https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=90343

As per the plan in the above alog, we did the following for IMC and IM alignment.

• Rotated JM3 in negative PIT to center the beam on MC2 in YAW (i.e. the input beam comes close enough to the nominal MC2-MC1 line measured at the location we chose in HAM3). The beam height was good.
• Rotated MC2 to bring the beam back to the center on MC3 (i.e. MC2-MC3 line comes close enough to the nominal line measured at the location we chose in HAM2). The height was good.
• The beam was already flashing, MC2_TRANS_SUM was already good enough according to Elenna so we didn't bother to turn MC1 and MC3, even though we could have refined further.
• The beam spot on the IFI output baffle was very low, so we made a big change to IM2 in PIT. It looked good in YAW but we steered IM2 in YAW to make the beam slightly move to +X direction on the IFI output baffle because so we don't have to do too much YAW for IM3.
• We started moving IM3 but didn't finish.

As for clipping, before making IM changes, I installed an iris between IM3 and IM4 to see if the beam from PRM was retroreflecting.

• It was not that useful for the intended purpose as I couldn't tell if the IFO refl beam is actually retroreflecting. If anything it looked off in PIT.but it was very hard to tell any difference for YAW even when we made +-300urad changes in PRM in YAW.
• However, I noticed that -100urad on PRM YAW makes the IFO refl beam clipping better on IFI input baffle, and -300urad made it disappear.  +X side of the IFI input baffle. However, this also resulted in a clipping of the IFO refl beam on the IFO refl baffle in +Y edge. We'll see how this goes after we're done with the IM2 alignment we did today.
• Clipping of the IFO refl beam on the IFI input baffle doesn't look like a ghost beam. I used an IR sensitive camera and it was a bright beam.

Numbers and pictures will follow.

Will continue doing the IM3 and IM4 alignment tomorrow.