I think these measurements look pretty good, and the result is not that much different than the model (at least in terms of where to put the diodes). The biggest surprise is that Keita and I were pretty sure the beam coming into HAM1 is just over 2 mm in radius, when in reality it is more like 3 mm in radius.

I have attached plots of both the horizontal and vertical propagations, but you can see that the results for each direction are very similar. The black points are the measurements Sheila and Camilla took today, and I fit them with a la mode and the 2 inch POP lens (f = 334 mm), using the distances from the dichroic mirror that Sheila and Camilla measured.

If we place the POP LSC diode about 140 mm from M15 and the POP WFS about 200 mm from M15, we should get the beam sizes we want on each. I think these positions are a little closer to M15 than they are in the drawing, but I don't think that's a problem.

I also attached my a la mode script.

Linking here that Keita added distances to the refl air and popair periscopes here: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=84345

And here's a memo of how we "measured" the height of the center of the bottom periscope mirror.

Providing the Geist units with a network connection to the ADMIN-LAN:

At the midstations, the ADMIN-LAN is provided by a fiber-to-ethernet converter box, originally directly connected to the PEM front-end computer IPMI port. This is now sent to a 4-port ethernet hub, which feeds the IPMI port and the Geist unit.

At EY it was possible to reconfigure sw-ey-stk(2) to give ADMIN 4 more ports, and remove 2 each from SLOW and FE. This required moving all four SLOW cables 4 ports to the right, which was done quickly with no impact to HWS, BRS, HEPI-PUMP.

At EX it was not possible to do the same, so here two unused SLOW ports (15,16) were reallocated the ADMIN.

To complete the install I removed the MY rack doors (front and rear) to make them the same as MX and improve front-end computer cooling (see trend).

I've run these three transfer function measurements with settings as follows:

• HAM5 in ISOLATED, although with HEPI locked but the HEPI ISO gain set to 0 to bypass the locked HEPI
• SR3 in ALIGNED
• SR3 DAMP gains all set to -0.1

The measurements can be found in /ligo/svncommon/SusSVN/sus/trunk/HLTS/H1/SR3/Common/Data/as 2025-05-07_0000_H1ISIHAM5_ST1_WhiteNoise_ISO_{X,Y,Z}_0p05to40Hz_calibration.xml. They have been committed to the svn as r12295.

Checking the coherence between each excitation channel (H1:ISI-HAM5_ISO_{X,Y,Z}_EXCMON) and SR3's euler basis DOFs, the coherence between 5 and 10 Hz was good between the following channels:

ISO_X -> DAMP_T

ISO_Y -> DAMP_L

ISO_Z -> DAMP_V, but also pretty good coherence with DAMP_L and DAMP_T
 

I have run the calibration script to get the calibration factors for the SR3 OSEMs. The (multiplicative) factors are:

    LF: 1.3206
    RT: 1.3705
    SD: 1.3806
    T1: 2.4539
    T2: 1.4819
    T3: 1.4125

The factors are calculated by fitting a frequency-independent real factor to the measured uncalibrated transfer functions to fit the modeled one. The fit range is from 5 to 15 Hz. The attached plots show the before and after of the process.

A few observations:

1) As we had seen before, the Left and Right (LF and RT) OSEMs are pretty well matched to one another, which bodes well for our PR3 Yaw OSEM estimator plans.
2) The T1|T2|T3 OSEMs that measure the vertical direction have their orientation flipped respect to the model. I don't think there's a problem, but it is worth pointing out.
3) The T1 OSEM, which is used to distinguish roll is 70% off from T1 and T2. The large factor feels concerning, but it is consistent with other measurements of SR3. See for example 83963, where in the attached .pdf the Vertical to roll coupling is very clean (page 12). And the difference of T1, T2, and T3 can be seen very directly in page 24.

- I think it might be worth revisiting some of these transfer functions after recalibrating just to confirm that we're getting the numbers right.

If we wanted the OSEM measurements to match with the GS13 calibrations between 5-15 Hz, the factors that should be in the OSEM input filters should be:

    T1: 3.627
    T2: 1.396
    T3: 1.345
    LF: 1.719
    RT: 1.490
    SD: 1.781

Since this change will increase the effective gain of the damping loops by a factor of 30% at a minimum, we must compensate by changing the gains for the filter modules in the M1 DAMP filter bank.

Late entry:- Yesterday, we moved SUS PM1 to its desired location in HAM1 chamber. Later we were able to fine tune the position mechanically (including the pitch and yaw of the mirror) with the IR laser beam. The pictures are attached below.

This morning I found that the Voltmon for PM1 was not working, Daniel fixed it by switching on the filter modules associated with it. Earlier, I crosschecked the wiring and chassis in the CER to confirm they are correctly attached and switched on.

I opened up the DM that had no flow to find that the internal tubing was not even connected, I swapped this one back this morning and it came right back no problem and we can see it on epics. The one that I took off has some kind of network issue.

Note that the same glitches we had in the original installation (alog 8934) were still there. Quoting my alog from 2013,

it was still difficult to obtain good data because of some kind of glitches. It's not clear if it was due to NanoScan or the beam, the beam was well damped and was not moving on the viewer card, there was no noticable intensity glitch either. But the symptom was that the statistics window shows nice steady data for anywhere from one second to 30 seconds, then there's some kind of glitch and the scan/fit image looked noticably different (not necessarily ugly), the diameter mean becomes larger and the stddev jumps to a big number (like 10% or more of the mean, VS up to a couple % when it's behaving nice), and the goodness of fit also becomes large. Somehow no glitch made the beam diameter number smaller. I just kept waiting for a good period and cherry-picked.

We measured the beam radius using NanoScan at four points around the WFS sled (roughly WFSA position, roughly WFSB position, far field 1, far field 2). We used D4sigma numbers instead of 1/e**2 numbers. NanoScan outputs diameter not the radius, and the table below shows the raw number.

We assumed that the WFS position would be ~0.5" from the +Y edge of the WFS sled for both A and B. Distances were measured using stainless steel rulers and are relative to the 50:50 splitter on the WFS sled that also acts as the steering mirror for WFSa.

In all of the above measurements, "Profile averages" was 10, "Rolling profile Averages" was 3.

We also measured between M5 and 50:50 splitter for ASC-LSC split as well as between M2 and RM1. Numbers will be added to this alog.

We'll also measure the beam size at LSC REFL_B location on Monday before proceeding to POP path.

Here are some comments about the measurement process:

The beam profiler is difficult to use because the profiler head easily swivels once it is place. The swivel seems to be driven by the fact that the cable is very stiff and made stiffer by the addition of the foil so it is cleanroom safe. Several times today, I would pick up or set down the profiler and the head would swivel. I tried tightening the screw holding the post to the base, and I tried tightening the screw that holds the post to the head, but it is not tight enough to prevent swiveling. I found the best method was to line up the profiler in the designed location, and hold the head and cable in place while someone else ran the measurement. That makes this a minimum two person job, but there was enough juggling that having a third person was sometimes helpful.

When we went in around 3 pm to do the final measurement of the day I measured the particle count: 0.3u was 10 and 0.5u was 0. I used the standing particle counter on the +Y side of the HAM1 chamber- briefly unplugged to carry it over to the -Y side for the measurement. I didn't measure when closing up because Keita is heading out to do a few more tasks on HAM1. The handhelp particle counter isn't working, so we have to carry this large one on a stand around to use.

WFS sled is still excellent, 84 to 85 deg Gouy phase separation.

In the attached, four measurement points have error bars both in the position and the beam size but it looks negligible. There's no concern for WFS, it's good to go as is. 

However, just for the record, the astigmatism is bigger now (which is inconsequential in that ASC DOF separation is determined by the Gouy phase even if there's an astigmatism). The waist location difference is ~49mm now VS ~14mm or so before (just eyeballing the old plot from alog 8932) for a beam with the Rayleigh range of ~200mm. Not sure if this is the result of the AOI change or beam position change on curved mirrors and lenses, but I won't fix/correct this.

This morning we entered to do one more beam profile measurement. First Jennie and I refoiled the cable of the nanoscan profiler, since it was very stiff from multiple layers of foil. Then, before opening the cover to the table, I measured the dust counts by carrying the stand particle counter over to our working side like I did on Friday. The read was 0 and 0 for 0.3um and 0.5 um particles. I know it was working however, because as I carried the counter over outside the cleanroom it counted 19 each of 0.3 and 0.5 um particles.

Then, Jennie and I took one more beam profile measurement, this time on the LSC REFL path, after the final beamsplitter (M18). LSC REFL A (on transmission of M18) is placed on the table as in the drawing, but the LSC REFL B sensor (reflection of M18) was further away relative to the splitter. My quick rough measurement showed that LSC REFL B was about 160 mm away from M18.

I measured the distance of LSC REFL A to the front surface of M18 to be 128 mm. Then, I set LSC REFL B off to the side, and placed the profiler about 128 mm away from M18 on reflection of the splitter. We measured the beam profile, and then I re-placed LSC REFL B, this time at a distance of 128 mm to M18.

I have attached a very rough drawing of the REFL path and the locations where we made beam profile measurements. Each X on this drawing marks a beam profile measurement location. I also marked the Xs with letters A-G.

The measurements Keita reports above correspond the measurements C, D, E and F on this drawing. The difference between E and F, which is not depicted in my drawing, is a different placement of the temporary steering mirror relative to the sled.

 We still need to report details on the measurements for locations A, B, and G.

Beam size upstream of the WFS sled

Unfortunately this is preliminary.

We measured the beam size at 4 different location upstream of the WFS sled marked as A, B, C and D. D data cannot be used as there's no data/picture of D locaiton but that's fine as far as position A data is good. Unfortunately, though, the position A horizontal width looks narrower than it really is (2nd attachment). The beam might be clipping in the nanoscan aperture or there might be a ghost beam or bright background light in the Region Of Interest (ROI), or ROI is defined poorly, effectively clipping the beam. Must remeasure.

LSC REFL_B (and therefore REFL_A) beam radius is ~0.1mm, which is tinier than my preference, the diode is 3mm (in diameter) so the beam could be larger.  The diodes are placed close to the focus of the lens upstream (number 18 in a circle in the first attachment) so the beam won't move when the beam position moves on that lens. Moving away from that position will be fine as far as the deviation is much smaller than the focal length (~200mm). Rayleigh range is like 3cm or maybe smaller (0.1mm waist -> RR=10*pi mm),  it should be easy to double the beam size by moving the sensors away from the lens by a couple inches. We'll do this after POP alignment.

After everything is done we'll make a good measurement of distances between everything by either using a long/short ruler (preferred) or counting bolt holes or both.

Yesterday Betsy and I measured the distances between these optics:

• 856mm from RM1 to RM2, measured 827mm between the front D1000767 plate structure of each SUS and Don and Rahul measured on D1001396 the horizontal distance between plate and optic is 14.3mm for each RM1 and RM2.
• 895mm from RM2 to M5: Front of RM2 mirror to HR of M5 mirror
• 758mm from M5 to M6 (BS): HR of M5 mirror to front HR of M6 BS (-X side of M6)
• 468mm from M6 (BS) to 2" Lens on SLED: front HR of M6 BS (-X side of M6) to front side of 2" lens (0.5" thick lens holder, from siskiyou FOH 2", so add 0.25" if you want center of lens).

Camilla and I went back out today to redo the measurements at the locations labeled "A" and "D" in Keita's diagram. This table reports the D4sigma values, like Keita's tables above.

We forgot that we had left ITMX aligned, so the original measurements in this alog are no good. Keita and I remeasured these again today (May 6) and I am updating the table below with the new data. We also got two more measurements in new locations that are not indicated in Keita's diagram.

Leaving this older comment: It is difficult to measure these distances well with the ruler, so I would guesstimate error bars of a few mm on each distance measurement reported here.

Some new notes: when we reduce teh purge air flow, the measurements become much more stable and there is no need to "cherry pick" data as Keita discussed in earlier comments. Also, I think we have finally managed to tighten the screws on the nanoscan posts enough that it doesn't slide around anymore.

Kiet, Sheila

We recently started looking into the whether nonlinearity of the ADC can contribute to this by looking at the ADC range that we were using in O4a. 

They are showed in the H1:OMC-DCPD_A_WINDOW_{MAX,MIN} that sum the 4 DC photodiodes (DCPD). They are 18 bits DCPD, so that channel should saturate at 4* 2^17 ~520,000 counts. 

Now there are instances that agree with Ansel report when there are violin mode ring up that we can see a shift in the count baseline.

Jun 29 - Jun 30, 2023 when the baseline seems to shift up and stay there for >1 months, Detchar summary page show significant higher violin mode ring up in the usual 500-520Hz region as well as the nearby region (480-500 Hz) 

Oct 9, 2023 is when the temporary calibration lines are turned off 72096, the down shift happened right after the lines are off (after 16:40 UTC)

During this period, we were using a~5% of the ADC range (difference between max and min channel divided by the total range - 500,000 to 500,000 counts), and it went down to ~2.5 % once the shift happenned on Oct 9, 2023. We want to do something similar with Livingston, using the L1:IOP-LSC0_SAT_CHECK_DCPD_{A,B}_{MAX,MIN} channels to see the ADC range and the typical count values of those channels.

Another thing for us to maybe take a closer look is the baseline count value increase around May 03 2023. There was a change to the DCPC total photocurrent during that time (69358). Maybe worth checking if there is violin mode contaimination during the period before that. 

Kiet, Sheila

More updates related to the ADC range investigation: 

• ADC ranges comparison between Hanford and Livingston: 
  • At Livingston we are using the L1:IOP-LSC0_SAT_CHECK_DCPD_{A,B}_{MAX,MIN} channels, which were not turned on until 1398035799; these channels saturate at 2^17 counts. 
  • At Hanford we are using the H1:OMC-DCPD_A_WINDOW_{MAX, MIN}, these channels saturate at 4 * 2^17 counts as they are sum over 4 DCPD
  • We looked through the data in Feb 2025 when the violin modes at Livingston were somewhat higher than usual. 
  • The range being used in compatible with Hanford (2-4%), and the count values are also similar as LHO counts/4 and LLO counts are in +- 5000 counts of each others.
• Comparing the comtaimination before the DARM offset change in ER15:
  • We saw hint of contaimination even before the change (Using Fscan spectrum of May 2nd) 

Further points + investigations:

• Ansel pointed out that it was odd to have a significant shift in the baseline count value + range when the temporary calibration lines turned off as these calibration lines were not that different in height than other calibration lines (see plot in the Alog 83997)
• Joseph from LLO gave us a spectrum comparison between H1, L1 raw ADC count, there is a notable difference in the higher order violin modes
  • To do: looking to periods of when the both (1st and 2nd) violin modes ring up and periods of only the first violin mode ring up to see the contaimination caused by the 2nd mode or higher down mixing
• Evan pointed out that during the period of high contaimination (June 30th - Aug 9th; 2023), the range stayed between 7 - 20%; and LHO in general seemed to have higher rate of saturation + intermitten increase of the ADC range than LLO. 
  • To do: Selecting the periods of stable ADC range in LHO data, and run the average spectrum over those periods to see the level of contaimination, assessing the contribution of the periods with increase ADC range. 
    
     

Kiet, Sheila

Following up on the investigation into potential intermixing between higher-order violin modes down to the ~500 Hz region:

The Fscan team compiled a detailed summary of the daily maximum peak height (log10 of peak height above noise in the first violin mode region) for the violin modes near 500 Hz (v1) and 1000 Hz (v2). They also tracked line counts in the corresponding frequency bands: 400–600 Hz for v1 and 900–1000 Hz for v2. This data is available in the Google spreadsheet (LIGO credentials required).

• We identified dates when both violin modes were elevated (n1_height > 7; n2_height > 8) and when only the fundamental mode was elevated (n1_height > 7; n2_height < 8). For each case, we computed average PSDs using an FFT length of 1800 s. The study period spans from August 10, 2023, to January 14, 2025, starting when ADC counts stabilized after the temporary calibration lines at 24.4 and 24.5 Hz were turned off (see alog  72096)
  • The psds comparisons is shown in vmodes_psds_comparison.png.
    • Note that the number of averages differs between the cases; there are significantly fewer days with only v1 elevated, which explains why the [v1 high, v2 low] spectrum appears noisier in some regions. However, similar features are still present in the [v1 high, v2 high] case.
    • Notably, there appears to be more spectral content in the 450–550 Hz range when both modes are elevated, with certain lines showing significant power (highlighted in green).

• Daily Fscan data around the violin modes is summarized in Pairwise_scatter_plots.png , where n1_height and n2_height are the max peak heights of v1 and v2, and n1_count and n2_count are the corresponding line counts. There appears to be a threshold in violin mode amplitude beyond which line counts increase (based on {n1_height, n2_height} vs. {n1_count, n2_count} trends).
• We also ploted how n1_count varies with n2_height when n1_height is high in n1_count_vs_n2_height_when_v1_high.png. 

Next: We plan to further investigate the lines that appear when both modes are high, the goal is to identify possible intermodulation products using the recorded peak frequencies of the violin modes.