While TJ was running initial alignment for the green arms, I noticed that the ALS X beam on the camera appeared to be too far to the right side of the screen. The COMM beatnote was at -20 dBm, when it is normally between -5 and -10 dBm. I checked both the PR3 top mass osems and the PR3 oplevs. The top mass osems did not indicate any significant change in position, but the oplev seems to indicate a significant change in the yaw position. PR3 yaw was around -11.8 but then changed to around -11.2 after the power outage. It also appears that the ALS X beam is closer to its usual position on the camera.
I decided to try moving PR3 yaw. I stepped 2 urad and which brought the oplev back to -11.8 in yaw and the COMM beatnote to -5 dBm. Previous slider value: -230.1, new slider value: -232.1.
The DIFF beatnote may not be great yet, but we should wait for beamsplitter alignment before making any other changes.
Actually, this may not have been the right thing to do. I trended the oplevs and top mass osems of ITMX and ETMX and compared their values during today's initial alignment before moving PR3, to the last initial alignment we did before the power outage. They are mostly very similar except for ETMX yaw.
| P then | P now | Y then | Y now | |
| ITMX oplev | -7.7 | -7.8 | 5.8 | 5.6 |
| ETMX oplev | 2.7 | 3.1 | -11.5 | -3.1 |
I put the PR3 yaw slider back to its previous value of -230.1 until we can figure out why ETMX yaw has moved so much.
I moved PR3 yaw back to -231.9 on the slider. This allowed us to see PRMI flashes on POPAIR. We can revist if we really want to keep this alignment of PR3 on Monday.