Performance Characterization of High Performance, Low Cost Wavefront Reconstructor System

Logicon RDA has participated in the Air Force Phillips Laboratory imaging efforts under the direction of Dr. J. Gonglewski during the past years. We just finished supporting an adaptive optics experiment using a 197 actuator deformable mirror that was installed on the 3.5 m telescope located at Starfire Optical Range in Albuquerque NM. The experiment initially called for all centroid and wavefront reconstruction calculations be performed using a CSPI multiple i860 processor board. It was quickly determined that the resulting bandwidth would be insufficient to support the experiment objectives so Logicon RDA was tasked with designing and implementing a hardware based centroid and wavefront reconstructor. A deformable mirror with a large number of actuators and a requirement for high speed control leads towards the current trend to dedicate a single processing element per actuator. While this allows flexible control with enhanced diagnostic capabilities, the size and complexity of the system increases as does the number of interfaces. Our approach, to quickly provide the needed bandwidth for this experiment, was to use a small number of inexpensive parallel processing paths that are capable of keeping up with the camera frame rate of 1000 fps. This reduced the size of our system (3, 6U VME boards) and kept the number of interfaces to a manageable number. The centroid areas used for each actuator are completely reconfigurable (size and location) via the host processor as is the matrix used to reconstruct the wavefront. The matrix multiply is a brute force approach with no shortcuts implemented allowing the user to tailor the matrix to account for local effects if needed. We believe that our approach is an inexpensive method to control a medium sized deformable mirror (up to 500 actuators) running at frame rates of up to 2000 fps. We discuss the processing system configuration, the methods used to predict and measure the performance of the Deformable Mirror system, actual system performance results and show a cost breakdown and photographs of the centroid calculator and the wavefront reconstructor.