ryan.crouch@LIGO.ORG - posted 13:13, Saturday 27 September 2025 - last comment - 15:11, Monday 29 September 2025(87175)
OPS Saturday DAY shift update - SQZ issues
- 18:22 The SQZ LO lost lock and struggled to relock and delayed the start of the calibration measurement
- The first issue was the OPO not wanting to lock, following the wiki I started by cycling through DOWN
- I restored FC2/FC1 alignments based on osems to when we locked the SQZer at the beginning of the lock, no dice
- I maximized the H1:SQZ-SHG_GR_DC_POWERMON using SHG_TEC_SETTEMP, accepted in SDF (36.05 -> 35.75)
- It was still struggling to get a trans of at least 80, it would go right past it. It would get just over 80 then keep adjusting the ISS setpoint and the trans would decrease. I ended up changing the setpoint from 80 to 75 in sqzparams which got it locked.
- Now the FC won't lock, the green trans is too low, I followed the wiki to maximize it
- Restored ZM3, moved FC2 to maximize H1:SQZ-FC_TRANS_C_LF_OUTPUT, I couldn't get it above 50. Now it loses it at IR ("CLF frequency out of range")
- I ran the SCAN_OPO_TEMP state and now it can lock IR
- The first issue was the OPO not wanting to lock, following the wiki I started by cycling through DOWN
- 19:33 during the calibration measurement it lost lock again
- The OPO keeps losing lock again. I maximized the SHG temp again, there was a suprising amount of gains still to be had (36.05 -> 35.05). Should I have done this again after running SCAN_OPO_TEMP earlier?
- FCs not locking again, as soon as the calibration measurement finished it finally was able to hold green lock
As Ryan correctly identified, the issue to why the SQZ dropped was there was no enough green power to keep the OPO ISS locked. So he had to reduced the setpoint in sqzparams from 80uW to 75uW. It wouldn't surprise me if this happens again as we are still close to the botton of the ISS's range.
Tomorrow AM we'll check if we can get any more power with the SHG waveplate, otherwise we may need to realign through the AOM and into the fiber again as we last did in 86323 or move crystal spots.