Generation Of Few-cycle Femtosecond Laser Pulses Via Coherent Synthesis Based On Femtosecond Fiber Laser Technology

Few-cycle femtosecond laser technology is an important branch of femtosecond laser technology due to its nearly optical-cycle-level pulse duration. It has been widely applied to molecular dynamics, strong field physics, nonlinear imaging, attosecond science and other fields. The coherent combination of two or more coherent femtosecond pulses has been confirmed as a new and promising approach to generate few-cycle light pulses. The femtosecond fiber laser is an ideal seed source for coherent synthesis for its superior performances such as high average power, short duration and environmental stability. We report the synthesis of few-cycle light pulses via coherent synthesis of the transform-limited fundamental solitons and the self-frequency-shifted solitons with a femtosecond fiber amplifier. The main contents of this thesis include:1. Numerical models about the nonlinear frequency conversion of femtosecond pulses in Photonic Crystal Fiber(PCF) and the synthesis of solitons are established via Matlab. Pulses with 7-fs(2 optical cycles) duration and octave-spanning spectrum are obtained in the simulation.2. The nonlinear frequency conversions in different high nonlinear PCFs are experimentally investigated. 34-fs laser pulses centered in 1200 nm are generated from the dual-zero-dispersion-points PCF. Notably, high-power self-frequency-shift solitons(55 fs, centered at 1150 nm) are produced from the home-made all-solid-state photonic bandgap fiber, which demonstrates that the latter is more suitable to be the solitons source of coherent combination.3. Nearly 4 optical cycles(14 fs) laser pulses are achieved via coherent synthesis of the fundamental solitons(62 fs, centered at 1040 nm) and the self-frequency-shifted solitons(55 fs, centered at 1150 nm). The average power of the synthesised pulses can achieve higher than 30 m W. The experimental device is simplified without the compression device for dispersion compensation. In addition, the system is reasonably designed and works steadily.