Research on the particular temperature-induced surface shape of a National Ignition Facility deformable mirror.

We investigate the changes in the shape of a deformable mirror used at the National Ignition Facility caused by differences in temperature between the working environment and the mounting temperature of the mirror. In general, the temperature-induced profile change of the mirror is dominated by a few low-order aberrations, which mainly result in defocus. However, after these low-order distortions are corrected, there remain special, higher-order, surface distortions caused by the particular arrangement, construction, and mounting of the mirror actuators. This work analyzes these special aberrations, and their dependence on the particular actuator design, using the finite element method. Experiments are carried out to verify the computational results, and finally, design considerations to help minimize the temperature-induced high-order aberrations are suggested.