TEAM SQZ
--- Pump laser multimode fixed and beat note optimized (Terry, Sheila, Nutsinee) ---
The setting that Daniel set on Monday (current 2.122, temperature 27.63C, see alog45518) no longer worked the next day. As Terry and I tried to optimize the beat note it keeps disappearing. Finally we could find the beat note on the wrong side of the PSL (above) but not below which seems to suggest that we were close to mode hopping region. Sheila and I then turned down the current to 2.116 A and turned up temperature to 29.57C. Once we were operating at a good region the beatnote strength measured -15.5dBm out of the detector (the best we've ever had), -19.2dBm out of the pre-amp monitor, -2dBm on the medm screen with ~183uW from each arm. BBPD volt was 1.58 V. The polarity has to be flipped when use beat note error to feed to PSL PZT (was negative, now positive).
We checked the PLL lock point for both ALS. One of them still locks at the same place as it did before the vent which indicated that the PSL frequency hasn't changed.
--- OPO locking ---
Self locking is now much worse than before now that green is better mode matched. To get any reasonable scan without asymmetry I'd have to shoot in .4mW into the OPO. PDH Vpk = 75.2 mV. 80MHz phase still okay. Attached a screenshot of a setting that works at 7mW input to the OPO (according to a model, we should get the same cross-over and UGF as before). I haven't had time to characterize anything before I left on a vacation. I suspect that the better mode match could cause more problem locking at high input power if the intensity isn't stabilize. Note that if the OPO is too noisy, you will have a hard time engaging the EOM. Without EOM engage it would be almost impossible (probably impossible) to lock LO.
--- LO locking with Mephisto LO (Daniel, Nutsinee) ---
Step 0) swap the PZT output back from OPO pzt to LO pzt. Actuating on OPO PZT with error signal from pump laser LO would be shooting yourself in the foot, as someone might say...
Attached the setting that works as of yesterday. Compensation and boost1 can be turned on. That would have a UGF of 4.6 kHz. The UGF can be pushed further if we install the LO notch filter box (which we had and was removed...)
--- Homodyne Recovery (Haocun, Nutsinee) ---
I tried to leveled both LO and seed beam a bit better to 4 inch height before I realized that the Homodyne diodes are slightly higher than 4 inch. Both LO and seed should be somewhat leveled but shoot up to HD in a small angle. The power somehow became imbalanced while I was trying to optimize the fringe visibility and got stuck at 97% (PD A) and 94% (PD B). Haocun rescued us and the best we had was 98% at least on one of the diode (I think this was true for both diodes).