[Yuta, Tega]

We aligned the BS, ITMY, and ETMY PIT and YAW to get the flashing on X-arm whilst also keeping the flashing of Y-arm. From attachment 1, it is clear that POXDC photodiode is not receiveing any light, so our next task is to work on POX alignment.

[Yuta, Tega]

We needed to sort out the POXDC signal so we could work on X-arm alignment. Given that POXDC channel value was approx 6 compared to POYDC value of approx. 180, we decided to open the ITMX chamber to see if we could improve the situation. We worked on the alignment of POX beam but could not improve the DC level which suggests that this was already optimized for.  As an aside, we also noticed some stray IR beam from the BS chamber, just above the POX beam which we cold not identify.

Next we moved on to the POP beam alignment, where we noticed that the beam level on LO1 and POP_SM4 was a bit on the high side. Basically, the beam was completely missing the 1" POP_SM4 mirror and was close to the top edge of LO1. So we changed TT2 pitch value from 0.0143 to -0.2357 in order to move the beam position on POP_SM4 mirror. This changed the input alignment, so we compensated using PR2 (0.0 -> 49.0) and PR3 (-5976.560 -> -5689.800). This did not get back the alignment as anticipated, so we moved ITMY pitch from 0.9297 to 0.9107. All of these alignment changes moved the POP beam down by approx 1/5 of an inch from outside the mirro to the edge of POP_SM4 mirror, where about half of the beam is clipped.

Next Steps:

We need to repeat these aligment procedures with say 1.5 time the change in TT2 pitch to center the beam on POP_SM4 mirror.

[Anchal, JC]

We first aligned the single arm cavity resonance for both arms to get maximum flashing. As we opened the chamber, I found that the POP beam was mostly hitting the POP_SM4 mirror but was clipping about 2 mm on the top edge.

I used TT2-PR3 to lower the injection beam angle and moved pairs of ITMY-ETMY, and ITMX-ETMX to recover as much flashing as I could in the both arms. Then, I moved PR2 in pitch from 49 to 71 to maximize the arm flashing again. After these steps, the POP beam was clearly within the POP_SM4 mirror but still in the upper half of the optic and there was maybe just a mm of clearance from the top edge. I decided to raise POP_SM4 mirror by 0.14" spacer. Now the beam is still in upper half of the mirror but has a good clearance from the edge.

The POP beam is coming outside in the in-air table at as a rising beam in the nominal path near the center of the window. This beam needs to be directed to the POP camera and RFPD on the far-side of the table.

Next steps:

• In-air table work: Setup POP camera and RFPD.
• In ITMX chamber, rotate ITMX Oplev mirror to clear the oplev beam off POP_SM5. Change oplev beam path outside accordingly.
• Install green transmission from X-arm steering mirrors in BS chamber.
• Install 4 steering mirrors in ITMY chamber at the two outputs of BHD BS to direct the beam outside.
• Figure out POX11 rotation angle and get XARM locking as well.

[Yuta, Tega]

In order to setup POP camera and RFPD on the ITMX table, we decided to first work on the IMC and X/Y-arm alignment.

IMC alignment:

We zeroed IMC WFS outputs and aligned IMC manually to get IMC transmission of 1200 and reflection of 0.35.

Y-arm alignment:

We used the new video game tool that moves the pairs of mirrors - PR3 & ETMY, ITMY & ETMY - in common and differential modes. This brought the Y-arm flashing to 0.8. Note that we used the _OFFSET bias values for PR3 & ETMY alignment instead of the _COMM bias values.

X-arm alignment:

We repeated the same procedure of moving the pairs of mirrors - BS & ETMX, ITMX & ETMX - in common and differential modes but manually this time. This brought the X-arm flashing to ~1.0.

I have made a Simulink diagram to use in the MICH modeling (attachment) for the homodyne angle detection scheme. The model will be used for each optic separately and the noises will be combined in quadrature.

I gathered some more bits of info to fill the Simulink boxes. This is what I have so far:

[Yuta, Anchal]

We investigated why WFS loop wasn't working. It seemed like WFS1 PIT error signal has a huge offset which would push the loop to misalign all optics' PIT. So we did the following steps:

• Cover the WFS with Aluminium foils. Run Sitemap>IOO>C1_IOO_WFS_MASTER>!Actions>Correct WFS DC offsets.
• Then center the WFS beams on the QPDS while looking at C1:IOO-WFS1/2_PIT/YAW_DC channels.
• Then Switch off WFS loop, Switch off Autolocker, toggler the PSL Shutter so that IMC unlocks and does not catch lock back, and tehn run Sitemap>IOO>C1_IOO_WFS_MASTER>!Actions>Correct WFS RF offsets.
• The above script found significant changes required in WFS1 RF offsets. After this, we opened the shutter and WFS loops were working fine.

As I went to correct the ITMX Oplev mirrors, I found that both mirrors were placed in very different positions than the design position. Part of the reason I think was to preserve outside oplev path, and party because a counterweight was in ITMXOL1 position. I had to do following steps to correct this:

• I noted down level meter readings of the table before making any changes.
• I removed the counter weight from near the center of the table.
• I placed the Oplev mirrors in the nominal positions.
• I placed the counter weight near previous position.
• I moved a edge hanging counter weight to get back the level meter to its previous state coarsely.
• Then I used dataviewer to find the previous OSEM PD monitor values and changed ITMX PIT and YAW to come closer to those PD values. And voila, I regained the flashing on Xarm. I nudged the ITMX pit and yaw bit more to maximize it.
• I then went back to aligning the Oplevs properly.
• Then I adjusted the POP mirrors to get the beam back through center of window. This was very tricky and took a lot of time.
• Now the beam is going through near center and the oplev beams are far away enough from POP_SM5.
• On the outside table, I noted the POP beam and the oplev beam. I corrected the pit of the returning beam to get the oplev beam at nominal height on outside table.

ITMX Sat Amp is flaky

[Anchal, Paco]

During the above work, i must have kicked the cable between the vacuum flange and the satellite amplifier box for ITMX. This disconnected all the OSEMs and Coils. We tried several things to debug this and finally found that nudging the connections on Sat Amp box brought the OSEMs and coils back online. Note that the connector was not partially out or in a state that obviously showed disconnection of the pins. I'm glad we are putting in new electronics soon for the vertex optics as well.

Next steps:

• I showed Tega the returning oplev beam and the POP beam coming out of the ITMX chamber.
• The Oplev beam paths need to be adjusted.
  • The ongoing beam steering mirror is blocking the returning beam, so the ongoing path needs to be changed.
  • First setup two irises to save ingoing path.
  • Then make space for the returning beam by changing the steering mirror positions.
  • Then recover the ingoing path to the center of irises.
  • Steer the returning beam to the QPD.
  • Then maximize the flashing on XARM and center the oplev to save this position.
• POP beam needs to be directed to previous setup on far side of table.
  • The POP beam is coming out at the rising angle.
  • This is good for us if we do bit unconventional stuff and transfer the beam to other side of table at an elevated height. Given how close all the beams are coming out of the viewport, I think this is the best solution in terms of saving time.
  • Get the beam down to the old setup which was camera and photodiodes all aligned.

[Paco, Tega]

Started work on the relocating the green transmission optics, cameras and PDs. Before removing the any of the optics, we checked and confirmed that the PDs and Cams are indeed connected to the GRN TRX/Y medm channels. Then added labels to the cables before moving them.

Plumbing:

• Moved all power and signal cables for the PDs and cameras from PSL table to BS table. See attachment #1

Relocated Optics & PDs & Cameras:

• TRX and TRY cameras
• TRX and TRY PDs
• 1 BS, 2 lens for PDs and a steering mirror, see Atachement #2

[Don, Koji]

Don is working on finalizing the BHD Platform design. All the components on the BHD platform are almost populated and aligned.

Don is still working on the table legs so that we can detach the legs when we need to float the table in the future.
The BHD BS mount will have a third picomotor so that we can steer 3 dof with the mount while the remaining dof needs to be provided by the OMC.
The BHD BS position is going to be adjusted so that the incident and trans beams have sufficient clearance.
The OMC legs (kinematic mounts) need more work so that we can adjust their positions for initial setup while they can be the reference for the reproducible placement of the OMCs.
The OMCs are rigidly held with the legs. For the damping of the 1-kHz body bode, which has a relatively high Q, there will be a dissipative element touching the glass breadboard.

I quickly ran the FEA model to check the resonant freqs of the BHD platform.
The boundary conditions were:

• The platform was not loaded
• FIxed constraints were given to the five legs

Don has optimized the cut-out size for the OMCs to increase the rigidity of the plate. Also, the ribbed grid is made at the bottom side.

The lowest mode is at 168Hz. Because there is no leg around, it seems reasonable to have this kind of mode as the fundamental mode.
The other mode lined up at 291Hz, 394Hz, 402Hz, ...
The mode freqs will be lower once the platform is loaded. But as the unloaded platform mode, these mode freqs sound pretty good numbers.

[JC, Tega]

Tega and I cleaned up the BS OPLEV Table and took out a couple of mirrors and an extra PD. The PD which was removed is "IP-POS - X/Y  Reversed". In addition to this, the cable is zip-tied to the others located on the outside of the table in case this is required later on. 

Next, we placed the cameras and mirrors for the green beam into their postions. A beam splitter and 4 mirrors were relocated from PSL table and placed onto the BS Oplev table to complete this. I will upload the picture of the newly updated photo with arrows of the beam routes.

Followed the steps below to complete the ITMX optlev installation. The ITMX optlev return beam now reaches its QPD without being blocked by the input steering mirror.

Although, I centered the ITMX optlev readout, this was not done when the XARM flashing is maximized bcos the IMC chamber was being worked on, so this should be done later when the IR beam is back.

[Yuta, Paco]

We installed GRX_SM1, GRX_SM2, and finished aligning the GRY_SM1, and GRY_SM2 steering mirrors in the BS and IMC Chambers. GRY_SM1 was slightly misplaced (by ~ 2 inches), so we had to move it slightly. Luckily this didn't grossly misaligned the IMC, and we could recover quickly by touching MC1 & MC3 pitch, and MC1 slight yaw.

Then, Yuta installed GRX_SM1, and GRX_SM2 by repurposing two 45 AOI P-Pol GR transmission mirrors on the flowbench. Because one of the weights on the BSC was in the way of GRX_SM2, it was shifted it before installation. This probably shifted the balancing of the whole table. The GRY beam is still not lock-able to the YARM, so as a proxy for GRY transmission beam we used the slight GRX reflection from the BS, and noted slight clipping through PR3 (in transmission). This should probably be checked with GTRY.

We believe this is the last installation operation of this vent.

We made sure the WFS feedback loop is working, and realigned the arm cavities to be flashing.

[Yuta, Tega]

We finally managed to steer the AS beam from ITMY chamber, through BS and IMC chambers, to the in-air AP table.

We moved the AS5 mirror north to its nominal position and we also moved the ASL lens on BS chamber back to its nominal position. Attached photos are taken after today's alignment work.

I successfully steered out the two output beams from BHD BS to ITMY table today. This required significant changes on the table, but I was able to bring back the table to balance coarsely and then recover YARM flashing with fine tuning of ITMY.

• The counterweights were kept at the North end of the table which was in way of one of the output beams of BHD.
• So I saved the level meter positions in my head and removed those counterweights.
• I also needed to remove the cable post for ITMY and SRM that was in the center of the table.
• I installed a new cable post which is just for SRM and is behind AS2. ITMY's cable post is next to it on the other edge of the table. This is to ensure that BHD board can come in later without disturbing existing layout.
• I got 3 Y1-45P and 1 Y1-0 mirror. The Y1-0 mirror was not installed on a mount, so I removed an older optic which was unlabeled and put this on it's mount.
• Note that I noticed that some light (significant enough to be visible on my card) is leaking out of the 45P mirrors. We need to make sure we aren't loosing too much power due to this.
• Both beams are steered through the center of the window, they are separating outside and not clipping on any of the existing optics outside. (See attachment 1, the red beam in the center is the ITMY oplev input beam and the two IR beams are the outputs from BHD BS).
• Also note that I didn't find any LO beam while doing this work. I only used AS beam to align the path.
• I centered the ITMY oplev at the end.

Next steps:

• LO path needs to be tuned up and cleared off again. We need to match the beams on BHD BS as well.
• Setup steering mirrors and photodiodes on the outside table on ITMY.

[Anchal, Yuta]

We checked POX and POY RF signal chains for sanity check since Xarm cannot be locked in IR stably as opposed to Yarm.
POX beam seems to be healthy. This issue doesn't prevent us from closing the vacuum tank.

POY
 - RF PD has SPB-10.7+ and ZFL-500NL+ attached to the RF output.
 - At the demodulation electronics rack, SMA connectors are used everywhere.
 - With Yarm flashing at ~1, RF output has ~24 mVpp right after RF PD, ~580mVpp after SPB-10.7+ and ZFL-500NL+, and ~150mVpp at right before the demodulation box.
 - There is roughly a factor of 3 loss in the cabling from POY RF PD to the demodulation rack.
 - Laser power at POY RF PD was measured to be 16 uW

POX
 - RF PD doesn't have amplifiers attached.
 - At the demodulation electronics rack, N connector is used.
 - With Xarm flashing at ~1, RF output has ~30 mVpp right after RF PD, and ~20mVpp at right before the demodulation box.
 - Losses in the cabling from POX RF PD to the demodulation rack is small compared with that for POY.
 - Laser power at POX RF PD was measured to be 16 uW

Summary
 - POX and POY RF PDs are receiving almost the same mount of power
 - POY has larger error signal than POX because of RF amplifier, but the cable loss is high

Conclusion
 - There might be something in the electronics, but we can close the vacuum tanks

After Xarm and Yarm were aligned by Anchal et al, I aligned AS and REFL path in the AP table.
REFL path was alreasy almost perfectly aligned.

REFL path
 -REFL beam centered on the REFL camera
 -Aligned so that REFL55 and REFL33 RFPDs give maximum analog DC outputs when ITMY was misaligned to avoid MICH fringe
 -Aligned so that REFL11 give maximum C1:LSC-REFL11_I_ERR (analog DC output on REFL11 RFPD seemed to be not working)

AS path
 -AS beam centered on the AS camera. AS beam seems to be clipped at right side when you see at the viewport from -Y side.
 -Aligned so that AS55 give maximum C1:LSC-ASDC_OUT16 (analog DC output on AS55 RFPD seemed to be not working)
 -Aligned so that AS110 give maximum analog DC output

I was finally able to set up a stable suspension model with the help of Yuta and I'm now ready to start doing some MICH noise budgeting with BHD readout. (Tip: turns out that in the zpk function in Matlab you should multiply the poles and zeros by -2*pi to match the zpk TFs in Foton)

I copied all the filters from the suspension MEDM screens into a Matlab. Those filters were concatenated with a single pendulum suspension TF with poles at [0.05e-1+1i, 0.05e-1-1i] and a gain of 4 N/kg.

I multiplied the OLTF with the real gains at the DAC/DAC/OSEMs/Coil Driver and Coils. I ignore whitening/dewhitening for now. The OLTF was calculated with no additional ad-hoc gain.

Attachment 1 shows the calculated open-loop transfer function.

Attachment 2 shows OLTF of ETMY measured last week.

Attachment 3 shows the step and impulse responses of the closed-loop system.

[Anchal, Paco, Yuta]

• We aligned AS path avoiding any clipping to the AP table where we setup a camera with a lens.
  • To do this we had to move AS6 in North direction for ~1cm.
  • The Injection table was imbalanced by this move to drop the IMC transmission to half.
  • We did not balance the table again, we steered the input mirror to reach to 1000 counts (out of 1200 nominal) and then used WFS loop to get to the last bit.
  • The input to the arm cavities did not change much, XARM was still flashing to 0.8 max height and YARM to 0.2. We recovered these easily using the cavity mirror pair.
• We aligned the LO beam to be spatially matched on BHDBS with AS path.
  • The LO beam was steered to roughly overlap with the AS beam outputs on the BHDBS.
  • However, the LO beam size is very large and diverges after LO4.
  • According to 40m/15379, the 0.15m ROC of LO4 right after the beam waist is supposed to collimate the beam to a 522 um waist.
  • We confirmed that LO4 is marked as a 0.15m ROC mirror on its edge and the HR coating is facing the incident beam.
    • Conjecture (AG): The coating was applied to the flat side of the optic instead of the curved side.
    • This would explain why the beam is continuing to diverge after reflecting from LO4, and diverging fast.
  • We need to fix this issue before pumping down otherwise the mode matching would be too poor in BHDBS to have any meaningful results.
• The output of BHDBS was steered out and a GigE camera is set up to see this path.
  • The camera is set to see the transmitted AS beam from BHD BS (and reflected LO beam).
  • But the camera is unable to see any LO beam due to large divergence.
  • The LO beam essentially disappears after ~30 cm from the BHDBS.

[Anchal, Paco, Yuta]

SRM Placement

• SRM was moved from its parked location to the nominal position in the ITMY chamber.
• This imbalanced the table a lot as all SOS towers ended up on the south side of the table.
• I needed additionally three SOS tower side walls to recover the balance of the table.
  • I initially tried to use a level meter on my phone which claimed to have 0.1 degrees of accuracy. But it turned out to be a bad idea.
  • Eventually, I used the spirit bubble level meter we have, along with the OSEM values of ITMY, AS1, and AS4.
• At the end, the table is balanced as it was before, all SOS are damping usually.

SRM Sat Amp Box setup

• SRM Gold Box Sat Amp was found near the BS chamber.
• This box was moved to the ITMY chamber.
• The new flange on the East end was marked earlier for SRM. This flange on the vacuum side was connected with new in-vacuum blue ribbon cables.
• We had previously moved the cable post for SRM (40m/16849) behind AS2. This cable post is connected to the old in-vacuum cable.
• It would have changed the table balance to remove this cable post and connect new in-vacuum cables to it, so we decided to do this in the next vent when we put the BHD board on the table.
• For now, we connected the old in-vacuum cable to the new in-vacuum blue ribbon cables inside.
  • Note, that the old in-vacuum cable has a gender flipping section which also mirrors the pin layout.
  • We installed pin mirroring cables on the outside between the Sat Amp Box and the vacuum flange to revert back the additional mirroring.
  • However it happened, now the Sat Amp Box is working, with all OSEMs and coils alive.
• One peculiarity we found was that the SRM face OSEMs have only about 250-300 um of range, which is roughly 3 times less than the other OSEMs in other SOSs.
• SRM side OSEM however behaves normally.
• After installment, at the free-hanging state, SRM LL OSEM is saturated (too bright) and other face OSEMs are close to total brightness state.
• We'll first put the alignment offsets to get the SRM perpendicular to the beam coming from SR2 and then center the OSEMs in this tiny range.
• The low OSEM range could be due to improper biasing from the Sat Amp Box. Hopefully, with new electronics, this issue would go away in future.

[Paco]

The SRM Oplev injection and detection paths interfere heavily with the POY11. Due to the limited optical access, I suggest we try steering POYM1 YAW and adapting the RFPD path accordingly.

I centered WFS1 PD so that IMC WFS Servo does not go out of range.

[Anchal, Paco, Yuta, JC]

SRM Oplev setup

• We setup SRM oplev path for the aligned position of SRM.
• This was bit hard, because the return beam was following almost the same path as the input beam, and the return beam had become about 1 cm in diameter.
• We replaced one of the in-air steering mirror of SRM op-lev input beam with a 1 inch BS on a non-steeerable mount.
• The returning oplev beam is picked at transmission from this BS.
• Note: we are not sure if this BS is actually coated for IR or Visible. We couldn't find a visible BS in the lab. We should order a 2 in diameter visible BS to be placed in this position.
• Half of the input beam would be used for PRM Oplev input.
• The returning beam was focused with a 100mm focal length lens. Again, this lens is not verified to be for visible wavelength. We think it might have an AR coating for IR. We should get a visible lens for this position also.

PRM Placement

• PRM placed in nominal position + 2 cm, East.
• Currently, PRM SOS tower is blocking BS oplev input beam, this needs to be adjusted.
• Installed PRMOL at nominal position + 2 cm East (to clear path from TT2)
• I balanced the table succesfully, first using spirit bubble level and then OSEM levels of BS, SR2, PR3 and LO2.
  • Note, that we need to adjust OSEM positions in many of these SOS before pumping down.
• Input beam from TT2 is going through center of PRM but the reflction is not coming back from PR2, maybe it is missing PR2 or PR2 alignment needs to be adjusted.

[Paco, Ian]

After agreement from Yuta/Anchal, I moved POYM1 yaw to clear the aforementioned path, and Ian restored the POY11 RFPD path. The demodulation phase might need to be corrected afterwards, before any lockign attempts.

Current OSEM sensor values with all the suspensions aligned are attached.
For 'BS','ITMX','ETMX','ITMY','ETMY','PRM','SRM','LO1','LO2', the ones out of the range [200,800] are marked, and for 'PR2','PR3','SR2','AS1','AS4', the ones out of the range [6000,24000] are marked.

[Anchal, Paco, Yuta]

BS Oplev Path

• The changed position of PRM (40m/16863) meant that BS oplev path is getting clipped by the PRM SOS tower.
• We had to move BSOL ~ 16 cm North and ~ 1.7 cm East.
• This means that the BS Oplev input beam is now coming behind TT2 instead of infront of it.
• We also had to align the beam such that input and returning beam are colinear.
• This meant we, had to change the mount of the upstream beamsplitter in the in-air table so that we can use that for separating the return beam.
• Again, we should order 2 inc visible BS for this path.
• Half of the return beam is making its way all the way back to the laser head. I'm not sure if that can be an issue for our oplev loops.
• We kept the SRM Oplev path same using irises on the table.

PRM Oplev

• Again, due to changed position of PRM and BS Oplev, it became very hard to setup oplev for PRM.
• We found a special position which allows us to catch returning beam through the center of the window.
  • But this returning beam is not prompt reflection from PRM, it is reflection of the HR surface.
  • We are hitting about ~5 mm from the edge of PRMOL mirror (because we cannot move the mirror anymore south to avoid clipping BS and SRM input oplev beams)
  • We put in a 1.1m focal length lens in the input beam to narrow the beam on PRMOL so that it doesn't clip
• We did not put any lens for the return beam. The sensitivity of this oplev might be low due to slighlty bigger beam on the QPD than others (SRM, BS). We can revisit and insert a lens later if required.

Interferometer alignment and PRM alignment

• The work on BS table did not change the table balance much. We got back the alignment pretty much instantly.
• We were able to maximize the arm transmissions.
• Then we used a beam card with hole to check for reflection from PRM and used PRM (mostly pitch correction) to get the return beam back in same way.
• This recovered REFL beam on the camera. We used REFLDC signal to align PRM better and maximized it.
• We centered BS, SRM and PRM oplevs after this point.

LO beam mode correction and spatial overlap

• We tried changing the distance between LO3 and LO4 to get a better output LO beam.
• We also tried to swap the LO4 mirror with the spare mirror but we had the same result.
• Eventually, we decided to move LO3 back to East and LO4 to the west edge of the table. This made the beam sizes comparable.
  • Future exercise: We think that LO1 or LO2 might be significantly off-spec in their ROCs which might cause this issue.
  • We should rerun the calculations with the ROC values of LO1 and LO2 written in the datasheets and figure out the correct LO3-LO4 length required.
  • We can make this change in the next vent if required.
• After the beam sizes were looking approximately similar but more iterations of changing length and realigning are required.

Remaining tasks before pumpdown

• Push/pull too bright/dark OSEMs in the SOSs (40m/16865).
• Finish LO beam mode correction and spatial overlap.
• Center all oplevs, note all beam positions on camera, and note down all DC PD values at proper alignment.

[Paco, Anchal, Yuta]

Today, in short we:

• Recovered alignment of arm cavities, PRC (only ITMX aligned), and then altogether with SRM and PRM aligned to maximize all DCPD levels (AS, POP, REFL, TRX, TRY), but SRC was not flashing and the SRM yaw alignment slider was around its max value, so after recording beam positions on cameras Anchal went into the BS chamber and helped steer the SRC alignment using a combination of SRM, SR2 and AS1. After this every beam was nominally aligned except for LO and AS, which remained to be mode matched.
• Mode matched LO3-LO4 by hand --  -- from the ITMY chamber, the final separation between these two mirrors grew by almost 3 inches with respect to the design (!!!) but the LO and AS beams came out nicely. The canonical path used for the steering was LO path, and then we overlapped the beams with the help of a gige basler camera and a couple of DCPDs (Thorlabs).
• Yuta and Paco started running final checks in preparation for Monday (pumpdown). We aligned the IFO, but noted that using Restore/Misalign sometimes results in hysteresis.. so it is not very reliable for fine alignment modes. Then we optimized DC levels, centered all oplevs, and tweaked Green input alignment on XARM and YARM. The XARM was maximized, but in YARM we could still not get high TEM-00 flashing ...
  • Unfortunately, we discovered a slight clipping of the GTRY beam through PR3 which could mean the current alignment (pointing) is not hitting PR3 center optimally.
• Attached are the screenshot of current aligned state after the work tonight, with oplevs centered, and the OSEM sensor values.

[Paco, Yuta]

Prep for closing and pump down.

• Aligned IFO to maximize DC levels.
  • YARM (flashing peak 0.05 with PRM misaligned), XARM (flashing peak 0.06 with PRM misaligned), PRC (PRY flashing -30 @ POPDC, offset -70 and REFL DC 270), SRC (SRY flashing -30 @ POPDC, offset -70), BHD.
• GTRY clipping
  • We tried moving the alignment of PR3, PR2, ETMY, ITMY to reduce clipping and retain IR flashing. We found it kind of difficult, so we only used the unclipped GTRY temporarily to improve the input YAUX injection after which the YAUX locked. We then restored the clipping in favor of the IR beam alignment.
• PR3 position
  • PR3 seems to be +1 inch away towards East, nominally placed along North-South, and offset in YAW.
• Aligned OPLEVs to center at around Mon May 23 13:20:32 2022
• Snapshot of all cameras in the control room around Mon May 23 13:24:51 2022

[Chub, JC, Jordan, Yuta, Yehonathan, Paco]

Closed in the following order:

• IMC chamber
• OMC chamber
• BS chamber
• ITMY chamber
• ITMX chamber

[Yuta, Paco]

After closing the heavy doors, we tried to have GTRY less clipped using PR2, PR3, ITMY and ETMY. During this adventure, we also aligned GRY injection beam by hand. Rotating a waveplate for GRY injection made GRY locking stably at GTRY of ~0.3.

I modified the script freeSwing.py to use damping loop output switches to free the optic instead of watchdog or coil output filters. This ensures that the free swing test is being done at the nominal position of the optic. I started tests for LO1, LO2, As2, As4, PR2, PR3, and SR2 in a tmux session names freeSwing on rossa.

Note: LO2 face OSEMs are hardly sensitive to any motion right now due to excessive pitch offset required for LO beam. We should relieve this offset to LO1 and rerun this test later.

[Yuta, Paco]

We aligned IMC to recover the IFO progressively. First step was to center the MC REFL beamspot on the camera as well as the WFS DC. Then slide MC2 and MC3 together. Below are the alignment slider positions before/after.

IFO aligned to maximize flashings, except for GRY and LO-AS.

What we did:
 0. After recovering IMC, C1:IOO-MC_TRANS_SUM was ~1300 with C1:IOO-MC_RFPD_DCMON of ~0.11 (~10% better than what we had during vent). Xarm and Yarm was already flashing and could see the beam at AS and POP cameras.
 1. Aligned ETMX and ITMX to green X input beam to maximize C1:ALS-TRX_OUT, to ~0.19.
 2. Aligned TT2-PR3 to get C1:SUS-ETMX_TRX_OUT flashing at 0.09 at max
 3. Aligned ITMY to have nice POP blinking of MICH at POP camera
 4. Aligned ETMY-PR3 to have C1:SUS-ETMX_TRX_OUT flashing at 0.06 at max
 5. Misaligned ITMY (with +2 in C1:SUS-ITMY_PIT_COMM), and aligned PRM to have PRX (PRM-ITMX cavity) flashing at C1:LSC-ASDC_IN1 at ~20 (offset -70) at max
 6. Misaligned PRM, and aligned SRM to have SRX (SRM-ITMX cavity) flashing at C1:LSC-ASDC_IN1 at ~20 (offset -70) at max
 7. Restored all the alignment. ITMY didn't quite come back, so I need to tweak the alignement to maximize TRY flashing.

Result:
Current alignment is as attached. IR beam at AS, REFL, MCR and green beam at GTRX cameras all seem slightly to the left from monitors, but looks as it was before the pump down. GTRY is still clipped, but green Y locks stably. Oplevs were not so useful to recover the alignment. ETMX/Y oplevs did not drifted too much probably because we don't have in-vac steering mirrors.

Next:
 - Tweak alignment of green Y input to follow Yarm
 - Do LO-AS alignment
 - REFL DC is not receiving beam. Re-alignment necessary
 - Oplev centering
 - BHD PDs need to be replaced to lower gain PDs and need to be connected to CDS

[Paco, Yuta]

We have aligned the IFO (except for LO-AS and GRY), and centered all the oplevs.
We have also restored Gautam's in-air BHD DCPD setup and placed it to ITMY table.
BHD DC PD signals are now online at C1:XO4-MADC1_EPICS_CH4 and CH5. 

Oplevs:
 Aligned the IFO following the steps in elog 40m/16875.
 When we were woking on BHD DCPDs, we lost REFL beam on camera and both arms flashing. Alignment was restored mostly with TT2 pitch.
 We centered all the oplevs after the recovery (see attached).

BHD DCPDs:
 1. We removed a circuit box with M2 ISS photodetector readout board from AP table, in-air BHD photodiodes from optics graveyard. (see LIGO-E2000436 and elog 40m/15493 for wiring diagram)
 2. Taken out temporary two Thorlabs PDA100A used for aligning LO-AS during the vent from ITMY table, and placed the BHD setup in ITMY table (see attached and attached).
 3. DB9 cable (15ft+10ft) was connected from M2 ISS box to anti-aliasing chassis for ADC1 of C1X04 at 1Y2 rack (see attached).
 4. +/-18V power for M2 ISS box was supplied from 1Y1 rack.
 5. BHD DCPD signals are now available at C1:XO4-MADC1_EPICS_CH4 and CH5 (see attached).

Next:
 - Tweak alignment of green Y input to follow Yarm
 - Do LO-AS alignment
 - Centering of PDs everywhere with IFO aligned
 - Update RTS model for BHD

[JC, Paco, Yuta]

After the IFO recovery (elog 40m/16881), we installed an analog camera for BHD fringe using a BNC cable for old SRMF camera so that we can see it from the control room.
We also aligned AS-LO using LO1,LO2 and AS4.
We then aligned GRY injection to get maximum GTRY.

Maximum TEM00s right now are
 C1:SUS-ETMX_TRX_OUT_DQ ~0.1
 C1:SUS-ETMY_TRY_OUT_DQ ~0.05
 C1:ALS-TRX_OUT_DQ ~0.20
 C1:ALS-TRY_OUT_DQ ~0.18

[Paco, Yehonathan]

We fixed the slow control over the green beam shutters.

At the Y arm the wrong BNC was connected to the shutter driver. We connected the correct BNC to the driver and switched the remote mode. The green Y shutter now works but in reverese, meaning that sending 1 to C1:AUX-GREEN_Y_Shutter closes the shutter and vice versa. This needs to be fixed.

At the X end the problem was a bit more complicated. Previously, the shutter was controlled by c1auxey. We figured that c1auxex has a lot of spare bio channels. We found an Acromag BNC front panel (with wires already soldered to the BNCs) lying around in the lab and installed it on the c1auxex Acromag chassie. We then connected the topmost BNC to channel 0 on XT1111A in the chassie. The BNC was connected to the green shutter driver on the X end.

EPIC channel was added to the c1auxex db file while it was commented out on the psl shutters db file. Modbus was restarted on c1auxex and c1psl. c1psl had to be burt restored to regain MC lock. Now the green X shutter works properly.

I made some progress in modeling MICH loop.

Putting all the LSC and SUS filters together with the MICH Finesse model I constructed an OLTF model and plot it with the measurement done by Paco and Yuta in this elog (attachment 1).

There are 2 unknown numbers that I had to adjust in order to fit the model with the measurement:

1. The SUS damping loop gain (found to be ~ 2.22), which seems to vary wildly from SUS to SUS.

2. The coil driver gain (found to be 45), which I should measure.

I find coil_driver_gain*SUS_damping_filter_gain by increasing it until the SUS damping loop becomes unstable.

The coil driver gain I find by making the measurement and model overlap.

However, there is one outstanding discrepancy between the measurement and the model: Paco and Yuta measure the MICH calibration to be 1.3e9 cts/m while my model shows it to be 1.3e10 cts/m, an order of magnitude larger.

Details

[Paco, Yuta]

We recovered the LO beam on the BHD port. To do this, we first tried reverting to a previously "good" alignment but couldn't see LO beam hit the sensor. Then we checked the ITMY table and couldn't see LO beam either, even though the AS beam was coming out fine. The misalignment is likely due to recent changes in both injection alignment on TT1, TT2, PR2, PR3, as well as ITMX, ITMY. We remembered that LO path is quite constrained in the YAW direction, so we started a random search by steering LO1 YAW around by ~ 1000 counts in the negative direction at which point we saw the beam come out of the ITMY chamber

We proceeded to walk the LO1-LO2 in PIT mostly to try and offload the huge alignment offset from LO2 to LO1 but this resulted in the LO beam disappearing or become dimmer (from some clipping somewhere). This is WiP and we shall continue this alignment offload task at least tomorrow, but if we can't offload significantly we will have to move forward with this alignment. Attachment #1 shows the end result of today's alignment.

I should write down what I didn't include for completeness:

1. AA filters

2. AS55 input 60Hz comb filter

3. Violin filters

After discussing with Paco, we agreed that the discrepancy in the MICH calibration might come from the IQ mixing angle which for the IFO is not optimized, while in Finesse is set such that all the amplitude is in one quadrature.

I'm curious why the actual OLTF included the 60Hz comb...? It is undesirable to have such structure in the OLTF around the UGF as it can cause servo instability.
And if you remove them, you don't need to model them :-)

After discussing with Anchal, we decided to route BHD related PD signals directly to ADC of c1sus2, which handles our new suspensions including LO1, LO2, AS1, AS4, so that we can control them directly.
BHD related PD signals will be sent to c1lsc for DARM control.

Re-cabling was done, and now they are online at C1:X07-MADC1_EPICS_CH16 (DC PD A) and CH17 (DC PD B) with 15ft DB9 cable.
Here, DC PD A is the transmission of BHD BS for AS beam, and DC PD B is the reflection of BHD BS for AS beam (see attached photo).

[Anchal, Yuta]

RTS models for BHD homodyne phase control (c1hpc) and angular control (c1bac) are created and added to c1sus2.
c1su2 and c1lsc models were modified accordingly.
We still have issues with IPC PCIE connection sending DCPD A and B signals to c1lsc and DC error 0x2000 in c1su2 model.

c1hpc (host: c1sus2) Attachment #1
 This model is for homodyne phase control.
 It can dither LO1, LO2, AS1, AS4 in POS and demodulate mixture of DCPD A/B signals for the phase control to feedback to those optics.
 It also sends DCPD A/B signals to c1lsc via cdsIPCx_PCIE.
 Dither and controls signals are sent to the optics via cdsIPCx_SHMEM.

c1bac (host: c1sus2)
 This model is for BHD angular control.
 It is basically the same as c1hpc, but it is for PIT and YAW dithering of LO1, LO2, AS1, AS4.

c1su2 (host: c1su2) Attachment #2
 LSC and ASCPIT/YAW feedback signals from c1hpc and c1bac via shared memory were added to send them to corresponding optics.
 Somehow Mux/Demux didn't work to send SHMEM signals inside the subsystem in the Simulink model (this works for ADC, but probably not for IPC stuff?), and we had hard time make-install-ing this model.

c1lsc (host: c1lsc) Attachment #3
 DCPD A/B signals from c1hpc via PCIE were added for our new error signals for LSC.

Starting and restarting the models
 After having some troubles make-install-ing modified models (be careful of goto and from tags!), we stopped all the models in c1sus, c1ioo, c1lsc, c1sus2 and started all of them, including new c1hpc and c1bac models.
 This somehow created RFM errors in c1scx and c1scy.
 So, we proceeded to do the same step we did in 40m/16887 and 40m/15646, now including c1sus2 for the restart.
 Initial attempt made c1lsc, c1sus, c1ioo mostly red, so scripts/cds/rebootC1LSC.sh was run again on pianosa.
 RFM issues for c1scx and c1scy were solved.
 Shared memory within c1sus2 seems to be working, but sending DCPD A/B signals from c1hpc to c1lsc is not working (see Attachement #4).

Next:
 - Fix C1:HPC-LSC_DCPC_A/B issue
 - Make/modify MEDM screens

The 0x2000 error in c1su2 happens whenever we make it and install it as the default data acquisition rates are too much in the suspension model. Earlier we used activateSUS2DQ.py to fix this. I followed the suggestion in 40m/16537 to include COIL_OUT at 16k, damping channels at 256 Hz and OL channels at 1024 Hz. I created new suspension model at /cvs/cds/rtcds/userapps/trunk/sus/c1/models/lib/sus_single_control_new.mdl. The model also contains filter modules names C1SUS_OPT_BIASPOS, C1SUS_OPT_BIASPIT, C1SUS_OPT_BIASYAW which acts on the alignment offsets so that a low pass filter can be added there and alignment offsets always happen slowly. The new suspension model is now used inc1su2 for teh 7 new suspensions, and now the model starts without errors.

Still remaining to fix: IPC communication between c1hpc and c1lsc.

[JC, Yuta]

To circumvent IPC error sending BHD DC PD signals from c1sus2 to c1lsc, DB9 cable from BHD DC PD box sent to c1sus2 is now split and sent also to c1lsc.
They are now available in both

c1sus2 ADC1
C1:X07-MADC1_EPICS_CH16 (DC PD A) and CH17 (DC PD B)

c1lsc ADC1
C1:X04-MADC1_EPICS_CH4 (DC PD A) and CH5 (DC PD B)

Next:
 - Add battery powered SR560 to decouple c1sus2 and c1lsc to avoid the ground loop

{Yuta, Yehonathan}

For MICH noise budgeting we measure the input electronics noise which includes the AS55 RFPD, preamp, demod board, the whitening, and the AA filters, and the ADC noises. To do so we simply close the laser shutter and take the spectrum of C1:LSC-AS55_I_ERR_DQ and C1:LSC-AS55_Q_ERR_DQ shown in attachment 1.

Next, we measured the output electronics noise which includes the DAC, dewhitening and AI filters, and coil driver noises. We disabled the BS watchdog and went to 1X4 rack. We measured the spectrum of one of the lemo outputs on the BS coil driver module using an SR785. Attachment 2 shows the spectrum together with the SR785 dark noise.

{Yuta, Yehonathan}

We measured the AS55 demod board conversion from the amplitude of a 55MHz signal to a demodulated signal. We hooked the unused REFL55 LO into the PD input port on the AS55 demod board.

The REFL55 LO was measured to be 1.84 Vpp. The IQ outputs were: I = 0.86 Vpp, Q = 2.03 Vpp giving an amplitude of 2.205 Vpp. The overall conversion factor is sqrt(0.86**2+2.03**2)/(1.82/2)=2.422.

We also set to measure the loss in the RF cable from AS55 PD to the demod board on 1Y2. REFL55 was connected with a long BNC cable to the input of the cable under test. REFL55 at the input was measured to be 1.466 Vpp and 1.28 Vpp at the output signifying a transmission of 87.6%.

I calculated a noise budget for the MICH using AS55 as a sensor. The calculation includes closed-loop TF calculations.

The notebook and associated files can be found on https://git.ligo.org/40m/bhd/-/blob/master/controls/compute_MICH_noisebudget.ipynb.

Attachment 1 shows the loop diagram I was using. The equation describing the steady-state of the loop is

, where G is the adjacency matrix given by

First, the adjacency matrix G is constructed by stitching the small ABCDE matrices together. Once the inverse of (I-G) is calculated we can simply propagate any noise source to  and then calculate  to estimate the displacement of the optics. 

Attachment 2 shows the calculated noise budget together with Yuta's measurement.

All the input and output electronics are clumped together for now. Laser noise is irrelevant as this is a heterodyne measurement at 55MHz.

It seems like there is some mismatch in the calibration of the optical gain between the measurement and model. The missing noise at 3-30Hz could be due to angle-to-length coupling which I haven't included in the model.

Looking good:

• I think the notches you see in he measured noise are a clue as to the excess noise source. You can try turning some notches on/off.
• Laser noise does matter a bit more subtley: the low freq noise couples to AS55 through the RMS deviation of the MICH loop from the zero crossing, and the noise of the 55 MHz modulation.
• Jitter in the IMC couples to MICH through the misalignment of the Michelson.
• As you rightly note, the optical lever feedback on the ITMs and BS also make length noise through the suspension actuator imbalance and the spot mis-centering.

I fixed some mistakes in the budget:

1. The BS pendulum resonance was corrected from 0.8Hz to 1Hz

2. Added missing X3 filter in the coil filters

3. Optical gain is now computed from MICH to AS55 instead of BS to AS55 and is calculated to be: 9.95e8 cts/m.

4. Coil driver gain is still unmeasured but it is found to be 1.333 to make the actuation calibration from BS to MICH match the measurement (see attachment 1).

Attachment 2 shows the resulting MICH OLTF.

Laser noise was added to the budget in a slightly ad-hoc fashion (will fix later): Yuta and I measured MC_F and computed MC_F*(Schnupp asymmetry)/(Laser frequency). Attachment 3 shows the updated noise budget.

the main laser noise coupling for a Michelson is because of the RIN, not the frequency noise. You can measure the RIN, in MC trans or at the AS port by getting a single bounce beam from a single ITM.

I measured the RIN by taking the spectrum of C1:MC_TRANS_SUMFILT_OUT and dividing it by the mean count on that channel (~13800 cts). Attachment 1 shows the result.

I updated the MICH AS55 noise budget but got a very low contribution (gold trace in attachment 2).

It seems too low I think. What could've gone wrong? Finesse calculates that the transfer function from laser amplitude modulation to AS55 is ~ 1.5e-9 at DC. If I turn off HOMs I get 1e-11 at DC, so this coupling is a result of some contrast defect. Should I include some RMS imbalances in the optics to account for this? Should I include it as a second-order effect due to MICH RMS deviation from zero crossing?

You should measure the coupling by noise injection. Noise budgeting does not need any modeling:

1) Measure the power spectrum density of the target signal (i.e. DARM) and the source noise (i.e. RIN this case)

2) Calibrate both using a calibration peak to convert 1) into the physical units (m/rtHz, 1/rtHz, etc)

3) Measure the transfer function from source to target using the noise injection. (i.e. RIN injection this case and look at the injection to RIN and injection to DARM)

4) Measure open-loop transfer functions if necessary. (i.e. DARM control open-loop transfer function to convert the error signal into the free running noise level)

Primarily, these are measured noise levels and noise couplings there is no room to involve a model there.
Once the noise budget was done, you can compare it with the model and say "the coupling is big/small/comparable".
 

Also, why don't you use C1:MC_TRANS_SUMFILT_IN1_DQ instead? Your _OUT signal seems affected by the bunch of comb notch filters to artificially remove the 60Hz harmonics. It's not a fair RIN measurement.