Danny, Craig, Dan Brown

We had a long lock run in low noise tonight. During this we were adjusting the PRC1 offset resulting in some slight alignment drifts of the BS and ITMs (45623). You can see the affect this has on the HWS spherical power here. The alignment offsets started around -3000 seconds on the time axis, first in pitch and then in yaw.

This drift was enough to see how the self heating spot moves relative to the HWS probe beam: ITMY before and after. The red cross is where the IFO beam was before the vent. The other thing to notice is that by choosing the reference time for when the point absorbers have heated up we can get the wavefront distortion without them included, so we see the broader absorption. We also ramped the CO2 heater to get a position of the CO2 relative to the interferometer beam, which is noticeably offset.

We did the same alignment shift images for ITMX, before and after. For ITMX the self heating spot wasn't in a bad position to begin with, however with the new offsets it's become misaligned to the HWS probe beam, so we need to do some picoing.

Lastly, we ramped CO2Y up and down to find the position on HWSY but also to see how the PRC gain and noise was affects. Turning the CO2Y power up 2X resulted in the ASC becoming unstable and noise increased at low frequencies, PRC gain didn't really change. Turning it down 1/2X did the same, DHARD yaw became unstable and we lost lock. We did notice a high frequency bump appearing at several kHz, similar to the frequency noise bump when changing the CO2 laser significantly. More investigation needed on that though. When HWSX is sorted out again we'll run some better comm and diff CO2 tuning.