Approximately 3 days ago (when the recent rain system moved in late Friday) the temperature in both the Anteroom and Laser Room increased, along with relative humidity in both rooms.  This corresponds with the increase seen in PMC Refl, as well as a shift in the RefCav TPD (which moved higher before starting to drop again sometime yesterday), the output power of both amplifiers (both dropped slightly), and changes in all 8 of the system's pump laser diodes (most increased, a couple decreased).  The temperature change could cause alignment drifts (both pre-PMC and pre-amplifiers), as well as the change in pump diode power potentially causing changes in the output beam quality.  All of this could contribute to the shift observed in PMC Refl, RefCav TPD, and ISS diffracted power %.

Given our previous inability to recover much PMC Trans via beam alignment into the PMC, and the fact that changing the operating current of the pump diodes doesn't seem to "stick" for very long, my suspicion is that we are seeing slight alignment changes through the amplifiers.  This could cause a change in output beam quality, as the beam hits the thermal lenses formed in the amplifier crystals in a slightly different spot.  Correcting this requires bringing down the PSL entirely, then bringing it back up in stages (NPRO only, then NPRO + Amp1, then NPRO+Amp1+Amp2, then finally adding the PMC into the mix) while tweaking alignment and mode matching into each amplifier and ultimately into the PMC.  This takes too long for a standard 4-hour maintenance window, and might require more than a full-day maintenance window (alignment and mode matching into the amps/PMC has, in the past, been a multi-day effort; this took us a couple of days during our PSL recovery in March 2023).  Not clear how urgent this is, as we are still outputting between 108W and 110W from the PMC (depending on how recently we've "tweaked things up") and are only utilizing 60W for the IFO (leaving us roughly 50W of headroom).