Assessing the stability of an ALPAO deformable mirror for feed-forward operation

Area of Science:

• Optical Engineering
• Adaptive Optics

Background:

• Deformable mirrors (DMs) are critical for correcting optical aberrations in systems like telescopes.
• Open-loop operation of DMs requires precise and repeatable surface shape control.

Purpose of the Study:

• To assess the surface shape repeatability of an ALPAO deformable mirror under prolonged use.
• To develop and validate a software-based solution for mitigating DM surface drift in open-loop configurations.

Main Methods:

• Repeatedly applied actuator commands to an ALPAO DM over hours, monitoring surface shape with an interferometer.
• Developed a predictive model to continuously adapt actuator commands, correcting for time-varying surface shape.
• Quantified surface deviation using root-mean-square (RMS) error.

Main Results:

• Observed significant surface drift in the DM, with deviations exceeding 30% of the target shape's RMS.
• The developed software stabilization procedure reduced surface drift to within 4 nm RMS after 6 minutes.
• Identified potential improvements for actuator command repeatability affected by surface drift.

Conclusions:

• DM surface drift poses a significant challenge for open-loop adaptive optics systems.
• Software-based drift correction is effective in maintaining DM surface stability.
• Further improvements in DM design could enhance actuator command repeatability.