Analysis on laser-induced thermoelastic deformation of DMs

摘要

Laser-induced static surface shape changes of deformable mirrors will cause difficulties for beam control of the laser system. The overall peak and valley (PV) value of the deformable mirror (DM) will reach the scale of micrometer when irradiated by high power lasers. We have investigated changes in the static surface shape of a 37-element DM caused by laser-induced thermoelastic deformation. It is found that the laser-induced profile change of the mirror shows a high-order characteristic. In this paper the finite element method is used to analyze the surface shape of the DM when it is irradiated by high power lasers. The surface shape is fitted using the Zernike polynomials and the influence functions to see the characteristic of it and the DM's ability to compensate it. The fitting results show that the lower-order aberrations can be corrected by the DM itself with the cost of a reduced ability of aberration correction, as the available amount of stroke will decrease. In addition, changes of the influence functions are simulated and the modified influence functions are calculated. Furthermore, the performances of the DM in three different situations are simulated to reveal the impact of thermoelastic deformation on the DM's aberration correcting ability.