked Er-doped fiber laser with nonlinear polarization rotation (NPR) and intra-cavity dispersion compensation. Meanwhile, all fiber all normal dispersion Yb-doped fiber laser has been realized with linear polarization output pulses.2) Low pump threshold low repetition rate self-start Yb-doped laser was demonstrated combing the nonlinear fiber loop mirror and semiconductor saturable absorber mirror (SESAM) in cavity. The mode-locking pump threshold was as low as29.5-mW, which could prolong the lifespan of SESAM in cavity. The repetition frequency was as low as1.5-MHz. The pulse duration could be adjusted from120ps to2ns by varying the pump power.2. Double clad fiber amplifiers have been realized by using divided pulse amplification (DPA) and chirped pulse amplification (CPA). Ultra-short pulses were obtained after the compression of gratings or single mode fiber. 1) The seed laser was amplified to18.2W in double clad Yb-doped and further compressed to334fs by a pair of diffraction gratings. Meanwhile, the1.8W Er-doped fiber chirped pulse amplifier was realized and the laser pulses were compressed to346fs.2) A polarization beam splitter based divided pulse amplifier was designed to obtained830-fs52.6-nJ3-W pulses in single mode fiber. In this divided pulse amplifier, the initial4-ps pulse was copied into64replicas covering1ns in time scale.76.8-fs12-nJ pulses were achieved after the nonlinear compression in single mode fiber. The compressed femtosecond laser pulses were frequency doubled to generated250-mW laser pulse around780nm corresponding to the second harmonic conversion efficiency of46.3%.