| The high power solid state laser facility construction is an ideal driving source in inertial confinement fusion(ICF), the precise physical experiments have some severe requirements for beam intensity distribution at the target, such as flating, steep side and low sidelobe, so beam smoothing has become a necessary part in laser irradiation. The technology of beam smoothing is a front topic in the field of high power solid state laser facility construction, which has important academic value and practical signifycance. In this paper, we studied distributed phase plates, the technology of polarization smoothing and optimization design of multiple distributed phase plates based on the need of intensity distribution at target in different driving mode. The main research topics included:1. Establishing the theoretical model of diffractive optical elements for uniform irradiation based on the scalar diffraction theory, studied the way of designing distributed phase plates to focal spot shaping and analyzed the statistical distribution and spatial spectral characteristics of focal spot theoretically, which ensured the validity of the method by numerical simulation.2. We proposed two kinds of multiple phase plates based on initial phase and compensated target beam to suppress small-scale non-uniformity of focal spot by the characteristics of optical components.The former took root mean square error of far-field distribution as criterion to get multiple phase plates; The latter got multiple phase plates by correcting the target beam. Numerical results showed that, compared with single phase plate, non-uniformity of the focal spot could be reduced by about70%.3. Based on the statistical characteristics of multiple speckles incoherent superposition, we analyzed the characteristic of birefringent wedge smoothing interference speckles, and obtained the optimum angle. We reduced small-scale uniformity by combining multiple phase plates with birefringent wedge, which was improved20%. |
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