Lockloss at the end of comissioning - looks like an ETM glitch.

Unknown cause lockloss that happened early in comissioning while ramping bias gains, but we are unsure if this is the cause of the Lockloss.

Summary: We can use single bounce scans in the OMC to constrain how the signal recycling cavity mode-matching affects mode-matching to the OMC - still a work in progress.

This is a collection of the single bounce scans we have done with the OMC in O4b and O4c (excluding some we did between April and July after the first OFI damage which might have made this meaasurement give some weird results) :

For the single bounce measurements we orginally thought that which ITM the beam bounced off did not affect the mode-matching, but this looks not to be the case so in the following analysis I will only compare measurements where we had ITMX mis-aligned and the beam bouncing off ITMY.

I already used the measurements from the first two rows to estimate the beam parameter just before OM2 in the single bounce configuration in alog #84255.

Since we had the SR3 heater on in the bottom four measurements mentioned above this gives us some points to constrain the mode-matching of the input beam to the signal recycling cavity as well as to the OMC.

The q parameter can be used to define the electric field amplitude transverse to the beam propagation direction z:

U = 1/q ( exp( -jk ( x² + y² ) / 2q ))

where k is the wavenumber of the light and x and y are the transverse distances from the center of the beam in the horizontal and vertical directions.

Using the overlap integral:

O(q₁,q₂) = | U₂ U₁^* |² / ( |U₁|² |U₁|²​ )​​​​​ 

where U₁ is the field amplitude for TM 00 mode of the OMC and U₂ is the field amplitude of the mode you are trying to work out the mode-matching to.

One can then define a mode mis-match between the modes U₁ U₂ :

MM % = (1 - O(q₁,q₂)) * 100,

In the previous alog I took a grid of possible q-parameters just before OM2 and plotted a contour on this grid showing which of the q values are compatible with the mode-matching I measured for hot OM2 and cold OM2.

Since I have two measurement showing SR3 hot with OM2 both cold and hot I will plot these two countours on the same plot.

The two possible qs this gives us are the overlap of the green and magenta lines - ie. the q parameter could be either of these values when SR3 is hot.

q1 = 0.748 + 0.967i

q2 = 1.44 + 1.01i

FAMIS 31096

No major changes this week, but the FSS RefCav trans TPD jumps I first noticed last week are still happening, so I continued my investigation into their cause.

Thinking these jumps were being caused by some frequency feedback from the IMC or the arms since they don't seem to line up with anything else in the PSL, I trended some IMC signals looking for similar behavior. Sure enough, several IMC electronics signals have trends that follow the jumps in power seen on the FSS TPD, including IMC-F. See final screenshot for a before/after comparison of these signals around last Tuesday's maintenance period when this change began. Also, in looking at more locking examples, I can say that the jumps start occurring towards the end of 'LOCKING_ALS' or during 'FIND_IR' states in main locking and persist until the next lockloss. Again, not sure that anything really needs to be done about this as it hasn't been causing problems that we've noticed so far, but it would be interesting to know why this change started and if it goes away for some reason, so I'll continue to keep an eye on it.

Closes FAMIS 26432, last checked in alog 85850

Laser Status:
    NPRO output power is 1.866W
    AMP1 output power is 70.15W
    AMP2 output power is 140.8W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 13 days, 0 hr 18 minutes
    Reflected power = 23.56W
    Transmitted power = 105.5W
    PowerSum = 129.1W

FSS:
    It has been locked for 0 days 2 hr and 27 min
    TPD[V] = 0.8073V

ISS:
    The diffracted power is around 3.9%
    Last saturation event was 0 days 2 hours and 28 minutes ago

Possible Issues:
    PMC reflected power is high

No changes from last week.

Mon Jul 28 10:09:24 2025 INFO: Fill completed in 9min 21secs

FAMIS27820

No water was added to either chiller, both at good levels. Updated T2200289 sheet.

Filters all looked good.

No water in leak detection Dixie cup.

Looking at the (few) locklosses over the weekend, there was only one that looked like it may have been from the TMSX_Y oscillation we've been seeing recently alog85973.

07/26/25 17:26 1437586004 No ASC

07/27/25 01:52 1437616362 NO ASC

07/27/25 13:39 1437658811 ASC?

07/28/25 03:13 1437707641 NO ASC

Took a calibration measurement as the first thing for comissioning this morning (since we missed our window over the weekend)

BB Start: 1437750930

BB End: 1437751248

Calibration Monitor Attached

notification: end of measurement
notification: end of test
diag> save /ligo/groups/cal/H1/measurements/PCALY2DARM_BB/PCALY2DARM_BB_20250728T151520Z.xml
/ligo/groups/cal/H1/measurements/PCALY2DARM_BB/PCALY2DARM_BB_20250728T151520Z.xml saved
diag> quit
EXIT KERNEL

2025-07-28 08:20:30,384 bb measurement complete.
2025-07-28 08:20:30,384 bb output: /ligo/groups/cal/H1/measurements/PCALY2DARM_BB/PCALY2DARM_BB_20250728T151520Z.xml
2025-07-28 08:20:30,384 all measurements complete.
 

We had a power glitch yesterday, Sunday 27jul2025 at 12:34:27 PDT. It was detected by the MSR UPS, but not by any other UPS. Attached plot shows the CS Mains Mon at this time. No reports of any issues arising from this glitch, H1 was in lock throughout.

Note, the MSR UPS sytem time is about 13 minutes fast, it reported this glitch as 12:47:13.

TITLE: 07/28 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Observing at 153Mpc
OUTGOING OPERATOR: Oli
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 5mph Gusts, 2mph 3min avg
    Primary useism: 0.01 μm/s
    Secondary useism: 0.04 μm/s
QUICK SUMMARY:

IFO is in NLN and OBSERVING as of 04:28 UTC. Planned comissioning will take place from 08:30 PT to 11:30 PT.

We dropped out of OBSERVING for 5 minutes due to the squeezer re-locking from 14:18 to 14:23 UTC.

TITLE: 07/28 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Observing at 155Mpc
INCOMING OPERATOR: Oli
SHIFT SUMMARY:

Rode through a surprisingly "big" M5 Iceland EQ which was seen on SUS PRM, and seismometers, only to have a random lockloss 3hrs later.
LOG:

• 0010 EX saturation (on Verbal) corresponding with seismic motion which is probably a M5.0 Iceland EQ
• 0313 LOCKLOSS, with ALSy having difficulties, but some ETM tweaks and a couple of SCAN Aligns it made it.  DRMI looked ugly as per usual, so went to CMFringes + PRMI and DRMI locked up (with a click on SRM.  Back to Observing at 0428utc.

TITLE: 07/27 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Observing at 151Mpc
OUTGOING OPERATOR: Ibrahim
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 25mph Gusts, 16mph 3min avg
    Primary useism: 0.04 μm/s
    Secondary useism: 0.05 μm/s
QUICK SUMMARY:

Ibrahim's handing over an H1 locked for 8.5hrs, and environmentally the only notable are the winds now and we just survived a M5.4 Aleutian Islands/Alaska EQ.

As part of the DQ shift, I was looking at the DARM spectrorams to identify non-stationary (of the order of hours) features. Below is a list of features that were relatively obvious from the spectrograms. I used GDS-CALIB_STRAIN_NOLINES channel data for July, 21, 2025. In order to see the frequency variations a bit clear, i used 100-second spectrograms.

• 17.8 Hz, wandering line with variation around 0.2 Hz
• 20.26 Hz with linewidth/variation of ~ 0.04 Hz 
  • This was also reported in the a-log 85856 recently. In addition to the narrow line, sometimes we also see ~1 Hz broad noise around the narrow line. It is not clear whether thest two features (narrow and broad) are related.  
• 25.6 Hz with ~0.2 Hz wander
• 27.1 Hz with ~0.1 Hz wander
• 33.0 Hz with ~0.2 Hz wander
• 40.1 Hz with linewidth/variation of ~ 0.02 Hz
  • Is this a harmonic of 20.26? Their temporal behaviour look similar. 
  • The bruco results show that most of the low frequency features listed above including 20.26 Hz come from the input part of the IFO such as HAM2-3, IMC, which was also reported in the a-log 85959. Further studies required to identify the exact coupling location and the mechanism.
• 126.24 Hz with linewidth/variation of ~ 0.02 Hz
• 136.36 Hz with linewidth/variation of ~ 0.02 Hz
• 151.48 Hz with linewidth/variation of ~ 0.02 Hz
  • All the three lines (126.24 Hz, 136.36 Hz, and 151.48 Hz) look similar in their variations over time and looking at the time scales the variations may be related to temperature; not sure if the source is the same for all three frequencies.
• 177.1 Hz with variation of 0.2 Hz
• 179.1 Hz with variation of 0.1 Hz
  • The temporal variations of 177.1 Hz and 179.1 Hz look similar. 
• 272.65 Hz with 0.2 Hz variation
  • Its variation looks similar to 126.24 Hz, 136.36 Hz, and 151.48 Hz (the frequency is very close to the next harmonic of 136.36 Hz)
• 540 Hz with 0.5 Hz width; excess noise at the beginning of the lock (input jitter?)
• 660 Hz with 1 Hz width; excess noise at the beginning of the lock (input jitter?)
  • We see something similar in LLO (alog 77265)also.
• 3073 Hz with ~2 Hz frequency ring down
• 3131 Hz with ~2 Hz frequency ring down
  • The 3073 Hz and 3131 Hz features look similar (the frequency of the feature decreases over time after the lock). Maybe down conversion of HOMs?
• 6556.8 Hz with 0.02 Hz variation
  • This one looks a bit different from 3131 Hz and 3073 Hz. It has more stable slope and small frequency variation. Maybe this is also realted to HOM, but one with high Q?

Using my model for the propagation from OM2 to the OMC I discussed in alog #84255, I made a contour plot for the mode overlap (O(q₁,q₂ ))_c between the mode propagated through cold OM2 to the OMC, q₁ and the fundamental mode of the OMC, q₂ divided by the mode propagated through hot OM2 overlapped with the OMC mode, (O(q₁,q₂ ))_h .

This is so I could comnpare it to measurements I made of the drop in optical gain, G when the curvature of OM2 was changed. Its hard to predict how much loss in total there is with the full interferomter locked but the optical gain change can tell us the change in optical loss between these two states which we assume to be due to mode-mis-match.

O^' / O = (G^' / G)²

In the plot I have used overlap ratio percentage, O % on the z axis, the real part of of the q I started with between OM1 and OM2 on the x-axis, and the imaginary part of this q on the y-axis.

O % = (O(q₁,q₂ ))_h / (O(q₁,q₂ ))_c × 100

The white line gives the square ratio of the optical gains measured in full-lock (alog #82559) for each of these states. The code to run this is in OM2_to_OMC_comp_full_IFO.m found at this respository on ligo gitlab.

The white line contains a contour of possible values of the q parameter between OM1 and OM2 for the full-locked state of the interferometer bar any changes since the end of January 2025 when I took these measurements.

Ivey used the ISO calibration measurements that I took earlier (85906) to calculate what the OSEMINF gains should be on SR3 (85907), and this script also calculates what it thinks the compensation gain in the DAMP filter bank should be.
The next step is to use OLG TFs to measure what values we would use in the DAMP filter bank to compensate for the change in OSEMINF gains, and we can compare them to the calculated values to see how close they are.

I took two sets of OLG measurements for SR3:
- a set with the nominal OSEMINF gains
    T1: 1.478
    T2: 0.942
    T3: 0.952
    LF: 1.302
    RT: 1.087
    SD: 1.290
- a set with the OSEMINF gains changed to the values in 85907
    T1: 3.213
    T2: 1.517
    T3: 1.494
    LF: 1.733
    RT: 1.494
    SD: 1.793

Measurement settings:
- SR3 in HEALTH_CHECK but with damping loops on
- SR3 damping nominal (all -0.5)
- HAM5 in ISOLATED

Nominal gain set:
/ligo/svncommon/SusSVN/sus/trunk/HLTS/H1/SR3/SAGM1/Data/2025-07-22_1700_H1SUSSR3_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz_OpenLoopGainTF.xml r12478

New gain set:
/ligo/svncommon/SusSVN/sus/trunk/HLTS/H1/SR3/SAGM1/Data/2025-07-22_1800_H1SUSSR3_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz_OpenLoopGainTF.xml r12478

Once I had taken these measurements, I exported txt files for each dof's OLG and used one of my scripts, /ligo/svncommon/SusSVN/sus/trunk/HLTS/Common/MatlabTools/divide_traces_tfs.m to plot the OLG for each dof to compare the traces between OSEMINF gain differences and then divide the traces and grab an average of that, which will be the compensation gain put in as a filter in the DAMP filter bank (plots). The values I got for the compensation gains are below:
    L: 0.740
    T: 0.732
    V: 0.548
    R: 0.550
    P: 0.628
    Y: 0.757

 These are pretty similar to what my script had found them to be last time before the satamp swap (85288), as well as being very similar to the values that Ivey's script had calculated.
Maybe the accuracy from Ivey's script means that in the future we don't need to run the double sets of OLG transfer functions and can jsut use the values that the script gives.