MagAO Commissioning Day 13: Closed loop – 400 modes at 1000 Hz

We passed a big milestone today with the ASM working in closed loop with 400 modes at 1 kHz (the most complex AO mode)!  This 400 mode interaction matrix has been made possible by the excellent trouble shooting from our friends at Arcetri Observatory, Simone, Enrico, Alfio, Armando and Marco!

It was such an exciting event that Alan Uomoto made a movie:

How did this happen?  Well, yesterday the AO loop was struggling to close on the bumps we were referring to as Viscachas:

The Viscacha is a bump causing a dark spot in the Pyramid pupils at around 2:30 o'clock.

When the loop tried to close on this, we would get a higher and higher unstable patch of actuators trying to correct it:

Here is the ASM display after closing the loop yesterday on 200 modes at 600 Hz. You can see the commands on the bad patch at ~2:30 o'clock; the mirror is working hard to correct something there, but we didn't know what.

So Simone and Enrico figured out that we were actually getting cross-talk from the Pyramid, because the phase bump was so high.  This is similar to a quad-cell Shack-Hartmann without a guard band, where a subpupil may wander into an adjacent subaperture.  Here is Simone’s drawing where he works out the solution:

Simone's drawing to solve the problem of the viscacha

So the solution is kinda a hack, whereby we applied a negative sign to the interaction matrix for that patch — and the bump and the viscacha disappeared!

Evolution of the Viscacha -- Final rendition, all corrected!

And so tonight we were able to close the loop with our new interaction matrix, and get a nice flat wavefront!

Result: Closed loop, flat wavefront, no viscacha!

New arrivals today: T.J. Rodigas (Steward) and Runa Briguglio (Arcetri).

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