Jennie W, Sheila

We wanted to inject into individual optics to optimise A2L gains today.

This was because we worried that the CHARD and DHARD injections we made on Friday to evaluate our ITM yaw A2L gains mean that we are moving our ETMs to cancel out the noise on our ITMs.

We injected into the channels of the form H1:SUS_{ETMX,ITMX,ITMY}_L2_LOCK_{Y,P}_EXC.

Today we tuned ETMX Y2L, ITMX P2L, ITMY P2L.

The green traces were measured with the new better value and the blue shows the reference value before injecting. We managed to get gains which decreased the transfer function of that test mass motion to DARM. Although it can be seen from the plots of coherence that the coherence was very small for our injections which might imply that there was some non-linear coupling at the frequencies we injected at.

The starting values are in this image and we changed them to these values.
 

This means we have finished retuning the camera servo that keeps the spot on the beam splitter constant (CAM1).

We need to retune the camera offsets for servo 2 which moves ITMX and ETMX to keep the spot on ETMX, and then retune the ETMX A2L gains for this new value.

We also still need to retune the camera offsets for servo 3 which moves ITMY and ETMY to keep the spot on  ETMY, and then retune the ETMY A2L gains for this new value.