Adding a plot to show the individual PR3 BOSEM Contributions

Reverted the attached tramp sdf diffs afterwards, see attached. Maybe the script needs to be adjusted to automatically do this.

I just ran Craig's script to analyze these results. The script fits a contrast defect of 0.742 mW using the 255.0 Hz data and 0.771 mW using the 410.3 Hz data. This value is lower than the previously 1 mW on July 11 (alog 79045), which matches up nicely with our reduced frequency noise since the OFI repair (alog 80596).

I attached the plots that the code generates.

This result then estimates that the homodyne angle is about 7 degrees.

Last year I added some code to plot_darm_optical_gain_vs_dcpd_sum.py to calculate the losses through HAM 6.

Sheila and I have started looking at those again post-OFI replacement.

Just attaching the plot of power at the anti-symmetric port (ie. into HAM 6) vs. power after the OMC as measured by the DCPDs.

The plot is found in /ligo/gitcommon/labutils/darm_offset_step/figures/ and is also on the last page of the pdf Elenna linked above.

From this plot we can see that the relationship between the power into HAM 6 (P_AS) is related to the power at the output DCPDs as follows.

P_AS = 1.220*P_DCPD + 656.818 mW

Where the second term is light that will be rejected by the OMC + that which gets through the OMC but is insensitive to DARM length changes.

The throughput between the anti-symmetric port and the DCPDs is 1/1.22 = 0.820. So that means 18% of the TM00 light that we want at the DCPDs is lost through HAM 6.

Trends of the ADF servo stabilizing the SQZ angle overnight. Looks good: the ADF SQZ ANGLE servo can hold the maximum squeezing level throughout the lock! Last night was running with the ADF SQZ angle servo + SQZ-IFO AS42 ASC together.

In the first lock of the screenshot, the ADF SQZ ANGLE servo is not yet running, and the squeezing level drifts quite a bit (~0.5-1 dB in ~2 hours, and ends up un-optimal). In the last 2 locks, the ADF SQZ ANGLE servo is running and successfully stabilizes the SQZ angle, though the 2 locks from last night stabilize at different SQZ angles (weird?). Note SQZ ASC is running in both of these locks, so it seems like ASC + ADF SQZ ANG servo work well when used together.

Naoki looked at sqz trends with/without the ADF servo before in LHO:75000. Looking at sqz trends for yesterday, the ADF servo stabilized the SQZ angle in the first ~25 minutes. Then over the first ~2 hours, the ADF servo needed to move the CLF_RF6 demod phase by 5-10 degrees to hold the SQZ angle stable. This implies something like, the optimal injected squeezing angle changed by about 2-5 degrees during IFO thermalization.

Also noting a reference to LHO:77292, where Naoki does an On/Off test with the ADF line at 322 Hz.

Checked against the 68139 list, can see that 322Hz is a good frequency for CW. We will look at trying to add this ADF line to the _CLEAN or _NOLINES subtractions. 

No FSS tag on the lockloss tool

Tagging OpsInfo: I've added an ndscope template to the lockloss select tool that provides some good channels to look at to help determine if it was caused by the PSL glitches. Running it for this lockloss, I would say this does not look like an "FSS glitch" lockloss (see attached).

Opened FRS32411

Notes from Fil:

The HAM6 PZT had to be restarted

Work on Beckhoff DAC power monitors

Both GC and CDS UPS units switched to battery backup power for both of these times. The GC unit sent email notifications, the CDS unit did not.

GC was on battery for 5 seconds, CDS for only 1 second.

FMC-EX_MAINS Channels seeing the outage at the reported times.

Outage 1: 4:15:48

Outage 2: 4:52:39

I neglected to mention that this is based on the nice data set that Camilla collected here: 80664, and that three is more work to be done with this, checking SRC detuning, mode mismatch, and including the +/- 10 deg data.

Sumary: seems the current (+) side of DARM is better for FDS, although it is opposite of our previous quantum noise models. But given the current sign is actually better for DARM, the model error doesn't really matter, and it's not really worth changing signs.

The wrong HD angle sign seems to be why none of our quantum noise models, despite fitting all other SQZ angles well, have ever fit FIAS properly. We will update our quantum noise models for the noise budget. Attached are some quantum noise models and DARM plots for Camilla's recent SQZ dataset lho80664.
 

Plots with optimal FDS (optimal fc detuning) for both signs of the homodyne angle: showing 1st just the quantum noise models without adding back non-quantum noise (NQN), and 2nd showing QN models + NQN.

• Current sign of DARM (+) has solid lines. "Other" sign (-) has dashed lines.
   
• Homodyne angle is only really obvious for FIAS (freq-indep anti-squeezing, turqoise traces).  It's almost indistinguishable for FIS otherwise (green, yellow, light blue). Marginally noticeable for FDS (but more sensitive to FC optimization).
  • Sheila made a super important observation that FIAS has never fit quantum noise models properly. 
  • Quantum noise models with the "other" (-) sign expect FIAS < No SQZ between 15-100 Hz, and FIAS < FIS between 15-50 Hz. This is not what we have observed with FIAS, despite QN models fitting all other SQZ angles fine.
  • Only flipping the HD angle sign was able to match the QN models to data, suggesting that previous quantum noise models used the wrong sign of the homodyne angle.
  • It turns out this doesn't really matter in real life, but we will update the noise budget models.
     
• Confusingly, the current (+) side is better with FDS, but the "other" (-) side is better for unsqueezed DARM. See the grey (+) vs. black (-) traces for unsqueezed DARM at +/- 10 deg homodyne angles.
  • Not sure where the notion of a "good side of DARM" comes from
  • Pre-O4a, there was a quick test to lock on the other side of DARM, lho68080...  But maybe this test just shows some technical noises change with the HD angle?
    • In the test, see the plot of how unsqueezed DARM (purple vs. red) is very different below 100 Hz for the two signs, but not in the pway predicted by quantum noise models (grey + black traces).
    • So, seems like this test suggests the +/- sign measured DARM noise differences are more likely technical (non-quantum) noises that change with homodyne angle.

Third attachment (3rd) shows a wider range of homodyne angles, from +15 deg to -10 deg. So far the code for these plots is living here.

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Altogether this is making progress on the quantum noise models for the noise budget!

Summarizing updates and what we're learning:

• As Sheila said, low freq frequency-independent anti-squeezing (FIAS) ---> homodyne angle (which sign it is + approx how many degrees): see light blue FIAS traces in 2nd plot.
  • Elenna recently measured the contrast defect in lho80806, corresponding to a upper homodyne angle of +7.4 deg (down from the +10.7 deg measured in O4a (lho71913)).
  • After subtraction, FIS matches reasonably well with this lower HD angle +7 deg.
    • Still +10.7 deg is only marginally different, so FIAS is not really precise enough to tell at the ~degree level.
• As in lho80318 79951, can use the frequency-independent squeezing (+mid-sqz) bronchosaurus (FIS) ---> SRCL detuning. 
  • After subtraction, FIS matches reasonably well with SEC detuning between 0 and -0.2 deg.
• Subtracted FDS data still WIP as the low frequency quantum noise estimate seems not totally right.
  • Maybe could fit the FC detuning at each SQZ angle (as SQZ angle can affect the RLF-CLF offset for such low (sub-linewidth) FC detunings), but haven't thought about this FDS data much yet.
• Important model degeneracies remain from having 4 model unknowns: [[ IFO arm power + readout loss, and SQZ NLG + injection loss ]] with which to fit 3 DARM measurements [[ unsqueezed shot noise + anti-squeezing (kHz level) + squeezing (kHz level) ]].
• Still need to factor in mode-matchings.

Vicky, Sheila

Based on the fit of total squeezing efficiency and nonlinear gain (which is based on subtracted SQZ and ASQZ from 1.5-1.8kHz), and known losses from loss google sheet, we can infer some possible maximum and minimum arm powers using the no squeezing data. 

The first attachment shows the same plot as above, but with the latest jitter noise measured by Elenna in 80808 We noticed this afternoon that there is a problem with the way these jitter noises are being added in quadrature by the noise budget, but we haven't fixed that yet.  In this data set, we have 15.1dB of anti-squeezing and 5.1dB of squeezing from 1.5-1.8kHz, we can use the Aoki equations to solve for nonlinear gain of 14.6 and total efficiency eta for squeezing of 73%.  Since the known readoutlosses are 7.3% and the known squeezer injection losses are 8.8%, this gives us a minimum readout efficency of (eta/(1-known injection loss) = 79% and a maximum of 1-known readout loss = 91.2%.  Using the level of noise between 1.5-1.8kHz with no squeezing (and an estimate of the non quantum noise) we can use these max and min readout efficencies to find min and max circulating powers in the arms. 

These arm power limits will be impacted by our estimate of the non-quantum noise, the homodyne angle, and the SRC detuning.  With 0 SRC detuning, and a homodyne angle of 7 degrees, this resutls in a range of arm powers of 324-375kW.  the estimate of non-quantum noise is the most important of these factors, while SRC detunings large engouh to change these estimates significantly seem outside the range that is allowed by other squeezing mesurements.

• If I reduce the technical noise estimate from the noise budget by 10% in the ASD, the arm power range is 330-383kW, raising the non quantum estimate by 10% gives a range of 328-375kW.
• Using a homodyne angle of 10.6 degrees instead of 7 gives an arm power range of 331-383kW. 
• using an SRC detuning of 0.48 degrees (which is clearly too large based on the mid frequency squeezing) results in a range of powers of 321-372kW. 

I've run the comparison of the model to different squeezing configurations for the low and high range and the nominal parameters (0 SRC, 7 degrees homodyne angle). Frequency independent squeezing and both types of mid squeezing are sensitive to the arm power from 50-100Hz, this comparison shows that the low end of the arm power range seems to have slightly too little arm power and the high range slightly too much.  However these frequencies are also sensitive to homodyne angle and SRC detuning. 

I ran an updated noise budget using these new measurements, plus whatever previous measurements were taken by Camilla in this alog. Reminder: the whole noise budget is now being run using median averaging.

I used a sqz time from last night where the range was around 165 Mpc, starting at GPS 1412603869. Camilla and Sheila took a no-sqz data set today starting at 1412607778. Both data sets are 600 seconds long. I created a new entry in gps_reference_times.yml called "LHO_O4b_Oct" with these times.

To run the budget:

>conda activate aligoNB

>python /ligo/gitcommon/NoiseBudget/aligoNB/production_code/H1/lho_darm_noisebudget.py

all plots found in /ligo/gitcommon/NoiseBudget/aligoNB/out/H1/lho_darm_noisebudget/

I made one significant edit to the code, which is that I decided to separate the laser and input jitter traces on the main DARM noise budget. That means that the laser trace is now only a sum of frequency noise and intensity noise. Input beam jitter is now a trace that combines the pitch and yaw measurements from the IMC WFS. Now, due to my changes in the jitter injections detailed above, these jitter injections extend above 900 Hz. To reiterate: the injections are still only band-limited around 2 kHz, which means that there could be unmeasured jitter noise above 2 kHz that was not captured by this measurement.

One reason I wanted to separate these traces is partly because it appears there has been a significant change in the frequency noise. Compared to the last frequency noise measurement, the frequency noise above 1 kHz has dropped by a factor of 10. The last time a frequency noise injection was taken was on July 11, right before the OFI vent, alog 79037. After the OFI vent, Camilla noticed that the noise floor around 10 kHz appeared to have reduced, as well as the HOM peak heights, alog 76794. She posted a follow-up comment on that log today noting that the IFO to OMC mode matching could have an effect on those peaks. This could possibly be related to the decrease in frequency noise. Meanwhile, the frequency noise below 100 Hz seems to be about the same as the July measurement. One significant feature in the high frequency portion of the spectrum is a large peak just above 5 kHz. I have a vague memory that this is approximately where a first order mode peak should be, but I am not sure.

There is no significant change in the intensity noise from July, except that there is also a large peak in the intensity noise just above 5 kHz. Gabriele and I talked about this briefly; we think this might be gain peaking in the ISS, but its hard to tell from alog measurements if that's possible. We think that peak is unlikely to be from the CARM loop. We mentioned the ISS theory to Ryan S. on the off-chance it is related to the current PSL struggles.

The other significant change in the noise budget is the change in the LSC noise. The LSC noise has reduced relative to the last noise budget measurement, alog 80215, which was expected from the PRCL feedforward implementation. Looking directly at the LSC subbudget, PRCL has been reduced by a factor of 10, just as predicted from the FF performance. Now, the overall LSC noise contribution is dominated by noise from MICH. Between 10-20 Hz, we might be able to win a little more with a better MICH feedforward, however that is a very difficult region to fit because of various high Q features (reminder alog).

Just as in the previous noise budget, there is a large amount of unaccounted-for noise. The noise budget code uses a quantum model that Sheila and Vicky have been working on extensively, but I am not sure of the status, and how much of that noise could be affected by adjustments to the model. Many of the noisy low frequency peaks also appear very broad on the timescale of the noise budget plot. We could try running over a longer period of time to better resolve those peaks.

Between 100-500 Hz there are regions where the sum of known noises is actually larger than the measured noise. I think this is because the input jitter projections are made using CAL DELTA L, but the overall noise budget is run on CALIB CLEAN where we are running a jitter subtraction.

I believe these couplings were pushed to aligoNB repo in commit bcdd729e.

I reran the jitter noise injections, trying to increase the excitation about 2 kHz to better see the high frequency jitter noise. The results were moderately successful; we could probably push even harder. The results indicate that jitter noise is with a factor of 2-3 of DARM above 1 kHz.

I have attached the updated DARM noise budget and input jitter budget. I'm also attaching the ASC budget (no change expected) just because I forgot to attach it in the previous post.