NAOJ GW Elog Logbook 3.2
We found that FC green error signal is very noisy. Fig 1,2 show the FC green error signal before/after lock. Fig 3 shows the spectrum of the FC green error signal after lock. There are two peaks around 20 kHz in the FC green error signal. It seems that the two peaks come from SHG. The SHG error signal is also shown in Fig 3. The SHG gain was 1.4. We decreased the SHG gain from 1.4 to 1, but the peaks around 20 kHz did not change.
During this investigation, we checked green power and OLTF of FC green lock. The measured green power is as follows. The green power seems reasonable. The UGF was 14kHz, which is also reasonable. Note that FC gain was 1.6.
| green power before AOM | 48.6 mW |
| green power before FC | 24.3 mW |
We also found that the Z correction is not very stable. We quickly checked the filters in filter bank of Z correction as follows.
| not bad filters | damp, damp2 |
| bad filters | DCdamp, dc_damp2, dc_damp3 |
The bad filters immediately caused FC unlock when they were engaged. The not bad filters didn't cause the immediate unlock, but FC was not very stable for long term. We need to investigate the Z correction.
