Sheila, Naoki
Before cooling down OM2, we aligned OMC by walking the OMC QPD offset. After the alignment, we could reduce the pitch jitter coupling by a factor of 3-5. The top left and top right plot in the first attached figure shows the DARM and the jitter coupling with original (green) and final (orange) QPD offset, respectively. The pitch jitter injection is between 80-90 Hz and yaw jitter injection is between 95-105 Hz. The pitch jitter coupling reduced by a factor of 3-5 with final QPD offset, while the yaw jitter coupling is almost the same.
The original and final OMC QPD offset are as follows.
| |
OMC A P |
OMC A Y |
OMC B P |
OMC B Y |
| original QPD offset |
-0.01 |
0.05 |
0 |
0 |
| final QPD offset |
0.15 |
0.09 |
0.19 |
-0.12 |
We injected the jitter noise and tried to minimize it by walking the OMC QPD offset. We injected the gaussian noise between 80-90 Hz for pitch (IMC-PZT_PIT_EXC) and between 95-105 Hz for yaw (IMC-PZT_YAW_EXC). We are not sure why, but the pitch and yaw excitation appear both in WFS DC PIT and YAW signals.
The second attached figure shows the jitter coupling from WFS A DC YAW to DARM with original (green) and final (orange) QPD offset.
The third attached figure shows the related signals including the optical gain (KAPPA_C). The optical gain before and after OMC alignment is 0.978 and 0.964, respectively.
If we keep changing the QPD offset around the optimal OMC alignment, we should see the sign flip of jitter coupling. Although we could not change the OMC alignment much due to optical gain drop, we did not see the sign flip of pitch jitter coupling and this might indicate that there are multiple jitter coupling path for pitch.
After the QPD alignment and before cooling down OM2, we took 5 minutes quiet time as follows.
2023/7/12 16:53-16:58 UTC
