A. Pele, K. Izumi, J. Kissel

After unlocking ITMX and pulling the first contact from SRM, we wanted to re-check our report of finding the IFO beam going through the HAM5 OFI. I outline the process below, but in summary, we have found an alignment that again gets the beam through the OFI, but with the beam mis-centered in YAW at SRM with +200 [urad] YAW offset on SR2 ~16 [m] away. Below are the alignment deltas from what we had in DRMI, i.e. pre-vent. We can be comforted in that the alignment change of the input chains are all ~0.5 [mrad] in P and Y, and within the range of the alignment sliders. This gives us confidence that IAS values for the new ITMX are quite good, and we should have only to do a similar amount of effort to get the Y-ARM beam also to go through the OFI hole.

Attached are pictures from the morning's activity, as well as a cartoon drawing of how the alignment into the OFI changes between an SR2 Y offset of -800 [urad] (clipping on input) vs. -600 [urad] (centered). The coordinate system drawn to the left the cartoon is global IFO coordinates. Finally, a screenshot of the alignments for all SUS.

Alignment Deltas:

     Pre-vent [urad]             Now [urad]          Diff [urad]
        P       Y              P         Y         P         Y
MC1   +1254   -2366.0     +1254.0    -2366.0    (none)    (none)
MC3   -550.0  -2467.0      -550.0    -2557.0    (none)      -90.0
IM1      0.0  +1469.0         0.0    +3786.1    (none)    +2317.1
IM2  +4600.0  +2000.0    +35849.3    +5154.7   +31249.3   +3154.7
IM3  -1397.9  +1060.8    +14057.0    +5464.0   +15454.9   +4403.2
IM4  -2350.0  -3607.0    -30000.0    -9337.0   -27650.0   -5730.0
PR2   +434.7   -355.7         0.0    +1350.0     -434.7   +1705.7
PR3   -245.5   -250.9         0.0     +250.0      245.5    +500.9
BS    +180.6   -266.4      +750.0     -600.0      569.4    -333.6
ITMX   +38.7    -48.9         0.0        0.0      -38.7      48.9
While we've changed the IMs quite a bit in both pitch and yaw (presumably to account for the bypass beam), but downstream all optics (PR2, PR3, BS) have not changed more than 0.5 [urad] in pitch, and PR2 is the worst offender with ~2 [mrad] in yaw, with the rest also below 0.5 [mrad]. These changes (at least of the large optics) are well within the range of the core optics. The largest offsets on the IMs are taking up ~80% of the DAC range.

Alignment process this morning (again, after release of ITMX and removal of SRM First Contact): 

- Check beam at SR3. Looks like clipping
- Check beam at AS port, AR side, output side of BS, see clipping.
- Check beam centering on ITMX -- is mis-centered. Tweak alignment of PR3 to center on ITMX.
- Check beam at AS port, AR side, output side of BS -- clipping alleviated.
- Check beam through HAM4 between HWS baffles, no clipping.
- Check beam at SR3 -- clipping alleviated.
- Re-center beam on SR3 using BS.
- Re-center beam on SR2 using SR3, making sure of no clipping on SR2 scrapper baffle.
- Re-center beam on SRM using SR2, still no clipping.
- Confirm that beam no-longer goes through input of OFI with SRM centering, using SR2 offset of Y = -800 [urad] (P as shown in IFO Align screen).
- Move SR2 to Y = -600 [urad], find that beam goes through OFI hole, but is now miscentered on SRM. Should be walk-able / recoverable, but we'll wait for beam from Y ARM before we move anything.