Mon Jan 26 10:08:13 2026 INFO: Fill completed in 8min 9secs

This morning, I finally got around to realigning the RefCav after having watched its transmitted power drop significantly over the past several weeks, which doesn't surprise me with the changing weather. Using the picomotors upstream of the RefCav, and with the ISS enabled, I was able to greatly improve the signal on the TPD from 250mV to 500mV. This isn't quite as high as we've seen it after a good on-table alignment, so perhaps sometime in the future we will go into the enclosure and touch up the alignment there.

Attaching a picture of the quad video display post-alignment for posterity; before I started the RefCav reflected spot looked like two distinct lobes vertically next to each other, showing a very obvious misalignment in pitch (which I found to be the area of most improvement when using the picos).

TITLE: 01/26 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 4mph Gusts, 3mph 3min avg
    Primary useism: 0.03 μm/s
    Secondary useism: 0.25 μm/s 
QUICK SUMMARY:

IFO is in IDLE for planned MAINTENANCE

This is subject to change following 8:30 Coordination meeting but planned activities for the day are as follows:

• HAM 1 - Install EOM
• HAM 1 - Align viewport simulator to Y-door
• Replace JM1/JM3 fixed mirrors with HTTS
• Roll up IOT1 -Y

Summary: Scattering studies before the end of O4 suggested that the non-linear vibration coupling that dominates DARM at 20 Hz and contributes significantly up to about 50 Hz, was produced by modulated retro-reflections of the annular beams coming from the bevels of the ITMs and the annular beams from the BS barrel and cage (87758).  End-of-run studies, reported here, support these conclusions, and a model estimating scattering noise from vibration time series suggests that reflection from the SR tube MC baffle near HAM4 is also a likely ambient noise source in the unusually high 80-200 Hz region of DARM. The annular beam noise from chamber walls would be mitigated by the already planned ITM cage baffles and the BBS. It is also likely that the HAM4 and SR MC baffle noise would be mitigated by the BBS. The safest route would be to go ahead and install the HAM4 table baffles and treat the HAM4 MC baffle, but we could also wait and see if their noise is mitigated by the BBS.

Noise at 20-50 Hz injection frequencies, likely from 20 and 45 degree annular beams

As noted at the end of alog 87758, the noise in DARM was most consistent with the motions of permanent accelerometers on ITMX, ITMY and the BS, consistent with what would be expected if the annular beams (83050) from optics in these chambers cause scattering noise. We have, since then, mounted temporary accelerometers around these chambers and elsewhere to further test this hypothesis, particularly placing accelerometers on the vacuum envelope at locations just outside of where the annular beams hit the inside of the enclosure.

We used two of the three vacuum enclosure techniques mentioned in 87758, the beating shaker technique and a variant of the consistency test for sweeps from shakers at different locations. However, we were not able to use the third technique, the hand-held shaker test in the region close to the vertex because of magnetic coupling, likely to magnets on the BS, even though the coil is much smaller than those in our other magnetic shakers.

Consistency technique

The accelerometers that were most consistent for 3 sets of 3-shaker injections were temporary accelerometers mounted near where the ITM annular beams hit the bellows of the spool pieces between the ITMs and BSC2, one for each ITM, and the permanent accelerometers “BSC3_Y” and “MCtube”. The BSC3-Y accelerometer is near where the annular beam from the BS likely shines (See Figure 1), but the MC tube accelerometer is probably coincidental because when a shaker was moved to the MC tube, the accelerometer there was no longer consistent with DARM.

Beating shaker technique

The accelerometers mounted just outside where the ITM annular beams hit were also the most consistent with DARM for the beating shaker technique. Figure 1 shows results of one of the most convincing beating shaker tests. A piezo shaker was mounted near where the ITMX annular bevel beam hits the bellows of the BSC2-BSC3 spool-piece (see photograph here ). A second shaker was mounted on the old H2 BSC7. The shakers were set to 31.005 Hz and 31 Hz respectively. The amplitudes of the two shakers were adjusted so that each individually produced the same amplitude of peak in DARM, before they were both turned on. Figure 2 shows that the timing of the beat envelope of the accelerometer on the bellows where the annular beam hits, matches the beat envelope timing in DARM, while timing for 14 other accelerometers that I examined (7 are shown) did not match as well. Also, the modulation depths of the beat in the accelerometer signals are greatest in this region of the enclosure, indicating that the two shaker peaks have similar amplitudes in the accelerometers near this location, like the two peaks in DARM (by adjustment). 

Potential noise at 80-200 Hz from MC baffle in SRtube near HAM4

Early in O4 we found that the MC baffles in the input arm were causing noise in DARM (74175). We fixed this by angling the baffles further (76969). We also found that the MC baffles in the output arm could make scattering noise but that this was at a lower level than the baffles in the input arm (74175).

During recent end-of-run studies, I shook the output arm to asses the current status of scattering noise from these output arm baffles. The injections made noise in DARM but It was difficult to determine whether injection-free ambient vibration levels would affect DARM, because the noise increased with frequency rather than forming a flat shelf, I think due to the optical transfer function of scattering noise from the SR cavity back into the interferometer (LIGO-T060073).  So I included a "BSSR" optical transfer function in my new model which combines accelerometer and seismometer time series to estimate the phase noise and radiation pressure noise from a source at any point in time (scattering noise, like the underlying vibration, often varies greatly in time). I was able to match the time evolution of the scattering noise in DARM during the vibration sweep by filtering external accelerometer data using resonant gains to simulate the resonances of the internal baffles. I used two resonances at 13.2 and 14.2, with Qs in the hundreds to simulate the DARM response - the results are shown in Figure 3.

However, the Qs that were needed seemed too high because Corey and I had tried to damp these (39156), and the only evidence that the source was the baffles was the low resonant frequency, consistent with the measured frequency of input arm MC baffles.  But the low frequency resonance might also be a resonance of the vacuum enclosure itself, so I decided to get the Qs and resonant frequencies from the baffles directly, using a laser vibrometer. I found that The MC (eye) baffle by HAM5 has a resonance of 12.1 Hz, the MC Baffle by HAM4, at 13.3 Hz, and the SR tube has a resonance at 14 Hz. Thus, based on the 13.2 and 14.2 Hz frequencies that made the original model reproduce DARM noise, the likely source of the scattering noise is the eye baffle by HAM4.  Using the measured Qs, resonances, and a simplified mechanical transfer function from the permanent accelerometer that was present when I did the original sweep to an accelerometer that I mounted last week right outside the baffle, I got the results shown in Figure 4 (the permanent accelerometer I used for Figure 3 underestimated tube motion at the location of the baffle which was why I had to use such high Qs - the measured Qs were 5 and 10, more consistent with our damping). The predicted level of noise in DARM for ambient vibration levels in Figure 4 is slightly lower than the more naive model of Figure 3, getting as close as a factor of 3 below the current noise floor in the 80-200 Hz region.

One possibility is that the eye baffle is reflecting light in the 45 degree annular beam coming from the BS. Based on the evidence for this in Figure 5, and the increasing evidence that the annular beams are bright enough to be problematic, I would guess that there is about an 80% likelihood that this is the source of the SR tube noise and that the Bigger Beam Splitter would mitigate this noise source. This was also my assessment for the noise produced by shaking the HAM4 table (87758), and I suggested that we could wait until after the installation of the BBS, and then mount table baffles if the noise had not been mitigated. I think this would also be a reasonable path for the eye baffle, waiting to see if the noise goes away with the BBS, and improving the baffle if it does not. Of course the safest path would be to mitigate the MC baffle(s) and install the HAM4 table baffles anyway. If we do mitigate the MC baffle(s), I would want to remove or treat the central portion of the baffle(s), as well as, or instead of, increasing the angle of the baffle(s) like we did in the input arm. This is because the reflection site, as evident in Figure 5, is likely to be in the central region of the baffle.

-Robert, helped especially by Sam and Joan-Rene

J. Freed,

Continuing From 88293, I took phase noise measurements of waveform generators relevant to SPI pathfinder with two different methods. This first method is the standard method that LIGO uses which follows the BluePhase 1000 manual. I used this method to highlight the issues this method has in the context of SPI. The second method is a slight modification to the standard method which shows a lower noise floor in the area of interest for SPI.

First Method:  BluePhase1000_Setup.png (from LIGO-T2400324) Shows a simplified Phase noise measurements set up of what the BluePhase 1000 manual provides. A simple way to take phase noise measurements is to mix the signal from the Device under Test (DUT) with a reference device (REF) outputting the same frequency but at quadrature. Ideally, this mix outputs only the differential noise between the two devices. If the reference device has much better performance, then the mix ideally outputs only the DUT noise. In this method, a feedback loop is used to keep the REF at quadrature with the DUT. For the REF device, I used the 80MHz OCXO housed in LIGO-D1100663. 

OCXOComparisonTOCXO.png Shows the results from the first method, I used 3 different devices as the DUT; a 80MHz OCXO here at LIGO LIGO-S1000565, a SRS SG382, and a Keysight 33600A. The main thing of note is that OCXO is expected to have a much lower noise floor than any other device; however, below ~60Hz the noise is not limited by the different DUTs. Since the REF is another OCXO, I believe the feedback loop that keeps the REF device in quadrature is limiting measurements below 60Hz.  Since SPI is interested in phase measurements well below 60 Hz this first method will not work for taking phase noise measurements for SPI. Especially since SPI has both an 80Mhz and an 80MHz -4096Hz signal and LIGO  does not have a 80MHz -4096Hz OCXO to use as a ref. 

Second Method: PhaseNoiseSetUp.png shows the modified set up; where the REF device is the SRS SG382. This method puts the REF device at quadrature by setting it manually and holding it there through the 10MHz timing port created by dividing by 8 the 80MHz OCXO signal. Since both the REF and DUT are referenced to the same OCXO (or the DUT is the OCXO itself), ideally both devices will be held at quadrature bypassing the need for a feedback loop. In practice, I did notice a small amount of drift from quadrature over time. 

OCXOComparisonSRS.png Shows the results from this method. This graph shows both the OCXO and the Double Mixer have phase noise performances well below the noise performance of a typical waveform generator (Keysight) below 100Hz. Though combined with the last alog, still very much better than SPI requirments.

Difference: OCXOComparisonSRSOC.png shows the mix of an 80MHz OCXO and the SRS using the two different methods to hold one at quadrature with the other. With the modified method, we are not limited as much below 60Hz, except those peaks at ~0.16Hz, ~0.45Hz, etc.. which I believe are caused by the divide-by-8, not the SRS; as the SRS measurement using the first method did not have these peaks. 

Extra:

OCXOComparisonFull.png Shows all measurements on one graph.

OCXOComparisonKey.png Shows that Keysight had strange harmonics at multiples of 5kHz but disappeared 12 hours later. 

Sun Jan 25 10:10:33 2026 INFO: Fill completed in 10min 29secs

EY followed EX's lead and also came back to life this morning at 10:34 causing our second VACSTAT alarm for today. EY had been flatlined since yesterday 06:23, close to EX's time.

I restarted VACSTAT at 10:45 to clear the alarm.

10-32x0.375" SHCS that was blocking the access to one 1/4-20 screw was replaced with a low profile 10-32 SHCS.

"Issue 2" in alog 88862 was solved.

See picture, Mitch found a 10-32x0.5" SHCS with a low profile head. 0.5" seemed to be OK in that it's not too long, but we used two washers to make sure that the scrwe doesn't bottom out.

At 10:11 the EX BT-Ionpump gauge came back to life, causing a VACSTAT ALARM. This gauge has been flat-lined since yesterday, 07:09 Fri23Jan2026.

Could be because today is a sunny day after a long period of cloudy weather (the EX_BT system is solar powered)?

At 10:18 I restarted VACSTAT to clear the alarm.

Sat Jan 24 10:10:15 2026 INFO: Fill completed in 10min 11secs

Jennie W, Sophie M, Sheila D,

First we checked that the MC mirrors top mass OSEMS matched their position at 00:00 UTC on December 19th. This was the last time when the IMC was locked in air after HEPI was locked on HAM2 before JAC install.

MC1 -678 mrad P, -1365 mrad Y.

Sheila and Sophie went to align in chamber using JAC_M3  (mirror right before JAC HAM1 output periscope) and JM2 (mirror right after JAC).

I looked with the beam card between the upper and lower periscope mirrors at the beam spot.

Sheila and Sophie walked the beam in pitch and the beam started to clip badly. They undid this and Sheila came to check the beam on the table and realised that it looked much dimmer than expected compared to the beam leaving the chamber.

She suggested it might be a ghost beam coming onto the table.

After lunch we checked this with the power metre and we had 40mW into HAM2 but 0.46 mW onto the bottom periscope mirror in IOT2L.

Sophie managed to unclip this mainly with pitch (in the JM2 basis) beam walking, with very slow changes on both mirrors in turn and checking the REFL output and the power onto the table we eventually got ~ 20mW, measured after the bottom periscope mirror.

We eventually made enough change that the beam was getting to both MC REFL WFS but not hitting the diodes.

Sophie did more beam walking in yaw on the two mirrors while looking at MC REFL PD and maximising the power on this. The power metre at the end of the day showed 23 mW just after the lower IOT2L periscope mirror but we were still not hitting the WFS PDs. The beam is low and right on MC REFL WFS B.

The workstation CDS conda environments will be updated by Saturday Jan 24.  This is a major update that affects many conda packages.  Many packages have been updated and some have been dropped.

Python is updated from python 3.10 to python 3.11.  Yes, 3.11 is old already, but the CDS environment tracks the IGWN environment, and important packages have not been push beyond python 3.11.

A complete list of changes in the new environment can be found here:

https://git.ligo.org/cds/packaging/cds-conda-distribution/-/wikis/Environments#version-2026-01-06-01

TITLE: 01/24 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY: Another productive day to wrap up the week.

• HAM7 alignment is essentially finished and irises are being removed from the table this afternoon
• The viewport assembly was removed from HAM5 in preparation for the relay tube to HAM7 to be reattached, which will happen next week in laser safe conditions (see alog88876)
• Alignment in HAM1 continued for the JAC, including downstream pointing into HAM2.
• Work progressed on the to-be-installed JAC EOM in the optics lab
• Jeff took some transfer functions on the OPO suspension and claims they're "good enough to say the suspension looks healthy" after finding issues with open-light values (see alog88872)

LOG:

In prep for HAM7 closeout, the temporary viewport assembly was removed from the HAM5 relay tube port. RV-1 was closed, and the volume vented with viewport covers still installed, with dry N2. I monitored the corner pressure (PT-120B) during venting, to make sure there were no leaks through the gate valve. No change in pressure, so I continued with viewport removal.

Viewport was removed first, then the pump-out tee. The mitered spool piece and bellows assembly was installed on HAM5 side. Lines were marked across the relay tube assembly prior to removal, so the install orientation remained the same. 

The ported spool piece will be installed next week during Laser Safe conditions. Bellows flanges were covered with foil for protection.

Jennie W, Jenne D, Masayuki N

Today Jenne and I went into HAM1 and onto IOT2L.

Our first priority was to check the input alignment to the JAC after alignment efforts yesterday to check we were not locking to a HOM mode. We locked the JAC with a power of 0.1 on the TRANS_A_LF_OUT channel.

I checked after lens JAC_L3 which is right before the steering mirror into the HAM1 output periscope. Here the beam looked like a 10 mode (two lobes in the horizontal axis). Further upstream (just after JAC cavity this was not obvious due to the beam size.

We used the steering mirror between the input periscope and JAC + the PSL periscope PZT mirror to improve the alignment. To do this we changed yaw in the closer mirror and pitch in the PSL PZT mirror as the input periscope switches the P and Y around.

We recovered a value of 0.22 on TRANS_A_LF_OUT which matches with the values we got on friday the last time we had a good TM00 lock on the JAC cavity.

After this Jenne went to the table to look at the beam we found yesterday which is at the edge of the MC REFL periscope mirrors in yaw and clips on the BS1 optic.

I started changing the tilt of the beam through HAM2 by changing the pitch of the mirror right before the HAM1 output periscope. This did not really change the beam position so we moved to a further away mirror (JM2) to translate the beam.

During this process we also became unable to lock the JAC using the guardian. More details at the end.

After some iteration we were able to see a beam on the MC REFL PD but have not been able to walk the beam to see any signals on the MC REFL WFS orflashing from the IMC on the MC TRANS PD.

After a break we went to the control room and did some checking of the MC sus alignments. We found problems with the alignment of MC3 - Dave and Ollie debugged this.

Jenne then did some walking of the MC mirrors and by moving MC1 she could get a larger signal on MC REFL. We might be able to use this tomorrow by moving MC1 to this 'wrong' ( ie. not consistent with the nominal IMC alignment before JAC was installed) place and walking MC1 back while changing the in-vac fixed mirrors in HAM1 to reover the beam on MC REFL PD.

During the day an electronics chassis was swapped that does the whitening for the TRANS PD A. The signal stopped getting to the diode so Daniel gave us the go-ahead to bypass this - this might need to be fixed properly at some point, it is level 10 on the rack closest to HAM1, next to the PSL enclosure. I took put IN3 and OUT 3 cables and connected them with a TNC connector.

This afternoon and evening we tried to trouble-shoot the JAC locking.

There was also an incorrect gain that got reset by the model restart for h1lsc earlier today but fixing this (JAC_DITHER_PD_IN gain was set to 200 and should be 4) did not allow us to lock.

After changing the servo gain in the dither lock Jenne noticed that this had no effect on the lock level/noise on the TRANS PD.

After checking with Masayuki the problem seems to be that the fast channel to drive the PZT is not connected somehow at the racks but the Beckhoff controller can be used to drive the PZT - will consult with Daniel/Marc tomorrow.

We have intalled the POP periscope stiffener.

Some dog clamps in the REFL path as well as the cable bracket for PM1 were relocated to accomodate. 1st and 2nd picture are "before" photo. 3rd one is after PM1 cable bracket relocation but before installing the stiffener.  There are also three "after" photos showing how things look on the table.

POP beam clearance:

I took the picture of the bottom periscope mirror through dichroic (HR for IR, transmission for green) to see the beam clearance. In the first such photo (POP_beam_clearance.jpg), the camera is close to the center of the dichroic and the short stiffener beam is close to the edge of the optic but not occulting the mirror, so we're OK. Just to make sure that we're absolutely safe, I moved the camera closer to the -Y edge (right on the picture) of the dichroic (POP_beam_clearance_extreme.jpg) and it still looks OK.

If it's hard to understand what was done, look at the annotated photo (the last attachment After_stiffener_installed_annotated.jpg), the cellphone camera was inserted to "Camera" position.

REFL beam path:

I confirmed that the long stiffener beam doesn't interfere with the motion of the REFL beam diverter. Also, when the REFL beam diverter is open, I looked into the last steering mirror for the REFL air path from the viewport position to make sure that the short stiffener beam won't occult the REFL path. 

Some hiccups:

We used D2500433 -11 variant S/N 4 and -1 variant S/N1 even though page 11 of T2500339 suggests it should be -10 and -2 variant, respectively.　We didn't have -10 variant, and -2 variant was absolutely too short.

B&K

We performed B&K hammer measurements before/after the stiffener installation for POP periscope. Before, there was a 70Hz-ish peak. After, it was pushed higher up in frequency. The transducer was attached to the ISI table and Jim hammered the top of the periscope.

Likewise we did B&K test for the input periscope of the JAC even though it was not absolutely necessary.

We haven't done B&K for the JAC output periscope because it's not even fully clamped down (we will move it).

Jim will post the data.