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

Dave, Ibrahim

A significant power glitch on all 3 phases occured at 4:15:48 Local. PSL power issues Ryan C had were due to this (alog 80782). Plots below.

The MCs and IMs alignment all looks fine. The AMPs and NPRO all went to disabled about an hour ago.

The NPRO and AMPs are all disabled as of 11:15 UTC

Running PSL weekly scripy yielded the following:
Laser Status:
    NPRO output power is 0.1373W (nominal ~2W)
    AMP1 output power is -0.4512W (nominal ~70W)
    AMP2 output power is 0.1128W (nominal 135-140W)
    NPRO watchdog is RED
    AMP1 watchdog is RED
    AMP2 watchdog is RED
    PDWD watchdog is GREEN

PMC:
    It has been locked 0 days, 0 hr 1 minutes
    Reflected power = -0.1761W
    Transmitted power = -0.02753W
    PowerSum = -0.2036W

FSS:
    It has been locked for 0 days 0 hr and 0 min
    TPD[V] = -0.01628V

ISS:
    The diffracted power is around 3.0%
    Last saturation event was 0 days 1 hours and 26 minutes ago

Possible Issues:
    NPRO power is low
    AMP1 power is low
    AMP2 power is low
    NPRO watchdog is inactive
    AMP1 watchdog is inactive
    AMP2 watchdog is inactive
    FSS TPD is low
    NPRO error, see SYSSTAT.adl

After talking to Jason, there's not much to do about this right now. More investigation needs to be done to see what happened to the laser, potentially needs to be swapped.

There power issues on the Hanford site that could have easily glitched our power and caused the npro to trip.

Fil re-enabled the PMC high voltage after arriving on site, then I brought the PSL back up with little issue. One hiccup I ran into was with the new PDWD for the amplifiers; when the NPRO shut off this morning, the regular power watchdogs tripped the system off, but the PDWD did not. This meant I had to disable the PDWD before I was able to reset the system and turn the NPRO back on. After that, there were no issues recovering the PSL.

H1 back to observing at 04:23 UTC. Fully automatic relock.

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.