Sheila, Camilla, Jennie
This morning we changed SRCL offset from -191 to -306 and FC de-tuning from -34 to -28, as discussed in 83570. Took some SQZ data here as we were interested if we could get FIS SQZ lower than No SQZ ~100Hz and below, Sheila's models (e.g. 83572) suggest we should but it looks like there's a low frequeceny noise source (in FIS not FDS) in our data sets preventing us from getting down to the modeled level of SQZ.
Sheila turned OPO trans setpoint up from 80uW to 95uW to increase NLG from 11 to 19 (similar to what we had earlier in O4). Measured NLG with 76542. OPO gain left at -8. Turned off SQZ ASC.
| opo_grTrans_ setpoint_uW | Amplified Max | Amplified Min | UnAmp | Dark | NLG (usual) | NLG (maxmin) | OPO Gain |
| 95 | 0.0176 | 0.000279 | 0.00002 | 0.00094 | 19.1 | 20.0 | -8 |
| 110 | 0.03315 | 0.000269 | 0.000879 | -0.00002 | 35 | -8 |
| Type | Time (UTC) | Angle | Notes | DTT Ref |
| No SQZ | 03/29 | N/A | ref 0 | |
| FIS SQZ | 171 | Angle tuned for FDS (maybe thermalized since) | ref1 | |
| FIS SQZ | 17:05:00 | 154 | Ang tuned for FIS | ref2 |
| FIS Mid(ish) | 17:15:00 | 101 | Little better than no SQZ at 60Hz | ref3 |
| FIS Mid(ish) | 92 | ref4 | ||
| ASQZ FIS | 68 | ref5 | ||
| ASQZ FIS -10deg | 17:24:00 | 58 | ref6 | |
| ASQZ FIS +10deg | 78 | ref7 | ||
| FIS Mid(ish) | 17:31:30 | 115 | ref8 | |
| FIS Mid(ish) other side | 17:43:00 | 27 | ref9 | |
| FIS Mid(ish) | 17:45:30 | 82 | Check data doesn't include a glitch | ref10 |
| Type | Time (UTC) | Angle | Notes | DTT Ref |
| FIS ASQZ +10deg | 17:53:00 | 82 | Plot seems similar with same ang, different SRCL offset | ref 11 |
| FIS ASQZ | 17:56:00 | 72 | ref12 | |
| FIS ASQZ -10deg | 62 | ref13 | ||
| FIS Mid (ish) | 104 | Can see that rotation is a little different with SRCL de-tuning different but low freq noise level is the same. | ref14 |
| Type | Time (UTC) | Angle | Notes | DTT Ref |
| Mid SQZ | 112 | Interesting data here. Low freq noise higher than with NLG 19. | ref 15 | |
| ASQZ | 18:20:00 | 70 | ref16 | |
| MidSQZ | 18:22:30 | 100 | ref17 |
Sheila turned OPO trans back to 96uW so expect NLG to be 19 going into Observing, larger than normal but closer to the value uses before the last OPO crystal move. SQZ angle servo off and angle set back to 171. ADF left on.
I had a brief look at some of this data to put bounds on losses and arm power in 83953:
The first attachment shows a plot of more of this data against models, focusing on the unexplained low frequency noise that we don't see with the filter cavity . The measured NLG matches the NLG infered from anti-squeezing and squeezing for the NLG 19 measurements, but for the NLG 35 measurements the infered NLG is 27.3, so that is what I've used here. As Camilla wrote above, the NLG 35 measurements were made with a different SRC detuning than NLG19, so that is included in this model. Squeezing angles are fit to the band from 2100 Hz to 2300 Hz.
The first plot shows the measured data in solid lines, the quantum noise model in dashed lines, and the dotted lines show the non quantum noise from subtraction added to the quantum noise models. There is a discrepancy where many of the measurements seem to have extra noise from 20-50 Hz, I've tried to make an easier to read version in the second plot, and finally removed some traces to try to make it easier to see.
In the above alog we thought perhaps that this could be explained as an excess noise that was larger with higher nonlinear gain but consistent with squeezing angle, the last attachment shows the residuals between the model and measurement for the measurements that had clear discrepancies, they all seem to be different, so this excess seems to depend both on squeezing angle and nonlinear gain.
The script used to make these plots can be found at this repo
