It was interesting to know that Xinetics still uses very strong actuators that can actually break the mirror even in the presence of electrical protection. Some say they just do not want to upgrade their technology as NASA buys from them. Therefore, if there are very powerful actuators, the beackage of a mirror is possible. Other, like Gleb Vdovin from OKO Technologies, use soft actuators (piezoelectric ones) and the force of them is not enough to break the mirror.
How to attach an actuator to a Deformable Mirror?
Simple answer: using epoxy glue. Surprisingly, even after many days of work epoxy glue still holds actuators very well. Moreover, there were special tests: for instance, one can write a program (DMKILL) that throws random "0" and "+max" voltages on the mirror. It was reported that the first actuator broken down after at least 10 days (!) of constant work in such a regimen.
In the case of broken actuator, many people suggested just to throw it away as a loss of one actuator does not effects the rest too badly.
Main problem is Tip\Tilt
Tip and Tilt are the major sources of problems caused by the atmospheric turbulence. An impact of the higher aberrations falls very quickly. The correction is therefore required for the tip/tilt.
For this, a WFS with Zernike fitting can be helpful.
However, as Guan Ming Dai notes in his paper "Comparison of wavefront reconstructions with Zernike polynomials and Fourier transforms." [J Refract Surg. 2006 Nov;22(9):943-8.],
Fourier full reconstruction was more accurate than Zernike reconstruction from the 6th to the 10th orders for low-to-moderate noise levels. Fourier reconstruction was found to be approximately 100 times faster than Zernike reconstruction. Fourier reconstruction always makes optimal use of information. For Zernike reconstruction, however, the optimal number of orders must be chosen manually.
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