Sat Feb 07 10:09:46 2026 INFO: Fill completed in 9min 42secs

Summary of investigation into the vertically split beam from the EOM

• First, we confirmed that the vertical beam splitting observed yesterday originates from the EOM itself. To check the possibility of multiple reflections from lenses, we inspected the back-reflection port of the JAC output mirror. Two reflected beams were observed, most likely originating from the planar and curved surfaces of the lens, and they were mainly separated in yaw. Since the space between the EOM and the lens was blocked during this test, these reflections were conclusively identified as lens reflections. No vertically split beams were observed from this source.

• A knife-edge–like test was performed by slowly lowering a metal ruler from the top at both the EOM input and output. At the EOM input, the entire beam disappeared simultaneously, whereas at the output the beam disappeared gradually from the top. This behavior confirmed that the vertical splitting is generated inside the EOM.

• To accurately determine the beam positions at the EOM input and output, beam positions were measured from photographs. Taking refraction and geometry into account, it was found that the beam is slightly displaced in the horizontal direction. Details of this analysis will be documented in Keita’s alog.

• Based on this result, the EOM was rotated in yaw. Dog clamps were placed at the ±y projection points of the EOM input and output, in contact with the base plate. One 0.5-mm shim was inserted between the base plate and each dog clamp to rotate the EOM counterclockwise. However, the beam pattern did not change. Additional shims were tested, but no significant change was observed. The EOM was fixed with one 0.5-mm shim at each position.

• Next, pitch adjustments were explored. The original shim configuration (two shims on the +y side and one on the −y side) was changed by moving shims to the +x side (one location at center) and the −x side (two locations, upper and lower). Each location initially had two shims, and by adding or removing shims, it was observed that the vertical positions of the split beams changed. When the +x (downstream) side was raised, the vertically split beams appeared in the upper part of the beam profile (approximately 5–7 beams; Keita will upload photos). Conversely, when shims were added to raise the −x side, the split beams moved toward the lower part of the beam. With the downstream side lowered by approximately 0.25 mm, about two beams were observed in the upper part and one in the lower part.

• 1W input power shows 6 or more beams, but 2-3 beams can be observed even with 100mW.

• With the last configuration, we proceeded the IMC scan measurement after alignment. The 2nd order mode peak was the same level as we observed when we sim up the EOM first time.

• In summary, the EOM shows highly questionable and nontrivial behavior. Possible causes include diffraction due to crystal defects or multiple reflections at the AR-coated surfaces. However, identifying the exact mechanism is challenging at this stage.

TITLE: 02/06 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
Super Bowl Weekend SHIFT SUMMARY:

JAC team continued with JAC alignment work in HAM1.  HAM3 AIP was swapped & started pumping over the weekend. 

(Go Seahawks!)

LOG:

• 1611-1725 Optics lab & LVEA technical cleaning (kim)
• 1612-1622 eMod retrofits/checks (randy)
  • 1636-1920 heading back out & will use crane for handrail moves (randy)
• 1836-1845 Opening lightpipe & increasing power via rotation stage for HAM1 team (ryanS)
• 1837-2014 HAM1 ghost beam search for JAC (keita, masayuki)
  • 2241 HAM1 work continues (keita, masayuki)
  • 2300 Jennie joins JAC team
• 1838-1851 power cycle volt meters (tony)
• 1906-2123 swapping out Annulus Ion Pump (AIP) at HAM3 (gerardo, jordan)
  • 2249 start pumping down HAM3 AIP (gerardo, jordan)
• 1925 Taking laser power from 1.0 to 0.100 W (ryanS)
• 2040 Had issues with the Ops Camera/Access system computer, named ACCESSCONTROL (it's not ZOTPSL2). Problem was with OpenEye (camera app) not working (Refresh would do nothing).  I restarted the app a few times, and also restarted the computer as well.  Access System (Intelli-Site) app was fine.  Thinking it was a network issue because it said there was no access to the internet, I clicked Network Reset.  But after this also lost Intelli-Site.  Tony and Dave did a few checks and also phoned Richard with no luck.  As workaround, using the OpenEye webpage on the Operator CDS computer and if someone is at the gate, we can open it via the ops phone.
• 2051 nds1 restart (dave)---this required a restart to FOM ndscopes.
• 2118-2220 Checking eMod rail parts at EY & EX. (randy)
• 2230-2301 HAM1/IOT2 checks (jennie, sheila)
• 2334 Timing checks at both EX & EY CERs (Dave)
• 0008 Input power raised to 1W for JAC (ryanS)
• 0033 HAM3 AIP is pumping over the weekend Aux-Cart near HAM3 & gerardo/jordan are done for the day.

FAMIS 28229

pH of PSL chiller water was measured to be between 10.0 and 10.5 according to the color of the test strip.

From the previous alog post, Sheila measured a power drop across BL2 lens.

Here I modeled the loss of the 700um beam waist across the 2.5mm BL2 lens aperture.

The expression for the transmitted power obtained by modifying the Gaussian beam equation to include a displacement d² = d_x² + d_y² is shown here.

And here's the contour plot for the loss (1-T) across the lens aperture for a beam transversing across various spots on the lens.

Following on from this log (alog #89046), we have already checked that the MC mirrors are restored to their previous positions from before the power cut in December. We know the seismic state now should be as close as we can manage to this time 2025-12-03 11:28:44 UTC when the mode cleaner was locked at 2W input power and before any HEPIs were locked for the vent.:

Summary of seismic state now:

HAM ISI locked. HAM 2, 3, 4, 5, 6 ISI isolated.

HAM1,2 and  BSC2 HEPI locked. HAM 3,4,5,6 HEPI isolated - ie. as per nominal operation.

I trended the IM osems and the MC2 and IM4 QPDs in HAM2 while the mode cleaner was locked for mode scans yesterday (reference time is 2026-02-05 18:44:36 UTC).

It seem as though the MC2 and IM4 trans powers we have are lower now, but also the IM mirrors have changed.

As Sheila did yesterday I will try and summarise these changes in a table and compare whether this makes sense with the greater HAM1 loss we have because of the JAC (~40 %).

Just posting an updated version of Sheila's table to compare this new time (3rd December).

So after this Sheila and I are going to try turning on the IMC ASC and working out if we can tune the alignment onto IM4-TRANS using the IMs.

WP13007

The rawminute trend copy to permanent archive completed 04feb2026. Today I reconfigured NDS1 to serve these data from their permanent archival location and started the deletion of the files from TW1.

NDS1 was restarted at 12:51 for the new configuration.

FAMIS 38837

CO2 lasers have been off for the past month for vent activities and HWS SLEDs were just turned on a few days ago, so this month's trends don't show much activity.

Fri Feb 06 10:08:33 2026 INFO: Fill completed in 8min 30secs

This is for FAMIS #39750.

Laser Status:
    NPRO output power is 1.841W
    AMP1 output power is 70.43W
    AMP2 output power is 139.4W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 0 days, 21 hr 23 minutes
    Reflected power = 27.19W
    Transmitted power = 103.9W
    PowerSum = 131.1W

FSS:
    It has been locked for 0 days 18 hr and 54 min
    TPD[V] = 0.4791V

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: 02/06 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: 0mph Gusts, 0mph 3min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.31 μm/s 
QUICK SUMMARY:

HAM1 JAC work will continue.  HAM7 is closed but pumpdown has not started yet.  LVEA continues in the Bifurcated Laser Safe state.

While Keita will report the detail about the heater wiring trouble shooting, here is the quick report for the JAC heater functionality.
The attatched plot shows the two thermistor signals (top/bottom) and the heater input (middle). The temperature is reasonably changing with the heater driver input.

[Jason, Masayuki]

• The laser power was increased to 1 W, and a beam dump campaign for ghost beams was carried out. First, a mirror-mount beam dump plate was installed on the JM2 mirror mount.
• Next, a beam dump to catch the AR reflection from the EOM was installed next to JAC_L1.
• Then, the s-polarized beam separated by the EOM was dumped between JAC_L2 and JAC_L3. Since a balance mass was present in this area, the beam dump height had to be adjusted. A dog clamp was inserted between the post and the beam dump to raise the height.
• When observing the beam between JAC_L2 and JAC_L3, multiple vertically separated beams were seen. At first, this was suspected to be a reflection returning from the HAM2 septum viewport; however, the beams did not disappear even after blocking the downstream path, indicating that this was not the cause. The most likely origin is multiple reflections from JAC_L1, although this has not been confirmed.

We still need to find the back reflection beam from the septum viewport, and discuss what we will do for the vertically separated beams.

I never made updated plots for the lock duration and prevelance of the DARM glitch locklosses for the last couple months of O4c (up to Sept 1st, 2025, up to Oct 1, 2025), so here they are. The performance during October and November mostly line up with what we had been seeing in August and September following the bias change (86027).

Through October and November, the frequency of DARM glitch locklosses, and locklosses in general, was still lower than they had been before the ESD bias change. October went realy well. November wasn't the best month for ETM glitch locklosses - we had 8 locklosses due to ETM glitch during the month. That's only slightly worse than the amount we saw in August right after the bias was doubled, but during November we were locked for less time overall due to O4c ending on November 18th and PEM week not requiring us to keep the IFO locked overnight or on weekends, so that's not the best. However, we still had longer locks on average during November vs before the bias change.

O4 DARM Glitch vs All Locklosses
O4c Lock Length Distribution
O4c Lock Stats

TITLE: 02/06 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY: Work continued in HAM1 on/around the JAC, including ghost beam hunting and fixing a shorting cable. OMC scans were also taken today at points when the IMC could be locked (manually, since the IMC_LOCK Guardian is struggling to lock the IMC itself). HAM7 sits with its doors on, but pumpdown timing is still being discussed.
LOG: