10.21.10

Finally, I think I'm just about done with the realignment. More screw-ups along the way than I would have liked considering I've done this countless times by now, but overall I think this was worth it. One problem worth mentioning was that I had to add an additional relay tele with unit magnification at the end. It turned out that despite all my careful measuring and CADing, I didn't account for the actual length of the WFS, and I wasn't able to place the lenslet array on the focal plane of the resizing telescope at the end. I thought about ordering a couple new lenses with a larger lens at one end, but I ended up just using a pair of 50mm lenses (compared to the 25mm lens at the end of the resizing tele) to reimage the beam onto a more spacious focal distance.

And holy shit the thing actually works pretty well. The beam does actually stay pretty constant when I apply random commands to both DM's. Although things go to shit quickly if I move them at their maximums, that never really happens in actual experiments. Plus its nice to know your actuator's have more range than your sensor's can deal with.

The beam diameter right now is around 1.5mm, meaning that I can meet my objective of using a WFS resolution of 220x220. With this size I can get WFS frame rates > 100 fps. Hopefully I can stay around 80 Hz closed-loop when I finally get the camera trigger installed.

Here's a video running the disturbance and control commands for a closed-loop experiment with the old setup. Obviously its nonsense, but its clear how consistent the beam size is compared to before.



Its pretty cool (to me at least) to see the spots dancing around like that without the beam drastically changing around the margins. Some of the spots are smeared out, but I think thats a result of the beam size. With a smaller diameter, each lenslet captures more relative area. Thus if there are high spatial frequency aberrations the portion of the beam entering each lenslet will have more to it than just tilt, and thus won't form a tidy spot.

An open question is how much I can mitigate the bias. The only way I can see to easily do this without messing up all the focal planes is to move the 500mm lens. Also, I have to start changing the slope calculation code to use this reduced beam. An open question is whether I should create a new reference wavefront or use the existing AOS file.