First results with an adaptive optics test bench

At TNO TPD we have realized an Adaptive Optics test bench. The bench has an in-house built turbulent atmosphere simulator. For the wavefront sensors there is the possibility to choose between a Shack-Hartmann sensor and a pyramid sensor. Compensation of the wavefront error is performed by a separate tip-tilt mirror and a deformable mirror. Both are off the shelf products. The AO system is controlled by a Multi-Input-Multi-Output control system with 40 actuator channels and 50 sensor channels. The proposed control strategy corresponds to a Linear Quadratic approach, in which the sum of the mean squared wavefront error over the sensor points and the weighted control effort is minimized. In the optimization process the dynamic properties (spatial-temporal correlation) of both the turbulence-induced wavefront error and the mirror/sensor combination are taken into account. Furthermore, important issues like closed-loop stability and robustness are included in the control design. An adaptive control algorithm has been derived, which converges to the LQ-solution and also enables tracking of changes in the characteristics of the turbulent wavefront. This paper presents the first results achieved with the Adaptive optics test bench. It shows that a simplified version of the adaptive feedback control strategy already gives promising results, both implemented in a commonly used AO simulation software package and in real-time on the AO test bench.