This is wrong! See following elog for corrected plot (and explanation)
I'm not done meditating on what's going on, but here's what I've got right now:

This is a beam profile, using the distances from the combined Kiwamu / Jenne sketch earlier today.
0 meters along the horizontal axis is meters from the Mode Cleaner waist. (Yes, I was bad and forgot to label it. Get over it.)
The pink and green dots to the left of the plot are the MC fitted waist measurements that we made in May 2010.
The pink and green dots in the ~center of the plot are the fitted waist measurements that Suresh and Keiko took yesterday, of the IPPOS path, so after the MMT.
The black dot is where we would like our non-astigmatic beam to be. This is the calculated waist size of the cavity mode, using the new ~37.76m distance, after we moved the ETMs to their current positions. The black dot indicates 3.036 mm at the ITM (averaged between the BS-ITMX and BS-ITMY distances).
The moral of the story that I'm getting from this plot: something funny is going on.
The distances Kiwamu quoted on the sketch are very close to the ones that I used for designing and checking the MMT in the first place, which were based off of measurements using rulers etc to measure distances. Steve said he looked at photos today, and agreed that Kiwamu's numbers looked reasonable also.
Something that we haven't done lately is measure the position of each optic from every other optic, along the beam path. I propose we come up with a clever way to put a target on top of / next to mirrors, and then a way to hold the laser distance measure-er at an optic, so that we can go thorough systematically and measure the actual path that our beam is seeing. Maybe this is too much work, and not worth it, but it would make me happier. In my head, these 'fixtures' are just small pieces of cleaned aluminum, one that can sit on a mirror mount, and one which we can use to align the laser ruler to approximately the front of an optic. Nothing fancy. |