Aritomi, Yuhang
There was an earthquake on 12th Dec. which caused mis-alignment of suspended mirrors. We worked on the re-alignment on 22th Dec. During the re-alignment, we found that the BS picomotor can be only moved in pitch direction but not in yaw direction. Fortunately, we were able to bring back the filter cavity alignment even in this situation.
Since BS picomotor couldn't be moved in yaw direction, we looked into the BS oplev spectrum. The result is shown in Fig.1 and we can see that the oplev signal is totally off from the nominal value. Note that input oplev was different because we took pre-amplifier from input temporarily.
For the time being, we can still work with this condition. But maybe we should correct BS mirror from touching in the near future.
The BS issue has been checked again today by switching off the oplev laser since I was suspecting that BS PSD maybe broken. Indeed, after switching off BS oplev laser, the BS oplev signal is as Fig.1 which is the same as what is taken last Thursday. So the strange signal we are seeing is from the broken BS PSD.
To confirm the health of BS suspension, we need to take an another PSD and use it to characterize BS suspension.