Nonlinear Transmission Characteristics Of High Power Chirped Gaussian Pulse In Single-mode Fiber

The research work in this thesis is supported by the National Natural Science Foundation of China"Nonlinear Transmission Characteristics of High-power Chirped Stacked Pulses in Single-mode Fibers"and 863 project"Propagation and Amplification of Super Large-mode-area High Power Broadband Pulse".The novel high power laser front-end system is an important part of the new high power laser system of China, which aims for the Inertial Confinement Fusion(ICF). It is composed of main oscillator and power amplifiers and should provide arbitrary shaping pulse for the subsequent systems. The front-end system adopts the technology of chirped pulse stacking to reduce the modulation of the stacking pulse arising from the interference of the contiguous unit pulse, meanwhile uses the all-solid, all-fiber structure to improve the stability of the whole systems. In the single-mode fiber, the nonlinear effect is obvious because of the large energy density in the small core area and makes the pulse distorted, so it is important to study the nonlinear transmission characteristics of the Gaussian pulse. In this thesis, we mainly study the nonlinear transmission characteristics of Gaussian pulse whose center wavelength is 1053nm, FWHM is 100ps, spectrum bandwidth is 1.2nm, peak power is several kW.The major results in the thesis are as followings:1. In our study, we adopt General Nonlinear Schrodinger Equation to study the influence of dispersion and nonlinear effects on the pulse, and mainly analyze the pulses with the peak power of several kW which is output by the high power laser systems.2. We give the dispersion length of the chirped pulse and validate its correctness. When chirped pulse pulses propagate in fiber, the influence of the dispersion on the pulse is related to the initial chirp of the pulse, and we find that the dispersion length which is defined under Fourier transform limit pulse cannot evaluate the influence of the dispersion on the chirped pulse, so we redefine the dispersion length to evaluate the influence of the dispersion on the chirped pulse.3. We define the factor of distortion to evaluate the distortion of the pulse, numerically simulate and analyze the relations among the factor of distortion, critical length of propagation, critical power of the pulse and initial chirp of the pulse when second-order dispersion and nonlinear effect is considered. We simulate and analyze the influence of peak power of input pulse on the pulse spectrum. The innovative results in this thesis are as followings:1. We simulate the relation between initial chirp and dispersion, advance the dispersion length of the chirped pulse LDC to evaluate the influence of dispersion on the chirped pulse, and provide a scientific basis for evaluating the influence of the of dispersion in theory and engineering..2. We define factor of distortion to evaluate the distortion of the pulse, simulate and analyze the relations among Factor of Distortion, initial chirp and length of propagation. The results show: the distortion of the positive chirped pulse is less than that of the negative chirped pulse and fourier transform limit pulse when the peak power of the input pulses is the same; critical length decreases along with the input power increasing; for specified propagation length, critical power is linear with the initial chirp, compared with the negative chirped pulse , positive pulses are more sensitive to be affected by the fluctuation of the chirp; simulate and analyze the relations between peak power of the input pulse and spectrum width, point out that the spectral width is linear with input power when the input power is high.