| The research devoted to this thesis focuses on the design and applications of large aperture diffractive optical elements (DOE) that will be used to realize uniform illumination on focal plane for inertial confinement fusion (ICF) system. The works are under the support of national project. The primary research and achievements are as follow:1. With the requirement of more large-size of beam control components DOE, we need much more sampling grid to satisfy sampling theorem and ensure appropriate calculation output window. However, with the expand of sampling matrix, the lack of calculation of PC is emerging. Using the Message Passing Interface (MPI) language, we have developed parallel computing methods for the design of DOE. The time of calculation is greatly shortened comparing to a single PC, which can meet the requirement of time-cost for the design of large-size DOE.2. Usually, we use simulate annealing (SA) algorithm to optimize the phase structure of DOE for more uniform output beam. However, due to the randomness of SA, the searching time is long, and the cost-effective is low compared to the improvement of uniformity. The difference feedback optimization (DFO) has overcome the randomness of SA. Through a mathematical approximation, It adjusts relative phase structure by the difference of real output and target output, which can quickly convergent to a better phase structure. Thus, this new algorithm has significantly reduced the time of design cycle.3. Traditionally, the target of beam shaping is a single plane, such as focal plane, and the uniformity of beam is degenerated when deviating from target plane. On the other hand, the target plane of indirect-driver ICF is not perpendicular to the optical axis but with a certain angle. So both of them propose 3D beam smoothing requirements. Through the dispersion of 3D space, setting of different feedback factor and launching recursive search, we have developed and realized a multi-plane iterative algorithm for 3D beam shaping. The results show that the uniformity and diffraction efficiency have been well maintained in the vicinity of 0.2mm around focal plane, which has enhanced the spatial specifications and adaptability of DOE.4. To solve the reversible propagation between vertical plane and incline plane, several propagation methods have been researched. According to the rotation of wave vector in Fourier space, we have found a reversible transform of spectrum rotation solving the hard problem. Then, using the reversible transform, we have developed the design method for eliminating sidelobe of output beam. Large-size design results show that it can inject most of laser energy to the target cavity with low sidelobe, meeting the needs of project.5. Whether the driver of ICF is direct or indirect, we have to consider the impact of caliber in DOE design because the beam diameter usually has a certain amount of zoom and a little deviation from center in actual target practice. Tradition design treat the input beam to be fixed, and it will inevitably lead to the measured results and design of large deviations. We take the aperture variation into the process of DOE design, and using the random incident way to ensure average output beam under a given variation of aperture. It has greatly increased the diameter tolerance of DOE.6. We have tested a DOE of 220mm diameter in the target experiment. The test results have some large difference to the design specifications, with higher center energy and sidelobe and lower diffraction efficiency. According to the computing analysis, the difference between design and experimental caliber and the lack of DOE unit will be the cause of these problems. Therefore, we should bring the diameter variation of incident beam into our design and enlarge sampling grid to make other diffraction orders as far as possible so that the loss of energy is as little as possible. Only in this way, DOE can be successfully applied to the beam control components of ICF system.
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