QPD centering

As is shown in my beautiful hand drawing below, the beam going through the OFI is reflected by OSTM then split by a BS and received by QPD1 and QPD2.

The beam on the QPD1 was centered by the rotation of OSTM yesterday.
However, the beam on the QPD2 was shifted toward the direction of the arrow indicated by the green dot.
It is convenient to work with the mirror image of QPD2 (red colored) by the BS plane. In the mirror image, the green dot is mapped to the blue dot.
The actual beam axis at that time was the line going through the center of QPD1 and the blue dot (the blue line).
This means the location of the OSTM was shifted to the right (blue mirror) from the ideal position (black one).
Therefore, we needed to move the OSTM in the direction indicated by the green arrow.

We did exactly that using pushers.
We pushed the OSTM frame to the left with one pusher. Rotated the OSTM in Yaw with another pusher to center the beam on QPD1.
We then checked the beam spot position on QPD2 with the IR camera (SONY alpha 7s). The beam gets closer to the center of QPD2.
After a few iterations, we were able to center both of the QPDs.

OMMT1 shield plates

After the OMC QPDs are centered, Akutsu-san attached the shield plates on OMMT1.
https://klog.icrr.u-tokyo.ac.jp/osl/?r=30050

X-arm alignment

We noticed that the X-arm transmission was low (~0.6).
Ushiba-san aligned the X-arm during the lunch time. The transmission recovered to near 1.

Since the upstream alignment was changed, we re-aligned SR2 with the iris in the OMMT chamber.
Then we centered the OMMT2 trans QPD with OMMT1.
After doing these, OMC QPDs started to receive beams again.

Aluminum foil covers

Since the wind from KOACH filters moved the OMMT1 and OMMT2 suspensions too much, we put aluminum foils on the flanges between the OMC and OMMT chambers.
We made small holes on the foils to let the beams go through.
This allowed us to fine adjust the centering of the OMC QPDs. We used OMMT2 and OSTM picomotors for this.

OSEM adjustment

Takahshi-san adjusted the OSEMs of the OSTM because they were completely out of range after the OMC QPD alignment.
The TF measurements after the adjustment showed strange shapes.
Takahashi-san found that EQ stops on the TM were in contact with the mirror.
Retracting these EQ stops recovered the transfer functions back to the normal state.

OSTM shield plates

Akutsu-san re-installed the shield plates for OSTM.
https://klog.icrr.u-tokyo.ac.jp/osl/?r=30050

QPD centering servo

We were able to engage the centering servo of OMMT2 trans QPD.
However, we could not engage the OMC QPD centering servo. Somehow, the loops went crazy.
We did not spend enough time to investigate this problem.

OMC flash

By moving the PZT slider manually, we were able to see the flashes of the OMC with the OMC trans DC PDs.
The OMC trans. camera seemed to be not centered (no flash image could be seen).

Beams on the AS table

We checked the beams coming out of the OMC chamber.
The OMC REFL beam can be seen at the periscope. So the beam path seems to be reasonably preserved.
The AS RF beam was not found on the AS table. We found that the OSTM transmitted beam was missing the steering mirror.
We need to readjust the position of this steering mirror.