Relocking is struggling, theres some ringup during DRMI_LOCKED_CHECK_ASC that keeps killing it.

These are recent measurements by Gabriele of DHARD Y and CHARD Y, plotted with the error shading as well.

CHARD Y has a UGF of 3.3 Hz and 44 deg of phase margin. DHARD Y has a UGF of 5 Hz and a phase margin of 22 deg.

DHARD Y has additional UGFs at 2.1 and 1.5 Hz. CHARD Y has some interesting peak features that cross zero a few times between 2.3 and 3.3 Hz. There also appear to be additional UGFs around 1.2, 0.9, 0.5, 0.4 and 0.3 Hz.

Taking another look at these measurements, DHARD P has about 6 dB gain margin at the highest UGF. DHARD Y's gain margin about 3 or 4 dB. Tagging CAL because this comment might be useful for DARM loop investigations.

Elenna, Sheila

We ran the noise budget code for this no squeezing time. 

• We updated the optical gain (Calibratations.py, in the closedLoopSenseing function) using the calibration report here which Jeff pointed us to.  (The most recent one with the exported tag is the current calibration.)  This is the same as the inverse of the gain in H1:CAL-CS_DARM_CFTD_ERR filter called O4 gain if you have the correct calibration report.  Elenna also found the ratio of DCPD mA to DARM err counts by running the template that measures their transfer function aligoNB/H1/couplings/check_DARM_gain.xml for the braodband pcal injection from alog 72047.  These two steps are what we needed to do to get the calibration right so that the semiclassical shot noise caluculation seems correct.  
• We are using CAL_DELTAL, since this noise budget was run before the calibration fix of last week that channel is more accurate.  We are also using the TDCFs kappa_c and the cavity pole to calculate the shot noise. The radiation pressure noise is calculated with the arm transmitted power monitors. 
• There is no DAC noise included in this budget, as we aren't confident in our usual DAC noise projection right now.  68869  With recent improvements in the low frequency noise it would be good for us to revisit the PUM DAC noise projections soon, by running in the higher noise state and running the noise monitor estimate for that higher noise state. 
• We have changed the frequency noise in this budget. We measure frequency noise by switching CARM onto one sensor, (REFL B), then using that sensor as a out of loop frequency noise sensor.  There was a mistake in the code where the psd was instead multiplied by sqrt(2).  We have now divided the PSD by 2, which should give us the correct frequency noise projection where we are frequency noise limited.  Interestingly, this correctly predicts the darm noise at 4-5kHz where it should be an underestimate by sqrt(2) in the ASD.
• Vicky is working on modeling the quantum noise with Kevin, we are just doing the no squeeze budget here and will return to the noise budget with squeezing with Vicky.  
• Also attached are the sub budgets for laser, asc and length noise, with the DARM noise plotted from a time with squeezing.
• Laser noise: The 120Hz peak is well predicted by the IMC PZT yaw injection.  The frequency noise has the factor described above applied, and there may be some double counting at low frequency although we aren't sure.  
• ASC: CSOFT P, and the hard loops are the dominant contribution.  CHARD Y in particular is large, this is because of Gabriele's recent loop change which helped reduce the RMS and improve some nonlinear noise in DARM. 71927 Elenna is looking at if we can roll that off to keep the low frequency gain without this additional noise at 40Hz. 
• LSC: MICH is the dominant contribution to LSC, it is similar to the level of the ASC total. 

This is all commited as 0f9ffe0e

Sheila, Vicky - we have re-run the noise budget for following times:

Noise budget with squeezing. Changes here: using GDS instead of CAL-DELTAL, closer thermalized FDS time to no-sqz, using updated IFO gwinc parameters related to quantum noise calculation.
(Edit: was a glitch in the old time; updated to an FDS time without glitches. All plots updated.)

PDT: 2023-08-10 08:45:00.000000 PDT
UTC: 2023-08-10 15:45:00.000000 UTC
GPS: 1375717518.000000

PDT: 2023-08-10 09:35:52.000000 PDT
UTC: 2023-08-10 16:35:52.000000 UTC
GPS: 1375720570.000000

Noise budget with no squeezing. Same time as above, now calculates using gwinc quantum noise calculation instead of semiclassical calculation used previously.

PDT: 2023-08-10 10:18:11.000000 PDT
UTC: 2023-08-10 17:18:11.000000 UTC
GPS: 1375723109.000000

Both sqz & no-sqz noise budgets now use the correlated quantum noise calculation from gwinc, instead of semiclassical calculations for SN & QRPN. The gwinc budget parameters related to quantum noise calculation are consistent with the recent sqz data set (8/2, alog 72565), with readout losses evenly split between IFO output losses that influence optical gain (20%) and SQZ injection losses (20%), parameters in plot title here. This is high on SQZ injection losses, and slightly conservative on IFO output losses. This updated FDS time is thermalized and closer to the No-SQZ time; the time used previously was several hours earlier near the start of lock, w/ ifo not yet thermalized.

Unlike before, both budgets now show GDS-CALIB STRAIN, which on 8/10 was more accurately calibrated (see Louis's alog on Aug 8, LHO:72075, comparing CAL-DELTAL and GDS vs. PCAL sweep, and his record from 72531). CAL-DELTAL was previously overestimating range due to calibration inaccuracies. We got GDS-CALIB_STRAIN data from nds servers, and at first weren't able to get input jitter data from nds, due to the sampling rate change of IMC-WFS channels from 2k to 16k, 71242. Jonathan H. helped us fix this issue, so we can now pull GDS data and input jitter data from nds.ligo-wa.caltech.edu:31200 -- thank you Jonathan!! With this, the input jitter sub-budget is kind of interesting, looks to be mostly IMC-WFS in YAW.

A quick thought on discrepancy between expected and measured DARM between below several hundred Hz-- I don't know if this could be related to the recent update to gwinc CTN parameters (high/low index loss angles), related to quantum noise, or mystery noise. The recent gwinc CTN update seemed to have dropped the calculated CTN level slightly (maybe 10-15% or so). In April 2023, Kevin helped update CTN parameters LHO:68499 to reconcile H1 budget with the official gwinc parameters, while Evan made a correlated noise measurement 68482 where noise in the bucket seems more consistent with the older CTN estimate from gwinc (or very slightly higher). Another idea is that it could be related to quantum noise, such as SRCL detuning or sqz angle which could've changed since the sqz dataset, as quantum noise can also affect the noise in this region.

All pushed as git commit 28cf2664.

Edit: All pushed again as git commit 33ffd60b.

Added noise budgets with squeezing for HVAC off time on August 17 from alogs 72308, 72297.

When comparing this HVAC off time on Aug 17 with the noise budget from above on Aug 10, it's interesting to note the broadband difference in input jitter (Aug 10 vs Aug 17, HVAC off). Between these times, worth noting that I think there were several additional improvements (like LSC FF or SUS-related) as well.

Edit: updated 8/10 input jitter budget to the less glitchy noise budget time.

Much of the gap between expected DARM (black traces) and measured DARM (red traces) in the noise budget looks compatible with elevating the CTN trace. Budget plots with 100 Hz CTN @ 1.45e-20 m/rtHz are attached below for the no-HVAC times. This is almost 30% higher than the new gwinc nominal CTN at 100 Hz (i.e., 1.128e-20 m/rtHz --> 1.45e-20 m/rtHz). Compared to the old gwinc estimate of 1.3e-20, this is ~11% higher. Quantum noise calculation unchanged here.

This CTN level is similar to the 30% of excess correlated noise that Evan H. observed in April 2023, see LHO:68482. His cross-correlation measurement sees ~30% excess correlated noise around 100 Hz after subtracting input jitter noise, where that "30%" is using the newer gwinc CTN estimate of 1.128e-20 m/rtHz @ 100 Hz. This elevated correlated noise, if attributed to CTN, corresponds to CTN @ 100 Hz of about 1.3*1.128 = 1.46e-20 m/rtHz. See this git merge request for the gwinc CTN update ; this update lowered the expected CTN at 100 Hz by ~15%, from 1.3e-20 (old) to 1.1e-20 m/rtHz (new), based on updated MIT measurements.

For reference, I have plotted these various CTN levels as dotted traces in the thermal sub-budget.

To elevate CTN levels by 30% in the budget code, I scaled both high+low index loss angles by a factor of 1.8, specifically Philhighn 3.89e-4 --> 7e-4 ; Phillown 2.3e-5 --> 4.14e-5. It seems like much higher than this level ~1.45e-20 might be difficult to reconcile with the full budget.

Noteworthy w.r.t. squeezing: from the laser noise sub-budget, laser frequency noise looks within 33% of squeezed shot noise with ~3.7dB of squeezing. By contrast, the L1 noise budget from Aug 2023 (LLO:66532) shows laser noise at the ~20% level of squeezed shot noise with 5.3 dB of squeezing -- i.e. a lower laser noise floor past shot noise.

The following plots can be found in /ligo/gitcommon/NoiseBudget/aligoNB/out/H1/lho_all_noisebudgets_081723_noHVAC_elevatedCTN, and not yet commited to the git repo.

Plots with higher CTN are attached here for the SQZ / no-SQZ proper noise budget times from 8/10, when injections were run.

Comparing the sqz vs. no-sqz budgets suggests there might be more to understand here, to tease apart the contributions from coating thermal noise (CTN) vs. quantum noise in the bucket. In particular, something disturbing that stands out, is that I imagined that if elevated CTN is the physical effect we're missing, it would reconcile both NBs with and without squeezing. However, there is still some discrepancy in the un-squeezed budget, which was not resolved by CTN, and seems to have a consistent shape. I'm wondering if this is related to the IFO configuration as it affects the quantum noise without squeezing. I think this could result from a non-zero but small SRCL detuning since it looks like elevated noise, with a clear shape, that increases below the DARM pole. Simply elevating CTN to match the no-sqz budget would put us in conflict with squeezed darm, so I don't think it makes sense to elevate CTN further. The budget currently has 0 SRCL detuning as it "seems small-ish", but this parameter is somewhat unconstrained in the quantum noise models.

In models, the readout angle is upper-bounded by Sheila's contrast defect measurement, though in principle it could probably be anything lower than that too, which could be worth exploring. It might be helpful to have an external measurement of the thermalized physical SRCL detuning, or in the models allowing the SRCL detunings to vary, to explore how it fits or is constrained by the fuller noise budget picture.

Plots with squeezing can be found in /ligo/gitcommon/NoiseBudget/aligoNB/out/H1/lho_all_noisebudgets. No squeezing plots are in /ligo/gitcommon/NoiseBudget/aligoNB/out/H1/lho_darm_nosqz_noisebudget.

I pushed to git commit 70ca191c without elevated CTN and the associated extra traces. The relevant parameters are left commented out at the bottom of the QuantumParams file, and relevant code to plot the extra traces is commented out in the lho_all_noisebudgets script.

I restored the FMCS alarm levels. Code to do this is under my home account in an fmcs directory.

If our overall goal is to remove peaks from DARM that dominate the RMS, reducing these damping gains is not the best way to acheive that. SR2 L damping gain was reduced by a factor of 5 in this alog, and a resulting 2.8 Hz peak is now being injected into DARM from SRCL. This 2.8 Hz peak corresponds to a 2.8 Hz SR2 L resonance. There is no length control on SR2, so the only way to suppress any length motion of SR2 is via the top stage damping loops. The same can be said for SR3, whose gains were reduced by 80%. It may be that we are reducing sensor noise injected into SRCL from 3-6 Hz by reducing these gains, hence the improvement Gabriele has noticed.

Comparing a DARM spectrum before and after this change to the damping gains, you can see that the reduction in the damping gain did reduce DARM and SRCL above 3 Hz, but also created a new peak in DARM and SRCL at 2.8 Hz. I also plotted spectra of all dofs of SR2 and SR3 before and after the damping gain change showing that some suspension resonances are no longer being suppressed. All reference traces are from a lock on Aug 9 before these damping gains were reduced and the live traces are from this current lock. The final plot shows a transfer function measurement of SR2 L taken by Jeff and me in Oct 2022.

Since we fell out of lock, I took the opportunity to make SR2 and SR3 damping gain adjustments. I have split the difference on the gain reductions in Gabriele's alog. I increased all the SR2 damping gains from -0.1 to -0.2 (nominal is -0.5). I increased the SR3 damping gains from -0.2 to -0.5 (nominal is -1).

This is guardian controlled in LOWNOISE_ASC, because we need to acquire lock with higher damping gains.

Once we are back in lock, I will check the presence of the 2.8 Hz peak in DARM and determine how much different the DARM RMS is from this change.

There will be SDF diffs in observe for all SR2 and SR3 damping dofs. They can be accepted.

SR2 and SR3 damping gains changes that Elenna made have been accepted

The DARM RMS increases by about 8% with these new slightly higher gains. These gains are a factor of 2/2.5 greater than Gabriele's reduction. The 2.8 Hz peak in DARM is down by 21%.

This is a somewhat difficult determination to make, given all the nonstationary noise from 20-50 Hz, but it appears the DARM sensitivity is slightly improved from 20-40 Hz with a slightly higher SR2 gain. I randomly selected several times from the past few locks with the SR2 gains set to -0.1 and recent data from the last 24 hours where SR2 gains were set to -0.2. There is a small improvement in the data with all SR2 damping gains = -0.2 and SR3 damping gains= -0.5.

I think we need to do additional tests to determine exactly how SR2 and SR3 motion limit SRCL and DARM so we can make more targeted improvements to both. My unconfirmed conclusion from this small set of data is that while we may be able to reduce reinjected sensor noise above 3 Hz with a damping gain reduction, we will also limit DARM if there is too much motion from SR2 and SR3.

Based on this measurement of MICH Y, it appeared the loop is stable for a 13 dB increase in gain, which would put the UGF closer to 1 Hz like MICH P. I raised the gain by a factor of 4, and the loop is stable and there doesn't appear to be excess noise in DARM. I ran a quick injection to check the level of MICH Y relative to DARM.

MICH Y gain is now -2.4 (was -0.6). This is updated in the guardian (lownoise ASC) and SDFed.

A few minutes after posting, Sheila and I noticed CSOFT Y motion increased significantly and the noise in DARM between 20-30 Hz worsened. This extra noise and motion reduced as I reduced the MICH Y gain back to -0.6. Looking at the spectra and RMS of both MICH Y IN1 and LSC DARM IN1, it appears that although the overall RMS of both decreases with the higher gain, the higher gain also increases a 1.3 Hz peak in both MICH Y and DARM. I am undoing these changes and keeping the MICH Y gain nominal (-0.6).

The above aLOG covers another *solution* top the on-going studies about the ~5-10% systematic error in the calibration -- namely, what's unique to LHO and *left over* after the flaw in GDS filters that was fixed in LHO:71787.

The filter was loaded by 2023-08-07 17:15 UTC.

This change has been added to the LHO record of calibration pipeline changes for O4, DCC:T2300297

Correction to the timing of this filter update -- The filter was loaded by 2023-08-07 17:15 PDT -- i.e. 2023-08-08 00:15 UTC

New stock arrived and has been added to ICS. Will be stored in the totes in the TCS LVEA cabinet. 

• ITMX: Superluminescent Diode QSDM-790-5 
  • S/N 11.21.380
  • S/N 11.21.382
  • S/N 05.21.346 (note the data sheet is labeled 04.21.346 but QPhotonics noted this is a typo) 
• ITMY: Superluminescent Diode QSDM-840-5
  • S/N 11.21.303

• ITMX: Superluminescent Diode QSDM-790-5 
  • S/N 06.18.002 - used spare
  • S/N 11.21.380
  • S/N 11.21.382
  • S/N 05.21.346 - Installed July 2023 71476
  • S/N 07.14.255 Old sled, removed 71476
• ITMY: Superluminescent Diode QSDM-840-5
  • S/N 03.20.479 
  • S/N 06.16.005 
  • S/N 11.21.303 - Installed July 2023 71476
  • S/N 11.17.127 Old sled, removed 71476

ISC has been updated. As of August 2023, have 2 spare SLEDs for each ITM HWS.  

• ITMX Superluminescent Diode QSDM-790-5 
  • S/N 06.18.002 - used spare
  • S/N 11.21.380 - Installed Oct 2023 73371
  • S/N 11.21.382
  • S/N 05.21.346 - Old sled, removed  73371
  • S/N 07.14.255 Old sled, removed 71476
• ITMY: Superluminescent Diode QSDM-840-5
  • S/N 03.20.479 - Installed Oct 2023 73371
  • S/N 06.16.005 
  • S/N 11.21.303 - Old sled, removed  73371
  • S/N 11.17.127 Old sled, removed 71476

ISC has been updated. As of October 2023, have 1 spare SLEDs for each ITM HWS, with more ordered.  

Spare 8240nm SLEDs QSDM-840-5 09.23.313 and QSDM-840-5 09.23.314 arrived and will be placed in the TCS cabinets on Tuesday. We are expecting qty 2 790nm SLEDs too. 

Spare 790nm SLEDs QSDM-790-5--00-01.24.077 and QSDM-790-5--00-01.24.079 arrived and will be placed in the TCS cabinets on Tuesday. 

In 84417, we swapped:

• HWSX from QSDM-790-5 11.21.380 to 11.21.382
• HWSX from QSDM-840-5 03.20.479 to 06.18.005

The removed SLEDs have been dispositioned, DEFECT-TCS-7839.

In 87353 we removed 11.21.382 and installed 01.24.077.