[Aritomi, Yuhang]

We continued the investigation of the 20kHz peaks in FC green error signal. We checked the IRMC error signal and there are no 20kHz peaks in the IRMC error signal. So the 20kHz peaks should not come from laser.

Then we measured SHG OLTF and found that there is a peak around 20kHz as shown in Fig 1. In this measurement, the SHG gain was 1.3. We decreased the SHG gain from 1.3 to 1 to avoid the 20kHz peak, but the FC green error signal is still noisy.

Regarding the Z correction, we found that the dc_damp2 filter was completely different from the one written in elog2608. We changed the dc_damp2 filter to the one written in elog2608. We set the dc_damp2 filter gain as 10 in foton and 4 in medm. However, FC is still not very stable.