R. Crouch, J. Oberling

This morning we measured the position of the BBSS after the HEPI actuators were installed to see if/how things moved during actuator installation.  Short version: Not much movement overall, but there are a couple spots that moved more than expected; there was a slight CW rotation of the BBSS of at most ~170 µrad.

The attached picture shows the position of our measurement points on the BBSS both before and after HEPI actuator installation; Round 5 is from last Wednesday, before the actuators were installed, and Round 6 is this morning.  As the deviations in the picture are all related to the CAD nominal, the table below shows the measured positions from Round 5 and Round 6 and the deviation between these 2 measurements, to give an idea of the amount of movement from actuator install (all units are in mm).

So all in all, not much motion, as we anticipate.  However, there are a couple points that did move: The +X/+Y point moved +X by 0.105 mm, and the -X/-Y point moved +X by 0.09 mm and +Y by 0.185 mm.  Overall this appears to indicate a +X shift and a CW rotation, but I can't really square that large +Y move in the -X/-Y point with anything else, it really stands out and doesn't make much sense to me.  I'll think on this some more and post any revelations as a comment, but for now everything is still within our position spec and we rotated a little more in the CW direction (which based on Keita's last alog should help the overall IFO alignment), so onward towards chamber closeout we go.

We suspect this is the final FARO measurement of the BBSS that we'll take, but to be on the safe side we have left the FARO set up outside of WHAM3 for now.

Mitchell, Disha, Robert

On Friday we finished alignment of the baffles on the +X side of HAM3. This took extra time because we didn’t expect 12 point flange bolts on the PR2 dog clamps that we were moving. Beam spot photos from the BBS showed that we had mitigated retroreflections from the dog clamps and other retro-reflectors that we were worried about, but the brackets for two of the SPI baffles formed strong 2-D corner reflectors with the table top (see figure). We need to hide them with something that is the same height but not normal to the BBS-PR3 beam, and we need to finish aligning the baffles on the –X side.  We may also need to treat two of the table baffle brackets on the +X side of HAM3 if they produce retroreflections in PR3 beam spot photos.

Following on from alog 90738, we last had the corner alignment with the BBSS at PIT +115 and YAW -1557.  We decided to offload this YAW to the HEPI so the team embarked on that yesterday, likely another alog from IAS/SEI on that move later.  Today we went and looked at the corner beam pointing with Keita refining the BBSS alignment to PIT +107, YAW +441 (see his alog coming). 

So now, Jim and Mitchell are embarking on Actuator attachment at the piers.  We will relook at the BBSS cage position with the FARO shortly after they are complete, and then re-peek at the corner alignment likely early next week.

Meanwhile, the BBSS PIT to YAW cross coupling investigaton continues...

Continued from 90691. Betsy, Keita, Sheila, Oli, Eric, Camilla, Ryan S, Jenne

First thing, we went back to alignment we had ITMX SQZ  the "flashes" and "fly-bys" yesterday, put the same size oscillation on the BS, but saw no flashes of fly bys. Betsy took a video of what the two SQZ beams looked like at PR2 at this alignment, they were crossing each other. 

We then rethought the alignments from yesterday, we are leaving:

• ITMX and ITMY at March DRMI top mass OSEM sensors
• ZM4 and ZM5 to get SQZ beam on SQZT7 irises
• ZM6 to O4 sliders.
• SR3 at the Oplev/slider positions of March DRMI/O4 (all similar)
• SR2 Yaw slider back to O4, Pitch to get SQZ ITMY beam on AS_AIR (+440urad PIT sliders different from O4).
• SRM aligned to improve SRY fringes (+200urad PIT sliders, +400urad YAW sliders different from O4).

Once we did this, we had SRY fringes, Betsy and I then adjusted the BS to bring the beams back on top of each other at PR2. This was a change in the BS sliders from (P 1000, Y 1290) to (P 1350, Y 1180).

Keita then wobbled ITMX and found the SQZ beam off ITMX! Aligned ITMX to get MICH flashes at AS_AIR, AS_A/B and ISCT1 REFL. He had to move ITMX from (P -96, Y 104) to (P -280, Y 94). 

He then got the PSL IX and IY reflection in the AS_AIR camera in this alignment. Sliders at this alignment attached. 

However as we are not sure we trust the ITMY alignment form top mass osems (from 90551), we want this Pitch change to be in ITMY, so ITMX is at it's known DRMI pointing. We could try to walk these, maybe along with SRC which might reduce some of our Pitch differences in SR2 and SRM. This change is so small that we will go ahead with mechanically offloading BS Pitch. The BS YAW will not mechanically changed. 

The OMs are also not currently in their O4 sliders/osems position, attached. We could verify the SQZ beam pointing by putting these back if we thought that was needed.

I increased both BRS damping threshold defaults to stop the ringing behavior that we've seen after Beckhoff restarts. The defaults are hard coded into the BRS Beckhoff control under the follow lines:

H1_ISI_GND_BRS_ETMY_LOWTHRESHOLD: INT:=2000;(*~ (OPC : 1 : visible for OPC-Server)
                                        (OPC_PROP[0005] :3: read/write)
                                        (OPC_PROP[0101] :Lower Damping Threshold: DESC)*)
H1_ISI_GND_BRS_ETMY_HIGHTHRESHOLD: INT:=4000;(*~ (OPC : 1 : visible for OPC-Server)
                                        (OPC_PROP[0005] :3: read/write)
                                        (OPC_PROP[0101] :Upper Damping Threshold: DESC)*)

I changed the LowThreshold from 800 to 2000 and the HighThreshold from 2000 to 4000.

J. Oberling, R. Crouch, J. Warner, B. Weaver, I. Abouelfettouh, O. Patane, S. Appert

And finally, here is the long-promised alog for our full set of measurements of the now-deinstalled aLIGO BS.  I will give a brief overview of the WBSC2 support tube and BS in-chamber measurements we took, but the bulk of this alog will concern the various test stand measurements we took and how they tie in to the in-chamber and support tube measurements.  As a reminder, our alignment tolerances for the aLIGO BS were:

• Relative to IAS equipment (set normal to the AR surface of the optic)
  • Horizontal: +/- 1.0 mm
  • Vertical: +/- 1.0 mm
  • Longitudinal: +/- 3.0 mm
• Relative to IFO axes
  • X: +/- 2.8 mm
  • Y: +/- 2.8 mm
  • Z: +/- 1.0 mm
• Pitch: +/- 55 µrad
• Yaw: +/- 190 µrad

Strap in folks, this is going to be a long one with a wall of text.  But first, I demand... A shrub, errr, a summary!

Summary

Earlier this year we measured the location of the ends of the WBSC2 support tubes.  They indicated a -X translation of the WBSC2 cartridge and a CCW yaw.  But, since the support tube length wasn't a controlled dimension for support tube construction we can't use them to definitively inform us about the cartridge assembly in the chamber (we've measure 4 tubes so far, and all 4 have been different lengths by several mm).  The -X translation was a little surprising because we translated the cartridge in the +X direction during our 2013 install, implying that the support tubes were already sitting too far in the -X direction.  The CCW yaw wasn't surprising since we yawed the cartridge CCW back in 2013.

At first we thought the in-chamber alignment looked pretty good, it was only after the cartridge had been removed from the chamber that we realized the mode we had used to make the measurements had a high potential to disguise positional deviations and make the measured point look closer to nominal than it actually was (see the in-chamber section below for full details).  The decision to use this mode was made during our planning for the alignment (it's in our alignment procedure), and was based on an incomplete understanding of how the underlying mode actually worked.  Well, now we know better, but unfortunately the consequence is that we cannot say how well the BS was aligned to the IFO XYZ coordinate system.  What we can say is that the BS was clearly yawed in the CW direction w.r.t. the SUS cage, by potentially several mrad, but have no insight into how it was yawed w.r.t. the IFO XYZ axes.

On the test stand, we found the BS SUS to be right on the edge of our position tolerances for the optic.  We never measured the SUS cage back in 2013, so this was the first time we had looked at it.  The optic itself was found to be within our position specs, but we did measure the position to be in a different place than we did in 2013.  We traced this primarily to 2 things: The large +/- 2.0 mm error bar in the total station's distance measurement mode (used to set the optic's longitudinal position in 2013) and errors in the position of the test stand's brass monuments (used to place the alignment equipment in 2013).  We were able to trace this using the FARO, using its much higher accuracy to measure both the BS longitudinal position and the test stand monuments.  We did find that the pointing of the BS was well outside of our specs: pitch was ~200 µrad up while yaw was ~710 µrad CW.  While the pitch being out of spec after the cartridge was craned was not surprising (looking back through my aLIGO install notes we never had a pitch alignment survive craning into a chamber), we were surprised at the yaw measurement.  The mispositioning of the test stand monuments did not explain this yaw, and we could find no obvious cause.

WBSC2 Support Tubes

The WBSC2 support tube ends were surveyed with FARO earlier this year.  From talks with Jim, my understanding is that support tube length was not a critical dimension for tube construction, and so far this is holding up.  We've measured the support tube ends for WBSC2 and WBSC3 so far (more to come as we're able), and the lengths have not been constant (the WBSC3 support tubes measured short of their design length, and each one was a different length, while both WBSC2 support tubes measured longer than their design length).  Because of this, we can't give any definitive numbers about the respective cartridges, but the info does offer some general guidance.  For WBSC2 this is:

• The cartridge was shifted in the -X direction (towards the PSL) by a couple mm
  • This is odd, as the old notes from WBSC2 installation in 2013 indicate that HEPI was shifted +X by over 4 mm
    • That said, the +X shift makes sense (the direction, not the exact number), see test stand section below
  • Only explanation I have is a guess that the support tubes were not well located before cartridge install; I have no knowledge of how the aLIGO SEI install team set the support tubes before the cartridge was installed, so I have no data to back up this guess
• The cartridge was rotated couterclockwise (CCW) when viewed from the top down by up to 1.3 mrad
  • My notes from the in-chamber pitch/yaw alignment back up the direction, as we initially requested a 400 µrad CCW yaw shift be done via HEPI

The important thing to note here, in my opinion, is the CCW yaw (again, the direction, not so much the exact number).  This will be important later on, once we get to the test stand measurements.

aLIGO BS In-Chamber

We took a series of measurements on the BS while in the chamber in mid-April, see the alog for more detail.  Some important takeaways, in my opinion:

• Due to the construction of our rods, as they are not repeatable in X and Y, we do not have a good idea of where the WBSC2 ISI optics table is w.r.t. the IFO X and Y axes (this will only be an issue with WBSC2, since for the other 4 BSC chambers we can set FARO right outside the open door and measure the ISI directly)
  • Averaging out the 7 Z axis deviations, the ISI is sitting too high by ~0.1 mm (average is -2.8 mm, and it should be -2.9 mm since this ISI should be lower by that amount to place the BS at the correct Z axis position; this wasn't corrected in CAD, hence the listed deviations)
• The SUS cage appears well positioned w.r.t. the IFO axes
  • Although I now question that, given the large potential for misreads of the Build/Inspect mode's results, but it's the info we have and we cannot measure it again
    • In future, we will not be using the Build/Inspect mode; its ease of use is attractive, especially for quick measurements, but we have found it to be error prone due to its automatic SMR radius compensation (explained in the paragraph immediately following these bullet points)
• Ruler measurements show the BS optic is well positioned w.r.t. the SUS cage
  • When looking directly AT the HR surface, it's sitting ~0.25 +/- 0.25 mm to the left, ~0.25 +/- 0.25 mm low, and ~0.7 +/- 0.7 mm too close to the HR Figure 8 section of the SUS cage
    • The error bar on the longitudinal measurement is large due to how the measurement had to be made, as explained in the 2nd comment to the in-chamber alog linked above
  • Rotating this to the IFO axes gives:
• The BS optic is yawed w.r.t. the SUS cage
  • Betsy said this was visible by eye
  • Ruler measurements from the lower Figure 8 of the SUS cage to the BS HR surface indicate this yaw is in the CW direction, but the error bar for this measurement is so large that the amount of yaw is largely unknown
    • Test stand measurements shed more light on this yaw

Because we used the Build/Inspect mode with the automatic SMR radius compensation turned ON to measure the BS SUS position in-chamber, we unfortunately do not have a good idea of where the SUS was located within WBSC2 and by extension do not have a good idea of where the BS optic was positioned.  Subsequent testing after the cartridge had been removed from the chamber showed that we did not have a good understanding of how the automatic SMR compensation worked.  Short version: It's dumb.  It simply compensates in the direction of the measurement object, regardless of where your measured point is.  For example, you're measuring a point on the the underside of a horizontal plate with Build/Inspect mode.  The SMR would sit below this plate in the -Z direction, so the SMR radius should be compensated in the +Z direction.  The automatic compensation does not compensate in the +Z axis alone, it compensates directly towards the nominal point.  This then can result in a measurement that looks dead on but in fact could be nowhere close; if the actual point is off several mm in the X and Y directions, the automatic compensation would make the resulting measurement look like it was dead on as it compensates towards the measurement object, removing the actual deviations in the process.  The final attached picture is a drawing showing this behavior.  We finally noticed this while testing the FARO test stand alignment procedure on an old HAM passive stack after the BS cartridge was removed, and then confirmed it while aligning the BBS SUS on the test stand; initial BBSS placement was done via Build/Inspect as a real time feedback, but we measured the points using a more involved method that tells PolyWorks what direction to compensate in instead of letting the software do it automatically.  The measured points were several mm off of the Build/Inpsect points, and we confirmed the automatic compensation was the cause by turning it on and off (when automatic compensation was turned off, Build/Inspect reported deviations that matched our direct measurement of the alignment points).

aLIGO BS Test Stand

FARO Measurements

And now we come to the test stand meausurements.  To start, we aligned the FARO to the ISI using 10 points on the ISI; these points and the resulting alignment are shown in the 1st attached picture, and show the FARO is well aligned to the ISI.  Once the FARO was aligned to the ISI we then measured several points along the bottom of the SUS cage, as well as the center of both the HR and AR sides of the lower Figure 8 structure; this is shown in the 2nd attached picture.  We did not measure the SUS cage position during aLIGO install, only the optic position, so it's good to see the cage is mostly in the neighborhood of the optic position tolerances.  One note about the Z axis numbers shown here: The CAD model used here is the in-chamber model, which places the BS at its in-chamber Z axis coordinate of -82.9 mm.  However, the BS SUS is the same length as the QUAD SUSs, so the BS is placed w.r.t. the ISI the same as the QUADs, i.e. at -80.0 mm; -82.9 mm was acheived in-chamber by lowering HEPI, but on the test stand the BS was aligned at -80.0 mm.  This was never properly corrected for in the CAD model; I think the SUS cage itself and its components were lowered while the ISI was left at its nominal height, so all the Z axis measurements should show a deviation of around +2.9 mm (since they are physically higher than the CAD would indicate).  This is seen most clearly with the HR and AR Figure 8 structure measurements.  Both Z axis positions measured right around -80.0 mm as they should, while the CAD model claims they are too high.  This has been corrected for in the BBS CAD model, so this is the only time we'll see this discrepancy.

The 3rd attached picture shows a set of lines created from the measurement points we took on the structure which show how the BS SUS cage is rotated w.r.t. the ISI; I also rotated the CAD model so that it matches the target yaw angle of the BS optic itself.  The angles here are reported w.r.t. their respective positive axes (i.e. X Ang is the angle measured from the positive X axis).  As can be seen, the SUS cage had a large CCW yaw w.r.t. the ISI.  Averaging the various yaw deviations gives a yaw of the BS SUS w.r.t. the ISI of 0.2762°, or 4.82 mrad CCW.  This explains the large CW yaw of the BS optic w.r.t. the SUS cage.

With those measurements done we then used the FARO to set a total station looking at the AR surface of the BS, set along the target AR surface normal so we can measure position deviations from nominal.  Once we had these position deviations we moved the total station to the HR side of the BS, mounted a laser autocollimator (LAC) on top of it, set it along the target HR surface normal and offset by 150.0 mm (to avoid the test stand leg) to measure the pitch and yaw of the BS.  The results were posted to the alog here, so the details follow below.

I should note here how we measured the longitudinal position of the BS AR surface.  As noted above, we used the FARO to measure the circle that represents the AR side of the lower Figure 8 structure of the BS SUS; PolyWorks calculates the center of this circle, and is what is shown on the 2nd attachement with the label "BS_FIG8_AR".  We also know the position of the total station, as we set that using the FARO.  We then use PolyWorks to measure the distance between the total station and the BS AR Figure 8, as well as measure the target distance from the total station to the BS AR surface.  We then measure the distance from the AR Figure 8 to the BS AR surface using a depth micrometer; this was done on the left, right, top and bottom of the Figure 8.  These 4 measurements are averaged together to give us a distance from the Figure 8 to the BS AR surface, which is then added to the measured distance from the total station to the AR Figure 8.  This final distance is compared to the target "total station to BS AR" distance to give us the longitudinal position deviation of the BS AR surface.

BS Position and Pointing

The original BS test stand alignment was completed in early February 2013.  The below table gives the final position and pointing deviations we measured in 2013 and those we measured now; I've rotated the position deviations to the IFO XYZ axes for both.  In 2013 we were on Test Stand #2 (currently disassembled due to filter cavity interference) and using pre-set brass monuments, and now we are on Test Stand #1 and using the FARO to precisely set the total station.

That's, uh, quite the difference, yeah?  A couple of things that should be noted here:

• The 2026 pointing measurements, like the 2013 ones, were done with the alignment bias sliders OFF.  With the alignment bias on we did not get a return in the LAC, as the beam was then too far in the CW direction.  The yaw slider was set to -388 µrad, which is CW per SUS sign conventions, so the alignment sliders were pushing the BS further CW.  This could be because of in-chamber yaw deviation, but we don't know for sure since the use of the automatic compensation in the Build/Inspect mode messed up the in-chamber measurements (as previously explained).
• We, obvously, did not have a FARO in 2013, so were using the total station entirely for positioning.  For the longitudinal position (position along the AR surface normal of the BS) we used the total station's internal distance measurement function, which has an error bar of +/- 2.0 mm.  Keep this in mind, as in 2013 we measured a longitudinal deviation of 0.0 mm, while now with the more accurate FARO assisting our setup we measured a longitudinal deviation of +1.8 mm (within the +/- 2.0 mm error bar of the total station's distance measurement).

Despite the large difference in position deviations between 2013 and 2026, these are still within our set position specification.  The pointing is decidedly not.  While it's entirely possible that things have drifted in the 13 years since the BS was installed, there are 2 somewhat obvious things that would contribute to this difference: The total station's +/- 2.0 mm error bar for distance measurements and error in the placement of the test stand's brass monuments.  We've already measured a difference in longitudinal position between 2013 and 2026 that is within the error bar of the total station's distance measurement, but what about the test stand monuments?  Well, we used FARO to measure those.

Test Stand #2 Monuments

To measure the test stand monuments we first had to align the FARO to the test stand coordinate system.  To do this, we used the set of monuments set along the XY axes of the stand and PolyWorks' Best-Fit Alignment routine (the same routine used to align the FARO to the ISI on the test stand); the test stand coordinate system was assumed to be flat along the floor and 2 dimensional (XY only), so I forced all of the Z axis nominals and measured to 0.0.  The results of the alignment are shown in the 4th attachment.  It's immediately apparent that our test stand monuments are not going to be where we thought they were, as the alignment routine was not able to fit a good alignment between the nominal and measured coordinates of the alignment monuments (the first attachment shows the results of the alignment routine when it can find a good fit between the nominal and measured data).  We re-did this a couple times and got very similar results each time (to <0.1 mm), so the monuments are definitely not where we thought they were.  We proceeded to use this alignment to measure the rest of the test stand monuments; those are shown in the 5th attachment.  As expected, none of the monuments are well positioned, all show large errors.  Well then.  So now we have both an error in the longitudinal measurement (but within the error bar) and test stand monuments not where we thought they were.  How could this have affected the 2013 BS XY alignment?  To figure this out, I used PolyWorks to recreate our 2013 alignment setup, now with our mispositioned monuments and with our longitudinal position error.  Since we had to rotate the cartridge to place it on the test stand, I created a new coordinate system that's rotated 90° CW, so the monuments are in the same coordinates as the BS would be once installed in-chamber (I was getting cross-eyed constantly flipping between the IFO and test stand coordinate systems, this made things much easier).

First I wanted to consider how these issues could have affected our 2013 XY position alignment, so I recreated the setup looking at the AR side of the BS.  The 6th attachment shows this.  There's a lot of info in this picture, so match the below numbered list with the red numbers in the picture.  Also, "Theo" is my shorthand for theodolite, which is another name for a total station.

1. These are our targets: The target XY position of the AR surface of the BS and the target theodolite sighting line.  I created the target sighting line by making a line from our total station monument, TS2-18, and the target AR position.  The listed angles are from the nearest axis, so X Acute Ang is measured from the -X axis and Y Acute Ang is measured from the +Y axis.  The listed angles are calculated by PolyWorks based on the nominal positions of TS2-18 and the BS AR surface.
2. These are our total station setup monuments.  The total station was set over monument TS2-18 and sighted TS2-11 to create the 0° horizontal angle reference, which is represented by the "Theo AR 0 Ref Line".  The measured column here is the error in our 0 reference based on the misposition of monuments TS2-18 and TS2-11.  Y Ang is the angle measured from the positive axis, +Y axis in this case, so while we thought we were setting our 0 reference parallel to the X axis, we were actually setting it 0.0012° CCW of the X axis.  0.0012° ~= 4 arcseconds ~= 20 µrad, so not a huge angular deviation.
3. Here's where things start getting a little tricky.  There's 2 boxes here, "Theo AR Actual Sighting Line" and "BS AR Center w/ Devs".  We'll consider the Actual Sighting Line first.
   1. So, according to PolyWorks we should have turned an angle of 45.1052° from our 0 Ref Line to sight the target center of the BS AR surface, but this is not the angle we were told to turn.  The actual angle we turned was 45.1047°.  Again, a very small difference (0.0005° ~= 2 arcseconds ~= 10 µrad).  So the "Theo AR Actual Sighting Line" nominal column shows the angle we actually turned back in 2013, and the line length is the target longitudinal length from the total station to the BS AR surface.  The Measured column shows what the angle actually is once the 0.0012° CCW deviation of our 0 Reference Line is taken into consideration.  I should also note that the Actual Sighting Line originates at TS2-18, with the nominal line originating at the nominal TS2-18 coordinates while the measured line originates at the measured TS2-18 coordinates.
   2. The box "BS AR Center w/ Devs" shows the point that we would have been pointing the total station at assuming we had no deviation in longitudinal distance (which is what we measured in 2013 with the total station's distance measurement function); in other words, if we had no positioning deviations with the BS at all, this is where the center of the BS AR surface would have ended up.  The nominal column only considers the small 0.005° angular deviation between the angle we turned and the angle PolyWorks calculated we should have turned.  As seen, this small angle does not cause much of a shift in AR surface position, a handful of µm in both X and Y.  The measured column, however, is much more interesting.  This column considers both the 0.0012° error in our 0 Reference Line and the mispositioning of monument TS2-18.  As can be seen, the misposition of TS2-18 puts the AR center well off of its target, but still within our positioning specification.
4. Number 3 assumed no longitudinal position deviation in the BS AR surface, and while that's what we measured in 2013 our 2026 measurements showed the longitudinal position of the AR surface was 1.8 mm longer than it should have been.  As I've said previously, this is within the error bar of the total station's distance measurement function that we used in 2013, so we would not have seen this deviation at the time.  But now that we have seen it, how did this change the 2013 alignment?  Queue the next set of boxes, "Theo AR Act Sighting Line + Length" and "BS AR Center w/ Devs + Length".  These boxes provide the same information as given in Number 3, but now I've included the +1.8 mm longitudinal deviation that we have now measured (thanks to the FARO).  The nominal column here is the same as Number 3, so I'll only talk about the measured column.
   1. Now the measured column is including 3 different deviations: The 0.0012° deviation in the 0 Reference Line, the misposition of monument TS2-18, and the +1.8 mm longitudinal position deviation measured with the FARO.  As can be seen, this pushes the AR center further away in X but closer in Y, but still within our position specification for the BS.
5. To see how this compares to our 2026 measurement I added that in as well.  I placed the point that we ended setting the total station over into this test stand coordinate, then created a line at the angle we turned for the measurement.  Interestingly, this was yet another different angle than the one we used in 2013.  The nominal column for the 2026 sighting line lists the angle calculated by PolyWorks, 45.1058°, which was slightly different from what we used for our real test stand measurement, 45.1061°, which again differs from the 45.1047° used in 2013.  This 0.0003° is approximately 1 arcsecond, or ~5 µrad, so a very small difference.  The measured column for the sighting line is slightly different, however.  I wanted to place a point where we measured the BS, which means I had to consider both the longitudinal deviation (seen in the length of the line) and the horizontal deviation.  To include the horizontal deviation I calculated the angle subtended by the -0.7 mm horizontal deviation and the measured distance to the BS AR surface (which includes the longitudinal deviation).  This angle was 0.0085° (arctan 0.7/4713.6).  I subtracted this angle from the 45.1061° we turned to sight the target center of the BS, since the horizontal deviation puts the AR side closer to the -X axis, then created a point at the end of the line.  The measured column of the box "2026 BS AR Measured Position" is this point.  As can be seen, it closely matches the deviation I calculated in the table above, but doesn't quite match the positional deviation seen in Number 4; X position is decently close, within a couple tenths of a mm, but Y deviation is roughly 0.5 mm.  While I don't have an explanation for these small differences, this does show that the mispositioning of the test stand monuments makes up a large portion of the difference between our 2013 BS position measurement and our 2026 one.

That's all well and good for X and Y, but what about the Z axis deviation between 2013 and 2026?  Again, all I have to fall back on is 2013 equipment setup errors or things drifting over the course of the last 13 years.  For equipment setup, we set optic height by setting the total station at a target distance down from the ISI, using a scale attached to a fixed-length rod, that matched the desired Z axis position of the BS.  There could have been an issue with the scale/rod setup (such as a mistake in rod length (not likely) or the scale not mounted properly) or an issue with the total station setup (such as not well levelled or sighting the scale along a zenith angle other than 90°).  While I'd like to think that 2013 me would not have made such obvious mistakes, 2026 me doesn't have perfect recall of events from over a decade ago so I cannot say for sure.

For pointing I made our HR test stand setup in PolyWorks, this is shown in the 7th attachment.  This is much simpler as I'm only looking to see if the monument misposition caused a large yaw error back in 2013.  Quick explanation, we set our total station/LAC combo over monument TS2-20 and sighted monument TS2-19 to set our 0° reference line.  We then turned 44.9711° so we were sighting parallel to the HR surface normal of the BS; the gap between the 2 lines in the picture was handled by a Lateral Hollow Transfer Periscope, a device that horizontally translates the beam by ~400 mm while keeping the output beam parallel to the input beam by 1 arcsecond (0.0003°).  For a 710 µrad CW yaw deviation in the BS to be caused by the monument mispositioning the deviation of the 0 Reference Line would have to be 0.0407° in the CW direction; this would be a measured X Angle of the line "Theodolite HR HA Ref" of 90.0407°.  Clearly, this is not the case.  In fact, the angle deviation caused by the monument misposition is only 0.0019°, or ~33 µrad, in the CCW direction.  At this point, the only explanation I have for the difference in yaw between 2013 and 2026 is an equipment setup error in 2013 or things subtly shifting in the last 13 years.  Keep in mind, we're not talking large shifts in the BS to cause this yaw.  If we hold one side of the BS fixed in position and then yaw it by 710 µrad, the opposite side only moves by 0.26 mm (0.000710 * 370.0 = 0.263).

Wrapping Up

So, what does this all mean?  Well, with the mistake in using the Build/Inspect automatic compensation mode we don't have any better of an idea where the BS was in the IFO XYZ coordinate system than we did before the cartridge was disassembled.  The measurement looks good, but as I explained above I do not trust it.  The support tube measurement indicates a -X shift from nominal and a CCW yaw, but these aren't good metrics since support tube length wasn't a critical dimension during tube construction (we've measured 4 so far and all 4 have been different by several mm).  I wish I had better news to report here, but we didn't notice the mistake until after the cartridge had been removed from the WBSC2 chamber so there was no way to remeasure the in-chamber position.

The test stand measurements show that the BS SUS was on the edge of our positional tolerance for the optic, with a few points just outside of it.  The optic itself, the object of primary importance and the only thing we actually measured in 2013, was within our positional tolerances but different from our 2013 measurements.  The primary causes of this were found to be errors in the positions of the test stand brass monuments that we used to set our alignment equipment during the intial 2013 alignment, and the large error bar in the total station's distance measurement mode.  The pointing was found to be well outside our tolerances, and I currently cannot explain the yaw deviation.  Looking back through my old install notes we never had our test stand pitch alignment survive being craned into the chamber (ITMx shifted by over 2 mrad in pitch after being craned into the WBSC3 chamber), so the pitch being off wasn't really surprising.  But the yaw was.  Our measurements of the test stand monuments, despite the position deviations, did not show a large yaw deviation.  The angle we turned the total station to measure the yaw was different between our 2013 alignment and 2026 measurements, but only by ~24 µrad so not enough to account for the 710 µrad CCW yaw we measured in 2026.  We couldn't find any obvious cause of this, so all I can offer are guesses (procedure mistake, equipment setup mistake, small drifts over 13 years, etc.).

R. Crouch, J. Warner, J. Oberling, M. Robinson

We made some more HEPI moves today to better position the BBS SUS cage.  The results are shown in the 1st attachment.  The deviations listed in the attachment are the deviations from nominal, but that is not our target here.  To better position the BBS optic we are trying to match our position and yaw from the test stand.  As a reminder, I've attached the final SUS cage alignment from the test stand (2nd and 3rd attachments).  The table below shows our current deviations from the test stand alignment (all units in mm):

We wanted to bias to the negative by ~0.3 mm in both X and Y since our BBS test stand alignment had a +0.3 mm deviation in both X and Y position, so this looks pretty good.  The Z axis indicates a potential off level in the cartridge assembly, but one has to be very careful in assessing level based on these measurements.  These measurements are all done in the LHO Global coordinate system, which is tilted w.r.t. the local level in the WBSC2 chamber (see T0900340), so you cannot level to global coordinates; if one did then the suspension would then hang weird as it doesn't care about our different coordinate systems, it just hangs along the local gravity vector.  Jim is planning on using an autolevel to measure the top of the keel mass of the ISI's Stage 2 to see how that looks (similar to what LLO did).

In addition, the yaw of the SUS cage also closely matches our test stand alignment.  Our target, from the 3rd attachment, is 44.9979° from the +X axis and we are currently measuring 45.0025°.  This is a difference of 0.0046°, or ~80 µrad, in the CCW direction, so pretty close to our target.  We won't know for sure how good the pointing alignment is until we can use the BBS OpLev, which is not currently available (the channels do not yet exist, per Oli the plan is to add them next week), but my hope from today's work is that we'll be pretty close.

So next steps are to have the BBS OpLev available so we can assess our pointing alignment and the attachment of the HEPI actuators.  We'll have to measure position again after the HEPI actuators are attached, so we aren't quite done yet.

Sheila, Begum, Keita, Camilla

We followed 80010 to set up, additionally Sheila had us stop the OMC ASC and DC centering loops before running the scan. We moved SRM in Pitch to center beam on AS AIR camera. Cheated the dark offset via adding an offset to H1:OMC-DCPD_SUM_OFFSET.

Started with 1.1mW on SQZt7 IR PD1.06mW on AS_C, 74 and 75 on AS_A and AS_B, 1.06mW on OMC_A and 0.82mW on OMC_B. We were seeing the OMC diodes saturating (via H1:OMC-DCPD_A_WINDOW_EXCEED and H1:OMC-DCPD_B_WINDOW_EXCEED), the same was true after increasing scan length to 200s and reducing SEED input power form 75mW to 50mW in, we checked this did not happen in September 86965. We also turned down the purge air in HAM7, again, did not help.

We tried locking the OMC with the SQZ beam and were unable. 

We did not saturate the PDs with SEED power down to 25mW but the peaks were noisy at the beam was moving and the mis-alignment peak was too large. We got an upper limit of 10% mode mismatch, which is not useful, attached.

We looked back at January data, should be very simular and although the misalignment is bad, the lower limit on modemamthcing is 1.18%, which is very good. See 90598

Pre door close suspension transfer function health check (taken while ISI was locked) measurements looks good. Oli Took IM1-4 (LHO alog 90579) and they look healthy as well.

I will process and post the results later on, the templates are stored at the following location (given below).

/ligo/svncommon/SusSVN/sus/trunk/HSTS/H1/MC1/SAGM1/Data

2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_L_0p02to50Hz.xml
2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_P_0p02to50Hz.xml
2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_R_0p02to50Hz.xml
2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_T_0p02to50Hz.xml
2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_V_0p02to50Hz.xml
2026-06-11_1600_H1SUSMC1_M1_WhiteNoise_Y_0p02to50Hz.xml

/ligo/svncommon/SusSVN/sus/trunk/HSTS/H1/MC3/SAGM1/Data

2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_L_0p02to50Hz.xml
2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_P_0p02to50Hz.xml
2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_R_0p02to50Hz.xml
2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_T_0p02to50Hz.xml
2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_V_0p02to50Hz.xml
2026-06-11_1630_H1SUSMC3_M1_WhiteNoise_Y_0p02to50Hz.xml

/ligo/svncommon/SusSVN/sus/trunk/HSTS/H1/PRM/SAGM1/Data

2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_L_0p01to50Hz.xml
2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_P_0p01to50Hz.xml
2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_R_0p01to50Hz.xml
2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_T_0p01to50Hz.xml
2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_V_0p01to50Hz.xml
2026-06-11_1700_H1SUSPRM_M1_WhiteNoise_Y_0p01to50Hz.xml

/ligo/svncommon/SusSVN/sus/trunk/HLTS/H1/PR3/SAGM1/Data

2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_L_0p02to50Hz.xml
2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_P_0p02to50Hz.xml
2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_R_0p02to50Hz.xml
2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_T_0p02to50Hz.xml
2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_V_0p02to50Hz.xml
2026-06-11_1800_H1SUSPR3_M1_WhiteNoise_Y_0p02to50Hz.xml

Summary

Whatever happened to IM1, Rahul did make it better again. Reasons for improvement is unknown but we proceeded with the alignment and we're mostly done.

There is a mystery scattering or maybe clipping somewhere close to the IFI output but not on the output baffle nor DKDP baffle. It could be a scatter from the CWP surface, or a ghost beam somewhere, or something else. It will take a LONG time to diagnose this, and quite likely this existed for a long time. I'm tempted to leave it at this time. But I'll try to take some more pictures.

There's also something weird about the 1st pico mirror PIT actuator for ISS array.

We'd still like to take pictures/measurements here and there on Tuesday.

Done: ASC REFL centering

Following the morning work (alog 90525), REFL ASC censors were centered using RM1 and RM2. About ~30% of DAC range was used for RM2 (RMs_happy_again.png). FYI, using flash peak, [P,Y]=[-0.003, 0.015] for REFL_A and [-0.020, 0.001] for REFL_B. (Doesn't matter how close these are to zero as far as they're within +-0.1 or so and the SUM is decent, but it feels better to be able to get close to zero.)

Done: ISS array centering

Then we looked at the ISS array and the QPD was not centered. A quick adjustment of the second pico that is closer to the array was all it needed (keita_ISS_happy1.png). [P, Y]=[-0.03, 0.05].

Done: IFO REFL baffle (HA13) adjustment

We looked at the IFO REFL baffle (HA13) in front of the HAM2-HAM3 septum window and it was too high even though it was not clipping, so we lowered it by a couple mm. Before: lower edge height = 105.5mm; upper edge = 206.8mm. After: lower edge = 103.6mm; upper edge = 204.5mm.

This baffle was already moved by a couple mm in +Y direction last week (because the beam was closer to +Y edge). See  IFOREFL_baffle_before_relocation.jpg and IFOREFL_baffle_after_relocation.jpg though it might be difficult to see the difference from this picture.

IFO REFL beam looked like IFOREFL_HA13_baffle_after.mov after the height adjustment.

Mystery flashes seen inside IFI output baffle aperture

We proceeded to check the IFI output baffle and I was bothered to find that something that looked like clipping was visible close to the left edge of the baffle using the IR camera. See IFI_OUT_clipped_720p.mov, this is a view from +Y door. But this was less frequent than the flashing itself. In a retrospect, this was probably the reflection from the PRM when the beam was swinging to the left of the video, but anyway we did various things:   

• We got suspicious about PRM somehow misaligned, checked it on the retroreflection check iris but it was fine in YAW (it was off in PIT so changed PIT offset from -1185 to -1115, not sure if it was PRM that changed or something else, but the important thing was that it wasn't off in YAW and that this is not something that I worry about now that we have a decent headroom for RM2 DAC).
• We closed the HAM3 door cover (which did quiet down the beam motion a lot) as well as the HAM2 -Y door cover. I used IR viewer and thought that nothing changed at the time. The bright thing didn't disappear after blocking the beam between PRM and IM4, again using the IR viewer, I thought.
• However, revieweing videos shot later, I haven't found anything to the left of the output baffle after the beam motion was reduced by closing unnecessary open door covers. But that revealed the next issue.

See IFI_out_another_view.mov, this is after the beam quieted down enough and after PRM PIT was changed. The bright thing at the left side of the baffle hole is not visible any more, but you can still see bright-ish scattering of some sort inside the baffle aperture which was there even when Rahul blocked the beam between PRM and IM4. IFI_out_another_view.jpg shows the same thing but with more useful exposure. This is concerning.

DKDP baffle behind the IFI output cwp baffle looked OK (IFI_DKDP_baffle.mp4). BTW, as was reported before, it looked to us that the IFI output baffle has an offset in -X+Y direction relative to DKDP. In the video, the beam on DKDP is slightly biased to the right on average because we tried to split the difference between two baffles.

We moved IM1 in YAW by +-200urad while observing the IFI output by IR viewer to see if there is a better beam position on IFI output. It seemed to me that actually we don't have much space here.

Look at IFI.png to see how the beam is routed through DKDP, output CWP and then passes by the parking beam dump pick-off.   

• If we give negative 200urad for IM1 YAW, the forward-going beam starts to interfere with the parking beam dump pick-off once in a while and the frosted barrel of that pick-off becomes bright. This is despite that the beam looks perfectly fine when IM1 is at the now-nominal position (see parkingBD_pickoff.mov, negative 200urad IM1 rotation would mean that the beam will be like 1mm to the right in this video).
• If we give positive 200urad for IM1 YAW, I thought that +X side of the IFI output cwp baffle starts to get brighter once in a while (my theory is that this is the same thing as shown in IFI_OUT_clipped_720p.mov where the edge of the baffle clips the back-propagating beam when the beam moves too much).

We'll be better once we're in vacuum because things will be quieter and the MC alignment will be better, so no beam motion and no HOM transmission, but I have to say that the clearance here looks to be unnecessarily narrow. I will NOT touch IFI itself so the only option for mitigation will be to move the parking BD pickoff, but it will be tedious to align that pickoff to steer the beam into the beam dump on top of HAM2. Given the limited time available I'll leave it as is.

We don't know what this scattering is, maybe it's the AR reflection of CWP or DKDP hitting something, maybe it's the surface scatter of CWP. I'll try to take the video from the back of the IFI output beamdump/CWP using a big inspection mirror.

Done: IM4 TRANS centering.

Rahul used pico mirror to roughly center IM4 TRANS while I was monitoring individual segments. IM4TRANS_ROUGHLY_BALANCED.png

Done: IM4 baffle (HA12) moved

As planned. The beam originally was offset in +X direction (IM4_HA12_before.jpeg shows the original location, IM4_baffle_HA12_before.mov shows the beam position), IM4 baffle was moved a bit in -X direction (IM4_HA12_after.jpg, IM4_baffle_HA12_after.mov).

Done but not really: Picturing the picos, one concern for the first ISS pico actuator.

The EndX BRS was stuck in a damping loop (I'm assuming caused by the power outage). Usually when this happens increasing the damping thresholds temperately fixes the issue, so we went ahead and did that.
It seems to only be effecting the ETMX BRS, so we left the ETMY one alone
Jim and I increased the damping thresholds from:
H1:ISI-GND_BRS_ETMX_HIGHTHRESHOLD: 2000-->4000
H1:ISI-GND_BRS_ETMX_LOWTHRESHOLD: 800-->2000

It also looks like the ETMX BRS drifted out of range (maybe due to the heater losing power and not returning to the original level?) so I've increased the voltage going to the heating plates and will check back in tomorrow to see if it's been restored

J. Oberling, R. Crouch

Yesterday we measured the initial position of the BBSS in the WBSC2 chamber, results shown in the 1st picture.  Our goal is to match the position deviations we had on the test stand for the BBS SUS cage, as that was the SUS cage position we aligned the BBS optic with; all alignment moves after the SUS cage were positioned were done with the SUS chain itself, the cage did not move again, so matching the cage deviations should correctly position the BBS optic.  As a reminder, the test stand deviations are shown in the 2nd attachment.

Based on this we will move the cartridge assembly with HEPI by approximately +2.5 mm along the X axis, +0.5 mm along the Y axis, and a CW rotation of ~500 µrad.

Robert, Ibrahim, Anamaria

We finished alignment of the CP cage baffle on ITMX, which was the last item to do regarding cage baffles. The panels are locked so they can now be removed and replaced while retaining the alignment. 

Both ITMs have the (new) face shield on. ITMY suspension is unlocked and ITMX is locked. 

J. Freed, S. Koehlenbeck, J. Kissel,

(Belated post)

Wednesday we continued from 90352, We installed the full rack for SPI in SUS R2 and made all connection between different SUS R2 racks as well as connections from TIA to DAC. (Front:IMG_6377.jpeg)(Back:IMG_6388.jpeg). As well as, hooked up to all the required power supplies. Still missing some connections namely SUS R2 to chamber connections 

The RF power measurement going out from the 2W amp to the SPI prep was measured to be 31.6 dBm for both outputs of the 2W amp (after the amp warmed up). 

This was measured by using the on site power mon w/ small power probe (Exact make and model will be added later). The site has a large power probe (the HP 8484A) but from 89523 it was found to have some strange nonlinearities. As such, the small probe was prefered for this test. Since the probe only has a 20dBm max power limit, 2x 10dBm attenuators (UNAT-10a) were used to lower the power to be able to be measured. Of course the UNATs have a 33dBm limit so special care was used to make sure that limit was not reached. This set up was calibrated by using a 0dBm signal which the probe measured as 0.1dBm. attaching the 2 attenuators the same signal read -20.0dBm (a 20.1dB difference). Then I measured the 2 ports which read 11.8dBm for the Meas output and 11.7dBm for the Ref output. Once the amp warmed up (~20 minutes of waiting with it on) these values both fell to 11.5dBm. Adding back that 20.1dB, this leaves both port with the expected output of 31.6dBm. With an error of +/-0.1dBm.

This value is 0.4dBm lower than the optics lab measurement with the larger probe but is a more precise measurement with less error.

The SPI wiring diagram D2400111 is labeled wrong. Namely it says Output 2 of 2W amp connects to the meas port of SPI prep. And Out 1 of of 2W amp connects to the ref port of SPI prep. This is wrong.  Out 1 of of 2W amp connects to the meas port of SPI prep (I physically labeled SPI_RFDist_008) and Out 2 of of 2W amp connects to the ref port of SPI prep (I physically labeled SPI_RFDist_009)

We also installed 3 BNC cables for the monitor channels of SPI Prep. These are not labeled in the wiring diagram but Jeff physically labeled them as SPI_LPMON_M1_PD, SPI_LPMON_M2_RFMEAS, and SPI_LPMON_M3_RFREF. Which monitor: the PD inside SPI prep, the RF power for the 80 MHz Meas signal, and the  RF power for the 80- MHz Ref signal respectively.

J. Kissel, T. Shaffer, M. Robinson

While in HAM2 doing BnK hammering (LHO:90493), Mitch asked us to note the serial numbers of all parts of HAM2 ISI Table Baffle Assembly (D1700335).

  Location           Drawing        Serial Number
  +Y Assembly         
       Baffle      D1700263-v1    004
       +Y Bracket  D1700264-v2    020
       -Y Bracket  D1700264-v2    014

  Middle Assembly
       Baffle      D2600042-v1    001
       +Y Bracket  D1700264-v2    013
       -Y Bracket  D1700264-v2    015

  -Y Assembly
       Baffle      D1700263-v1    006
       +Y Bracket  D1700264-v2    022
       -Y Bracket  D1700264-v2    017

Happy ICS'ing!
(Will post picture proof in due time.)

Mitchell and I placed the new central beard baffle with a cutout for SPI on HAM2. It went on without issue after Mitch reminded me how to adjust the panels.

I then attached the accelerometer to the L bracket and tried hammering in various places. There wasn't much real estate, so I'm not sure how this will turn out. Data still needs to be analyzed, and I'll post pictures of hit locations then as well.