The measurement done last week shows RMS locking noise is much lower than we expect(entry 1486). It was almost 50 times lower than the measurement done last year(entry 642). So we decide to double-check by using time series.

I did the measurement of RMS locking noise when the gain is 7 and 10. The result is shown in the attached figure 1. However, I just realized the gain of 10 sometimes brought some resonance(I didn't find this resonance last week). Now the gain of filter cavity lock should be 7.

Then I measured the time series of the error signal. And the calibration result is attached in figure 2.

The measurement of time series shows RMS as 4.33Hz while FFT shows 1.5Hz. Basically, they are very similar.