Hirata, Yano, Satou N., Akutsu

Summary

Completed installing the mid-size baffles in the PRM chamber. Note importantly that the nominal point at which the main IR beam passes through is about 6-mm displaced from the center of the aperture of the AR mid baffle so that the surrounding two ghost beams can be peacefully arrested.

Installation procedure

We mostly followed the installation procedure document (JGW-T2214066), so please have a loot at it. The preparation was reported in 20783.

• Fig. 1 shows the mid-side baffles before installed. The one in front is for the HR side, while the other is for the AR side. The AR side baffle has a smaller aparture than the HR side one (there was a discussion at the design review at that time...); the AR side baffle needs to catch two main ghost beams, surrounding the main beam, so it has such a smaller aperture.
• Called SAFE state to the PRM and PR2, turned the KOACH filters at the relevant places, and set the PR HR target and PR2 HR target.
• Set a laser level (in green) in front of PR2 HR to throw a vertical reference line by illuminating the PR2 HR and PRM HR. Also set a laser level (in green) in front of the PRM HR to throw a horizontal reference line onto the PRM HR.
• Set the mid-size baffles at HR and AR side of PRM by referring these vertical and horizontal refrence lines. As anticipated, some shims were inserted under the baffles to match the height. Every time the suspended optical bench for the baffles was once lowered to sit on the bottom structure, and set teh baffle, did some fine adjustement with respect to the reference, and release the table to check the situation, and again let it sit down on the bottom, and fixed the clamps, and then, release the table again.
• The HR one was not so difficult to set.
• The AR one needed some iterations with using two positioners. Anyway finally we put it with respect to the reference line. Maybe partly due to the suspended table is pitching (see 17635).
• Fig. 2 just shows a scene of still mid-way of the installation, but you can feel how these mid-size baffles have been residing in the PRM chamber.

Confirmation

• We called ALIGNED state to PRM to see where the two ghost beams will come on the AR mid-size baffles. Fig. 3 shows an IR viewer's view for the AR side baffle surface. You can see two ghost beam spots. The nominal positions of these ghost beams can be found in the installation procedure document (JGW-T2214066).
• Need to revisit the IR beam optical axis. With respect to the vertical reference line from the laser level (located at close to PR2) illuminating PR2 and PRM, the IR beam axis seemed horizontally displaced (3-4 mm at PR2 target in the plus Y direction (Fig. 4), while 2-3 mm at the in-between the PRM-IMM chambers in the minus Y direction (Fig. 5)) with respect to this reference when IO guardian is at PROVIDING_STABLE_LIGHT. I also tried to compare them by additonially calling XARM guardian to ALIGN_IMMTs, but checking the IR beam will mean cutting the IR beam so it was difficult to say something definite today. Need to re-consider the tactics. Anyway, maybe this relative horizontal displacement would be due to IMMT1's arbitrary alignment. So, later we need to revisit this issue for more precise adjustment of the optical axis just before closing the central chambers.