Date: 2024/5/24

Ushiba, Hirata, Akutsu, D. Chen

Contains duplicate content with klog-29629.

Summary

We aligned the IR beam referenced with Yarm up to the SRM surface. At this time, SR2 alignment adjustments were performed and oplev centering was also performed.
We searched for the reflected light from the SRM, and although we found one that seemed to be it, we haven't been able to find the other one.

Details

1. As the GViya was opened, we checked the beam alignment again and aligned it up to the surface of SRM.

   1. Aligned the IR beam inputting into the SR area with the Yarm as the reference.

   2. Checked the beam position at SR3 with the target -> it is almost at the center of the target. (Fig 1 on klog-29629)

   3. Checked the beam position at SR2 with the target -> it is at the center of the target. (Fig 2 on klog-29629)

   4. Checked the beam position at SRM with the target -> the beam was about 25mm below the center of the target. (Fig 4 on klog-29629)

   5. Adjust the beam position at SRM by changing the alignment of SR2 -> the beam was adjusted to the center of the target of SRM. (Fig 5 on klog-29629)

      • To do this, the direction of SR2 had to be moved so far beyond the oplev range at this time.

      • Especially the beam position of the tilt oplev went out of the upper side range of the QPD.

   6. With the beam centered on the SRM target, the SR2 oplev (tilt and length) was adjusted to the center of each QPD by changing the QPD positions.

      • We did not touch the length direction of the length oplev QPD.

      • At the time, we confirmed that the oplev beam coming out of the SR2 vacuum chamber was not clipped by the first mirror. = We looked at the first mirror and made sure the edges were not shining with the oplev beam. (Forgot to take a picture.)

      • Closed the windshield of SR2 oplev.

   7. We closed the loop using SR2 peoplev and checked the beam position at SRM -> the beam still was at the center of the SRM target. (Fig 6 on klog-29629)

2. SRM reflected beam searching

   1. SRM state was kept at SAFE.

   2. We tried to find the reflected light by SRM. There should be two, one from the front surface (+y side) of the SRM and the other from the back surface (-y side) with the edge.

   3. We found one faint beam between SRM and the its front (+y side) mid-size baffle. This beam was shifted about 20 mm from the main beam at a position about 20-30 cm away(+x side) from SRM. Because we could not find other faint beam around, this one might be the beam reflected by the back surface of SRM. This faint beam hits the mid-size baffle of SRM. Once the main beam was blocked, this beam disappeared, suggesting that it originated downstream from the SRM surface. Since no other beams were observed in this region, this beam might be the beam reflected by the backside of the SRM.

   4. We looked for the assumed beam being reflected from the front surface of the SRM.

      1. Looked for it in the SRM chamber but could not find it.

      2. Looked for it in the SR2 chamber but could not find it.

      3. Looked for it in the SR2 chamber while swinging the SRM in the tilt direction, but could not find it. The vertical movement of the reflected beam on SR2 was assumed to be a few mm.

   5. As a result, we found one beam that we think was reflected by the SRM back surface(?), but not the other.