[Uchiyama, Miyoki, Yokozawa, Ushiba (remote)]

Abstract:

We found IR beam reflected by BS at Y end.
So, current BS alignment should be good enough for aligning downstream optics.

Detail:

First, we aligned XARM with the same manner as reported in klog29346.
Then, we aligned SR3 so that GRY beam hit the center of ETMY (fig1).
To achieve this condition, SR3 set point was changed as follows:
SR3 pitch: 0 (old) -> 17 (new)
SR3 yaw: -100 (old) -> -90.5 (new)

After SR3 alignment, IRMY was tweeked so that GRY reflection hit on the center of GRY REFL PD (fig2 and 3).
As a result, ITMY setpoint was changed as follows:
ITMY pitch: 25.9 (old) -> -11 (new)
ITMY yaw: -16.2 (old) -> -52 (new)

Then, we tweeked BS alignment so that IR reflection at ITMY hit the center of REFL PD (fig4 and 5).
Followings are the change of BS setpoint:
BS pitch: 18 (old) -> -20.5 (new)
BS yaw: -13.9 (old) -> 18 (new)

Then, to find the good alignment of BS by using TMSY GR PD, we first checked the current GRY beam position on TMSY when GRY hit on ETMY center.
However, Yokozawa-san found that GRY beam is not on even the first in-air mirror (upper mirror of the periscope) (fig6).
So, we gave up using TMSY PD to find the good alignment of BS.

Instead of using TMSY GR PD, we set an additional PD in the EYA chamber and connected it to NAB PD channel temporary (K1:NAB-EYA_BAFFLEPD_A).
PD is set so that GRY beam, which is aligned to ETMY center, hits on it.
Then, we closed GRY and found that IR beam can be observed on the PD signals without any additional BS adjustment!!
After that, I slightly move BS to maximize the PD output, and the setpoint became as follows:
BS pitch: -20.5 (old) -> -10.5 (new)
BS yaw: 18 (old) -> 20 (new)

Figure 7 shows the PD output, BS OpLev signals, and IMC trans power.
As you can see, PD power goes to zero when IMC lost lock: so we could confirm that the main IR beam hit on the PD.
So, BS is well aligned with respect to Y arm now.

Note:

With the same alignment, GRX also hit on the PD at Y end (fig8).
So, overlap of GRX and IRX at BS should be also fine.