Here is a plot showing the effect of the cleaning that is currently ongoing.  Since Robert was able to significantly mitigate the 120 Hz peak yesterday, there is not much difference between the strain channel and the cleaned channel there anymore.  But, our LSC FF needs tuning (measurements to be taken later this commissioning period), so there's lots of effect down there.

Both the Jitter and LSC noises were retrained on data from our most recent lock.  The high frequency laser noise I havne't retrained in several weeks, and it's still doing quite nicely.

This quiet period ended at 20:22 UTC (for calibration measurements).

Attached is the range plot from the control room wall, where we can see the improvement due to the cleaning being engaged.

Since we have lost lock, I re-accepted in the h1oaf Observe.snap file the correct value of 0 gain for H1:OAF-NOISE_WHITENING_GAIN, so NonSENS will be off (without any SDF diffs) when we get relocked.

Tagging Facilities as well.

Thank you for getting these out Oli, this is great! I agree with you that it doesn't seem like this chiller pump has any direct impact on our range, though perhaps we might want to consider looking further into a possible correlation of VEA temps and our range.

Clarification: It is not the chiller "pump" that was reconfigured to run only when demanded. It was the chiller themselves. It's also not clear that this was the status quo for all chillers across site. It was only recently discovered on one chiller in particular. 

The chiller "pump" has always and will continue to run regardless of the state of the chiller itself as glycol needs to be continually cycled through the AHU cooling coils at all times.

H1 is back to observing as of 04:14 UTC

I checked H1:OMC-DCPD_SUM_OUT_DQ and don't see the comb in any of the three listed intervals (neither state A nor B). Tested with a couple of SFT lengths (900s and 1800s) in each case.

Since it seems that the coupling is NOT a direct electronics coupling from Beckhoff -> OM2 -> DCPD, we fully connected the Beckhoff cable to the OM2 heater driver chassis and locked the OMC to the shoulder with an X single bounce beam (~20mA DCPD_SUM, not 40mA like in the usual nominal low noise state). That way, if the Beckhoff is somehow coupling to OMC PZT that might cause visible combs in the DCPD.

We didn't see the comb in this configuration. See the 1st attachment, red is the shoulder lock and green is when 1.66Hz comb was visible with the full IFO (the same time reported by Ansel in alog 73000), showing just two largest peaks of 1.66Hz harmonics visible in the green trace. (It seems that the 277.41Hz and 279.07 Hz peak are 167th and 168th harmonics of 1.66Hz.) Anyway, because of the higher noise floor, even if the combs are there we couldn't have seen these peaks. We've had a different comb spacing since then (alog 73028) but anyway I don't see anything at around 280Hz. FYI I used 2048 FFTs for both, red is a single FFT and the green is an average of 6. This is w/o any normalization (like RIN).

In the top panel of 2nd attachment, red is the RIN of OMC-DCPD_SUM_OUT_DQ of the shoulder lock, blue and dark green are RIN of 2nd loop in- and out-of-loop sensor array. Magenta, cyan and blue green are the same set of signals when H1 was in observing last night. Bottom panel shows coherence between DCPD_SUM during the shoulder lock and ISS sensors as well as IMC_F, which just means that there's no coherence except for high kHz.

If you look at Georgia's length noise spectrum from 2019 (alog 47286), you'll see that it's not totally dissimilar to our 2nd plot top panel even though Georgia's measurement used dither lock data. Daniel points out that a low-Q peak at around 1000Hz is a mechanical resonance of OMC structure causing the real length noise.

Configurations: H1:IMC-PWR_IN~25.2W. ISS 2nd loop is on. Single bounce X beam. DCPD_SUM peaked at about 38mW when the length offset was scanned, and the lock point was set to the middle (i.e. 19mA). DC pointing loops using AS WFS DC (DC3 and DC4) were on. OMC QPD loops were not ON (it was enabled at first but was disabled by the guardian at some point before we started the measurement). We were in this state from Oct/17/2023 18:12:00 - 19:17:20 UTC.

BTW Beckhoff cable is still fully connected to the OM2 heater driver chassis. This is the first observation data with such configuration after Fil worked on the grounding of Beckhoff chassis (alog 73233).

Detchar, please find the comb in the obs mode data starting Oct/17/2023 22:33:40 UTC.

The comb indeed re-appeared after 22:33 UTC on 10/17. I've attached one of the Fscan daily spectrograms (1st figure); you can see it appear in the upper right corner, around 280 Hz as usual at the start of the lock stretch.

Two other notes:

• The comb is now back to its original spacing of 1.6611 Hz.
• There are new strong lines visible at +/- 1.235 Hz from the comb teeth. If this structure has appeared before, I'm not aware of it. I've attached an image showing the lines (2nd figure, average of DMT-ANALYSIS_READY data between 22:00 10/17 and 02:00 10/18) and a comparison with older data from Sept 20th (3rd figure).

Just to see if anything changes, I used the switchable breakout board at the back of the OM2 heater driver chassis to break the thermistor connections but kept the heater driver input coming from the Beckhoff. The only two pins that are conducting are pins 6 and 19.

That happened at around Oct/18/2023 20:18:00 to 20:19-something UTC when others were doing the commissioning measurements.

Detchar, please look at the data once the commissioning activities are over for today.

Because there was an elevated noise floor in the data from Oct/17/2023 18:12:00 mentioned in Keita's previous comment, there was some doubt as to whether the comb would have been visible even if it were present. To check this, we did a direct comparison with a slightly later time when the comb was definitely present & visible. The first figure shows an hour of OMC-DCPD_SUM_OUT_DQ data starting at UTC 00:00 on 10/18 (comparison time with visible comb). Blue and yellow points indicate the comb and its +/-1.235 Hz sidebands. The second figure shows the time period of interest starting 18:12 on 10/17, with identical averaging/plotting parameters (1800s SFTs with 50% overlap, no normalization applied so that amplitudes can be compared) and identical frequencies marked. If it were present with equivalent strength, it looks like the comb ought to have been visible in the time period of interest despite the elevated noise floor. So this supports the conclusion that the comb *not* present in the 10/17 18:12 data.

Following up, here's about 4 hours of DELTAL_EXTERNAL after Oct 18 22:00. So this is after Keita left only the heater driver input connected to the Beckhoff on Oct/18/2023 20:18:00. The comb is gone in this configuration.

Screenshot summarizing homodyne measurements today. With measured carrier NLG=11 (for generated squeezing ~14.7-14.8 dB), we observe

• squeezing           = - 6 dB
• anti-squeezing    = +13.5 dB
• mean-squeezing = +10.5 dB

Comparing sqz/anti-sqz to generated sqz: ~7% unexplained homodyne losses. This is consistent with our last estimate of excess HD losses (8/29/2023, LHO:72802, ~7% mystery loss). Since then, we swapped the HD detector and improved readout losses (visibility). We now measure more homodyne squeezing at 6 dB, consistent with expected loss reductions. That is compared to 8/29 (LHO:72802), we have less total loss, less budgeted hd loss && more squeezing, but the same unexplained hd losses as before.

Comparing mean-squeezing to generated sqz: could be consistent with sqz/asqz losses. I think there is a mis-estimate of the generated squeezing level from non-linear gain. If we ignore our NLG11 measurement, and instead use the generated squeezing level to match observed 13.5 dB of anti-squeezing, then we allow losses to determine the measured 6 dB squeezing level, we would have an NLG=10 (not 11) for a generated squeezing level of 14.5 dB. This would suggest 7% unexplained losses, same as the sqz/asqz measurements.

For ~7% mystery losses, this is compared to total HD losses of 21%, of which we budget 15% losses. From the sqz wiki, the budgeted losses are:

• opo escape 98.5% 
• in-chamber ham7 95.3%
• beam diverter 99%
• SQZT7 on-table optics losses 2% (72604)
• HD PD QE 97.7%  (73241)
• visibility 95.6%  (from 97.8% fringe visibility on PD B) 

If we include phase+dark noise that degrades squeezing but is not loss, then 21% total loss can explain the 6dB measured squeezing, see e.g. from the gsheet calculator (edited to include ranges for NLG=10 and NLG=11):

DTT homodyne template saved at $userapps/sqz/h1/Templates/dtt/HD_SQZ/HD_SQZ_101023.xml .

Edited to include some history of homodyne measurements:

• 6 dB SQZ -  10/10/23 LHO:73365 = 21% total loss, 15% known loss, 7% mystery (this time)
• 5.2dB SQZ - 8/31/23, LHO:72802 = 27% total loss, 21% known loss, 7% mystery (bad PD-B QE, lower visibility?)
• 5.5dB SQZ -   2/3/23, LHO:67219 = 25% total loss, 15% known losses, < 10% mystery (tech noise -10dB), NLG was varied.

It could still be interesting to vary NLG to see if we can obseve any more squeezing, or if an additional technical noise floor (aside from dark noise) is needed to explain the NLG sweeps.

We revised the sqz loss wiki table again today, and are including it to explain what we think our current understanding of losses is. 

It seems likely that the 7% extra losses we see on homodyne measurements are in HAM7, so we've nominally added that to the loss budget. 

In addition to this, there would be an additional 8% loss on the sqz beam if we didn't correct it's linear polarization with a half wave plate.  72604  At the time of the chamber close out, (65110) we measured throughput from HAM7 to HAM5 that would implies that two passes through the OFI were giving us 97.6% transmission, so this is not compatible with the polarization being wrong by this much.  We haven't included this as a loss in the loss budget because it seems incompatible with our measurement in chamber. 

The wiki currently lists the OMC transmission as 92%, and the PD QE as 98%.  The PD QE may be worse than this (see 61568), but measurements of the product of QE and OMC transmission for 00 mode seem to indicate that is in the range 90-92%, so this is close. 

With the infered losses of from the measured sqz/anti-sqz in the IFO, the plausible range of losses is 30-35%, we are using 32%.  With only known losses (including the values for OMC trans and PD QE), we have 14% unexplained loss. If we include the 7% apparent HAM7 losses, we have 9% unexplained losses in the IFO.  This does seem similar to the 8% polarization problem, but it would also include SQZ-OMC mode matching.  

Possible future scenarios:  We may be able to reduce the 7% HAM7 losses, and we may be able to swap the OMC to reduce those losses from 92% to 97%.  

These numbers come from the aoki equations that Vicky added to the google sheet here: gsheet

Don G. and Sheila have very likely resolved the homodyne polarization issue as being due to the SQZT7 periscope. So, the mis-polarization is likely not an issue for squeezing in the interferometer.

The sqz beam leaves HAM7 via reflection off the sqz beam diverter. From the latest CAD layout from Don, the outgoing reflected beam (blue) is ~75.58 degrees from global +X. The periscope re-directs the beam to travel along SQZT7, approximately along +Y. The CAD layout thus suggests that the SQZT7 periscope re-directs the beam in yaw (counter-clockwise) by an estimated 90 - 75.58 = 14.4 degrees. 

From recent homodyne measurements LHO:72604, of the sqz light leaving HAM7 and arriving on SQZT7, ~8% of the power was in the wrong polarization, this calculates to a ~16.5 degrees polarization misrotation. Compared to this 16.5 degree misrotatation we were searching for, the 14.4 degrees polarization rotation induced by the periscope image rotation can plausibly explain the misrotation.

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.