Jennie W, Sheila, Minhyo

Summary: We tried to walk the beam on the OFI with SR2 and 3 and cannot find another 'good spot' at least with moves in yaw of the SRC cavity axis.

Today we set the IFO up in single bounce with 10W input and ITMX mis-aligned. Then we moved the sliders back to what they were before Jenne made changes to them on Wednesday

Then we stepped SR2 down in yaw in steps of about 0.6 - 1.0 uradians and compensated for this movement on AS_C QPD by moving SR3 down in yaw also to recentre. Eevery few steps we had to tweak the pitch of SR2 or 3 in pitch as well as pitch motions of the SRs are slightly cross-coupled with yaw motions on the QPD.

Jeff then pointed out we should be moving SR3 first, as this is the mirror closest to the OFI so I switched to moving this mirror first and then SR2 to compensate. We tried to move the same amount down on SR3 that Jenne moved. The power got worse on AS_C, only imrpoving when we were very mis-centred in yaw on this QPD so that is not a good reference.

See a zoomed in image of the steps in SR2 and 3 and the effect they had on ASC-AS_A_DC_NSUM and ASC-AS_C_NSUM.

From this it looks as though the power throughput to ASC-AS_C (anti-symmetric port) was maximum when we were well-centred on ASC-AS_C just after the first cursor before we had started walking the beam.

I think this suggests that there is no small burnt spot in this degree of freedom across the OFI surface that we can walk to the other side of and see our throughput improve.

However the beam looked cleaner at points when it was positive in yaw on the QPD - not sure if this was real or not.

After these moves we reverted back (first cursor) to the alignment sliders we had before Jenne's moves on Wednesday 24th and took an OMC scan.

Then we went back to the 'nominal' alignment from this morning (second cursor) before maintenance started and took another OMC scan.