Research On Key Technologies Of Hundreds KHz Level High Power Chirped Pulse Amplification

High repetition rate and high power ultra-short pulse lasers are widely used in physics,micro-nano processing,biomedicine and other fields due to their short pulse duration and high peak power.The chirped pulse amplification(CPA)system with all-fiber laser as the seed light source and space solid-state amplifier as the main amplification stage combines the high reliability and high stability of the all-fiber laser and the high energy output characteristics of the solid-state amplifier,which has considerable advantages in high average power and high stability ultra-short pulse laser generation and has become a research hotspot in recent years,in which the amplification ability of the solid-state amplifier determines the power output level of the laser.This paper mainly focuses on the repetition rate of hundreds kHz,the need for high-energy ultrashort pulse generation,and the requirements of atto second pulse generation for high power carrier envelope phase(CEP)stabilized lasers.The main research contents and innovative results of the thesis are as follows:1.Aiming at reducing the crystal heat dissipation and crystal end-face damage in Yb:YAG high-power laser amplification,an end-pumped laser amplifier technology scheme based on Yb:YAG/undoped YAG bonding structure is designed.The power density of the incident end face of the dielectric pump light and the thermal distortion effect of the end face can effectively improve the amplifying output power ability while avoiding the damage of the end face.The amplifier module structures of semiconductor TEC refrigeration and direct water-cooling refrigeration are designed respectively.The CPA is carried out for the two refrigeration methods,and the seeder is an all-fiber laser with a repetition rate of 250 kHz and a power of 7.4 W.Results show that the direct watercooled end-pumped amplifier structure has better heat dissipation effect,and finally obtained an average output power of 38 W.When the amplified output power is 30 W,the beam quality M2 factor is less than 1.12,and the power is stable.The characteristic rms value is 1.4%.Amplified laser is compressed by a chirped volume Bragg grating(CVBG),an ultrashort pulse output with a pulse width of 985 fs and an average power of 23.9 W is obtained.Using the finite element method,starting from the steady-state heat conduction equation and boundary conditions,the thermal lens effect inside the crystal is studied by calculating the optical path difference inside the crystal,and the different pumping conditions are analyzed.2.Taking advantage of the high single-pass amplification gain in the Yb:YAG single crystal fiber(SCF),the research on the CPA technology based on the SCF gain medium is carried out.Firstly,the temperature distribution and refractive index distribution of the SCF amplifier were studied by the finite element method.With the all-fiber laser used as the seed light source,the two-stage SCF used as the amplification gain medium,and the CVBG used as the compressor,the CPA system realizes a high-power laser output with a power of 52 W at a repetition rate of 200 kHz.By adjusting the temperature gradients adding on the chirped fiber Bragg grating(CFBG)to achieve accurate dispersion compensation in the pulse compression process,an ultrashort pulse width of 740 fs is obtained.In order to achieve higher power output,a three-stage power amplifier is designed with an all-fiber laser as a seed light source,a traditional rodshaped Yb:YAG medium as a pre-amplification stage,a two-stage SCF amplifier as the main power amplifying stage,and a CVBG as a compressor.The traveling wave highpower chirped pulse amplification system obtained a high repetition rate,high energy laser amplification output with an energy of up to 0.48 mJ at a repetition rate of 200 kHz and a pulse compressed output power of 67.8 W and a pulse duration of 2.5 ps.Benefiting from the stable structural design of the entire experimental system,the power stability is as high as 0.6%when the output power is 96 W.This is the maximum energy laser output obtained from a SCF amplifier at a repetition rate of 100 kHz.3.In view of the current demand for high-repetition-frequency CEP-stabilized highpower laser-driven light sources for attosecond pulse generation,experimental research on CEP-stabilized 100 kHz repetition rate high-power laser generation and amplification was carried out.Theoretically designed and built a high-power laser system based on passive locking of CEP,using the method of stable filament formation in YAG medium to achieve stable white light supercontinuum generation,and then using the nonlinear process of DFG,OPA,SHG to achieve repeated frequency CEPstabilized seed optical signal at 100 kHz,wavelength 1030 nm,and output power 150 mW.At the same time,combined with the chirped pulse amplification technology and spectral shaping technology based on Yb:YAG,CEP-stabilized small-signal amplification with a repetition frequency of 100 kHz is realized,and the average amplification power reaches 19.5 W.The system combines the passive stabilization characteristics of CEP and Yb:YAG.The high stability of the amplifier,as well as the power scalability,explores a new technical approach for the generation of highrepetition high flux attosecond pulses.