Studies On Energy Stabilities Of Output Pulses From Multi-pass Solid State Lasers

Along with the rapid progresses of high power solid-state laser drivers, several types of multi-beam laser systems, such as National Ignition Facility (NIF) have bet-r. developed aiming at achieving super-high powers or super-high energies. Elimination the energy (or power) difference between various beams of the multi-beam laser system is an important issue in order to effectively use the laser facility. Based on the probability and statistics, energy spread from various beams of the multi-beam laser system has been studied in this work in order to provide basic theory for energy redundance optimization design of SGIII facility. As a result, following progresses have been achieved:1. Based on a detail review of literatures on solid-state high power laser systems, a physical model was put forward to model the multi-pass amplification of Nd:glass lasers. Based on the multi-beam laser system of SGIII facility, a computer code was developed for calculating energy spread.2. Based on the theory of the probability and statistics, relationship between the energy spread and the success probability of ignition has been established. In the mean time, method was put forward to transform a series of random number from uniform distribution to Gaussian distribution in order to overcome the shortcoming that most of computer programming languages don't give Gaussian random numbers. At last the method was confirmed by calculation.3. Studies have been made on the energy spread of the output step pulses from the amplifiers of the multi-beam laser for input exponential pulses. The simulationsindicate that for pulses of 1-ns, the energy spread of the output is larger than that of 13-ns. Moreover, if the gain medium is saturated by laser radiation, the output energy spread reduces with the increase of the input pulse energy.4. It is realized that slight increase on the average energy of output pulse may increase the success probability of ignition; this has been confirmed by theoretical analysis and numerical calculation. The operation risk of SGII1 facility was evaluated for 1-ns pulses when the success probability of ignition was increased to 80% by slight increase on the average energy. The calculations suggested that slight increase on the output energy could be achieved on the laser system under construction provided certain modifications can be made. Meanwhile, it should be pointed out that these modifications couldn't reduce the energy spread of output pulses. To reduce the energy spread of the output pulses, it is necessary to strengthen the constrains imposed on the parameters of various optics of the facility.5. Based on the calculation and analysis of energy amplification process for input pulses of 13-ns, it is realized that by forcing the amplifiers working at deep saturation states the output energy spread can be minimized, and the energy extraction rate of the amplifiers can be increased.