After recovering PLLs I hoped that everything would go smoothly to recover squeezing so of course it didn't.
The alignment of SHG is sufficient but not great. I turned on DDS1 DAC1 (SHG/IRMC demod) and checked the phase for the error signal. It seems fine, not much (if any) change from previous phase and 4.88Vpk signal. However, when I locked, there is oscillation of the output power (IR transmission). Specifically, it oscillates at about 5.5 kHz, max ~ 1.9 V, min ~ 1.5 V (0.4 Vpk). For green, the power meter reads 210 mV which is roughly correct but the SHG temperature hasn't been optimized for a long time so it should be closer to 280 mV. I do not think the cause of this oscillation is mechanical since the lowest SHG resonance is about 7 kHz (Yuhang thesis fig 4.7). Likewise it shouldn't be temperature because temperature is slow to respond. There isn't any of this frequency in the demodulation LO from the DDS board (DDS1 DAC 1 into spectrum analyzer). It seems like a recent issue between June and now, possibly due to the lightning strike power outage in Mitaka a couple of weeks ago.
Marc and Logan adjusted the polarization to get rid of HOM splitting when they reconnected electrical things. Indeed I just did some other check - the BSF10C that goes to the transmission DCPD has significantly smaller reflection for p-pol than s-pol, and indeed at the set polarization the total power at the DCPD is minimized (SHG requires p-pol infrared). So the HWP is at the correct place (~ 195 degrees). Actually looking through some of my old photos, during Yuhang's New Years visit it was at 120 degrees - I have no idea why. Rotating the polarizer can reduce the oscillation but it also reduces the transmitted power, and besides it should have already been the correct setting anyway.
Peak optical power at the RFPD was about 3 mW (power meter MAX reading method), which is maybe a little bit low (3.6 mW before). The signal from the (amplified) DCPD on the oscilloscope (coming from TRANSMISS IN) is much larger now than what it was before, even with the gain on 0 dB. It was 550 mV from my old pictures at 30 dB, but is now 1.7 V at 0 dB. This 1.70 V on the DCPD is also the average value of the oscillating locked IR transmission as noted above. Another strange thing is that when I checked the lock threshold it seemed to be at a very large (i.e. not reasonable) value > 1.7 V. Previously it was set at 250 mV (a bit less than half of 550 mV). Did this have something to do with the power outage? I don't know how there is more DCPD voltage for probably similar input power, with the amplification turned down.
Eventually I could not lock SHG anymore. I'm not sure what is the problem right now. I will guess at some items to check:
I left both PLLs locked to see if they stay locked overnight.