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  12289   Mon Jul 11 15:13:22 2016 gautamUpdateGeneralVent progress: in-date First Contact procured

I have obtained 2x100cc bottles of in-date first contact from Garilynn (use before date is 09/14/2016) for cleaning of our test-masses. They are presently wrapped in foil in the plastic box with all the other first contact supplies.

Attachment 1: image.jpeg
  12327   Fri Jul 22 23:03:23 2016 gautamUpdateGeneralETMX suspension - progress

[ericq, gautam]


Today, we attempted to progress as far as we could towards getting the mirror suspended and gluing the second wire standoff. We think we have a workable setup now. At this stage, the suspension wire has been looped around the magnet, the second wire standoff has been inserted, coarse pitch balancing has been done, and we have verified that side OSEM/magnet positioning is tenable. Details below.


  1. First we verified that the epoxy on the side magnet re-glued yesterday had dried (verified using control setup of epoxy in aluminum foil + copper wire - we didn't perform any further tests like pulling the magnet off the tabletop as we were satisfied)
  2. We placed the optic inside the suspension cage, resting on the 4 lower earthquake stops.
  3. We looped the suspension wire around the optic. This is a somewhat challenging procedure. After consulting the documentation, we decided to follow the given advice and loop the wire around from the bottom of the optic, one side at a time. It is tricky to thread the wire between the two lower earthquake stops and get it up around the side. The side magnets were an unexpected ally in this effort as they served as some sort of intermediate checkpoint from which we could pull the wire further up. We then lightly clamped it to the winches mounted atop the suspension cage.
  4. After verifying that we had routed the wire correctly through the various stages (primary and secondary suspension points at the top of the cage), we placed the wire under very slight tension by had, and then tightly clamped the wires in the winches (we then cut off the excess length).
  5. In this state, we proceeded to install the second wire standoff (having verified that the wire was indeed sitting in the groove on the other side). 
  6. We then proceeded to raise the optic to the desired height (center of optic to 5.5 inches above the table top) with the help of the microscope and the lines on the barrel side. 
  7. Next, we attempted to freely suspend the optic (i.e. no contact with the viton tips). We were initially unsuccessful but Eric did some fine adjustment of the (unglued) standoff to achieve a stable configuration. However, the wire is now really close to the magnet - although it is not clear to me if it is touching the magnet as we initially suspected - see Attachment #1, it may be that if the wire is touching something, it is the dumbbell and not the magnet itself. While this is clearly not ideal, we think that this setup is workable as is. If after doing the pitch balancing, if the deviation of the wire becomes much more pronounced, we may have to re-glue the side magnet. In any case, both the horizontal scribed lines are now 5.5 inches above the table top.
  8. We then brought over the OSEMs from the ETMX vacuum chamber to the cleanroom. As a first check, we wanted to ensure that one of the side magnets could accommodate an OSEM (because both side magnets have been re-attached after the optic was removed from the old suspension). Attachment #2 suggests that this is possible, even though the relative positions of the side magnet and the shadow sensor may be sub-optimal. We will only really know after hooking up the electronics.


  1. We found that after a few hours, there was some sag introduced in the wire, presumably it stretched into an equilibrium position under the weight of the optic. We will re-check the heights tomorrow while conducting further tests.

Immediate to-do:

  1. Insert all OSEMS. Ensure that the magnet positions relative to the coil are compatible.
  2. Enable damping loops. We have a cable coming from the IFO area into the cleanroom through a hole-in-the-wall. We are missing a DB25 gender changer at the moment. 
  3. Do the pitch balancing.
  4. Glue the second standoff in place. 

Other attachments:

Attachment #3 - Unglued stand off with wire in the groove, mirror freely suspended.

Attachment #4 - Glued stand off with wire in the groove, mirror freely suspended. Clearance between wire and magnet looks reasonable.

Attachment #5 - Barrel of optic (underside), mirror freely suspended. The wire seems to be in a reasonable orientation along the barrel, albeit not perfectly parallel.

Koji just pointed out that we should check that the unglued ruby standoff is in good contact with the barrel of the optic. Attachment #1 suggests that maybe this is not the case. If you zoom into Attachment #1, it is not clear if the standoff is sitting on the glue.

Attachment 1: IMG_2828.JPG
Attachment 2: IMG_2826.JPG
Attachment 3: IMG_2821.JPG
Attachment 4: IMG_2822.JPG
Attachment 5: IMG_2823.JPG
  12335   Mon Jul 25 20:37:46 2016 gautamUpdateGeneralETMX suspension - Side OSEM test

[Lydia, gautam]

Summary: We did some preliminary tests to check if at least one of the side magnet positions is usable for the side OSEM. We mainly wanted to check how much dynamic range we lose because of the sub-optimal longitudinal positioning of the side magnet. We found that when the side magnet was mainly moving along the axis of the side OSEM (with minimal yaw motion as gauged by eye), the PD voltage bottomed out at ~80 counts (while the completely unoccluded readout was ~800 counts). 


  1. First, we placed the face OSEMs into their holders one by one, and adjusted their position till the readout was approximately half the saturation value (as judged by the average value of the readout, at this point, the mirror was still swinging around a fair bit).
  2. Next, we enabled the POS, PIT and YAW damping (with all existing settings unchanged), but with the SD coil input and output disabled. We had to increase the watchdog threshold to ~600mV.
  3. Once the optic was reasonably well damped (~70mV on the watchdog was the best we saw), I put in the side OSEM till the PD was completely occluded. At this point, I enganed the earthquake stops, and then released the mirror such that it was freely hanging. I then observed the optic by eye, and noted a time when the dominant motion was along the axis of the side OSEM coil (i.e. minimal YAW motion). 
  4. Attachment #1 shows time series plots of the 5 OSEM PD voltage monitors. Perhaps because the side OSEM input was disabled, the damping wasn't as efficient as it normally is (also there is a fan blowing air around the clean bench). But at the point indicated on the plot, the YAW motion was negligible to the eye, while the dominant motion was along the axis of the coil. During this time, the readout bottomed out at approximately 10% of the saturation value (towards the end of these plots, I disabled the damping loops and began pulling the OSEMs out one by one). Because the damping was imperfect, this is only an approximate guess of how much dynamic range we are losing. But does this warrant regluing the side magnet?

Other remarks:

  • The 4 face magents were reasonably well centered in the coil. While Eric and I were looking at this earlier today, the LL magnet looked a little close to the coil, but after putting all 4 OSEMs in, the situation looked reasonable to the eye. I couldn't take pictures because of space constraints, and furthermore, it's almost impossible to hold the camera in the correct vertical position. 
  • Steve, Eric and I couldn't find the OSEM gender changer anywhere in the lab and it wasn't in the box it was advertised to be in. So we made a custom cheater cable, and cleaned it by wiping with Isoprop., and wrapped it in foil for use in this test. The OSEM pins should probably be cleaned before we put these back in vacuum. 
Attachment 1: osem_test_2016_07_25.png
  12340   Tue Jul 26 18:07:57 2016 gautamUpdateGeneralETMX suspension - Further OSEM Tests

Today, we did the following:

  • Once again, inserted all four face OSEMs till the sensor voltage readouts were approximately half their saturation value. The presence of some ferromagnetic material in the Honeywell components makes this tricky as each coil is coupled to the other three, but we were able to converge to a point where all the voltage readouts were oscillating around a mean value of ~40-60% of their maximum value, with all the damping loops OFF.
  • Turned on all damping loops, and verified that the OSEM positioning was indeed such that the sensor readout is nominally around 50% of the saturation value. The air buffeting around the clean bench means that the damping isn't nearly as effective as it is inside the vacuum chamber.
  • Attempted to increase the gain on the damping loops - we first switched out the Chebyshev low-pass filter in all the damping loops for something a little less aggressive, to allow us to turn up the gain. However, this experiment wasn't a success, when we turned the damping loops on, they were ringing the optic up.
  • At this point, Eric checked the offset sliders (summed in via the slow system) and saw that they were not zero. We zeroed these, but naturally, they destroyed the OSEM positioning equilibrium we had established earlier. So we had to go back and re-position the OSEMs
  • After re-centering the face OSEM magnets relative to the LED-PD pair, we insertd the side OSEM such that the side magnet completely occluded the PD. Interestingly, Eric noticed that the magnetic attraction between OSEM and magnets conspired to center the side magnet fairly well in the side OSEM, when it completely blocked the PD. However, when he returned the side OSEM coil to its nominal operating position of approximately half-blocking the PD, some minor misalignment was re-introduced (i.e. even when the optic was swinging mostly along the axis of the side OSEM, the voltage readout did not quite go down to 0). 
  • We then decided to compare the spectra for the error signals for the 4 DOFs with the current configuration (i.e. suspension clamped down to table top, optic freely hanging, all OSEMs reasonably well centered, and with the ETMX SUS model reverted to its normal state) to some reference (see Attachment #1). I initially thought I would wait for the optic to settle down a bit more before taking the spectra, but it doesn't seem to be showing any signs of getting any quieter in the last one hour. In Attachment #1, I have plotted as reference the spectra of the error signals from the early hours of 4 July 2016, at which point we were at atmosphere but the heavy doors were not yet off, so this is not really a fair comparison, but we don't really have a period in which the optic was exposed to the atmosphere and with the OSEMs in place, at least from this vent. Colors are identical for a given DOF, with todays trace as a solid line, and the reference dashed.
  • We did not check the room available to install some shimming piece of metal in the side OSEM holder, as a possible solution to solve the misalignment problem. Steve has already found pieces of varying thickness, and they are soaking in acetone right now, we plan to air bake them tomorrow. 

I will have another look at the spectra tomorrow morning, to see if the damping improves overnight. 

Attachment 1: OSEM_spectra.pdf
  12347   Thu Jul 28 13:49:44 2016 gautamUpdateGeneralETMX magnets re-reglued

[gautam, ericq]

Brief summary, some pictures and such follow in the daytime. 

  • All magnets enclosed by OSEMS were knocked off. (This means one side magnet remained, on the guiderod side)
  • Glue residue cleaned from ETMX
  • Dumbbell feet were cleaned of glue, finely sanded, re-scored with a razor blade
  • The magnet gluing fixture was painstakingly aligned multiple times, adjusting the shim height to get a magnet/wire groove clearance of 0.25-5mm
  • Epoxy mixed, test batch cured perfectly, applied to 5 dumbbells (after triple-checking polarities) and set to glue. 

The epoxy needs at least 12 hours of room temperature air curing, so no touchy until 3:30PM on Jul 28!

Attachment #1 - After multiple trials shimming the magnet gluing rig with teflon spacers, we think that we managed to find a configuration in which the side magnet edge is between 0.25 mm and 0.5 mm from the groove in the ruby wire standoff in which the wire will sit. 

Attachment #2 - Zoomed in view of the side magnet.

Of course we won't know until we suspend the optic, but we believe that we have mitigated the misalignment between the side OSEM axis and side magnet.

The short term plan is to try and suspend ETMY in the end chamber and have a look at the alignment between all magnets and OSEM coils for it. Once the epoxy on ETMX is cured, we will try and suspend the optic again, this time taking extra care while tightening the wire clamps.

Unrelated to this work: Bob just informed me that we had left the air bake oven on overnight - this unfortunately melted the plastic thermocouple inside.

Attachment 1: ETMX_sideMagnet.JPG
Attachment 2: ETMX_sideMagnet_zoomed.JPG
  12349   Thu Jul 28 17:48:17 2016 gautamUpdateGeneralETMY LR magnet broke off

While ETMX magnets were curing, I wanted to try and suspend ETMY in the endchamber, put in the OSEMS and see if the magnets aligned well with the coils, and run the same type of diagnostics we have been doing for ETMX. However, while I was trying to slip the optic into the wire, the UL magnet on ETMY broke off. I recovered the magnet and now both optic and magnet are back in the cleanroom. The magnet dumbbell has been cleaned with acetone and then sandpaper to remove residual epoxy - it remains to clean the residue off the optic itself before re-gluing the magnet tonight

I also noticed that the existing wire in the suspension had a kink in it. It looks fairly sharp, and I think we should change the wire while re-inserting the optic. Putting the optic into an existing loop of wire is tricky, as if you go in from the front of the suspension cage, the magnets on the AR side attract the wire, and makes it quite difficult to loop the wire around. I have to think of some way of holding the wires in place while the optic is being placed, and then, once the optic is roughly in position, slip the wire into the grooves in the standoffs. 

I took the opportunity to replace the face OSEM coil holder screws while the chamber was open. 

EDIT 9 August 2016: It was in fact the LR magnet that was knocked off.

  12357   Fri Jul 29 20:12:54 2016 gautamUpdateSUSthird time - no luck

[lydia, gautam]

Summary: Third unsuccessful attempt at getting ETMX suspended. I think we should dial the torque wrench back down to 1.0 N m from 1.5 N m for tightening the primary clamp at the top of the SOS tower. No damage to magnets, standoff successfully retrieved (it is sitting in the steel bowl)


  • We burned through two sets of wires today.
  • First, the assembly Eric and I had put together last night failed when Eric tightened the wire clamp (no torque wrench was used I think?)
  • This afternoon, Lydia and I re-assembled the suspension once again. Standoff was successfully inserted, coarse pitch balancing was achieved relatively easily - we think that the coarse pitch balance can be achieved if the end of the wire standoff closer to the groove is ~0.5mm ahead (i.e. towards HR side) of the guide rod.
  • Checked leveling of scribe lines, gave an extra 0.25 turns on the winches in anticipation of the wire sagging
  • Inserted OSEMs just short of magnets, verified that they were approximately centered, if anything, slightly above center, again in anticipation of the wire sagging. 
  • After taking pictures, we went ahead and attempted to clamp the wire (ALL EARTHQUAKE STOPS WERE ENGAGED)
  • Eric commented that the clamp piece did not slide in smoothly on the dowels (indeed it does not come off very easily either, I have just left it on for now). I don't remeber it being so difficult prior to us sending it into the maching shop to get rid of the grooves made by the suspension wire the first time around. But with the torque wrench, the piece moved in relatively easily (we had sanded down rough edges prior to putting this piece onto the suspension earlier in the afternoon.
  • I could feel that the torque wrench coming up on its limit. But the wire snapped before the torque wrench clicked. As far as I am aware, there were no rough edges on the piece, but perhaps we missed a spot?
  • I took the opportunity to discharge the optic using ionized nitrogen at 40psi. After about 2-3 minutes of a steady stream, I verified that a piece of the suspension wire no longer gets attracted to the barrel, as was the case earlier today.

Unfortunately I don't know of a more deterministic way of deciding on a "safe" torque with which to tighten the bolts except by trial and error. It is also possible that the clamping piece is damaged in some way and is responsible for these breakages, but short of getting the edges chamfered, I am not sure what will help in this regard.

Unrelated to this work: earlier today before the first wire failure, while I was optimistic about doing fine pitch balancing and gluing the standoff, I set up an optical lever arm ~3m in length, with the beam from the HeNe on the clean bench at 5.5 in above the table, and parallel to it (verified using Iris close to the HeNe and at the end of the lever arm). I also set up the PZT buzzer - it needs a function generator as well for our application, so I brought one into the cleanroom from the lab, isopropanol wiped it. The procedure says apply 5Vrms triangular wave at 1000Hz, but our SR function generators can't put out such a large signal, the most they could manage was ~2Vrms (we have to be careful about applying an offset as well so as to not send any negative voltages to the PZT voltage unit's "External input". All the pieces we need for the fine pitch balancing should be in the cleanroom now.

  12362   Wed Aug 3 00:15:39 2016 gautamUpdateSUSETMX suspended

[lydia, steve, ericq, gautam]


  • ETMX is now suspended by wire clamps (winches have been removed) yes
  • Wire clamp was machined by shop, D groove widened to spec, old wire grooves removed from face
  • We also sanded the part of the suspension tower in contact with the primary wire clamp, as there were a couple of craters there which looked dangerous (pictures to follow)
  • Height was adjusted by centering magnets on OSEMs. We then winched an extra half turn in anticipation of wire sag
  • I then proceeded to tighten, first, the primary wire standoff (I reduced the torque on the torque wrench to ~1.25Nm), and then the secondary wire clamps.
  • Checked that the ruby standoff is sitting on the optic barrel and not on glue 
  • Later in the evening, I inserted OSEMs, centered magnets, and checked that the damping scheme set up last week works (I'm leaving the damping on, bottom EQ stops are ~0.5mm from the optic)
  • Checked the pitch balancing - initially, we were ~60mrad off. By using the tweezers to gently adjust the position of the ruby standoff (after clamping the optic, turning the damping off), I was able to improve the situation a little bit - now we are ~20 mrad off. I am not attempting to do the fine pitch balancing tonight, but all parts of the PZT buzzer set up are ready to go in the cleanroom.
  • Unfortunately, in the process of doing the pitch balancing, the position of the magnets relative to the OSEM coils have moved. Now the UR magnet looks a little high relative to the coil, but perhaps after any sag has set in, we should be alright. Else, we can probably get away by inserting one of the little metal shim pieces, the adjustment required is small.
  • Lydia will upload some photos soon. 
  • We actually went through another failed attempt today - this time, the problem was that the winches were not sufficiently secure at the top, such that when the range of the winch was nearing its end, the whole assembly twisted and took the wire along with it. Perhaps this would not have happened if we had a winch adaptor plate handy...
  • Plan for tomorrow:
    • ​Fine pitch balancing using PZT buzzer
    • Clean ETMY epoxy residue from knocked off magnet
    • Glue wire standoff
    • Glue ETMY magnet
  12370   Thu Aug 4 03:14:39 2016 gautamUpdateSUSETMX suspended

[lydia, steve, ericq, gautam]


  • ETMX is now suspended by wire clamps (winches have been removed) yes
  • Unfortunately, in the process of doing the pitch balancing, the position of the magnets relative to the OSEM coils have moved. Now the UR magnet looks a little high relative to the coil, but perhaps after any sag has set in, we should be alright. Else, we can probably get away by inserting one of the little metal shim pieces, the adjustment required is small

[lydia, ericq, gautam]

  • Turns out setting the height of the optic with the OSEMs isn't quite reliable. We were indeed too high, for all the OSEMs
  • Related to the above - we observed no sag (which is one of the reasons we winched a little bit extra in the first place)
  • Eric and I re-did the suspension in the afternoon. We found no wire grooves in the primary (or secondary) clamps, so we just reused them (is this a red flag? should we be using more torque?)
  • This time we set the height using the traveling microscope - double checked the height to which the microscope was levelled = 5.5"
  • Having checked the height of both scribe lines, we proceeded to clamp the suspension, with ~1.35Nm of torque (since 1.25Nm seemed a little low, no wire grooves were made in the clamps) - clamping was successful
  • In the evening, Lydia and I attempted to do the fine pitch balancing
  • Both left side magnets (as viewed from the AR side) are low (within 0.5mm of the teflon). Right side magnets are pretty well centered. But left side ones seemed usable so we went ahead and tried to turn the damping on.
  • Damping worked reasonably well
  • Tried to do fine pitch balancing with PZT buzzer. Reduced voltage from Fn generator to 0.4Vrms (down from 1.7Vrms) but had limited success. 
  • I was able to do much better with just the teflon tipped tweezers. So gave up on the PZT buzzer
  • After ~3hours of a random walk between two pretty-close-to-ideal positions, we have now realized a fine pitch balancing of ~1mrad (~3mm off the ideal height of 5.5" over a lever arm of ~1.5m, but the mirror tilt is half of this angle)
  • Actually, I was able to do much better - at one point, we even had the reflected beam dead center on the iris 1.5m away. But adjusting the OSEM positions even a little bit (say from oscillating around 40% to 50% of the maximum value) has a BIG effect on the pitch balance (it caused a misalignment of 4mrad)
  • I think gluing the standoff without destroying the fine pitch balancing is going to be very challenging, judging by how gently I had to touch the standoff to destroy the fine pitch balance completely. Perhaps we want to consider using some 3 axis stage to bring the needle with glue in and perturb the standoff as little as possible

    Lydia also briefly played around with the IR camera to inspect the OSEMs. A more thorough investigation will be done once the cage is in for air baking. From our initial survey, we feel that the beams are pretty well aligned along the straight line between PD and LED - we estimate the upper bound on any misalignment to be ~10 degrees.


  12377   Fri Aug 5 02:17:10 2016 gautamUpdateSUSETMX Ruby Wire Standoff Ready for Gluing

Part 1: Rotation of optic

  • As reported in my elog yesterday, both the left magnets (UL and LL) seemed too low relative to the OSEM coils
  • Eric and I checked the height of the scribe lines using the microscope and found that the scribe lines were low on the left side and high on the right side (as viewed from the AR side) by approximately the same amount, confirming our suspicion that the optic was rotated. The position of the scribe line on the bottom of the optic relative to the bottom-rear face EQ stop also suggested the same
  • Eric brought in the bottom EQ stops, and once the wire was slightly unloaded, rotated the optic by the required amount by hand 
  • This process took two tries, but we were successful
  • Re-checked heights of scribe lines using microscope, and once we were satisfied, re-did the coarse pitch balancing

Part 2: Replacement of holder for top pair of OSEMs

  • Eric and I had difficulty removing the UR OSEM-holding screw
  • This is the non-silver-coated new variety of screw
  • It got to a point where I could neither move the screw in or out, even with the help of a pair of pliers
  • I decided to swap out the piece of the suspension tower holding the top two OSEMs (UR and UL) with the same piece from the old ETMX tower that is currently residing on the flow bench at the south end (along with the accompanying piece that overhangs the optic and holds the front-face and top earthquake stops
  • I cleaned the piece 3-4 times with acetone, and then a couple of times with isopropanol. I adjudged this to be sufficient as we are going to air bake the tower anyways prior to installation in the vacuum chamber
  • I then swapped the pieces:
    • First I brought in the bottom pairs of EQ stops
    • Next, I secured the optic using the three lower face EQ stops
    • Then, I removed the EQ stop screws from the overhanging piece, after which I removed the overhanging piece itself
    • After removing the top-back EQ stop, I removed the OSEM-holding piece from the suspension tower
    • Did the above steps in reverse, installing the new piece
  • All went smoothly. This piece does not have a serial number unfortunately
  • After this, I re-inserted the OSEMs, and judged the magnet-coil alignment to be satisfactory to proceed further
  • We decided to use the old variety of silver plated OSEM holding screws for the top two OSEMs (by choice) and the side OSEM (the new variety is too short anyways). During the course of my work tonight, I found this worked way better. The bottom pair of OSEMs remain held by the new variety of unplated screws. We may want to review whether we really want to use this new type of screws (I believe the idea is to make it easier to tighten and loosen the screws)

Part 3: Fine pitch balancing

  • As per the SOS assembly procedure, I turned off the HEPA filters at the clean bench for this part of the work
  • Checked that the HeNe beam incident on the optic was level with the tabletop, beam height set to 5.5"
  • Proceeded to do the fine pitch balancing the same way as described in yesterday's elog (i.e. no PZT buzzer, just fine touches by hand)
  • I was able to converge fairly quickly to a good point in configuration space
  • After re-centering the OSEM coils such that the PD output was ~50% of its maximum value (see Attachment #1), I found over a lever arm length of 56" (=1.42m) a beam height deviation from 5.5" by <2mm. This corresponds to 0.7mrad pitching forwards towards the HR side
  • The suspension assembly procedure tells us to aim for 0.5mrad, but I think this is close enough for standoff gluing, as this misalignment is extremely sensitive to the OSEM coil positions (although I would say, from Attachment #1, that they are actually pretty well centered)
  • The only thing that concerns me is that the LL magnet is still a little low relative to the coil. This can be fixed by shimming if necessary...

Attachment #1: Striptool trace showing OSEMs are pretty well centered (towards the end, I turned on the HEPA filters again, which explains the shift of the traces). The y-axis is normalized such that the maximum displayed corresponds to the fully open PD output of the coils

Attachment #2: Fine pitch balancing optical lever setup

Attachment #3: Tower assembly

Attachment #4: SIDE OSEM close-up

Attachment #5: UR OSEM close-up

Attachment #6: UL OSEM close-up

Attachment #7: LL OSEM close-up (this is the concerning one)

Attachment #8: LR OSEM close-up

We should also check the following (I forgot and don't want to wear my clean jumpsuit again now to take more photos):

  1. Wire is still in groove
  2. Standoff is sitting on the optic barrel and not on epoxy residue of the guiderod
Attachment 1: OSEMs.PDF
Attachment 2: IMG_2932.JPG
Attachment 3: IMG_2934.JPG
Attachment 4: IMG_2935.JPG
Attachment 5: IMG_2936.JPG
Attachment 6: IMG_2937.JPG
Attachment 7: IMG_2938.JPG
Attachment 8: IMG_2939.JPG
  12381   Fri Aug 5 18:21:28 2016 gautamUpdateSUSETMX Ruby Wire Standoff GLUED
  • The latest twist in this apparently never-ending saga was that even though fine pitch balancing was achieved, the wire was out of the groove on both sides!
  • I rectified this situation in the morning, did the fine pitch balancing in the afternoon
  • Koji's suggestion of adjusting the OSEM holding plate totally did the trick, all four magnets are reasonably well centered relative to the vertical now...
  • After the latest round of fine pitch balancing, we are now tilted in pitch backwards (i.e. towards the AR face) by <0.7mrad. 
  • Prior to gluing, I visually inspected the optic to check that (see attachments):
    • Wires are in grooves on both sides
    • Unglued ruby standoff has the correct "rotation", i.e. that the wire contacts the standoff after the groove has started, and leaves it before the groove ends, since the groove doesn't go all the way around the standoff
    • Section of wire around the bottom half of the optic has no obvious kinks/other funny features
    • Unglued standoff is in contact with the barrel
    • All magnets are well clear of teflon in OSEM coils on both sides
  • Eric also checked the frequencies of the various modes (PIT, YAW, POS and SIDE) by looking at the power spectrum of the free-swinging error signals on the coils. The pitch mode is now softer than before, at ~710mHz
  • We then proceeded to glue the optic, using a needle to apply the glue (optic was clamped using face EQ stops, bottom EQ stops were not engaged as we felt this would affect the fine pitch balancing
  • During the process, it looks like we may have inadvertently gotten some glue onto the wire (see attachments) - it doesn't look like any has seeped into the groove itself, but there is definitely some on the wire. We can possibly try cleaning this once the optic is out. In the worst case scenario, we will have to loop another section of wire, but the fine pitch balancing should be unaffected provided we did not perturb the optic too much
  • Bob has said the large oven will be available to bake the cages on Tuesday, August 9th. By this time, we should have ETMY suspended as well (we were unable to glue the knocked off magnet on ETMY as the glass bowl we had for soaking the edge of the optic in acetone to remove the epoxy residue broke while I was assembling the various pieces of Teflon inside it. Steve is procuring a new one on Monday). It is still unclear when we can vacuum bake the two ETMs...


Attachment #1: Wire is in the groove in the unglued wire-standoff, groove rotation looks pretty good.

Attachment #2: Ruby standoff is sitting on the barrel of the optic (if you zoom in)

Attachment #3: Side magnet is well centered w.r.t OSEM coil

Attachment #4: UR magnet is well centered w.r.t OSEM coil

Attachment #5: UL magnet is well centered w.r.t OSEM coil

Attachment #6: LL magnet is well centered w.r.t OSEM coil

Attachment #7: LR magnet is well centered w.r.t OSEM coil

Attachment #8: Wire is in the groove in the glued Ruby standoff

Attachment #9: Standoff after gluing. 3-4 drops of epoxy are visible on the wire, but none looks to have seeped into the groove itself

Attachment #10: Side view of newly glued Ruby standoff

Attachment #11: Before and After gluing shots.




Attachment 1: IMG_2966.JPG
Attachment 2: IMG_2969.JPG
Attachment 3: IMG_2970.JPG
Attachment 4: IMG_2972.JPG
Attachment 5: IMG_2972.JPG
Attachment 6: IMG_2973.JPG
Attachment 7: IMG_2974.JPG
Attachment 8: IMG_2967.JPG
Attachment 9: IMG_2980.JPG
Attachment 10: IMG_2985.JPG
Attachment 11: BeforeNAfter.PDF
  12396   Wed Aug 10 19:37:08 2016 gautamUpdateElectronicsMic Amplifier

In order to help Praful do his huddle test, I have temporarily arranged for the outputs of the 3 channels he wants to monitor to be acquired as DQ channels at 2048 Hz by editing the C1PEM model. No prior DQ channels were set up for the microphones. Data collected overnight should be sufficient for Praful's analysis, so we can remove these DQ channels from C1PEM before committing the updated model to the svn. There is in fact a filter that is enabled for these microphone channels that claims to convert the amplified microphone output to Pascals, but it is just a gain of 0.0005. 

In the long term, once we install microphones around the IFO, we can update C1PEM to reflect the naming conventions for the microphones as is appropriate.

  12401   Thu Aug 11 11:56:40 2016 gautamUpdateSUSETMY re-suspended

How much pitch bias do you need in order to correct this pitch misalignment?
That may give you the idea how bad this misalignment is.

I needed to move the pitch slider on the IFO align screen to -2.10 (V?) from 0 to get the HeNe spot to the center of the iris. The slider runs from -10V to 10V, so this is something like 10% of its range. I am not sure if it means anything, but the last saved backup value of this pitch slider was -3.70. Of course, application of the bias will affect all the coils, and when the optic is pitch balanced, the lower magnets are a little too far out and the upper magnets are a little too far in (see Attachment #1), as we expect for a downward pitch misalignment to be corrected. I suppose we can iteratively play with the coil positions and the bias such that the coils are centered and we are well balanced (maybe this explains the old value of -3.70). 

I also checked that the side magnet can completely occlude its PD. With the damping on, by pushing the coil all the way in, the output of the side PD went down to 0.

Attachment 1: pitchBalancingWithBias.PDF
  12407   Sat Aug 13 18:25:22 2016 gautamUpdateCOCRC folding mirrors - Numerical review

This elog is meant to summarize my numerical simulations for looking into the effects of curvature on the RC mirrors. I've tried to go through my reasoning (which may or may not be correct) and once this gets a bit more refined, I will put all of this into a technical note.


  • Both the G&H (PR2, SR2) and Laseroptik (PR3 SR3) are convex on the HR side with RoCs of approximately -600m and -700m (though as stated in the linked elog, I'm not actually sure if there are measurements of this number) EDIT AUG15: There are measurements for the Laseroptik mirrors here
    GV April 8 2017: This elog by Jenne suggests that the installed PR2 has an RoC of approximately -700m. Koji has uploaded the phase map data for the RC TT mirrors to
    /users/public_html/40m_phasemap/40m_TT and 
    /users/public_html/40m_phasemap/40m_TT2. The G&H mirror data seems to be in the former folder, and it looks like there are two mirrors, one with RoC of ~ -700m and the other with RoC of ~ -500m. Does this mean PR2 has RoC -700m and SR2 has RoC -500m?
  • As a result, both the PRC and SRC were close to instability
  • By flipping the folding mirrors, the instability has been mitigated, but at the expense of the non-ideal situation where the AR coated side and the substrate are now inside the recycling cavity
  • We would like to order some new folding mirrors. In order to avoid receiving convex mirrors from the vendor, we want to specify a concave curvature for the HR side
  • The aim of this investigation is to look at how concave we should make these mirrors, because although the cavity stability improves with concavity of the HR side, possible disadvantages of having too convex mirrors are:
    • ​Mode-mismatch between the recycling cavities and the arms
    • Astigmatism

The study:

  • I've built a Finesse model for the 40m, which has been used for all the numerical studies quoted here
  • In constructing this Finesse model, I've used the following sources to specify various paramaters:
    • ​RoCs, R, T and physical dimensions of 4 test-masses, PRM, SRM and BS: Core optics wiki page
    • Losses - arm losses from Yutaro's measurements in elog11857 and elog11818 (distributed equally between ITM and ETM). For other optics, a generic value of 25ppm was used
    • "Ideal" lengths for our current modulation frequency were used for the various cavities (37.795m for the arms, 6.753m for PRC, 5.399 for SRC)
    • The folding mirrors (PR2, PR3, SR2, SR3) are initialized as flat in the model
  • I performed some low-level checks (e.g. arm linewidth, PRC FSR etc) to check that the model was sensible
  • I then proceeded to investigate the effects of curvature on the folding mirrors. Specifically, I investigated the following:
    • What is the mode mismatch between the recycling cavity mode and the arm as a function of the RoC of the folding mirror?
    • What is the effect of the RoC of the folding mirrors on the round-trip gouy phase accumulated (and hence the transverse mode spacing) in the recycling cavities?
  • For now, the parameter space explored is from 300m concave to 1000m concave. An RoC of 1km for a 2" optic corresponds to a sag of ~0.3 microns. I will explore the 1km-10km concave space and update the results shortly


  • Attachments #1 and #2 show the mode mismatch between the recycling cavity and the arm for various curvatures. The colorbars have been normalized to span the same range in all the plots
  • For both the PRC and the SRC, if we have folding mirrors with an RoC of 1000m concave, we will have a mode mismatch of 2-3%. The number gets worse the more convex the mirror
  • Attachments #3 and #4 show the one-way accumulated Gouy phase. Here, I have varied the curvature of the folding mirrors along a specific axis at a time (i.e. I've assumed that the folding mirrors are identical). I've also added the transverse mode spacing as a second y-axis. I have yet to check how these numbers compare with the linewidth of the 00-mode for the various fields, but for 1km concave folding mirrors, the TMS is in the region of 2MHz 

To do:

  • I will extend the range of RoCs explored to 10km concave and post results - but I will have to check with EricG to make sure that it is feasible for us to specify curvatures in this range
  • I was trying to use the RT gouy phase as calcluated by my Finesse simulations to plug into some analytical expressions to try and generate plots like this for various RoCs of the folding mirrors, but if the TMS calculations suffice, I will abandon these efforts
  • What are the other specifications we need to worry about before placing an order? Some thoughts from Rana's earlier elog:
    • The coatings need to be dichroic to allow extraction of the green beam (but only PR3/SR3 is currently dichroic?)
    • Wedge angle on the AR side?
  • Are there any other obvious sanity checks I should carry out?


Attachment 1: PRX_consolidated.pdf
Attachment 2: SRX_consolidated.pdf
Attachment 3: Gouy_PRC.pdf
Attachment 4: Gouy_SRC.pdf
  12411   Mon Aug 15 18:28:15 2016 gautamUpdateSUSAir-bake preparation

I assume that we are prepared to live with the pitch bias situation of ETMY (i.e. we can achieve a configuration in which there is some pitch bias to the coils, and the OSEMs are inserted such that the PD outputs are half their maximum value). Or at least that we don't want to go through the whole standoff-regluing procedure for ETMY as well.

So today I took the optic out, and began to make some preparations for the air bake.

  • Both optics are now sitting in their respective metal donuts. 
  • How do we want to bake the optics? Bob has said he has prepared the oven for this bake, and that he has configured the temperature controller to a setpoint of 34C, and a ramp time of 2 hours to reach that temperature from lab temperature (we should check this before putting the optics in there with our independent temperature sensor - also, he is away for the week now so we can't get his input on any of these). But what about the actual logistics of how the optics are going to be housed? Specifically:
    • Do we want the donut to sit on some sort of tray? Presumably it is not ideal to have the HR surface in close proximity to the oven floor? 
    • Does the oven need any special cleaning?
    • Do we cover the donut+optic setup with a glass jar? If we do, any particles we eject off the optic can't escape the confines of the bowl, and if we don't, detritus from elsewhere may settle on the optic?
    • How long do we want this bake to last? 24hours? 48 hours? Bob didn't have an answer when I asked him earlier in the afternoon...
  • I also removed the suspension block from the top of the towers of both ETMX and ETMY, so that Steve could work on sanding them before we acetone-wipe and bake the towers themselves.
    • It was very apparent that the weights of the two pieces were largely different (ETMY suspension block ~350g, ETMX suspension block ~960g), even though they have the same physical dimensions.
    • Investigation into why this was yielded nothing conclusive. But Steve and I think that the ETMY suspension block is made out of Aluminum rather than SS, which would explain why the wire grooves seem deeper in the ETMY piece than the ETMX piece. It is worth noting that the specification calls for SS and not aluminum. But the top piece of the ETMY suspension (and indeed the old ETMX suspension) looks different from the specification, in that they don't have tapped holes for the secondary wire clamps (see Attachment #1).
    • I'm not sure if this is important, but it is worth noting. Steve and I also checked the remaining suspension towers. We think that ITMY, BS, SRM and PRM have the correct (to specification) suspension block. We couldn't get a look at ITMX and didn't want to take the door off. So ETMY (and possibly ITMX) will be the only suspension(s?) with a different suspension block.
  • Steve's sanding efforts did not go ideally.
    • He was successful in removing the wire grooves.
    • But the sharp edge which is supposed to clamp the wire seems to have been rounded a little bit (see Attachment #1). 
    • Overall, the section that we was sanded looks lower (i.e. its like we've dug a small channel into the plane of the suspension block)
    • Given that we suspect the ETMY suspension block is Aluminum, it is likely that attempting to sand it will yield an even deeper channel.
  • Do we want to bake the suspension towers in the large baking oven? Presumably we don't want to bake the optics with anything else. But does the large oven need any special cleaning before we stick the towers in there?
  • ETMY has some acetone marks on it. I will try and have this removed by drag wiping with more acetone and isopropanol prior to the bake tomorrow. Anyways we will first-contact clean the HR (and AR) sides after the bake before installing the optic.

In summary, the questions that remain (to me) are:

  1. Are we okay using an Al suspension block?
  2. How perfectly do we want wire grooves from prior suspensions removed? It looks like sanding doesn't work well, do we want to consider sending this into the shop?
  3. Baking logistics, as described above.

I think we can start the baking of the optics tomorrow. The timeline for the suspension towers is unclear, depends on how we want to deal with the sanding dilemma.

Attachment 1: IMG_6816.JPG
  12413   Tue Aug 16 11:51:43 2016 gautamUpdateCOCRC folding mirrors - Numerical review

Summary of roundtable meeting yesterday between EricG, EricQ, Koji and Gautam:

We identified two possible courses of action.

  1. Flip the G&H mirror (PR2/SR2) back such that the (convex) HR face is the right way round. We want to investigate what are the requirements on a new PR3/SR3 optic that will guarantee cavity stability and also give good mode matching.
  2. Order two new sets of mirrors (i.e. replace all 4 folding mirrors). In this case, we want to spec a flat (how flat is reasonable to specify? EricG will update us) PR3/SR3, and design a PR2/SR2 with some concavity that will guarantee cavity stability in the event PR3/SR3 deviates from flatness (but still within what we spec). The choice to make PR3 as close to flat as possible is because the angle of incidence in our arrangement means that any curvature on PR3 dominates astigmatism.

I have done some calculations to evaluate the first alternative. 

  • Based on yesterday's preliminary discussion, we felt it is not reasonable to spec mirrors with RoC > 4km (sag of ~80nm). So I restrict my analyses to the range 300m-4km
  • Koji has a measurement of the phase maps for the G&H mirrors. The measured curvature is ~-500m. In my simulations, I've tried to allow for error in this measurement, so I look at the range -450m to -700m for the G&H mirror.
  • The Gouy phase analysis suggests we should look for an RoC of +500m (concave) for the new PR3/SR3 to have a TMS of ~1.5 MHz. Anything flatter (but still concave) means the TMS gets smaller.
  • The mode-matching in this region also looks pretty good, between 98% and 99%
  • I will post results of the analysis for the second alternative here for comparison

Something else that came up in yesterdays meeting was if we should go in for 1" optics rather than 2", seeing as the beam spot is only ~3mm on these. It is not clear what (if any) advantages this will offer us (indeed, for the same RoC, the sag is smaller for a 1" optic than a 2").


Attachment #1: Mode-matching maps between PRX and Xarm cavities, PRY and Yarm cavities with some contours overlaid.  

Attachment #2: Mode-matching maps between SRX and Xarm cavities, SRY and Yarm cavities with some contours overlaid. 

Attachment #3: Gouy phase calculations for the PRC

Attachment #3: Gouy phase calculations for the SRC


Attachment 1: PRC_consolidated.pdf
Attachment 2: SRC_consolidated.pdf
Attachment 3: GouyPRC.pdf
Attachment 4: GouySRC.pdf
  12414   Tue Aug 16 16:38:00 2016 gautamUpdateCOCRC folding mirrors - Numerical review

Here are the results for case 2: (flat PR3/SR3, for purpose of simulation, I've used a concave mirror with RoC in the range 5-15km, and concave PR2/SR2 - I've looked at the RoC range 300m-4km).

  • This is where we order two new sets of mirrors, one for use as PR2/SR2, and the other for use as PR3/SR3.
  • RoC of flat PR3/SR3 in simulation explored in the range 5km-15km (concave)
  • RoC of concave PR2/SR2 in simulation explored in the range 300m-4km (concave)

Attachment #1: Mode matching between PRC cavities and arm cavities with some contour plots

Attachment #2: Mode matching between SRC cavities and arm cavities with some contour plots

Attachment #3: Gouy phase and TMS for the PRC. I've plotted two sets of curves, one for a PR3 with RoC 5km, and the other for a PR3 with RoC 15km

Attachment #4: Gouy phase and TMS for the SRC. Two sets of curves plotted, as above.

Hopefully EricG will have some information with regards to what is practical to spec at tomorrow's meeting.

EDIT: Added 9pm, 16 Aug 2016

A useful number to have is the designed one-way Gouy phase and TMS for the various cavities. To calculate these, I assume flat folding mirrors, and that the PRM has an RoC of 115.5m, SRM has an RoC of 148m (numbers taken from the wiki). The results may be summarized as:

Cavity One-way Gouy phase [rad]           TMS [MHz]           
PRX 0.244 1.730
PRY 0.243 1.716
SRX 0.197 1.743
SRY 0.194 1.717

So, there are regions in parameter space for both options (i.e. keep current G&H mirrors, or order two new sets of folding mirrors) that get us close to the design numbers...

Attachment 1: PRC_consolidated.pdf
Attachment 2: SRC_consolidated.pdf
Attachment 3: GouyPRC.pdf
Attachment 4: GouySRC.pdf
  12415   Tue Aug 16 21:54:27 2016 gautamUpdateSUSAir-bake - IN PROGRESS

I put in both ETMX and ETMY into the air-bake oven at approximately 8.45pm tonight. They can be removed at 8.45am tomorrow morning. 

  • Given that we had previously melted a thermocouple in this oven, and there have been no high temperature bakes in it since, we ran the oven at 100C for about 3 hours in the afternoon
  • After that, I left the oven door open for an hour for the interior to return to room temperature
  • I then re-connected the controller (which doesn't seem very precise, it pulses the AC power to the oven in order to control the temperature), and dialled the oven back down to heating level 4, which is what Bob had it set at. I then waited for a couple of hours for the oven to reach ~34C
  • Before putting the optics in, I gave the inside of the oven a quick wipe with a clean wipe, and palced a layer of Al foil on the bottom of the oven
  • The optics are sitting on their donuts (see Attachment #1) - the copper wire elevates the optic+donut slightly and provides a path for air flow
  • ETMY was drag wiped with acetone+isopropanol prior to baking (to remove acetone stains from soaking to remove epoxy residue
  • We will of course be cleaning the optics with first contact prior to re-installation in the vacuum chambers
  • I am not sure what the extra cylindrical piece in there is, but Bob advised me to leave it in there so that's what I did
  • I've observed the temperature over ~2hours since I first put it in, and the oven/controller isn't going bonkers, so I'm trusting the controller and leaving for the night
Attachment 1: IMG_3005.JPG
  12417   Wed Aug 17 14:37:36 2016 gautamUpdateCOCRC folding mirrors - Numerical review


Cavity One-way Gouy phase [rad]           TMS [MHz]           
PRX 0.244 1.730
PRY 0.243 1.716
SRX 0.197 1.743
SRY 0.194 1.717

So, there are regions in parameter space for both options (i.e. keep current G&H mirrors, or order two new sets of folding mirrors) that get us close to the design numbers...

Keeping these design numbers in mind, here are a few possible scenarios. The "designed" TMS numbers from my previous elog are above for quick reference.

Case 1: Keep existing G&H mirror, flip it back the right way, and order new PR3/SR3. 

  • Spec PR3 to be concave with RoC 600 +/- 50m
  • This means the TMS in the PRC is in the range 1.4 MHz - 1.6 MHz [see this plot]
  • The mode matching efficiency for the PRC is > 98.5% [see this plot]
  • The TMS in the SRC is in the range 1.6 MHz - 1.8 MHz [see this plot]
  • Mode matching efficiency for SRC is > 98.5% [see this plot]
  • PRG between 34-38, depending on uncertainty in measurement of RoC of existing G&H mirror [see Attachment #1, added Nov 11 2016]

Case 2: Order two new sets of folding mirrors

  • Spec PR3/SR3 to be flat - for purposes of simulation, let's make it concave with RoC 10 +/- 5 km
  • Spec PR2/SR2 to be concave with RoC 1500 +/- 500m
  • The TMS in the PRC is between 1.7 MHz and 1.85 MHz [see this plot]
  • Mode matching efficiency is >98.5% in the PRC [see this plot]
  • TMS in the SRC is between 1.7 MHz and 2 MHz [see this plot]
  • Mode matching efficiency >99.0% in the SRC [see this plot]

At first glance, it looks like the tolerances are much larger for Case 2, but we also have to keep in mind that for such large RoCs in the km range, it may be impractical to specify as tight tolerances as in the 100s of metres range. So these are a set of numbers to keep in mind, that we can re-iterate once we hear back from vendors as to what they can do.

For consolidation purposes, here are the aLIGO requirements for the coatings on the RC folding mirrors: PR2, PR3, SR2, SR3

Attachment 1: PRG.pdf
  12420   Wed Aug 17 23:00:57 2016 gautamUpdateSUSAir-bake of towers

I just put in the following into the air bake oven for a 12 hour, 70C bake:

  • ETMX and ETMY cages (with sanded suspension blocks loosely tightened for now, we will tighten them after the bake)
  • 13 new wire clamps that were recently made by the shop
  • 7 lengths of suspension wire (since the new wire is unlikely to arrive for another 2 weeks). This should be sufficient in case we overtighten the wire clamps a couple of times and the wire snaps.

I put these in at 10.30pm. So the oven will be turned off at 10.30am tomorrow morning. The oven temperature seems stable in the region 70-80 C (there is no temperature control except for the in built oven control, I just adjusted the dial till I found the oven remains at ~70C.

Tomorrow, we will look to put on first contact onto the ETMs, and then get about to re-suspending them.

Attachment 1: IMG_3006.JPG
  12422   Thu Aug 18 14:14:20 2016 gautamUpdateSUSAir-bake of towers - finished

I took the two cages, wires and wire clamps out this morning, back into the cleanroom after their 12 hour 70C bake. 

I've also applied first contact to the AR face of the optics. Steve is preparing a jig which will allow us to apply first contact on the HR side with the optic horizontal. The idea is to apply a large coating first, to clean the bulk of the HR surface, and peel it off before re-suspending the optic. Then we can paint on a smaller area, suspend the optic (and hope the pitch balancing is alright) before taking the whole assembly into the chamber where it will be peeled off. 

Calum recommended that we buy a new ionizing gun + electrometer assembly (apparently our current set up is woefully obsolete) but I don't know if we can have these in time for the first contact peeling...

  12424   Fri Aug 19 22:51:12 2016 gautamUpdateSUSETMs first-contacted

I've applied first contact to both the ETMs. They're now ready to be suspended. I've also cut up some lengths of the new wire and put them in the oven for a 12 hour 70C bake. 

  • For both ETMs, I first applied first contact to the bulk of the HR and AR surfaces (all the way out to the edge for the HR, for the AR as large an area as possible without getting too close to the magnets). Calum recommended pouring first contact onto the horizontal optic, but since I had no practise with this method, I opted not to try it out for the first time on our ETMs
  • After allowing this to dry for 24 hours, I peeled this layer off. Visual inspection suggests that the whole film came off cleanly. 
  • I then applied first contact to a smaller area around the center of the optic for only the HR surface. This will only be peeled off once the suspended optic is back in the vacuum chamber. This way, we keep the HR face protected for as long as possible.
  • Even though we applied F.C to both faces of the ITMs, I don't think its so important to keep a film on the AR side of the ETMs till we take it in. So I didnt re-coat the AR side with a smaller area of F.C. This way, if we want, we can do the OSEM assembly in the cleanroom without having to worry about peeling the F.C off with limited access to the rear of the optic.
  • I also opted to bake some lengths of the newly arrived steel wire for suspension. Not sure how important/useful this bake will be.

Unless we want the AR surface to also have a small F.C coat until the optic is in the vacuum chamber, I think I will proceed with re-suspending the ETMs..

  12426   Sun Aug 21 16:23:05 2016 gautamUpdateSUSETMX suspended
  • ETMX has been successfully suspended
  • I've used one of the new wire clamps, and also the new suspension wire 
  • Because the HR face has first contact, pitch balancing cannot be checked at this point. But since the pitch balance was checked after the standoff was glued, there is no reason to believe it would have changed
  • Heights of the two scribe lines were checked with the microscope and verified to be at 5.5" above the tabletop. Also checked the position of the scribe line on the bottom of the optic to make sure the optic wasn't somehow rotated
  • Checked that wire was in the groove in the standoff on both sides, and that the optic was freely hanging with no EQ stops engaged. I also verified that there are no obvious kinks/other funny features where the wire is in contact with the optic barrel below the standoffs.
  • Wire clamps were tightened with the new torque wrench and 5 in. lb. (0.56 N m) of torque. Primary clamp was successfully tightened. However, the wire snapped between the primary and secondary clamps on one side. It is unclear to me how or why this happened. But since the primary wire clamp is the important one, I don't think it is worth re-suspending ETMX all over again
  • I've left the cage on the flow bench for now, with EQ stops engaged. OSEM coils have yet to be inserted, but I suppose we want to do this in the vacuum chamber now to do the fine rotation to minimize the bounce mode in the OSEM signals
  • I've prepared ETMY and its cage for suspension, will work on it tomorrow
Attachment 1: IMG_3018.JPG
  12428   Mon Aug 22 13:06:11 2016 gautamUpdateSUSETMY suspended

Today morning, I suspended ETMY and made the same checks dscribed below. The clamping went smoothly, 5 in. lb. of torque seems sufficient, in the limited observation time, there has been no evidence of wire sag. Today afternoon, we will go about putting the OSEM coils in, setting their equilibrium points etc. This may need to be re-done once the optic is in the chamber and the first contact has come off, but at least we can coarsely place them in the relative convenience of the cleanroom. 

GV EDIT 9.15pm 22 Aug: Eric had a look at both towers and pointed out that I had neglected to use washers on the wire stops. After consultation with Steve, I decided that it is not worth it to remove the clamp and re-suspend the optic - it is likely that the current suspension process will have caused new grooves in the suspension block, which will have to be removed, and the sanding process did not work so well last time. In any case, the net effect of this will be that the actual torque with which the clamp is tightened will be slightly different from 5 in. lb., but since there is no evidence that the clamp isn't tight enough / is too tight, I think it is okay to push ahead. 

  • ETMX has been successfully suspended
  • I've used one of the new wire clamps, and also the new suspension wire 
  • Because the HR face has first contact, pitch balancing cannot be checked at this point. But since the pitch balance was checked after the standoff was glued, there is no reason to believe it would have changed
  • Heights of the two scribe lines were checked with the microscope and verified to be at 5.5" above the tabletop. Also checked the position of the scribe line on the bottom of the optic to make sure the optic wasn't somehow rotated
  • Checked that wire was in the groove in the standoff on both sides, and that the optic was freely hanging with no EQ stops engaged. I also verified that there are no obvious kinks/other funny features where the wire is in contact with the optic barrel below the standoffs.
  • Wire clamps were tightened with the new torque wrench and 5 in. lb. (0.56 N m) of torque. Primary clamp was successfully tightened. However, the wire snapped between the primary and secondary clamps on one side. It is unclear to me how or why this happened. But since the primary wire clamp is the important one, I don't think it is worth re-suspending ETMX all over again
  • I've left the cage on the flow bench for now, with EQ stops engaged. OSEM coils have yet to be inserted, but I suppose we want to do this in the vacuum chamber now to do the fine rotation to minimize the bounce mode in the OSEM signals
  • I've prepared ETMY and its cage for suspension, will work on it tomorrow


Attachment 1: IMG_3019.JPG
  12430   Mon Aug 22 18:04:24 2016 gautamUpdateSUSETMY OSEMs inserted

[Johannes, gautam]

We worked on trying to insert the OSEMs in the optimal positions such that the coupling of the bounce mode into the OSEM sensor signals was minimised.

First, I gave the barrel of the optic a wipe with some optical tissue + acetone in order to remove what looked like some thin fibres of dried first contact. It may be that while I was applying the F.C., the HEPA air flow deposited these on the barrel. In any case, they came off easily enough. There is still a few specks of dust on various parts of the barrel, but it is likely that these can just be removed with the ionized air jet, which we can do after putting the optic in the chamber.

We then did the usual OSEM insertion till the magnets neutral position was such that the sensor output was ~50% of the fully open value (turned the HEPA off for the remainder of this work). I tweaked the bottom OSEM plate a little in order to center the magnets relative to the coil as best as possible. Once this was done, we attempted to look at spectra of the sensor outputs, with 0.05 Hz bandwidth - however, we were unable to identify any peak at 16.4 Hz, which is what a Jan 2015 measured value wiki page claims the bounce mode frequency is (although this was an in vacuum measurement). There were a couple of peaks at ~15.7 Hz and ~16.7 Hz, but I can't think of any reason why the bounce mode resonance should have changed so much - after all, this is ETMY for which no standoff regluing was done. The only difference is that there is some first contact + peek mesh on the HR face now, but I doubt this can modify the bounce resonance frequency so much (this is just my guess, I will have to back this up with a calculation).

Anyways we decided to take this up again tomorrow. Things are progressing fairly well now, I hope to be able to put in ETMY back into the chamber at some point tomorrow and commence re-alignment of the interferometer. I've left the OSEMs in for today, with the EQ stops not engaged but close by. HEPA has been turned back on.

  12434   Tue Aug 23 19:35:38 2016 gautamUpdateSUSETMY back in IFO

[johannes, gautam]

Summary: Today we moved the suspended ETMY optic back into the chamber from the cleanroom. Once in the chamber, we positioned the optic using the stops that marked the previous position of the optic. We then shortened the arm length by 19mm (in order to match the X and Y arm lengths. The F.C. coat on the HR face was removed prior to the final placement of the optic. We then adjusted the OSEM positions in their holders to get the sensor outputs to half their maximum value.

We did not get to check where the input beam hits the optic or see if the pitch balance of the optic is such that the reflected beam makes it back to the ITM. The plan for tomorrow is to do this. 

Part 1: Cleanroom work

  • We worked a little more on trying to adjust the rotational position of the OSEM coils in order to minimize the coupling of the bounce mode into the sensor signals. 
  • We had limited success in this regard. After about an hour, we concluded that it made more sense to do this in the chamber itself. For one thing, the drive electronics for the Y end are different (in the cleanroom, we are using the X end electronics, satellite box etc.).
  • We adjusted the position of the OSEMs till the sensor output readout was half the open value as best as we could. We also made sure that the wire was in the groove on both sides and that the magnets were well centered in the vertical direction relative to the OSEM coils and that there was no danger of knocking any magnets off (see attached pictures).
  • We then engaged all the EQ stops, and transferred the suspension cage to a cart (topped with Al foil, wiped clean) for transportation to the Y-end (with OSEMs left in).

Part 2: Transportation of optic

  • Nothing special here, just took great care while going over bumps near doors between the cleanroom and the IFO, and along the Y-arm itself.
  • Definitely a 2 man job - one person can lift a pair of wheels over any bumps while the other can make sure there is no danger of the cage toppling over. 

Part 3: Chamber work

  • PSL shutter was closed for this part of work. Earlier today, I found that C1SUSAUX had failed yet again (why are all the slow computers dying more often nowadays?!). I restarted the slow machine, and locked the mode cleaner. The alignment hadn't drifted so much from when EricQ had last aligned the IMC, and with only minimal tweaking, I was able to lock the IMC and see a beam on the REFL camera.
  • First, I transferred the suspension cage onto the edge of the table inside the chamber. Care was taken not to accidentally place the cage onto the trailing OSEM wires.
  • There were some specks of dust on the barrel of the optic, and also the cage. These were removed with clean wipes and isopropanol.
  • I judged that it would be too precarious to remove the F.C. with the optic in its final desired position. So we decided to take the coat off with the optic at the edge of the table. The central part of the HR face looks pretty clean. Even though the whole HR face was cleaned with F.C., the part that was left uncovered prior to putting the optic back into the chamber has a few specks of dust on it (see attachments). These could not be removed just by blowing ionized air. I was hesitant to drag wipe the optic, so I left things as is. In any case, the optic as a whole is MUCH cleaner (to my eye at least) than prior to the cleaning. 
  • Conveniently, the stops marking the previous position of the optic were on the far side and back.
  • Since we wanted to shorten the Y arm length by 2 cm, we placed a clean steel ruler of width 19mm in front of the rear stop (see attached pictures). I then moved the cage back along the side stop till I hit the ruler.
  • I then clamped the optic down, removed the spacing ruler, and re-adjusted the position of the rear stop to mark the new position of ETMY.
  • We were concerned that the change of position of the cage on the table affected the leveling. Checking with a clean spirit level, we found evidence of a slight tilt in the direction towards the vertex of the IFO, as expected from the way the ETMY cage was moved. To compensate for this, I moved one of the counterweight masses (see attachments) till the spirit level showed the table to be level (to its resolution) in two perpendicular directions
  • We then plugged in the OSEMs into the DB25 connectors on the table. We found that the Y-end electronics were giving different readouts from what we had been seeing in the cleanroom with the X end electronics (not surprising I guess). We resolved to pull out all the OSEMs, check their maximum sensor output values, and re-insert them till the sensor output was half this maximum as best as we could. NOTE TO SELF: UPDATE THE WIKI PAGE!
  • We turned on the damping, and found that the exisiting input matrix performs fairly well.
  • We took a quick look at the spectra of the sensor outputs - interestingly, with the suspension on the seismic stacks inside the chamber, the 16.4 Hz bounce mode peak showed up clearly (these were totally absent in the cleanroom). I did not attempt any fine rotation of the OSEMs in the holders (it is not even clear to me how good/bad the present configuration is) because I reasoned we first need to apply a pitch bias to get the beam back to the ITMY chamber and then re-adjust the OSEM coils. The bounce mode decoupling will be the last step. 
  • For tonight, we decided to leave the optic freely swinging (with EQ stops close by) so that tomorrow, we can look at the offline spectra of sensor outputs and if necessary, re-diagonalize the suspension. 
  • After checking nothing unwanted was left behind in the chamber, we closed it up for tonight.

Plan for tomorrow:

  • Pitch balancing check (by looking at reflected beam at ITMY)
  • Re-adjust OSEMs on ETMY, minimize bounce mode coupling into sensor outputs
  • Make Y arm cavity by re-positioning ITMY


Attachment #1: Wire is in groove in side without OSEM

Attachment #2: Wire is in groove in side with OSEM (picture taken with OSEM coil removed)

Attachment #3: UL magent relative to OSEM coil

Attachment #4: LL magent relative to OSEM coil

Attachment #5: LR magnet relative to OSEM coil

Attachment #6: UR magnet relative to OSEM coil

Attachment #7: Side magnet relative to OSEM coil

Attachment #8: ETMY HR face with F.C. film removed. Non-covered part isn't super clean, but the covered part itself does not have any large specks of dust visible.

Attachment #9: Scheme adopted to shorten Y arm length by 19mm.

Attachment #10: Current situation inside EY chamber. Counterweight that was moved to balance the table is indicated.


Attachment 1: IMG_3025.JPG
Attachment 2: IMG_3035.JPG
Attachment 3: IMG_3030.JPG
Attachment 4: IMG_3029.JPG
Attachment 5: IMG_3028.JPG
Attachment 6: IMG_3027.JPG
Attachment 7: IMG_3026.JPG
Attachment 8: IMG_3036.JPG
Attachment 9: IMG_3038.JPG
Attachment 10: IMG_3045.JPG
  12443   Thu Aug 25 20:07:35 2016 gautamUpdateSUSOSEM issues - maybe resolved?

[lydia, johannes, gautam]

While struggling to minimize the bounce mode coupling into the sensor signals, we briefly poked into the ITMY chamber, and think that we understand the origin of the problem, at least for the SRM.

Essentially, we believe that moving the ITM from its nominal position to the edge of the table has shifted the table leveling such that the optic (SRM) is tilted backwards (hence the magnets are completely occluding the LEDs) and that perhaps the optic is in contact with one or more of the bottom EQ stops (hence the signal is stationary, no oscillations visible. The timing of the signals going dark as Eric mentioned supports this hypothesis. The reason why we believe this to be the case is that when I was trying to loosen the screw on the clamp holding the ITMY cage to the table, we saw ~1Hz signals from all 5 SRM OSEM sensors, though they were well away from the nominal equilibrium values. The arrangement of towers in the chamber right now did not permit me to get a good look at the SRM magnets, but I believe they are all still attached to the optic, and that they are NOT stuck to the OSEM coils. If this is indeed the case, putting ITMY back in will solve the issue completely.

It is not clear what has happened to the LR coil on the PRM - could it be that during the venting process, somehow the LR magnet got stuck to the OSEM? If so, can we free it by the usual bias jiggling?

  12444   Thu Aug 25 21:11:43 2016 gautamUpdateSUSETMY back in IFO

There was some confusion as to the order in which we should go about trying to recover the Y arm. But here are the steps we decided on in the end.

  1. Use the tip tilts to make sure the input beam is hitting roughly the center of ETMY, with ITMY left out.
  2. Use the reflected beam from the ETM as viewed in the ITM chamber to set the pitch bias on ETM.
  3. Center OSEM coils on ETM, rotate them to minimize bounce mode coupling into the sensor signals.
  4. Install the ITM, look for cavity flashes, and use alignment biases to try and lock the Y arm in air.

Yesterday, Eric, Johannes and I tried to do step 1, but after some hours of beam walking, we were unsuccessful. Today morning, Koji suggested that the ITM wedge could be playing a part - essentially, over 40m, the wedge would shift the beam horizontally by ~30cm, which is kind of what we were seeing yesterday. That is, with 0 biases to the tip tilts, we could find the beam in the ETM chamber, towards the end of the table, ~30cm away from where it should be (since the input pointing is adjusted taking this effect into account, but we were doing all of our alignment attempts without the ITM in).

So, we shifted strategy today. The idea was to trust that the green beam was well aligned to the cavity axis (we had maximized the green transmission before the vent), and set the pitch bias voltage to ETMY by making the reflected beam overlap with itself. This was done successfully, and we needed to apply a pitch bias of ~-2.70 (value on the MEDM screen slider), which agrees well with what I was seeing in the cleanroom. We then adjusted the OSEMs to bring the sensor outputs to half their nominal maximum value. Next, we went into the ITMX chamber, and were able to find the green beam, at the right height, and approximately where we expect the center of the ITM to be (this supports the hypothesis that the green input pointing was pretty good). I am however concerned if this is truly the right value of the bias for making a cavity with the ITM, because the pre-vent value of the pitch bias slider for ETMY was at -3.7, which is a 30% difference from the current value (and I can't think of a reason why this should have changed, the standoffs weren't touched for ETMY). If we go ahead and fine tune the OSEMs rotationally assuming this is the right bias to have, we may end up with sub-optimal bounce mode coupling into the sensor signals if we have to apply a significantly larger/smaller offset to realise a cavity? The alternative is to put in the ITM, and set the pitch balance using the IR beam, and then go about rotating OSEMs. The obvious downside is that we have to peel the F.C. off, risking dirtying the ITMs.

For much of the rest of the day, we were trying to play with the rotation of the OSEM coils in order to minimize the bounce mode coupling into the sensor signals. We weren't able to come up with a good scheme to do this measurement, and I couldn't find any elog which details how this was done in the past. The problem is we have no target as to how good is good enough, and it is extremely difficult to gauge whether our rotation has improved the situation or not. For instance, with no rotation of the OSEMs, by observing the bounce mode peak height over a period of 20-30 minutes, we saw the peak height change by a factor of at least 3. This is not really surprising I guess, because the impulses that are exciting the bounce mode are stochastic (or at least they should be), and so it is very hard to make an apples to apples comparison as to whether a rotation has improved the situation on.

After some thought, the best I can come up with is the following. If anyone has better ideas or if my idea is flawed, or if this is a huge waste of time, please correct me!

  1. Adopt this spectrum (except the side signal) as a reference for what constitutes "good" rotational orientation of the OSEMs (even though it is for ETMX not ETMY).
  2. Start with one coil. The suspension assembly document tells us to expect the orientation with minimal bounce coupling to be located within 20 degrees of "the vertical", the vertical being defined as that orientation in which the line connecting the LED and PD as seen by eye is vertical. So start with the coil oriented vertically, as best as possible by eye.
  3. Damp the optic for ~1min, with the curtain covering the chamber entrance. Ideally, we want the door back on, as this lowers the noise floor significantly, but it is too cumbersome to replace even the light door so I suppose we will have to compromise.
  4. Take a reference spectrum. In the interest of time, I think a bandwidth of 0.1Hz on the Fourier Transform should be sufficient. (Tangentially related - the BW you specify in the measurement setup in DTT doesn't seem to be the BW with which the spectrum is computed, I wonder why that is?)
  5. It is basically impossible to rotate the coil continuously. So divide the range to be explored into steps (so each step will involve rotating the coil by ~2 degrees (I don't know if this number is physically feasible, but some discrete step will be involved). Rotate the coil, center it such that the sensor output is close to half the maximum.
  6. Pull the curtain down, damp the optic, and take another spectrum. If the bounce mode peak is higher, abandon this direction of rotation, and rotate the other way. We accept as the optimal position the one from which the bounce mode peak height gets worse by rotating to either side.

Of course, this method assumes that the excitation into the bounce mode is a constant over time. I'm also attaching the spectrum of the OSEM sensor signals right now - the optic is in the chamber, free swinging (no damping) with the door on (so it is fairly quiet). The LR signal seems to be the best (indeed seems to match the levels in this plot), but it is not clear whether the others can be improved or not.

There was also some concern as to whether we will be able to see the beam in the ETMX chamber once the ITM has been re-installed. Assuming we get 100mW out of the IMC, PRM transmission of 5.5%, and ITM transmission of 1.4%, we get ~35uW incident on the ETM, which while isn't a lot, should be sufficient to see using an IR card.

Attachment 1: ETMY_BounceSpectra_25Aug2016.pdf
  12445   Fri Aug 26 11:35:44 2016 gautamUpdateSUSETMY UL sensor problematic

I've been noticing that the ETMY UL sensor output has been erratic  over the last few days. It seems to be jumping around a lot, even though there is no discernable change in any of the other sensor signals. Damping is OFF, which means the sensor signals should just be a reflection of actual test mass motion. But the fact that only one sensor output is erratic leads me to believe that the problem is in the electronics. I've also double checked that we aren't touching any EQ stops. Also, we had centered all the sensor outputs to half their maximum value pretty carefully. But looking at the Striptool traces, I now find that the UL sensor output has settled at some other value. Simply removing the OSEM connector and plugging it in again leads to the sensor output going back to the carefully centered value. Could it be that the photodiode has gone bad? If so, do we have spare OSEMs to use? I will also re-squish the satellite box cables to see if that fixes the problem.


Attachment #1: Sensor output spectra around the bounce mode peak. Nothing was touched inside the chamber between the time this spectrum was taken and the spectrum I put up last night (in fact the chamber was closed)

Attachment #2: UL sensor output is erratic, while the others show no glitching. This supports the hypothesis that the problem is electronic. The glitch itself happened while the chamber was closed.

Attachment #3: The only difference between this trace and Attachment #2 is that the UL connector was removed and plugged in (OSEM wasn't touched)

Attachment 1: ETMY_BounceSpectra_26Aug2016.pdf
Attachment 2: 41.png
Attachment 3: 19.png
  12448   Fri Aug 26 17:48:14 2016 gautamUpdateSUSbounce mode coupling reduction

We worked on reducing the bounce mode coupling into the sensor signals today. After some trial and error, essentially following the procedure I had put up in my previous elog, we think we were successful in reducing the coupling. We have now left the optic free swinging, so that we can collect some data and look at a spectrum with finer bandwidth. But as per the methodology we followed, we saw that the peak height corresponding to the bounce mode increased when we rotated the OSEM either side of its current position (except for the side OSEM, which we felt was in a good enough position to warrant not touching it and messing it up - of course only the spectrum will tell us if we are right or not. I also took some pictures with the camera with the IR filter removed, but we couldn't get any real information from these photos. I also checked with Jenne and Jamie who both suggested that they didn't have any metric with which they judged if the rotation of the OSEM was good enough or not. So we will wait to have a look at the spectrum from later tonight, and if it looks reasonable enough, I vote we move on. As Eric suggested, perhaps we can repalce the UL OSEM coil and see if that solves the apparent UL coil problem. Then we should move on to putting the arm cavity together.

Addendum 11pm 26 Aug 2016: I've uploaded the spectra - looks like our tweaking has gained us a factor of ~2 on LL, LR and SD, and no significant improvement on UL and UR compared to yesterdays spectrum.

Attachment 1: ETMY_BounceSpectra_26Aug2016_1.pdf
  12449   Sun Aug 28 21:40:11 2016 gautamUpdateSUSETMY UL sensor problematic

I wanted to observe the UL coil for any excursions over the weekend. Looking at the 2 day trend, something is definitely wrong. These glitches/excursions are much more pronounced than what is seen in the pre-vent plots Steve had put up.

In order to try and narrow down whether the problem is with the Satellite box or the LED/PD themselves, I switched the Satellite box at the Y end with the Satellite box for ITMY (at ~930pm tonight). Hopefully over a 12 hour observation period, we see something that will allow us to make some conclusion. 

Attachment 1: ETMY_UL_problematic.png
  12450   Mon Aug 29 09:37:05 2016 gautamUpdateSUSETMY UL sensor problematic

It looks like the problem is indeed in the Satellite box. Attachment #1 shows the second trend for the last 12 hours (~930pm 28 Aug 2016 - 930am 29 Aug 2016) for the ITMY and ETMY sensor signals. The satellite boxes for the two were switched during this time (the switch is seen at the leftmost edge of the plots). After the switch, ETMY UL has been well behaved, though ITMY UL shows evidence of excursions similar to what we have been seeing. All the ITMY coils are pulled out of the suspension cage currently, and are just sitting on the optical table, so they should just be reading out a constant value. I think this is conclusive evidence that the problem is with the Satellite box and not the OSEM itself. I will pull the Satellite box out and have a look at its innards to see if I can find the origin of the problem...

Attachment 1: satelliteBox.png
  12451   Mon Aug 29 14:42:06 2016 gautamUpdateSUSETMY Satellite box diagnostics

I opened up the ETMY satellite box to investigate the glitches seen in the UL sensor output. 

Attachments #1 & 2: The connection to J4 from the satellite amplifier goes through a "satellite amplifier termination board", whose function, according to the schematic, is to prevent oscillations of the output amplifiers for the PD outputs. This seems to have been attached to the inside cover of the Satellite box by means of some sort of sponge/adhesive arrangement. The box itself gets rather hot however, and the sponge/adhesive was a gooey mess. I believe it is possible that some pins on the termination board were getting shorted - so if the 100 ohm resistor for the Ul channel that is meant to prevent the output amplifier oscillating was getting shorted, this could explain the problem.

For now, I cleaned off the old sponge/adhesive as best as I could, and used 4 pads of thick double sided tape (with measured resistance > 60Mohm) to affix the termination board to the inside of the box lid. In the ~3 hours since I have plugged the satellite box back in, there has been no evidence of any glitching. 

Of course, it could be that the problem has nothing to do with the termination board, and perhaps an OpAmp in the UL signal chain is damaged, but I stopped short of replacing these for now. I plan to push on with putting the IFO back together, and will keep an eye on this problem to see if more action is needed.

Also, if the inside of the ETMY satellite box had this problem of the sponge/adhesive giving way, it may be that something similar is going on in the other boxes as well. This remains to be investigated.

Attachment 1: IMG_6840.JPG
Attachment 2: IMG_6841.JPG
  12455   Tue Aug 30 20:26:36 2016 gautamUpdateSUSITMY installed

[gautam, johannes, lydia]

Today we installed ITMY into position in the chamber.

  • First, we took the F.C coat off both faces
  • A stream of ionized nitrogen was used during the peeling process. We took as much care as possible not to blow towards the SRM. 
  • F.C. films came off smoothly. But when we looked at a picture we took prior to putting the optic in place, it looks like there may be a sliver of F.C. left on the optic. There are also a few specks of dust visible on the HR face, but well away from the clear aperture (see Attachment #1). Do we want to use isopropanol + optical tissue to try and remove these?
  • After F.C removal, we moved the optic into place against its stops. Returned OSEM connector tower to approximately its original place as it was moved to facilitate shifting the ITM to the edge of the table. 
  • I cleaned up the tangled mess of OSEM connector wires. On the ITMY tower, the OSEM cables have been tied using pieces of thin copper wire so as to avoid the wires straying into the beam path. Checked that wires are in grooves on both sides.
  • Unfortunately we were not able to start on setting up a cavity today, because when we checked the leveling of the ITM, we found that it was significantly not level. This is probably because the ITM was at the edge of the table. The cage is rather heavy and the location it was put in had a large lever arm. In any case, the table is slowly relaxing back to their usual state, Steve recommended we leave it overnight.
  • Other issues:
    • the UL sensor on ITMY also seemed to show some evidence of glitchy behaviour. Looking in the Satellite box, I didn't see any obvious probelms like I did for the ETMY box (for which I am not even sure if I did a legitimate fix anyways). I guess we have to keep observing and think about doing something about this if it really is problematic.
    • SRM barrel is pretty dusty. So is SR3. Do we want to clean these? If so how? F.C. or isoprop drag wipe?

We did some quick checks with the green beam and the IR beam. With the help of the custom Iris for the suspension towers, we gauged that both beams are pretty close to the center of the test mass. So we are in a not unreasonable place to start trying to align the beam. Of course we didn't check if the beam makes it to the ETM today.

The SRM OSEM sensor problem seems to have been resolved by moving the ITM back to its place as we suspected. The values are converging, but not to their pre-vent values (attachment #2). We can adjust these if necessary I guess... Or perhaps this fixes itself once the table returns to its neutral position. This remains to be monitored.

In the never-ending B-R mode reduction saga - we found what we think is an acceptable configuration now. Spectrum attached (Attachment #3). The top two OSEMs are now nearly 90 degrees rotated, while the bottom two are nearly horizontal. Anyways I guess we just have to trust the spectra. I should also point out that the spectra change rather significantly from measurement to measurement. But I think this is good enough to push ahead, unless anyone thinks otherwise?

Attachment 1: IMG_3052.JPG
Attachment 2: SRM_sensor_level_comp.png
Attachment 3: ETMY_BounceSpectra_30Aug2016.pdf
  12457   Wed Aug 31 22:09:18 2016 gautamUpdateSUSY arm locked to Green

Koji tweaked the alignment sliders till we were able to get the Y arm locked to green in a 00 mode, GTRY ~ 0.5 which is the prevent number I have in my head. The green input pointing looks slightly off in yaw, as the spot on the ITM looks a little misaligned - I will fix this tomorrow. But it is encouraging that we can lock to the green, suggests we are not crazily off in alignment.

[Ed by KA: slider values: ETMY (P, Y) = (-3.5459,  0.7050), ITMY (P, Y) =  (0.3013, -0.2127)]

While we were locked to the green, ITMY UL coil acted up quite a bit - with a large number of clearly visible excursions. Since the damping was on, this translated to somewhat violent jerking of ITMY (though the green impressively remained locked). We need to fix this. In the interest of diagnosis, I have switched in the SRM satellite box for the ITM one, for overnight observation. It would be good to narrow this down to the electronics. Since SRM is EQ-stopped, I did not plug in any satellite box for SRM. The problem is a difficult one to diagnose, as we can't be sure if the problem is with the LED current driver stage or the PD amplifier stage (or for that matter, the LED/PD themselves), and because the glitches are so intermittent. I will see if any further information can be gleaned in this regard before embarking on some extreme measure like switching out all the 1125 OpAmps or something...

Does anyone know if we have a spare satellite box handy? 

  12458   Wed Aug 31 23:01:02 2016 gautamUpdateSUSthe chamber HEPA tents are back

Some more numbers we found while working in/around the chamber today:

Particle counts
Area 0.3 micron count (per cfm) 0.5 micron count (per cfm)
Vacuum chamber (vented) ITMY  ~5000 ~600
HEPA enclosure on ITMY door <100 0
Lab ~100,000 ~6000

These numbers were measured using our particle counter, which has a pump rate of 0.1 cfm, so the numbers above are 10x the numbers shown on the instrument after a measurement to account for this.

Essentially, the chamber is pretty dirty. Peeling the F.C with hard to reach optics like the ITM installed in place is not really feasible, and after peeling the F.C, we are looking at a best case of an additional 1-2 weeks in air to align the IFO, during which the optic is apparently exposed to quite a lot of particulates. In fact, with the high intensity flashlight left on, I actually saw some flecks of dust occassionally floating around inside the chamber while I was working on the optic. But this is just something we have to accept I guess.

  12466   Fri Sep 2 21:09:08 2016 gautamUpdateSUSY arm locked in air

[johannes, lydia, gautam]

  • The Y arm has been locked to IR in air using POY11 as an error signal yes
  • We had been seeing flashes in the arm since yesterday, but were unable to lock
  • Today we re-did the alignment procedure much the same way as yesterday
    • It is useful to put in the slide-on irides onto the suspension tower for this sort of alignment
    • We were a bit more systematic in aligning back-reflections to overlap each other today
    • It is useful to stick the IR card just in front of the iris, and align the tip tilts by looking at the scatter on the camera. At least for Yaw, this works pretty well, probably a more reliable reference than contorting oneself inside the vacuum chamber to see if we are well aligned or not.
  • Two fixes that made locking possible today:
    • The POY error signal had a large DC offset. I zeroed the offset and adjusted the demod phase to make the error signal 0 when the IMC was unlocked
    • I replaced the 50-50 beam splitter that was dividing the transmitted light between the QPD and Thorlabs PDs with a 2" Y1 CVI mirror - this meant that the flashes we had with the arm roughly aligned went from < 0.1 to a healthier 0.25, which allowed easier locking
  • The POY whitening gain was unchanged from when we locked the Y arm in air just after venting and before taking the doors off
  • The mode is barely visible on ITMY face, although I guess this is to be expected given we are at low power
  • Lydia then tuned the arm alignment more finely such that the transmission is now ~0.65 (See Attachemnt 2 for slider values)
  • From values from normal (pre-vent) IFO operation, I would have expected us to get a transmission of about 1 assuming 100mW going into the IFO from the IMC - and so with the BS switched out for an HR mirror, a transmission of ~2. What we get is about 1/3 of this value. Perhaps the IMC isn't so well aligned, but it is hard to imagine we have only 30mW going into the IFO. Or perhaps the input pointing is sub optimal (I did not run ASS, perhaps I should have)

GV EDIT Sep 5: These numbers do make sense if the ND filter that was on the Transmon QPD had ND = 0.6 (there are two at the end, one labelled ND 0.6 and the other labelled ND10 though the latter label looks like some custom label so I don't really trust that value), even though only one was on, unfortunately I don't remember which. So, for 10% of input power with a factor of 8 increase because the ND filter is removed and also that the 50% BS has been replaced with a HR mirror, we expect a transmission level of ~0.6 (compared to the normalized value under normal IFO operation) which is close to what we see...

  • The UL coil problems continue to plague us but we were able to lock the arm regardless

In any case, I think we can work on putting in the X arm now and work on recovering that. 

To do for the Y-arm (now that the F.C. is off, we should try and do this in as few chamber openings as possible):

  • Fix problematic ITMY UL coil
  • Rotation of all 5 ITMY OSEM coils for B-R peak reduction in sensor outputs
  • Adjustment of axial position of all OSEM coils on ITMY and ETMY to better center the PD outputs to half their saturation value, given that the pitch and yaw biases to the optics have changed since this was last done
  • Insertion of new baffles - try and center the IR and green beams as best as possible on these so that they serve as an alignment reference in the future

Then we need to do all of this for the X arm as well. The PRM LR coil is still giving no output - I will try moving the bias sliders around to see if this is a stuck magnet situation, but perhaps it is not. Since Eric's 3-satellite-box-monte did not yield any positive results, we have to consider the possibility that the LED or PD themselves are damaged. If so, I don't see any workaround without opening up the BS-PRM chamber, but if we can avoid this, we should. Perhaps when ITMX is open we can use the camera with the IR filter removed to see if all the OSEM LEDs are functional through the beam tube.

We are also piping POY11 error to the DAFI model and can hear it in the control room.

Rana suggested reviving the MC autolocker - I've made some changes to the low power MC autolocker scripts and they've been working the few times I tried today evening, but let's see how it does over the weekend. I've also changed the Y axis of the StripTool on the wall to better reflect the low-power range..

Attachment 1: 03.png
Attachment 2: 56.png
  12467   Fri Sep 2 21:15:53 2016 gautamUpdateSUSITMX and ETMX preemptive table leveling

The ITMX table had relaxed overnight into a slightly misaligned state overnight - since the ITMX table holds PR2 and hence can affect the input pointing, we decided to fix this before commencing alignment work today. The misalignment was not as bad as what Johannes observed prior to his first re-leveling attempt, but was ~1 division on the spirit level. So I decided to move one set of weights to level the table again. It is entirely possible that over the next couple of days, the table will shift slightly again, but the hope is that we are closer to the 'ideal' orientation of the table now... Pictures to follow...

  12471   Tue Sep 6 00:14:14 2016 gautamUpdateElectronicsSatellite Amplifier


If we have some data with one of the optics clamped and the open light hitting the PD, or with the OSEMs removed and sitting on the table, that would be useful for evaluating the end-to-end noise of the OSEM circuit. It seems like we probably have that due to the vent work, so please post the times here if you have them.

The ETMX OSEMs have been attached to its Satellite box and plugged in for the last 10 days or so, with the PD exposed to the unobstructed LED. I pulled the spectrum of one of the sensors (mean detrended, I assume this takes care of removing the DC value?). The DQed channels claim to record um (the raw ADC counts are multiplied by a conversion factor of 0.36). For comparison, re-converted the y-axis for the measured curve to counts, and multiplied the total noise curve from the LISO simulation by a factor of 3267.8cts/V (2^16cts/20V) so the Y axis is noise in units of counts/rtHz. At 1Hz, there is more than an order of magnitude difference between the simulation and the measurement which makes me suspect my y-axis conversion, but I think I've done this correctly. Can such a large discrepancy be solely due to thick film resistors?

Attachment 1: osempdComparison.pdf
  12474   Tue Sep 6 20:45:14 2016 gautamUpdateSUSX arm test masses back in chamber

[Teng, Johannes, Lydia, gautam]

  • The goal was to peel F.C. off both the X arm test masses and start work on aligning the arm
  • However the F.C. peeling wasn't successful - Johannes spotted spme residual junk close to the center of the optic on ITMX and I saw a whole bunch of specks in and around the center of the ETM (see Attachment #1)
  • Moreover, the PRM LR OSEM issue meant that we decided to re-paint the X arm optics and only take it off after debugging this OSEM PD issue
  • Attachment #2 and #3 show the AR and HR face of the ITM respectively after F.C painting
  • Attachment #4 shows the ETM HR face after HR painting
  • Both towers have been moved, so any pre-emptive levelling has probably gone out the window, just something to be aware of when we put the towers back in place....
  • There looks to be some filaments of F.C towards the edge of both the ITM and the ETM. These have been successfully removed with isopropanol + optical tissue, we should take care to do so before peeling the F.C....
Attachment 1: IMG_3137.JPG
Attachment 2: IMG_3143.JPG
Attachment 3: IMG_3142.JPG
Attachment 4: IMG_3148.JPG
  12475   Tue Sep 6 20:52:42 2016 gautamUpdateSUSOSEM issues

The modes look like they're at the right frequencies, so pointing more and more towards a LED or satellite box issue.

We peeked into the BS-PRM chamber via the ITMX chamber to see if we could shed any light on this situation. It's hard to get a picture that is in focus, but it looks quite clear that the LR LED (in the lower left when viewed from the HR side) isn't anywhere near as bright as the rest (see Attachment #1). Various hypothesis include failed LED / piece of Al foil blocking the LED / teflon aperture slipped over the LED. But looks like we can't solve this without opening up the BS-PRM chamber. The plan tomorrow is to open up the chamber, pull out the problematic coil. Once we have a better idea of what is going wrong, we can decide what the appropriate course of action is - replace the OSEM or something else. 

As part of the diagnosis, I switched the PRM and SRM satellite boxes earlier today evening around 6pm. They remain in this switched state for now.

Steve, we plan to take the BS-PRM heavy door off tomorrow morning.

Attachment 1: P9060254.JPG
  12476   Wed Sep 7 17:23:26 2016 gautamUpdateSUSPRM LR fixed for now

[johannes, gautam]

  • We took the heavy door off in the morning with Steve's help
  • The problem was quickly identified as the Al foil on the back of the PRM OSEMs (placed to mitigate scattered light making it into the OSEM that was making locking difficult) shorting out the pins on the rear of the OSEM
  • We decided against using a black glass beam stop behind the PRM - rather, we decided to go for Al foil hats that were
    1. More "domed" - so the back plane of the OSEM isn't in direct contact with the Al foil, though the hats themselves are secure and shouldn't simply fly off during pump down etc
    2. Have a piece of kapton (courtesy Koji from the OMC lab) in the dome so that even if the foil hats move around slightly, there should be no danger of accidentally shorting out any pins
  • Without removing the PRM OSEMs, we were only able to image UR and UL unambiguously showing that they have no filters. Not a single of the 5 spare 'short' OSEMs have filters. We have to open the ITMY chamber to reposition the OSEMs in the near future, which is when we will inspect SRM for filters.
  • Attachment #1 shows a picture of these foil hats - the ones actually put on are shaped slightly differently, but the idea is the same
  • Attachment #2 shows the PRM with its new OSEM hats (we also used a piece of clean copper wire to tie the OSEM cables to the tower on the bottom left of the cage as viewed from the BS-PRM chamber door)
  • After closing up the BS-PRM chamber, I locked the IMC to see if the input pointing had gone way off because of our work on the table and the reputation of the tip-tilts hysteresis - I can see weak flashes in the Y arm but not enough to lock - so I will tweak the alignment a little
  • Once I can recover the Y arm alignment, we can move on to peeling first contact and putting the X arm optics in.

Edit 7.30pm: I have managed to recover Y-arm in air locking, and the transmission is up at ~0.6 again which is what we were seeing prior to touching anything on the BS-PRM table, so it looks like the tip-tilt has not gone badly astray... I have also restored the Satellite boxes so that both PRM and SRM have their designated boxes

Attachment 1: IMG_3208.JPG
Attachment 2: IMG_3211.JPG
  12478   Thu Sep 8 22:12:36 2016 gautamUpdateSUSX arm in place, locked to green, IR flashes visible

Detailed elog to follow but summary of todays activities:

  • ITMX and ETMX are back in their respective positions
  • F.C was peeled, OSEMs were inserted after releasing EQ stops
  • X arm was aligned to green
  • IMC was locked, BS was used to adjust IR input pointing till beam was cleanly passing through irides (slid on to the tower)
  • After best efforts for today - we see flashes as judged from TRX signal and also POX11_I. Unfortunately these are really weak and we can't lock, let alone see anything on the screens. Tomorrow we can try some more fine alignment
  12480   Fri Sep 9 17:50:02 2016 gautamUpdateSUSHeavy doors on BS-PRM, ETMY chambers

[steve, teng, johannes, lydia, gautam]

  • we set about doing some final checks on the Y arm while Johannes and Lydia worked on the X arm alignment
  • locked IMC, turned on Oplev HeNes for ITMY, SRM, PRM, BS and ETMY
  • I first went into the BS-PRM chamber. Traced Oplev paths for PRM and BS, checked that the beam is approximately centered on all the steering mirrors, and traced the beam with a clean beam card to make sure there was no clipping. The beams make it out of the vacuum onto the PDs, but are not centered
  • I also checked the Y arm green - the beam isn't quite centered on the periscope mirrors but I guess this has always been the case and I didn't venture to make any changes
  • Checked new PRM foil hats were secure
  • Checked the main IR beam out of the IMC, and also the IPANG beam - Steve suggested we keep track of the way this moves during pumpdown. However, I didn't quite think this through and we put the heavy door on the BS-PRM chamber before checking where the IPANG beam was on ETMY table (we later found that the beam was a tad too high. Anyways, this isn't critical, wouldve been nice to have this reference though
  • Checked that there were no tools lying around inside the chamber, and proceeded to put the heavy door on
  • Moved to ETMY table, and did much of the same as above - Oplev beam makes it successfully out off the ETM, OSEM cables aren't a risk to clipping the green input beam
  • Proceeded to put the heavy door on ETMY chamber
  • I would have liked to put the heavy door on the ITMY chamber today evening too, but while freeing the SRM from its EQ stops, I noticed that the LL and LR OSEM PD readouts are approximately 60 and 75 % of their saturation values. I think this warrants fixing (I also checked against the frame files from our last DRFPMI lock in march and the PD signals are significantly different) so we should do this before putting the heavy door on. It would also be a good idea to check the table leveling
  • The Oplev beams for ITMY and SRM make it cleanly out of the chamber so all looks good on that front
  • IR and green beams are well clear of any OSEM cables

Depending on how the X arm situation is, we will finish putting back all the heavy doors on Monday and start the pumpdown

GV Edit 11.30pm: 

  • We succeeded in locking the X arm as well, although the transmission peaked at 0.1 (but this is the high gain PD and not the QPD, and also, unlike the Y arm, the 50-50 BS splitting the transmitted light between the QPD and the high gain PD is still in place, so can't really compare with the Y arm value of 0.6)
  • To get the lock going, we had to change a bunch of things like the POX DC offset, demod phase, sign of the gain etc. It is unclear whether we are locking on the TEM00 mode, but we judged it is sufficient to close doors and pump down
  • Johannes and I centered the ETMX and ITMX OL spots on their respective QPDs. Earlier today, Johannes and Lydia had checked ITMX and ETMX OL paths, everything looks decent
  • JE piggyback edit : We also tied the upper ITMX OSEM cables to the suspension cage side using copper wire since particularly UR looked like it could slip and possibly fall down into the beam path
  • JE piggyback edit: While leveling the ITMX table, Gautam and I found that some of the screws that secure the weights were not vented. None of these were put in during this vent. We replaced them all with vented screws.
  • Rana also checked PRM and SRM alignment, all looks okay on that front - the OSEM problem I had alluded to earlier isn't really a problem, once the SRM is aligned, all the OSEMs are reasonably close to 50% of their saturation value.

Looks like on Monday, we will look to put the heavy doors on ITMY, ITMX and ETMX chambers, and begin the pumpdown

  12526   Fri Sep 30 19:53:07 2016 gautamUpdateendtable upgradeX end IR pickoff fiber coupled

[johannes, gautam]

Today we re-installed the fiber coupler on the X-endtable to couple some of the PSL light into a fiber that runs to the PSL table, where it is combined with a similar PSL pickoff to make an IR beat between the EX AUX laser and the PSL. The main motivation behind this was to make the process of finding the green beatnote easier. We used JAMMT (just another mode matching tool) to calculate a two lens solution to couple the light into the collimator - we use a +200mm and -200mm lens, I will upload a more detailed mode matching calculation + plot + picture soon. We wanted to have a beam waist of 350um at the collimator, a number calculated using the following formula from the Thorlabs website:

d =4\lambda (\frac{f}{\pi*MFD})

where d is the diameter of the output beam from the collimator, f is the collimating lens focal length and MFD is 6.6um for the fiber we use.

There is ~26mW of IR light coming through the BS after the EX AUX - after playing around with the 6 axis stage that the coupler is mounted on, Johannes got the IR transmission to the PSL table up to ~11.7mW. The mode matching efficiency of 45% is certainly not stellar, but we were more curious to find a beat and possibly measure the X arm loss so we decided to accept this for now - we could probably improve this by moving the lenses around. We then attenuated the input beam to the fiber by means of an ND filter such that the light incident on the coupler is now ~1.3mW, and the light arriving at the PSL table from the EX laser is ~550uW. Along with the PSL light, after the various couplers, we have ~500uW of light going to the IR beat PD - well below its 2mW threshold.

The IR beat was easily found with the frequency counter setup. However, there was no evidence of a green beat. So we went to the PSL table and did the near-field-far-field alignment onto the beat PD. After doing this, we were able to see a beat - but the amplitude was puny (~-60dBm, we are more used to seeing ~-20dBm on the network analyzer in the control room). Perhaps this can be improved by tweaking the alignment onto the PD while monitoring the RF output with an oscilloscope.

Moreover, the green PDH problems with the X end persist - even though the arm readily locks to a TEM00 mode, it frequently spontaneously drops lock. I twiddled around with the gain on the uPDH box while looking at the error signal while locked on a oscilloscope, but was unable to mitigate the situation. Perhaps the loop shape needs to be measured and that should tell us if the gain is too low or high. But ALS is getting closer to the nominal state...

Johannes is running his loss measurement script on the X arm - but this should be done by ~10pm tonight.


  12532   Wed Oct 5 16:28:10 2016 gautamUpdateendtable upgradeEX laser power monitor PD installed

I installed a 10% BS to pick off some of the light going to the IR fiber, and have added a Thorlabs PDA55 PD to the EX table setup. The idea is to be able to monitor the power output of the EX NPRO over long time scales, and also to serve as an additional diagnostic tool for when ALS gets glitchy etc. There is about 0.4mW of IR power incident on the PD (as measured with the Ophir power meter), which translates to ~2500 ADC counts (~1.67V as measured with an Oscilloscope set to high impedance directly at the PD output). The output of the PD is presently going to Ch5 of the same board that receives the OL QPD voltages (which corresponds to ADC channel 28). Previously, I had borrowed the power and signal cables from the High-Gain Transmon PD to monitor this channel, but today I have laid out independent cabling and also restored the Transmon PD to its nominal state.

On the CDS side of things, I edited C1SCX to route the signal from ADC Ch28 to the ALS block. I also edited the ALS_END library part to have an additional input for the power monitor, to keep the naming conventions consistent. I have added a gain in the filter module to calibrate the readout into mW using these numbers. The channel is called C1:ALS-X_POWER_OUT, and is DQed for long-term trending purposes.

The main ALS screen is a bit cluttered so I have added this channel to the ALS overview MEDM screen for now..

  12533   Wed Oct 5 19:10:04 2016 gautamUpdateGeneralArm loss measurement review


There are multiple methods by which the arm loss can be measured, including, but not limited to:

  1. Cavity ringdown measurement
  2. Monitoring IR arm transmission using ALS to scan the arm through multiple FSRs
  3. Monitoring the reflected light from the ITM with and without a cavity (Johannes has posted the algebra here)

We found that the second method is extremely sensitive to errors in the ITM transmissivity. The first method was not an option for a while because the AOM (which serves as a fast shutter to cut the light to the cavity and thereby allow measurement of the cavity ringdown) was not installed. Johannes and Shubham have re-installed this so we may want to consider this method.

Most of the recent efforts have relied on the 3rd method, which itself is susceptible to many problems. As Yutaro found, there is something weird going on with ASDC which makes it perhaps not so reliable a sensor for this measurement (unfortunately, no one remembered to follow up on this during the vent, something we may come to regret...sad). He performed some checks and found that for the Y arm, POY is a suitable alternative sensor. However, the whitening gain was at 0dB for the measurements that Johannes recently performed (Yutaro does not mention what whitening gain he used, but presumably it was not 0). As a result, the standard deviation during the 10s averaging was such that the locked and misaligned readings had their 'fuzz' overlapping significantly. The situation is worse for POX DC - today, Eric checked that the POX DC and POY DC channels are indeed reporting what they claim, but we found little to no change in the POX DC level while misaligning the ITM - even after cranking the whitening gain up to 40!

Eric then suggested deriving ASDC from the AS110 photodiode, where there is more light. This increased the SNR significantly - in a 10s averaging window, the fuzz is now about 10 ADC counts out of ~1500 (~<1%) as opposed to ~2counts out of 30 previously. We also set the gains of POX DC, POY DC and ASDC to 1 (they were 0.001,0.001 and 0.5 respectively, for reasons unknown).

I ran a quick measurement of the X arm loss with the new ASDC configuration, and got a number of 80 +/- 10 ppm (7 datapoints), which is wildly different from the ~250ppm number I got from last night's measurement with 70 datapoints. I was simultaneously recording the POX DC value, which yielded 40 +/- 10 ppm.

We also discovered another possible problem today - the spot on the AS camera has been looking rather square (clearly not round) since, I presume, closing up and realigning everything. By looking at the beam near the viewport on the AS table for various configurations of the ITM, we were able to confirm that whatever is causing this distortion is in the vacuum. By misaligning the ITM, we are able to recover a nice round spot on the AS camera. But after running the dither align script, we revert to this weirdly distorted state. While closing up, no checks were done to see how well centered we are on the OMs, and moreover, the DRMI has been locked since the vent I believe. It is not clear how much of an impact this will have on locking the IFO (we will know more after tonight). There is also the possibility of using the PZT mounted OMs to mitigate this problem, which would be ideal.

Long story short -

  1. Some more thought needs to be put into the arm loss measurement. If we are successful in locking the IFO, the PRG would be a good indicator of the average arm loss.
  2. There is some clipping, in vacuum, of the AS beam. It may be that we can fix this without venting, to be investigated.

GV Edit 8 Oct 2016: Going through some old elogs, I came across this useful reference for loss measurement. It doesn't talk about the reflection method (Method 3 in the list at the top of this elog), but suggests that cavity ringdown with the Trans PD yields the most precise numbers, and also allows for measuring TITM

  12534   Wed Oct 5 19:43:13 2016 gautamSummaryGeneralVent review

This elog is meant to review some of the important changes made during the vent this summer - please add to this if I've forgotten something important. I will be adding this to the wiki page for a more permanent record shortly.

Vent objectives:

  2. Replace ETMX suspension cage, replace Al wire standoffs with Ruby (sapphire?) standoffs.
  3. Shorten Y arm length by 20mm
  4. Replace 40mm aperture baffles in ETM chambers with 50mm black glass baffles

Optics, OSEM and suspension status:


  • ITMX and ITMY did not have any magnets broken off during the vent - all five OSEM coils for both were removed and the optic EQ stopped for F.C. cleaning.
  • Both HR and AR faces were F.Ced, ~20mm dia area cleaned.
  • The coils were re-inserted in an orientation as close to the original (as judged from photos), and the shadow sensor outputs were made as close to half their open values as possible, although in the process of aligning the arms, this may have changed
  • OSEM filter existense was checked (to be updated)
  • Shadow sensor open values were recorded (to be updated)
  • Checked that tables were level before closing up
  • The UL OSEM on ITMY was swapped for a short OSEM while investigating glitchy shadow sensor outputs. This made no difference. However, the original OSEM wasn't replaced. Short OSEM was used as we only had spare short OSEMs. Serial number (S/N 228) and open voltage value have been recorded, wiki page will be updated. Does this have something to do with the input matrix diagonalization weirdness we have been seeing recently?
  • ITMX seems to be prone to getting stuck recently, reason unknown although I did notice the LL OSEM was kind of close to the magnet while inserting (but this magnet is not the one getting stuck, as we can see this clearly on the camera - the prime suspect is UL I believe)
  • OL beam centering on in vacuum steering optics checked before closing up


  • UL, UR and LR magents broke off at various points, and so have been reglued
  • No standoff replacement was done
  • Re-suspension was done using newly arrived SOS wire
  • Original OSEMs were inserted, orientations have changed somewhat from their previous configuration as we did considerable experimentation with the B-R peak minimization for this optic
  • OSEM filter status, shadow sensor open voltage values to be updated.
  • New wire suspension clamp made at machine shop is used, 5 in lb of torque used to tighten the clamp
  • HR face cleaned with F.C.
  • Optic + suspension towers air baked (separately) at 34C for curing of EP30
  • Checked that tables were level before closing up
  • 40mm O.D. black glass baffle replaced with 50mm O.D. baffle.
  • Suspension cage was moved towards ITMY by 19mm (measured using a metal spacer) by sliding along stop marking the position of the tower.


  • Al wire standoffs <--> Ruby wire standoffs (this has changed the pitch frequency)
  • All magnets were knocked off at some point, but were successfully reglued
  • New SOS tower, new SOS wire, new wire clamp used
  • OSEM filter status, shadow sensor open voltage values to be updated.
  • OSEM orientation is close to horizontal for all 5 OSEMs
  • Table leveling was checked before closing up.
  • 40mm O.D. black glass baffle replaced with 50mm O.D. baffle.\


  • Some issues with the OSEMs were noticed, and were traced down to the Al foil caps covering the back of the (short) OSEMs, which are there to minimize the scattererd 1064nm light interfering with the shadow sensor, shorting one of the OSEMs
  • To mitigate this, all Al foil caps now have a thin piece of Kapton between foil and electrical contacts on rear of OSEM
  • No OSEMs were removed from the suspension cage during this process, we tried to be as gentle as possible and don't believe the shadow sensor values changed during this work, suggesting we didn't disturb the coils (PRM wasn't EQ stopped either)


  • The optic itself wasn't directly touched during the vent - but was EQ stopped as work was being done on ITMY
  • It initially was NOT EQ stopped, and the shift in table level caused by moving ITMY cage to the edge of the table for F.C. cleaning caused the optic to naturally drift onto the EQ stops, leading to some confusion as to what happened to the shadow sensor outputs
  • The problem was diagnosed and restoring ITMY to its original position made the OSEM signals come back to normal.


  • Was cleaned by drag wiping both front and back faces


  • These optics were NOT intentionally touched during this vent
  • The alignment on the OMs was not checked before close-up

Other checks/changes

  • OL beams were checked on in-vacuum input and output steering mirrors to make sure none were close to clipping
  • Insides of viewport windows were checked for general cleanliness, given that we have found the outside of some of these to be rather dirty. Insides of viewports checked were deemed clean enough.
  • Steve has installed a new vacuum guage to provide a more realiable pressure readout. 
  • We forgot to investigate the weird behaviour of the AS beam that Yutaro and Koji identified in November. In any case, looks like the clipping of the AS beam is worse now. We will have to try and fix this using the PZT mounted OMs, and if not, we may have to consider venting again

Summary of characterization tasks to be done:

  1. Mode matching into the Y arm cavity given the arm length change
  2. HOM content in transmitted IR light from Y arm given the arm length change (Finesse models suggest that the 2f second order HOM resonance may have moved closer to the 00 resonance)
  3. Arm loss measurement
  4. Suspension diagonalization
  5. Check the Qs of the optics eigenmodes - should indicate if any of our magnets, reglued or otherwise, are a little loose
  12542   Mon Oct 10 11:48:05 2016 gautamUpdateCDSPower-cycled c1susaux, realigned PMC, spots centered on WFS1 and WFS2

[Koji, Gautam]

We did the following today morning:

  1. I re-aligned the PMC - transmission level on the scope on the PSL table is now ~0.72V which is around what I remember it being
  2. The spot had fallen off WFS 2 - so we froze the output of the MC WFS servo, and turned the servo off. Then we went to the table to re-center the spot on the WFS. The alignment had drifted quite a bit on WFS2, and so we had to change the scale on the grid on the MEDM screen to +/-10 (from +/- 1) to find the spot and re-center it using the steering mirror immediately before the WFS. It would appear that the dark offsets are different on WFS1 and WFS2, so the "SUM" reads ~2.5 on WFS1 and ~0.3 on WFS2 when the spots are well centered
  3. Coming back to the control room, we ran the WFSoffsets script and turned on the WFS servo again. Trying to run the relief servo, we were confronted by an error message that c1susaux needed to be power cycled (again). This is of course the slow machine that the ITMX suspension is controlled by, and in the past, power cycling c1susaux has resulted in the optic getting stuck. An approach that seems to work (without getting ITMX stuck)  is to do the following:
    • Save the alignment of the optic, turn off Oplev servo
    • Move the bias sliders on IFO align to (0,0) slowly
    • Turn the watchdog for ITMX off
    • Unplug the cables running from the satellite box to the vacuum feedthrough
    • Power cycle the slow machine. Be aware that when the machine comes back on, the offset sliders are reset to the value in the saved file! So before plugging the cables back in, it would be advisable to set these to (0,0) again, to avoid kicking the optic while plugging the cables back in
    • Plug in the cables, restore alignment and Oplev servos, check that the optic isn't stuck
  4. Y green beat touch up - I tweaked the alignment of the first mirror steering the PSL green (after the beam splitter to divide PSL green for X and Y beats) to maximize the beat amplitude on a fast scope. Doing so increased the beat amplitude on the scope from about 20mVpp to ~35mVpp. A detailed power budget for the green beats is yet to be done

It is unfortunate we have to do this dance each time c1susaux has to be restarted, but I guess it is preferable to repeated unsticking of the optic, which presumably applies considerable shear force on the magnets...

After Wednesday's locking effort, Eric had set the IFO to the PRMI configuration, so that we could collect some training data for the PRC angular feedforward filters and see if the filter has changed since it was last updated. We should have plenty of usable data, so I have restored the arms now.

  12545   Mon Oct 10 18:34:52 2016 gautamUpdateGeneralPZT OM Mirrors

I did a quick survey of the drive electronics for the PZT OM mirrors today. The hope is that we can correct for the clipping observed in the AS beam by using OM4 (in the BS/PRM chamber) and OM5 (in the OMC chamber).

Here is a summary of my findings.

  • Schematic for (what I assume is) the driver unit (located in the short electronics rack by the OMC chamber/AS table) can be found here
  • This is not hooked up to any HV power supply. There is a (short) cable on the back that is labelled '150V' but it isn't connected to anything. There are a bunch of 150V KEPCO power supplies in 1X1, looks like we will have to lay out some cable to power the unit
  • The driver is also not connected to any fast front end machine or slow machine - according to the schematic, we can use J4, which is a Dsub 9 connector on the front panel, to supply drive signals to the two PZTs X and Y axes. Presumably, we can use this + some function generator/DC power supply to drive the PZTs. I have fashioned a cable using a Dsub9 connector and some BNC connectors for this purpose.

I hope these have the correct in-vacuum connections. We also have to hope that the clipping is downstream of OM4 for us to be able to do anything about it using the PZT mirrors. 

ELOG V3.1.3-