Jenne, Evan

Tonight we ran through initial alignment of the corner in order to get back to DRMI locking (without arms). This is a bit different than usual, since we cannot use the X arm as a reference for PR3 (via the COMM beat note) or for IM4 and PR2 (via the IR input pointing).

Initially we just restored the suspension slider values for PRM, PR2, PR3, SR2, SR3, SRM, and IM4 to their pre-vent values. Then we tried locking PRX, but found that we could not get decent fringing, even by moving the PRM a milliradian or so in pitch and yaw. So we instead restored the pitch and yaw values of PR3 as seen by the oplev, and then optimized the fringing using PR2 and PRM. This allowed us to lock PRX with a decent amount of light at the AS port (>1000 ct on ASAIR_LF with 10 W PSL power), and we then engaged the PRX WFS loops as usual.

We were able to lock the dark Michelson and optimize the BS angle without issue.

We were able to lock SRY using a similar philosophy as PRX: we restored the SR3 alignment to its pre-vent values as seen by the oplev. After that, we saw fringing and were able to optimize it by moving SRM. Then we were able to lock SRY and engage the SRC alignment loops without issue.

Then we tried moving on to DRMI locking. The flashes at the AS port look more or less normal, but there seems to be very little going on in POP18. We saw some flashing with peaks < 1 ct, but for normal DRMI acquisition we expect hundreds of counts. We went onto ISCT1, and found that the beams were low (by about 1 mm) on both the POPAIR diodes. We adjusted the spot on POPAIR_B so that it is more centered, but this only brough the flashing up to at most 15 ct (at 20 W PSL power).

Since it seemed that the POP path was somehow not aligned, we then relocked PRX (with WFS loops feeding back to PRM) and moved IM4 while watching the spots on the POP QPDs. We centered the spots as best we could, then ran through the other initial alignment steps again, and then tried locking DRMI. However, this did not improve the flashing in POP18. For the time being, we reverted our change to the POPAIR_B pointing on ISCT1.

JCD:  Since we were able to lock the individual pieces of the vertex, it seems like the vertex optics are all aligned to one another, however I am less confident in the overall alignment (e.g., the input pointing doesn't match what the Xarm will want, so we're not hitting all of our PDs simultaneously).  I am not quite sure how to resolve this, with the sensors that we have at our disposal right now.