Starting with yesterday's alignment, we tried to move the beam spots on IFI input baffle (using IM1), IFI output baffle (using IM2) and the baffle in front of IM4 (using IM3).

We had to make a huge change in all of the optics used: IM1 yaw: -500 urad, IM2 yaw: -900 urad, IM3 yaw: -720 urad.

Forgot to measure PIT/YAW position of IM4_TRANS (and we cannot trend it as we need fast data of segments) but the beam was on IM4_TRANS with almost full IM4_TRANS_SUM.

IMs didn't rail but this is clearly NOT the right way to move. Instead, what we need seems to be to shift the beam position on MC3 by a few mm in -X-Y direction.

We didn't bother to move PRM nor IM4 so the IFO REFL was again misaligned badly.

(One thing to note is that with this drastic change in the input alignment, the beam was still hitting the IM4 TRANS but not ISS QPD. However, just by turning IM3 we were able to regain the beam on ISS QPD. Now I'm fully confident that, whatever alignment we end up having after pumping down, as far as the beam is on IM4 TRANS, we can find the beam on ISS QPD by scanning IM3 (and IM2 if necessary) and slowly walk the beam using the picos to have a good alignment in the ISS path.)

We also measured the beam position (both height and Y position relative to the ideal beam path measured at specific X coordinate) to better understand the IMC beam. Numbers are to follow, but the gist is that the beam position is good (i.e. likely centered) on MC3 but is off in -Y direction by 3mm or so on MC2 even though MC TRANS is close to center.

So, for tomorrow:

• Finish the beam position numbers for IMC.
  • Starting from there, see how much beam spot moves on baffles when we center the beam on MC2 AND move the beam spot by a few mm in -X-Y direction on MC3.
  • Figure out how much we have to move JM3, MC1, MC2 and MC3 to cause such a change.
• If we can do that calculation before noon,
  • Transition to hazard in the afternoon.
  • See IM4_TRANS PIT and YAW.
  • Back off the changes we did today (Tuesday).
  • Change JM3, MC1, MC2 and MC3, refine to get decent flashes.
  • Use IM2 and IM3 to unclip the beam on IM4 baffle.
  • See IM4_TRANS PIT and YAW. Adjust IM3 further to steer the beam on IM4_TRANS where it should be.
  • Check IM4 baffle again.
  • Check the beam position on PRM.
  • Use IM4 to steer the beam on PR2. Measure the beam position on PRM and  PR2 like we did for MC.
  • Make sure that the beam is retroreflected by PRM as good as we can. See the IFO REFL beam on the baffle before HAM2-HAM1 septum window.

My guess is that the beam has been (at least very close to) clipped by some of the IO baffles for a long time, and the above practice is to see if there is an alignment where the beam is at least not clipped.