[Jenne, Alicia, Joan-Rene, with suggestions from Sheila]

Today we tested using ETMY to transition the ETMX ESD, rather than the usual locking procedure of ITMX.  I had checked on the guardian code for this last week, alog 87997.  It worked!  The first time we tried transitionining back to ETMX, we lost lock, but the second time that also worked.  We are currently locked at NLN and observing, having gotten here using ETMY and not any stages of ITMX for the ESD transition. This means that we're ready to try grounding the ITM ESDs, to see if that helps reduce the combs that Alicia and Joan-Rene have been investigating. 

• The first time we tried locking, we went through the state LOWNOISE_ESD_ETMY by hand, so that we could transition ETMX -> ETMY slowly and measure the DARM loop along the way.  
  • We measured the DARM open loop gain before any transitioning, then after 25%, after 50%, after 75%, and after we were fully on ETMY.  See attached plot with the measurements labeled on the right side with percent of actuation on ETMY.
  • When we tried to transition back ETMY -> ETMX 25% of the way, (doing the state LOWNOISE_ESD_ETMX by hand), we lost lock.
    • After looking through the settings, it could be that the ETMX L1 Lock L filter bank wasn't set correctly (FM2 not on), even though I see that in my guardian shell I told it to turn on. 
    • Or, as Sheila points out to us, it could be that this transition back to ETMX is rather delicate, and we're going from using 2 stages of the temporary (ETMY) suspension to 3 stages on low noise ETMX, and we just can't do that part way.  
• The second time we tried locking, we let the guardian go through LOWNOISE_ESD_ETMY, which was successful.  We also checked that the ETMX L1 LOCK L filter bank was set up correctly. Since we were worried about going partially back to ETMX being delicate, we just ran the LOWNOISE_ESD_ETMX state to ramp all the way back to ETMX at once, and that was also successful. 
  • It turns out that I had forgotten that we'd need to disable the ETMY L3 Length actuation after we were done using it, since ETMY is used as part of our LSC FF actuation path, and that signal is only supposed to go to L2.  We had a funny bump in the DARM spectrum, and also some SDF diffs on ETMY that helped us find that easily.  
  • I have added (but not tested) a few lines in LOWNOISE_ESD_ETMX to reset the ETMY L3 settings to match the Observe.snap SDF, which should also fix the lump from improper feedforwarding. 

As of now, the guardian is set to acquire lock still using the nominal ITMX ESD.  So, before we ground the ITM ESDs we'll need to modify the weights in the guardian path, to make it so that the nominal path uses the ETMY and not ITMX.

Gerardo, Jordan, Travis

Today, we finished the installation of the replacement purge air piping at EY.  The system still needs to be tested for gross leaks, new filter elements on the supply line installed, an additional support added to the mechanical room side of the purge piping, and the new compressor and purge line validated via FTIR testing.  We plan to finish these installations and tests in the next week or two.  

20:00 UTC I swept the LVEA, I didn't see anything of note.

M. Todd, Kar Meng, S. Dwyer

We took more OMC scans today with OM2 hot. We measured a quadratic mismatch of about 6.8%, but the HG10 peak (misalignment) has enough power that I think this could be an underestimate by a percent or so. 

We struggled a lot to get good measurements at first, though we followed the directions I wrote last time to the letter. So I'm adding some "bewares" for future reference.

1. The OPO IR locked on 0.2 counts when last time we had a level of around 1 count. We didn't catch this right away but this was essentially locking on a 10 mode and sending that to the OMC and it was giving REALLY strange OMC scans. 

2. Once we figured this out, it ensured that we had enough power on the OMC QPDs and the OMA/OMB WFS-DC to get a pretty good centering. Once we ran the OMC scan, we found much better data compared to last week, though we notice here that the 10 peak still has about 50% of the power as the 20 peak (which we're after). This means that the estimate of quadratic mismatch using the P00/(P00+P20+P02) is probably underestimating the mismatch a bit. Note, using the cursors to calculate the power in the peaks means it is just the 00peak/(00peak+20peak) because the power in the 20peak contains both HG20 and HG02 as the OMC has very little astigmatism.

Tue Nov 11 10:04:05 2025 INFO: Fill completed in 4min 2secs

M. Todd

Summary: I do not think the ISS is limited by the input jitter (IMC PZT) from 1-1000 Hz. I have attached the injections I've made to the IMC PZT here. Below 1Hz I suspect the ISS is dominated by the IMC motion.

I unlocked the ifo at 2025-11-11 16:03:17 UTC so we could start maintenance Tuesday

TITLE: 11/11 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Observing at 153Mpc
OUTGOING OPERATOR: Ibrahim
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 3mph Gusts, 2mph 3min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.29 μm/s 
QUICK SUMMARY:

Currently Observing and have been Locked for over 11 hours. Today is maintenance day. It's also super foggy outside

Workstations were updated and rebooted.  This was an os packages update.  Conda packages were not updated.

TITLE: 11/11 Eve Shift: 0030-0600 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Observing at 153Mpc
INCOMING OPERATOR: Ibrahim
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 6mph Gusts, 3mph 3min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.29 μm/s
SHIFT SUMMARY:
After a lockloss early tonight relocking was simple after an Iniital_Alignement.
H1 has been locked for 1.5 hours. everything seems like it should be running well for the rest of the night.

LOG:
No log.

02:44:29 Lockloss
ETMX_L3 Master out looks to have had a glitch about 300 ms before hand and then was the first channel to deviate at 146ms before the lockloss.
Obligitory Lockloss ndscopes attached.
 

TITLE: 11/11 Eve Shift: 0030-0600 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Observing at 150Mpc
OUTGOING OPERATOR: Ibrahim
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 5mph Gusts, 2mph 3min avg
    Primary useism: 0.03 μm/s
    Secondary useism: 0.30 μm/s 
QUICK SUMMARY:
H1 has been locked and Observing for 5.5 hours.
Violins, secondary microseism & the wind forecast  are all looking great! 
The range seems to have settled down too.
Looks to be a great night for Observing.
 

TITLE: 11/11 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Observing at 152Mpc
INCOMING OPERATOR: Tony
SHIFT SUMMARY:

IFO is in NLN and OBSERVING as of 19:45 UTC (but locked at 19:09). 

Very well behaved IFO today with short reacquisition. Wind is still low and microseism continues to fall.

Had one LL during commissioning (lockloss alog 88043)

OFI temp is stepping once an hour for the next 4ish hours - should not interfere with relocking or anything, Alog 88046.

Additionally, there was a power glitch (not on-site but in town) that flickered lights and caused IY to saturate until power came back a few ms later. Alog 88049.

LOG:

Ibrahim, Ryan S, Tony

H1 saw a power glitch after lights flickered (Ryan S noticed NUC21 flickered) and IY SUS saturated. Dave confirms GC UPS saw the glitch.

Power has gone out (temporarily?) in-town according to friends.

Plots attached.

I noticed that in the high-frequency spectra (2000–5000 Hz) of both detectors from O4a data, there are spectral lines exactly at 2048 and 4096 Hz. They are so narrow that only the power at the exact frequency bins of 2048 Hz and 4096 Hz is significantly elevated.

This might be due to artifacts from the data-acquisition process. I searched the aLOGs for H1 and L1 but haven’t found relevant entries. Does anyone know the origin of these two lines?

Tony, Ibrahim, Sheila

While we are observing, the OFI temperature will be stepped once an hour for the next 7 hours.  I wouldn't expect this to impact the IFO or noise much, but tagging Detcahr just in case.  

The script is running on cdsws39, I'll leave the terminal open on the 1st workspace.  I'm hoping to get 7 hours of data from this with the IFO locked, but if the IFO unlocks this script shouldn't interfere with relocking so it can just be left running. 

Here is how the PR3 and SR3 signals show up at various ports.

I drove a pitch line from PR3 M3 and SR3 M3 at 8.125 Hz with the ASC notches on. I was able to see at signal with a 10 ct drive on PR3 pitch and 60 ct drive on SR3 pitch.

Templates saved as {PR3,SR3}_M3_injection_all_ports.xml in /ligo/home/elenna.capote/POPX_test in case the data is useful to you.

PR3 appears strongly at REFL and POP in I and at AS in Q. SR3 appears strongly at AS in Q and POP in Q.

Will try to repeat for yaw.

Keita, Rahul

We received three mirrors (JM1, 2 and 3) for the Jitter Attenuation Cavity (JAC) from CIT and were asked to characterize these mirrors before installing them in HAM1 chamber for the upcoming vent at LHO. JM1 and JM3 optics will be used in Tip Tilt supension and JM2 optic will be on a fixed mount inside the HAM1 chamber. Given below are the details of our setup and the results after characterizing them in the optics lab.

Aim of the experiment:- (a) to measure the reflectivity of the three mirrors as a function of its Angle Of Incidence (AOI) for P polarization of the input beam (1064nm laser), (b) measure the transmission of the optics at its AOI (defined in T2400360).

Experimental setup in Optics lab:- The optical layout is shown in figure1. We used a 1W 1064 nm laser (the power was reduced to 15mW approximately using a half wave plate). A polarizing beamsplitter was used to transmit P polarization waves to the steering mirror and the S polarization waves were reflected towards beam dump. The steering mirror used over here is dichroic (reflecting 1064nm light and transmitting/rejecting spurious green light emerging from the laser towards the beam dump). We used two lens to focus the input beam - one located upstream of the steering mirror and another one downstream of the same. The optic was installed on a Siskiyou mount, which was placed on a rotational stage - as shown in the picture. Thorlabs Power meter was used to measure the input, output and transmitted beam. 

Results:-

We did coarse and fine measurement to characterize the mirrors. For coarse measurement, we started at zero degree AOI (when the input beam was reflected back towards the iris) and then rotated the optic until the output power nulled - while recording the reflected power at every 5 degree interval. 

For fine measurements we set each optic at its AOI (as defined in T2400360) and then carefully measured the input, output and transmitted power. The results are given below,

M. Todd, S. Dwyer

As derived in previous alogs, we are able to relate the HOM spacing observed in each arm to the surface defocus of the test masses -- which is a combination of self-heating and ring heater power (ignoring CO2 affects on the ITM RoC). From the fits we've made of the HOM spacing / surface defocus change as a function of ring heater power we can get a value for the ring heater to surface defocus coupling factor.

Theoretically from this we should be able to solve for the self heating contribution in the test masses as well -- allowing us to constrain things like the coupling of absorbed power to surface defocus at the ITMs if we assume to know the arm power and absorption values (from HWS).

Upper Limits

If we assume no absorption in ETMs (obviously not physical), and we assume the HWS values for the ITM absorptions are correct, then with a HOM spacing measurement from each arm we can get an upper limit of the coupling factor of self-heating to surface defocus for each ITM (they shouldn't be different but this is a good exercise).

Assuming alpha is the absorption coefficient, i subscript is for the ITM, and x/y is which arm. P_y,i_rh is the itmy ring-heater. G-factors are the product of ITM and ETM g-factors. Then from the formula in section 1.2 of the notes file : Gy = Gyc - B*L*gyic*(Pyerh+Pyirh) - L*(Ai*alpha_yi*Pyarm*gyec + beta*Ai*alpha_e*Pyarm*gyic), we can solve for Ai which is the coupling factor of self-heating to surface defocus.

Middling Values

If we assume quoted absorption in ETMs (measured by LIGO, on galaxy), and we assume the HWS values for the ITM absorptions are correct, then with a HOM spacing measurement from each arm we can get a more realistic value of the coupling factor of self-heating to surface defocus for each ITM (they shouldn't be different but this is a good exercise).

Assuming alpha is the absorption coefficient, i subscript is for the ITM, and x/y is which arm. P_y,i_rh is the itmy ring-heater. G-factors are the product of ITM and ETM g-factors. Then from the formula in the notes file : Gy = Gyc - B*L*gyic*(Pyerh+Pyirh) - L*(Ai*alpha_yi*Pyarm*gyec + beta*Ai*alpha_e*Pyarm*gyic), we can solve for Ai which is the coupling factor of self-heating to surface defocus.

Summary

Both of these values indicate there is certainly an overestimation of the self-heating impact on surface defocus.

For reference, the current TCS-SIM values for this coupling factor are Ai_y = Ai_x = -36.5 uD/W.   More examination is required into this.

Links to previous alogs:

1. Estimating HOM spacing shift from self-heating alone:  https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=84172