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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
Attachment 1: OM1Moved.pdf
Attachment 2: IMG_3304.JPG
Attachment 3: OMCchamber.pdf
Attachment 4: IMG_3292.JPG
Attachment 5: IMG_3307.JPG
Attachment 6: IMG_3297.JPG
12568   Tue Oct 18 18:56:57 2016 gautamUpdateGeneralOM5 rotated to bypass OMC, green scatter is from window to PSL table

[ericq, lydia, gautam]

• We started today by checking leveling of ITMY table, all was okay on that front after the adjustment done yesterday. Before closing up, we will have detailed pictures of the current in vacuum layout
• We then checked centering on OMs 1 and 2 (after having dither aligned the arms), nothing had drifted significantly from yesterday and we are still well centered on both these OMs
• We then moved to the BS/PRM chamber and checked the leveling, even though nothing was touched on this table. Like in the OMC chamber, it is difficult to check the leveling here because of layout constraints, but I verified that the table was pretty close to being level using the small (clean) spirit level in two perpendicular directions
• Beam centering was checked on OMs 3 and 4 and verified to be okay. Clearance of beam from OM4 towards the OMC chamber was checked at two potential clipping points - near the green steering mirror and near tip-tilt 2. Clearance at both locations was deemed satisfactory so we moved onto the OMC chamber
• We decided to go ahead and rotate OM5 to send the beam directly to OM6 and bypass the partially transmissive mirror meant to send part of the AS beam to the OMC
• In order to accommodate the new path, I had to remove a razor beam dump on the OMC setup, and translate OM5 back a little (see Attachment #1), but we have tried to maintain ~45 degree AOI on both OMs 5 and 6
• Beam was centered on OM6 by adjusting the position of OM5. We initially fiddled around with the pitch and yaw knobs of OM4 to try and center the beam on OM5, but it was decided that it was better just to move OM5 rather than mess around on the BS/PRM chamber and introduce potential additional scatter/clipping
• OMC table leveling was checked and verified to not have been significantly affected by todays work
• It was necessary to loosen the fork and rotate OM6 to extract the AS beam from the vacuum chambers onto the AP table
• AS beam is now on the camera, and looks nice and round, no evidence of any clipping. Some centering on in air lenses and mirrors on the AP table remains to be done. We are now pretty well centered on all 6 OMs and should have more power at the AS port given that we are now getting light previously routed to the OMC out as well. A quantitative measure of how much more light we have now will have to be done after pumping down and turning the PSL power back up
• I didn't see any evidence of back-scattered light from the window even though there were hints of this previously (sadly the same can't be said about the green). I will check once again tomorrow, but this doesn't look like a major problem at the moment

Lydia and I investigated the extra green beam situation. Here are our findings.

1. There appears to be 3 ghost beams in addition to the main beam. These ghosts appeared when we locked the X green and Y green individually, which lead us to conclude that whatever is causing this behaviour is located downstream of the periscope on the BS/PRM chamber
2. I then went into the BS/PRM chamber and investigated the spot on the lower periscope mirror. It isn't perfectly centered, but it isn't close to clipping on any edge, and the beam leaving the upper mirror on the periscope looks clean as well (only the X-arm green was used for this, and subsequent checks). The periscope mirror looks a bit dusty and scatters rather a lot which isn't ideal...
3. There are two steering mirrors on the IMC table which we do not have access to this vent. But I looked at the beam coming into the OMC chamber and it looks fine, no ghosts are visible when letting the main beam pass through a hole in one of our large clean IR viewing cards - and the angular separation of these ghosts seen on the PSL table suggests that we would see these ghosts if they exist prior to the OMC chamber on the card...
4. The beam hits the final steering mirror which sends it out onto the PSL table on the OMC chamber cleanly - the spot leaving the mirror looks clean. However, there are two reflections from the two surfaces of the window that come back into the OMC chamber. Space constraints did not permit me to check what surfaces these scatter off and make it back out to the PSL table as ghosts, but this can be checked again tomorrow.

I can't think of an easy fix for this - the layout on the OMC chamber is pretty crowded, and potential places to install a beam dump are close to the AS and IMC REFL beam paths (see Attachment #1). Perhaps Steve can suggest the best, least invasive way to do this. I will also try and nail down more accurately the origin of these spots tomorrow.

Light doors are back on for the night. I re-ran the dithers, and centered the oplevs for all the test-masses + BS. I am leaving the PSL shutter closed for the night

Attachment 1: OMCchamber.pdf
Attachment 2: greenGhosts.JPG
Attachment 3: IMG_3322.JPG
Attachment 4: IMG_3326.JPG
12570   Wed Oct 19 14:43:15 2016 SteveUpdateGeneral Viewports & coating of 2001

Tilted viewports installed in horizontal position. Atm2

Attachment 1: vacViewp2001.PDF
Attachment 2: tiltedViewport.PDF
12571   Wed Oct 19 16:41:55 2016 gautamUpdateGeneralHeavy doors back on

[ericq, lydia, steve, gautam]

• We aligned the arms, and centered the in-air AS beam onto the PDs and camera
• Misaligned the ITMs in a controlled ramp, observed ASDC level, didn't see any strange features
• We can misalign the ITMs by +/- 100urad in yaw and not see any change in the ASDC level (i.e. no clipping). We think this is reasonable and it is unlikely that we will have to deal with such large misalignments. We also scanned a much larger range of ITM misalignments (approximately +/-1mrad), and saw no strange features in the ASDC levels as was noted in this elog - we used both the signal from the AS110 PD which had better SNR and also the AS55 PD. We take this to be a good sign, and will conduct further diagnostics once we are back at high power.
• Opened up all light doors, checked centering on all 6 OM mirrors again, these were deemed to be satisfactory
• To solve the green scattering issue, we installed a 1in wide glass piece (~7inches tall) mounted on the edge of the OMC table to catch the reflection off the window (see Attachment #1) - this catches most of the ghost beams on the PSL table, there is one that remains directly above the beam which originates at the periscope in the BS/PRM chamber (see Attachment #2) but we decided to deal with this ghost on the PSL table rather than fiddle around in the vacuum and possibly make something else worse
• Re-aligned arms, ran the dither, and then aligned the PRM and SRM - we saw nice round DRMI flashes on the cameras
• Took lots of pictures in the chamber, put heavy doors back on. Test mass Oplev spots looked reasonably well centered, I re-centerd PRM and SRM spots in their aligned states, and then misaligned both
• The window from the OMC chamber to the AS table looked clean enough to not warrant a cleaning..
• PSL shutter is closed for now. I will check beam alignment, center Oplevs, and realign the green in the evening. Plan is to pump down first thing tomorrow morning

AS beam on OM1

AS beam on OM2

AS beam on OM3

AS beam on OM4

AS beam on OM6

I didn't manage to get a picture of the beam on OM5 because it is difficult to hold a card in front of it and simultaneously take a photo, but I did verify the centering...

It remains to update the CAD diagram to reflect the new AS beam path - there are also a number of optics/other in-vacuum pieces I noticed in the BS/PRM and OMC chambers which are not in the drawings, but I should have enough photos handy to fix this.

Here is the link to the Picasa album with a bunch of photos from the OMC, BS/PRM and ITMY chambers prior to putting the heavy doors back on...

SRM satellite box has been removed for diagnostics by Rana. I centered the SRM Oplev prior to removing this, and I also turned off the watchdog and set the OSEM bias voltages to 0 before pulling the box out (the PIT and YAW bias values in the save files were accurate). Other Oplevs were centered after dither-aligning the arms (see Attachment #8, ignore SRM). Green was aligned to the arms in order to maximize green transmission (GTRX ~0.45, GTRY ~0.5, but transmission isn't centered on cameras).

I don't think I have missed out on any further checks, so unless anyone thinks otherwise, I think we are ready for Steve to start the pumpdown tomorrow morning.

Attachment 1: IMG_2332.JPG
Attachment 2: IMG_2364.JPG
Attachment 3: IMG_2337.JPG
Attachment 4: IMG_2338.JPG
Attachment 5: IMG_2356.JPG
Attachment 6: IMG_2357.JPG
Attachment 7: IMG_2335.JPG
Attachment 8: Oplevs_19Oct2016.png
12572   Wed Oct 19 17:02:34 2016 ranaUpdateGeneral Viewports & coating of 2016

These old specs are not so bad. But we now want to get replacements for the TRX and TRY and PSL viewports that are R <0.1% at 532 and 1064 nm.

I don't know of any issues with keeping BK-7 as the substrate.

12576   Fri Oct 21 02:06:20 2016 gautamUpdateGeneralIFO recovery

The pressure on the newly installed gauge on the X arm was 6E-5 torr when I came in today evening, so I decided to start the recovery process.

1. I first tried working at low power. I was able to lock the IMC as well as the arms. But the dither alignment didn't work so well. So I decided to go to nominal PSL power.
2. I first changed the 2" HR mirror that is used to send all the MC REFL light to the MC REFL PD in low power operation with a 10% BS. I then roughly aligned the beam onto the PD using the tiny steering mirror. At this point, I also re-installed the ND filters on the end Transmon QPDs and also the CCD at the Y end.
3. I then rotated the waveplate (the second one from the PSL aperture) until I maximized the power as measured just before the PSL shutter with a power meter. I then re-aligned the PMC to maximize transmission. After both these steps, we currently have 1.09W of IR light going into the IMC
4. I then re-aligned MC REFL onto the PD (~90mW of light comes through to the PD) and maximized the DC output using an oscilloscope. I then reverted the Autolocker to the nominal version from the low power variant that has been running on megatron during the vent (although we never really used it). The autolocker worked well and I was able to lock the IMC without much trouble. I tweaked the alignment sliders for the IMC optics, but wasn't able to improve the transmission much. It is ~14600 cts right now, which is normal I think
5. I then centered the beams onto the WFS QPDs, ran the WFSoffsets script after turning the inputs to the WFS servos off, and ran the relief script as well - I didn't try anything further with the IMC
6. I then tried to lock the arms - I first used the green to align the test-masses. Once I was able to lock to a green 00-mode, I saw strong IR flashes and so I was able to lock the Y arm. I then ran the dither. Next, I did the same for the X arm. Even though I ran LSCoffsets before beginning work tonight, the Y arm transmission after maximization is ~5, and that for the X arm is ~2.5. I refrained from running the normalization scripts in case I am missing something here, but the mode itself is clearly visible on the cameras and is a 00-mode.
GV edit 21Oct2016: For the Y-arm, the discrepancy was down to TRY being derived from the high gain PD as opposed to the QPD. Switching these and running the dither, TRY now maxes out at around 1.0. For TRX, the problem was that I did not install one of the ND filters - so the total ND was 1.2 rather than 1.6, which is what we were operating at and which is the ND on TRY. Both arms now have transmission ~1 after maximizing with the dither alignment...
7. The AS spot looks nice and round on the camera, although the real check would be to do the sort of scan Yutaro and Koji did, and monitor the ASDC levels. I am leaving this task for tomorrow, along with checking the recycling cavities.
8. Lastly, I centered the Oplevs for all the TMs

12578   Mon Oct 24 11:39:13 2016 gautamUpdateGeneralALS recovered

I worked on recovering ALS today. Alignments had drifted sufficiently that I had to to the alignment on the PSL table onto the green beat PDs for both arms. As things stand, both green (and IR) beats have been acquired, and the noise performance looks satisfactory (see Attachment #1), except that the X beat noise above 100Hz looks slightly high. I measured the OLTF of the X end green PDH loop (after having maximized the arm transmission, dither alignment etc, measurement done at error point with an excitation amplitude of 25mV), and adjusted the gain such that the UGF is ~10kHz (see Attachment #2).

Attachment 1: ALSOutOfLoop20161024.pdf
Attachment 2: XendPDHOLTF20161024.pdf
12579   Tue Oct 25 15:56:11 2016 gautamUpdateGeneralPRFPMI locked, arms loss improved

[ericq,gautam]

Given that most of the post vent recovery tasks were done, and that the ALS noise performance looked good enough to try locking, we decided to try PRFPMI locking again last night. Here are the details:

PRM alignment, PRMI locking

• We started by trying to find the REFL beam on the camera, the alignment biases for the 'correct' PRM alignment has changed after the vent
• After aligning, the Oplev was way off center so that was fixed. We also had to re-center the ITMX oplev after a few failed locking attempts
• The REFL beam was centered on all the RFPDs on the ASDC table

Post the most recent vent, where we bypass the OMC altogether, we have a lot more light now at the AS port. It has not yet been quantified how much more, but from the changes that had to be made to the loop gain for a stable loop, we estimate we have 2-3 times more power at the AS port now.

PRFPMI locking

• We spent a while unsuccessfully trying to get the PRMI locked and reduce the carm offset on ALS control to bring the arms into the 'buzzing' state - the reason was that we forgot that it was established a couple of weeks ago that REFL165 had better MICH SNR. Once this change was made, we were readily able to reduce the carm offset to 0
• Then we spent a few attempts trying to do blend in RF control - as mentioned in the above referenced elog, the point of failure always was trying to turn on the integrator in the CARM B path. We felt that the appearance of the CARM B IN1 signal on dataviewer was not what we are used to seeing but were unable to figure out why (as it turns out, we were locking CARM on POY11 and not REFL11 , more on this later)
• Eric found that switching the sign of the CARM B gain was the solution - we spent some time puzzling over why this should have changed, and hypothesized that perhaps we are now overcoupled, but it is more likely that this was because of the error signal mix up mentioned above...
• We also found the DC coupling of the ITM Oplev loops to be not so reliable - perhaps this has to do with the wonky ITMY UL OSEM, more on this later. We usually turn the DC coupling on after dither aligning the arms, and in the past, it has been helpful. But we had more success last night with the DC coupling turned off rather than on.
• Once the sign flip was figured out, we were repeatedly able to achieve locks with CARM partially on RF - we got through about 3 or 4, each was stable for just tens of seconds though. Also, we only progressed to RF on CARM on 1 attempt, the lock lasted for just a few seconds
• Unfortunately, the mode cleaner decided to act up just about after we figured all this out, and it was pushing 4am so we decided to give up for the night.
• The arm transmissions hit 300! We had run the transmission normalization scripts just before starting the lock so this number should be reliable (compare to ~130 in October last year). The corresponding PRG is about 16.2, which according to my Finesse models suggest we are still undercoupled, but are close to critical coupling (this needs a bit more investigation, supporting plots to follow). => Average arm loss is ~150ppm! So looks like we did some good with the vent, although of course an independent arm loss measurement has to be done...
• Lockloss plot for one of the locks is Attachment #1

Other remarks:

• Attachment #2 shows that the ITMY UL coil is glitchy (while the others are not). At some point last night, we turned off this sensor input to the damping servos, but for the actual locks, we turned it back on. I will do a Satellite box swap to see if this is a Sat. Box problem (which I suspect it is, the bad Sat. Boxes are piling up...)
• Just now, eric was showing me the CM board setup in the LSC rack, because for the next lock attempts, we want to measure the CARM loop - but we found that the input to the CM board was POY and not REFL! This probably explains the sign flip mentioned above. The mix-up has been rectified
• The MICH dither align doesn't seem to be working too well - possibly due to the fact that we have a lot more ASDC light now, this has to be investigated. But last night, we manually tweaked the BS alignment to make the dark port dark, and it seemed to work okay, although each time we aligned the PRMI on carrier, then went back to put the arms on ALS, and came back to PRMI, we would see some yaw misalignment in the AS beam...
• I believe the SRM sat. box is still being looked at by Ben so it has not been reinstalled...
• Eric has put together a configure script for the PRFPMI configuration which I have added to the IFO configure MEDM screen for convenience
• For some reason, the appropriate whitening gain for POX11 and the XARM loop gain to get the XARM to lock has changed - the appropriate settings now are +30dB and 0.03 respectively. These have not been updated in some scripts, so for example, when the watch script resets the IFO configuration, it doesn't revert to these values. Just something to keep in mind for now...
Attachment 1: PRFPMIlock_25Oct2016.pdf
Attachment 2: ITMYwoes.png
12580   Tue Oct 25 18:07:28 2016 KojiUpdateGeneralPRFPMI locked, arms loss improved

Great to hear that we have the PRG of ~16 now!

Is this 150ppm an avg loss per mirror, or per arm?

12581   Wed Oct 26 16:06:01 2016 JohannesUpdateGeneralAutolocker maintenance

[Gautam, Johannes]

The autolocker was acting up today, Gautam traced it to EPICS channels ( namely C1:IOO-MC_LOCK_ENABLE and C1:IOO-MC_AUTOLOCK_BEAT ) served by c1iool0 not being responsive and keyed the crate. This restored it nominal operation.

12583   Thu Oct 27 12:06:39 2016 gautamUpdateGeneralPRFPMI locked, arms loss improved
 Quote: Great to hear that we have the PRG of ~16 now! Is this 150ppm an avg loss per mirror, or per arm?

I realized that I did not have a Finesse model to reflect the current situation of flipped folding mirrors (I've been looking at 'ideal' RC cavity lengths with folding mirrors oriented with HR side inside the cavity so we didn't have to worry about the substrate/AR surface losses), and it took me a while to put together a model for the current configuration. Of course this calculation does not need a Finesse model but I thought it would be useful nevertheless.

In summary - the model with which the attached plot was generated assumes the following:

• Arm lengths of 37.79m, given our recent modification of the Y arm length
• RC lengths are all taken from here, I have modelled the RC folding mirrors as flipped with the substrate and AR surface losses taken from the spec sheet
• The X axis is the average arm loss - i.e. (LITMX+LITMY+LETMX+LETMY)/2. In the model, I have distributed the loss equally between the ITMs and ETMs.

This calculation agrees well with the analytic results Yutaro computed here - the slight difference is possibly due to assuming different losses in the RC folding mirrors.

The conclusion from this study seems to be that the arm loss is now in the 100-150ppm range (so each mirror has 50-75ppm loss). But these numbers are only so reliable, we need an independent loss measurement to verify. In fact, during last night's locking efforts, the arm transmission sometimes touched 400 (=> PRG ~22), which according to these plots suggest total arm losses of ~50ppm, which would mean each mirror has only 25ppm loss, which seems a bit hard to believe.

Attachment 1: PRG.pdf
12584   Thu Oct 27 13:48:20 2016 KojiUpdateGeneralPRFPMI locked, arms loss improved

It is also difficult to have a high arm transmission without having high PRG.

What about to plot the arm trans and the REFL DC power in a timeseries?
Or even in a correlation plot (X: Arm Trans or PRG vs Y: REFL Reflectivity)

This tells you an approximate location of the critical coupling, and allows you to calibrate the PRG, hopefully.

12585   Thu Oct 27 23:29:47 2016 ericqUpdateGeneralPRFPMI locked, arms loss improved

As Gautam mentioned, we had some success locking the PRFPMI last night. (SRM satellite box is still in surgery...)

Unsurprisingly, changing the loss/PRG/CARM finesse means we had to fiddle with the common mode servo parameters a little bit to get things to work. However, before too long, we achieved a first lock on the order of a few minutes. Not long afterwards, we had a nice half hour lock stretch where we could tune up the AO crossover and loop UGFs. The working locking script was committed to SVN. Really, no fundamentally new tactics were used, which is encouraging. (One thing I wondered about was whether a narrower CARM linewidth would still let our direct ALS->REFL11 handoff with no offset reduction work. Turns out it does)

However, the step where we increase the analog CARM gain isn't as bulletproof as it once had been. The light levels "sputter" in and out sometimes if the gain increases are too agressive, and can cause a lockloss. Maybe this is an effect of the narrower linewidth and injecting more ALS noise at high frequencies with the higher CARM bandwidth.

The spatial profiles of the light on the cameras is totally bananas. Here's AS and REFL.

As Koji suggested, here is a 2D histogram of TRY vs REFLDC. It appears that the visibility would max out at 75% or so at arm powers around 400. Indeed, we briefly saw powers that high, but as can be seen on the plot, we were usually a little under 300. Exploring the transmon QPD offset space didn't seem to have much effect here.

One thing that I hadn't looked at in previous locks is coherence with our ground seismometers. It would be cool to have more seismic feedforward, and looking at the frequency domain multiple coherence, it looks like we can win a lot between 1 and 20 Hz. I expected more of a win at 1Hz, though.

Attachment 4: seis_sub.pdf
12586   Fri Oct 28 01:44:48 2016 gautamUpdateGeneralPRFPMI model vs data studies

Following Koji's suggestion, I decided to investigate the relation between my Finesse model and the measured data.

For easy reference, here is the loss plot again:

Sticking with the model, I used the freedom Finesse offers me to stick in photodiodes wherever I desire, to monitor the circulating power in the PRC directly, and also REFLDC. Note that REFLDC goes to 0 because I am using Finesse's amplitude detector at the carrier frequency for the 00 mode only.

Both the above plots essentially show the same information, except the X axis is different. So my model tells me that I should expect the point of critical coupling to be when the average arm loss is ~100ppm, corresponding to a PRG of ~17 as suggested by my model.

Eric has already put up a scatter plot, but I reproduce another from a fresh lock tonight. The data shown here corresponds to the IFO initially being in the 'buzzing' state where the arms are still under ALS control and we are turning up the REFL gain - then engaging the QPD ASC really takes us to high powers. The three regimes are visible in the data. I show here data sampled at 16 Hz, but the qualitative shape of the scatter does not change even with the full data. As an aside, today I saw the transmission hit ~425!

I have plotted the scatter between TRX and REFL DC, but if I were to plot the scatter between POP DC and REFL DC, the shape looks similar - specifically, there is an 'upturn' in the REFL DC values in an area similar to that seen in the above scatter plot. POP DC is a proxy for the PRG, and I confirmed that for the above dataset, there is a monotonic, linear relationship between TRX and POPDC, so I think it is legitimate to compare the plot on the RHS in the row directly above, to the plot from the Finesse model one row further up. In the data, REFL DC seems to hit a minimum around TRX=320. Assuming a PRM transmission of 5.5%, TRX of 320 corresponds to a PRG of 17.5, which is in the ballpark of the region the model tells us to expect it to be. Based on this, I conclude the following:

• It seems like the Finesse model I have is quite close to the current state of the IFO
• Given that we can trust the model, the PRC is now OVERCOUPLED - the scatter plot of data supports this hypothesis
• Given that in today's lock, I saw arm transmission go up to ~425, this suggests that at optimal alignment, PRG can reach 23. Then, Attachment #1 suggests the average arm loss is <50ppm, which means the average loss per optic is <25ppm. I am not sure how physical this is, given that I remember seeing the specs for the ITMs and ETMs being for scatter less than 40 25ppm, perhaps the optic exceeded the specs, or I remember the wrong numbers, or the model is wrong

In other news, I wanted to try and do the sensing matrix measurements which we neglected to do yesterday. I turned on the notches in CARM, DARM, PRCL and MICH, and then tuned the LO amplitudes until I saw a peak in the error signal for that particular DOF with peak height a factor of >10 above the noise floor. The LO amplitudes I used are

MICH: 40

PRCL: 0.7

CARM: 0.08

DARM: 0.08

There should be about 15 minutes of good data. More impressively, the lock tonight lasted 1 hour (see Attachment #6, unfortunately FB crashed in between). Last night we lost lock while trying to transition control to 1f signals and tonight, I believe a P.C. drive excursion of the kind we are used to seeing was responsible for the lockloss, so the PRFPMI seems pretty stable.

With regards to the step in the lock acquisition sequence where the REFL gain is turned up, I found in my (4) attempts tonight that I had most success when I adjusted the CARM A slider while turning up the REFL gain to offload the load on the CARM B servo. Of course, this may mean nothing...

Attachment 1: loss.pdf
Attachment 2: REFLDC.pdf
Attachment 3: CriticalCoupling.pdf
Attachment 4: PRFPMI_Oct282016.pdf
Attachment 5: PRFPMI_scatter.pdf
Attachment 6: 1hourPRFPMILock.png
12588   Fri Oct 28 19:13:57 2016 ranaUpdateGeneralPR gain

I don't think the loss of 25 ppm is outrageous. Its just surprisingly good. The SIS model predicted numbers more like 1 ppm / mirror taking into account just the phase map and not the coating defects.

However, we should take into account the lossed in the DRMI to be more accurate: AR coating reflectivities, scatter loss on those surfaces, as well as possible clipping around BS or some other optics.

https://chat.ligo.org/ligo/channels/40m

12593   Thu Nov 3 08:07:52 2016 SteveUpdateGeneralpower glitch

Building:         Campus Wide

Date:             Thursday 11/03/16 at Approx. 6:20 a.m.

Notification:     Unplanned City Wide Power Glitch Affecting Campus

*This is to notify you that the Caltech Campus experienced a campus wide power glitch at approx. 6:20 a.m. this morning.

The city was contacted and they do not expect any further interruptions related to this event.

The vacuum was not effected. ITM sus damping restored. IFO room air conditions on.

PSL Innolight and ETMY Lightwave lasers turned on

Attachment 1: powerGlitch.png
12594   Thu Nov 3 11:33:24 2016 gautamUpdateGeneralpower glitch - recovery

I did the following:

• Hard reboots for fb, megatron, and all the frontends, in that order
• Checked time on all FEs, ran sudo ntpdate -b -s -u pool.ntp.org where necessary
• Restarted all realtime models
• Restarted monit on all FEs
• Reset Marconi to nominal settings, fCarrier=11.066209MHz, +13dBm amplitude
• In the control room, restarted the projector and set up the usual StripTool traces
• Realigned PMC
• Slow machines did not need any touchups - interestingly, ITMX did not get stuck during this power glitch!

There was a regular beat coming from the speakers. After muting all the channels on the mixer and pulling the 3.5mm cable out, the sound persisted. It now looks like the mixer is broken

12596   Thu Nov 3 12:40:10 2016 gautamUpdateGeneral projector light bulb is out

The projector failed just now with a pretty loud 'pop' sound - I've never been present when the lamp goes out, so I don't know if this is usual. I have left the power cable unplugged for now...

Replacement is ordered Nov 4

12614   Mon Nov 14 19:15:57 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

Looking back at elog 12528, the uncertainty in the armloss number from the individual quantities in the equation for $\mathcal{L}$ can be written as:

$\delta\mathcal{L}^2=\left(\frac{T_1(1-\frac{P_L}{P_M}-2T_1)}{4\gamma}\right)^2\left(\frac{\delta T_1}{T_1}\right)^2+T_2^2\left(\frac{\delta T_2}{T_2}\right)^2+\left(\frac{T_1(1-\frac{P_L}{P_M}-T_1)}{4\gamma}\right)^2\left(\frac{\delta\gamma}{\gamma}\right )^2+\left(\frac{T_1}{4\gamma}\right )^2\left[\left(\frac{\delta P_L}{P_L}\right )^2+\left(\frac{P_L}{P_M} \right )^2\left(\frac{\delta P_M}{P_M}\right )^2\right ]$

Making some generous assumption about the individual uncertainties and filling in typical values we get in our measurements, results in the following uncertainty budget:

$\delta\mathcal{L}^2\approx\left(12\,\mathrm{ppm}\right)^2\left(\frac{\delta T_1/T_1}{5\%}\right)^2+(0.7\,\mathrm{ppm})^2\left(\frac{\delta T_2/T_2}{5\%}\right)^2+\left(2\,\mathrm{ppm}\right)^2\left(\frac{\delta\gamma/\gamma}{1\%}\right )^2+\left(140\,\mathrm{ppm}\right )^2\left(\frac{\delta P/P}{2.5\%}\right )^2$

In my recent round of measurements I had a 2.5% uncertainty in the ASDC reading, which completely dominates the armloss assessment.

The most recent numbers are 57 ppm for the YARM and 21 ppm for the XARM, but both with an uncertainty of near 150 ppm, so while these numbers fit well with Gautam's estimate of the average armloss via PRG, it's not really a confirmation.

I set the whitening gain in ASDC to 24 dB and ran LSC offsets, and now I'm getting a relative uncertainty in measured reflected power of .22%, which would be sufficient for ~25ppm accuracy according to the above formula. I'm going to start a series of measurements tonight when I leave, should be done in ~2 hours (10 pm) the latest.

If anybody wants to do some night work: I misaligned ITMY by a lot to get its reflection off ASDC. Approximate values are saved as a restore point. Also the whitening gain on ASDC will have to be rolled back (was at 0dB) and LSC offsets adjusted.

12616   Tue Nov 15 19:22:17 2016 gautamUpdateGeneralhousekeeping

PRM and SRM sat. boxes have been switched for some time now - but the PRM sat. box has one channel with a different transimpedance gain, and the damping loops for the PRM and SRM were not systematically adjusted to take this into account (I just tweaked the gain for the PRM and SRM side damping loops till the optic damped). Since both sat. boxes are nominally functioning now, I saw no reason to maintain this switched configuration so I swapped the boxes back, and restored the damping settings to their values from March 29 2016, well before either of this summer's vents. In addition, I want to collect some data to analyze the sat. box noise performance so I am leaving the SRM sat. box connected to the DAQ, but with the tester box connected to where the vacuum feedthroughs would normally go (so SRM has no actuation right now). I will collect a few hours of data and revert later tonight for locking activities....

12618   Tue Nov 15 20:35:19 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I had a mistake in my script that reported the wrong error after averaging several datapoints, and because I hadn't looked at the individual numbers I didn't catch it so far. Thanks to Gautam it is no more.

The updated numbers are (with fresh, more trustworthy data):

XARM: 21 +/ 35 ppm
YARM: 69 +/- 45 ppm

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

12621   Wed Nov 16 17:07:12 2016 AshleyUpdateGeneralPreliminary Microphone Data

I am currently looking at the acoustic noise around both arms to see if there are any frequencies from machinery around the lab that stand out and to see what we can remove/change.

• Attachment 1 is a picture of the microphone and suspension system (bungee cords) that hangs from the cable trays to isolate it from vibrations.
• To record data, I used both the microphone (attachment 1) attach it its preamp connected to a spectrum analyzer in order get a graph of power spectral density, recording from 0-10k Hz and 10-100kHz. I started recording data at the furthest end of the x arm and worked towards the center taking measurements every couple of feet (ten rungs on the cable tray).
• The second attachment is the first 5 psd I got from the furthest end of the x arm going 10 rungs on the cable tray closer each measurement.
• Going forward, I am going to take more measurements with greater resolution at the lower frequencies from 0-200 and stepping up from there by factors of 2.

Attachment 1: first_PSD_12kHz.pdf
12624   Thu Nov 17 21:54:11 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I don't like AS110 or AS55. Neither of them are designed for DC and so the DC readout chain is hokey. How about use an actual transimpedance PD with a 100-1000 Ohm resistor and a 3 mm diode? This would eliminate the alignment sensitivity and the drifts due to electronics and room lights.

 This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

12626   Fri Nov 18 15:10:06 2016 SteveUpdateGeneral projector shipped out for repair

Vivitek D952HD sn2160130 was send out for warranty repair. It's hard to believe that it has a 5 year warranty...... RMA - WR16004483.....expected to be back by Friday, Dec 2

 Quote: The projector failed just now with a pretty loud 'pop' sound - I've never been present when the lamp goes out, so I don't know if this is usual. I have left the power cable unplugged for now... Replacement is ordered Nov 4

12659   Fri Dec 2 16:21:12 2016 gautamUpdateGeneralrepaired projector, new mixer arrived and installed

The most recent power outage took out our projector and mixer. The projector was sent for repair while we ordered a new mixer. Both arrived today. Steve is working on re-installing the projector right now, and I installed the mixer which was verified to be working with our DAFI system (although the 60Hz issue still remains to be sorted out). The current channel configuration is:

Ch1: 3.5mm stereo output from pianosa

Ch2: DAFI (L)

Ch3: DAFI (R)

I've set some random gains for now, but we will have audio again when locking

12695   Sun Jan 8 12:47:06 2017 ranaUpdateGeneralOptical Layout in DCC

Manasa pointed me to the CAD drawings in the 40m SVN and I've now uploaded them to the 40m DCC Tree so that EricG and SteveV can convert them into SolidWorks.

12697   Mon Jan 9 16:12:30 2017 SteveUpdateGeneralOptical Layout in DCC

Caltech Facilities promissed to email the 40m facility drawings in Cad format.

I organized the old of optical , vacuum and facility layout drawings on paper in the old cabinet.

 Quote: Manasa pointed me to the CAD drawings in the 40m SVN and I've now uploaded them to the 40m DCC Tree so that EricG and SteveV can convert them into SolidWorks.

Attachment 1: drawings_on_paper.jpg
12704   Thu Jan 12 02:45:53 2017 JohannesUpdateGeneralNext armloss steps

As stated in elog 12618, using an oscilloscope to average the reflected powers and thus circumventing all filtering yielded much better results than before:

XARM: 21 +/- 35 ppm
YARM: 69 +/- 45 ppm

We can probably decrease the measurement uncertainty further by using a larger photodiode that is more suited for DC measurements. It will be placed in the AS pathtemporarily. If we get below 10 ppm systematic errors will begin to matter. To get those under control I will have to re-determine the visibility in the arm cavities and the modulation indices. The numbers to match from an estimate via the power recycing gain are <= 50 ppm arm average from elog 12586. Once the measurement scheme is up and running, we can proceed to generate ETM lossmaps. ITM will still be tricky but let's see what we can do.

Following Yutaro's approach, we can move the beams on the optcs in a deterministic way by several mm on the ETMs. Moving the beam is achieved by introducing offsets into the ASS auto alignment. As an example, the Yaw dither for ETMY is shown:

Each of the 8 test mass rotational degrees of freedom is driven by a particular frequency, and 2 signals are digitally demodulated in the real-time system: The arm transmission ("T") and the LSC arm length feedback signal to the ETM (L). The T signal feeds back to the input pointing, aka Tip Tilts and BS. This maximizes the transmission for a given test mass orientation. The L feedback controls the beam position on the mirrors in the arms. It minimizes the coupling of the dither to the length feedback, which is achieved when the beam goes through the axis of the rotational motion. This is where we introduce the offset:

The signal C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET (for this example) moves the locking point of the dither-to-length coupling and thus moves the beam around on the ETM. This is true for the PIT and YAW of all test masses except ITMX. In the current configuration the TTs optimize the alignment into the YARM, and for the X we only have the BS, which is why the beam spot on ITMX cannot be independently controlled as-is. We could, however, for the sake of this measurement, temporarily temporarily give TT authority to the XARM feedback to control the ITMX beam position. I imagine something like dither-aligning with ASS the normal way, and then run a customized script in which the XARM is treated as the YARM, feecback to the BS is cut, and the YAW signals are inverted due to the reflection on BS.

Knowing the angle of the offset gives us a way to calculate the beam spot displacement with the cavity geometry. For best results I want to make sure our OpLev calibration is still good (laser power decay, although last time this was done was only about a year ago), which would be analogous to elog 11831.

As for ITM beam position, this scheme only works partially, because it would require the beam to steer further off its axis than in the ETM case. This is problematic because of the spacing between tip tilts and ITMs. I summarize:

1. Place larger DCPD in AS path
2. Confirm mode-matching and mod-indices
3. Assess loss in center with zero offsets
4. Uncertainty low enough? If not get better.
5. Calibrate OpLevs
6. Introduce calibrated offsets in dither alignment
7. Wander beam on test masses, recording arm losses
8. ???
9. Profit
Attachment 1: ass_illustration.pdf
12710   Fri Jan 13 08:54:32 2017 JohannesUpdateGeneralDC PD installed

I installed a DC PD (Thorlabs PDA 520) in the beam path to AS55. I placed a 2" 90/10 BS on a flip mount that picks of enough light for the PD to spit out ~8V when the port is bright. Single arm continuous signal will be ~2V. While most of the light still continues towards AS55, the displacement from the BS moves the beam off AS55, so I used the flip mount in case anyone needs to use AS55. The current configuration is UP.

When we're done with loss investigations the flip mount should be removed from the bench.

I hooked the PD up to an ethernet-enabled scope and started scripting the loss map measurement (scope can receive commands via http so we can automate the data acquisition). The scope that was present at the bench and had been used for the MC ringdown measurements had a 'scrambled' screen that I couldn't fix so I had to retrieve another scope ("scope1"). I'll try to find out what's wrong with it but we may have to send it in for repair.

12716   Fri Jan 13 23:39:46 2017 gautamUpdateGeneralETMX suspension electronics problems?

[Koji,gautam]

After Koji's leap second fix, we were playing around with the X arm locking. In particular, we were playing around with the limit value on the X arm LSC filter bank - the nominal value is 4000, we wanted to see if we could increase this without kicking the optic while acquiring arm lock. We initially increased it to 8000, and then turned it off altogether. Then we rapidly turned the output of the servo ON/OFF, and looked at the arm transmission to see if it came back to the level before unlocking, as an indication of whether the optic was kicked.

These trials suggested a value of 8000 for the limiter was OK, so we left the LSC mode on with the limiter set to 8000. But just as we were about to leave for the night, I noticed on the wall Striptool that the X arm was unlocked. Investigating, we found that the green wasn't even locking to a HOM. Further investigation of the Oplev spot showed that ETMX had received a large kick (both pitch and law errors were ~200urad). ITMX was unaffected.

We initially tried lowering the LSC limit value back to 4000, then used first the Oplev spot and then the green to align the arm. But turning on LSC misaligned the arm after acquiring lock. So we decided to leave LSC off, thinking that the notorious ETMX suspension problems have resurfaced. As a diagnostic, we figured we'd leave the watchdog tripped, and use the Oplev to see if the optic was getting kicked. But the act of turning the watchdog off kicked the optic again (WHY?!).

Looking at the ETMX sus screen, turning off all the damping and LSC (but watchdog on) still leaves a non-zero offset in the "Vmon" field, between 0.02-0.05V depending on the coil. Turning the watchdog OFF takes all these to 0.009V, although I can see the LR value fluctuating between 0.004V and 0.009V. I went to the Xend and squished all the cables on the Sat. Box, but the problem persisted.

At this time, I can't think of any explanation, so I am giving up for the night. To avoid unnecessarily kicking the optic, I am going to unplug the suspension from the Sat. Box and leave one of our tester boxes plugged in, lets see if that sheds any light on the situation...

Notes:

1. The +/-20V sorensens at this end were "tripped" for a few days after the power glitch until they were reset and turned back on yesterday. But this should not affect Vmon, as these Sorensens only supply the DC voltage for the coil bias, which is a slow machine channel?
2. The X arm was staying locked and well aligned for hours on end earlier this afternon - in fact it was locked for about 2 hours 6-8 hours ago, I can still see the trace on the wall StripTool....
12729   Tue Jan 17 21:31:57 2017 gautamUpdateGeneralETMX suspension electronics problems?

Last night, I plugged the ETMX suspension coils back into the satellite box. Tonight, we turned on the damping loops for ETMX. Rana centered the Oplev so we can use that as an additional diagnostic to see if the optic gets kicked around overnight. We will re-assess the situation tomorrow.

Sometime earlier today, Lydia noticed that the +/- 5V Sorensens at the X end were not displaying their nominal voltage/current values (as per the stickers on them). She corrected this.

12730   Wed Jan 18 10:41:14 2017 gautamUpdateGeneralETMX suspension electronics problems?

Summary pages show no kicking in the ETMX watchdogs from midnight to 6 AM (0800 - 1400 UTC):

https://nodus.ligo.caltech.edu:30889/detcharsummary/day/20170118/sus/watchdogs/

12738   Thu Jan 19 10:21:54 2017 AshleyUpdateGeneralPreliminary Microphone Data

Brief Summary: I am currently looking at the acoustic noise around both arms to see if there are any frequencies from machinery around the lab that stand out and to see what we can remove/change. I am using a Bluebird microphone suspended with surgical tubing from the cable trays to isolate it from vibrations. I am also using a preamp and the SR875 spectrum analyzer taking 6 sets of data every 1.5 meters (0 to 200Hz, 200Hz to 400Hz, 400z to 800Hz, 800Hz to 3200Hz, 3.2kHz to 12kHz, 12kHz to 100kHz).

·                Attachment 1 is a PSD of the first 3 measurements (from 0 to 12kHz) that I took every 1.5 meters along the x arm with the preamp and spectrum analyzer

·                Attachment 2 is a blrms color map of the first 6 sets of data I took (from 2.4m to 9.9m)

·                Attachmetn 3 is a picture of the microphone set up with the surgical tubing

Problems that occurred: settings on the preamp made the first set of data I took significantly smaller than the data I took with the 0dB button off and the last problem I had was the spectrum analyzer reading only from -50 to -50 dBVpk

Attachment 1: xend_psd.png
Attachment 2: xblrms.png
Attachment 3: IMG_3734.JPG
12788   Thu Feb 2 12:17:48 2017 SteveUpdateGeneral USB microscope

This AmScope microscope would have 3.5x-180x magnification, calibratable measurement function, 5MP picture and good working distance to work on printed circuit boards.

12808   Tue Feb 7 16:23:49 2017 SteveUpdateGeneralpower interruption tomorrow

received this note: at 4:11pm Tuesday, Feb 7, 2017

Building:         Campus

Date:             Wednesday, February 8, 2017

Time:             7:30 AM – 8:30 AM

Contact:          Rick Rodriguez x-2576

Pasadena Water and Power (PWP) will be performing a switching operation of the

Caltech Electrical Distribution System that is expected to be transparent to Caltech,

but could result in a minor power anomaly that might affect very sensitive equipment.

IMPACT: Negligible impact......?

There may be temporary  power interruption tomorrow!

PS:we did not see any effect

12813   Thu Feb 9 08:03:08 2017 SteveUpdateGeneral USB microscope ordered

http://www.amscope.com/3-5x-180x-boom-stand-trinocular-zoom-stereo-microscope-with-144-led-ring-light-and-10mp-camera.html will be ordered today.

The actual unit we are getting has lockable zoom for better repeatability after calibration: SM-3NTPZZ-144

Quote: CWQ6-020817

12814   Thu Feb 9 11:22:56 2017 gautamUpdateGeneralSorensens and DIN connections at 1X1

I'd like to fix a few things at 1X1 when we plug in the new amplifier for the 29.5MHz modulation signal.

1. Split off separate +24 and ground wires to the green BBPD RF amplifiers and the AOM driver (they are sharing a single fuse at the moment)
2. Tap a new +24 GND -24V set for the FSS Fast summing box - this is currently running with a bench power supply underneath the PSL table set to +/-18V, but I checked the 7815/7915 datasheets and they accept up to 35V input for a 15V output, so it should be fine to use 24V
3. Hook up the ZHL-2A for the IMC modulation.

Steve has ordered rolls of pre-twisted wire to run from 1X1 to the PSL table, so that part can be handled later.

But at 1X1, we need to tap new paths from +/- 24V to the DIN connectors. I think it's probably fine to turn off the two Sorensens, do the wiring, and then turn them back on, but is there any procedure for how this should be done?

Attachment 1: Screen_Shot_2017-02-10_at_9.01.46_AM.png
12826   Mon Feb 13 17:39:45 2017 AshleyUpdateGeneralPreliminary Microphone Data Update
• Problems that have occurred since my last post: All of the sudden, I was getting very strange data that was very quiet and did not match the previous input range of my last locations (see attachment). After resoldering the custom bnc connection cables with Lydia, which were in disrepair, and checking almost everything we could think of, we found that the gain dial on the preamp was turned all the down. Immediately after it was fixed, the data returned to expected values (based on neighboring locations and data taken at the last location before the problem occurred).
• Updates: Since my last post, I have created a normalized blrms color map in addition to the one I already have. Additionally, I have started working on plotting the color maps next to a labeled, to-scale drawing of the lab, but have yet to complete it.
• Attachment 1: comparison of the psds
• Attachment 2: blrms color map
• Attachment 3: normalized color map
 Quote: Brief Summary: I am currently looking at the acoustic noise around both arms to see if there are any frequencies from machinery around the lab that stand out and to see what we can remove/change. I am using a Bluebird microphone suspended with surgical tubing from the cable trays to isolate it from vibrations. I am also using a preamp and the SR875 spectrum analyzer taking 6 sets of data every 1.5 meters (0 to 200Hz, 200Hz to 400Hz, 400z to 800Hz, 800Hz to 3200Hz, 3.2kHz to 12kHz, 12kHz to 100kHz).   ·                Attachment 1 is a PSD of the first 3 measurements (from 0 to 12kHz) that I took every 1.5 meters along the x arm with the preamp and spectrum analyzer ·                Attachment 2 is a blrms color map of the first 6 sets of data I took (from 2.4m to 9.9m)  ·                Attachmetn 3 is a picture of the microphone set up with the surgical tubing  Problems that occurred: settings on the preamp made the first set of data I took significantly smaller than the data I took with the 0dB button off and the last problem I had was the spectrum analyzer reading only from -50 to -50 dBVpk

Attachment 1: figure_1.png
Attachment 2: x_and_y_blrms_03.png
Attachment 3: xblrms_median.png
12834   Thu Feb 16 13:29:38 2017 gautamSummaryGeneralAlternative Calibration Scheme

Summary:

Craig and I have been trying to put together a Simulink diagram of the proposed alternative calibration scheme. Each time I talk the idea over with someone, I convince myself it makes sense, but then I try and explain it to someone else and get more confused. Probably I am not even thinking about this in the right way. So I am putting what I have here for comments/suggestions.

What's the general idea?

Suppose the PSL is locked to the MC cavity, and the AUX laser is locked to the arm cavity (with sufficiently high BW). Then by driving a line in the arm cavity length, and beating the PSL and AUX lasers, we can determine how much we are modulating the arm cavity length in metres by reading out the beat frequency between the two lasers, provided the arm cavity length is precisely known.

So we need:

1. Both lasers to be stabilized to be able to sense the line we are driving
2. A high bandwidth PDH loop for locking the AUX laser to the arm cavity such that the AUX laser frequency is able to track the line we are driving
3. An accurate and precise way to read out the beat frequency (the proposal here is to use an FPGA based readout)
4. An accurate measurement of the arm length (I think we know the arm lengths to <0.1% so this shouldn't dominate any systematic error).

To be able to sense a 1kHz line being driven at 1e-16 m amplitude, I estimate we need a beat note stability of ~1mHz/rtHz at 1kHz.

Requirements and what we have currently:

• The PSL is locked to the mode-cleaner, and the arm cavity is locked to the PSL. The former PDH loop is high BW, and so we expect the stabilized PSL to have frequency noise of ~1mHz/rtHz at about 1kHz (to be measured and confirmed)
• The AUX laser is locked to the arm cavity with a medium-BW (~10kHz UGF) PDH servo. From past out-of-loop ALS beat measurements, I estimate the expected frequency noise of the AUX laser at 1kHz to be ~1Hz/rtHz with the current PDH setup
• Rana suggested we "borrow" the stability of the PSL by locking the AUX laser and PSL in a high bandwidth PLL - if we want this loop to have ~300kHz BW, then we need to use an EOM as an actuator. The attached Simulink diagram (schematic representation only, though I think I have measurements of many of those transfer functions/gains anyways) shows the topology I had in mind. Perhaps I did not understand this correctly, but if we have such a loop with high gain at 1kHz, and the error signal being the beat between PSL and AUX, won't it squish the modulation we are applying @1kHz?
• Is it feasible to instead add a parallel path to the end PDH loop with an EOM as an actuator (similar to what we do for the IMC locking)? Ideally, what we want is an end PDH loop which squishes the free-running NPRO noise to ~1mHz/rtHz at 1kHz instead of the 1Hz/rtHz we have currently. This loop would then also have negligible tracking error at 1kHz. Then, we could have a low bandwidth PLL offloading onto the temperature of the crystal to keep the beat between the two lasers hovering around the PSL frequency.

Hardware:

On the hardware side of things, we need:

• FSS box to drive the EOM (Rana mentioned there is a spare available in the Cryo lab)

Koji and I briefly looked through the fiber inventory we have yesterday. We have some couplers (one mounted) and short (5m) patch fibers. But I think the fiber infrastructure we have in place currently is adequate - we have the AUX light brought to the PSL table, and there is a spare fiber running the other way if we want to bring the PSL IR to the end as well.

I need to also think about where we can stick the EOM in given physical constraints on the EX table and the beam diameter/aperture of EOM...

Attachment 1: AltCal.pdf
12835   Thu Feb 16 21:55:47 2017 ranaSummaryGeneralAlternative Calibration Scheme

Question for Craig: What does the SNR of our lines have to be? IF we're only trying to calibrate the actuator in the audio band over long time scales, it seems we could get by with more frequency noise. Assuming we want a 1% calibration at 50-500 Hz, what is the requirement on the frequency noise PSD curve?

12837   Fri Feb 17 20:04:43 2017 KojiUpdateGeneralProjector not functional / Zita partially working

Koji, Gautam, Johannes

We quickly checked the situation of the projector in the control room.

- We found that the proejctor was indicating "lamp error".
==> Steve, could you remove the projector from the ceiling and check if it still does not work?
If it still does not work, send it back to the vender. It should be covered by the previous service.

- Zita seemed happy with the DVI output. We tried the dual display configration and  VGA and DVI are active right now.
The DVI output (from RADEON something video card) is somewhat strange. We probably need to look into the video display situation.

12842   Tue Feb 21 13:51:35 2017 CraigSummaryGeneralAlternative Calibration Scheme

We get SNR in two ways: the amplitude of applied force and the integration time.  So we are limited in two ways: stability of the lock to applied forces and time of locklosses / calibration fluctuations.

At the sites, you probably know that we blow our spectrum out of the water with the calibration lines, with SNRs of about 100 on the scale of about 10 seconds.  For us this might be impossible, since we aren't as quiet.

If we want 1% calibration on our sweeps, we'll need  0.01 = Uncertainty = sqrt( (1 - COH^2)/(2 * Navg * COH^2) ), where COH is the coherence of the transfer function measurement and Navg is the number of measurements at a specific frequency.  This equation comes from Bendat and Piersol, and is subject to a bunch of assumptions which may not be true for us (particularly, that the plant is stationary in time).

If we let Navg = 10, then COH ~ 0.999.

Coherence = Gxy^2/(Gxx * Gyy), where x(t) and y(t) are the input signal and output signal of the transfer function measurement, Gxx and Gyy are the spectral densities of x and y, and Gxy is the cross-spectral density.

Usually SNR = P_signal / P_noise, but for us SNR = A_signal / A_noise.

Eric Q and Evan H helped me find the relationship between Coherence and SNR:

P = Pn + Pc, Pn = P * (1 - Coh), Pc = P * Coh

==> SNR = sqrt( Pc / Pn ) = sqrt( Coh / 1 - Coh )

From Coh ~ 0.999, SNR ~ 30.

 Quote: Question for Craig: What does the SNR of our lines have to be? IF we're only trying to calibrate the actuator in the audio band over long time scales, it seems we could get by with more frequency noise. Assuming we want a 1% calibration at 50-500 Hz, what is the requirement on the frequency noise PSD curve?

12843   Tue Feb 21 17:05:14 2017 SteveUpdateGeneralProjector lamp replaced

This bulb was blown out on Feb 4, 2017 after 2 months of operation.

Attachment 1: blownup.jpg
12845   Wed Feb 22 10:16:54 2017 ranaSummaryGeneralAlternative Calibration Scheme

OK, but the questions still stands: "Assuming we want a 1% calibration at 50-500 Hz, what is the requirement on the frequency noise PSD curve?"

 Quote: We get SNR in two ways: the amplitude of applied force and the integration time.  So we are limited in two ways: stability of the lock to applied forces and time of locklosses / calibration fluctuations.
12848   Thu Feb 23 14:50:26 2017 SteveUpdateGeneral USB microscope returned

The microscope shipped back to the vendor for credit yesterday.

 Quote: http://www.amscope.com/3-5x-180x-boom-stand-trinocular-zoom-stereo-microscope-with-144-led-ring-light-and-10mp-camera.html will be ordered today. The actual unit we are getting has lockable zoom for better repeatability after calibration: SM-3NTPZZ-144 Quote: CWQ6-020817

12871   Mon Mar 6 16:32:36 2017 SteveUpdateGeneralold NPRO

16 years old Lightwave NPRO M126-1064-700, sn 415 power output is tripping continously to zero.

The Lightwave Controller 125/126-OPN-POS sn516 was used in this test. Settings were lowered to close to nominal values without any success.

One can not determine what is broken: head or controller. This NPRO head was under Manasa's desk.

12872   Tue Mar 7 15:17:19 2017 SteveBureaucracyGeneralproperty tag

Property tag found.

Attachment 1: property_tag.jpg
12875   Thu Mar 9 15:25:12 2017 KojiUpdateGeneralIMC/XYarms aligned/locked

As per Steve's request, I've checked the alignment of the IMC and the arms. These three cavities are locked and aligned.

12876   Thu Mar 9 17:26:43 2017 SteveUpdateGeneralattempted ETMY picture taking

I removed the video monitoring can and replaced it with Olympus SP-570UZ camera. It has no IR blocker. The OSEM light are dominant because I can not zoom in more.

I left the camera in place so you can try it. Leave the LEXAN plate on the glass window so no accident can happen. The illuminator is on and you can turn it off-on with the manual switch, close to the camera. Camera manual is on my desk.

12877   Thu Mar 9 20:11:04 2017 KojiUpdateGeneralattempted ETMY picture taking

The attached is the ETMY image with the single arm locked. This was the best I could do. Here is the recipe

• Turn on SP570UZ
• Switch to "M" mode (Manual aperture and exposure)
• Set the aperture to be the widest (smallest F number) and the exposure to be maximum (15 second).
• Switch to AF mode by the lens side switch
• Use the lens dial to adjust the zoom until the OSEMs fill the central 1/3 box (i.e. 1/9 area of the field of view). If you zoom more, you can't focus the spot later.
• Use menu button to switch to ISO1600 (You are now capable to see the beam spot)
• Switch to MF mode by the lens side switch
• Use the lens dial to adjust the focus to have the sharpest image of the spot. This can be achieved at the focal distance of ~1m
• Use menu button to switch back to ISO64
• Push the shutter (I didn't use it, but you should be able to use 2sec timer)
Attachment 1: P3090032.JPG
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