NAOJ GW Elog Logbook 3.2
Aritomi and Yuhang
Recently we found the lock of filter cavity always has problems. For example, after we try to remote lock, it takes a while to lock or it doesn't lock.
So we checked several setting for that. Firstly, the injected green power confirmed to be 24.2mW. According to elog1886, we checked the setting of remote lock.
| Offset from DGS(unlock) | 3V |
| Offset from DGS(lock) | 0V |
| Threshold in rampeauto | -0.5V |
If I understand well entry1886, I think they are fine. (But it seems the offset from DGS(unlock) should be 1.5V. Although it is different from what we measured, it should not make difference for the remote lock performance)
Then we checked the Green_tra_DC with osilloscope, the transmission peak was only around 1V. So we decide to scan FC_green by sending a ramp signal to END mirror length. The measurement is shown in the attached figure.
It is clearly shown in the figure that there are visible sidebands around Green TEM00. Surprisingly, these sidebands are about half the magnitude of TEM00. Compared with elog1674, this is so much different.
We also checked the sideband of modulation from EOM by looking at the spectrum of GRMC reflection DC channel on oscilloscope. For GRMC ref_DC, the sideband is barely visible. So it should not be the problem of EOM modulation.
Today, we find that we were injecting 25kHz noise inside the PZT.
After removing the injected signals, the cavity scan was performed again. The diaggui file for cavity scan (green) is saved in Desktop/cavity as cavity_green_scan.xml.
This time, the spectrum is good.
Apart from this, FC green locking is normal again.