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:
When the loop tried to close on this, we would get a higher and higher unstable patch of actuators trying to correct it:
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:
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!
And so tonight we were able to close the loop with our new interaction matrix, and get a nice flat wavefront!
New arrivals today: T.J. Rodigas (Steward) and Runa Briguglio (Arcetri).