Abstract:

According to the comparison before and after the laser trouble, IMC CMS error signals seem to be noisy.
At high frequency, current noise level is 2.2 times larger than before.

Detail:

I compared IMC and CARM CMS signals before and after the laser trouble.
Figure 1 and 2 show the time series data related to LSC controls before (Aug. 10 20:00 UTC) and after (Oct. 5 18:00 UTC) the laser trouble.
Though I compared OBSERVATION state before the trouble and INCREASINGLAS_POWER state after the trouble and some of signals are not suitable to direct comparison, CARM control should be the same between these states.

The largest difference would be the IMC error signals (K1:IMC-SERVO_MIXER_DAQ_OUT_DQ), which seemed stable before and brething after the trouble.
Figure 3 shows the close-up view of fig2 around the time when breathing happened.
There seems no significant frequency component in the breathing.

I also checked the spectrum of IMC error signals at those times (fig4).
Green and brown show the IMC CMS IN1 input equivalent noise on Oct. 5 and Aug. 10, respectively.
At high frequency, the residual frequency noise is 2.2 times larger than before.