[Hirata, Ushiba]

Abstract:

We reconstructed POP forward beam path.
Though beam is still close to the knob of mirror mount just after periscope, the beam doesn't seem clipped.
Now, IR beam hits almost center of the both QPDs when the alignment to PR2 is good.

Detail:

1. Check of beam position at high power beam dump:

First, we requested aLIGNED state for IMMT1, IMMT2, and PRM.
Then, to confirm the good alignment has been kept from yesterday, we checked the beam spot on the PR2 HR target, which is almost center (fig1): good.

After confirming the alignment is good, we checked beam at high power beam dump (fig2).
Beam path seems far enough from the beam dump: also good.

2. Check beam spot on in-vac POM behind PR2:

After confirming the IR alignment to PR2, we checked beam spot on in-vac POM behind PR2 (fig3)
It is hard to say from the picture, but no clip happens at in-vac POM in my eyes.

3. Reconstruction of POP forward beam path:

After confirming beam spot on in-vac POM is not so bad, we started reconstruction of POP forward beam path.
At upper mirror on the periscope, the beam is not center but it seems no clip (fig4), so we keeep it as it is.
Then, we moved upper periscope actuators and hit the beam on the mirror center of lower mirror on the periscope (fig3).
After that, we moved FST1 in JGW-T1909623-v11, because it is hard to avoid clipping without moving the mirror.
Then, we aligned the beam to lower right of the FST1 (fig6) to avoid clipping at the knob of the mirror mount.
Figure 7 shows the current beam spot near the knob, which seems not so bad in my eyes.
After that, we realigned all the downstream and centered the QPDs.

Note:

During the work, on of the actuators of lower mirror mount on the periscope hits the periscope itself and cannot rotate to CW direction (we can rotate it in CCW direction).
So, we cannot move up the beam spot on FST1 without moving periscope mirror upward.
Since I am not familiar with the periscope installed for the POP forward, I didn't lift it up and keep it as it is.