Kevin, Sheila
Over the last few days we've run ADF sweeps a few times. Here's a record of what happened and file names.
The files are in /ligo/gitcommon/squeezing/sqzutils/data
Nov 22 08:31 HF_10kHz_11_2025.h5 IFO had been powered up for 11:00, sweep started at about 14:50 UTC Nov 22. NLG 24.3, measurement is in 88224. Something seemed to go wrong towards the end of the sweep, we aren't sure what.
Nov 22 12:38 HF_10kHz_11_2025_2.h5 IFo had been powered up for 15:10, same lock as the previous measurement, same NLG measurement, sweep started at about 19 UTC.
Nov 25 00:36 HF_10kHz_11_2025_b4_CO2_step.h5 IFO had been powered up for 4:20, in this sweep I didn't turn off the SQZ angle servo based on the ADF, so the demod phase was moved around during the sweep, making this data not useful.
Nov 26 01:56 HF_10kHz_11_2025_b4_CO2_step2.h5 last night's first scan, started only 38 minutes after power up at about 8:18 UTC Nov 26th. The amplified seed was 7.8e-3, unamplified seed didn't happen correctly with the script but the waveplate hasn't moved since previous measurements of that level at 2.9e-4 (88223), giving an NLG of 26.9. (Edit, I redid the unamplified seed measurement, it looks like 3.2e-4 now, making the NLG 24.4 for these last two measurements, which has been consistent (24.3 or 24.4) for the last week.
Nov 26 08:15 HF_10kHz_11_2025_after_CO2_1hour.h5 this morning's sweep, IFO had been powered up for 7 hours, CO2s had been stepped from 1.7W each to 0.9W each for 1.5 hours when the sweep started at about 14:37 UTC Nov 26th. NLG should be the same as for above, 26.9. 24.4
The goal of these measurements is to use the ADF to measure the rotation of the squeezed state around higher order mode arm cavity resonances as described in section IV.B of LIGO-P2500132. Ultimately we would like to be able to use such measurements to diagnose the thermal state as a guide in how to tune TCS in order to improve mode matching.
While we are still digesting the results, the first plot shows the preliminary inferred squeezed state rotation for the three good data sets that we got. pre-step 1 and pre-step 2 are the two taken on Nov 22. (Everything turned out to be fine with the first sweep.) post-step is the last one taken this morning after the CO2s had been stepped and the IFO had been up for 7 hours. There is a small arbitrary constant offset in the SQZ angle of order a degree, so all angles have been shifted to be zero at 10.450 kHz. The second plot shows the OMC DCPD spectra 5 min before the start of each of these three sweeps.
Two rotation peaks are visible rather than the one shown in Fig 7 of P2500132. This is expected since the arms are astigmatic in reality, and our more detailed models show the same behavior. Each eigenmode is resonant at a slightly different frequency and is responsible for a rotation as in Fig 7 which are superimposed as observed in this data.
The post-step rotation is slightly smaller in magnitude and is shifted to slightly lower frequencies. Since the CO2 is mainly a higher order actuator, this is consistent with our expectations that this rotation is predominantly sensitive to quadratic mismatch with higher order aberrations altering the detailed behavior. However, seeing as how the pre-step was not taken just prior to the CO2 step in the same lock, I think it's just as likely that this is due to it being in a slightly different thermal state before the CO2 step. The peaks in the OMC DCPD spectra also appear slightly lower in frequency for the post-step.
I think the main takeaway from these measurements so far is showing that we can measure this rotation and resolve changes on the scale that our modeling suggests would be useful.
This analysis was done in the aligoNB environment by running
pytest /ligo/gitcommon/squeezing/sqzutils/analysis/T_10kHz_ADF.py --tb short -s -k T_Nov_CO2_step