Daniel, Camilla, Vicky
After PSL laser frequency change 81073, we adjusted the SQZ + ALS X + ALS Y laser crystal temperatures again, as before in lho80922.
- SQZ: 26.31 C --> 27.02 C * initially could've been mode hopping to lock to new psl freq
- dT = +0.71 C, dF -2.14 GHz (TTFSS crystal frequency readback)
- suggests dF/dT = -3 GHz / C
- ALS Y: 30.05 C --> 28.88 C ** clamp issue
- dT = -1.17 C, dF = +3.5 GHz (TTFSS crystal frequency readback)
- suggests dF/dT = -3.0 GHz / C
- ** Daniel backed off the laser current, as the "clamp" light was on (ALS Y laser current was gettig clamped at the max). After unclamping, the ALS Y temp settled at 28.85 C.
- ALS X: 26.62 C --> 25.44 C
- dT = -1.18 C, dF ~ +3.898 GHz (TTFSS crystal frequency readback)
- suggests dF/dT = -3.3 GHz / C
Again the steps we took:
- record "new nominal" laser temperature with TTFSS locked to the new PSL laser frequency
- turn off TTFSS ("Disable")
- on laser controller, move temperature knob to get it back to the "new nominal" temp
- turn on TTFSS ("Enable", and make sure it locks OK)
- check for mode hopping: Disable TTFSS again, set crystal frequency +/- 100 MHz, check beatnote strength is OK (if no beatnote, could be mode hopping).
Squeezer recovery at NLN was complicated after this temp change, but after fixing laser mode hopping and updating OPO temperature, SQZ is working again at NLN.
OPO TEC temperature adjusted from 31.468 C --> 31.290 C, to maximize seed NLG. Change is consistent with last time lho80926 (though not obvious that laser freq changes mean the red/green opo co-resonance should change, but ok).
Squeezer laser was likely modehopping at the new settings above. Symptoms:
- Screenshot of TTFSS beatnote before / after / afterAfter the PSL laser freq change.
- PMC_TRANS was 430 (nominal H1:SQZ-PMC_TRANS_DC_POWERMON~675)
- PMC_REFL was 370 (nominal H1:SQZ-PMC_REFL_DC_POWERMON~44)
- Bad PMC transmission meant not enough SHG power, and while OPO could lock, the OPO PUMP ISS could not reach the correct pump power. So aside from mode hopping being bad, it would have meant bad squeezing.
Camilla and I went to the floor. SQZ Laser controller changes made to avoid mode hopping:
- SQZ Laser current 1.935 A --> 1.885 A
- SQZ Laser crystal temp 27.02 C --> 27.07 C
This adjustment seemed quite sensitive to laser current and crystal temperature, with a tunable range kinda less than I expected.
Compared to previous SQZ laser adjustments to avoid mode-hopping (see old laser 51238, 51135, 49500, 49327), this temperature adjustment seems small for the current (amps) adjustment.. but, seemed to work.
PMC cavity scans look clean at these new settings (laser looks single-mode), see screenshot. For +/- 200 MHz steps of crystal frequency, still see a 160 MHz beatnote. Later could double-check a PMC cavity scan at +200 MHz just to be sure. PMC cavity scan template added to medm SQZT0 screen (! PMC) and at $(userapps)/sqz/h1/Templates/ndscope/pmc_cavity_scan.yaml.
