Yaochin and Yuhang
Since last week we had again the problem of filter cavity. We saw filter cavity transmission varied from 2000 counts to 3000 counts. In the end, we found out actually we are not operating SHG in the optimal temperature. Also, we had a temperature change due to the change of air-conditioner mode, so it varied.
After everything settles down, we fixed again the setting of the filter cavity lock loop.
|
Attenuation |
2.9 |
|
Gain |
2.0 |
Then we measured the open-loop transfer function again. Also, GR locking accuracy and IR locking accuracy. Especially this time we measured more accurately the low-frequency part of it. And compared with the measurement we did more one year ago(elog 690), the high-frequency part is the same while the low-frequency part is quite different. We should consider more why we have this big difference in IR error signal now.
We should also measure coherence between IR error signal and each oplev spectrum.
As pointed out in the last FC meeting, the error signal for green and infrared around 10kHz is similar. This is actually strange for me. Due to the cavity pole for infrared and green has a factor around 25 difference. Above their pole frequency, the green error signal should be around 25 times larger than infrared.
However, I checked several times this entry and compared with elog642, I couldn't find what is wrong. I will try to measure it again.
As pointed out by Aritomi-san, the formula used to calibrate the measurement had some problem (check entry642). After correcting that, the measurement result becomes reasonable.