B. Weaver, C. Compton, R. Short
Carrying on from alog90708 posted at lunch, Betsy, Camilla, and I offloaded the BS pitch sliders mechanically at the suspension. This was a tad tricky since we were looking at the beam(s) at HAM3 in front of PR2, so we had to work out blocking 1 ITM beam in order to not be confused by both beams crossing each other after the long PR chain of optics. In the end, we worked out the process to bring the BS PIT slider from +1000 to 0 which meant pitching the BS optic HR "up" (PUM roll bar "in"). Unblocking the other ITM, we got both beams overlapping onto each other with a little more slider to see how much better we could get them and see flashes in the AS_AIR camera (PIT = -300, YAW +1560).
Once back in the control room, Keita scanned BS alignment to find the SQZ beam reflected by ITMX as well as ITMY in AS camera as well as ISCT1 camera, ending with BS PIT = -520, YAW = 1677. With this alignment, IMC flashes reflected by ITMX as well as ITMY were visible in both of the cameras. Though SQZ beam and IMC flashes are not coaligned, the corner alignment is already pretty good as of now.
At this point we want to:
1) Recenter the OPLEV
2) Go in and physically calibrate which way the sliders go as seen on the oplev and at the HAM3 PR Beams since there is confusion around the sliders (direction, calibration, cross coupling)
3) Based on 2) Potentially make a request for HEPI YAW correction tomorrow when they resume HEPI "fine" alignment and actuator reattachment (TBD convo with SEI/IAS)
4) Get on with landing HEPI/actuator attachment, etc.
5) Final round of BS PIT SUS mechanical Offloading
The BBS OpLev has been recentered. I had to yaw the beam onto the QPD, as it was not on it. Once recentered, the SUM counts were around 2400, which is much lower than for the old BS, which was up around 20k. I checked the Output Configuration Switch on the BBS OpLev chassis in the biergarten and it has not changed, the amount of gain is still 0 dB. The other explanations are the coating on the BBS (OpLev beam is at 635 nm, which is not a design wavelength for the coating, so the %R at 635 nm for the BBS could be very different than the old BS) and a failing OpLev laser. I'll check the power output from the laser to see how it's doing (likely tomorrow).
Keita's note: After Jason recentered BS oplev, we changed the BS sliders to see the sign of the sliders (we knew that they were flipped) and how bad the pit to yaw coupling was.
Sign of the H1:SUS-BS_M1_OPTICALIGN_P_OFFSET and H1:SUS-BS_M1_OPTICALIGN_P_OFFSET are systematically wrong.
Positive PIT (right column top) in the slider consistently makes negative PIT on oplev, M2 OSEM and M1 OSEM, i.e. positive PIT tilts the BS up when positive offset is added to the pit slider.
Same story for YAW, negative PIT (left column top) in the slider consistently makes positive YAW for all sensors available, i.e. positive YAW rotates the BS clockwise when viewed from the top.
Arnaud and the gang will fix the sign issue.
PIT to YAW coupling is about 2 YAW per 1 PIT (i.e. PIT actuation make BS move more in YAW). YAW to PIT is not bad.
Positive PIT of 50 counts (uncalibrated) made negative 10urad in PIT and negative 20urad in YAW according to oplev. This agrees with our experience of observing how the beam spot moved in chamber as well as on the AS and ICST1 cameras when trying to move BS in PIT using the slider.
Interestingly, P2Y coupling seems to be OK for M1 (1:0.17 if we trust the QOSEMs), bad (about 1:0.7) for M2 and absolutely terrible (1:2) for M3 oplev.
Negative YAW of 20 counts made positive YAW of about 30urad and almost unmeasurable amount of PIT according to oplev.
LLO also saw a drop in power output on the BS oplev. The current sum is around 12 percent of what the sum was before the vent which matches the drop in LHO BS oplev power.