Software compensation method for achieving high stability of Alpao deformable mirrors.

Deformable mirrors (DMs) are used in adaptive optics for correcting optical aberrations: the DM surface can be deformed to compensate for them. Recently we reported the results on investigation of the stability of Alpao DMs, i.e. how accurately a DM surface shape can be maintained over minutes and hours without any optical feed-back. We observed a creep behavior of the DM surface and we presented a proof-of-concept software compensation for it, showing that very high stability is achievable. In this paper we develop a generalized creep compensation method that covers a wide range of DM use-cases and compensates for 90% - 95% of the creep observed. Furthermore, we report an observation of a DM shape dependence on the magnitude of the DM steering commands over the last few minutes. This effect is likely due to the warming up of the structure supporting the DM surface. Similarly as for creep, we have developed a compensation in software which corrects for about 90% of this effect. Both compensation mechanisms are based solely on pre-calibration input and do not receive any optical feedback about the actual DM surface shape. With the application of these two compensation mechanisms, the Alpao DM exhibits excellent stability and is well suited for feed-forward operation, where high reliability of the DM surface is crucial for operation in the absence of an optical feedback.