Movie of the Loop closing

Here is a short film of the VisAO camera at i’ (765 nm) in 0.8″ seeing (33mph wind) with the loop open (0.3% SR, FWHM~0.6″) and closed (55% Strehl, FWHM=0.027″) at 800 Hz (400 modes) in the test tower.

This is a >180 increase in peak counts (and >20x gain resolution) obtained by turning on the loop!

Note that the PSF is saturated out to the first Airy ring in this (rather poor) stretch. The red dot is the focus light from the videocamera (ignore it).

A Better Closed Loop

On July 21 we closed the loop again (but without wind on the outside of the tower). In these calm conditions we were able to obtain 55% Strelh at i’ (765 nm) which is excellent correction in 0.8″ seeing and 33mph winds. I attach a log10 stretch image below to show the very high contrast PSFs that are obtained with the Magellan AO system. This is slightly better performance then was predicted for an R=8 mag guide star in a 33 mph wind with ro=14cm at 0.55um. Normally at Magellan the seeing should be better (and the wind lower) than what we simulated here, giving us some confidence that VisAO will be an excellent visible AO science camera in >75% of the weather seen at the Magellan telescope.(clockwise) perfect PSF, the MagAO PSF, The AO ON PSF, and the AO OFF PSF (Log Scale)

Note by Jared: due to the way turbulence is simulated in the tower using the mirror itself, there is some missing power in the modes higher than ~585 (the number of actuators on our mirror). This results in an optimistic fitting error during these tests. We can estimate how much lower Strehl at the telescope would be due to this unsimulated turbulence using some AO theory (see Noll 1976). Our most conservative estimate for this correction brings our telescope Strehl down to 37%, from the 55% measured in the tower. Compared to the correction calculated by a more empirical method for the LBT (see Esposito 2010) this correction is probably a little large (resulting in a low estimate for Strehl). Even with this conservative correction, our tower results are exceeding our performance predictions for an 8th magnitude guide star by more than 5% Strehl. This is very exciting!

Our First Closed Loop Visible AO Images

Yesterday, in strong winds on the outside of the test tower, we closed the loop at 400 modes and 800 Hz for the first time. The results were very nice and better than expected. In simulated 15m/s winds with injected 0.8″ seeing we recovered 44% Strehl in i’ (765 nm) and 28 milliarcsec resolution (this is an improvement of 293 times in peak amplitude over the AO loop off image, and 24 times sharper image). The corrected PSF is very high contrast and drops by 1000x inside 0.1″. Overall we are very pleased, the loop is very stable and has yet to crash or open when running. A very exciting day.

Log images of a perfect PSF, and those obtained with the loop on, with and without injected 0.8″ seeing

A linear version of the plot