The FSS RefCav TPD has been on a downward trend again, so I tuned up the alignment on the PSL table this morning.  All work was done with the ISS ON and diffracting ~3.8% unless otherwise noted.  As usual, I began with a power budget of the FSS path:

• FSS In: 273.8 mW
• AOM In: 273.1 mW
• AOM Out, Single Pass: 188.6 mW
  • Single Pass Diffraction Efficiency: 69.1%
• AOM Out, Double Pass: 135.0 mW
  • Double Pass Diffraction Efficiency: 71.6%
• EOM Out: 135.0 mW

The AOM's single pass diffraction efficiency was a little low, so I touched up the AOM alignment to improve it.  I also tweaked the alignment of mirror M21 (that reflects the RefCav beam back through the AOM for the double pass) to improve the double pass diffraction efficiency (since the AOM moved).  Finally I slightly tweaked the EOM alignment to center the beam on the input and output apertures and measured the power transmitted through the EOM:

• AOM Out, Single Pass: 196.3 mW
  • Single Pass Diffraction Efficiency: 71.9%
• AOM Out, Double Pass: 137.9 mW
  • Double Pass Diffraction Efficiency: 70.2 %
• EOM Out: 138.1 mW

I then tweaked the alignment into the RefCav using the alignment iris and manually tweaking the picomotor-equipped mirror mounts.  The RefCav locked on the first attempt, with an initial TPD of ~0.735 V.  I then used the picomotors to fine tune the alignment and managed to get a TPD of ~0.845 V.  To end, I unlocked the RefCav and tweaked the beam alignment onto the RefCav's RFPD, then measured the RefCav visibility using the RFPD voltage:

• Unlocked: 1.176 V
• Locked: 0.197 V
• Visibility: 83.2%

I then turned off the ISS (we turn it off while the enclosure returns to thermal equilibrium, because during this process the PMC transmission can change; we don't want the ISS to actuate on the laser power until things stabilize), left the enclosure, and returned it to Science Mode operation.  I let the enclosure return to thermal equilibrium for about an hour and then checked on things.  When I turned the ISS back ON I had to increase the ISS RefSignal from -1.99 V to -1.98 V to hold our diffracted power at ~4%.  I then did on final tweak of the RefCav alignment using our picomotor mirrors; I was able to get the RefCav TPD up to ~0.854 V.  At this point the RefCav tune up is complete and the PSL is ready for post-maintenance IFO recovery.  This closes LHO WP 12751.