M. Todd, S. Dwyer
This morning we were not locked before Tuesday maintanence, so I skipped the HWS transient measurement and started immediately with the IMC and input jitter measurements I had planned. For posterity, the IFO was unlocked but the IMC was locked and input power taken to 62W, and then the ISS was turned on.
I continued attempting to tune injections of the IMC DOFs, but was not able to see any coherence to either the corresponding DOF error signal or the ISS loop, in the bands I was interested in. I think the DOF loop bandwidths are just tooo low for this kind of measurement without saturating the suspensions. I may continue to try some very small bands but nothing above 15 Hz anymore, as I'm just not convinced there is any reasonable coupling to the ISS there. The list of figures shows the injections from this injection set.
I then took some coherence measurements of the various sensors to the IMC ASC/LSC with the ISS loops during a quiet locked time to wrap my head around things better, and noticed a large coherence between the ISS first loop diodes and the ISS second loop witness sensor. I was initially confused by this but after talking with Keita, this is not surprising as there is most likely intensity noise that the 2nd loop is seeing and suppressing and thus imposing that suppression into the first loop sensors (thus the coherence).
Then I did some input jitter excitations, and without actually calculating the transfer functions ( those estimates will come later in a comment using Sheila's excess power code, due to the lack of coherence to ISS ) I don't think the ISS loops are limited by the input jitter at these frequencies. The list of figures shows the plots from this injection set.
List of Figures
