Investigation On Optimization Of Dynamic Evolution In A Femtosecond Laser System Based On Photonic Crystal Fiber

As ultrafast laser has found expanding application in basic science research and industrial machining,the desire for high average power,good pulse quality and high beam quality laser source has grown greatly.The thesis is dedicated to improve the performance of femtosecond amplifier system by optimizing the dynamic evolution.The work focused on high average power amplifier system,with mode selection,nonlinear coupling in photonics crystal fiber and application in supercontinuum generation.The detailed work of this dissertation was summarized as follows:1.A numerical model based on propagation-rate equations by considering the multi-transverse mode is constructed to describe the multicore photonics crystal fiber amplifier.By optimizaiton the dopant distribution in the fiber design,the output percentage of in-phase supermode can be incerased from 19% to 70%.The new fiber design helps in-phase supermode dominating the output.2.An amplifier based on 18 core photonics crystal fiber is built with output average power of 110 W,pulse duration of 83 fs.This is the highest average power obtained from multicore photonics crystal fiber as we know.With the adjustment of the pre-shaper consisting of filter and gratings,the output pulses of the amplifier with sub 100 fs duration can be obtained ranging from average power of 20 W to 110 W.3.The nonlinear coupling between the supermodes is experimentally investigated.We observe and discuss the superposition mode evolution with different input pulse power and pump power.Mode distribution within different wavelength range is also considered.4.A numerical model is used to simulate the influence of peak power and pulse duration of the input pulse,the filter bandwidth to the performance of the regenerative amplifier.The experimental setup of the regenerative amplifier can operate 13 circulation steadlily,at last pulse energy of 20 nJ and spectrum bandwidth of 60 nm can be obtained.5.As an important application of femtosecond laser,a supercontimuum from 560 to 1470 nm is generated from an all-solid photonics crystal fiber with average power of 2 W.Spectral broadening not only occurs within the first bandgap,but also emits a phase-matched dispersive wave within the adjacent bandgap.Energy transfer between two bandgaps with simultaneous mode conversion in the noninear process.Supercontinuum generation in the multicore photonics crystal fiber is firstly investigated.The spectrum spanned from 500 nm to 700 nm with average power of 5.4 W.The output beam profile features an in-phase mode operation with long fiber length while the superposition of supermodes operation with short fiber length.