J. Kissel

As the title suggests, I used this week's calibration measurement time to gather some before & after thermalization measurements of the sensing function. Further, because Lilli saw improvement in the uncertainty in the response function around 50 Hz when using more actuator data (LHO aLOG 48968), I grabbed more actuator data. I'll process the data in due time, for now I just list where the data lives.

    ^/trunk/Runs/O3/H1/Measurements/FullIFOSensingTFs
        2019-05-08_H1_DARM_OLGTF_LF_SS_5to1100Hz_15min.xml     # During thermalization
        2019-05-08_H1_PCAL2DARMTF_LF_SS_5t1100Hz_10min.xml

        2019-05-09_H1_DARM_OLGTF_LF_SS_5to1100Hz_15min.xml     # After thermalization
        2019-05-09_H1_PCAL2DARMTF_LF_SS_5t1100Hz_10min.xml

    ^/trunk/Runs/O3/H1/Measurements/FullIFOActuationTFs
        2019-05-08_H1SUSETMX_L2_iEXC2DARM_8min.xml
        2019-05-08_H1SUSETMX_L2_PCAL2DARM_8min.xml 

        2019-05-08_H1SUSETMX_L3_iEXC2DARM_8min.xml
        2019-05-08_H1SUSETMX_L3_PCAL2DARM_8min.xml

As a sneak peak of the analysis, I attach a comparison between all previous sensing function data vs. the 2019-05-08, pre-thermalized data. You'll notice that the detuned spring frequency is quite low (~2.2 Hz), even lower than the 2019-05-02 measurement. However, Jenne and I noticed that we took the IFO out of observe about ~15 minutes in to nominal low noise, and the ADS loops (aka the spot positions on the TMs) had not yet converged. And looking at the past 45 minutes of power signals in the IFO (arm powers, POP power, SRC power, etc, the standard traces on the wall) after the measurement was complete, we saw a steady increase. Once we went back to nominal low noise to let it thermalize for an ~hour, the ADS lines came back on, finished converging, and the power signals dropped a bit.
Our guess is that because of the changes in SR3 disc heater power, the "best" spot position may not be the best any more, and revisiting the spot positions for this new cavity mode may be beneficial.