As the FSS RefCav TPD has been trending down and a remote alignment did not improve it, I went into the PSL enclosure this morning to tweak the beam alignment on the table.  All work was done with the ISS ON unless otherwise noted; I had to increase the ISS RefSignal from -2.00V to -1.98V to keep the ISS stable with the enclosure environmental controls ON.  In addition, the IMC was OFFLINE for the duration of my time in the enclosure.

I started by taking a power budget of the FSS path:

• FSS In: 290.9 mW
• AOM In: 289.9 mW
• AOM Out, Single-pass: 175.0 mW
  • Single-pass diffraction efficiency: 60.4%
• AOM Out, Double-pass: 125.7 mW
  • Double-pass diffraction efficiency: 71.8%
• EOM Out: 125.7 mW

Seeing the single-pass diffraction efficiency low, I adjusted the AOM alignment to improve it; the AOM had to be moved DOWN.  This resulted in the single-pass AOM output at 216.9 mW and a single-pass diffraction efficiency of 74.8%.  The double-pass AOM output was then measured at 155.4 mW, so I adjusted mirror M21 to see if I could improve it.  This resulted in the double-pass AOM output at 160.1 mW and a double-pass diffraction efficiency of 73.8%.  Much better.

I then double checked the beam centering on the EOM, which was good so I relocked the RefCav.  I needed to adjust mirror M23 slightly in pitch to get the RefCav REFL beam in roughly the same place on the REFL camera, then the RefCav autolocker locked it with no issues.  I used the picomotor mounts to tweak the RefCav alignment to max the TPD; this gave a TPD of 0.99 V.  Very good.  To finish I unlocked the RefCav, tweaked the beam alignment on the RFPD, then locked the RefCav again and measured the visibility:

• Unlocked: 1.326 V
• Locked: 0.225 V
• Visibility: 83.0%

Job done, I left the enclosure.  During my time in there the PMC Refl power had increased from ~16.1 W to ~17.9 W (this increase is normal with enclosure incursions), so I turned the ISS OFF while the PSL enclosure and PMC returned to thermal equilibrium.  At the time of this writing the PMC Refl power has dropped back to ~16.8 W, so I will continue to monitor it over the remaining maintenance time and turn the ISS back on once it gets closer to its normal value.  Also at the time of writing the IMC has been relocked; with the IMC locked the FSS TPD is ~0.96 V (the change with the IMC locked is normal).  This completes WP 11474.