Research On Multi-beam Smoothing

In the inertial confinement fusion(ICF)experiments,the uniformity quality of the high power laser for irradiation on the targets is more stringent,including flat top,sharp edge and low side-lobe.Therefore,the approach to achieve uniform irradiation of laser on target surface in ICF attracts much attention and has been intensively investigated for a long time.In this thesis,the effect of the mutual compensation phase plate(MCPP)on the uniform irradiation on target has been studied through analyzing the laser arrangement in the ICF indirect drive.Moreover,the intensity distribution of all laser beams on the inner wall in the black chamber has been simulated.The main research topics of this thesis are as follows:1.The theoretical model of multi-beam transmission has been established based on the scalar diffraction theory.The design method and the evaluation parameters of the MCPP have been clearly introduced.The influence of the MCPP on the laser's uniformity is analyzed by using the modified Gerchberg Saxton(GS)algorithm and simulated annealing algorithm.According to simulation results,the MCPP can effectively improve the uniformity of the far field spot in comparison with the ordinary phase plate.2.The tolerance of the MCPP is studied in details and it allows a better tolerance in contrast with the conventional method,as illustrated in the numerical results.For the beam with the same wave-front distortion,about 62.44%improvement on top uniformity has been achieved by adopting MCPP.3.The intensity of the incident laser beam on the inner wall in the black chamber is simulated and the numerical results show that:(1)there is no plugging effect;(2)the size of the spot on the inner wall in the black chamber decreases gradually with the incident angle increasing;(3)the small energy density of the inner ring and poor uniformity of the intensity distribution in the black cavity.The uniformity of the intensity distribution in the black cavity can be improved by adjusting the outer ring focal spot size.