This morning I performed an on-table alignment of the FSS RefCav beam, since yesterday's T.O.O. remote alignment tweak did not get the cavity transmission back above 0.8 V.  As usual, I began with a power budget of the FSS beam, and left the ISS ON to keep the power in the FSS path stable:

• FSS In: 277.5 mW
• AOM In: 276.8 mW
• AOM Out, Single Pass: 196.5 mW
  • Single Pass Diffraction Efficiency: 71.0%
• AOM Out, Double Pass: 53.3 mW (135.3 mW)
  • Double Pass Diffraction Efficiency: 27.1 % (68.9%)
• EOM Out: (136.0 mW)

Immediately it looks like the beam alignment through the AOM in its second pass is way off, but I've never seen the double pass diffraction efficiency this low so I decided to check alignment through the components in the beam path from the AOM to the RefCav before I started making adjustments.  Sure enough, the beam was being clipped by the iris that sits between M22 and L11 (this iris block the undesired orders output from the AOM).  I opened the iris and measured the power again, this is the number in parenthesis in the above bullets.  So the diffraction efficiencies look around normal, but the beam was not well aligned to the iris.  This was also seen in the EOM, as it was off alignment as well (but not enough that it was clipping the beam).  I went ahead and slightly adjusted the AOM to maximize the single pass diffraction efficiency, and M21 to maximize the double pass diffraction efficiency, with the following results:

• AOM Out, Single Pass: 200.1 mW
  • Single Pass Diffraction Efficiency: 72.3%
• AOM Out, Double Pass: 137.5 mW
  • Double Pass Diffraction Efficiency: 68.7%

At this point, I adjusted the iris position to center it horizontally, and then adjusted M22 to get the beam a bit better centered vertically (iris is on a fixed mount with no vertical adjustment, and I didn't want to go too far and cause problems downstream; not super important that the beam be centered, as the iris is left open enough to pass the desired beam while blocked the others).  This done, I opened the iris just enough to let the desired beam pass while still blocking the others.  The EOM alignment was adjusted until the beam was centered on both the input and output EOM apertures; I measured 137.3 mW transmitted through the EOM, so free of clipping (the slight difference in double pass AOM Out and EOM Out is normal, the power meter never reads exactly the same).  I then manually adjusted the picomotor equipped mounts (M32 and M47) to recenter the beam on the front and back of the RefCav input iris, then locked the RefCav.  It locked without issue, so I proceeded to use the picomotors to fine tune the beam alignment into the RefCav.

• Initial RefCav TPD: 0.719 V
• Final RefCav TPD: 0.816 V

To end the work in the enclosure I unlocked the RefCav, aligned the reflected beam onto the RFPD, then relocked the RefCav and calculated the visibility:

• Unlocked: 1.150 V
• Locked: 0.207 V
• Visibility: 82.0%

I then turned the ISS OFF (so it's not actuating on the beam power while the enclosure is returning to thermal equilibrium after the incursion), cleaned up equipment I had used, placed the enclosure into Science Mode, and left the LVEA.  I checked on the PSL after about 45 minutes and things appeared to have settled out, so I did one final remote beam alignment of both the PMC (to account for any alignment changes during the incursion) and the RefCav.  The PMC alignment was done with the ISS OFF, I then turned the ISS ON (RefSignal of -1.99 V, diffracted power moving between ~3.6% and ~4.0%) to record the final PMC Trans and Refl values and tweak the RefCav alignment.  Results:

• PMC
  • Initial (ISS OFF)
    • Trans: ~104.9 W
    • Refl: ~23.4 W
  • After Alignment (ISS OFF)
    • Trans: ~105.9 W
    • Refl: ~22.7 W
  • Final (ISS ON)
    • Trans: ~106.0 W
    • Refl: ~22.8 W
• RefCav (ISS ON)
  • Initial TPD: ~0.836 V
  • Final TPD: ~0.838 V

This ended the RefCav tune up for today.  I'm not sure why the iris was clipping the beam, I have not seen that in the time I've been working on the PSL.  Best guess I have is drift of mirror M22 due to slow temperature changes, since the diffraction efficiencies of the AOM were still pretty good and this is the only mirror between the AOM and the iris (could also be the PBS cube PBS01, but I don't think so as there was not an increase in the power of the rejected polarization beam).  We will continue to monitor this as we usually do, but things are in decent shape right now.  This closes LHO WP 12683.