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ID Date Author Type Category Subject
  12485   Mon Sep 12 20:19:25 2016 LydiaUpdateGeneralMC REFL beam splitter not replaced

The beam splitter that directs light into the MC REFL photodiode has not been replaced; there is still a mirror there. Gautam suggested we wait to replace it until the PSL shutter is open so the beam can be aligned. However, this must be done before going to high power.

GV addendum: What I suggested was to try and recover the arm alignment using the current low power configuration after pumpdown - since we were well aligned just before pumpdown, we should be able to recover this alignment pretty easily at low power. After locking both arms and running the dither align (also center all Oplevs), we can go ahead do the following:

  • Replace mirror in MC Refl path with 10% reflection BS (Johannes, Lydia and I confirmed that this is on the AP table earlier today). Then align the reflected beam onto the PD using the tiny mirror
  • Replace HR mirror in Transmon path at the EY table
  • Replace ND filters on Transmon QPDs at EX and EY tables
  • Repalce ND filter on Transmon CCD at EY table
  • Revert MC autolocker to the nominal version instead of the low power version we have been using during the vent
  • Turn up MC to nominal power by rotating the wave plate on the PSL table - confirm that we have nominal levels by measuring with power meter
  • Recover single arm locks, green beatnotes etc at nominal operating conditions
  12484   Mon Sep 12 20:15:22 2016 LydiaUpdateSUSDiagonalization in air

[Lydia, Teng]

We ran the scripts to diagonalize the damping matrices using the free swinging data from staurday night/sunday morning. The actual entries used for damping have not been changed. However, we did generate updated matrices for all the main optics (not including the mode cleaner optics, which were not free swinging over the weekend).

  • The scripts appear to be mostly working as intended, with a couple of issues:
    • The plots made by makeSUSSpectra claim to be showing spectra of the individual OSEM readings, but are actually dofs calculated using the ideal input matrix.
    • The existing parameters file (for the peak finding) was only fitting the lorentz peaks to a very narrow band of data, close to the bandwidth of the spectrum. Too narrow a band means that the initial guess must be very close, and also means there are not enough points to fit to.
      • We modified a copy of the paramters file to use a wider band (~.1 Hz) for fitting, and also use updated estimates of the mode frequencies.
      • This was largely successful, but the ITMY POS peak is very close to the SIDE peak, and POS is also stringly coupled to SIDE, so the wider bandwidth fitting can't separate the peaks. (See attachment 1)
      • A longer time series, plus more accurate initial guesses for the resonance frequencies, would allow us to fit to a smaller (~.03 Hz) band without encountering the stated issues.
      • A better way than manually examining plots to choose an initial frequency guess would be to automatically start at the overall maximum point in the spectrum between 0.4 and 1.5 Hz
  • Most of the diagonalization results seem good: "Badness" numbers of 4-6 and secondary peaks very supressed or absent on spectra plotted in dof basis (See attachment 2). ITMY, perhaps beacuse of a related issue, has phase problems with the matrix elements that result in messages like "osem/dof 2/1 is imaginary."
  12483   Mon Sep 12 17:54:24 2016 SteveUpdateVACpumpdown 79

 We are pumping down. The annuloses are below 10 mTorr

The vacuum gauges are not communicating with the medm so there is no plot available.

The main volume pumping is stopped at P1 = 220 Torr  ( New SuperBee 174 Torr ) for overnight.

note: SuperBee was reading 791 Torr at atm and it was not set to 760 !

  12482   Mon Sep 12 17:15:22 2016 JohannesUpdateGeneralPRM SRM alignment

[Gautam, Steve, Johannes]

We put on the remaining heavy doors on the chambers (ITMY, ITMX,ETMX, in this order) this morning. On the ITMY and ETMX tables we placed old OpLev steering mirrors that are clean and baked as witness plates such that may one day provide some insight into dust accumulation on optics.

With the heavy doors on we confirmed that we were still able to lock both IFO arms and used the dither scripts to optimize the alignment. Following that we centered all OpLevs and aligned the X and Y green beams.

ITMY table witness plate
ETMX table witness plate


  12481   Sat Sep 10 14:26:01 2016 ranaUpdateGeneralPRM SRM alignment

For the PRM, I aligned it until the arm flashes were maximized and the REFL camera showed a centered spot with dips happening during the arm pops. AS port was more messy since the Michelson alignment wasn't perfect, but the spots were both near the center of the cam and the SRM alignment maximized the wangy fringiness of the image as well as the angry cat meow sounds that the full IFO makes as heard through the DAFI (listening to POX).

On Monday, Osamu should be back and can help with doors and then alignment recovery and locking.

  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

  12479   Fri Sep 9 11:24:15 2016 SteveUpdatesafetysafety training

Visiting graduate student Teng Zhang from Glasglow received 40m specific safety training yesterday.

  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
  12477   Wed Sep 7 18:00:47 2016 LydiaUpdateGeneralAcromag Progress

[Teng, Lydia]

We would like to establish a system for setting up ADC channels and integrating them into the existing EPICS framework, so that we can gradually switch over channels that are currently handled by the aging slow machines. Otherwise, we will be stuck when they eventually fail. As a preliminary test for this method, we are in the process of setting up an Acromag ADC to read the "Diagnostic" output of the PSL controller. This information will also be useful to monitor the health of the PSL. 

Today, we accomplished the following:

  • Configured the Acromag XT1221 for use on the martian netowrk. It is assigned the static IP, with hostname iocPSLmon. 
  • Connected the Acromag to a switch on the 1X6 cabinet, and set it up on a desk near the X arm door with a 24V DC power supply. 
  • Verified that the IP was reachable from a control room desktop. 
  • Modified the files from Aiden's wiki page (myiocconfig.cmd and IOCTEST.db) to reflect our setup. 
  • Attached input 0 to a DC voltage and retrieved the output over the network. 
    • Channel name: "C3:ACROMAG_INPUT0" 
    • Values are currently uncalibrated, the voltage is represented by a 16 bit signed integer
    • We changed the value of the DC input and verified that the channel output changed in the expected direction

The power supply has been turned off for the night. 

  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

  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.

  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....
  12473   Tue Sep 6 20:30:56 2016 ranaUpdateSUSITMY_UL is sick

In the morning, Steve will start opening the north BS door so that we can enter to inspect the PRM LR OSEM.

For the ITMY, I squished together the cables which are in the 'Cable Interface Board' which lives in the rack. This thing takes the 64 pin IDC from the satellite module and converts it into 2 D-sub connectors to go to the PD whitening board and the coil driver board. Lets see if the ITMY OSEM glitches change character overnight.

  12472   Tue Sep 6 18:21:13 2016 ranaUpdateSUSOSEM issues

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

  7/2011 9/2016
POS 0.993 0.94
PIT 0.612 0.60
YAW 0.833 0.76
SIDE 0.999 0.993

Some of the frequencies have changed between the 2011 in-vac measurement and our 2016 in-air measurement, but that seems within usual parameters.

  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?

  12470   Mon Sep 5 21:05:06 2016 ranaUpdateElectronicsSatellite Amplifier

The attached PDF shows the output noise of the satellite amp. This was calculated using 'osempd.fil' in the 40m/LISO GitLab repo.

The mean voltage output is ~1 Vdc, which corresponds to a current with a shot noise level of 100 nV/rHz on this plot. So the opamp current noise dominates below 1 Hz as long as the OSEM LED output is indeed quantum limited down to 0.1 Hz. Sounds highly implausible.

To convert into meters, we divide by the OSEM conversion factor of ~1.6 V/mm, so the shot noise equivalent would be ~1e-10 m/rHz above 1 Hz.

After adding the sat amp to the 40m DCC tree (D1600348), I notice that not only is the PD readout not built for low noise, neither is the LED drive.  The noise should be dominated by the voltage noise of the LT1031 voltage reference. This has a noise of ~500 nV/rHz at 1 Hz. That corresponds to an equivalent current noise through the LED of 25 mA * (500e-9 / 10) ~ 1 nA/rHz. Or ~45 nV/rHz at the sat amp output. This would be OK as long as everything behaves ideally. BUT, we have thick film (i.e. black surface mount) resistors on the LED drive so we'll have to measure it to make sure.

Also, why is the OSEM LED included in the feedback loop of the driver? It means disconnecting the cable from the sat amp makes the driver go unstable probably. I think one concept is that including the device in the feedback loop makes it so that any EMI picked up in the cabling, etc. gets cancelled out by the opamp. But this then requires that we test each driver to make sure it doesn't oscillate when driving the long cable. frown 

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.

  12469   Mon Sep 5 19:57:24 2016 OsamuUpdateSUSOSEM adjustments

Hi 40m people,

As Rana is saying, the bounce mode does not matter, or we cannot do anything. Generally speaking, the bounce mode cannot be damped by the setting of 40m SUS. Some tweak techniques may damp a bounce mode by res-gain or something, but it is not a proper way, I think.

This is also that Rana is already saying that the important thing is to find a good direction of OSEM to hit the LED beam to the magnet. Even if the magnet is not located at the center of OSEM hole, still you can find the optimal orientation of OSEM to hit the LED beam to the center of magnet by rotating the OSEM.

I know only an old document of T040054 that Shihori summarized how to adjust the matrix at the 40m. Too bad input/output matrix may introduce some troubles, but even roughly adjusted matrix should be still fine.

I will be at Caltech on 12-14 of September. If I can help something, I am willing to work with you!

  12468   Fri Sep 2 21:16:45 2016 ranaUpdateElectronicsSatellite Amplifier

In November of 2010, Valera Frolov (LLO), investigated our satellite amplifiers and made some recommendations about how to increase the SNR.

In light of the recent issues, we ought to fix up one of the spares into this state and swap it in for the ITMY's funky box.

The sat amp schematic is (D961289). It has several versions. Our spare is labeled as version D (not a choice on the DCC page).

  1. U13-17 seem superfluous. Why would we need a high current buffer to drive the slow EPICS ADCs ?
  2. The Radd resistors indicated on the B2 schematic have not been added to this board. What would be the purpose of adding them anyway?
  3. The transimpedance resistors are, in fact, 29.4k as indicated on the B1 schematic.
  4. The LT1125: V_n = 3 nV w/ f_corner = 5 Hz. I_n = 0.4 pA w/ f_corner = 100 Hz. So at 1 Hz the current noise is limiting at ~120 nV/rHz or 650 nV/rHz using the 161k that Valera recommends.
  5. Even in that case the ADC noise is higher than the opamp noise.
  6. We should be using metal film resistors instead of the thick film junk that's installed now.

Edit (Sep 6): The purpose of the Radd resistors is to lower the resistance and thus up the current through the LED. The equivalent load becomes 287 Ohms. Presumably, this in series with the LED is what gives the 25 mA stated on the schematic. This implies the LED has an effective resistance of 100 Ohms at this operating point. Why 3 resistors? To distribute the heat load. The 1206 SMD resistors are usually rated for 1/4 W. Better to replace with 287 Ohm metal film resistors rated for 1 W, if Steve can find them online.

  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...

  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..

  12465   Thu Sep 1 19:59:22 2016 JohannesUpdateSUSIR mode flashes in Y arm

[Gautam, Lydia, Johannes]

  • After placing the irises on the ETMY and ITMY cages we found that the green beam pointing was off in YAW and corrected it to hit the center of ITMY
  • The green beam was well centered on ETMY to begin with, so we used it as a reference for the alignment of ITMY, sending it back through the ETMY iris
  • We used the green transmission to tune the pitch and yaw of ETMY
  • Using TT1 and TT2 we steered the beam IR through both irises and were hoping to see mode flashes in the IR arm transmission, which we did

The next step is the tip tilt fine alignment of the IR into the arm, using TRY, from which we removed the ND filter for the time being.

  12464   Thu Sep 1 19:18:14 2016 JohannesUpdateSUSITMX and ETMX preemptive table leveling

I balanced the ITMX and ETMX tables into level position today, for which I had to move quite a few of the on-table weights. I'm recording their original positions for future use here.


This table was only off in 'pitch', I moved the middle weight to a new location as shown in the pictures. I added secondf disk weight on top of the one I moved, this one has to come out again when we install ETMX.

ETMX chamber original configuration
Reference for original position
Moved weight here


I moved some weights around as shown in the image, but didn't have to add any. We simply have to move them back to their original location when the time comes.

ITMX chamber original configuration
Reference for square blocks: the lower one is a double stack
Reference for disk weights: These two are stacked.


While in the chambers, I also took some pictures of the ETMX window and PR2, motivated by the dirty state of SR2. We might want to consider cleaning both, specifically PR2 is relatively easily accessible and can be cleaned when we open the ITMX chamber to remove its FC and move it back into position.


  12463   Thu Sep 1 17:25:02 2016 PrafulUpdateElectronicsAcoustic Tab and Amp Suspension

I'll add a picture of the installation when I get back to campus and finish hooking up the power cable. I haven't added this channel to the actual pages yet because there's not any data right now- the box is still unpowered because my braided power cable wasn't long enough. I just changed the format of the spectrum to ASD and added spectrograms. Here's how the tab looks now: https://ldas-jobs.ligo.caltech.edu/~praful.vasireddy/1155014117-1155015017/pem/acoustic/

Let me know if there's anything else to change.

  1. add photo of installation
  2. no more secret personal pages! put channels into the actual pages that we look at
  3. make it ASD instead of PSD, same as the other channels
  4. add specgram (whitened and not)

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:


This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.



  12462   Thu Sep 1 15:43:16 2016 ranaUpdateSUSOSEM adjustments

On the bounce roll balancing:

Recall that back in 2006, the main issue was not with the bounce mode coupling into the OSEMs but instead with too much cross-coupling between the damping loops themselves:

Old elogs from Osamu (reader / readonly). Osamu will be here in a couple weeks and can try to explain what he was doing back then.

The problem was that without a good input matrix, the low frequency motion of the suspension point was dominated by the damping noise rather than the seismic noise. The bounce mode is a nice indicator of whether the OSEM is oriented up/down but its not the most important thing. More important is that the magnet is in the actual LED beam, not just the apparent center of the OSEM.

Then we should be able to fix things by running the diagonalization script and correcting the input matrix (which depends somewhat on the DC alignment).

  12461   Thu Sep 1 15:40:52 2016 SteveUpdateSUSHEPAs on each chamber door

This is an option to isolate the vacuum chamber from the dusty 40m lab: 4x8 HEPA unit or Air Curtain

It does not limit crane operations. Here is some  science based approach to air filters

Lets put horizontal and vertical witness plates next to our arm cavity TMs just before pumpdown.


  12460   Thu Sep 1 15:28:01 2016 ranaUpdateElectronicsAcoustic Tab and Amp Suspension
  1. add photo of installation
  2. no more secret personal pages! put channels into the actual pages that we look at
  3. make it ASD instead of PSD, same as the other channels
  4. add specgram (whitened and not)

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:


This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.


  12459   Thu Sep 1 08:30:24 2016 SteveUpdateSUSITMY_UL is sick

So if the SRM satellite box is good, than the ITMY sensor UL or vacuum cabeling from sersor to sat amp is bad.


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? 

Is the spare sat amp is bad ?

  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.

  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? 

  12456   Wed Aug 31 18:07:43 2016 JohannesUpdateSUSITMY free swinging

[Lydia, Gautam, Koji, Johannes]

Summary of things done today:

  • Rebalanced ITMY table
    • After waiting until today to see if the table would relax into a level position, engaged the earthquake stops for SRM and moved the large counterweight by ~4 inches. The table is now level to within ~0.1 mrad in direction of the access port
    • Since the relaxing seems to take some time, we will open ITMX and ETMX chamber tomorrow and level the tables with additional weights, so the springs can get used to 'levelness' again
  • Cleaned ITMY, SRM and SR2 optics
    • Koji drag-wiped all three optics and cleaned the table in general where accessible. He was able to remove the sliver discussed in elog https://nodus.ligo.caltech.edu:8081/40m/12455
    • We measured the particle count in the chamber and found it to be 4000 for 0.3 microns and 660 for 0.5 microns.
  • We pulled out stops on ETMY ITMY and roughly centered the OSEMs half-way, using photos of the previous OSEM rotation as a reference point for their orientation. We foudn that the green beam is hitting ITMY almost centered and that the reflection doesn't seem to steer off too much, but were not yet able to see any returned light on the ETMY cameras.

Unless we get lucky and get the green light to flash in the cavity by playing with the mirror alignment, we will open the ETMY chamber tomorrow. On one hand we can look for the reflected green light in the chamber, or alternatively the IR beam transmitted by ITMY. This way we can obtain estimates for the OSEM biasing and perform the final centering of the OSEMs. We will then also address the bounce mode minimization in ITMY and check if the previous orientations still hold.

  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?

  12454   Tue Aug 30 15:44:28 2016 SteveUpdateSUS wire standoffs update

100 Sapphire prisms ordered. Delivery date 9-30-2016

~60 deg. prisms,

Size A=B=C=2 mm, length 5 mm

Material: sapphire

Surface quality: 5 micron RMS

Tolerances: +- 0.1 mm

This prism will be used as a mechanical component

No crystal orientation required



There are some issues with 5 mm sapphire prism Atm5. It will cause  interference between one of the prisms and the Side OSEM.

Here are some drawings to see the issues with larger wire standoff.

The 2 mm prism will work.with a 1 mm longer dumbell.

Quotes requested from http://photomachining.com/laser-micromachining-photomachining-contact.html and http://www.optocity.com/ 




  12453   Tue Aug 30 09:51:37 2016 SteveUpdateSUSthe chamber HEPA tents are back

How to minimize particles entering the vacuum envelope.


Just the way it was in August 2011 vent and before.

The portable HEPAs were set up at ETMY and ITMY with CP STAT 100 curtains.

The  40m particles on the floor at ITMY 3000-5000 counts  of 0.5 micron cf / min and 0.3 micron size particles are 55,000 - 65,000 counts cf / min

At this condition the MET One Counter #3 on the floor inside the tent goes to zero count  of 0.5 micron and 20-40 counts cf / min  for 0.3 micron when the tent is slightly overpressured.






  12452   Mon Aug 29 21:53:14 2016 LydiaUpdateSUSETMY bounce mode coupling

[gautam, johannes, lydia]

We decided to try some different approaches on minimizing the ETMY bounce coupling today, since the peak height in the previously attched spectrum was  higher than the previously recorded levels in 2011 for all but the LR OSEM.

  • We recoreded a coarse reference spectrum with the light door off and the HEPA filter on. 
  • We attempted to match UL, UR and LL orientation to their apparent position in photos takes before the OSEMs were initially removed. We found that every OSEM showed a stronger bounce coupling, including those that had not been moved. We repeated the spectrum a few times, damping the optic and then turning the damping back off between each data set. The effect persisted, so we decided to move them back to where they started today (the final posiitons of our earlier optimization attempt). 
  • The peaks returned to approximately their reference levels for all except LL. UL was still the worst overall, so we attempted to more finely tune its angle without success: we saw increases in the peak height in both directions again (when turned approx. 3-4 degrees). 
  • We then turned the UL OSEM by 90 degrees. (See Attachment 1). Surprisingly, the 16.4 Hz peak height was greatly reduced (by a factor of 7-9). We took another spectrum to confirm and the peak was significantly lower than the reference yet again. We decided to leave the OSEM in this configuration in order to take a finer spectrum (See Attachment 2). However, this means that while the magnet looks well centered in the OSEM, the sideways range of motion is reduced and there are no earthquake stops preventing string side to side swings, so care should be taken in the ETMY chamber. 
  • Before starting, we had discussed a possilbe mechanism for bounce coupling that could potentially be minimized by turning the OSEM so that the nominal beam direction was horizontal. This would be possible if the beam of light inside the OSEM were directed toward the front or back, i.e. if it had some component parallel to the POS axis. Then, if the component of the beam in the plane of the optic's surface is oriented vertically, the bounce mode will move the edge of the magnet's shadow in and out of the center of the beam, allowing for strong coupling (proportional to the size of the angle). Turning the OSEM by 90 degrees would eliminate this kind of coupling. 
  • It's also true that (regardless of the mechanism) minimizing bounce couling for an OSEM maximizes the side coupling. The side coupling values of the pre-vent diagonalization matrices might be useful to compare to what we see now, to find out if the minimization we do in fact increases the side coupling (if not, maybe we are not truly minimizing the bounce coupling but observing some other effect, or our measurement method is too inconsistent.) Thoughts on this are welcome. 
  • Now that this improvement has been found, we should do a more thorough investigation to see where the true optimum position is (no small steps have been taken around this new position, and the minimum could also be at some angle in between).
  • In the interest of finishing the vent, should we try to find out exactly why the optimal angles seem so different than expected, or should we just try to minimize as best we can and move on to setting up the Y arm cavity? 
  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.

  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...

  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. 

  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.

  12447   Fri Aug 26 14:09:46 2016 ericqUpdateSUSETMY UL sensor problematic

We do indeed have a box of clean spare OSEMs, it should be out with all of the other boxes of clean stuff we had for the suspension building. You could also try swapping in a different satellite box, to see if the circuit powering the OSEM PD is to blame.

  12446   Fri Aug 26 14:05:38 2016 SteveUpdateSUSETMY UL sensor problematic

This problem has existed well before the vent


  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)

  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.

  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?

  12442   Thu Aug 25 19:03:56 2016 PrafulUpdateElectronicsAcoustic Tab and Amp Suspension

My box has been suspended in the PSL using surgical tubing, and it has been connected to C1:PEM-MIC_1 (C17) with a BNC. I made a braided power cable as well but it turned out to be slightly too short... Once this is fixed, everything should be ready and we can see if it's working correctly. I also set up a new tab on the summary pages for this channel:


This data is back from when I had my solderless breadboard running near MC2. I'll add this tab to the real pages once the box is working (which could be a while since I'm gone for a month). Let me know if you see any issues with either the tab or the box/cables.

  12441   Thu Aug 25 15:43:29 2016 ericqUpdateSUSOSEM issues

We've seen for some time now that one of the PRM OSEM signals has been gone, and all of the SRM signals seem dark. We had tried squishing various cables to no avail.

Today I played some "musical satellite boxes," in an attempt to see if the problems are in the chambers or in the signal chains. That is, I swapped the OSEM cables from the vacuum feedthroughs between the satellite boxes, and observed what happened.

It seems clear that something is up with SRM inside the chamber. For PRM, it's not so clear...

  PRM Satellite SRM Satellite BS Satellite
PRM OSEMs LR low + small fluctuations LR low + small fluctuations LR low + small fluctuations
SRM OSEMs No signals No Signals No Signals
BS OSEMs LR low, flat OK OK

Somehow, issues with the LR channel follow both the PRM OSEMs and the PRM satellite box. frown

PRM LR first went dark on Jul 2nd, after the IFO was vented, but before we took any doors off (which happened on the 5th). I'm not sure what may have caused this.

SRM OSEMS first went dark on the evening of Jul 18, the day before ELOG 12310, when ITMY was moved in the same chamber. Maybe this ELOG was written about work the day before, but the sensors show disturbances over the course of hours. I think we need to double check the connections in chamber. 

  12440   Thu Aug 25 08:19:25 2016 Max IsiUpdateGeneralSummary pages down due to cluster maintenance

The system is back from maintenance and the pages for last couple of days will be filled retroactively by the end of the week.


Summary pages down today due to schedulted LDAS cluster maintenance. The pages will be back automatically once the servers are back (by tomorrow).


  12439   Wed Aug 24 23:47:30 2016 PrafulUpdateElectronicsFinished Prototype Box

Gautam helped me drill holes in a metal box and I set up my circuit inside. Everything seems to be working so far. Tomorrow I'll be suspending the box near the PSL and setting up a data channel. Attached are some pictures of the box- sorry some of the angles turned out weird.

  12438   Wed Aug 24 19:37:55 2016 KojiUpdateElectronicsDecoupling capacitor 101


Interesting articles how they should only be used for power decoupling and not in the signal path.



  12437   Wed Aug 24 14:44:33 2016 PrafulUpdateElectronicsDecoupling capacitor 101

Do these look good for the ceramic capacitors? We're running low.



What I suggested was:
- For most cases, power decoupling capacitors for the regulators should be ~100nF "high-K ceramic capacitors" + 47uF~100uF "electrolytic capacitors".
- For opamps, 100nF high-K ceramic should be fine, but you should consult with datasheets.
- Usually, you don't need to use tantalum capacitors for this purpose unless specified.
- Don't use film capacitors for power decoupling.

79XXs are less stable compared to 78XXs, and tend to become unstable depending on the load capacitance.
One should consult with the datasheet of each chip in order to know the proper capacitors values.
But also, you may need to tweak the capacitor value when necessary. Above recipe works most of the case.


  12436   Wed Aug 24 14:11:09 2016 PrafulUpdateElectronicsMicrophone Testing

I added an EM172 to my soldered circuit and it seems to be working so far. I have taken a spectra using the EM172 in ambient noise in the control room as well as in white noise from Audacity. My computer's speakers are not very good so the white noise results aren't great but this was mainly to confirm that the microphone is actually working.


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