Research On Dispersion-controlled Fiber Femtosecond Laser Amplification System

In recent years,femtosecond fiber lasers have become an important tool in the field of processing featuring excellent beam quality,good thermo-optical properties,robust and compactness.This thesis focuses on dispersion controlled,high-pulse-energy and high-pulse-quality fiber chirped-pulse amplification.Based on the dynamics of fiber amplifiers,fiber chirped pulse amplification is studied theoretically and experimentally.High-power fiber chirped pulse amplification systems based on different fiber stretchers is built and studied.Then by using an acousto-optic modulator as a repetition cutter,a dispersion tunable CFBG as a stretcher,large mode area photonic crystal fiber as gain fiber,a high-pulse-quality Yb³⁺doped fiber amplifier delivering pulse energy at ten microjoule level with hundreds of femtosecond pulse duration is obtained.The work of this thesis is summarized as bellow:1.The historical development of femtosecond fiber laser and large mode area fiber is introduced.The principle and development of widely-used amplification technologies and dispersion compensation technique are covered,advantages and disadvantages of which are analyzed.2.From the nonlinear Schr?dinger equation,the numerical model which describes how ultrashort pulses transmit in fiber is established.On this basis,the actual propagation of pulses in fiber amplifiers is established by introducing the actual emission/absorption cross section of the Yb³⁺doped fiber.3.Two kinds of chirped pulse amplification system based on different fiber-type stretchers are built and compared on the output power and pulse quality.On this basis,a low repetition rate and high pulse energy femtosecond fiber amplification system based on dispersion tunable CFBG stretcher and photonic crystal fiber amplifier is built.Laser pulses with pulse energy of 10?J and duration time of 250 fs at a repetition rate of 500 k Hz are obtained by optimizing the parameters.