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ID Date Author Type Category Subjectup
  478   Thu May 15 10:40:21 2008 steveHowToGeneralLisa Goggin, PhD
Lisa Goggin successfully defended her thesis on May, 13 2008

"A Search For Gravitational Waves from Perturbed Black Hole Ringdowns in Ligo Data"

She started out as a surf student in the 40m.

Congratulation!
Attachment 1: lisa.JPG
lisa.JPG
  7247   Wed Aug 22 01:54:03 2012 JenneUpdateGeneralList o' things: YarmASS, ETMXTcamera, POXwhiteningTriggering

While meditating on other things, I have noticed / found the following today:

YARM ASS works okay.  Yesterday I measured the sensing matrix for the ASS for both arms (although I forgot to copy one of the matrix elements to my text file for Xarm - needs remeasuring).  I put the Yarm matrix in (after appropriate inversion, only non-zero pitch-to-pitch, yaw-to-yaw elements).  I turned on the Yarm ASS, and  the yaw converged pretty quickly (couple of minutes), with gains of -1 in the servos, overall gain of anywhere between 0.005 and 0.010.  The pitch took much longer, and I had to 'pause' several times by turning off the overall gain for the yarm ass when the MC lost lock (which has happened several times tonight - unknown cause).  Eventually, the pitch settled out, and quit changing, but the lockin outputs weren't zero, even though the error signal for the servos were almost zero (gains for the pitch servos were -0.5, overall gain ~0.005 was better than 0.01 - higher gain caused oscillations in the lockin outputs).  I think this means that I need to remeasure the yarm pitch ass matrix.  It's still much, much faster to just turn on the dithers, watch the striptool of the lockin outputs, and align the cavity by hand.

I think the ETMX Trans camera view is clipped a little bit.  I went down there, and it doesn't seem to be on the last optic before the camera, and moving the spot on the camera doesn't change the shape of the image, so I don't think it's on the camera.  We should look into this, since it's either clipping on the BS that separates some camera beam from the TRX beam, or TRX is getting a clipped beam too.  If the clipping is any earlier in the Trans path, the Trans QPD could also have some clipping.  This requires investigation.  The xarm trigger needs to be reset/disabled so we don't lose lock every time we block the TRX beam (as was happening to me).

XARM really doesn't like to relock unless the POX whitening is turned off.  Good flashes, doesn't really catch (10+ min waiting (while working on Yarm stuff) ).  After turning off the whitening, it catches almost immediately. Even though it's on the to-do list to rethink the tuning of our whitening, we should probably implement the whitening triggering now anyway.  It'll make things easier.

The double integrator that Rana implemented in the X and Y arm servo filters last week take 8 seconds to turn off (due to Foton settings), so even though they are triggered to turn off immediately upon lockloss, they sit around and integrate for 8 seconds, so have huge signals.  If the cavity flashes and the locking trigger engages during that 8 seconds, we send a huge kick to the ETMs.  I'm modeling the response of the filters to an impulse and noise, particularly in the case of ramping on the double integrators.  The problem is that a flat filter has 0deg phase, but the double integrator has 180deg phase at low frequencies, so there's some weird sign flipping that can happen as we ramp - this is part of what I'm modeling.

MC is losing lock unusually often tonight.  Everything on the servo board screen looks normal (which is good since that's all set by the autolocker).  I just disabled the test exc in, but that's been left enabled for a while now, and it hasn't (I think?) been a problem since there shouldn't be anything connected to the board there.  PMC transmission is a little low, 0.816, and FSS is starting to get near -1 on the slow actuator adjust, but we've seen locking of the PMC problems around -1.5 or -2 of the FSS, and the adjust value was at -0.8 earlier tonight and we still had MC locking problems.  I have had the seismic channels open on Dataviewer for the last several hours, and I'm not seeing any spikes in any of the Guralp channels which correspond to the times that the MC loses lock.  BLRMS don't seem particularly high, so MC lockloss cause is still a mystery for today.

The ETMX monitor selector on the VIDEO screen seems not to be switching the actual camera that's shown on the monitor.  Using the script command itself works, so my screen is wrong.

  11190   Wed Apr 1 16:52:02 2015 JenneUpdateLSCList of measurements

I'd like to get a concrete list of measurements written down, so that it's clear what needs to be done before I graduate.

Noise couplings:

  • Laser amplitude noise coupling to DARM
    • We don't have an AOM for ISS right now, but we should be able to just stick it back in the beam path, right?  I think Koji checked that the AOM was all okey-dokey recently.
    • AOM calibration should tell me how much the single-pass amplitude changes as a function of input signal.
  • Laser frequency noise coupling to DARM
    • Inject signal at the CM board input, which should be calibrated by looking at response to calibrated MC2 motion.
  • Marconi phase noise coupling to DARM
    • Marconi can produce internally or accept via BNC 0-10 rad of phase modulation.  Marconi spec sheet should give me rad/V for the input calibration.
  • Marconi amplitude noise coupling to DARM
    • Using external input of Marconi.  Marconi spec sheet should give me input calibration.
  • MICH err to DARM
    • Compare with Optickle model
  • PRCL err to DARM
    • Compare with Optickle model

Noise cancellation:

  • PRC angle
  • MICH noise removed from DARM (compare flat gain FF vs. Wiener FF)
  • PRCL noise removed from DARM (compare FF shape from model vs. Wiener FF)
  • MC length noise (equiv. to laser freq noise) removed from CARM & DARM

Are there things that I'm missing?  I've never had an IFO to characterize before.

  14582   Sun Apr 28 16:00:17 2019 gautamUpdateComputer Scripts / ProgramsList of suspension test

Here are some tests we should script.

  1. Checking Coil Vmons, OSEM PDmons, and watchdog enable wiring
    • Disable input to all the coil output filter modules using C1:SUS-<OPTIC>_<COIL>_SWSTAT (this is to prevent the damping loop control signals from being sent to the suspension)
    • Set ramptimes for these filter modules to 0 seconds.
    • Apply a step of 100 cts (~15 mV) using the offset field of this filter module (so the test signal is being generated by the fast CDS system).
    • Confirm that the step shows up in the correct coil Vmon channel with the appropriate size (in volts), and that other Vmons don't show any change (need to check the sign as well, based on the overall gain in this filter module).
    • Confirm that the largest response in the PDmon signals is for the same OSEM. There will be some cross-coupling but I think we always expect the largest response to be in the OSEM whose magnet we pushed provided the transimpedances are the same across all 5 coils (which is true except for PRM side), so this should be a robust criterion.
    • Take the step off using the watchdog enable field, C1:SUS-<OPTIC>_<COIL>_COMM. This allows us to confirm the watchdog signal wiring as well.
    • Reset ramptimes, watchdogs, input states to filter modules, and offsets to their pre-test values.
    • This test should tell us that the wiring assignments are correct, and that the Acromag ADC inputs are behaving as expected and are calibrated to volts.
    • This test should be done one channel at a time to check the wiring assignments are correct.
  2. Checking the SUS PD whitening
    • Measure spectrum of individual PD input (fast CDS) channels above 30 Hz with the whitening in a particular state
    • Toggle the whitening state.
    • Confirm that the whitened sensor noise above 30 Hz is below the unwhitened case (which is presumably ADC noise.
    • This test should be done one channel at a time to check the wiring assignments are correct.

Checking the Acromag DAC calibration is more complicated I think. There are measurements of the actuator calibration in units of nm/ct for the fast DACs. But these are only valid above the pendulum resonance frequency and I'm not sure we can synchronously drive a 10 Hz sine wave using the EPICs channels. The current test which drives the PIT/YAW DoFs with a DC misalingment and measures the response in the PDmon channels is a bit ad hoc in the way we set the "expected" response which is the PASS/FAIL criterion for the test. Moreover, the cross-coupling between the PDmon channels may be quite high. Needs some thought...

  10126   Wed Jul 2 22:58:11 2014 JenneUpdateLSCLittle Bo-Peep has found her phase

Never mind.  This is just the low pass filter that Den put in to try to deal with the moving cavity pole. 

Before I realized this, just in case it was a computer quirk, Koji and I rebooted the end station front end machines.  This had no effect other than to keep me searching and measuring until I figured it out.  If I turn off the low pass, the phase pops back up to very close to the reference.  The low pass currently comes on automatically as part of the carm_cm_up script.

  10125   Wed Jul 2 21:30:42 2014 JenneUpdateLSCLittle Bo-Peep has lost her phase
Little Bo-Peep has lost her phase,
And can't tell where to find it;
Leave it alone, and it'll come home,
Bringing its degrees behind it.
 
Seriously.  What?  I was holding CARM on sqrtTrans with arm powers of about 1, DARM was still ALS diff, PRMI on REFL33.  CARM was actuating on +ETMX+ETMX, since I kept kicking the MC out of lock, but other than that, everything was set by the carm_cm_up script, so I don't think there should be any big differences.  I took a CARM transfer function, and it seems like the phase bubble has all but disappeared compared to the reference from mid-May. 

CARM_loop_ArmPowers1_2July2014.pdf

I need to figure this out before it's worth trying any acrobatic AO path turn-on scenarios.

 

Also this evening, I went to the Yend and did another tweak-up of the green beam alignment. 

  2284   Tue Nov 17 21:09:17 2009 Jenne, ranaUpdateGeneralLittle Thorlabs Photodiode

[Rana, Jenne]

We opened up the little Thorlabs battery operated PD to see what was inside.  Rana took some pictures, and I drew a schematic (attached).  It's just a diode, biased with a battery (albeit a crazy 22.5V battery).

---------------
Comment by KA: PD is Hamamatsu S1223-01 Si PIN diode.


What a crazy battery. The main point is that it looks like this can be used for reasonable purposes: uses a load resistor on the BNC connector and you can use some pre-amp (e.g. Busby box or SR560) to have a low noise PD readout. You can also use the SR560 in its A-B mode as an 'opamp'. Ground the A input and the use a pole at 1 Hz and make the Output go into the B input through some large series resistor. The BNC from the PD gets Teed into the B input as well.

Then this becomes a transimpedance circuit readout of the diode, using the current noise of the SR560 as the limit.

Attachment 1: ThorlabsPD.png
ThorlabsPD.png
  6511   Mon Apr 9 17:03:38 2012 DenUpdateEnvironmentLms vs Wiener

I tried to figure out why offline LMS filter subtract seismic noise much better from MC_F then the Wiener filter. I did the calculations twice - with my codes and with Matlab in-build functions, the results are the same. So this is not a code error.

The coherence between GUR 1, 2 and MC_F is still poor. Wiener filter is linear and its performance is confined to the frequency ranges where we see coherence. Lms filter is non-linear and it may be possible to subtract the noise even if non-linear effects are present in the system.

gur12_mcl.png

I've checked seismometer readout box again. I've soldered 50 Ohms to plus and minus inputs to VERT 1,2 N/S 1,2, E/W 1,2 - GUR 1 and 2 use these channels. Then I put the box back and connected it to the ADC.

seismboxnoise.png

The plot shows that the readout box noise is below the ADC noise. It is possible that amplifiers introduce non-linear effects. To check this I plotted the coherence between OSEM sensors and GUR1X signal:

gur1_osem.png

The coherence between OSEM sensors and GUR1X is pretty good, so may be witness path is not responsible for low coherence at 0.1 - 0.5 Hz between MC_F and GUR 1,2. IT seems that MC_F is bad at low frequencies. I terminated the input to the Channel 1 of the Pentek Generic board, where MC_F is plugged in.

mcl_noise.jpg

ADC is also good. Something else is wrong.

  10543   Fri Sep 26 11:44:55 2014 nicolasFrogsComputer Scripts / ProgramsLoaded larry's fake filter into C1:ALS-OFFSETTER2

 Larry and Nicolas

Larry's transfer function measurements suddenly started returning 0dB 0degrees when before there was some fake filter in the C1:ALS-OFFSETTER2 filter bank.

We looked in the filter bank and his filter was gone. So I created a new filter called LARRYP in FM2. We also disabled the output so he could drive the filter bank and test his TF code.

  15633   Mon Oct 19 15:38:42 2020 KojiUpdateElectronicsLoan: A file binder "40m wiring diagram"

I'll bring a file binder "40m wiring diagram" to home at the next chance.
There is another one on the shelf in the control room.

(I thought I put it in my bag, but it looks like that I left it somewhere around the fax area)

  10122   Wed Jul 2 15:35:34 2014 ericqUpdateComputer Scripts / ProgramsLocal Chiara backups

Koji has provided a 2TB USB3 external hard drive that will get daily backups of chiara:/home/cds, the idea being that if the internal HD at /dev/sdb1 fails, we can physically open the external up, and swap the hard drive into chiara. 

We're running an rsync job on it right now, which should be done in a few hours. (USB3 is fast!)

I've also written a backup script at scripts/backup/rsync_chiara.backup which keeps its books in scripts/backup/rsync_chiara.backup.log 

I'm adding a entry to the root crontab on chiara to execute the script every day at 7am. 

 

  10236   Fri Jul 18 15:21:12 2014 ericqUpdateComputer Scripts / ProgramsLocal Chiara backups

Quote:

I've also written a backup script at scripts/backup/rsync_chiara.backup which keeps its books in scripts/backup/rsync_chiara.backup.log 

I'm adding a entry to the root crontab on chiara to execute the script every day at 7am. 

 I had some syntax errors in the script that prevented the script from doing the right thing. The backup is now up to date, and the cronjob should work. 

  15167   Tue Jan 28 17:36:45 2020 gautamConfigurationComputersLocal EPICS7.0 installed on megatron

[Jon, gautam]

We found that the caput commands were taking much longer to execute on megatron than on pianosa (for example). Suspecting that this had something to do with the fact that megatron was using EPICS binaries from the shared NFS drive which were compiled for a much older OS, I installed the latest stable release of EPICS on megatron. The new caput commands execute much faster. I also added the local EPICS directory to the head of the $PATH variable used by the MC autolocker and FSS Slow scripts, so that they use the new caput command. But mcup is still slow - maybe my new path definition isn't picked up and it is still using the NFS binaries? To be looked into...

Quote:

There were a bunch of medm processes stalled on megatron (connected with screenshot taking). To see if they were interfering with the other scripts, I killed all of the medm processes, and commented out the line in the crontab that runs the screenshots every 10 mins. Let's see if this improves stability.

  390   Fri Mar 21 17:01:21 2008 ranaConfigurationDMFLocale change on Mafalda & seisBLRMS restart
Ever since we moved the accelerometers to be around the MC and changed their names, the seisBLRMS
has not been working. I tried to restart it today after fixing the channel names in the par file
but I ran into a PERL / UBUNTU bug.
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LC_TIME = "en_US.ISO8859-1",
        LC_MONETARY = "en_US.ISO8859-1",
        LC_CTYPE = "en_US.ISO8859-1",
        LC_COLLATE = "en_US.ISO8859-1",
        LC_MESSAGES = "C",
        LC_NUMERIC = "en_US.ISO8859-1",
        LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I don't know how this crept up or when it started. There were a bunch of fixes on the Ubuntu
forums which didn't work.

In the end I just set the 'unset' environment variables via our cshrc.40m file and this seemed
to make ligotools/perl happy. Lets hope this lasts...I love Linux.
  9360   Thu Nov 7 14:39:49 2013 JenneUpdateLSCLock Acquisition Game Plan

Between the 40m meeting, and chatting with Gabriele, there was lots of talking yesterday about our 40m Lock Acquisition game plan. 

From those talks, here is my current understanding of the plan, in a Ward-style cartoon:

 LockAcquisition_7Nov2013.pdf(This is a 2 page document - description of steps is on 2nd page)

If you look closely, you will notice that there are several places that I have used "?" rather than numbers, to indicate what RFPD signal we should be using.  To fill these in, I need to look at some more simulations, and think more carefully about what signals exist at what ports, and what SNR we have at each of those ports.

Also, while the overall scale of the arm power plot is correct, the power level at each step is totally arbitrary right now, and should just be taken to mean places (in time) where the CARM offset is reduced a little more.


There are several things at this point that we know we need to look into:

* POP 22/110 PD and filtering electronics should be switched to a broadband PD, rather than the Thorlabs PD + Miniciruits filters. (Hardware)

* Whitening for the transmission QPDs needs to be thought about more carefully. (Calculation, then hardware)

* Chose a good SNR REFL DC signal, which may or may not be from the PD we are currently using (I think it's the DC of REFL11, but I'll have to check). (Calculation)

* For DRMI locking, what is the size of the SRCL error signal at AS55, AS165, and the REFL ports?  Do we need to lock with AS port, and then switch over to a REFL 3f port, to make acquisition easier?  (Simulation)

* Similarly, I want to make the equivalent of Figure 3 of T1000294, with our 40m parameters. (Simulation)

* To set the phase of AS110, simulate the demod phase of AS110 in both DRMI and SRMI cases.  If no (significant) change, maybe we can set the phase in the real system by misaligning the PRM, and watching the SRMI flash.  (Simulation)

* Simulate an arm sweep, up to many orders of the sidebands, to see how close to the carrier resonance any sideband resonances might be.  If something like the 4th order sideband resonates, and then beats with a 1st order sideband, is that signal big enough to disturb our 3f locking of the PRMI / DRMI?  We want to be holding the arms off resonance with ALS closer to the carrier than any "important" sideband resonances (where the definition of "important" is still undetermined).  (Simulation)

* Check if we can hand DARM from the DC transmission signals to the final RF signal while we still have a large CARM offset. Is there a point where the CARM offset is too large, and we must be still using the DC signals? (Simulation)

* At what arm power level can we transition from ALS to IR DC transmission signals for the individual arms? (Simulation)

* Still need to finish calculating what could be causing our big arm power fluctuations (Test mass angular motion?  PRM angular motion? ALS noise?) (Calculation)


Replys, and comments are welcome, particularly to help me understand where I may have (likely did) go wrong in drawing my cartoon. 

  10998   Wed Feb 11 00:07:54 2015 ranaUpdateLSCLock Loss plot

Here is a lock loss from around 11 PM tonight. Might be due to poor PRC signals.  \oint {\frac{\partial PRCL}{\partial x}}

This is with arm powers of ~6-10. You can see that with such a large MICH offset, POP22 signal has gone done to zero. Perhaps this is why the optical gain for PRCL has also dropped by a factor of 30 crying.

This seems untenable no. We must try this whole thing with less MICH offset so that we can have a reasonable PRCL signal.cool

Attachment 1: 1107673198.png
1107673198.png
  15348   Tue May 26 02:15:36 2020 gautamUpdateLSCLock acquisition portal entry

Summary:

Provided the IMC is cooperative, the input pointing isn't drifting, and the RF offsets aren't jumping around too much, the locking sequence is now pretty robust.

Details:

Most of the analysis uses data between the GPS times 1274418176 and 1274419654 that are recorded to frames.

  15349   Tue May 26 02:31:00 2020 gautamUpdateLSCLock acquisition sequence

Here, I provide some details of the sequence. Obviously, I am presenting one of the quickest transitions to the fully locked state, I don't claim that every attempt is so smooth. But it is pretty cool that the whole thing can be done in ~3 minutes.

See Attachment #1 for the labels.

  • A --- Arms are locked on POX/POY, and EX/EY lasers are also locked to their respective arms. The phase tracker outputs are averaged in preparation for transitioning control from POX/POY to ALS. 
  • B --- Aforementioned transition has been realized. CARM offset of -4 is applied. Based on this calibration, this is ~ 4 nm.
  • C --- PRM is aligned in preparation for 3f vertex locking. Between C and D, the long pause is because I also use this time to DC couple the ITM Oplev servos, which requires some averaging. 
  • D --- PRMI is locked. CARM offset reduction begins. Between D and E, I scan CARM through a resonance, and look at the necessary offset requried in the CARM_B (=RF) path. It is a mystery to me why this is required.
  • E --- Ramp CARM offset completely to 0. Twiddle CARM_A and DARM_A offsets (=ALS path) to maximize the arm transmitted powers. Between E and F, you can see that the arm powers stabilize somewhat before any RF control is engaged (more on this later), which means we are approximately in the linear regime of the CARM PDH signal, and the switchover can be effected. As I write this, I wonder if there is any benefit to normalizing the REFL_11 error signal (=CM_SLOW) by the arm transmission for a broader capture range?
  • F --- CARM_B and DARM_B (=RF) paths engaged. I ramp off the ALS servos between F and G using a 10 second ramptime.
  • G --- IFO is now under RF control, ALS control has been turned off completely.
  • H --- Rudimentary ASC is enabled. The ITMs are already running with DC coupled Oplev servos, and for the ETMs, I use the Transmon QPDs. The loop shapes/gains for this part haven't been finalized yet, but some improvement in the stability is seen.

This particular lock held for ~20 minutes so I could run some loop characterization measurements etc.

I am struggling to explain:

  1. Why POP22 goes to 0 when we zero the CARM offset? The arm length is such that the 2f fields don't experience any abrupt changes in reflectivity from the arm cavity for a wide range of offsets. This signal is the trigger signal for the PRMI LSC control - right now, I get around this problem by mixing in some amount of POP DC once the PRMI is locked. But if the lock is lost, this requires some EPICS button gynmastics to try and salvage the lock... I guess the 1f field components experience a different phase on reflection at various offsets, so maybe I should be looking at sqrt(POP22_I^2 + POP22_Q^2) instead of just POP22_I.
  2. Why is an error point offset required in the CARM RF path?
Attachment 1: PRFPMIlock_1274418200_1274418550.pdf
PRFPMIlock_1274418200_1274418550.pdf
  15360   Wed May 27 20:14:51 2020 KojiUpdateLSCLock acquisition sequence

I see. At the 40m, we have the direct transition from ALS to RF. But it's hard to compare them as the storage time is very different.

  15364   Wed Jun 3 01:34:53 2020 gautamUpdateLSCLock acquisition update portal

Highlights:

  • With better ASC servos implemented, I think the lock stability has been improved. 
  • Arm transmission of ~350 was stably maintained (PRG~20, overcoupled). It went as high as 410, so this is now very close to the highest (~425) I've ever managed to get.
  • I was trying to get the vertex transitioned to 1f control but it remains out of reach for now.  The noise at ~100 Hz is dominated by MICH-->DARM coupling (as judged by coherence, I haven't yet done the broadband noise injection characterization). I figured I'd try the 1f transition before thinking about feedforward.
  • The biggest problems remain flaky electronics (poor IMC duty cycle, jumping RF offsets, newly glitchy seismometer, ...)

Details:

  15369   Wed Jun 3 03:29:26 2020 KojiUpdateLSCLock acquisition update portal

Woo hoo!

Which 1f signals are you going to use? PRCL has sign flipping at the carrier critical coupling. So if the IFO is close to that condition, 1f PRCL suffers from the sign flipping or large gain variation.

  15371   Wed Jun 3 11:40:56 2020 gautamUpdateLSCLock acquisition update portal

For these initial attempts, I was just trying to transition MICH to REFL55Q. I agree, the PRCL situation may be more complicated.

Which 1f signals are you going to use? PRCL has sign flipping at the carrier critical coupling. So if the IFO is close to that condition, 1f PRCL suffers from the sign flipping or large gain variation.

  11443   Fri Jul 24 13:49:09 2015 SteveUpdatesafetyLock doors please !

Thursday morning I found the control room emergency exit not locked.

Please check the doors when leaving the lab , specially when you are the last one out.

  8376   Fri Mar 29 19:56:02 2013 GabrieleMetaphysicsLSCLock of PRMI on sidebands

I finally managed to get long stretches of PRMI lock, up to many minutes. The lock is not yest very stable, it seems to me that we are limited by some yaw oscillation that I could not trace down. The oscillation is very well visible on POP.

Presently, PRCL is controlled with REFL55_I, while MICH is controlled with AS55_Q. This configuration is maybe not optimal from the point of view of phase noise couplings, but at least it works quite well. I believe that the limit on the length of locks is given by the angular oscillation. I attach to this entry few plots showing some of the lock stretches. The alignment is not optimal, as visible from a quite large TEM01 mode at the dark port.

Here are the parameters I used:

MICH gain -10   PRCL gain -0.1

Normalization of both error signal on POP22_I with factor 0.004

Triggering on POP22: in at 100, out at 20 for both MICH and PRCL.

POP55 demodulation phase -9

MICH and PRCL control signal limits at 2000 counts

 

There is a high frequency (628 Hz) oscillation going on when locked (very annoying on the speakers...), but reducing the gain made the lock less stable. I could go down to MICH=-1.5 and PRCL=-0.02, still being able to acquire the lock. But the oscillation was still there. I suspect that it is not due to the loops, but maybe some resonance of the suspension or payload (violin mode?). There is still some room for fine tuning...

Lock is acquired without problems and maintained for minutes.

Have a nice week-end!

Attachment 1: lock_prmi5.pdf
lock_prmi5.pdf
Attachment 2: lock_prmi6.pdf
lock_prmi6.pdf
Attachment 3: lock_prmi7.pdf
lock_prmi7.pdf
Attachment 4: oscillation.pdf
oscillation.pdf
Attachment 5: lock_prmi8.pdf
lock_prmi8.pdf
  8378   Sun Mar 31 17:26:32 2013 ranaUpdateLSCLock of PRMI on sidebands

 

 Our first move has to be fixing the whitening switching for REFL55. That's the configuration we need to start and then move onto REFL165 to get to FPPRMI.

  8380   Mon Apr 1 09:25:35 2013 JenneMetaphysicsLSCLock of PRMI on sidebands

[Gabriele, Jenne]

I put a notch in FM10 for both MICH and PRCL at 628Hz, to try to prevent us from exciting the mode that Gabriele saw on Friday.  Since those filter banks were all full, I have removed an ELP50 (ellip("LowPass",4,1,40,50)).  I write it down here, so we can put it back if so desired.

  6509   Mon Apr 9 15:02:30 2012 JenneUpdateLSCLocked MICH

I was going to try some locking, but things are a little too noisy. 

Just so Kiwamu knows what I did today, in case he comes back....

I ran LSCoffsets, and aligned both X and Y arms and saved their positions, and aligned MICH, and saved the BS position. 

I'll play with it more later, when there aren't trucks driving around outside that I can hear / feel in the control room.

  6510   Mon Apr 9 15:09:34 2012 JenneUpdateLSCLocked MICH

Quote:

I was going to try some locking, but things are a little too noisy. 

Just so Kiwamu knows what I did today, in case he comes back....

I ran LSCoffsets, and aligned both X and Y arms and saved their positions, and aligned MICH, and saved the BS position. 

I'll play with it more later, when there aren't trucks driving around outside that I can hear / feel in the control room.

 After giving up on locking, the MC is getting unlocked every now and again (2 times so far in the last few minutes) from transient seismic stuff.

  58   Fri Nov 2 12:18:47 2007 waldmanSummaryOMCLocked OMC with DCPD
[Rich, Sam]

We locked the OMC and look at the signal on the DCPD. Plots included.
Attachment 1: 071102_OMC_LockedDCPD.gif
071102_OMC_LockedDCPD.gif
Attachment 2: 071102_OMC_LockedDCPD.pdf
071102_OMC_LockedDCPD.pdf
  17126   Thu Sep 1 09:00:02 2022 JCConfigurationDaily ProgressLocked both arms and aligned Op Levs

Each morning now, I am going to try to align both arms and lock. Along with that, sometime at towards the end of each week, we should align the OpLevs. This is a good habit that should be practiced more often, not only by me. As for the Y Arm, Yehonathan and I had to adjust the gain to 0.15 in order to stabilize the lock.

Attachment 1: Daily.pdf
Daily.pdf
Attachment 2: Daily.pdf
Daily.pdf
  4313   Thu Feb 17 11:51:14 2011 josephbUpdateCDSLockin filter names too long - broke loading

Problem:

Could not load filters into the C1:SUS-ETMX_LOCKIN1_SIG filter bank.

Reason:

Apparently the filter bank name was too long.  I'm not sure why this isn't caught by the real time code generator, I'm planning on asking Alex and Rolf about it today.

Solution:

Reduce the name of the components.  Basically LOCKIN1 needs to become something like LOCK1 or LIN1.

 

In related news, it looks like the initial filters are hard coded to be 2048 Hz.  Given that they start out empty they won't cause things to break immediately, and if you're editing the file you can update the rate as you add the filter.  I'll also bring this up with Alex and Rolf and see if the RCG can't be more intelligent about its filter generation.

 

  1316   Tue Feb 17 05:20:11 2009 YoichiUpdateLSCLocking
Since we excluded *.snap and *.req files from the svn control in the medm directory and these were not restored by the svn co, the burt part of the align/mis-align scripts were not working correctly this evening. So I recreated .req files and cooked up some mis-aligned .snap files.
After some cut-and-try work, I was able to run the dither alignment scripts fine.

Due to the above mentioned delay, the locking work started around midnight.

Tonight, the DD hand-off was not robust. I spent sometime to optimize this.
After the optimization, the locking proceeded to the DC CARM/DARM control state stably.
The CARM->MCL hand-off failed because the LSC-MC offset button was off.
I added a line to turn on the button in the ontoMCL script.
Today, the offloadMCF script worked fine.

Next, the cm_step script stumbled on the "ENGAGERIZING" of the AO path.
I got a hunch that the AO path might not be connected to the MC board.
Indeed, OMC_OSC_FM was connected to the IN2 of the MC board. Looks like it was used for the optimization of the modulation frequencies.
Probably I had the hunch because I did it Smile

I was able to increase the arm power up to 3.9.
The script failed when it tried to switch the CARM signal from TR_DC to SPOB_DC.
I haven't tackled on this issue yet.
  16247   Wed Jul 14 20:42:04 2021 gautamUpdateLSCLocking

[paco, gautam]

we decided to give the PRFPMI lock a go early-ish. Summary of findings today eve:

  1. Arms under ALS control display normal noise and loop UGFs.
  2. PRMI took longer than usual to lock (when arms are held off resonance) - could be elevated sesimic, but warrants measuring PRMI loop TFs to rule out any funkiness. MICH loop also displayed some saturation on acquisition, but after the boosts and other filters were turned on, the lock seemed robust and the in-loop noise was at the usual levels.
  3. We are gonna do the high bandwidth single arm locking experiments during daytime to rule out any issues with the CM board.

The ALS--> IR CARM handoff is the problematic step. In the past, getting over this hump has just required some systematic loop TF measurements / gain slider readjustments. We will do this in the next few days. I don't think the ALS noise is any higher than it used to be, and I could do the direct handoff as recently as March, so probably something minor has changed.

  1317   Wed Feb 18 03:17:40 2009 YoichiUpdateLSCLocking
Yoichi, Kakeru,

Last night, the cm_step script failed at the hand-off of CARM error signal from TR_DC to PO_DC.
This was fixed by reducing the PO_DC gain by a factor of 2.
Currently the script fails when changing C1:LSC-DEMOD_GAIN to zero.
To be honest, I don't fully understand the purpose of this step.
  15471   Sun Jul 12 02:42:01 2020 gautamUpdateLSCLocking (on rossa)

Main goals tonight were:

  1. Check if I can lock the interferometer by working on rossa - indeed, I could! It is much snappier than the ageing pianosa. The viewing angle of the CRT monitors from this corner isn't so good though.
  2. Measure step responses for the arm ASC loops to see if any insight can be gained into these loops. Analysis forthcoming...
Attachment 1: ASCsteps.png
ASCsteps.png
  1334   Tue Feb 24 02:23:40 2009 YoichiUpdateLockingLocking - MC board bad
Rob, Yoichi, Alberto, Kiwamu, Kakeru

We found that the OMC alignment feedback was on for the POS X loop even though the OMC was not locked.
This caused the PZT mirror to be tilted in yaw a lot. This was probably the reason for the mysterious shift in the AS beam last week, because the AS RF beam is picked up after this PZT mirror.
Rob aligned the OMC and we re-centered the AS PDs and the CCD.
This changed the DARM RF gain, so we changed it from 3 to 1. This gain used to be -1. It is still not understood why the polarity was changed.
The MC length was changed ? We should check the sideband transmission.

After this, we reached to the arm power 4. But the IFO loses lock immediately after the moving zero is turned off.
At this stage, the CARM loop bandwidth is supposed to be high enough that the moving zero is no longer necessary.
However, when we measured the MCL loop gain with several different AO path gains, the loop shape did not change at all.
This led us to suspect the AO path may not be connected. The cabling from the common mode board to the MC board seemed ok.
We tested the signal flow in the MC board using a signal generator and an oscilloscope.
Then we found that a signal injected to the IN2 (AO path) does not reach to the TP1A (right after the boost stages), though the signal is visible in the OUT2 (monitor BNC right after the initial amplifier (B-amp) for the AO path). The signal from IN1 (MC REFL) can be observed at TP1A. This means something is broken between the B-amp and the sum-amp in the AO path.
We will check the MC board tomorrow.
  15037   Wed Nov 20 01:07:18 2019 gautamUpdateLSCLocking - progress

Summary:

  1. CARM offset was reduced to 0 with the PRMI locked.
  2. TRY levels touched ~200 (Recycling gain ~10, IFO is still undercoupled).
  3. TRX level never went so high - I suspect QPD issues or clipping in the beampath.

Details:

  • Attachment #1 is a StripTool summary of the lock - encouragingly, the PRMI stayed locked for several 10s of minutes even when the CARM offset was brought to 0.
  • The MICH signal was pretty glitchy - we increased the gain of the MICH and PRCL loops and thought we saw some improvement, but needs more quantitative investigation.
  • Main differences in locking procedure today were:
    • Added some POPDC to the MICH/PRCL trigger elements in addition to POP22
    • Tried adding a DARM offset before doing the final steps of CARM offset reduction, and then zerod the DARM offset too.
  • The TRX level never went as high as TRY - even though on the CRT monitors, both arms seemed to saturate somewhat more evenly. Potentially the EX QPD needs a checkout, or there is some clipping in the in-air TRX path. Although, puzzilingly, the POXDC level never goes as high as POYDC either. So maybe the buildup is really lower in the XARM? For the daytime tomorrow.

Next steps:

  1. Check the EX QPD / TRX situation.
  2. Figure out how to make the PRMI lock more stable as I reduce the CARM offset.
  3. Start figuring out the CM board, as we'd want to do the handoff to RF at some point.
Attachment 1: PRFPMI.png
PRFPMI.png
  15038   Wed Nov 20 12:14:17 2019 gautamUpdateLSCLocking - progress

I took a look at the TRX/TRY RIN reported in the single arm POX/POY lock, and compared the performance of the two available PDs at each of the two ends. Attachment #1 shows the results. Some remarks:

  1. The noise performance of the two QPDs at each end isn't identical - is there some transimpedance gain difference?
  2. The lower plot shows the angular motion reported by each QPD when the arm cavity is locked. The EX QPD seems much more sensitive than the EY QPD.
  3. I estimate that in this condition, each photodiode is receiving ~20uW of power, corresponding to a shot noise limited RIN of ~10^-7. None of the photodiodes saturate this bound.
  4. There are some ND filters placed in front of the QPDs at both ends. Do we really need these ND filters? I estimate that for the highest buildups, we will have ~10kW * 15ppm * 0.5 ~75mW of power incident on the QPD, so ~20mW per segment. Assuming silicon responsivity of 0.2 A/W, a transimpedance of 1kohm would give us 4V of signal. But the schematic shows higher transimpedance. Do we still have the switching capability for this QPD?
Quote:

Next steps:

  1. Check the EX QPD / TRX situation.
Attachment 1: TRX_TRY_comparison.pdf
TRX_TRY_comparison.pdf
  15034   Mon Nov 18 21:04:38 2019 gautamUpdateLSCLocking - some ideas

Some ideas Koji suggested:

  1. Try approaching the CARM offset zero point "from the other side" - i.e. start with a CARM offset of the opposite sign (I typically use negative CARM offset).
  2. With the PRMI locked, try bringing one arm onto resonance while the other arm is held off resonance. 

For the second idea, it is convenient to be able to control the arms in the XARM/YARM basis as opposed to the CARM/DARM basis as we usually do when going through the locking sequence. After some fiddling, I am able to reliably execute this transition, and achieve a state where the FP arm cavities are resonant for the IR with the ALS beat note frequency being the error signal being used. Some important differences:

  1. The frequency actuator (ETM) is weaker in this case than in the CARM/DARM basis (where MC2 is the frequency actuator) due to the longer length of the arm cavity (and for ETMX, the higher coil driver series resistance). I had to twiddle the limits of the servo banks to accommodate this. 
  2. The ALS error signal is significantly noisier than POX/POY. Hence, the control signal RMS is often in danger of saturating the DAC range. I implemented a partial fix by adding a 1st order Butterworth LPF with 1kHz corner frequency. According to the model, this eats <5 degrees of phase at the desired UGF of ~150 Hz.
  1329   Fri Feb 20 03:52:23 2009 YoichiUpdateLockingLocking Tonight
Yoichi, Peter

Tonight, we had a problem with the DD hand off.
It failed when the RG filters of MICH for the bounce-roll modes are engaged.
The reason for the failure was that the MICH UGF was too low (~10Hz).
As in the Peter's elog entry, we found that the AS PDs are mis-centered.
Even after we fixed the centering, the MICH UGF was still too low. So we increased the MICH feedback gain by a factor of 10.
The reason for the gain decrease is unknown. It seems almost like the BS coils get weaker.
I checked the UGF of the BS OL loops. These are around 4Hz, so fine. We should check the HWP on the AP table tomorrow.

After the DD hand-off goes ok, the switching of DARM signal from DC to RF failed.
I found that the gain and the polarity of the RF signal were wrong.
AS166 is one of the PDs we found mis-centered (and re-centered). But how can you flip the sign of the signal ?

After this, the cm_step script goes until the activation of the moving zero, but fails when the arm power is increased to 0.7.
Also the ontoMCL script succeeds only 50% of the time.
  17087   Wed Aug 17 10:27:49 2022 CiciUpdateGeneralLocking X-arm AUX laser

TL;DR: Got the x-arm aux laser locked again and took more data - my fit on my transfer functions need improvement and my new method for finding coherence doesn't work so I went back to the first way! See attached file for an example of data runs with poor fits. First one has the questionable coherence data, second one has more logical coherence. (ignore the dashed lines.)

------------------------------------------------------------------------------------

  • The aux laser on the x-arm was still off after the power shutdown, so Paco and I turned it back on, and realigned the oplev of the ETMX - initial position was P = -0.0420, Y = -5.5391.
  • Locked the x-arm and took another few runs - was calculating coherence by I/Q demodulation of the buffers and then recombining the I/Q factors and then taking scipy.signal.coherence(), but for some reason this was giving me coherence values exclusively above 0.99, which seemed suspicious. When I calculated it the way I had before, by just taking s.s.coherence() of the buffers, I got a coherence around 1 except for in noisy areas of the data where it dropped more significantly, and seemed to be more correlated to the data. So I'll go back to using that way.
  • I also think my fits are not great - my standard error of the fits (calculated using the coherence as weight, see Table 9.6 of Random Data by Piersol and Bendat for the formula I'm using) are enormous. Now that I have a good idea that the UGF is between 1 - 15 kHz, I'm going to restrict my frequency band and try to fit just around where the UGF would be. 

--------------------------------------------------------------------------------

To do:

  • Reduce frequency band and take more data
  • Get fit with better standard error, use that error to calculate the uncertainty in the UGF!
Attachment 1: rpi_OLG_2022_08_16_17_00_41.pdf
rpi_OLG_2022_08_16_17_00_41.pdf
Attachment 2: rpi_OLG_2022_08_16_17_01_21.pdf
rpi_OLG_2022_08_16_17_01_21.pdf
  2583   Tue Feb 9 17:18:45 2010 josephbSummaryComputersLocking Y arm successful with fully replaced front-end for ITMY

We were able to lock the Y-arm using Megatron and the RCG generated code, with nothing connected to c1iscey.

All relevant cables were disconnected from c1iscey and plugged into the approriate I/O ports, including the digital output.  Turns out the logic for the digital output is opposite what I expected and added XOR bitwise operators in the tst.mdl model just before it went out to DO board.  Once that was added, the Y arm locked within 10 seconds or so.  (Compared to the previous 30 minutes trying to figure out why it wouldn't lock).

  9945   Tue May 13 03:30:10 2014 JenneUpdateLSCLocking activities - no progress

[Jenne, Rana, EricQ]

We tried a few times to engage the AO path while holding CARM on sqrtTrans and DARM on ALS, but failed every time.  Since we cannot stably hold lock at arm powers of 1, even though we were able to do so early last week, we think that we have a problem (obviously).  One noticeable thing is that while held with ALS, the Xarm transmission fluctuates almost full power.

As we were seeing late last week, the Xarm IR transmission while held with ALS was fluctuating wildly, whether we were locked on individual arms or on CARM/DARM. 

Tonight we took some out of loop spectra, with different HEPA settings, to see how that affected things.  It looks like HEPA at the nominal ~20% is okay, but anything higher than that starts to affect the Xarm beatnote sensing, while it mostly leaves the Yarm beatnote sensing okay.  Perhaps this is something that isn't tightened enough in the Xarm path, or something on a skinny floppy mount that needs to be more secure.

I am still a little confused though, why we don't see large power fluctuations in *both* arms while using ALS to control CARM/DARM.  Why are we not seeing this Xarm noise being fed back into the Yarm, through either the ETM via DARM, or common stuff via CARM actuating on MC2.

Note that the change at high frequency is because I switched from using non-DQ channels to DQ channels, so that's not anything to pay attention to.  The noise reduction we see is below about 20Hz.

ALS_outofloop.pdf


Rana pointed out that our POPDC level was very small.  We don't have screens for them, but the DC PDs have the same analog whitening as the RF PD signals do.  I changed C1:LSC-POPDC_WhiteGain.VAL from 0 to 11.  Now our POPDC while locked on sidebands is about 8,000 counts.

We also swapped the cables between the SR785 and the CM board around.  Now channel 2 of the 785 goes to TP2A, channel 1 goes to TP2B, and the source goes to EXCB.  This is so that we can break the AO loop with the disable switch just after the slow/fast split, and look at the transfer function before we close the loop. 

  10485   Wed Sep 10 02:53:32 2014 JenneUpdateLSCLocking activities - nothing new :(

[Jenne, EricQ]

No major progress today.  

I fixed a bug in my lockloss script that was asking it to start gathering data just after the lockloss, rather than some seconds beforehand.  Ooops.  Anyhow, with this handy-dandy plotting, I still don't know why we are losing lock when we have PRMI on REFL33, CARM on sqrtInvTrans, and DARM on AS55.  I don't see any oscillations, just the arm power drops off, and a moment later the POP power drops.  

For example, here is one of the best states we got to tonight.  Data for this is in ..../scripts/LSC/LocklossData/1094369700 .  You can re-create the plot by going to ..../scripts/LSC/LocklossData/  and doing ./PlotLockloss.py 1094369700 .  We had set the triggers for the trans PD/QPD such that we were using the QPD transmission signals the whole time (above trans of 0.2).  We saw that the noise at high frequency during low transmission powers for sqrtInvTrans as an error signal was higher using the QPDs than with the Thorlabs PDs, but that both cases are below the noise for ALS.  The arm powers were pretty steady above 3 for the last bit of this lock stretch.  I lost lock while trying to transition DARM over to AS55Q.  CARM was on sqrtInvTrans(QPDs), PRMI on REFL33 I&Q as usual.

LocklossZoom.png

 


Other things from this evening:

* When I was starting, I saw that when I locked the PRMI, the PRM was oscillating in pitch. Oscillation only happened when PRM pitch oplev was on.  I'm not sure what could have changed to make the oplev loop unstable, but the gain was 7.0, and now I have left it at 5.0.

* I recentered the PRM and ITMY oplevs.

* Plugged in the Yend PDH error monitor and pzt output monitors, since I forgot them last week.  Hopefully this will allow the Yend SLOW servo to work, and keep us away from the limits of the PZT range.

  10486   Wed Sep 10 02:59:42 2014 ericqUpdateLSCLocking activities - nothing new :(

Some small things I did tonight which did little to nothing to help:

  • I reset the offsets in the SQRTINV FMs to try and match the DC level of the ALS CARM error signal as best as possible, to avoid moving away from the set-point too much, as I was worried we were wandering into regions of too low optical gain. 
  • I turned off the WFS, and hand tweaked the MC alignment. The WFS loops / matrices definitely have some room for improvement, and I was worried that excess angular motion of the MC was coupling into CARM. MC refl is much calmer in the last ~1.5 hrs since I turned off the WFS. 

My main concern with tonights situation was the huge low frequency fluctuations of TRY while CARM/DARM locked on ALS. We saw this being very smooth very recently, but when one arm is fluctuating by multiple line widths, it isn't surprising that locks aren't stable. I want to know why the out of loop stability is so unpredictable. 

  6420   Wed Mar 14 23:02:09 2012 KojiUpdateLSCLocking activity

Kiwamu and Koji

The target is to realize DRMI or PRMI + one arm with ALS.

The focus of the night is to achive stable lock of the PRMI (SB resonant) with 3f signals.
Particularly, REFL165 is back now, we are aiming to see if any of the 165 signals is useful.

We made a comparison between  REFL33Q/REFL165Q/AS55Q to find any good source of MICH.
However, none of them showed a reasonable shape of the spectra. They don't have reasonable coherence between them.

Nonetheless, we have tried to lock the IFO with those REFL signals. But any of them were useful to keep the PRMI (SB resonant).
The only kind of stable signal for MICH was AS55Q as we could keep the PRMI locked.

  11180   Fri Mar 27 20:32:17 2015 KojiSummaryLSCLocking activity

- Adjutsed the IMC WFS operating point. The IMC refl is 0.42-0.43.

- The arms are aligned with ASS

- The X arm green was aligned with ASX. PZT offsets slides were adjusted to offload the servo outputs.

- I tried the locking once and the transition was successfull. I even tried the 3f-1f transition but the lock was lost. I wasn't sure what was the real cause.

I need to go now. I leave the IFO at the state that it is waiting for the arms locked with IR for the full locking trial.

  14974   Thu Oct 17 11:19:28 2019 gautamUpdateLSCLocking activity last night
  1. Tuning the MICH-->PRM output matrix element
    • Locked the PRMI with the carrier field resonant in the PRC.
    • REFL11 used to control PRCL, AS55 for MICH.
    • Turned on the sensing notches in the control filter bank. Drove a line in MICH at 311.10 Hz.
    • Tweaked the MICH-->PRM matrix element to minimize the coupling witnessed.
    • As shown in Attachment #1, the minimum coupling was found to be at the value -0.34 (the old value was -0.2655).
    • The minimum was very sharp. A 1% change from the optimum value increased the peak height by > x2. Is this reasonable?
  2. Some sensing matrix measurements: After tuning the output matrix element, I locked the PRMI (ETMs misaligned) in four configurations:
    • PRMI locked with carrier resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
    • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
    • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, REFL165_I used for MICH control (based on sensing matrix measurement and offsets from previous config).
    • PRMI locked with sidebands resonant. REFL33_I used for PRCL control, AS55_Q used for MICH control.
    • The attached GIF shows the evolution of the demodulated sensing lines as we move through configurations.
       
    • The actual PDFs are attached as a zip, Attachment #2.
  3. PRMI locking with arms under ALS control
    • The arm cavity lengths were controlled as usual with ALS. This system needs some noise budgeting.
    • I set the CARM offset to -8 (arbitrarily chosen, approximately equal to 20nm, but anyways well above the cavity linewidth).
    • Then I re-aligned the PRM, and attemped to lock the PRMI using the 3f settings determined with no arm cavities --> no success.
    • Tried locking using the 1f error signals instead - in this config, the lock could be established.
    • However, I saw that there was significant light on the AS camera, and I had to put in an offset into the MICH loop to make ASDC go as low as possible.
    • I guess it is possible that the ALS control wasn't precise enough and the leaked light to the dark port was because of differential reflectivity of the arm cavities?
    • Anyways, I ran a sensing matrix measurement with the interferometer in this configuration, and I found that the MICH signal in REFL165 had rotated significantly.
    • I also found that the 3f DC offsets in this configuration were ~5x greater than what was the case for the lock with no arm cavities.

This is as far as I got last night. The first step is to see how reliable the settings determined last night are, today. I don't understand how changing the output matrix element can have brought about such a significant change in the MICH/PRCL separation in all the RF photodiodes.

Attachment 1: MICH2PRCLnulling.pdf
MICH2PRCLnulling.pdf
Attachment 2: consolidatedSensingMatrices.pdf.zip
  8491   Thu Apr 25 10:19:10 2013 KojiSummaryLSCLocking activity on Apr 24th

Last night I worked on the several locking configurations:

General preparations / AS table inspection

- The AS beam looked clipped. I went to the AP table and confirmed this is a clipping in the chamber.
  This may be fixed by the invacuum PZTs.

Modulation frequency tuning

RFPD Mon of the MC demodulator was check with the RF analyzer. Minimized the 25.8MHz (=55.3-29.5MHz) peak by changing the marconi freq.
This changed the modulation freq from 11.066147MHz to 11.066134MHz. This corresponds to the change of the MC round-trip length from
27.090952m to 27.090984m (32um longer).

Michelson tests

- I wonder why I could not see good Michelson signal at REFL ports.

- I roughly aligned the Michelson. On the AP table, the RF analyzer was connected to the REFL11 RF output.
  By using "MAX HOLD" function of the analyzer, I determined that the maximum output of the 11.07MHz peak
  was -61.5dBm.

- I went to the demodboard rack. I injected -61dBm from DS345 into the RFEL11 demodboard. This produced
  clean sinusoidal wave with the amplitude of 4 count. The whitening gain was 0dB.

- The output from the PD cable was -64.0dBm. So there is ~2.5dB loss in the cable. Despite this noise, the demodulation
  system should be sufficiently low noise. i.e. the issue is optical

- The Michelson was locked with AS55Q. And the REFL11 error signals were checked.Fringe like feature was there.
  This suggested the scattering from the misaligned PRM. The PRM was further misaligned. Then some reasonable
  (yet still noisy) Michelson signal appeared. (Usual misaligned PRM is not at the right place)

  Q. How much scattering noise (spurious cavity between PRM and the input optics) do we have when the PRM is aligned?
  Q. Where should we put the glass beam dumps in the input optics?
  Q. Can we prepare "safe" misaligned place for the PRM with the beam dump?

- The Michelson was locked with REFL11Q. From the transfer function measurement, the gain difference between AS55Q (whitening gain 24dB)
  and REFL11Q was 32dB. The whitening gain was 0dB. In fact I could not lock the Michelson with the whitening gain 33dB (saturation???)
  The element in the Input matrix was 1, The gain of the servo was +100. BS was actuated.

Coupled cavity tests

- At least REFL11 is producing reasonable signals. So what about the other REFL ports? The Michelson signals in the other frequencies
  were invisible. So I decided to use three-mirror coupled cavity with the loss PRC.

- Aligned X arm, Misaligned ETMX, ITMY. Aligned PRM.

- Locked the PRM-ITMX cavity with REFL11 and REFL33.

- Aligned ETMX. If I use REFL11I for the PRC locking, I could not lock the coupled cavity. But I could with REFL33I.
  This is somewhat familiar to me as this is the usual feature of the 3f signal.

- The coupled cavity could be locked "forever". To realize this I needed to tweak the normalization factor from 1.0 to 1.6.
  Q. How does the coupled cavity change the response of the cavity? Can we compensate it by something?
  Q. Measure open loop transfer functions to check if there is any issue in the servo shapes.

- Transmission during the lock is 3.2 while the nominal TRX with PRM misaligned was 0.93.
  This corresponds to power recycling gain of 0.17.

 - X arm:

    - Source: POX11I, phase 79.5 deg, whitening gain 36dB
    - Input matrix: POX11I->1.0->XARM, Normalization TRX*1.60
    - XARM servo gain +0.8, actuation ETMX
    - XARM trigger 0.25 up, 0.05 down. XARM Filter trigger untouched.

- PRC: (sideband locking)
    - Source: REFL33I, phase -34.05 deg, whitening gain 30dB
    - Input matrix: REFL33I->1.0->PRCL, Normalization None
    - PRCL servo gain +4.0, actuation PRM
    - PRCL trigger None

- Same test for the Y arm. At the moment ETMY did not have the OPLEV.
  Same level of transmission (~3.3)

 - Y arm:

    - Source: POY11I, phase -61.00 deg, whitening gain 36dB
    - Input matrix: POY11I->1.0->YARM, Normalization TRX*2.1
    - YARM servo gain +0.25, actuation ETMX
    - YARM trigger 0.25 up, 0.05 down. YARM Filter trigger untouched.

- PRC: (sideband locking)
    - same as above

Sideband PRMI attempt

    - Now I got some kind of confidence on the REFL33 signal.
    - So I tried to get any stable setup for sb PRMI, then to find any reasonable MICH signals anywhere else than AS55Q.
    - With REFL33I(PRCL) & AS55Q(MICH), I got maximum ~10sec lock. It regularly locked. It was enough long to check
      the spectrum on DTT. But it was not enough long to find anything about the MICH signals at the REFL ports.

    - I tried REFL33Q for MICH. The lock was even shorter but could lock for 1~2 sec.

    Q. What is the cause of the lock loss? I did not see too much angluar fluctuation. The actuation was also quiet (below 10000).

- PRCL: (sideband locking)
    - Same as above except for
      - the PRCL servo gain +0.05, No limitter at the servo output.
      - Trigger POP22I (low pass filtered by LP10) 20 up, 3 down

- MICH:
    - AS55Q -24.125 24dB -> x1.0 -> MICH -0.7, No limitter -> ITMX/Y differential
    or
    - REFL33Q -34.05dB -> x2.0 -> MICH same as above
    - For both case, trigger POP22I (low pass filtered by LP10) 20 up, 3 down

 

At this point Jenne came back from dinner. Explained what I did and handed over the IFO.

  8500   Sat Apr 27 00:21:06 2013 KojiUpdateLSCLocking activity on Apr 26th

When I talked with Den via phone, he recommended to use the trigger and normalization with POP110I.
So I decided to try this approach. Also I investigated how the REFL33 signals are useful.

I could find the state where the PRMI(sb) locks regularly, although the lock is ~1min at most.

PRCL: REFL33I
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain 0.2~0.12 FM3, 4, 5, 6 always on, no triggered FMs
-> PRM

MICH: REFL33Q
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain -20 FM4, 5 always on, no triggered FM
-> ITMX (-1.0) and ITMY (+1.0)

I needed to tune the phase very precisely to reach this state. Also the alignment of the michelson and PRM
was very crtiical to acquire the lock.

Later in the same night I was plagued by PRM alignment drift. It seems that the PRM alignment is bistable or
slightly drifting in pitch. I had to align PRM continuously. When the PRMI is locked, the alignment fluctuation
was mainly in yaw. This was as people commented before.

Attachment 1: Screenshot.png
Screenshot.png
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