Optimize The Design Of High Power Solid State Laser Device And Comprehensive Assessment Of Research

Inertial Confinement Fusion(ICF) is an important research field of science and technology, which has an important scientific significance and application value in developing the new energy resource in the 21 century.New generation giant ICF drivers are the complex laser systems, which work properly under the condition of high power and large energy. Own to the complexity of the structure and expensive cost of system, the optimal design is necessary to improve the performance/price ratio, balancing project difficulty and cutting down the building risk.In this dissertation, the methods of the optimal design of the high power laser, especially about the multi-pass laser amplifier, were studied in order to improving the performance /price ratio. And a set of multi-objective comprehensive evaluation theory for the high power laser was firstly founded to provide a criterion of the system design scheme. The works in this thesis are on the basis of the National 863-416 project "The study on the design of Shenguang-III laser facility" , and is the the key part of the research on the design and optimization of the high power solid-state laser facility. The follows are the contents and results in this thesis:1. The basis theories and technology problems of the high power laser design and optimization were discussed. The amplification principle of Nd: glass amplifier was analyzed in detail. The energy conversion efficiency is the key factor to obtain a very good cost/performance ratio of high power laser facility. It consists mainly of energy storage efficiency of the amplifier, extracted efficiency of the storage energy and triple frequency conversion efficiency. The decision factors of the three energy conversion efficiencies were discussed in emphasis. The limited conditions of the laser system design were given. One is the B integral effect on the long laser pulses(≤1ns), which is the power-limited condition;the other is the maximal fluence that laser material can endure on the short pulses, which is the energy-limited condition. And besides, the gain saturation effect was mentioned. The above research is the theory basis of the design and optimization of the high power laser.2. The optimal design of the laser amplifier chain is the key of the optimal design of the high power laser facility. The multi-pass amplifications are fine laser amplifier configurations and are widely used for the ICF laser driver. The influence of relaxation between the laser levels on the properties of amplifier was studied and a physical model in consideration of the influence of thermalization and depletion between laser levels was founded for multi-pass amplification of laser pulses. The multi-pass amplification configuration characteristic and several key technologies were analyzed. The fluence distribution performances of four different multi-pass amplification configurations were simulated and analyzed by the amplification model, including the gain and loading capacity, the injected energy, the maximum output capacity, the extracted efficiency of energy and the capacity of laser output pulse duration flexibility at long and short pulses. The numerical simulated results would provide the fluence parameters and theory foundation for the evaluation and optimal design of the laser system configurations.3. For the given configuration, for example, the configuration of four-pass main amplification and single-pass booster amplificarion, the influences of the key design parameters on the performances of the laser fluence distribution were analyzed. The design parameters involve the confoguration of Nd:glass number, the size of Ndrglass, the product of g and d, the dynamic wasting coefficient, the small-signal gain coefficient, the nonlinear refractive coefficient and the times of thermalization and depletion. The simulated results showed that the system output energies were influenced by the various parameters and the different parameters values. It is necessary for improving system output capabilities and debasing system costs to select the appropriate values of the different design parameters.4. The optical and laser properties of several laser glasses were discussed. The analysis showed that the best laser materials for high power lasers, particularly for short-pulse lasers, should have both low n2 and high a. According to the properties of the different neodymium glass types and the fluence distribution characteristic of laser amplifier chain, an optimal amplifier configuration was advanced and analyzed for the first time that the different types of laser glass were place in the different amplifier stages of the amplifier chain. That means the higher gain Ndrphosphateglass is desirable at the front flux-limited stage where I(z) is low and gain is unsaturated. Otherwise for the last amplifier stage contributing to the B integral greatly (I(z) is high), the laser glass with lower ri2 such as fluorophosphate is the best choice to reduce the limiting A B^ \.%u rod and improve the output capability. Through using this way, the restriction of the B integral effect to the maximal output capability can be weaken;the output capability of high power laser at short pulses can be improved;and the output capability difference between short pulses and long pulses can be decreased. The simulated result showed that the optimal configuration could potentially provide a 30%~40% output energy improvement as compared with the present configuration at Ins. A feasible direction for the optimization of laser materials, even for the system optimization of high power laser systems was given.5. In order to evaluate the different design schemes of high-power laser facility and choose the best configuration, the theories of multi-objective comprehensive evaluation were set up for the first time in China. The theories consist of the foundation of the evaluation criterion and the complete system of evaluation indices, the unitariness of the evaluation indices values, the weight adding and the multi-level comprehensive evaluation methods. Then, mathematical model of the evaluation system was established based on the above theory and methods. The evaluation software was written. Through calculating by the model and the software, comprehensive evaluation results, including the performance and cost, of four typical multi-pass amplifier configurations were achieved. The results showed that the model was reasonable. This evaluation theory is very important for the optimization and aggregate decision of the high-power laser design.