J. Kissel

Picking up from yesterday's work (2026-05-18, LHO:90270), today I:
    - Verified Bram's idea on how to resolve yesterday's UNSOLVED SIDEQUEST (1) regarding ~120 Hz noise seen on FBR_PWRIN_REF PD (LHO:90279) -- it's just the room lights. Check out this pic of o-scope timeseries of that PD readout with no lights, room lights, then clean room lights on. *sigh* Alright. RESOLVED: no big deal; when I want to use that PD, turn off the lights.

    - Resumed migration of optics:
        . Finish up REF beam path by migrating and installing M_B3 to steer REF beam into IFO_MEAS_A. Confirmed that Reflective surface is within the mount, and protruding AR surface faces M_M2 and IFO_MEAS_B. 
        . Nothing to align here, it's a fixed optic, but checked alignment of REF beam into both IFO_MEAS_A and IFO_MEAS_B with irises in D2400143 breadboard holes 85 and 82.
        . Migrated D_IFO_MEAS_A and D_IFO_MEAS_B and aligned PD reflection into them with slop of PD housing moutning holes
           :: For D_IFO_MEAS_A Changed out smaller 1.0"x075" D1800140 Type 07 plate for bigger 1.16" x 1.16" D2000228-v1 DLC coated plate that we'd found to rectify the (lesser) stray beam from FBR_PWRIN_REF during D2400107-v4 build. As discussed, in the D2400107-v5 build, we're gunna need a whole different solution (LHO:90277).
        . Migrated and aligned M_B1 using holes 103 and 94.
        . Migrated M_M1, but needed to swap left-handed mount with right-handed mount due to interference of pico motor body with alignment pegs. More on this in the comments.
        . Aligned M_M1 using holes 92 and 87 (M_M4 and M_M5 are NOT installed)
        . Secured alignment adjustment screw set screws for M_F1 and M_B1 since these shall never be touched again. Tweaked M_M1 alignment to follow minor beam change when securing those screws.
        . Migrated and aligned M_M4 using holes 81 and 79
        . Migrated and aligned M_M2, and 
        . et voila! A little tweak of M_M2 and I had a heterodyne beat note to use for finishing alignment.

Attached are End-of-day board status, and the MEAS IFO heterodyne victory lap.

Crude estimate of the efficiency (without accounting for dark offsets): 
        Max = 6.60 V
        Min = 1.08 V
        Amp = 5.52 V
	Mean = 3.85 V
	
        efficiency = Amp / (2*Mean)
        MEAS A     5.52 / (2*3.85) = 0.717 = ~72%
        MEAS B     5.52 / (2*3.82) = 0.723 = ~72%
Excellent.

Tomorrow we install the last two optics and align the REF IFO, and we're back in business!
Estimated readiness for install May 26 2026!