Simulation And Design Of High Power Laser Front-end System

The works in this dissertation are under the support of 863-804 project "The Simulation and Design of High Power Laser Front-end System". The ongoing high power laser with the structure of Master Oscillator (i.e. Front-end System) plus Power Amplifier (MORA) is going to be the major laser driver for Inertial Confinement Fusion (ICF) research in our country. The Front-end system of the High Power Laser provides several beams of high quality optical shaped pulse seed for the power amplifier system, the pulse seeds are requested to have the energy of mJ level and certain spectrum span, high signal to noise ratio, high beam quality and high stability. In the dissertation, we systematically studied the fundamental physical problems such as optical pulse shaping, pulse smoothing, system stability and et al. in the all-fiber front end system. A simulation platform is developed to emulate the performance of the subsystems and the designs in the all-fiber front end system. Some technologies for the front end system are proposed and studied, and the optimal parameters of the front end system are given using this platform.The major results in the dissertation are obtained as the fallowings:1. A physical model of the front end system is built, and a corresponding simulation platform is developed to emulate the performance of the designs. The software can emulate the optical fiber systems realistically. It's the first software system to emulate all-fiber front end system in China. The Copyright was registered.2. The initial pulses that inject into the shaping system of the front end should have high stability to satisfy the requirement of pulse shaping. We studied the stability of mode lock laser using Fourier transform to sample the gain spectrum of the laser. The results show that the amplitude of the mode locked laser pulse will fluctuate with the phase diversity between locked modes. The fluctuation is in-inversely proportion to the mode number. The pulse fluctuation ratio after narrow band filter is proposed as an important parameter to evaluate the quality of the mode locked laser pulse.A multimode interference (MMI) power splitter for ultra-short pulse was designed. Beam propagation method (BPM) and Finite-difference time-domain (FDTD) were used to emulate the performance of the splitter. 49.5% splitting coefficient can be obtained for continuous wave inputs. For pulsewidth longer than 40 fs, the splitting coefficient will be higher than 47.5%. Pulse tail will appear for shorter pulses input and the power loss will be serious. The splitter is a vital component for the all planar waveguide pulse stacking system proposed as the next generation front end system.3. Pulse shaping technologies were researched in the paper for the shaping ability requirements of the front end system.The amplitude modulation shaping was modeled by using the developed software platform.Several kinds of pulse stack shaping were modeled in this dissertation. The estimation method was established. The coherent pulse stacking can be realized by choose parameters from the given region. Very high stability was required for the optical fiber and environment to obtain stable coherent stacking pulses. Frequency chirped pulse stacking can obtain stable output pulses and the frequency dithering along the long shaped pulses is very suitable to apply the smoothing by spectrum dispersion (SSD). The correlation between target pulses and obtained pulses will be larger than 95% by pulse stack shaping.A pulse stacker scheme based on Faraday rotation mirror is proposed and discussed to get a...