I checked once again the green path. SHG now operates normally, outputting 310 mW green (1.88 V on transmission monitor).

GRMC was a bit misaligned seemingly from PZT hysterisis. I adjusted a bit the steering mirror after the MZ and it went back to good alignment - 1460 mV + (60, 34, 34, 22) -> 90.68% mode matching. GRMC demod phase was changed to 230 degrees, error signal 1.74 mVpp.

GRMC/MZ locks fine and outputs 25 mW stable green (312 mV on the transmission monitor) at the usual 4.2 MZ offset.

OPO error signal was 832 mVpp with good phase. ppol to OPO mode matching was 87.43% which is ok. OPO lock is fine.

I checked how much the CC PLL servo can maximally correct using the fast loop. When the setting is far from resonance (~ 32 MHz) and the fast loop is activated, the CC frequency goes to about 14 MHz. i.e. the fast loop maximum correction is about 18 MHz. This is consistent with what I had read previously in Matteo's thesis. It seems the CC PLL behaves well when the laser starts at a detuning of about 15-20 MHz.

I came across the first hitch which is that I cannot see nonlinear gain on the CC1 error signal and very little on CC2 error signal. Green alignment, ppol frequency and OPO temperature are all optimized. I remember that I was using some old short cables but only remembered after I left and was writing this elog. I should check the LEMO cables monitoring CC EPS and make sure they aren't bad. Considering I saw 6 dB squeezing a couple of weeks ago I don't think CC, BAB or ppol lasers suddenly misaligned. For reference, if the green phase shifter is scanning (nonzero scan amplitude on CC1 servo), you should be able to see about 500 mVpp sine wave from the CC1 unlocked error signal, which indicates that the green phase is being cycled between amplification and deamplification of the CC infrared beam.

Then I ran into a worse problem which is that IRMC servo does not work properly. I saw that the reflected power was extremely unstable (about 20-30% fluctuation in output level), and then got worse in that auto lock didn't work at all. I closed CC and ppol, checked main laser current and temperature, turned main laser noise eater off and on, turned NIM rack off and on, PZT off and on, but it didn't fix the issue. The error signal randomly reduced to about half the amplitude of what it was before (200 mVpp). I checked the demodulation LO - it's fine (4.75 dBm). I put the IRMC near resonance and checked the amplified IRMC REFL RF signal - it seems ok and goes up to about -8 to -9 dBm which is what it was before. The error signal size seems fluctating a bit before the error happened, but it's now stuck at half. When the threshold is at the good value, it seems like the servo is trying to force the PZT to the correct position, but it doesn't reach the lock value. A guess might be the interplay between the PZT scan and threshold. Maybe the correction signal is not strong enough to stop the PZT from scanning? I'm not entirely sure but it's just a guess. But I also tried adjusting the PZT scan amplitude and period and it didn't really fix anything. I have also read previously that the IRMC threshold is a bit strange and usually works best at about 90% of the peak value rather than say 50%.