Preparation for Experiment 2: Open Loop Control

On-the-ground Testing Results

Power Spectrum

Power spectra of the reconstructed wavefronts with the spinning atmospheric turbulence simulator plate. The black line is the spectrum of the uncorrected wavefront. The dark blue line is the spectrum of the closed-loop corrected wavefront. The light blue line is the ratio of the open to closed loop spectra, showing the classic one-pole low-pass rejection behavior of the AO control loop.

Movies

See movies of the turbulence simulator reconstructed wavefront:

Open Loop WFS & MEMS mirror
Wavefronts from the testing on 3/21/08 using the rotating atmospheric turbulence simulator plate. On the left is the reconstructed wavefront using data from the open-loop wavefront sensor. On the right is the DM shape (actually, the voltages being sent to the DM) with the system operating in closed loop, i.e. controlled using the closed-loop wavefront sensor. The data are simultaneous and show how similar the open-loop measured wavefront is to the actual wavefront (which is being followed by the DM in closed loop). Notice that the tubulator motor sticks once in a while, causing the pattern to momentarily pause.

Closed Loop WFS & Open Loop WFS & MEMS mirror
The two wavefronts on the right are the same data as show above, however now shown on the left is the residual wavefront, as measured by the closed-loop wavefront sensor during closed loop operation. Again, the data are simultaneous. Notice that when the turbulator motor sticks, the residual gets low, and more "white noise" (spatially decorrelated) in appearance as expected. But when the motor jerks loose and the "wind" is blowing by fast, he wavefront pattern is imprinted on the residuals i.e. demonstrates a control bandwidth lag error.