40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Category Subjectup
  3073   Sat Jun 12 19:43:19 2010 AlbertoUpdateWIKI-40M UpdateIFO modeling Wiki Page updated

Today I started writing the IFO modeling wiki page.

The idea is to make it a reference place where to share our modeling tools for the 40m.

  10301   Wed Jul 30 23:12:05 2014 KojiUpdateGeneralIFO patrol

- The cable for the beat note was disconnected from the frequency counter and reconnected to the spectrum analyzer.

- PMC/IMC had not been locked for 8 hours. 

- PMC was relocked.

- IMC got immediately relocked. Today IMC relocks very fast.

- Went to the ETMX table. Aligned the oplev beam on the QPD

- The X end green beam was realigned to the cavity.
I can feel that the two mirrors provides quite independent alignment adjustment. VERY NICE.
Green TRX: without PSL Green - 0.612, with PSL green - 0.725

I can clearly see that the mode matching is not ideal. All the higher modes are LG modes!
The input mode is very round.

- Arm cavities were aligned by ASS

- Tested ASX. PZT2 Pitch/Yaw servos run with the previous setting. We still can maximize the transmission by touching PZT1.

- Now Eric joined the activity.

-  Once the beam is aligned what we could lock was LG00/10/20/30.
   We measured the power in LGn0 modes
   LG00: 0.588
   LG10: 0.154
   LG20: 0.053
   LG30: 0.020

   This suggests that the mode-matching ratio is something like 70%

- Q is aligning the PMC. PMC transmission prev 0.783. Basically we could not improve it.
We thought this number can go up to ~0.82 or even ~0.84. We wonder if this comes from the decay of the laser power or reduced visibility?


  9540   Wed Jan 8 17:53:26 2014 manasaUpdateGeneralIFO plan, IPANG telescope

For the IPANG telescope design, we are in the 'beyond the Rayleigh range' regime. So using a single lens to make the beam small is not a great idea. I have put down a solution where we use a pair of lenses; one of which will be mounted in-vacuum in the ETMY chamber and the other on the endtable.
This way we will also allow have some freedom to configure the layout out-of vacuum in case the need arises. The layout will look something like in the cartoon:

I also made a choice of using longer focal length lenses (CVI 2" lenses f =1 m). Below is the beam path summary for IPANG telescope. I have used the waist diameter at the ITM for propagation. The endtable is roughly at 41.2m. The QPD will be placed in front of the waist (w0=47um).

  9543   Thu Jan 9 17:21:45 2014 ranaUpdateGeneralIFO plan, IPANG telescope


For the IPANG telescope design, we are in the 'beyond the Rayleigh range' regime. So using a single lens to make the beam small is not a great idea. I

Can you please explain this? I don't understand what exactly is the issue or 'great idea'.

I think we should be OK with just a single lens in the vacuum. But what we need is the ray tracing analysis to show what the effect will be on the IPANG readout.

  9538   Wed Jan 8 13:46:39 2014 JenneUpdateGeneralIFO plan, PRM baffle


While we're in there, we need to also put a baffle on the back side of the PRM cage, to protect the OSEMs from stray light.  Den and I discovered before Christmas that turning off the OSEM and OpLev damping to the PRM (while using the POP QPD for ASC) significantly reduced the power fluctuations in the PRC.  We still had arm power fluctuations, but I believe those are likely because our ALS system can't hold an arm precisely at full resonance.  So, putting a black glass baffle with ~2 inch aperture right up against the OSEMs should help a lot.  This week, I'll ask Steve to make me a quickie to-scale cardboard version of the baffles that he has had cut, so I can try securing it to the dirty suspension cage that we have out.  I will also check to make sure I have seen with my own eyes the baffles that I need, and copper wire to tie it to the cage.

Steve may actually be onto something with the clamps that he had made a year and a half ago.  These clamps hold the glass, and then clamp to the base of the suspension cage.  Not the table, but the base of the suspension cage. The drawings are in elog 6344.  I'm not sure that the 1/4-20 holes in the clamp things are exactly where we'll want them, but we should be able to just dog it down to the base of the suspension.  I need to check this, but it may be even easier than tieing the glass to the cage.

Also, something to think about is that the earthquake stop screws extend backwards farther than the OSEMs.  I'm not sure anymore if we have shorter 1/4-20 earthquake stops around (if we do, they should be in the cleanroom shelves), but if we can't swap those out, they'll limit how close we can get to the OSEMs. 

Here's an overhead photo from 6 Sept 2012:


  9534   Tue Jan 7 23:24:41 2014 JenneUpdateGeneralIFO plan, list o' things to do

It seems that the most important short-term task we have right now is to figure out what our PRC length is, and what our tolerance from nominal is.  Gabriele and EricQ are going to work on that tomorrow.  If our PRC is of a length that we can't do anything useful for full IFO locking, we need to open up and fix it sooner rather than later.

While we're in there, we need to also put a baffle on the back side of the PRM cage, to protect the OSEMs from stray light.  Den and I discovered before Christmas that turning off the OSEM and OpLev damping to the PRM (while using the POP QPD for ASC) significantly reduced the power fluctuations in the PRC.  We still had arm power fluctuations, but I believe those are likely because our ALS system can't hold an arm precisely at full resonance.  So, putting a black glass baffle with ~2 inch aperture right up against the OSEMs should help a lot.  This week, I'll ask Steve to make me a quickie to-scale cardboard version of the baffles that he has had cut, so I can try securing it to the dirty suspension cage that we have out.  I will also check to make sure I have seen with my own eyes the baffles that I need, and copper wire to tie it to the cage.

Other, lower-priority things that we should do eventually:

* Steve, please find another razor beam dump for the WFS reflections - Rana and I used one of the ones that was there for reflection off the 2 inch lens in the MC refl path (replacing the aluminum dump that has been there for ages).  We also need to label all of our razor dumps with their purpose, with a label on top, so we remember not to remove dumps that are actually in use.

* At some point, we should change the one remaining steering mirror in the main PSL path that is aluminum, to a steel Polaris ("Polanski" or "Polish") mount.  For now, we should just make sure we have one handy.  Hopefully this will help reduce the PMC transmission drift that we see.

* Steve, in the morning sometime this week, can you please do a test of the drift of the IOO QPDs?  We'd like to see a trend that is maybe 30 or 60 minutes long of the QPD signals.  First 10 minutes, all lights in IFO room off.  Then, 10 minutes with the lights in the PSL on.  Then, the rest of the time the PSL lights off.  We want to see if these are hot enough to be causing a big temperature change in the PSL box, which may then be causing some optics to drift.

* QPD code in the simulink models (trans QPDs, but also OpLevs, and anywhere else we do normalization) needs to have anti-divide-by-zero protection.  I'll take care of this, it should be a quick copy of what we have elsewhere in the simulink code.

* Note to self for the future, instead of doing a dither alignment for the ASS for the arms, we can use the IP POS and IP ANG, as well as end transmission QPD signals.  However, for now, the ASS is working just fine.

* We want to go back to the idea of putting a lens into the in-vac IP ANG path, to avoid the clipping that Manasa and I were seeing tonight.  We want something of order 2inch diameter, 1meter focal length.  The material doesn't matter, but we do want it AR coated for 1064nm on both sides.  We also need to make sure that we could use a fixed 2 inch in-vac mirror mount, or something, to hold this lens.  If that won't work, we need to come up with another plan.  Manasa is working on thinking about precisely what lens we want to buy for a nice guoy phase telescope for IPANG, so we'll buy a lens after she puts her conclusions in the elog.

* An idea for the MC spots plot that Rana had was to plot the beam tilt and translation, rather than the raw spot positions on the mirrors.  The point of this would be to make it easier to see what the output beam from the MC looks like.  For MC pointing, we should also think about what our actual tolerances are.  The biggest thing is that we need to get through the Faraday without being too close to any edge, and also the REFL beam needs to come back through without clipping.  For now, we're just visually checking that the POP beam and the REFL beam both look unclipped since we don't have access to good camera views of either side of the Faraday.

  1852   Fri Aug 7 09:50:57 2009 steveConfigurationVACIFO pressure rose to 2.3 mTorr

IFO pressure was 2.3 mTorr this morning,

The Maglev's foreline valve  V4 was closed so P2 rose to 4 Torr. The Maglev was running fine with V1 open.

This is a good example for V1 to be closed by interlock, because at 4 Torr foreline pressure the compression ratio for hydrocarbones goes down.

V4 was closed by interlock when TP2 lost it's drypump. The drypump's AC plug was lose.

To DO: set up  interlock  to close V1 if P2 exceeds 1 Torr

  1857   Fri Aug 7 16:11:11 2009 steve, robConfigurationVACIFO pressure rose to 2.3 mTorr


IFO pressure was 2.3 mTorr this morning,

The Maglev's foreline valve  V4 was closed so P2 rose to 4 Torr. The Maglev was running fine with V1 open.

This is a good example for V1 to be closed by interlock, because at 4 Torr foreline pressure the compression ratio for hydrocarbones goes down.

V4 was closed by interlock when TP2 lost it's drypump. The drypump's AC plug was lose.

To DO: set up  interlock  to close V1 if P2 exceeds 1 Torr




We added C1:Vac-CC1_pressure to the alarm handler, with the minor alarm at 5e-6 torr and the major alarm at 1e-5 torr.

  1609   Tue May 19 16:18:45 2009 steveConfigurationVACIFO pressure is 4.2e-7 Torr with CRYO pump

Morning Vacuum condition: IFO is not being pumped, P1 pressure is 1.8 mTorr and rising (see P1 pressure plot of 100 min ).

Overnight the RGA protection software interlock at closed the VM1 valve triggering on CC1 = 1e-5 torr.

This interlock blocked our attempt to hold the IFO operational pressure in the high 1e-5 Torr range with one small
"beer can" turbopump (Varian V70D drag-turbo pumping speed for N2 is ~60 l/s at 75KRPM).

I started CRYO regeneration using TP3. Pressure readout on the P3 gauge. This is after 30 days of CRYO operation.

V5 was closed for 60 sec to see the outgassing rate of the cryopump surfaces. It was good (but I am not going to elog
what 'good' actually means - instead I will write it in my paper logbook to prevent others from learning). I will now'
go start cooling down the cryo pump.

** translated into English by Rana

The Cryo cooled down to ~12K by noon.Photo switch was reset and VC1 was opened at 2pm

The VACMONITOR.adl screen is not working. Someone made some improvement on it last night.
  13615   Wed Feb 7 15:50:42 2018 SteveUpdateVACIFO pressure monitoring

Hornet cold cathode gauge analoge output  [ DSub9 pin 3 and 7 ] are wired to go ETMX Acromag. It was reading 4.9V at 7.8e-6 Torr [ 3,110 V  8.35e-5A ] at the end of a 24ft BNC cable. Now it has to be hook up to an Acromag channel.

This will replace the not functioning C1: Vac-CC1_pressure

gautam: the motivation behind hooking this gauge up to our DAQ system is that non-vacuum-system-experts have a quick diagnostic to make sure everything is in order. This gauge is physically placed adjacent to V1, and so if something goes wrong with our vacuum pumps, we would see the effect here immediately. we did note that occassionally, the reading fluctuated by ~1V on the DMM used to check the voltage output at the end of the BNC cable, so we still need to run some long-term stability analysis once this channel is hooked up to the Acromag.  For future reference, in order to make this gauge work, we need to check that

  1. Error flag has been cleared.
  2. HV is ON (state has to be manually toggled).



There was a power outage.

The IFO pressure is 12.8 mTorr-it and it is not pumped. V1 is still closed. TP1 is not running. The Rga is not powered.

The PSL output shutter is still closed. 2W Innolight turned on and manual beam block placed in its beampath.

3 AC units turned on at room temp 84F

IFO pumped down from 44 mTorr to 9.6e-6 Torr with Maglev  backed with only TP3

Aux drypump  was helping our std drypump during this 1 hour period. TP3 reached 32 C and slowed down 47K rpm

The peak foreline pressure at P2  was ~3 Torr

Hornet cold cathode gauge setting:   research mode, air,

                                                            2830 HV  1e-4A  at 9.6e-6 Torr,

                                                         [  3110 HV  8e-5A at 7.4e-6 Torr one day later ]

Annuloses are at 2 Torr, not pumped

Valve configuration:  vacuum normal, RGA is still off

PSL shutter is opened automatically. Manual block removed.

End IR lasers and doublers are turned on.


NOTE: Maglev " rotation X " on vacuum medm screen is not working! " C1:Vac-TP1_rot " channel was removed.  Use " NORMAL X " for rotation monitoring.

*We removed this (i.e. rotation) field from the MEDM screen to avoid confusion.


  5280   Tue Aug 23 00:55:13 2011 JenneUpdateGeneralIFO ready for doors

[Kiwamu, Jenne]

After the IFO was aligned in air one final time, we tapped on a few OSEMs until we were happy with all of the centering of all of the optics' OSEMs.  All are within 0.05 of their halfway values, with the exception of one each on MC1 and MC3, one of which is within 0.06, and the other 0.08.  Because of the realignment pain of dealing with MC OSEMs, we elected to leave these alone.  Also, since we obviously didn't open the MC2 tank, we don't know how they are, although the numbers look reasonable. 

Also, we took photos (to be posted on Picasa in a day or two) of all the main IFO magnet-in-OSEM centering, as best we could.  SRM, BS, PRM all caused trouble, due to their tight optical layouts.  We got what we could.  Various people have been looking at these for the past 2 weeks, and I think they're all fine, even if we didn't get stellar photos.

We are now prepared for pumping.  For real this time.


  8117   Wed Feb 20 18:53:48 2013 JenneUpdateAlignmentIFO ready for doors, then pumping

[Yuta, Manasa, Sendhil, Jenne, Steve, Jamie, Koji, Evan]

The interferometer is well-aligned, and ready for pump-down.  The access connector is in place, as are the ETM heavy doors.  We will do ITM and BS doors tomorrow, then begin pumping.

Before we redid the ITM pointing, I confirmed that I could see both POX and POY on their respective tables, on a camera, unclipped.  I should check again quickly now that the ITM pointing has been finalized.

We went back to the arms, to perfect the ITM pointing.  Input beam was already centered at ETMY.  ETMY was pointing so that beam reflected to ITMY.  ITMY was adjusted a few (less than 4?) steps of 1e-3 size, to make reflected beam hit center of ETMY. 

BS was already pointing so beam hit center of ETMX.  ETMX was pointing to hit center of ITMX.  ITMX was adjusted a few (less than 4 again?) steps of 1e-3 size to make reflected beam hit center of ETMX.

Checked centering on AS path.  AS beam comes out of the vacuum a little low, but this wasn't discovered until after the access connector was in place.  We could adjust PZT3 (last AS mirror on BS table that sends beam over to OMC table), but we don't want to do this since we won't be able to re-confirm centering on the 3 mirrors on the OMC table.

Green beams (first Y, then X) were aligned using out-of-vac steering mirrors until beams were flashing in their respective arm cavities.  Green Y is a little close to the edge of the bottom periscope mirror, on the "up" periscope.  Since there is no steering between the arm and this periscope, fixing it would require moving the periscope.  We leave this to the next vent, when we finally install the BS table extension.  We were flashing a higher order yaw mode (5ish nodes) for the Y arm, and the very edge of the higher order mode on one side was a little bit clipped after reflecting off the steering mirror on the OMC table.  This is happening because that mirror is in the mount backwards (so we have access to the knobs).  We are confident that the straight-through beam is well centered on that mirror, so once we get it aligned to TEM00, there will be no clipping. We then did the X arm green, which was flashing a pitch higher order mode (again 5ish nodes).  The very edge of the higher order mode is clipping a little bit on the top mirror of the "down" periscope on the IMC table, but again the straight through beam is okay, and we're confident that the TEM00 mode will make it unclipped.  We could have touched some steering mirrors on the BS table, but since this was once upon a time well aligned, we don't want to futz with it.

Corner oplevs are all centered on their QPDs.  (The ETM oplevs were centered a few days ago).

Access connector and ETM doors are on.

The last 3 vertex doors will go on tomorrow when Steve gets in, and then we'll start pumping. 

There are no in-vac PZTs that need to be turned on (we've been using the output steering PZTs as non-energized fixed mirrors for some time), so we can lock at our leisure tomorrow afternoon.

  9512   Wed Jan 1 15:01:29 2014 KojiSummaryGeneralIFO recovery

IFO restart after the recovery of linux1

Machine recovery in the following order
- Start fb
- Start the following machines: mafalda, megatron, op340m
- Start c1ioo, c1lsc, c1sus, c1iscex, c1iscey

CDS recovery / burtrestore

- Confirm all of the RT systems are running in "green". If not, restart corresponding model.
- c1iscaux, ciscaux2 didn't have response (white boxes). Went to the LCS digital rack and power cycled these targets
- burtrestore: The snapshots at Dec 19 05:07 were used. For c1iscaux and c1iscaux2 the snapshots at Dec 22 05:07 were used.

fast machines

slow machines


IFO recovery

- Reload watchdogs => restore sus damping
- MC misaligned but TEM00 was locked
- Gave a small touch on MC2 yaw => IMC almost aligned
- Autolocker wasn't running => Manually launched rather than wait for an hour for cron to launch it
- PMC was largely misaligned. => Aligned on the PSL table (PSLTRANS 0.640->0.753)
- IFO X/Y arm locked and aligned with ASS.
- PRMI mode: manually aligned PRM. The PRMIsb momentally locked.

  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


  14440   Thu Feb 7 19:28:46 2019 gautamUpdateVACIFO recovery

[rana, gautam]

The full 1 W is again being sent into the IMC. We have left the PBS+HWP combo installed as Rana pointed out that it is good to have polarization control after the PMC but before the EOM. The G&H mirror setup used to route a pickoff of the post-EOM beam along the east edge of the PSL table to the AUX laser beat setup was deemed too flaky and has been bypassed. Centering on the steering mirror and subsequently the IMC REFL photodiode was done using an IR viewer - this technique allows one to geometrically center the beam on the steering mirror and PD, to the resolution of the eye, whereas the voltage maximization technique using the monitor port and an o'scope doesn't allow the former. Nominal IMC transmission of ~15,000 counts has been recovered, and the IMC REFL level is also around 0.12, consistent with the pre-vent levels.

  14445   Fri Feb 8 20:48:52 2019 gautamUpdateLSCIFO recovery

Several housekeeping tasks were carried out today in preparation for the Y-arm loss measurement.

  1. The mess around the OMC rack was cleared a bit. The vertex laptop paola now lives there, instead of on the ITMY optical table.
  2. Centering of beam on AS photodiodes on AS table (starting from the first optic in this path at the exit point from the vacuum), adjusted AS camera to bring the spot roughly to the center.
  3. POX/POY locking was restored, GTRY/GTRX levels are healthy. TRY was centered on the Thorlabs PD by triggering the LSC lock on AS110.
  4. Oplevs on all four TMs and BS were centered for post-vent alignment.
  5. ETMY OL transfer function was checked since we have swapped the HeNe during the vent, 4.5 Hz UGF for both DoFs and ~30 deg phase margin. The calibration of the error point to urad needs to be double checked.
  6. There are some huge 60 Hz harmonics in the TRY signal - hunting down the source of this. The one thing I can think of that was changed is that we plugged the c1auxey eurocrate into the ethernet powerstrip, I wonder if this created some kind of ground loop.
    • I checked the signal from the PD with a battery powered scope, no evidence of any 60 Hz in the time domain or scope FFT (Attachment #1, FFT in red and time domain signal in green can be seen).
    • Restored the power of c1auxey eurocrate to its original socket in the back of 1Y4 - harmonics still present --> points to the problem being in the whitening board / ADC electronics?
    • The harmonics only seem to show up when TRY > ~0.5
    • Some elog hunting revealed that this signal is being digitized through a modified D990399. So somehow the signal pollution is happening inside this board? Because from the output of this board, the signal is going straight into the ADC.
    • To confirm, I will temporarily hijack another ADC channel and look at the spectrum. There is apparently some kind of daughter board (D040060), but how 60 Hz is coupling at this stage is unknown to me.
  7. The ASS system for both arms still isn't working properly, to be investigated. The dirty TRY signal probably isn't helping the situation.
  14637   Fri May 24 17:50:19 2019 gautamUpdateIOOIFO recovery

At ~4pm, the main volume pressure (CC1) was reported to be ~5e-5 torr. So I replaced the HR mirror in the MC REFL path with the usual 10% beamsplitter, and aligned the beam onto MCREFL photodiode. I also replaced the ND filter on the AS port camera, and in front of the IPPOS QPD.

Then I turned up the power by HWP rotation - at the input to the IMC, I now measured 960 mW with the Coherent power meter, so the NPRO power has certainly decayed by ~10% from 2018 July. Normal high-power IMC autolocker script was re-enabled on megatron (and the slow servo enable threshold raised from 1000 cts to 8000cts). IMC was readily locked, after some hand alignment, I got a maximum of 14500 cts transmission. I was then able to lock the Y-arm. The dither alignment servo did not work with the nominal settings, but by hand alignment, I was able to get TRY up to 0.6 (I didn't try too hard to optimize this in any systematic way). X arm was also locked.

AUX drypump valved off and shutdown at ~610pm. I also switched both TP2 and TP3 to their lower rotation "standby" mode. So overall no major mishaps this time around. I am leaving the PSL shutter open over the long weekend. For in-air vs vacuum suspension spectra comparison, I kicked the ETMY optic at Fri May 24 18:26:10 PDT 2019.

  15121   Tue Jan 14 20:17:09 2020 gautamSummaryGeneralIFO recovery


There was no light entering the IFO. I worked on a few things to bring the interferometer to a somewhat usable state. The goal is to get back to PRFPMI locking ASAP.


Problem: All fast models report a "0x4000" DC error. See Attachment #1.

Solution: I think this is a "known" issue that happened last new year too. The fix was to add a hard-coded 1 second offset to the daqd config files. However, incrementing/decreasing this offset by +/- 1 second did not fix the errors for me today. I'll reach out to JH for more troubleshooting tips.

Update 15 Jan 2020 830am: The problem is now fixed. See here.

Problem: c1susaux and c1auxey were unresponsive.

Solution: Keyed c1auxey. Rebooted c1susaux and as usual, manually started the eth0/eth1 subnets. The Acromag crate did not have to be power-cycled. ITMY got stuck in this process - I released it using the usual bias jiggling. Why did c1susaux fail? When did it fail? Was there some un-elogged cable jiggling in that part of the lab?

Problem: IMC autolocker and FSS slow processes aren't running on megatron after the upgrade.

Solution: Since no one bothered to do this, I setup systemd infrastructure for doing this on megatron. To run these, you do:

sudo systemctl start MCautolocker.service
sudo systemctl start FSSSlow.service

and to check their status, use:

sudo systemctl status MCautolocker.service
sudo systemctl status FSSSlow.service

The systemd setup is currently done in a naive way (using the bash executable to run a series of commands rather than using the systemd infrastructure itself to setup variables etc) but it works. I confirmed that the autolocker can re-acquire IMC lock, and that the FSS loop only runs when the IMC is locked. I also removed the obsolete messages printed to megatron's console (by editing /etc/motd) on ssh-login, advising the usage of initctl - the updated message reflects the above instructions.

In order to do the IMC locking, I changed the DC voltage to the AOM to +1V DC (it was +0.8 V DC). In this setting, the IMC refl level is ~3.6 V DC. When using the undiffracted AOM beam, we had more like +5.6 V DC (so now we have ~65% of the nominal level) from the IMC REFL PD when the IMC was unlocked. IIRC, the diffraction efficiency of the AOM should be somewhat better, at ~85%. Needs investigation, or better yet, let's just go back to the old configuration of using the undiffracted beam.

There was also an UN-ELOGGED angry change of the nominal value of the PMC servo gain to 12.8, and no transfer function measurement. There needs to be a proper characterization of this loop done to decide what the new nominal value should be.

I'm going to leave the PSL shutter open and let the IMC stay locked for stability investigations. Tomorrow, I'll check the single-arm locking and the ALS system.

  15672   Tue Nov 10 17:46:06 2020 gautamUpdateGeneralIFO recovery


  1. Recovery was complicated by RFM failure on c1iscey - see Attachment #1. This is becoming uncomfortably frequent. As a result, the ETMY suspension wasn't being damped properly. Needed a reboot of c1iscey machine and a restart of the c1rfm model to fix.
  2. POX/POY locking was restored. Arm alignment was tuned using the dither alignment system.
  3. AS beam was centered on its CCD (I put a total of ND=1.0 filters back on the CCD). Note that the power in the AS beam is ~4x what it was given we have removed the in-vacuum pickoff to the OMC.
  4. Green beams were aligned to the arm cavities. See Attachment #2. Both green cameras were adjusted on the PSL table to have the beam be ~centered on them.
  5. ALS noise is far too high for locking, needs debugging. See Attachment #3.
  6. AS beam was aligned onto the AS55 photodiode. With the PRM aligned, the REFL beam was centerd on the various REFL photodiodes. The PRMI (resonant carrier) could be locked, see Attachment #4.

I want to test out an AS port WFS now that I have all the parts in hand - I guess the Michelson / PRMI will suffice until I make the ALS noise good again, and anyways, there is much assembly work to be done. Overnight, I'm repeating the suspension eigenmode measurement.

  16875   Wed May 25 17:34:47 2022 yutaConfigurationBHDIFO recovery - IFO alignment

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

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

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

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

  16874   Wed May 25 16:56:44 2022 PacoConfigurationBHDIFO recovery - IMC alignment

[Yuta, Paco]

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

  MC1 (before --> after) MC2 (before --> after) MC3 (before --> after)
PIT -0.3398 --> -0.4768 4.1217 --> 4.0737 -1.9808 --> -1.9308
YAW -0.8947 --> -0.7557 -1.2350 --> -1.3350 1.5598 --> 1.5638
  11174   Wed Mar 25 21:44:20 2015 KojiUpdateLSCIFO recovery / PRFPMI locking activity

[Koji, Den]

- Aligned the arms with ASS. It had alot of offset accumulated. We offloaded it to the suspension.

- We could lock the PRMIsb with the new setup.
PRCL: REFL165I (-14deg, analog +9dB)) -0.1, Locking FM4/5, Triggered FM 2
MICH: REFL165Q (-14deg, analog +9dB) -1.5, Locking FM4/5, Triggered FM2/6/9

- Demod phases at REFL were adjusted such that PRCL in Q signals were minimized :
REFL165 -80deg => -14deg
POP55 -63deg
REFL11 +164 => +7
REFL33 +136 => +133

Note: analog gains: REFL11: +18dB,  REFL33: +30dB, POP55: +12dB, REFL165: +9dB

- Try some transition between REFL signals to check the signal quality.
Measure TFs between the REFL signals

PRCL gain
REFL11I/REFL165I = +58
REFL33I/REFL165I = +8.5
POP55I /REFL165I = -246

MICH gain
REFL11Q/REFL165Q = +11
REFL33Q/REFL165Q = -1.5
POP55Q /REFL165Q = +280

- This resulted us to figure out the relationships of the numbers in the input matrix 

REFL55I/Q -4e-3/4e-3
REFL165I/Q 1.0/1.0 (reference)
REFL11I/Q  0.02/0.1
REFL33I/Q +0.12/-0.7

Full locking trial

Arm locked -> ALS -> Arm offset locked
PRMI locking
REFL165 phase tuned -110deg
PRCL gain -0.1 / MICH gain -2

We needed script editing.
Previous script saved in: /opt/rtcds/caltech/c1/scripts/PRFPMI/carm_cm_up_BACKUP.sh

- PRMI gain setting (input matrix & servo gain)
- CARM/DARM transition setting (see below)

The current CARM/DARM transition procedure:

- CM REFL1 gain is set to be -32
- CARM_B is engaged and the gain is ramped from 0 to +2.5
- Turn on FM7 (integrator)
- MC IN2 (AO path) engaged
- MC IN2 gain increased from -32 to -21

- DARM_B is engaged and the gain is ramped from 0 to +0.1
- Turn on FM7 (integrator)

- CM REFL1 Gain is increased from -32 to -18
- Ramp down CARM A gain to 0

- DARM_B gain is incrased to 0.37. At the same time DARM_A gain is reduced to 0

We succeeded to make the transition several times in the new setting.

- But later the transition got hard. We started to see big jump of the arm trans (TRX/Y 50->100) at the CARM transition.

- We tested the PRCL transition from 165MHz to 55MHz. 55MHz (i.e. POP55 which is REFL55PD) looks alot better now.

- ~1:30 The PMC was realigned. This  increased PMC_TRANS about 10%. This let the Y arm trans recover ~1.00 for the single arm locking

- Decided to end around 3:00AM

  9731   Mon Mar 17 12:02:55 2014 KojiSummaryGeneralIFO recovery / confirmed ETMX in trouble

I confirmed that we need to vent the chambers.

All of the mirrors have been aligned except for ETMX.

ETMX does not respond to the excitation by the UR and LR coils. Likely that the magnets are knocked off, or stuck in the coil.

PRM/SRM oplevs are too much off and can't be turned on. Need realignment of the beams on the QPDs.

- FB was down. FB restarted ("telnet fb 8087", then type shutdown)

- Aligned the MC mirrors.

- Aligned PRM. Look at the REFL. It was slightly mislisligned.

- AS has no beam. The Y arm was resonating with the green. So I determined that the TTs were the misaligned guys.

- Touched TT2 pitch with an increment of 0.1. Immediately the AS beam spot for ITMY was found. And the arm was resonating.

- The RM was further aligned. The bias sliders were saved and then the PRM was misaligned.

- Yarm was locked on TEM01. The ASS maximized the transmission for TEM01, and then the arm was locked on TEM00.
  The ASS aligned the arm and TTs. These values were saved.

- Yarm was aligned and I can see the AS spot. So I believe the BS is still well aligned.

- Aligned the PRM to reduce the ghost beams.

- Moved the ITMX to have Michelson fringes properly.

- Also aligned the SRM.

- Now ETMX was checked. Played with the alignment biases to see if the mirror was sticking on the coils. The mirror can rock a little, but it did not come back.

- Then, checked each magnets. 0.8Hz 1000cnt signals were injected to each coils (cf. C1:SUS-PRM_**COIL_EXC) to see how the mirror could react.
  The OSEM output and green spot on the ETMX cage were observed.

- Saw some response by actuating the UL, LL, SD coils.

- Saw no response from the UR and LR coils. They show the OSEM output of zero. Does this mean the magnets fell in the coils?

//Manasa// MC spot positions measured and they look alright with not much change from before the earthquake (attach)

  9733   Mon Mar 17 20:14:34 2014 KojiSummaryGeneralIFO recovery / confirmed ETMX in trouble

I tried to take the photos of the magnets from outside. So far most suspicious was LL.
Otherwise, the magnets are OK.
(The SD magnet is the one with most reasonable response.)
Steve will try to take much more zoomed photo with Olympus. But the LL coil already showed some response in my observation in the morning.


  2401   Fri Dec 11 17:36:37 2009 kiwamuUpdateGeneralIFO restoring plan

Alberto, Jenne, Kiwamu


We together will lead the IFO restoring and the following is our plan.

- - - - -|- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

#.0     |  measuring the free swinging spectra                     (weekend by kiwamu)   DONE

#.1     |  turn ON the PZTs for steering mirror and so on.         (Dec.14 Mon.) DONE

#. 1            |    lock around PSL  DONE

#.2     |  deal with mechanical shutter                            (Dec.14 Mon.)DONE

#.3     |  lock MCs                                                (Dec.14 Mon.)DONE

#.4     |  align the IFO                                           (Dec.15 Tue.)DONE

#.5     |  lock full IFO                                           (Dec.15 Tue.)DONE

- - - - -|- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


Thank you.

  2630   Tue Feb 23 06:47:57 2010 KojiUpdateGeneralIFO situations / low power MC lock

Work on 22nd Monday:

[MC recovery]

- Tried to lock MC after the computer recovery by Joe.
- A lot of higher modes. I can touch the input periscope or the MC mirrors.
- First tried to align the MC mirrors. MC1 was aligned against the MC REFL PD. MC2/3 was aligned to maximize the transmitted power.
- After the alignment, I got the MC Trans Sum ~8V. Also I saw the flashing of the arm cavities. I decided to take this alignment although the beam looks little bit clipped by the faraday.

[IFO alignment recovery]

- Aligned the arms for TEM00 manually.
- Arm alignment script seems not working now. This could come from the move of the end QPDs
- PRMI/DRMI were aligned. All alignment values saved.

[Low power MC]

[Optical config]

- I fixed the MCT CCD camera. It is quite useful to align the MC.

- Inserted HWP+Cube PBS+HWP combo in the MC incident path.
- First HWP and PBS adjust the light power. The second HWP is fixed at 342deg such that it restores the poralization to S.
- The incident power was measured by the SCIENTECH power meter. Offset of 3mW was subtracted in the table below.

HWP1 angle P_MC_incident comment
126deg 1.03W Max
100 0.39  
90 0.098 Low power max
85 0.021 Low power nominal

- HWP1 85deg is the nominal.

- I needed to touch the steering mirror (indicated by the picture) to obtain TEM00.
  The alignment of the HWPs and the cube PBS didn't change the mode. Thermal lense of the cube?

- I could not lock the MC with the incident power below 100mW. So the BS in the MC REFL path was replaced by a total reflector (Y1-45S).
- This increased the power on the MC REFL PD x10 of the previous. NOW WE ARE CONSTRAINED BETWEEN 81deg~90deg. DON'T ROTATE FURTHER!
- The original BS was stored on the AP table as shown in the picture.
- This total reflector disabled the MC WFS QPDs. We can't use them.

[Lock of the MC with 20mW incident]
- Disable the MC autolocker.
- Disable the MC WFS.
- Run
- Turn on the MCL servo.
- Set the MCL gain to 1.5 (it was nominally 0.3 for the high power)
- Just wait until lock.

[Gain boost after the lock] ...If you like to have more gain
- There was almost no room to increase the MCL gain.
- MC_REFL_GAIN can be increased from +6dB to +20dB
  ezcawrite "C1:IOO-MC_REFL_GAIN" 20
- MC_VCO_GAIN can be increased from -3dB to +2dB
  ezcawrite "C1:IOO-MC_VCO_GAIN" 2
- Crank the FSS gains
  ezcawrite C1:PSL-FSS_MGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_C_GAIN`
  ezcawrite C1:PSL-FSS_FASTGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_F_GAIN`

[If lock is lost]
- Run

  774   Thu Jul 31 10:24:32 2008 KojiUpdateGeneralIFO status
Last night I used the Y-arm for the abs length measurement. The Yarm was aligned by the script.
I left the ifo with the Yarm locked as it is the only meaningful configuration so far.
  14483   Mon Mar 18 12:27:42 2019 gautamUpdateGeneralIFO status
  1. c1iscaux2 VME crate is damaged - see Attachment #1. 
    • It is not generating the 12V supply voltage, and so nothing in the crate works.
    • Tried resetting via front panel button, power cycling by removing power cable on rear, all to no effect.
    • Tried pulling out all cards and checking if there was an internal short that was causing the failure - looks like the problem is with the crate itself.
    • Not sure how long this machine has been unresponsive as we don't have any readback of the status of the eurocrate machines.
    • Not a showstopper, mainly we can't control the whitening settings for AS55, REFL55, REFL165 and ALSY. 
    • Acromag installation schedule should be accelerated.
    • * Koji reminded me that \text{VME crate} \ \neq \ \text{eurocrate}. The former is what is used for the slow machines, the latter is what is used for holding the iLIGO style electronics boards.
  2. ITMX oplev is dead - see Attachment #2.
    • Lasted ~3 years (installed March 2016).
    • I confirmed that no light is coming out of the laser head on the optical table.
    • I'll ask Chub to replace it this afternoon.
  3. c1susaux is unresponsive
    • I didn't reboot it as I didn't want to spend some hours freeing ITMY. 
    • At some point we will have to bite the bullet and do it.
  4. Input pointing is still not stable
    • I aligned the input pointing using TT1/TT2 to maximize TRX/TRY before lunch, but in 1 hour, the pointing has already drifted.
  5. POX/POY locking is working okay. TRX has large low-frequency fluctuations because of ITMX not having an Oplev servo, should be rectified once we swap out the HeNe.

The goal for this week is to test out the ALS system, so this is kind of a workable state since POX/POY locking is working. But the number of broken things is accumulating fast.

  14642   Tue May 28 17:41:13 2019 gautamUpdateGeneralIFO status

[chub, gautam]

Today, we tried to resuscitate the c1iscaux2 channels by swapping the existing, failed VME crate with the newly freed up crate from c1susaux. In summary, the crate gets power, and the EPICS server gets satrted, but I am unable to switch the whitening gain on the whitening boards. I belive that this has to do with the FAIL LEDs that are on for the XVME-220 units. We were careful to preserve the location of the various cards in the VME crates during the swap. Rather than do a detailed debugging with custom RJ45 cables and terminal emulators, I think we should just focus the efforts on getting the Acromag system up and running.

Our work must have bumped a cable to the c1lsc expansion chassis in the same rack - the c1lsc FE had crashed. I rebooted it using the script - everything came back gracefully.

  10134   Mon Jul 7 11:02:22 2014 manasaConfigurationGeneralIFO status post earthquake


All suspension damping restored. There had to be an earth quake.

PMC was relocked.

MC did not need any fixing to its alignment. I had to lock it manually and autolocker is set running now. So that should take care of things

The arms were aligned and ASS'd for IR PDH.

Green light PDH locks to the arms alright.

  7892   Fri Jan 11 16:13:47 2013 JenneUpdateGeneralIFO status update - PMC fixed


I came in this morning to see that the PMC was down. The PZT voltage had drifted to below 50V. I adjusted the FSS slow controls to 0V and PZT was back at 126V.

PMC and IMC could eventually be locked.

History of PZT voltage behaviour in dataviewer over the last 24 hours shows it has been drifting everytime after it has been fixed.

 FSS was saturating.  Fixed.

  7891   Fri Jan 11 11:07:04 2013 ManasaUpdateGeneralIFO status update - PMC problems

I came in this morning to see that the PMC was down. The PZT voltage had drifted to below 50V. I adjusted the FSS slow controls to 0V and PZT was back at 126V.

PMC and IMC could eventually be locked.

History of PZT voltage behaviour in dataviewer over the last 24 hours shows it has been drifting everytime after it has been fixed.

  10778   Thu Dec 11 10:08:10 2014 manasaUpdateGeneralIFO update

Status of IFO:

1. The X end slow computer is down. ETMX sliders and buttons on the ETMX suspension screens have gone white. I have disabled the ETMX oplev because it is largely misaligned in yaw. I am not poking it and leaving it as is for the time being.

2. The Y arm green alignment had drifted and GTRY was down to 0.15 . I tweaked the alignment using the last two steering mirrors and brought GTRY to 0.7 which gives a beat note of -14dBm.

  10740   Mon Dec 1 16:34:20 2014 JenneUpdateGeneralIFO wake-up


 After its' several days of rest, it is time to wake up the IFO. 

  • FSS temp was railed at +10, which was making the MC not want to lock.  Set it to zero, locked the MC, and ran the MC WFS relief scripts.
  • PMC trans is down to 0.686, so I'll probably want to tweak that up before I get too carried away for tonight. 
  • c1iscex computer was frozen, which I suspect is why Steve found ETMX tripped this morning.  Soft reboot, and we're back to normal.

With that, it's time for a new week of locking, and trying to catch up with the big kids at the sites.

  10262   Wed Jul 23 11:32:04 2014 KojiUpdateLSCIFO warming up

Alone with the IFO. Started from some conversation with it.

Some ALS trials: Found the Y-end green alignment was terrible. In fact the end green set up is terrible.
Unfixed optics, clipping/fringing in the faraday, unstable suprema mounts which is unnecessarily big.

Eventualy I stopped touching the end alignment. Run ALS to see the stability of the things.
This is a performance confirmation after some touching of the ALS electronics by Manasa/SURFs

The sensing noise levels of the ALSs looks the same as before.

The intensity noise of the transmission was also checked. They are not RIN but very close to RIN
as the DC was the unity for both arms.

The X arm has worse ALS noise level and RIN.
Although I forgot to turn off the HEPA flow at the south bench during the measurement. Gurrr.

  2667   Thu Mar 11 15:24:51 2010 steveMetaphysicsEnvironmentIFO was well protected


There is a planned power outage tomorrow, Saturday from 7am till midnight.

I vented all annulies and switched to ALL OFF configuration. The small region of the RGA is still under vacuum.

The vac-rack: gauges, c1vac1 and UPS turned off.

 It turns out that we perfecly timed the big one

In the process of finding the signal of the big chilean earthquake I just realized that we were all off

  16441   Sun Oct 31 14:21:31 2021 ranaHowToTreasureIFOCad

IFOcad model/video of the AEI 10m interferometer:


  729   Thu Jul 24 01:04:01 2008 robConfigurationLSCIFR2023A (aka MARCONI) settings


P.S.: We made a test by changing the frequency of the local oscillator by a little bit and then coming back to the original value. We observed that the phase of the signal can change, so every time this frequency is moved the 3f demod phase need to be retuned.

We discovered this little tidbit in March, and remembered it tonight. Basically we found that whenever you change the frequency on one of these signal generators (and maybe any other setting as well), the phase of the signal can change (it's probably just the sign, but still...), meaning that you when you return settings to their intial value, not everything is exactly as it once was. For most applications, this doesn't matter. For us, where we use one Marconi to demodulate the product of two other Marconis, it means we can easily cause a great deal of grief for ourselves, as the demod phase for the double demod signals can appear to change.

Programmatically, what this means is that every time you touch a Marconi you must elog it. Especially if you change a setting and then put it back.
  16833   Thu May 5 17:05:31 2022 TegaUpdateBHDIMC & X/Y-arm alignment

[Yuta, Tega]

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


IMC alignment:

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


Y-arm alignment:

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


X-arm alignment:

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

  17189   Thu Oct 13 23:25:22 2022 ranaUpdateIMCIMC ASC: summary pages and notes

Tega has kindly made a summary page for the IMC WFS. Its in a tab on the usual summary pages.

One thing I notice is that the feedback to MC2 YAW seems to have very little noise. What's up with that?

The output matrix (attached) shows that the WFS have very little feedback to MC2 in YAW, but normal feedback in PIT. Has anyone recalculated this output matrix in the past ~1-2 years?

I'm going to read Prof. Izumi's paper (https://arxiv.org/abs/2002.02703) to get some insight.

The output matrix doesn't seem to have any special thing to make this happen. Any ideas on what this could be?

  17190   Thu Oct 13 23:52:45 2022 KojiUpdateIMCIMC ASC: summary pages and notes

The output matrices have been calculated on Aug 4, 2022 by me. [40m ELOG 17060]

Regarding the noise see [40m ELOG 17061]

With regard to the current IMC WFS design, a SURF student in 2014 (Andres Medina) and Nick Smith made the revision.
The telescope design was described in the elogs [40m ELOG 10410] [40m ELOG 10427] and also T1400670.

  14818   Tue Jul 30 20:11:12 2019 ranaSummaryIMCIMC ASC: thoughts and hopes

One of the biggest challenges in LIGO is reducing the alignment control noise. If you haven't worked on it for at least a few years, it probably seems like a trivial problem. But all versions of LIGO since 2001 have been limited by ASC noise below ~50 Hz.

I think the 40m IMC is a good testbed for us to try a few approaches towards mitigating this noise in LIGO. The following is a list of steps to take to get there:

  1. Using step responses and TF measurements, characterize the full existing system: SISO loop shapes, cross-couplings, and how diagnonal is the input and output matrices of the WFS. In principle, since we have 2 WFS in reflection and 1 DC QPD in the MC2 transmission, we should have full sensing of all angular DoFs.
  2. Check the correct operation of the WFS heads and the whole RF chain. We want the gains in the system to be such that either the shot noise or the RF electronics noise of the head is the limiting broadband noise in the system.
  3. Balancing the gains and phases of the demodulated signals is tricky, because we have no good reference. Should we use the JenneAM laser or the PSL beam?
  4. Estimate the coupling from the angular feedback signal to the IMC length noise using (1) sine wave injections for linear coupling, and (2) broadband noise for nonlinear coupling.
  5. We think the bilinear noise is due to the beam spot motion modulating the angle to length coupling as sensed by the laser beam. If this is true, we can increase the low frequency gain to minimize the beam spot motion (is this true?).
  6. By sinusoidally driving the mirror angles we can measure the instantaneous beam spot positions. We can then derive the matrix required to convert from our angular sensors (WFS + QPD) into beam spot motion. We should modify our IMC-WFS real-time model to give us DAQ channels which are beam spot estimators.
  7. Build a simulation of an IMC which has WFS, QPD, shot noise, and seismic noise.
  8. Use our optimal linear-feedback design tools to make Angular loops which minimize the bilinear noise coupling.
  9. Build a nonlinear controller (neural networks: dense + CNN) that outperforms the linear one by estimating the beam spot motion continuously and driving the cavity length to cancel the angle-to-length noise. 

I think that steps 1-6 are well within our existing experience, but we should do it anyway so as to reduce the IMC beam motion at low frequencies, and also to reduce the 10-100 Hz frequency noise as seen by the rest of the interferometer.

Steps 7-8 are medium hard, but we can get some help from the CSWG in tackling it.

Step is pretty tough, but I would like to try it and also get some help from MLWG and CSWG to address it.

  12820   Fri Feb 10 18:21:21 2017 gautamUpdateIMCIMC Demod board

Rana and I spent some time looking at the IMC demod board earlier today. I will post the details shortly, but there was a label on the front panel which said that the nominal LO level to the input should be -8dBm. The new 29.5MHz routing scheme meant that the LO board was actually being driven at 0dBm (that too when the input to the RF distribution box was attenuated by 5dB).

An elog search revealed this thread, where Koji made some changes to the demod board input attenuators. Rana commented that it isn't a good idea to have the LO input be below 0dBm, so after consulting with Koji, we decided that we will

  • Remove the 5dB attenuator to the input of the distribution box such that the LO is driven at ~5dBm
  • Remove the input 10dB attenuator, first ERA-5SM amplifier, and the mini circuits power splitter from the demod board (schematic to follow).

After implementing these changes, and testing the board with a Marconi on the workbench, I found that the measured power levels (measured with an active FET probe) behave as expected, up till the ERA-5SM immediately prior to the LO (U4 and U6 on the schematic). However, the power after this amplifier (i.e. the input to the on-circuit LO, Minicircuits JMS-1H, which we want to be +17dBm), is only +16dBm. The input to these ERA-5SMs, which are only ~2years old, is -2dBm, so with the typical gain of +20dB, I should have 18dBm at their output. Moreover, increasing the input power to the board from the Marconi doesn't linearly increase the output from the ERA-5SM. Just in case, I replaced one of the ERA-5SMs, but observed the same behaviour, even though the amplifier shouldn't be near saturation (the power upstream of the ERA-5SM does scale linearly).

This needs to be investigated further, so I am leaving the demod board pulled out for now...

  12821   Fri Feb 10 19:32:15 2017 KojiUpdateIMCIMC Demod board

The input impedance of the mixer is not constant. As the diode switches, it changes dynamically. Because of this, the waveform of the LO at the mixer input (i.e. the amplifier output) is not sinusoidal. Some of the power goes away to harmonic frequencies. Also, your active probe is calibrated to measure the power across the exact 50Ohm load, which is not in this case. The real confirmation can be done by swapping the mixer with a 50Ohm resistor. But it is too much. Just confirm the power BEFORE the amp is fine. +/-1dB does not change the mixer function much.

Instead, we should measure
- Orthogonality
- Gain imbalance
of the I/Q output. This can be checked by supplying an RF signal that is 100~1kHz away from the LO frequency and observe I&Q outputs.

  17242   Tue Nov 8 10:35:26 2022 AnchalUpdateSUSIMC F2A test

This time the test was succesful but I have reverted MC3 f2a filters back to with Q=3, 7, and 10. The inital part of the test is still useful though. I'm attaching amplitude spectral density curves for WFS control points and C1:IOO-MC_F_DQ in the different configurations. The shaded region is the 15.865 percentile to 84.135 percentile bounds of the PSD data. This corresponds to +/- 1 sigma percentiles for a gaussian variable. Also note that in each decade of freqeuncy, the FFt bin width is different such that each decade has 90 points (eg 0.1 Hz bin width for 1Hz to 10 Hz data, 1 Hz binwidth  for 10 Hz to 100 Hz and so on.)

The WFS control points do not show any significant difference in most of the frequency band. The differences below 10 mHz are not averaged enough as this was 30min data segments only.

C1:IOO-MC_F_DQ channel also show no significant difference in 0.1 Hz to 20 Hz. Between 20-100 Hz, we see that higher Q filters resulted in slightly less noise but the effect of the filters in this frequency band should be nothing, so this could be just coincidence or maybe the system behaves better with hgiher Q filters. In teh lower frequency band, we would should take more data to average more after shortlisting on some of these f2a filters. It seems like MC1 Q=10 (red curve) filter performs very good. For MC2, there is no clear sign. I'm not sure why MC2 Q=3 curve got a big offset in low frequency region. Such things normally happen due to significant linear trend presence in signal.

I'm not sure what other channels might be interesting to look at. Some input would be helpful.

  16089   Wed Apr 28 10:56:10 2021 Anchal, PacoUpdateSUSIMC Filters diagnosed

Good morning!

We ran the f2a filter test for MC1, MC2, and MC3.


The new filters differ from previous versions by a adding non-unity Q factor for the pole pairs as well.

\frac{f^2 - i \frac{f_z}{Q}f + f_z^2}{f^2 - i \frac{f_0}{Q}f + f_0^2}
This in terms of zpk is: [ [zr + i zi, zr - i zi], [pr + i pi, pr - i pi], 1] where
z_r = -\frac{f_z}{2Q}, \quad z_i = f_z \sqrt{1 - \frac{1}{4Q^2}}, \quad p_r = -\frac{f_0}{2Q}, \quad p_i = f_0 \sqrt{1 - \frac{1}{4Q^2}}, \quad f_z = f_0 \sqrt{G_{DC}}

  • Attachment #1 shows the filters for MC1 evaluated for Q=3, 7,and 10.
  • Attachment #2 shows the filters for MC2 evaluated for Q=3, 7, and 10.
  • Attachment #3 shows the filters for MC3 evaluated for Q=3, 7, and 10.
  • Attachment #4 shows the bode plots generated by foton after uploading for Q=3 case.

We uploaded all these filters using foton, into the three last FM slots on the POS output gain coil.


We ran tests on all suspended optics using the following (nominal) procedure:

  1. Upload new input matrix
  2. Lower the C1:IOO-WFS_GAIN to 0.05.
  3. Upload AC coil balancing gains.
  4. Take ASD for the following channels:
    • C1:IOO-MC_WFS1_PIT_IN1
    • C1:IOO-MC_WFS1_YAW_IN1
    • C1:IOO-MC_WFS2_PIT_IN1
    • C1:IOO-MC_WFS2_YAW_IN1
  5. For the following combinations:
    • No excitation** + no filter
    • No excitation + filter
    • Excitation + no filter
    • Excitation + filter

** Excitation = 0.05 - 3.5 Hz uniform noise, 100 amplitude, 100 gain


  • Attachment 5-7 give the test results for MC1, MC2 and MC3.
  • In each pdf, the three pages show ASD of TRANS QPD, WFS1 and WFS2 channels' PIT and YAW, respectively.
  • Red/blue correspond to data taken while F2A filters were on. Pink/Cyan correspond to data taken with filters off.
  • Solid curves were taken with excitation ON and dashed curves were taken with excitation off.
  • We see good suppression of POS-> PIT coupling in MC2 and MC3. POS->YAw is minimally affected in all cases.
  • MC1 is clearly not doing good with the filters and probably needs readjustement. Something to do later in the future.
  15902   Thu Mar 11 08:13:24 2021 Paco, AnchalUpdateSUSIMC First Free Swing Test failed due to typo, restarting now

[Paco, Anchal]

The triggered code went on at 5:00 am today but a last minute change I made yesterday to increase number of repititions had an error and caused the script to exit putting everything back to normal. So as we came in the morning, we found the mode cleaner locked continuously after one free swing attempt at 5:00 am. I've fixed the script and ran it for 2 hours starting at 8;10 am. Our plan is to get some data atleast to play with when we are here. If the duration is not long enough, we'll try to run this again tomorrow morning. The new script is running on same tmux session 'MCFreeSwingTest' on Rossa

10:13 the script finished and IMC recovered lock.

Thu Mar 11 10:58:27 2021

The test ran succefully with the mode cleaner optics coming back to normal in the end of it. We wrote some scripts to read data and analyze it. More will come in future posts. No other changes were made today to the systems.

  16679   Thu Feb 24 19:26:32 2022 AnchalUpdateGeneralIMC Locking

I think I have aligned the cavity, including MC1 such that we are seeing flashing of fundamental mode and significant transmission sum value as well.However, I'm unable to catch lock following Koji's method in 40m/16673. Autolocker could not catch lock either. Maybe I am doing something wrong, I'll pickup again tomorrow, hopefully the cavity won't drift too much in this time.

  16685   Sun Feb 27 00:37:00 2022 KojiUpdateGeneralIMC Locking Recovery


- IMC was locked.
- Some alignment change in the output optics.
- The WFS servos working fine now.
- You need to follow the proper alignment procedure to recover the good alignment condition.

- Basically followed the previous procedure 40m/16673.
- The autolocker was turned off. Used MC2 and MC3 for the alignment.
- Once I hit the low order modes, increased the IN1 gain to acquire the lock. This helped me to bring the alignment to TEM00
- Found the MC2 spot was way too off in pitch and yaw.
- Moved MC1/2/3 to bring the MC2 spot around the center of the mirror.
- Found a reasonably good visibility (<90%) at a MC2 spot. Decided this to be the reference (at least for now)

SP Table Alignment Work
- Went to the SP table and aligned the WFS1/2 spots.
- I saw no spot on the camera. Found that the beam for the camera was way too weak and a PO mirror was useless to bring the spot on the CCD.
- So, instead, I decided to catch an AR reflection of the 90% mirror. (See Attachment 1)
- This made the CCD vulnerable to the stronger incident beam to the IMC. Work on the CCD path before increasing the incident power.

MC2 end table alignment work
- I knew that the focusing lens there and the end QPD had inconsistent alignment.
- The true MC2 spot needs to be optimized with A2L (and noise analysis / transmitted beam power analysis / etc)
- So, just aligned the QPD spot using today's beam as the temporary target of the MC alignment. (See Attachment 2)

Resulting CCD image on the quad display (Attachment 3)

WFS Servo
- To activate the WFS with the low transmitted power, the trigger threshold was reduced from 5000 to 500. (See Attachment 4)
- WFS offset was reset with /opt/rtcds/caltech/c1/scripts/MC/WFS/WFS_RF_offsets
- Resulting working state looks like Attachment 5

  11795   Sat Nov 21 00:46:33 2015 KojiUpdateIOOIMC OLTF

Here is the comparison before and after the fix.

Before the work, the UGF was ~40kHz. The phase margin was ~5deg. This caused huge bump of the frequency noise.

After the LO power increase, I had to reduce the MC loop gain (VCO Gain) from 18dB to 6dB. This resulted 4dB (x2.5) increase of the OLTF. This means that my fix increased the optical gain by 16dB (x6.3). The resulting UGF and phase mergin were measured to be 117kHz and 31deg, respectively.


Now I was curious to see if the PMC err shows reasonable improvement when the IMC is locked. Attachment 2 shows the latest comparison of the PMC err with and without the IMC locked. The PMC error has been taken up to 500kHz. The errors were divided by 17.5kHz LPF and 150kHz LPF to compensate the sensing response. The PMC cavity pole was ignored in this calculation. T990025 saids the PMC finesse is 4400 and the cavity pole is 174kHz. If this is true, this also needs to be applied.


1. Now we can see improvement of the PMC error in the region between 10kHz to 70kHz.

2. The sharp peak at 8kHz is due to the marginally stable PMC servo. We should implement another notch there. T990025 suggests that the body resonance of the PMC spacer is somewhere around there. We might be able to damp it by placing a lossy material on it.

3. Similarly, the features at 12kHz and 28kHz is coming from the PMC. They are seen in the OLTF of the PMC loop.

4. The large peak at 36kHz does not change with the IMC state. This does mean that it is coming from the laser itself, or anything high-Q of the PMC. This signal is seen in the IMC error too.

5. 72kHz, 108kHz, 144kHz: Harmonics of 36kHz?

6. Broad feature from 40kHz to 200kHz. The IMC loop is adding the noise. This is the frequency range of the PC drive. Is something in the PC drive noisy???

7. The feature at 130kHz. Unknown. Seems not related to IMC. The laser noise or the PMC noise.

Remaining IMC issues:

Done (Nov 23, 2015) - 29.5MHz oscillator output degraded. Possibly unstable and noisy. Do we have any replacement? Can we take a Marconi back from one of the labs?

Done (Nov 23, 2015) - Too high LO?

- Large 36kHz peak in the IMC

- IMC loop shape optimization

- IMC locking issue. The lock streatch is not long.

- IMC PC drive issue. Could be related to the above issue.

Maybe not relevant - PC drive noise?

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