Nakano, Ge, Akutsu

After the work yesterday, we found the beam spots were, even they were in resonance, out of the CCD viewsites! So we investigated what happened (or what I did...).

What we did

First we found that the green light beam was going through almost the center (or little bit lower) of the optics in the BRT part; those positions were seemed to the same with the ones yesterday. Even the final output sterring mirrors of the BRT (for green), the spot seemed around center. On the other hand, the resultant beam spot on periscope mirrors (out of the chamber) for green was moved, and the green beam spot was scraped a lot. Roughly speaking, the green spot moved about a few mm at 1m away, meaning a few mrad rotation in yaw...

After some discussion, we determined to tweaked the alignment of the final steering mirror for green. Then the green beam spot came back to the CCD. (Fig 1 and 2 show before the tweak, and Fig 3 and 4 after)

As for IR, as some of you know, a ghost beam of green went together the IR beam line, so we can estimate the IR spot somehow. Surprisingly, the IR beam path was not so much shifted... anyway it was shigted, so we tweaked a steering mirror just in front of the IR CCD to center the spot. The following work will be done in the next week.

Why this happened?

Actually we have no idea.... Considering what I did yesterday, the suspecious work was just tightening M10 screws. I can estimate the yaw move by the LVDT signal log, and the jump was 210 urad. There is still another suspicion that the whole TMS-VIS might moved with respect to the base plate in the chamber (is it really possible????). Interestingly the IR beamline was not so shifted. If the somehow-happened yaw rotation really happened, the effect should be the same as the input beam was rotated to TMS, so it would be possible to estimate the amount...