A deformable membrane mirror is often used in closed loop adaptive optics systems to correct for aberrations and improve image

quality. In certain applications, the correction of only one type of aberration is sufficient, the calibration procedure of the mirror can

be simplified and the control scheme can be reduced to a fast feed forward system. For these cases we developed a procedure that is easy

to implement, accurate and delivers a large correction range. An application example is the writing and readout of three-dimensional

optical memory. Here the spherical aberration component is dominant and can be inferred from the focussing depth. We describe

the principle of the new calibration and feed forward control scheme and give experimental results.

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