Today Randy T and I ran power for the Cross Flow HEPA fans on the platform around BSC2.  The fans are on and turned down to low at the moment.  We also moved the dust monitor from the floor to the platform to monitor dust counts to have a better understanding before pulling the dome.

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.

Masayuki found that the JAC heater driver shuts itself down as soon as it is turned on. 

Daniel traced this back to that the heater elements are grounded somewhere. Turns out that the DB15-DB9-DCPD to DB25 in-vac tri-cable (D2500336) has a defect. One pin for Heater B Terminal D is shorted to the shield. Since the shield is ultimately connected to the chassis ground of the heater driver, and since the driver is differential, this effectively short-circuits the output of one power amplifier to the ground. Masayuki has a spare, we'll check it in the lab and will replace it.

From outside of the chamber, using DB25 breakout board on D4-F10, when everything is connected in chamber, in-air pin 13 (shield of the cable inside the chamber) is shorted to pin 8, 9 and 22 with only 2 or 3 Ohm. These are all connected to Heater B Terminal D, which is one leg of the Heater B.  In addition, pin13 and pin 10 and 23 show 54 Ohm, these are Heater B Terminal C, so this is expected (nominal resistance of the heater is 50 Ohm). Nothing is shorted to the chamber gound, which is a good news.

When the DB15 connector (that goes to the two heater elements and a thermistor) was disconnected in chamber, the only short-circuit that was observed from outside the chamber was pin 13 to pin 22 (still 3 Ohm).

When the DB25 connector was disconnected at the cable bracket, nothing shorts to anything.

The conclusion is that something is wrong with the DB15-DB25 part of the tri-cable.

Oh, D2500119-v2 says that the JAC control is on D4-F9 of HAM1, but it's on D4-F10 at LHO. This is already captured in D1002872-v10.

Squeezed in a quick photoshoot of HAM7 (right after ISI-unlocking/measurements by Jim + purge air being turned up and before Door Team sealed it up).  HAM7 was open roughly from 11:16am-11:48amPDT for photos.  Since there was only one door off, lighting wasn't great and limited to shots from the -X side of HAM7.  Used Canon DSLR camera followed by iPhone shots; snapped a handful of macro lens shots for fun.  

Photo Album (109photos) uploaded to Google folder HERE.

We have identified two mechanical issues with the JAC EOM and its mount.

Issue 1. Crystal isn't captured in the EOM assembly when we install it in a certain way, but installing it in another way to capture it might (or might not) put overly strong force on the crystal.

No I haven't dropped the real crystal, I did drop alumina piece with the same outer dimensions as the RTP crystal while testing the installation procedure.

It's probably hard for you to understand this issue if you're not familiar with the EOM assembly (D2500130) and the assembly/test procedure (google doc), look at my super-simplified cartoon (ideal.png).

EOM comprises the face plate, RTP crystal and everything else. Everything else is already assembled. The task is to sandwich the RTP between the electrode board (which is a part of "everything else") and the face plate. You'll put the face plate on a table, put RTP on top of the face plate, carefully lower everything else until the board touches the RTP along its entire length, and you bolt the face plate to the side panels. Simple.

It can be much different from that if the board is not orthogonal to the side panels, look at the second attachment. Here, the board is crooked, the distance to the face plate on the output side is smaller than on the input side (this cartoon).

Suppose that I choose to make the face plate contact with the output side plate, and bolt the face plate down. The face plate is squared up relative to the side plate, not the board, and the "everything else" part will rotate away from the face plate (or face plate rotates away from everything else) and RTP is free to move. I think this is what happened consistently (10 or so trials) in the lab today, no matter what we did, the alumina piece (i.e. fake RTP for excercize) slid out of the assembly but only after tightening the screws.

On the other hand, if I choose to make the face plate contact with the input side plate (notsoideal.png), the rotation will be in the opposite direction, the face plate is not reqlly squared up but will put a pressure on the RTP, securely captureing it. After switching the side where the face panel contacts in the lab, the alumina piece (fake RTP) never dropped (3 trials so not much statistics but 3/3 success is much better than 10/10 failure).

The problems are that we don't have any control over how much force is applied to the crystal. Moreover, in our "successful" trials, the board might not be touching the alumina piece along its entire length. Look at the picture, this is after the last (3rd) "successful" attempt with the alumina piece still in, the board and the face plate are not parallel with each other, we might be pinching the alumina thing at the corner closest to the output side. Not sure if it's always like this but it's likely.

Stephen and Michael suggest that instead of bolting the face plate firmly to the input side, there could be a gap on each side, the face plate is supported by the tension of the screws, making sure that the face is parallel to the board. I'm not necessarily a fan of the idea but we'll try.

Issue 2. One of the bolts for the EOM base is blocked by another screw head.

See the last picture. One 1/4-20 screw cannot be tightened because the 10-32 bolt head just above that blocks access. We might replace the offending bolt with 10-32x0.375" pan head screw AND use the ball head Allen key for 1/4-20, that might work.

Other issues.

We can move the mount in PIT/ROLL and YAW, but somehow it's very difficult to cause pure PIT motion, it always couples to ROLL.

When we use set screws to tilt the base and then back them off, the mount won't return to the original position, I have to push down the pivot plate toward the base plate firmly, then there's a metal clicking sound and the mount goes back. This might be related to the fact that, as of now, the dowel pin (part #14 of the assembly drawing) is a REALLY tight fit for the pivot plate as of now. 

Finally, the cable strain relief post could not be set at a desired angle using the supplied slotted washer (the only difference I was able to make is either bad angle or 180 degrees off of the bad angle). But using other washers on top of the slotted one(s) I was able to manage good-ish angle.

[Sheila, Ryan, Karmeng]

We have returned ZM2 to the original position at the beginning of O4, we alleviated some of the saturation but the ZM3 iris still require adjustment.

Power budget looks good so far. With 0.77mW exiting the OPO and reaches AM3 at the same power. We observed 0.75mW of OPO trans and 18.1mW of OPO refl on SQZT7 periscope.

R. Crouch, J. Oberling

Yesterday we began measuring the locations of the vacuum chamber support tube ends using the FARO laser tracker.  We started with the support tubes for the WBSC3 chamber and the +X ends of the WBSC2 support tubes as these were the most readily accesible.  The remaining support tubes in the LVEA (WBSC1, WBSC2 -X ends, and all WHAM chambers except WHAM7) have iLIGO-era PEM Interface Plates on them that block the support tube; some of these plates have undocumented spacers between them and the support tubes they are attached to, meaning we cannot accurately locate the support tube end w.r.t. the PEM interface plate and therefore making an accurate measurement of the support tube location impossible.  As an aside, Jim is in the process of removing these plates from the chambers (so far WHAM3 and WHAM4 are complete, WHAM1 and WHAM2 are 75% complete), so we can get at these support tube ends as the opportunity arises (he will then reinstall these plates, as they make for very convient mounts for dial indicators).

Measurement Method

This is a fairly straightforward measurement, but there is a somewhat subtle "gotcha" that needs to be accounted for to get an accurate measurement.  But first things first, we aligned the FARO to the LVEA's Building Coordinate system using our red alignment nests, then applied the X and Y axis rotations required to align the FARO to the site global coordinate system (see T0900340 for a brief overview of the coordinate systems in use).  We then loaded CAD models of the support tubes, that Ryan downloaded from the SolidWorks vault with each model in the site global coordinate system, into the FARO's control software, PolyWorks.  PolyWorks automatically reads the coordinate system information contained in the CAD files and places these models in position w.r.t. to the site global coordinate system.  This gives us nominal locations of the support tube ends, a guide for our measurements, and also a nice visual reference for where everything is positioned.

Now for the "gotcha."  The physical support tubes have a hole in the center of each end that is not represented in the CAD model, and this hole is large enough that the FARO target (a Spherically Mounted Retroreflector, or SMR, with a 1.5" diameter) sits slightly inside the hole.  This means that when you're taking a measurement of the center of the support tube end using this hole the SMR is not measuring the location of the actual support tube end, it is a few mm inside of it.  To account for this we did the following:

1. Use the SMR to get the coordinate corresponding the the axial length of the support tube on either side of the end and calculate the average (to remove any yaw in the support tube)
   • Using WBSC3 as an example, the support tubes lie parallel to the y-axis.  So we touch the SMR to either side of the support tube and record the y-axis coordinate, then calculate the average
   • We do this for each individual support tube end, as each one is slightly different
2. Use the SMR to get the same coordinate, but this time with the SMR sitting in the center of hole of the support tube
3. Calculate the difference between the two, to get the offset required for an accurate measurement
4. In the PolyWorks software:
   • Use the CAD model to create points representing the center of each end of the support tube
   • Create a line between each end point, representing the theoretical centerline of the support tube
   • Create a Measurement Point by offsetting the support tube end point along the centerline and to the inside of the support tube by the amount calculated in steps 1-3
5. Congratulations, you now have a measurement point that represents the nominal location of the support tube end, taking into account the offset required due to SMR positioning inside the center hole

To take the measurement we used the Build/Inspect mode in PolyWorks.  In this mode we have to be sure to select the "Towards Object" compensation method, which automatically compensates for the radius of the SMR (3/4", or 19.05 mm).  If "None" is selected the FARO measures to the center of the SMR, but our measurement point is at the edge of the SMR, since that's what is physically touching the support tube, so we need to compensate for that radius.  This gives us the deviations of the measurement point, which can then applied to the point representing the center of each support tube end to give their measured location.  The results of our measurements are shown in the attachment.  Since we had measurements for each end of the WBSC3 support tubes I also added a distance feature representing the measured length of each WBSC3 support tube.

Wrapping Up

Some points for discussion/further thought.  Keep in mind that the BSC support tubes are not exact representations of where their respective optics are; we only aligned the optic during aLIGO install, and in the end didn't really care where the support tubes ended up as long as HEPI had enough range to work.  This means that any deviation from nominal seen in the support tube ends is not an indication of misalignment of that chamber's optic.

1. The WBSC2 support tubes were supposed to be lowered by ~2.5 mm to account for the BS z-axis position being at -82.9 mm instead of -80.0 mm; this was done because, while the 4km arm cavities are flat in global coordinates the IFO input and output arms are not, so the BS had to be lowered to properly direct the beam (which rises in elevation while traversing the PRC) into the arms.  Therefore our expectation is that the WBSC2 support tubes are below the nominal z-axis coordinate of 1130.3 mm (we recently discovered that this change was not accounted for in the SolidWorks models for the sites).  While the global z-axis coordinate for all BSC support tubes is 1130.3 mm, if WBSC2 was lowered as required we would still expect to see a z-axis deviation in the measured points, but this is clearly not the case.
   • I was at LLO working on PRC alignment when the WBSC2 in-chamber alignment was started, so I have no memory of the initial positioning of the BS in-chamber; this was done by Hugh Radkins and Doug Cook (I had returned in time for pitch/yaw alignment).  Looking back at their notes they had to move HEPI +X by 4.6 mm, -Y by 2.3 mm, and +Z by 0.4 mm to position the BS, so this does not fully account for apparent lack of support tube lowering.  But as stated above, this does not necessarily mean the BS is too high (we'll know that for sure when we measure it once WBSC2 is opened in March 2026).
2. The measured length for the WBSC3 support tubes is shorter than their as-designed length of 3657.6 mm.  Not sure why at this point.
   • Once we get more full BSC support tube measurements we'll have more info to work from
3. The WBSC3 +X/-Y support tube end is a decent bit further in the +Y axis than expected.  Again, not sure why.
   • Looking back at my notes from install we had to move WBSC3 HEPI in the +Y dircection to properly place ITMx, so the overal deviation direction of these support tubes isn't a surprise.

This work was associated with LHO WP 12947, which also included the WBSC1 +X support tube ends.  Those support tubes still have PEM interface plates installed, so we are currently unable to measure them (will do in the future once the plates are removed).  Since we completed the rest of the measurements involved, I've closed the WP.

Betsy, Fil, Rahul

Today we kicked started the installation activities in HAM1 chamber for the Jitter Attenuation Cavity (JAC). Given below are the things we placed on the ISI table - they are all roughly positioned and dog clamped. 

1. Tip Tilt JM1 - now connected to electronics chain, having some issues with the bosem adc counts etc, will continue looking into it.

2. Tip Tilt JM3 - now connected to the electronics chain, bosem centered, will proceed for health checks once the chassis and electronics chain looks okay.

3. The two periscopes for the JAC, Type 121 and 132 - assembly report posted by Jennie - 88574.

4. Some optics on Siskiyou mount were also added to the table.

I am attaching pictures which shows the above mentioned things added to the table - and for comparison a picture showing before any addition was (here) made.

Fil also performed group loop checks on JM1 and JM3 and did not find any issues with them.

J. Kissel, D. Sigg, D. Barker
ECR E2100485
ECR E2200401
WP 12901

Continuing on the deprecation of 18-bit DAC path (ECR E2100485), we upgraded the h1iscex's DAC0 card today from an 18- to a 20-bit DAC. One of the front-end models that use that DAC is the h1pemex model.

Here's the before vs. after for the models. While there, I found and left the new ADC card from ECR E2200401's PEM sensor array expansion. I'd thought it was installed solely for characterizing the 32CH LIGO DAC, but it had only been temporarily used for that. It should be there! And also, the electric field meter ADC should also remain there.

If the PEM team wants to account for the factor of 4x gain change in the DAC calibration, I installed new DACOUTF filters upstream of the GDS filters that are used to drive the DACs.

The model has been committed to
    /opt/rtcds/userapps/release/pem/h1/models/
        h1pemex.mdl : r28026 --> r34059

Randy and I installed new CR ceiling.

Betsy had a local company fabricate a C3 ceiling for our Mega Cleanroom. This ceiling has velcro opening to allow access for Septum removal. Opening extends to end of CR opening on the -X side and ends just short of the +X opening. 

J. Kissel, M. Todd, S. Dwyer

Just recording this for posterity in case: Matt and I wanted to (continue) parallelizing our work on characterizing the ISS Array at full / nominal power (60W into the PSL) and characterizing RPM dynamics for future HSTS Estimator modeling, respectively. The estimator team discovered a week or two ago that PRM has a different dynamical response when the SUS is ALIGNED vs. MISALIGNED. So, I misaligned IM4 and PR2 to ensure the 60W didn't go anywhere but a fixed location, and aligned PRM. 

The worry is that IM4 doesn't have a "safe" designated fixed location to dump its reflected beam when misaligned -- there's no "parking dump" like there is for PRM. So -- this an aLOG to indicate the times of high power with IM4 misaligned and what little info we have about the physical position.

I say "what little information about the position we have" because IM4, which is a HAUX suspension -- while IM4 has recently had its OSEM sensor PD sat amp upgraded, we have not measured or installed an absolute calibration for the sensors with an ISI injection. We know from other suspensions, that OSEM PDs can have factors of 2x to 3x errors between the "generic calibration based on electronics and [likely ancient] open light current measurement" and the modern absolute calibration from the ISI GS13s.

There *is* a calibration of the IM4 alignment sliders -- installed in Apr 2024 (LHO:77211). 
However, that calibration was based on the OSEM sensor PDs. 
So we have to take the fidelity of this calibration with a huge grain of salt a la the above distrust in OSEM PD calibration.

So -- IM4 had the following alignment offsets requested of its sliders: 
              OFFSET       OUT16
             ["urad"]    [EB-DAC ct]
    P        +114.539     +1248.53
    Y        +111.103      +625.387

and its *misalignment* offsets -- which are not calibrated in the front-end, but I've calibrated them using the (P,Y) = (10.9005 , 5.6289) [EB-DAC ct / "urad"] calibration from LHO:77211 here: 
              OFFSET       OUT16
             ["urad"]   [EB-DAC ct]
    P         +50.915      +555.0
    Y         +98.598      +555.0

So, misaligned, that give a total requested displacement of  
              OFFSET       OUT16
             ["urad"]   [EB-DAC ct]
    P         165.454     1803.532
    Y         209.701     1180.388

IM4 was misaligned, with PRM aligned and PR2 misaligned, and 60W into the IMC from 2025-10-28 16:08 UTC to 2025-10-28 17:06 UTC. 

After 17:06 UTC, the IMC power remained at 60W, but I aligned IM4 and PR2 and misaligned PRM. (The normal "IFO DOWN" configuration).
(So yes, we didn't turn the IMC power down before we went from misaligned to aligned, either.)

Trying to narrow down why TMS x is involved in lock losses we have replaced the TMS coil driver that works on F1,2,3 and LF.  Chassis S1102670 was replaced with S1102666.  The operator returned the system to damping.  This is a wait and see test.

We're assembling the first unit that incooporates all upgrades including the QPD tilt and here are minor problems we've stumbled upon. (No ISS array unit with an upgrade to tilt the QPD (E1400231) has been assembled before as far as I see and nobody seems to have cared to update all drawings.)

First picture is an example of the QPD before upgrade. QPD assembly (D1400139) and the cable connector assembly (D1300222) are mounted on the QPD platform by the QPD clamp plate (D1300963-v1, an older version) and a pair of split QPD connector clamps (d1300220). Two pieces of kapton insulation sheets are protecting the QPD assy from getting short-circuited to the platform.

After the upgrade, the QPD assy sits on top of a tilt washer (D1400146, called beveled C-bore washer) that tilts the QPD by 1.41deg in a plane that divides YAW and PIT plane by 45 degrees (2nd picture). The bottom kapton will go between the washer and the QPD platform plate.

Problem 1: Insulation between the QPD clamp and the QPD pins is a bit sketchy.

Titled QPD means that the bottom of the QPD assy is shifted significantly in YAW and PIT. A new asymmetric QPD clamp plate with tilted seating for the screws  (D1300963-v2) has been manufactured to accommodate that. But we have no record of updated kapton insulators, so the center of the clamp bore doesn't agree with the kapton (3rd picture, note that the QPD rotation is incorrect in this picture, which had to be fixed when connecting the cable). Since the tilt washer is not captured by anything (it's just sandwiched between the clamp and the platform plate), it's not impossible to shift the QPD assy such that some of the QPD pins will be grounded to the clamp and thus to the QPD platform plate.

You must check that there's no electrical connection between the QPD assy and the platform each time you adjust the QPD position in the lab.

Problem 2: New QPD connector clamp posts are too long, old ones are too short.

Old posts for the QPD connector are 13/16" long, which is too short for the upgrade because of the tilt washer, see 4th picture where things are in a strange balance. It seems as if it's working OK, but you can wiggle the post a bit so the post slides laterally relative to the clamp and/or the platform, it settles to a different angle and suddnly things become loose. To avoid that, you tighten the screws so hard that they start bending (which may be already starting to happen in this picture).

Also, because the clamp positions are 45 degrees away from the direction of tilt, one clamp goes higher than the other.

To address these, somebody procured 1" and 15/16" posts years ago, but they're just too tall to the point where the clamps are loose. If anything, what we need are probably something like 27/32" and 7/8" (maybe 7/8" works for both).

We ended up using older 13/16" posts, but added washers. Two thin washers for the shorter clamp, two thin plus one thick for the taller one (5th picture). This works OK. Shorter screw is the original, longer screw was too long but it works.

Problem 3: It's easy to set the rotation of the QPD wrong.

When retrofitting the tilt washer and the newer QPD clamp plate, you must do the following.

1. Completely loosen the connector clamps and the QPD clamp to remove the QPD/connector assy as one unit.
2. Put the tilt washer on top of the kapton insulation sheet at the bottom. The notch mark on the washer must be pointing the 45deg edge of the platform plate (D1300719-v2), see the 6th picture.
3. Separate the cable connector from the QPD to free the now-obsolete QPD clamp (-v1) that is captured between the QPD and the connector. I inserted a razor blade between the connector and the QPD assy and pried.
4. Put the assymmetric QPD clamp (-v2) on the top kapton insulation, paying attention to the direction of the new clamp using the 3rd picture as the reference.
5. Make sure that the rotation of the QPD assy is the same as before because the pins of the QPD are not symmetric. There's no physical mark on the QPD assy itself.
   1. If you're unsure, rotate the QPD assy such that the QPD pins will go to the right sockets on the connector using picture 7. Remember that QPD surface faces the platform down and the drawing of the connector is viewed from the top.
   2. After checking it several times, tighten the QPD clamp.
   3. Put the connector on. Again use picture 7 to put it on at the correct angle.
   4. After checking it several times, tighten the connector clamps.

I screwed up and put the QPD on the connector at a wrong angle. It's easy to catch the error because no quadrant responds to the laser, but it's better not to make a mistake in the first place. It will help if the QPD assy barrel is marked at the cathode-anode1 corner.

It seems that D1300222 and D1101059 must be updated. Systems people please have a look.

D1300222: A tilt washer (D1400146), a new QPD clamp (D1300963-v2) and two sheets of kapton insulation are missing. Spacers are longer than 13/16".

D1101059: Explicitly state that part #28 (D1300963, QPD clamp) must be D1300963-v2.

To investigate the 70Hz feature in HAM1 chamber, which Jim reported in his alog (LHO 84638) I started looking into the structural resonances of the periscope which is installed in HAM1 (see two pictures which TJ sent me, was taken by Corey here - view01, view02) .

Betsy, handed me a periscope (similar but not exactly the same) for investigation purpose, which is now setup in staging building. I attached an accelerometer to the top of the periscope and connected it to the front end of the B&K setup for hammer impact measurements - see picture of the experimental setup here. 

At first I used two dog clamps to secure the periscope. The results of the two dog clamp B&K measurement is shown in this plot (data from 0.125 to 200Hz)) - one can see a 39Hz feature in the Z hit direction. See zoomed-in (30-100Hz) figure here.

Next, I attached a third dog clamp, just like in HAM1 chamber and took a second round of measurements (especially for Z direction impact). 

This plot compares the two vs three dog clamps scenario on the periscope and one can see that the resonance mode has been pushed up from 39Hz to 48Hz. 

Attached is the Trello snapshot showing the last week or so of progress and this week's trajectory to opening gate valves and recommissioning the H1 detector.  Pretty on target.

For chamber closeout finalization, this morning I 

* placed a 3" contam control wafer on the center of the HAM1 table today
* took a few last pics, removed the stowed 3x septum covers (missed removing the 4th one from the septum, thanks vac good eye, pic 4)
* looked around for left behind tools
* retraced the beam path to look for errand in-the-way cables (none observed)
* inspected under and around lower area of table for left goods (none found)
* cleaned up last tool pans to get ready for doors
* particle counts were <50 all sizes, zero most often
* purposefully coiled the to-be-used in post O4 next vent cable with the peek connector not grounding to anything - it sits in the PSL side door well below the table

* all subsytems have signed for doors, so we are putting doors on.

Morning (JennieW, Rahul, Keita)

We used the PRX flashes to align the POP path.

POP periscope location is good but the drawing is not.

The POP periscope position, which was set yesterday by Camilla and others, was right. That means that the drawing on D1000313-v19 is wrong. The periscope in reality is about an inch toward -Y direction relative to D1000313-v19. See the first picture, which was shot with a cellphone inserted under the top periscope mirror and looking straight down the bottom mirror. This means that the dichroic (M12) needed to be shifted by the same amount too.

Since the distance betwen the IFO and the lens for POP WFS doesn't matter that much, everything downstream (i.e. 90:10, PM1 tip-tilt, a lens, 50:50 and POP LSC as well as POP WFS) will be installed using the drawing.

We mainly rotated the periscope mirror clamps around the post for rough alignment, but we might have changed the mirror height by a millimeter or two in the process. 

PM1, which is calld that because it's the 1st (and the last) suspended Mirror for POP, is somehow called RM3 in D1000313. Systems please fix it.

Set the IR beam spot height/position on the periscope as well as the dichroic

The IR beam is supposed to be about 6mm or 1/4" lower than the center line of both of the periscope mirrors as well as the dichroic. This is because the green ALS beams are supposed to be ~13mm higher than IR. See L1200282 “CPy-X, CPx-Y” case on Table 1.

Top Periscope Mirror

It was almost impossible to see how much the beam is lower than the center of the top and bottom periscope mirror. Using the IR viewer card, I and Jennie agreed that the beam is lower than the center, but we could not quantitatively say how much especially on the top. We'll leave it as is, and if the green beam from the end station is too high we will have to use pico because we periscope is already as high as possible.

Bottom peri mirror

If everything is as intended, the bottom periscope mirror is 4" high from the ISI surface and the POP beam is 1/4" lower than that, therefore the POP beam is (1-0.25*sqrt(2)) = 0.646" = 16.4mm away from the bottom edge of the mirror.

Using a ruler in chamber (and measuring the dimensions of a spare Siskiyou mount using caliper), the height of the bottom periscope mirror center was calculated to be ~4.07" from the ISI surface, i.e. 0.7" too high. This means that, when the beam height measured from the ISI is as designed (i.e. 4"-1/4"), the POP beam is (1-(0.25+0.07)*sqrt(2))=0.547"=13.9mm away from the bottom edge of the mirror.

If you have difficulty understanding this, see the cartoon.

POP beam radius is ~2mm, so 13.9mm (or even 13mm for that matter) looks like a safe distance to me. I don't see the need to readjust the height of the bottom periscope mirror.

I adjusted the top periscope mirror to set the beam height right after the bottom peri mirror to be ~3.75" using the IR viewer card and a ruler.

Dichroic

I placed the dichroic about 1" into -Y direction relative to the drawing (because I had to), and used the bottom periscope mirror to set the beam height close to the dichroic to be ~3.75".

Then I used the dichroic to steer the beam into the direction of the location for PM1 without placing 90:10.

For the beam profile measurement, the downstream alignment is done without 90:10. Later we will install 90:10 back in place and do the final alignment.