[Erin, Daniel]
The goal of today was to calibrate the Shack-Hartmann sensor in order to make sure that we are ready to start pressing the mirror to view higher order modes tomorrow. This meant we wanted to better focus the lens array, so that the points are directly on the center of each microlens (see the Thor Labs setup linked) and align the end mirror mount so that the contribution by the tilt in the Zernike coefficents is as close to 0 as possible.
To do this, we made a few changes made to the setup:
- Moved the end mirror mount, the quarter wave plate, and the camera closer to the beam splitter to make sure changing the tilt on the 5 axis stage didn't move the beam out of the view of the camera.
- Mounted the MLA to a lens mount and placed it right in front of the CCD camera so that there is about a focal length between the MLA and the sensor. This vastly improved how the images look (see attached images).
- Added an alignment mirror before the camera to better adjust the setup.
When it came to reducing the tilt, I got as close to zero as I could, which ended up being a coefficent of around 1.8 for the contribution of the x and the y tilt. I plan to try to keep moving around the 5 axis to get it lower. The points on each of the micro lenses are much more distinct now, not like the squares they looked like before. I also made a wavefront map using these coefficents, and it looks similar to the fizeau data, with a small astigmatism on the mirror that we observed before.
Finally, just for a quick test, I added a f=300mm lens in front of the mirror to see what would happen and to simulate a curavture. The points appear to move closer together, which we would expect, since it is a converging lens that moves each of the points some relative displacement from the centers of the microlenses.
