Summary

We improved the IMC mode matching by repositioning JM2 and JM3 based on the calculation from yesterday. The mode mismatch was reduced from about 10% to ~2% after iterative alignment and mirror position optimization. Further improvement is expected with additional calculations and tuning, which will be continued tomorrow.

Details

We worked on improving the IMC mode matching following the calculation from yesterday. As a first step, JM2 was moved by approximately 3 inches; the new position is shown in the attached photos. The alignment to the IMC was performed using the newly placed iris in front of JAC_L2 and the iris after the output periscope, as described in the previous alog. By centering these two irises, the alignment could be brought to the level where IMC flashes were visible. From that point, adjusting JM3 allowed us to easily reach an alignment where the TEM10 content was at the ~10% level.

After achieving a reasonable alignment using a scratched mirror, we replaced it with a newly cleaned narrow-angle mirror for JM2. The scratched mirror was moved to JACR_M1. As a note, the scratch was oriented on the +y side; by keeping the beam closer to the −y side, the impact of the scratch was minimized.

With this configuration, the mode mismatch improved from about 10% to approximately 4%. Since the calculation suggested that further improvement should be possible, we continued tuning by adjusting the JM3 position. Based on the previous calculation indicating an offset in JM3, we first moved JM3 by about 1/2 inch in the −x direction (increasing the L1–L2 distance). This resulted in a degradation of the mode mismatch to about 6%. We then moved JM3 in the +x direction by a total of 1.5 inches (i.e., 1 inch further from the original position), effectively shortening the L1–L2 distance. With this adjustment, the mode mismatch recovered to approximately 2%.

We stopped the work at this point and plan to perform updated calculations tomorrow to guide the next iteration of tuning.

TITLE: 02/03 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:
LVEA was Bifircated via a Laser Hazard areas around HAM 1& 2, while the rest of the LVEA is LASER SAFE unless at height. See M2600004 for details.

PM1 was mysteriously dancing & Saturating too much for Rahul's transfer function measurement all day long. While he was troubleshooting. Update!!! Rahul dragged the EE guys out and found a dead Coil Driver! Mystery solved!

JAC work continued all day starting with mode matching in HAM1, and starting a JM2 swap. JAC table now has all the mounts and Cables but no optics yet. 

HAM7 & ITMY ISI Watchdogs tripped at 23:33 UTC due to mysterious high frequency ground noise that was louder at HAM7 than ITMY.  Jim & Betsy went to go look for fallen wrenches or other watchdog tripping phenomena..... No explanation was ever found. 

OPS info: 
New conda ENV doesn't run watchdog untripping scripts unless you run Conda Kill first.  Tagging CDS. 

LOG:

Dave, Oli, Marc, Fil, Rahul

This morning I switched PM1 (Tip Tilt suspension) in HAM1 chamber from safe state to damped state and immediately the DAC output was saturating. I suspected purge air (which Travis turned it down twice during the day) and later Masayuki also covered PM1 with foil. However, nothing stopped the suspension from saturating.

Then Oli, Dave and I did a model restart and later I power cycled the Satamps for PM1 in the LVEA - nothing helped.

Next, Marc, Fil and I went to the LVEA (checked the satsamp, which was fine) and CER and found the Coil Drivers to be faulty.

New Coil driver - E2400048 s/n 22001180

Old Coil Driver - E2100430 s/n S1106046

SUS PM1 is now not saturating. I will perform the heath checks later on.

Just noting that this kind of thing can happen when platforms are in different states. Something caused large-ish high frequency ground motion in a short burst this afternoon and tripped HAM7 and ITMY, because those chambers were damped, but not any of the other chambers because they had high gain isolation loops running, or were already tripped/locked. What ever it happened was louder at HAM7, than the ITMs, as shown in the top left of the attached plot. Because the motion was high frequency, where the isolation loops had enough gain to keep the ISI seismometers from saturating, only HAM7 and ITMY tripped because their isolation loops were off, and damping only engaged. And the event was small enough to not saturate the actuators.

Oli, Rahul, Tony, Marc, Fil, Daniel, Dave.

At 15:41 we restarted the h1susham1 model as part of the PM1 noise investigation. This did not change anything.

Later (16:40) Marc and Fil found that the problem was a dead power rail in the PM1 coil driver.

Used 1W into JAC.

9 (26.8dBm into EOM), 45 (27dBm) and 118MHz (10.76dBm) -> Used a single bounce beam from ITMX and scanned OMC. Successful for 9 and 45, nothing visible for 118. Detailed will be posted later.

24MHz (IMC, 14.2dBm) -> Scanned IMC length and tried to find something in IMC transmission. Nothing visible.

43MHz (JAC, 12.2dBm) -> Scanned JAC, saw nothing in JAC transmission. Boosted RF  power with an amp to 29.67dBm -> m=0.092. Without the amp modulation index would be 0.012.

Jennie W

This morning I re-centred the beam on MC TRANS in-air camera on IOT2. This was using the IO_MCT_M5 mirror, see layout here.

I did this while the JAC was locked and the IMC was flashing through modes.

I only had to move the steering mirror in yaw to centre the mode flashes on the camera.

As noted on Friday, RLF QPD A segment 3 railed Nov 29th, and has been railed since then.  

Filiberto, Kar Meng, Marc and I went to the rack and swapped the two cables for WFS1 + WFS2 on D2000552.  The saturaed segment moved with the cable which could indicate the problem is the in vacuum QPD.  

The 105kHz segment went quiet at the same time as the problem on the DC segment.  This happened on a Saturday, before the chamber was vented.  It had been two days of not locking the squeezer or the IFO before this happened.  

Edited to add:  This is the QPD used for filter cavity length control.  We did lock the filter cavity after the segment broke, December 4th.  

The LVEA is now in a LASER Safe Bifricated configuration, which means that HAM1 is still in LASER HAZARD along with any work done at height.  There are barricades up designating the Bifricated area.

WP: https://services2.ligo-la.caltech.edu/LHO/workpermits/view.php?permit_id=13010
SOP: https://dcc.ligo.org/LIGO-M2600004

The rest of the LVEA is Laser Safe.  So if you are heading into the LVEA, have your laser goggles with you so if you are forced to walk over near HAM1 you'll have your goggle with you. 

Mon Feb 02 10:11:57 2026 INFO: Fill completed in 11min 53secs

PSL Status Report - Weekly Famis 39749

Laser Status:
    NPRO output power is 1.845W
    AMP1 output power is 70.43W
    AMP2 output power is 138.7W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 4 days, 15 hr 14 minutes
    Reflected power = 27.01W
    Transmitted power = 103.8W
    PowerSum = 130.8W

FSS:
    It has been locked for 2 days 15 hr and 50 min
    TPD[V] = 0.4976V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 0 days 0 hours and 0 minutes ago

Possible Issues:
    PMC reflected power is high

TITLE: 02/02 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: 8mph Gusts, 5mph 3min avg
    Primary useism: 0.05 μm/s
    Secondary useism: 0.53 μm/s 
QUICK SUMMARY:
Dust alarms for the VAC Prep lab were going off when I came into the control room. Likely due to the elevated winds we had yesterday.
Untripped ITMY ISI  Stage  2 WD. 

More HAM1 & 7 work is expected today Doors may start going on later this week. 
LVEA is bifurcated with LASER hazard work being done near HAM1. Please bring your LASER Saftey Goggles with you into the LVEA.






 

Summary

Based on the post-EOM IMC scan results showing significant mode mismatch, we performed a detailed mode-matching analysis using the as-built HAM1 layout. Optics positions were identified from chamber photos, beam traces were reconstructed, and the expected IMC mode-matching and higher-order mode fractions were calculated. The analysis shows that the dominant source of the mode-mismatch degradation is a longitudinal shift of JM2 introduced by the EOM installation, and that moving JM2 can effectively recover good mode matching.

Procedure

• The positions of the HAM1 optics were identified from chamber photos.
  • The identified optics locations are marked with purple circles in the attached layout figure.
  • Since the JM2 position differs before and after the EOM installation, two circles are shown for JM2 (pre- and post-EOM positions).

• Using these as-built positions, we reconstructed the beam trace and calculated the mode matching into the IMC and the expected 2nd-order mode fraction.

  • This prediction is shown in the first plot.

  • The lensing effect of the EOM was included using the test results from the actually installed crystal (see p12 of slides).

• The measured 2nd-order mode fractions obtained from the IMC scan (reported in the previous post) are overlaid on the same plot for direct comparison.

Notes

• From the reconstructed layout, JM2 is shifted by approximately 2 inches between the pre- and post-EOM configurations.
  • Due to the reflection geometry, this corresponds to roughly 4 inches of effective beam path length change.
  • This shift is identified as the primary cause of the observed degradation in mode matching after the EOM installation.
  • The calculated 2nd-order mode fraction agrees well with the independently measured values from the IMC scan, validating the beam-trace model.
• The model indicates that shortening the total path length by approximately 6.3 inches optimizes the mode matching for 100 W input power as shown in the second plot.
  • This corresponds to moving JM2 by about 3 inches, which is feasible within the current layout.
  • Around the optimum, a JM2 placement error of ±1 inch degrades the mode matching by only ~1%, suggesting that achieving <1% mismatch is realistic from an installation-accuracy standpoint.
• The third plot shows that, when JM2 is placed at the optimal position, the expected change in mode matching over 0–100 W input power variation is at the ~0.1% level, indicating low sensitivity to power-dependent effects.

Result

• The dominant contributor to the post-EOM mode mismatch is the longitudinal shift of JM2 associated with the EOM installation.
• Moving JM2 is expected to be highly effective in recovering good mode matching to the IMC.
• If JM3 is replaced with a tip-tilt mount in the future, keeping its longitudinal position within ±0.5 inch would be desirable to avoid introducing additional mode mismatch.

Proposal (Practical Implementation)

1. Install one iris in the reflected beam immediately after JM3, and place another iris on the IOT2L table.
2. Change the longitudinal position of JM2.
   • The target position will be documented in a follow-up figure.
   • After moving JM2 and roughly passing the beam through the irises, fix the mount using dog clamps.
   • Replace the JM2 mirror at this stage.
3. Perform alignment using the iris just after JM3 and the iris after the periscope.
   • Use JM2 to center the beam on the first iris and JM3 to center on the output iris.
   • This procedure is expected to provide sufficient alignment accuracy; if needed, the IOT2 table can be used for further refinement.
4. Repeat the IMC scan measurement to confirm the improvement in mode matching.

LIGO git repo: https://git.ligo.org/masayuki.nakano/lho_jac_installation/-/tree/2bd2518c1e08635017066b16d4b7c5f752ed0ea5/

Summary

We performed IMC scans to evaluate mis-polarization and spatial mode content associated with the JAC installation. First, reference measurements were taken before the EOM installation using intentional MC2 yaw/pitch misalignment to robustly identify higher-order modes. After the EOM installation, the same type of IMC scan was repeated. The post-EOM measurement shows that the mis-polarization signature observed before the EOM is strongly reduced, while a significantly larger higher-order mode content is present, indicating substantial mode mismatch in the current post-installation layout.

Procedure

• The HAM1 output beam was aligned to the IMC as well as possible using HAM1 mirrors.
• The FSS autolocker was stopped, and a laser frequency scan was applied using the laser PZT:
  • Triangle ramp: 0.1 Hz, ±8 V.
• IMC alignment was slightly optimized using MC2, but not perfectly:
  • Some TEM10/01 content was intentionally kept to aid robust peak identification.
• Data acquisition:
  • Channels recorded:
    • JAC-PZT_DRV_OUT_DQ (frequency proxy)
    • IMC-MC2_TRANS_NSUM_OUT_DQ (IMC transmission)
  • Each scan was recorded for 200 s.
• Pre-EOM reference scans were taken with three alignment conditions:
  • Nominal alignment (reference) GPS: 1453668961
  • MC2 pitch returned to the initial (bad-alignment) value: GPS: 1453672393
  • Pitch restored, MC2 yaw returned to the initial value: GPS: 1453677200

After the EOM installation, a representative post-EOM scan was taken with the same scan settings. For this measurement, the IMC transmission whitening gain was set to 30 dB. Unfortunately, the GPS start time for the post-EOM dataset was not logged at the time of measurement.

Notes

• The IMC is free-swinging during the scan; the JAC PZT signal is used as a proxy for the instantaneous laser frequency.
• Intentional yaw/pitch misalignment in the pre-EOM scans enhances TEM10/TEM01 as expected, confirming reliable mode identification and peak labeling.
• The IMC scan after the EOM installation exhibits noticeably stronger higher-order mode resonances than the pre-EOM reference scans.
• Calculation details can be found in the LIGO Git repo.

Result

• In the pre-EOM scans, the p-polarization resonance (π-shifted from s-pol) is visible at the \sim 0.1\% level, indicating a small but measurable mis-polarization component as shown in the second attached plot. The wider peak at the center is the p-pol resonance. The MC mirrors has higher transmissivity for p-pol the finesse for p-pol is lower than s-pol peaks.
• After the EOM installation, this p-polarization signature is no longer apparent, indicating that the mis-polarization is strongly reduced. It might be due to the filtering effect of the EOM. The mispolarized component caused by the input periscope is filtered by the EOM birefringence.
• In contrast, the post-EOM scan shows a substantially larger higher-order mode content (notably a large 2nd-order component ~10%), indicating significant mode mismatch in the current post-installation layout.
• A dedicated mode-matching calculation based on the as-built post-EOM layout will be reported separately in the near future.

Sun Feb 01 10:08:16 2026 INFO: Fill completed in 8min 12secs