Author: Laird Close

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

On July 18 we succesfully mounted the NAS on the tower. Then recabled the system. Illuminated the the ASM at the top of the tower with the white light fiber source. Checked the optical alignment (which was unchanged from before). Then we moved the the PWFS on the 3axis stage (while tilting the dummy 50/50 beamsplitter) till the image of the ASM was round and centered on the PI stage (with its 12mm mirror it is the smallest optic). Then we took a 10 mode interaction matrix. Closed the loop! Then we took 50 and 200 mode IMATs with loop closed at 0.05 gain to clean up errors in the tower vibrations on the windy day we were working with (the tower was not floating since this was just an engineering test). Then closed the loop with the 200 modes to yield great images on the CCD47. A great day!Mounting the NAS

The lowest 50 KL modes from our interaction matrixClosed loop Pupils and ASM Mirror positionsThe Arizona team after the first closed loop (Jared, Laird, Derek)Alfio after closing the loop

This week we finished the optical alignment in the optical lab. We also mounted the NAS on the tower as a test. Then we pulled the NAS off the tower and mounted all the optics into the the NAS for the first time. Then we aligned the flowerpot (calibration point source) to the NAS and the board to the the flowerpot. See photos below

Laird bolting board on NASThe optical board on the NAS (flowerpot at top with calibration source)

A well aligned PWFS

The PWFS is now aligned on the bench. In the image you can see to the right a single frame of the CCD39 showing a flat wavefront with a slight tilt from our lamp source. On the left you an see the diffraction-limited image of the source on our VisAO camera in r’ band (resolution of 18 milliarcsec on the sky).An r’ band image of the lamp and its “flat” wavefront on the PWFS

Here is the current view of the, almost complete, integration of the wavefront sensor, VisAO camera, and their electronics and control computers. Derek Kopon (right) is working on the alignment of the optics and Jared Males (left) is working on the software. 

Wavefront Sensor (below Jared), CCD electronics box (on top of bench), VisAO camera electronics box (below bench)alignment fiber (flower pot), with VisAO camera and wavefront sensor behind