Study On Mechanical Characteristics Of Low-stress Clamping Subassembly Of KDP Crystal With Large Diameter-to-thickness Ratio

With the development of high-power laser technology, the diameter-thicknessratio of optical elements in the Inertial Confinement Fusion device is alsoincreased, therefore, how to mount the KDP frequency conversion crystalsprecisely, with good surface accuracy and stress distribution, becomes a seriousproblem. In that case, the study on the relation between the crystal mechanical andoptical parameters and the frame surface profile, frame residual stress, andsubassembly structure, has a great significance.Based on the elastic plate theory, the crystal deformation differential equationunder gravity is derived and solved. The mathematical model of the relationbetween the harmonic conversion efficiency loss and the crystal mechanicalparameters is established.Based on the profile, flatness and roughness obtained by frame surfaceexperiment, the fractual reconstruct algorithm is established, and the similaritybetween the test and the reconstructed profile is analyzed. Based on the bottom-upmodeling approach and the reconstruction result, the crystal and frame contactfinite element model is established, and the calculation reveals the relationbetween the crystal harmonic loss and the frame flatness, continuous clampingforce and non-continuous clamping force.Through the compare of the different clamping subassembly structure, thefinite element models of different crystal support mode and subassembly fixedmode are established, then the crystal deformation and harmonic loss in each modeis calculated. The relation between the support area flatness and the structuralparameters of indirect-support four-corner-fixed mode is obtained.Through the calculation of the force load and heat load, a two-dimensionalgrinding finite element model is established, then the internal and surface grindingstress distribution is obtained. The frame surface residual stress was tested by holedrilling method, which comforts well with the simulation results. Based on theresults of the grinding simulation, the relation between residual stress relaxationand the frame surface accuracy is calculated, according which a three-dimensionalequivalent model is established. The subassembly model considering the residualstress relaxation is established, then the relation between the crystal har monic lossand the residual stress is calculated.