[Shimoda, Nakano]

The IMC with the FSS loop has been locked from last week, but it was not really stable. A reflection light from the IMC was not quite and oscillating at some frequencies.
We found that the 60Hz line noise and harmonics were so terrible that we can see higher than 100th(6kHz) harmonic noise! I attached error signal spectrum and a IMC REFL DC PD output and you can see so many line noise.

The offset circuit for AOM would be the problem because it receive the control signal of IMC control loop for AOM as single ended. it would make the ground loop and it would cause the noise. We would try to open the ground loop tomorrow and continue to try stabilization.

memo
70Hz peak also exist.
around 10kHz bump seems because of the loop instability