Influence and control of spherical aberration in polishing off-axis aspherical mirrors by the stressed method.

The redundant spherical aberration of deformation can be caused by the weight of the stressed mirror polishing (SMP) apparatus in the continuous polishing (CP) process, and the elastic model to correct the spherical aberration by exerting center lateral loading is proposed. Subsequently, the analytic solution of mirror deformation is given by using a piecewise method. Next, the variation trend of mirror deformation with the loading force and the loading area size by the center lateral loading method is discussed. Following corresponding simulation calculation is carried out using finite element analysis (FEA) software. And the FEA result is compared with analytical solution. The experiment for the edge-loading force case is accomplished. Furthermore, a comparison between theoretical calculation and experiment results is provided. All of these verify the validity of the theoretical model and the analytic solution. Finally, we introduce another method called the bending mirror technique for correcting additional spherical aberration of mirror deformation, calculating and acquiring the optimum inner radius for bending and the corresponding surface residual error.