40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Category Subject
  12566   Mon Oct 17 22:45:16 2016 gautamUpdateGeneralAS beam centered on all OMs

[ericq, lydia, gautam]

IMC realignment, Arm dither alignment

  • We started today by re-locking the PMC (required a c1psl restart), re-locking the IMC and then locking the arms
  • While trying to dither align the arms, I could only get the Y arm transmission to a maximum of ~0.09, while we are more used to something like 0.3 when the arm is well aligned this vent
  • As it turns out, Y arm was probably locked to an HOM, as a result of some minor drift in the ITMY optical table leveling due to the SOS tower aperture being left in over the weekend

ITMY chamber

  • We then resolved to start at the ITMY chamber, and re-confirm that the beam is indeed centered on the SRM by means of the above-mentioned aperture
  • Initially, there was considerable yaw misalignment on the aperture, probably due to the table level drifting because of the additional weight of the aperture
  • As soon as I removed the aperture, eric was able to re-dither-align the arms and their transmission went back up to the usual level of ~0.3 we are used to this vent
  • We quickly re-inserted the aperture and confirmed that the beam was indeed centered on the SRM
  • Then we removed the aperture from the chamber and set about inspecting the beam position on OM1
  • While the beam position wasn't terribly bad, we reasoned that we may as well do as good a job as we can now - so OM1 was moved ~0.5 in such that the beam through the SRM is now well centered on OM1 (see Attachment #1 for a CAD drawing of the ITMY table layout and the direction in which OM1 was moved)
  • Naturally this affected the beam position on OM2 - I re-centered the beam on OM2 by first coarsely rotating OM1 about the post it is mounted on, and then with the knobs on the mount. The beam is now well centered on OM2
  • We then went about checking the table leveling and found that the leveling had drifted substantially - I re-levelled the table by moving some of the weights around, but this has to be re-checked before closing up... 

BS/PRM chamber

  • The beam from OM2 was easily located in the BS/PRM chamber - it required minor yaw adjustment on OM2 to center the beam on OM3
  • Once the beam was centered on OM3, minor pitch and yaw adjustments on the OM3 mount were required to center the beam on OM4
  • The beam path from OM3 to OM4, and OM4 to the edge of the BS/PRM chamber towards the OMC chamber was checked. There is now good clearance (>2 beam diameters) between the beam from OM4 to the OMC chamber, and the green steering mirror in the path, which was one of the prime clipping candidates identified on Friday

OMC chamber

  • First, the beam was centered on OM5 by minor tweaking of the pitch and yaw knobs on OM4 (see Attachment #2)
  • Next, we set about removing the unused mirror just prior to the window on the AP table (see Attachment #3). PSL shutter was closed for this stage of work, in order to minimize the chance of staring directly into the input beam!
  • Unfortunately, we neglected checking the table leveling prior to removing the optic. A check after removing the optic suggested that the table wasn't level - this isn't so easy to check as the table is really crowded, and we can only really check near the edges of the table (see Attachment #3). But placing the level near the edge introduces an unknown amount of additional tilt due to its weight. We tried to minimize these effects by using the small spirit level, which confirmed that the table was indeed misaligned
  • To mitigate this, we placed a rectangular weight (clean) around the region where the removed mirror used to sit (see Attachment #3)Approximately half the block extends over the edge of the table, but it is bolted down. The leveling still isn't perfect - but we don't want to be too invasive on this table (see next bullet point). Since there are no suspended optics on this table, I think the leveling isn't as critical as on the other tables. We will take another pass at this tomorrow but I think we are in a good enough state right now. 
  • All this must have bumped the table quite a bit, because when we attempted re-locking the IMC, we noticed substantial misalignment. We should of course have anticipated this because the mirror launching the input beam into the IMC, and also MMT2 launching the beam into the arms, sits on this table! After exploring the alignment space of the IMC for a while, eric was able to re-lock the IMC and recover nominal transmission levels of ~1200 counts. 
  • We then re-locked the arms (needed some tip-tilt tweaking) and ran the dither again, setting us up for the final alignment onto OM6
  • OM5 pitch and yaw knobs were used to center the beam on OM6 - the resulting beam spot on OMPO-OMMTSM and OM6 are shown in Attachment #4 and Attachment #5 respectively. The centering on OMPO-OMMTSM isn't spectacular, but I wanted to avoid moving this optic if possible. Moreover, we don't really need the beam to follow this path (see last bullet in this section)
  • Beam path in the OMC chamber (OM5 --> OMPO-OMMTSM --> OM6 --> window was checked and no significant danger of clipping was found
  • Beam makes it cleanly through the window onto the AP table. We tweaked the pitch and yaw knobs on OM6 to center the beam on the first in-air pick off mirror steering the AS beam on the AP table. The beam is now visible on the camera, and looks clean, no hint of clipping
  • As a check, I wondered where the beam into the OMC is actually going. Turns out that as things stand, it is hitting the copper housing (see Attachment #6, it's had to get a good shot because of the crowded table...). While this isn't critical, perhaps we can avoid this extra scatter by dumping this beam?
  • Alternatively, we could just bypass OMPO-OMMTSM altogether - so rotate OM5 in-situ such that we steer the beam directly onto OM6. This way, we avoid throwing away half (?) the light in the AS beam. If this is the direction we want to take, it should be easy enough to make the change tomorrow

In summary...

  • AS beam has been centered on all steering optics (OM1 through OM6)
  • Table leveling has been checked on ITMY and OMC chambers - this will be re-checked prior to closing up
  • Green-scatter issue has to be investigated, should be fairly quick..
  • In the interest of neatness, we may want to install a couple of beam dumps - one to catch the back-reflection off the window in the OMC chamber, and the other for the beam going to the OMC (unless we decide to swivel OM5 and bypass the OMC section altogether, in which case the latter is superfluous)

C1SUSAUX re-booting

  • Not really related to this work, but we couldn't run the MC relief script due to c1susaux being unresponsive
  • I re-started c1susaux (taking care to follow the instructions in this elog to avoid getting ITMX stuck)
  • Afterwards, I was able to re-lock the IMC, recover nominal transmission of ~1200 counts. I then ran the MC relief servo
  • All shutters have been closed for the night
  12565   Mon Oct 17 14:48:12 2016 SteveUpdatesafetysafety training

Ashley Fowler  "high shool" student received basic 40m safety training and Lydia is her guarding angle.


  12564   Fri Oct 14 19:59:09 2016 YinziUpdateGreen LockingContinuing work with the TC 200

Oct. 15, 2016

Another attempt (following elog 8755) to extract the oven transfer function from time series data using Matlab’s system identification functionalities.

The same time series data from elog 8755 was used in Matlab’s system identification toolbox to try to find a transfer function model of the system.

From elog 8755: H(s) is known from current PID gains: H(s) = 250 + 60/s +25s, and from the approximation G(s)=K/(1+Ts), we can expect the transfer function of the system to have 3 poles and 2 zeros.

I tried fitting a continuous-time and a discrete time transfer function with 3 poles and 2 zeros, as well as using the "quick start" option. Trying to fit a discrete time transfer function model with 3 poles and 2 zeros gave the least inaccurate results, but it’s still really far off (13.4% fit to the data).


1. Obtain more time domain data with some modulation of the input signal (also gives a way to characterize nonlinearities like passive cooling). This can be done with some minor modifications to the existing code on the raspberry pi. This should hopefully lead to a better system ID.

2. Try iterative tuning approach (sample gains above and below current gains?) so that a tune can be obtained without having to characterize the exact behavior of the heater.

Oct. 16, 2016

-Found the raspberry pi but it didn’t have an SD card

-Modified code to run directly on a computer connected to the TC 200. Communication seems to be happening, but a UnicodeDecodeError is thrown saying that the received data can’t be decoded.

-Some troubleshooting: tried utf-8 and utf-16 but neither worked. The raw data coming in is just strings of K’s, [‘s, and ?’s

-Will investigate possible reasons (update to Mac OS or a difference in Python version?), but it might be easier to just find an SD card for the raspberry pi which is known to work. In the meantime, modify code to obtain more time series data with variable input signals.

  12563   Fri Oct 14 18:33:55 2016 gautamUpdateGeneralAS clipping investigations


In the afternoon, we took the heavy door off the OMC chamber as well, such that we could trace the AS beam all the way out to the AP table. 

In summary, we determined the following today:

  1. Beam is centered on SRM, as judged by placing the SOS iris on the tower
  2. Beam is a little off on OM1 in yaw, but still >2 beam diameters away from the edge of the steering optic, pitch is pretty good
  3. Beam is okay on OM2 
  4. Beam is okay on OM3 - but beam from OM3 to OM4 is perilously close to clipping on the green steering mirror between these two steering optics (see CAD drawing). We think this is where whatever effect of the SR2 hysteresis shows up first.
  5. Beam is a little low and a little to the left on OM4 (the first PZTJena mirror)
  6. Beam is well clear of other optics in the BS PRM chamber on the way from OM4 to OM5 in the OMC chamber
  7. Beam is a little low and a little to the left of OM5 in the OMC chamber. This is the second PZTJena mirror. We are approximately 1 beam diameter away from clipping on this 1" optic
    Link to IMG_2289.JPG
  8. Beam is off center on OMPO-OMMTSM partially transmissive optic, but because this is a 2" optic, the room for error is much more
    Link to IMG_2294.JPG
  9. Beam is well clear of optics on OMC table on the way from OMPO-OMMTSM to OM6, the final steering mirror bringing the AS beam out onto the table
  10. Beam is low and to the left on OM6. It is pretty bad here, we are < 1 beam diameter away from clipping on this optic, this along with the near miss on the BS/PRM chamber are the two most precarious positions we noticed today, consistent with the hypothesis in this elog that there could be multiple in vacuum clipping points
    Link to IMG_2306.JPG
  11. Beam clears the mirror just before the window pretty confortably (see photo, CAD drawing). But this mirror is not being used for anything useful at the moment. More importantly, there is some reflection off the window back onto this mirror frame which is then scattering and creating some ghost beams, so this could explain the anomalous ASDC behaviour Koji and Yutaro saw. In any case, I would favour removing this mirror since it is serving no purpose at the moment.
    Link to IMG_2310.JPG

Attachment #5 is extracted from the 40m CAD drawing which was last updated in 2012. It shows the beam path for the output beam from the BS all the way to the table (you may need to zoom in to see some labels. The drawing may not be accurate for the OMC chamber but it does show all the relevant optics approximately in their current positions.

EQ will put up photos from the ITMY and BS/PRM chambers.

Plan for Monday: Reconfirm all the findings from today immediately after running the dither alignment so that we can be sure that the ITMs are well-aligned. Then start at OM1 and steer the beam out of the chambers, centering the beam as best as possible given other constraints on all the optics sequentially. All shutters are closed for the weekend, though I left the SOS iris in the chamber...

Here is the link to the Picasa album with a bunch of photos from the OMC chamber prior to us making any changes inside it - there are also some photos in there of the AS beam path inside the OMC chamber...

  12562   Fri Oct 14 15:47:00 2016 ranaUpdateTreasurefilters + clip

I say just fix the clipping. Don't worry about the PRM OSEM filters. We can do that next time when we put in the ITM baffles. No need for them on this round.

  12561   Fri Oct 14 10:31:53 2016 gautamUpdateGeneraldoors are off ITMY and BS/PRM chambers


We re-checked IMC locking, arm alignments (we were able to lock and dither align both arms today, and also made the michelson spot look reasonable on the camera) and made sure that the AS and REFL spots were in the camera ballpark. We then proceeded to remove the heavy doors off ITMY and BS/PRM chambers. We also quickly made sure that it is possible to remove the side door of the OMC chamber with the current crane configuration, but have left it on for now.

The hunt for clipping now begins.

  12560   Thu Oct 13 19:28:14 2016 gautamUpdateGeneralin-air alignment

I did the following today to prepare for taking the doors off tomorrow.

  • Locked MC at low power
    • low power autolocker used during the last vent isn't working so well now
    • so I manually locked the IMC - locks are holding for ~30 mins and MC transmission was maximized by tweaking MC1 and MC2 alignments. The transmission is now ~1150 which is what I remember it being from the last vent
    • I had to restart c1aux to run LSCoffsets
  • Aligned arms to green using bias sliders on IFO align
    • X green transmission is ~0.4 and Y green transmission is ~0.5 which is what I remember it being before this vent
  • Removed ND filters from end Transmon QPDs since there is so little light now
  • Locked Y arm, ran the dither
    • Some tip tilt beam walking was required before any flashes were seen
    • I had to tweak the LSC gain for this to work
    • TRY is ~0.3 - in the previous vent, in air low power locking yielded TRY of ~0.6 but the 50-50 BS that splits the light between the high gain PD and the QPD was removed back then so these numbers are consistent
  • Tried locking X arm
    • For some reason, I can't get the triggering to work well - the trigger in monitor channel (LSC-XARM_TRIG_IN) and LSC-TRX_OUT_DQ are not the same, should they not be?
    • Tried using both QPD and high gain PD to lock, no luck. I also checked the error signal for DC offsets and that the demod phase was okay
    • In any case, there are TRX flashes of ~0.3 as well, this plus the reasonable green transmission makes me think the X arm alignment is alright
  • All the oplev spots are on their QPDs in the +/- 100 range. I didn't bother centering them for now

I am leaving all shutters closed overnight.

So I think we are ready to take the doors off at 8am tomorrow morning, unless anyone thinks there are any further checks to be done first.

Vent objectives:

  1. Fix AS beam clipping issues (elog1, elog2)
  2. Look into the green scatter situation (elog)

Should we look to do anything else now? One thing that comes to mind is should we install ITM baffles? Or would this be more invasive than necessary for this vent?

Steve reported to me that he was unable to ssh into the control room machines from the laptops at the Xend and near the vacuum rack. The problem was with pianosa being frozen up. I did a manual reboot of pianosa and was able to ssh into it from both laptops just now.

  12559   Thu Oct 13 16:48:34 2016 SteveUpdateVACvent 79 is completed

IFO is at atmosphere. The MC can be locked in air now.

The doors will be coming off tomorrow 8am sharp.

Do we want to install the ITM baffles?

What about the found OSEM filters?


  12558   Thu Oct 13 14:49:57 2016 KojiConfigurationPEMXLR(F)-XLR(M) cable took from the fibox to the Blue microphone

[Gautam Koji]

XLR(F)-XLR(M) cable for the blue microphone is missing. Steve ordered one.

We found one in the fibox setup. As we don't use it during the vent, we use this cable for the microphone.
Once we get the new one, it will go to the fibox setup.


  12557   Thu Oct 13 09:30:38 2016 SteveUpdateGeneralvent 79 is happening

I have completed the following non-Steve portions of the pre-vent checklist [wiki-40m.ligo.caltech.edu]

  • Center all oplevs, transom QPDs (and IPPOS + IPANG if they are set up)
  • Align the arm cavities for IR and align the green lasers to the arms.
  • Update the SUS Driftmon values
  • Reconcile all SDF differences
  • Reduce input power to no more than 100mW (measured at the PSL shutter) by adjusting wave plate+PBS setup on the PSL table BEFORE the PMC. (Using the WP + PBS that already exist after the laser.)
  • Replace 10% BS before MC REFL PD with Y1 mirror and lock MC at low power.
  • Close shutter of PSL-IR and green shutters at the ends

All shutters are closed. Ready for Steve to check nuts and begin venting!

- checked all jam nuts

- checked all viewports are covered

- turned oplev servos off

- took pictures of medm screens: sus summs, aligned oplev centering, IFO& MC alignment biases and vac configuration

- checked particle counts

- checked crane operational safety

- closed V1, VM1, annuloses

- opened VV1  and vented with Airgas brand, Industrial Grade Nitrogen [ 99.99% ] to 25 Torr

- switched over to Airgas brand compressed air, Alphagas " AI UZ300 "  with Total Hydro Carbon 0.1 PPM

  12556   Thu Oct 13 00:23:54 2016 ericqUpdateVACPre-vent prep

I have completed the following non-Steve portions of the pre-vent checklist [wiki-40m.ligo.caltech.edu]

  • Center all oplevs, transom QPDs (and IPPOS + IPANG if they are set up)
  • Align the arm cavities for IR and align the green lasers to the arms.
  • Update the SUS Driftmon values
  • Reconcile all SDF differences
  • Reduce input power to no more than 100mW (measured at the PSL shutter) by adjusting wave plate+PBS setup on the PSL table BEFORE the PMC. (Using the WP + PBS that already exist after the laser.)
  • Replace 10% BS before MC REFL PD with Y1 mirror and lock MC at low power.
  • Close shutter of PSL-IR and green shutters at the ends

All shutters are closed. Ready for Steve to check nuts and begin venting!

  12555   Wed Oct 12 22:51:26 2016 KojiUpdateGeneralClipping could not be improved by the PZTs - NEED ANOTHER VENT

[Gautam Koji]

We engaged the HV driver to the output port PZTs, hoping to mitigate the AS port clipping. Basically, the range of the PZT is not enough to make the beam look clean. Also, our observation suggested there are possible multiple clipping in the chamber. We need another vent to make the things clearly right. Eric came in the lab and preparing the IFO for it.

1. Before the test, the test masses have been aligned with the dither servo.

2. We looked at the beam shape on the AS camera with a single bounce beam. We confirmed that the beam is hard-clipped at the upper and left sides of the beam on the video display. This clipping is not happening outside of the chamber.

3. We brought an HV power supply to the short OMC rack. There is a power supply cable with two spades. The red and black wires are +150V and GND respectively.

4. The voltage of +/-10V was applied on each of the four PZT drive inputs. We found that the motion of the beam on the camera is tiny and in any case, we could not improve the beam shape.

5. We wondered that if we are observing ANY improvement of the clipping. For this purpose, we aligned AS110 sensor every time we gave the misalignment with the PZTs. Basically, we are at the alignment to have the best power we can get. We thought this was weird.

6. Then we moved the AS port spot with the ITMX. We could clearly make the spot more round. However, this reduced the power at the AS port reduced by ~15%. When the beam was further clipped, the power went down again. Basically, the initial alignment gave us the max power we could get. As the max power was given with the clipped beam, we get confused and feel safer to check the situation with the chambers open.

During this investigation, we moved the AS port opitcs and the AS camera. So they are not too precise reference of the alignment. The PZT HV setup has been removed.

  12554   Wed Oct 12 18:09:25 2016 LydiaUpdateGeneralAcromag Progress

[Lydia, Johannes]

Johannes acquired a crate to contain the Acromag setup and wiring, and installed a rail along the bottom panel so that the ADC units will be oriented vertically with the ehternet ports facing up. We briefly talkes about what the layout should be, and are thinking of using 2 rails, one for ADCs and one for DACs. We want to design a generic front panel to accept 25 pin D-Sub inputs and maybe also BNCs, which we can use for all the Acromag crates. 

I got the epics session for the acromag to run on c1iscex and was able to access the channel values using caget on donatella. However, I get the following warning: 

cas warning: Using dynamically assigned TCP port 48154,
cas warning: but now two or more servers share the same UDP port.
cas warning: Depending on your IP kernel this server may not be
cas warning: reachable with UDP unicast (a host's IP in EPICS_CA_ADDR_LIST)


It seems like there might be a way to assign a port for each unit, if this is a problem. 

Also, c1iscex doens't have tmux; what's the best way to run the modbusApp and then detach? Right now I just left an epics session running in an open terminal. 


  • Deisgn crate connections and interior layout. Set up front panel to accept desired connections. 
  • Set up the crate with the Acromag XT1221 reading the diagnostic info from the X end NPRO in the X end rack.
  • Figure out how many of each type we need to replace c1auxex functionality, and order them.
  • Generate appropriate EPICS db files for acromag based on slow machine channels.
  • Add necessary units to X end Acromag crate and read in the same inputs as c1auxex. 
  • Set up everything else to look for c1auxex channels from Acromag instead. (Not sure about nuances of this step: should we name the channels something different at first? How to find everything that relies on c1auxex? Must be careful with SUS channel connections.)
  •  Determine number of units needed to replace all slow machines, and order thm. Likewise assemble as many crates as necessary with the right connections. 
  • Once we are confident that the replacement is complete and fully functional, disconnect c1auxex and repeat process for other slow machines. 
  12553   Wed Oct 12 15:01:22 2016 steveUpdateSUSSOS ITM baffles plates are ready

The two 40 mm apeture baffles at the ends were replaced by 50 mm one. ITM baffles with 50 mm apeture are baked ready for installation.


 Green welding glass 7" x 9"   shade #14 with 40 mm hole and mounting fixtures are ready to reduce scatter light on SOS

PEEK 450CA shims and U-shaped clips  will keep these plates damped.



  12552   Wed Oct 12 13:34:28 2016 gautamUpdateSUSPRM LR problematic again

Looks like what were PRM problems are now seen in the SRM channels, while PRM itself seems well behaved. This supports the hypothesis that the satellite box is problematic, rather than any in-vacuum shenanigans.

Eric noted in this elog that when this problem was first noticed, switching Satellite boxes didn't seem to fix the problem. I think that the original problem was that the Al foil shorted the contacts on the back of the OSEM. Presumably, running the current driver with (close to) 0 load over 2 months damaged that part of the Satellite box circuitry, which lead to the subsequent observations of glitchy behaviour after the pumpdown. Which begs the question - what is the quick fix? Do we try swapping out the LM6321 in the LR LED current driver stage? 

GV Edit Nov 2 2016: According to Rana, the load of the high speed current buffer LM6321 is 20 ohms (13 from the coil, and 7 from the wires between the Sat. Box and the coil). So, while the Al foil was shorting the coil, the buffer would still have seen at least 7 ohms of load resistance, not quite a short circuit. Moreover, the schematic suggests that that the kind of overvoltage protection scheme suggested in page 6 on the LM6321 datasheet has been employed. So it is becoming harder to believe that the problem lies with the output buffer. In any case, we have procured 20 of these discontinued ICs for debugging should we need them, and Steve is looking to buy some more. Ben Abbot will come by later in the afternoon to try and help us debug.

  12551   Tue Oct 11 13:30:49 2016 gautamUpdateSUSPRM LR problematic again

Perhaps the problem is electrical? The attached plot shows a downward trend for the LR sensor output over the past 20 days that is not visible in any of the other 4 sensor signals. The Al foil was shorting the electrical contacts for nearly 2 months, so perhaps some part of the driver circuit needs to be replaced? If so a Satellite Box swap should tell us more, I will switch the PRM and SRM satellite boxes. It could also be a dying LED on the OSEM itself I suppose. If we are accessing the chamber, we should come up with a more robust insulating cap solution for the OSEMs rather than this hacky Al foil + kapton arrangement.

The PRM and SRM Satellite boxes have been switched for the time being. I had to adjust some of the damping loop gains for both PRM and SRM and also the PRM input matrix to achieve stable damping as the PRM Satellite box has a Side sensor which reads out 0-10V as opposed to the 0-2V that is usually the case. Furthermore, the output of the LR sensor going into the input matrix has been turned off.


  12550   Tue Oct 11 10:38:51 2016 SteveUpdateSUS wire standoffs update

100 Sapphire prizms arrived.


  12549   Tue Oct 11 10:15:04 2016 SteveUpdateSUSPRM LR problematic again

It started here


  12548   Tue Oct 11 08:09:46 2016 Max IsiUpdateDMFsummar pages dead again

Summary pages will be unavailable today due to LDAS server maintenance. This is unrelated to the issue that Rana reported.


I've re-submitted the Condor job; pages should be back within the hour.


Been non-functional for 3 weeks. Anyone else notice this? images missing since ~Sep 21.



  12547   Tue Oct 11 02:48:43 2016 ericqUpdateLSCRevival Attempts

Still no luck relocking, but got a little further. I disabled the output of the problematic PRM OSEM, it seems to work ok. Looking at the sensing of the PRMI with the arms held off, REFL165 has better MICH SNR due to its larger seperation in demod angle. So, I tried the slightly odd arrangement of 33I for PRCL and 165Q for MICH. This can indefinitely hold through the buzzing resonance. However, I haven't been able to find the sweet spot for turning on the CARM_B (CM_SLOW) integrator, which is neccesary for turning up the AO and overall CARM gain. This is a familiar problem, usually solved by looking at the value far from resonance on either side, and taking the midpoint as the filter module offset, but this didn't work tonight. Tried different gains and signs to no avail.

  12546   Tue Oct 11 00:43:50 2016 ericqUpdateSUSPRM LR problematic again

Tonight, and during last week's locking, we noticed something intermittently kicking the PRM. I've determined that PRM's LR OSEM is problematic again. The signal is coming in and out, which kicks the OSEM damping loops. I've had the watchdog tripped for a little bit, and here's the last ten minutes of the free swinging OSEM signal:

Here's the hour trend of the PRM OSEMS over the last 7 days a plot of just LR since the fix on the 9th of September.

It looks like it started misbehaving again on the evening of the 5th, which was right when we were trying to lock... Did we somehow jostle the suspension hard enough to knock the foil cap back into a bad spot?

  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. 

  12544   Mon Oct 10 17:42:47 2016 Max IsiUpdateDMFsummar pages dead again

I've re-submitted the Condor job; pages should be back within the hour.


Been non-functional for 3 weeks. Anyone else notice this? images missing since ~Sep 21.


  12543   Mon Oct 10 17:27:29 2016 ranaUpdateDMFsummar pages dead again

Been non-functional for 3 weeks. Anyone else notice this? images missing since ~Sep 21.

  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.

  12541   Mon Oct 10 09:31:25 2016 SteveUpdateSUSPRM damping restored

Local earth quake 3.7 mag  trips PRM

ETMY_UL glitch

What about the MC?


  12540   Fri Oct 7 20:56:15 2016 KojiUpdateSUSOutput matrix diagonalization

I wanted to see what is the reason to have such large coupling between pitch and yaw motions.

The first test was to check orthogonality of the bias sliders. It was done by monitoring the suspension motion using the green beam.
The Y arm cavity was aligned to the green. The damping of ITMY was all turned off except for SD.
Then ITMY was misaligned by the bias sliders. The ITMY face CCD view shows that the beam is reasonably orthogonally responding to the pitch and yaw sliders.
I also confirmed that the OPLEV signals also showed reasonablly orthogonal responce to the pitch and yaw misalignment.

=> My intuition was that the coils (including the gain balance) are OK for a first approximation.

Then, I started to excite the resonant modes. I agree that it is difficult to excite a pure picth motion with the resonance.

So I wanted to see how the mixing is frequency dependent.

The transfer functions between ITMY_ASCPIT/YAW_EXC to ITMY_OPLEV_PERROR/YERROR were measured.

The attached PDFs basically shows that the transfer functions are basically orthogonal (i.e. pitch exc goes to pitch, yaw exc goes to yaw) except at the resonant frequency.

I think the problem is that the two modes are almost degenerate but not completely. This elog shows that the resonant freq of the ITMY modes are particularly close compared to the other suspensions.
If they are completely degenerate, the motion just obeys our excitation. However, they are slightly split. Therefore, we suffer from the coupled modes of P and Y at the resonant freq.
However, the mirror motion obeys the exitation at the off resonance as these two modes are similar enough.

This means that the problem exists only at the resonant frequencies. If the damping servos have 1/f slope around the resonant freqs (that's the usual case), the antiresonance due to the mode coupling does not cause servo instability thank to the sufficient phase margin.

In conclusion, unfortunately we can't diagnalize the sensors and actuators using the natural modes because our assumption of the mode purity is not valid.
We can leave the pitch/yaw modes undiagnalized or just believe the oplevs as a relatively reliable reference of pitch and yaw and set the output matrix accordingly.


The figures will be rotated later.

  12539   Fri Oct 7 20:25:14 2016 KojiUpdateCDSPower-cycled c1psl and c1iool0

Found the MC autolocker kept failing, It turned out that c1iool0 and c1psl went bad and did not accept the epics commands.

Went to the rack and power cycled them. Burt resotred with the snapshot files at 5:07 today.

The PMC lock was restored, IMC was locked, WFS turned on, and WFS output offloaded to the bias sliders.

The PMC seemed highly misaligned, but I didn't bother myself to touch it this time.

  12538   Fri Oct 7 15:36:03 2016 SteveUpdatePEMthe lab temp is up

The IFO room temp is up


The IFO room temp is up a bit and it is coming down. The out side temp is not really high.


  12537   Fri Oct 7 10:29:57 2016 SteveUpdateVACRGA removed

The RGA is removed for repaire. It's volume at atmophere and sealed.. P4 reading of 38 Torr is not correct.


  12536   Thu Oct 6 15:42:51 2016 LydiaUpdateSUSOutput matrix diagonalization

Summary: At the 40m meeting yesterday, Eric Q. gave the suggestion that we accept the input matrix weirdness and adjust the output matrix by driving each coil individually so that it refers to the same degrees of freedom. After testing this strategy, I don't think it will work. 

Yesterday evening I tested this idea by driving one ITMY coil at a time, and measuring the response of each of the free swing modes at the drive frequency. I followed more or less the same procedure as the standard diagonalization: responses to each of the possible stimuli are compared to build a matrix, which is inverted to describe the responses given the stimuli. For the input matrix, the sensor readings are the responses and the free swing peaks are the stimuli. For the output matrix, the sensors transformed by the diagonalized input matrix as the responses of the dofs which are compared, and the drive frequency peak associated with a coil output is the stimulus. However, the normalization still happens to each dof independently, not to each coil independently. 

The output matrix I got had good agreement with the ITMY input matrix in the previous elog: for each dof/osem the elements had the same sign in both input and output matrices, so there are no positive feedback loops. The relative magnitude of the elements also corresponded well within rows of the input matrix. So the input and output matrices, while radically different from the ideal, were consistent with each other and referred to the same dof basis. So, I applied these new matrices (both input and output) to the damping loops to test whether this approach would work. 

drive-generated output matrix: 

      UL      UR      LR       LL      SD
pit    1.701  -0.188  -2.000  -0.111   0.452  
yaw    0.219  -1.424   0.356   2.000   0.370  
pos    1.260   1.097   0.740   0.903  -0.763  
sid    0.348   0.511   0.416   0.252   1.000  
but    0.988  -1.052   0.978  -0.981   0.060

However, when Gautam attempted to lock the Y arm, we noticed that this change significantly impacted alignment. The alignment biases were adjusted accordingly and the arm was locking. But when the dither was run, the lock was consistently destroyed. This indicates that the dither alignment signals pass through the SUS screen output matrix. If the output matrix pitch and yaw columns refer instead to the free swing eigenmodes, anything that uses the output matrix and attempts to align pitch and yaw will fail. So, the ITMY matrices were restored to their previous values: a close to ideal input matrix and naive output matrix. We could try to change everything that is affected by the output matrices to be independent of a transformation to the free swing dof basis, and then implement this strategy. But to me, that seems like an unneccessary amount of changes with unpredictable consequences in order to fix something that isn't really broken. The damping works fine, maybe even better, when the input matrix is set by the output matrix: we define pitch, for example, to be "The mode of motion produced by a signal to the coils proportional to the pitch row of the naieve output matrix," and the same for the other dofs. Then you can drive one of these "idealized" dofs at a time and measure the sensor responses to find the input matrix. (That is how the input matrix currently in use for ITMY was found, and it seems to work well.) 


  12535   Thu Oct 6 03:56:43 2016 ericqUpdateLSCRevival Attempt

[ericq, Gautam, Lydia]

We spent some time tonight trying to revive the PRFPMI. (Why PR instead of DR? Not having to deal with SRM alignment and potentially get a better idea of our best-case PRG). After the usual set up and warm up, we found ourselves unable to hold on to the PRMI while the arms flash. In the past, this was generally solved through clever trigger matrix manipulations, but this didn't really work tonight. We will meditate on the solution.

  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
  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

  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..

  12531   Tue Oct 4 22:18:24 2016 JohannesUpdateGeneralX/YARM loss measurement

[gautam, johannes]

We let the PSL shutter closed overnight and observed the POXDC, POYDC and ASDC offsets. While POY has small fluctuations compared to the signal level, POX is worse off, and the drifts we observed live in the DC reading are in the same ballpark as the offset fluctuations. The POXDC level also unexpectedly increased suddenly without the PSL shutter being opened, which we can't explain. The data we took using POXDC cannot be trusted.

Even the ASDC occasionally shows some fluctuations, which is concerning because the change in value rivals the difference between locked and misaligned state. It turns out that the green shutters were left open, but that should not really affect the detectors in question.

We obtained loss numbers by measuring the arm reflections on the ASDC port instead. LSCoffsets was run before the data-taking run. For each arm we misaligned the respective other ITM to the point that moving it no longer had an impact on the ASDC reading. By taking a few quick data points we conclude the following numbers:

XARM: 247 ppm +/- 12 ppm
YARM: 285 ppm +/- 13 ppm

This is not in good agreement with the POYDC value. The script is currently running for the YARM for better statistics, which will take a couple hours.

ITMX is misaligned for the purpose of this measurement, with the original values saved.

GV edit 5Oct2016: Forgot to mention here that Johannes marked the spot positions on the ITMs and ETMs (as viewed on the QUAD in the control room) with a sharpie to reflect the current "well aligned" state.

  12530   Tue Oct 4 11:02:31 2016 SteveUpdateVACRGA is out of order

The last good rga scan at vent 78  day 38




RGA background scan


Vacuum Status: Chamber Open

All chamber annuloses are vented.  Vac Monitor screen is not communicating with gauges. The valve position indicator are working.

RGA is pumped by Maglev through VM2





  12529   Tue Oct 4 02:59:48 2016 ericqUpdateGeneralmucking about

[ericq, gautam]

We poked around trying to figure out the X PDH situation. In brief, the glitchiness comes and goes, not sure what causes it. Tried temp servo on/off and flow bench fan on/off. Gautam placed a PD to pick off the pre-doubler AUX X IR light to see if there is some intermittant intensity fluctuation overnight. During non-glitchy times, ALSX noise profile doesn't look too crazy, but some new peak around 80Hz and somewhat elevated noise compared to historical levels above 100Hz. It's all coherent with the PDH control up there though, and still looks like smooth frequency noise...

NB: The IR intensity monitoring PD is temporarily using the high gain Transmon PD ADC channel, and is thus the source of the signal at C1:LSC-TRY_OUT_DQ. If you want to IR lock the X arm, you must change the transmon PD triggering to use the QPD.

  12528   Mon Oct 3 21:24:02 2016 JohannesUpdateGeneralXARM loss measurement

[gautam, johannes]

I started a script on Friday night to collect some data for a reflection armloss measurement of the XARM. Unfortunately there seemed to have been a hickup in some data transfer and some errors were produced, so we couldn't really trust the numbers.

Instead, we took a series of manual measurements today and made sure the interferometer is well behaved during the averaging process. I wrote up the math behind the measurement in the attached pdf.

The numbers we used for the calculations are the following:

While we average about 50 ppm +/-15 ppm for the XARM loss with a handful of samples, in a few instances the calculations actually yielded negative numbers, so there's a flaw in the way I'm collecting the data. There seems to be a ~3% drift in the signal level on the PO port on the order of minutes that does not show in the modecleaner transmission. The signals are somewhat small so we're closing the shutter over night to see if it could be an offset and will investigate further tomorrow. I went back and checked my data for the YARM, but that doesn't seem to be affected by it.

  12527   Sat Oct 1 10:03:28 2016 ericqUpdateGeneralmucking about

Some things I did last night:

I measured the X PDH OLG, and turned the gain down by ~6dB to bring the UGF back to 10kHz, ~50deg phase margin, 10dB gain margin. However, the error signal on the oscilloscope remained pretty ratty. Zooming in, it was dominated by glitches occuring at 120Hz. I went to hook up the SR785 to the control signal monitor to see what the spectrum of these glitches looked like, but weirdly enough connecting the SR785's input made the glitches go away. In fact, with one end of a BNC connector plugged into a floating SR785 input, touching the other end's shield to any of the BNC shields on the uPDH chassis made the glitches go away.

This suggested some ground loop shenanigans to me; everything in the little green PDH shelves is plugged into a power strip which is itself plugged into a power strip at the X end electronics rack, behind all of the sorensens. I tried plugging the power strip into some different places (including over by the chamber where the laser and green refl PD are powered), but nothing made the glitches go away. In fact, it often resulted in being unable to lock the PDH loop for unknown reasons. This remains unsolved.

As Gautam and Johannes observed, the X green beat was puny. By hooking up a fast scope directly to the beat PD output, I was able to fine tune the alignment to get a 80mVpp beat, which I think is substaintially bigger than what we used to have. (Is this plus the PDH gain changed really attributable to arm loss reduction? Hm)

However, the DFD I and Q outputs have intermittent glitches that are big enough to saturate the ADC when the whitening filters are on, even with 0dB whitening gain, which makes it hard to see any real ALS noise above a few tens of Hz or so. Turning off the whitening and cranking up the whitening gain still shows a reasonably elevated spectrum from the glitches. (I left a DTT instance with a spectrum on in on the desktop, but forgot to export...) The glitches are not uniformly spaced at 120Hz as in the PDH error signal. However, the transmitted green power also showed intermittant quick drops. This also remains unsolved for the time being. 

  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.


  12525   Fri Sep 30 10:37:57 2016 SteveUpdateVACvacuum VME machines rebooted

[ Gautam and Steve ]

c1vac1 and c1vac2 were rebooted and the gauges are communicating now. V1, VA6, V5 and V4 were closed and disconnected to avoid unexpected valve switching. All went smoothly.

The new ITcc gauge is at 1e-5 Torr as CC1   This is the gauge that should be logged in slow channel.

TP2 fore line dry pump was replaced this morning after 382 day of operation.

TP3 dry pump is very noisy, but it's pressure still 47 mTorr


[ericq, Gautam, Steve]

Following roughly the same procedure as ELOG 11354, c1vac1 and c1vac2 were rebooted. The symptoms were identical to the situation in that ELOG; c1vac1 could be pinged and telneted to, but c1vac2 was totally unresponsive. 

The only change in the linked procedure was that we did not shut down the maglev. Since I unwittingly had it running for days without V4 open while Steve was away, we now know that it can handle shorter periods of time than that...

Upon reboot, many channels were readable again, unfortunately the channels for TP2 and TP3 are still blank. We were able to return to "Vacuum normal state," but because of unknowned communication problems with VM1's interlock, we can't open VM1 for the RGA. Instead we opened VM2 to expose the RGA to the main IFO volumn, but this isn't part of the "Normal" state definite, so things currently read "Undefined state".


  12524   Thu Sep 29 20:21:29 2016 JohannesUpdateGeneralYARM loss measurement

[Gautam, Johannes]

I scripted a series of YARM DC reflectivity measurements last night alternating between locked state and unlocked state (with ETMY misaligned) for measuring the after-vent armloss. The general procedure is based on elog 11810, but I'll also give a brief summary here.

  • To measure the locked reflectivity the dither script is executed with a stop condition that depends on the rms values of its error signals.
  • The dithering is stopped, and while the arm is locked the reflected power is recorded from both POX/POY DC and ASDC, as well as the mode cleaner transmission for normalization.
  • The arm locking is switched off, and ETMY moved to is 'misaligned' position. This gets rid off unwanted mode flashes.
  • In the unlocked state the same quantities are recorded.
  • Rinse and repeat for a set number of times (for this run I set it to 100 and left the interferometer alone).

I did this back in June (but strangely never posted what I found, shame on me). What I found back then was a YARM loss of 237 ppm +/- 41 ppm and an XARM loss of 501 ppm +/- 105 ppm

Last night's data indicates a YARM loss of 143 ppm +/- 24 ppm after cleaning with first contact. yeslaugh

THIS IS STILL ASSUMING THAT THE MODE-MATCHING HASN'T CHANGED. We had however moved ETMY closer to ITMY during the vent by 19mm. Gautam and I had some trouble setting up the ALS to confirm the mode-matching, but we're in the process of recovering the XARM IR beat.

  12523   Thu Sep 29 16:19:29 2016 LydiaUpdateSUSFree swing eigenmodes

[Lydia, Teng]

Motivated by the strange pitch/yaw coupling behavior we ran into while doing diagonalization, we looked at the oplev pitch and yaw free swing spectra for all 4 test masses (see attachment 1). We saw the same behavior there: At the peak frequencies for the angular degress of freedom, the oplevs saw significant contributions from both pitch and yaw. We also examined the phase between pitch and yaw at these peaks and found that consistently, pitch and yaw were in phase at one of the resonance frequencies and out of phase at the other (ignoring the pos and side peaks). 

This corresponds physically to angular motion about some axis that is diagonal, ie not perfectly vertical or horizontal. If we trust the oplev calibration, and Eric says that we do, then the angle of this axis of rotation with the horizontal (pitch axis) is

 \theta = \arctan \frac{Y\left ( f_{peak} \right )}{P\left ( f_{peak} \right )}  

Where Y and P are yaw and pitch ASD values. This will always give an angle between 0 and 90 degrees; which quadrant the axis of rotation occupies can be dermined by looking at the phase between pitch and yaw at the same frequencies. 0 phase means that the axis of rotation lies somewhere less than 90 degrees counterclockwise from the horizontal as viewed from the AR face of the optic, and a phase of 180 degrees means the axis is clockwise from horizontal (see attachment 2). Qualitatively, these features show up the same way for segments of data taken at different times. In order to get some quantitative sense of the error in these angles, we found them using spectrogram values with a bandwidth of 0.02 Hz averaged over 4000 seconds. 

Results (all numbers in degrees unless otherwise specified):

peak 1 ( 0.692  Hz):
mean: 24.991
std: 1.23576
ptich/yaw phase: -179.181
peak 2 ( 0.736  Hz):
mean: 21.7593
std: 0.575193
pitch/yaw phase: 0.0123677


peak 1 ( 0.502  Hz):
mean: 17.4542
std: 0.745867
ptich/yaw phase: -179.471
peak 2 ( 0.688  Hz):
mean: 74.822
std: 0.455678
pitch/yaw phase: -0.43991


peak 1 ( 0.73  Hz):
mean: 43.1952
std: 1.54336
ptich/yaw phase: -0.227034
peak 2 ( 0.85  Hz):
mean: 60.7117
std: 0.29474
pitch/yaw phase: -179.856

peak 1 ( 0.724  Hz):
mean: 78.2868
std: 2.18966
ptich/yaw phase: 6.03312
peak 2 ( 0.844  Hz):
mean: 26.0415
std: 2.10249
pitch/yaw phase: -176.838

ETMY and ITMX both show a more significant (~4x) contribution from pitch on one peak, and from yaw on the other. This is reflected in the fact that they each have one angle somewhat close to 0 (below 30 degrees) and one close to 90 (above 60 degrees). The other two test masses don't follow this rule, meaning that the 2 angular frequency peaks do not correspond to pitch and yaw straightforwardly. 

Also, besides ITMX, the axes of rotation are at least several degrees away from being perpendicular to each other. 


  12522   Thu Sep 29 09:49:53 2016 ranaUpdateGeneralmucking about

With the WFS and OL, we never have figured out a good way to separate pit and yaw. Need to figure out a reference for up/down and then align everything to it: quad matrix + SUS output matrix

  12521   Wed Sep 28 04:27:33 2016 ericqUpdateGeneralmucking about

PMC was terribly misaligned. The PMCR camera seems to have drifted somewhat off target too, but I didn't touch it.

Realigned ITMX for the nth time today.

Finding ALSY beatnote was easy, ALSX eludes me. I did a rough one-point realignment on the X beat PD which is usually enough, but it's probably been long enough that near/far field alignmnet is neccesary. 

ALSY noise is mostly nominal, but there is a large 3Hz peak that is visible in the spot motion, and also modulates the beat amplitude by multiple dBs.

It looked to me that the ETMY oplev spot was moving too much, which led me to measure the oplev OLGs. There is some wierd inter-loop interference going on between OLPIT and OLYAW. With both on (whether OSEM damping is on or off, so input matrix shenanigans can't be to blame) there is a very shallow "notch" at around 4.5Hz, which leads to very little phase at 3Hz, and thus tons of control noise. Turning the OL loop not being measured off makes this dip go away, but the overall phase is still signfinicantly less than we should have. I'm not sure why. I'll just show the PIT plot, but things look pretty much the same for YAW. 

I did some more ETMX tests. Locked arm, raised the servo output limit to 15k, then increased the gain to make the loop unstable. I saw the SUS LSC signals go up to tens of thousands of counts when the unlock happened. I did this a dozen times or so, and every time the ETM settled in the same angular position according to the oplev.

Right now, another hysteresis script is running, misaliging in pitch and yaw. Amplitude 1V in each direction. So far, everything is stable after three on/off cycles.

  12520   Tue Sep 27 18:04:50 2016 LydiaUpdateSUSITMX slow channels down, ITMY diagonalization update

[Teng, Lydia]

When we plugged in the back cables yesterday on the whitening boxes after switching them, two of the ITMX PDMon channels (UR and LR) got stuck at 0. This caused me to believe ITMX was still stuck even when it was freed. However, it was left in a stuck state overnight and freed again today after this issue was discovered. The alignment sliders have been set to 0 as a safety net to keep ITMX from getting stuck again if c1susaux is restarted again. We switched the cables back and the problem was still there.

The ITMY UL whitening filter problem, which the cables were originally switched to diagnose, was also still there. Ericq suggested we turn off all the whitening filters in order to get diagonalization data that would not show a phase difference between coils. We ran the diagonalization again with all the dewhitening filters off and got much cleaner results, with no visible cross-coupling peaks remaining between the degrees of freedom (see attachemnt 1). We did not apply this matrix to the damping, however, because there are elements which have the wrong sign compared to the ideal matrix. Significant adjustments to the output matrix will probably need to be made if this result is to be used. We also verified that the phase problem had been solved in DTT, where we saw the same sign discrepancies as in the matrix below. 

Damping can be turned back on, using the old, non-diagonalized matrix currently in effect. There is enough free swing data to diagonalize ITMY now, so feel free to mess with it. 

Matrix (wrong signs red, suspiciously small elements orange):

           pit     yaw     pos         side    butt
UL    1.633   0.138   1.224   0.136   0.984  
UR   -0.202  -1.768   1.179   0.132  -1.028  
LR   -2.000   0.094   0.776   0.107   1.001  
LL   -0.165   2.000   0.821   0.111  -0.987  
SD    0.900   1.131  -1.708   1.000  -0.107  


  12519   Tue Sep 27 08:49:47 2016 SteveUpdateSUSseismic activity is up

The earth quake shook ITMX free for a  short while.


  12518   Mon Sep 26 19:48:09 2016 LydiaUpdateSUSITMX stuck again, ITMY whitening issue

This afternoon around 2:45, ITMX started ringing up at ~.9Hz for about a minute and then got stuck again. When I noticed this evening, I tried to free it with the alignment sliders but was unable to see any signal on UL or UR. It also looks like the damping for ITMY was turned off at the same time ITMX got stuck (not at the start of its ring up). SRM also has a spike in its motion at this time, and another one minute later that ended up with the LR OSEM at a much higher level, though the mirror does not appear to be stuck. We didn't see any strange behavior from any of the other optics.

Teng and I were working on diagnosing a problem with the ITMY UL whitening, but by the time we disconnected any applicable cables, the damping for ITMY was already off. Later we unplugged the ITMX PD whitening cables after verifying that the ITMX damping was also already off. This problem may have occured earlier, while Teng, Eric, and I were examining and pushing in the cables at 1X5 without unplugging anything.

We found that the reason for the bad phase on the ITMY free swing data is because the whitening filter for UL is not being properly turned on. We are in the process of investigating the source of this problem. Right now all the cables to the PD whitening boxes in 1X5 are switched between ITMY and ITMX.

  12517   Sat Sep 24 11:04:00 2016 ericqUpdateSUSETMX hysteresis test

Seems like the angular position was fairly stable, though there is some change in the ETMX pitch that could be hysterisis or normal drift. I didn't mention it explicity in the previous log, but the misalignment was purely in pitch. I'll give it another shot with a bigger misalginment, and maybe a mix of pitch and yaw.

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