JAC EOM Monday (Elenna, Keita, with remote help from Stephen, Michael, Matt and Gabriele)

Nothing wrong with our previous reflection dip measurements with alumina.

We (MichaelL, StephenA, MattH, Gabriele, Elenna and myself) had a meeting in the morning. 

Looking at the "with the alumina" reflection screen shots, Michael didn't see any serious problem so we decided that the electrode-crystal-face plate capacitance is OK. We won't worry about that, we'll just make sure that there's no visible gap.

Third mounting method ("in-between") was proposed and tested.

Stephen proposed an in-between method where we use washers between the input side plate and the front plate (bottom of three_methods.png cartoon). After the washer contacts the face plate AND the input side plate, screws are gently tightened in a balanced manner like in Appert method.  (In a retrospect this is not that different from Laxen method except the way screws are tightened and that the input side plate contacts with the face plate at two points.) 

We first tried to use a presicion thickness shim washer for 1/4-20 screws but I didn't like that they're too big. We ended up using smaller stamped washers that is 0.039" or 0.99mm thick (according to the caliper). That's not flat but seems OK to me.

This in-between method worked in that it was doable and gave us a reasonable reflection dips.

Mechanical stability test of Appert method and in-between method. The latter is better, we'll use that for the real RTP.

My original concern for the original Appert method (middle of three_methods.png cartoon) was that somehow the screw gets loose during transport or after a large change in the in-chamber temperature and the tuning will be off. Upon hearing this, Stephen proposed a test to loosen one screw and see if the tuning changes. We performed this test for both Stephen method and the in-between method. (Spoiler: yes.) We measured all four dip frequencies right after the alumina piece was mounted but only tracked the frequency change of 118MHz peak.

Loosening one screw changes the frequency, but the frequency change for the in-between method is an order of magnitude smaller (10 to 30kHz) than the original Appert method (300kHz) when the FWHM (or rather the width between the points where reflection is 6dB larger than the bottom of the dip) is about 70kHz or so. This is just one trial but I'm convinced that in-between method (or maybe Laxen method too though we haven't tried) is better, so that's what we'll do for the real crystal.

We only loosened the screws on the output side for both mounting methods. 

	Initial four frequencies	Shaking?	Loosen 1st screw	Loosen 2nd screw
In-between method	9.142, 24.110, 45.972, somewhat smaller than 118.214kHz	changed to 118.214kHz, unclear why. (Something like 10k or 20kHz change, couldn't cause another change by gentle tapping.)	118.214 -> 118.240 (+26kHz)	118.240 -> 118.251 (+11kHz)
Original Appert method	9.14685, 24.107, 46.066, 118.322	118.322 -> 118.592, caused by gentle tapping. (+270kHz)	118.592 -> 118.876 (+284kHz)	118.876 -> noman's land (>1MHz)

Shake and it will shift, we need to measure it again in chamber?

It's good to know that the in-between method can somewhat withstand the loosening of the second screw (because the tighter screws still support the face plate). However, it's disappointing to find that the assembly is susceptible to shaking.

In the in-between method, we couldn't record the initial 118MHz dip because it jumped up by 10kHz or so in front of our eyes when we were moving around the table. Not sure what happened but I assumed that it was some kind of shaking. However, I gently tapped the front and side plates and couldn't cause another shift.

In the original Appert method, since we knew something could happen, I tapped the front and side plates and there was a huge jump. See the difference between initial_118.jpg and taptap_118.jpg.

Even though we'll use in-between mounting method, it's plausible that the frequency shifts during transport or when the EOM lands on the ISI surface. I'm thinking we'll have to measure it in situ after everything is tuned in the lab.

What's to come tomorrow.

We'll install RTP and tune. Before doing that, though, I'll discuss inserting indium foil between the crystal and the front plate with Masayuki. Michael suggested that (and even between the crystal and the electrode, though that would be tricky) today, Masayuki and I talked about the possibility briefly last week, it just sounds like a good thing as a buffer to absorb gaps here and there.

Other things.

In the previous alog (88886) in one of the pictures (gap.jpg), there was a time when it looked as if the circuit board was slightly bowed. We took a picture of the electrode today (electrode_contactpoint.jpg) and it looks as if the electrode is more abraded close to the outside edge of the crystal, so maybe the board bowing is real.

 

 

JAC work today

Jennie W, Sheila D, Rahul K

 

Before we went into chamber today we checked the fringes in the JAC cavity transmission to see if we had the same power in the TM00 modes as Friday (when it was ~ 0.15). From the image you can see that the level on the JAC-TRANS_A PD is now around 0.1, and it looks as though the 01 mode could be near the size of the TM00 mode.

This implies the input alignment (which we recovered on Thursday to 0.22) has been drifting.

In chamber Sheila found that the JAC cavoity was locking on a 01 mode (two vertical lobes).

She tried moving the JM1 mirror and found the base was slightly loose in the mount. Not sure if this is enough to really explain the mis-alignment fully.

She tweaked up the alignment of this mirror and I tweaked up the alignment using PSL PZT periscope mirror until the beam went up to 0.22 on the JAC TRANS A PD.

We checked the power in chamber right before the input coupler to JAC and it is now 93 mW.

The power measured after JAC (right before mirror JM2) is 58 mW.

The power measured on IOT2L after the bottom periscope mirror is 44mW.

After continuing tweaks to the input alignment we got 0.28 on the JAC TRANS A PD 0.28 with input alignment changes.

---

We maximised the power onto the table by moving JM2 and JAC-M3 and looking at the IMC REFL PD.

We have 76mW power after bottom periscope mirror and

 a 0.96 - 1.2 level on MC REFL PD.

Still have 0.28 level on JAC trans out.

We started to notice fringing (see image) on the IMC TRANS camera and on MC2 TRANS QPD NSUM.

I did a quick check of the mode-matching and it looks like our mis-match is now about 11% (for the second highest mode in the scan).

We therefore switched to using these as our metric while we optimised the alignment into the IMC with the same two mirrors JAC_M3 and JM2.

Eventually Sheila and Rahul discovered clipping on the last iris before the beam leaves HAM1 so marked the height with a C clamp and took it out. This was our reference for the original beam into HAM2 before the JAC install was started.

Continued to optimise with these two mirrors.

At the end of the day we placed new iris after output periscope and moved iris on IOT2L in reflection of first table steering mirror to mark the placement of the beam.

---

Since we still are not aligned to our references on the table - ie. the WFS, the iris placed at the HAM1 output before JAC was installed, we will double check the MC mirrors position relative to our most recent in-air lock and the last in vacuum lock.

Compared to the 19th December 00:25 UTC, the position of MC3 M1 DAMP INMON has increased by 6 uradians in pitch and has not changed in yaw.

Compared to the 19th, the position of MC2 M1 DAMP INMON has decreased by 10 uradians in pitch and has decreased by 1 uradian in yaw.

Compared to the 19th, the position of MC1 M1 DAMP INMON has decreased by 3 uradians in pitch and has increased by 3 uradian in yaw.

Cursors show current values in this ndscope plot.

CHETA Progress - second table

S Muusse, M. Todd

---

New QCL unit (0920) has been put in place of original unit (0923) which is malfunctioning (cause unknown). Initial profiling has taken place and L1 focal length is 10% larger than spec.

---

QCL unit failure summary:

All day on 2026-01-21 we were running the laser at 900mA doing beam profiles and alignment work. No malfunctioning was witnessed and the laser unit was operating as expected, similar to the laser unit we had run in December for a week. Before lasing we set the following limits on the LD and TEC, per the datasheet.

1. LD current limit was set to 1.05A
2. LD voltage limit was set to 12.9V
3. TEC operating temperature was set to 20C

On 2026-01-22 we turned the laser on to do some more beam profiling with the same limit settings as yesterday, but setting the LD current to 1A (forward voltage was around 12.2V) as was done when we originally profiled this laser in September. We were in the middle of setting up for a new beam profiling measurement (alignment showed the beam was fine, as usual) and we blocked the beam with a high power beam dump at the laser head while installing the profiler. Upon removing the beam dump, we noticed no power was coming out of the laser, and then noticed the forward voltage had dropped to around 800mV. We noticed no sounds or smells or any other signs that something had stopped, only sudden lack of light coming from the unit. All other settings were fine, meaning the controller had not faulted and was still outputing 1A LD current and the TEC was maintaining 20C.

We ran the following checks to see if we could remedy the problem, without success.

1. Checked the cable connection to the laser unit (pins on the laser unit looked fine)
2. Checked the Laser Controller cable connections (pins in the DSUB connectors looked fine)
3. We tried a completely new laser controller box and new cable. The settings were similarly set and the same behavior was seen with the forward voltage response to the LD current setpoint.
4. We tried changing the TEC setpoint to be 25C, and the same behavior was seen with the forward voltage response to the LD current setpoint, and failing to lase as usual.
5. We used the same cable and laser controller on the previous QCL unit, and it operated as expected --- lasing fine as usua

---

QCL 0920 profiling summary:

Replaced broken unit with 0920 and confirms it lases as spec'd. We built telescope as modelled but beam profile was 75% of expected beam width at L2. We subsequently profiled the laser output and confirmed QCL output q measured previously by Matt was still correct. We became suspicious of the true focal length of L1. Then we profiled multiple places after L1 and fit a q parameter using a non-linear fit. A plot of this fit is attached. Using these 2 q parameters the focal length of L1 was estimated to be 220mm instead of 200mm as spec. We think this is mostly because L1 focal length stated by manufactorer is for 588nm where the refractive index is almost 3% larger than at 4.6um. Focal length in the model was modified to reflect our estimated f1 which predicted a beam size closer that measured earlier. 
Side note: the scanning slit beam profiler reflects significant amount of 4.6um light which is observable on a thermal beam card. 

Started work on WP 12998 (installing new VM hosts)

Jonathan, Dave, Erik,

We started on WP 12998.  After doing WP 12997 we had freed up the space we needed to install the new VM hosts.

What we have done so far is to move the computers and the associated switch from the test stand and rack mount them in rack 12 in the MSR.  Jonathan has started the reconfiguration of the switch.

Todo tomorrow:

• change the ipmi address of the computers to the production settings
• run the fibers from the vm switch to the core
• connect all the firbers/copper to the computers

The new computers will be pve-node[0,1,2] and the switch is sw-msr-pve0.

OPS Day Shift Summary

TITLE: 01/27 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:

A very productive day with the following activities:

1. EOM - Work continued on the EOM in the Optics Lab.

2. HAM1 - MC Trans has been recovered! Meaning that light has been aligned from the input through the JAC to the Mode Cleaner!

3. HAM7 - OPO work is continuing.

4. VAC - Relay tube work ongoing.

LOG:                                                                                                                                                                                                                                                                  

Start Time	System	Name	Location	Lazer_Haz	Task	Time End
22:49	SAF	LVEA IS LASER HAZARD	LVEA	YES	LVEA IS LASER HAZARD \u0d26\u0d4d\u0d26\u0d3f(\u239a_\u239a)	16:49
15:57	FAC	Kim, Nellie	LVEA	Y	Technical Cleaning'	16:19
16:49	OPS	Corey	Optics Lab	N	Part Search	17:03
16:58	FAC	Kim, Nellie	LVEA	Y	Technical Cleaning	17:49
17:19	FAC	Randy	LVEA	Y	BSC2 Platofrm Work	18:44
17:23	COC	Keita	Optics Lab	N	EOM Work	20:22
17:35	VAC	Travis, Jordan	LVEA	Y	Relay Tube Work	19:30
17:46	SQZ	Jennie	LVEA	Y	Opening PSL Light Pipe	17:48
18:12	SUS	Betsy	LVEA	Y	HAM7 OPO	22:29
18:12	SUS	Rahul	LVEA	Y	HAM7 OPO	21:51
18:23	COC	Jennie	LVEA	Y	HAM1	21:51
18:49	FAC	Randy	LVEA	Y	HAM7 Help	19:31
18:59	JAC	Elenna	Opt Lab	N	EOM work	19:59
19:12	OPS	Corey	Optics Lab	N	Parts	19:23
19:27	ISC	Matt	Vac-Prep/JOAT Lab	N	Checking on laser	21:51
19:42	SUS	Kar Meng	LVEA	Y	HAM7	18:42
21:35	PCAL	Tony	PCAL Lab	N	Meas. prep	23:34
21:52	COC	Keita, Elenna	Optics Lab	N	EOM	23:40
22:18	ISC	Matt, Sophie	Vac-Prep, JOAT	N	Checking on laser (CHETA)	22:34
22:19	SQZ	Sheila	LVEA	Y	HAM7	18:19
22:20	VAC	Gerardo, Jordan	MY	N	Part Grab	23:53
22:22	SUS	Rahul	LVEA	Y	HAM1/7	22:29
22:40	EE	Fil	LVEA	Y	HAM6 Rack Work	01:40
23:09	SUS	Rahul, Sheila, Jennie	LVEA	Y	HAM1 Work	02:09
23:10	ISC	Matt, Sophie	Vac-Prep, JOAT	N	CHETA	01:10
23:27	SAF	Jenne D	Input arm		Look at Ham2 Ham3 layoutg	23:53
23:47	SUS	Betsy	LVEA	N	HAM1	01:47

HEPI Pump Trends - Monthly FAMIS 38863

Closes FAMIS 38863. Last checked in alog 88726

Trends similar to post-outage plots from last check.

H1 ISI CPS Sensor Noise Spectra Check - Weekly FAMIS 39335

Closes FAMIS 39335, last checked in alog 88829

Comparable to last check. Elevated sensors are the open chambers.

O4 scattering noise would likely be mitigated by: (1) ITM cage baffles, (2) the BBS, (3) HAM4 table baffles, and (4) SR tube MC baffle improvement

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

IMC REFL DC With HAM1 In Air During JAC Install/Alignment Recovery; ISIs ISOLATED (Aligned) vs DAMPED (Floating) Positions and IMC SUS Alignments

J. Kissel, J. Driggers, J. Wright

While we recover the alignment into to the IMC using the amount of DC light on the IMC REFL PD (on IOT2L) (and eventually MC2 TRANS on HAM3) -- e.g. LHO:88869 -- there's been some confusion about the state of the HAM2 and HAM3 ISIs alignment, and whether that matters. 

Here, I compare 3 times:

    Date Time                       2025-12-19 00:15 UTC                     2026-01-24 01:28 UTC                      2026-01-26 17:26

    Description                     HAM1 in AIR Pre-JAC reference           Post-JAC install, Pre EOM Install        Post-JAC Install, Pre-EOM Install

    IMC State                       LOCKED                                  OFFLINE                                  OFFLINE
    IMC REFL Power [mW]               0.65                                  0.22                                     0.18
    IMC MC2 TRANS Power [mW]        307.0                                   0.4 (confidently dark noise)             0.4 (dark noise)

    MC1 P/Y                         +852.04 / -2229.74                      +874.30 / -2233.84                       +874.30 / -2233.84
    MC2 P/Y                         +582.28 /  -627.99                      +568.40 /  -628.20                       +568.40 /  -628.20
    MC3 P/Y                           +9.23 / -2433.51                        -1.07 / -2430.71                         -1.07 / -2430.71

    HPI HAM2/HAM3 Physical State    locked/locked                           locked/locked                            locked/locked
    HPI HAM2/HAM3 ISO Gain          disabled/enabled(?)                     disabled/enabled                         disabled/disabled
    ISI HAM2/HAM3 ISO State         ISOLATED/ISOLATED                       DAMPED/DAMPED                            ISOLATED/ISOLATED
    ISI Residuals (w.r.t. "they've been that way forever alignment position")
                                       HAM2       HAM3                         HAM2       HAM3                          HAM2       HAM3 
        X [um]                         0.00 /     0.00                         +8.9 /    -56.4                          0.00 /     0.00
        Y [um]                         0.00 /     0.00                         +4.8 /    +36.6                          0.00 /     0.00
        Z [um]                         0.00 /     0.00                         -6.6 /     -6.7                          0.00 /     0.00
        RX (Roll) [urad]               0.00 /     0.00                         +0.4 /     +1.2                          0.00 /     0.00
        RY (Pitch)[urad]               0.00 /     0.00                         +1.4 /      0.0                          0.00 /     0.00
        RZ (Yaw)  [urad]               0.00 /     0.00                         +5.2 /    -28.6                          0.00 /     0.00

In summary -- having the ISI tables DAMPED (Floating) vs. ISOLATED with HEPI physically locked does make a tens-of-micro level shift in alignment of the tables. 
This is evident by the amount the IMC SUS had to move (from 2025-12-19 to 2026-01-24) in order to start recovering even 0.2 [mW] on the IMC REFL DC PD.
On the scale 0.7 [mW], and without changing the SUS positions (from 2026-01-24 to 2026-01-26) it (HAM2 only, of course) makes the difference between 0.22 [mW] and 0.18 [mW] or (0.22-0.18)/0.22 = 20%-ish percent difference.
When checking / chasing in-air alignment of the beam projected into HAM2 with HAM1 optics, we should make sure that the ISIs are ISOLATED, if possible.

To bring the ISIs to ISOLATED, with HEPI Locked:
   - Set the HPI-HAM{2,3}_ISO_GAIN to 0.0 (disabling the HPI controls), and 
   - Requesting SEI_HAM{2,3} Guardians to ISOLATED (which brings the ISI to HIGH_ISOLATED)

PSL 10-Day Trends

FAMIS 31122

I touched up RefCav alignment this morning (alog88891) and turned on the ISS. PMC alignment may be drifting slightly, but I left that alone so as not to significantly change the output power and potentially disturb the JAC installation team. Not much else to report this week.

Mon CP1 Fill

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

 

PSL FSS RefCav Remote Alignment Tweak

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).

OPS Day Shift Start

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

SPI Pathfinder, Comprehensive Phase Noise measurements

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 (ignore the title on this plot) 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 CP1 Fill

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

 

EY BT Ionpump gauge also caused VACSTAT alarm at 10:34

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.

JAC EOM update Friday Jan/23 (MattT, Mitch, Keita)

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.