[Begum, Sheila]

Alignment: After the preliminary alignment work yesterday, see Camilla log 90593, we proceeded to attack the OMC scan problem step by step, starting with alignment. We aligned ZM4 and ZM5 using the two irises on SQT7 table as references. ZM4 was used for the first iris just past the periscope, ZM5 for the further iris. We reverted ZM6 and SRC alignment to O4 slider settings.  Then we used ZM6 and SRC to align the beam on AS-AIR camera and AS_C QPD. 
Then we turned on AS_A/B DC centering servos (actuators: OM1 & OM2), and OMC QPD DC centering servos (acutators: OM3 & OMC). This saturated the OMC_M1 T2&T3 outputs. AS_A/B servos align the input beam to the right pos/ang on OM3 and QPD servos should be able to align this beam to the OMC without saturating. While HAM6 is isolated and HAM7 is locked, HAM5 isn't isolated. Aligning the beam to the SQZT7 irises should condition the beam out of HAM7 well, so perhaps the issue is the HAM5 nonaligned state. (I did try to reset the watchdog, it immediately went back to tripped state.) 
Then we tried turning on only the OMC QPD DC centering loops, without the AS_A/B loops, and this worked! OMC sus is no longer saturating, and the mode scans look more reasonable, see attached preliminary scan. The beam is also bouncing a lot less on OMC QPDs compared to when the AS_A/B centering loops are on. 

Setting the scan: Conducting OMC scans in air is no easy feat. The PZT scan should be quick enough to not inherit the beam jitter, but also slow enough to properly sample the maxima of peaks, without running into anti whitening problems. During new HAM6 installation at LLO, this meant turning of HAM6 and corner purge as well as cleanrooms nearby (vertex cleanroom was okay to leave off, although vertex purge needed to be turned off). Keita suggested installing a PD in the OMC trans camera can, and using such a (non-whitened) PD for the OMC scans. 
Screenshot of the sliders for the preliminary scan we took today, plot showing the magnitude of the second order mode, and the fundamental mode, with these awggui pzt scan settings. Once a reliable measurement flow is achieved, we would like to automate ZM4/5 psam scan + OMC scan to estimate the achievable SQZ-OMC & SQZ-IFO mode matching limits.