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ID Date Author Type Categoryup Subject
  9650   Wed Feb 19 00:35:23 2014 KojiUpdateLSCALS locked with LSC!

Great. I indeed disabled all of the triggers and the normalization during my trial but in vain.
So I'm curious this is actually because of the filter shape or not.

  9651   Wed Feb 19 01:33:03 2014 JenneUpdateLSCALS locked with LSC!

I am also not able to lock the ALS using the 'regular' LSC filters.  To figure out what filters were doing what, I made several comparison plots from Foton.

The first one is the progression of ALS locking, using the filters from ALS-XARM.  FM5 is always engaged, then FMs 2, 3, 6, 7, and 8, and finally FM 10 (the low frequency boost) is engaged.

ALS_XARM_LockingFilters.pdf

The next plot is a comparison between the ALS version of the filters, and the LSC-XARM equivalents. 

ALSvsLSC_AllLockingFilters.pdf

Finally, just so I remember which LSC filters do what, I made an equivalent of the first plot, but for the LSC filters.

LSC_XARM_LockingFilters.pdf

When I try to lock the Xarm ALS using the regular LSC filters, I'm getting an oscillation somewhere, that grows and eventually knocks me out of lock.  It looks from dataviewer to be in the ~few Hz range, but it's hard to see it in DTT, since I don't stay locked all that long once the oscillation starts.  (If I catch it, I can back off the gain and turn off the servo without losing lock, but if I don't turn off the servo, I inevitably push the ETM too hard and lose green lock to the arm.)  I tried engaging the 3.2 Hz resonant gain filter, and it just makes things oscillate sooner, so that's not a solution with the current filter designs. 

Also, I'm not able to lock the IR using the ALS version of the XARM filters.  I'll have to meditate more on the situation, but the filters seem to be different enough that there's no crossover at this point.

  9652   Wed Feb 19 03:07:22 2014 JenneUpdateLSCALS locked with LSC!

No more progress tonight.  I am still unable to lock the ALS using the regular LSC filters.  I went back to putting the ALS filters into the LSC filter banks, and locked both arms with ALS, and found their IR resonances. I then held them off resonance, and tried to lock PRMI with REFL 55 I&Q, with no success.  Just before locking the arms, I had redone the whole IFO alignment (lock arms in IR, ASS, lock and align MICH, lock and align PRMI), and the PRMI was flashing very nicely.  I'm not sure why I wasn't able to catch lock, except that perhaps 3 or 6 ALS offset counts isn't far enough away from the IR resonance to make the 1f signals happy. The MC lost lock, which I then took as a sign that it's time to go home. (I was hoping to do a quick PRMI + 2arms, and see that we don't lose PRMI lock.  I was going to catch lock with REFL55, then transition to REFL33, although if I had thought about it before the MC lost lock, I would have tried just catching lock with REFL33).

I restored the regular LSC filters for the X and Y arms, and locked the arms in IR just to make sure it's all honkey-dory.  Which, it's not quite.  I don't know why, but right now, neither arm wants its boost (FM9) enabled.  It's part of the restore script that FM9 is triggered along with the rest of the filters, but even if I turn on the filters manually, I can turn on all but FM9, and then when I turn on the boost, the arm falls out of lock. Same behavior for both arms.  Anyhow, they lock, and they seem okay modulo the boost not being able to engage.

  9654   Wed Feb 19 11:00:16 2014 ericqUpdateLSCSome Simulation Efforts

 Q EDIT: THIS IS WRONG. I LOCKED PRC ON THE CARRIER

 As Koji measured the other day: MICH and PRCL seem very degenerate in the 3f REFL PDs. 

I'm using this as a motivation to do some simulation in MIST and try to understand the best way to implement the 3F locking scheme. Hopefully my thinking below isn't nonsense...

First, I modeled the PRC with no arm cavities and the estimated cavity length I got with the PRM kick measurement, and looked at the REFL sensing matrix.

PRMISensingAsIs.pdf

This agrees with the observed degeneracy. I then modeled the case of the PRC length that gives coincident SB resonance, again with no arm cavities.

PRMISensingCoinc.pdf

Now there is good separation in REFL165. (REFL33 still looks pretty degenerate, however). This raised the question, "What does the angle between MICH and PRCL in REFL165 do as a function of macroscopic PRC length?" 

MICHvPRCLangle.pdf

  • We see ~90 degrees at coincident resonance
  • Shortening the cavity, which we did to account for the arms, quickly shrinks the angle
  • Presuming we moved to make the cavity 4cm shorter implies we had ~45 degrees between MICH and PRCL in REFL165 before the move. (Is this consistent with earlier observations?)

To me, this implies that locking the PRC on 3F from scratch won't be simple. However, the whole point of the PRC length choice is to have coincident SB resonance when the arms are resonating.

So: even if we're not spot on, we should be relatively close to the PRC length where having arms resonant gives us simultaneously resonant upper and lower sidebands, where MICH and PRCL should be orthogonal-ish. I.e. building up a little bit of IR power in the arms may start to break the degeneracy, perhaps allowing us to switch from 1F to 3F locking, and then continue reducing the CARM offset. 

So, I ultimately want to model the effect of arm power buildup on the angle between MICH and PRCL in the 3f PDs. This is what I'm currently working on. 

So far, I have reproduced some of the RC modeling results on the wiki to make sure I model the arms correctly. (I get 37.7949 m as the ideal arm length for a modulation freq of 11.066134 MHz vs. 37.7974m for 11.065399 MHz as stated on the wiki). Next, I will confirm the desired PRC length that accounts for the arms, and then look at the MICH vs PRCL angle in the REFL PDs as a function of arm power or detuning. 

ArmLengthChoice.pdf

  9655   Wed Feb 19 11:45:12 2014 JenneUpdateLSCScripts for ALS being modified

We need to change several scripts for use with the new ALS-in-the-LSC paradigm:

* Watch arms (to turn off ALS if we lose the beatnote, before pushing optics too hard)

* Find IR resonance

* Offset from resonance

None of these should be difficult, just changing the filter bank names to match the new ones (ex. LSC-XARM rather than ALS-XARM, and LSC-ALSX rather than ALS-OFFSETTER1). 

So far, I have changed the "find resonance" script (ALSfindIRresonance.py).  I believe, in principle, to first order, that my modifications should work, however I have not yet tested the script.  So.  If you use it, watch the output of the script and ensure it's doing what it ought.  I'll check it after the lunch meeting and update this log entry.  (I changed the name of the "OFSFILT" variable, line 26, and also modified line 114.  Both of those lines have comments on how to revert the changes).

I have also changed the "offset from resonance" script (ALSchangeOffset.py).  Again, since I'm not locking right now, I have not tested this script either.  So, pay attention if you need to use it, before I check it.  (I changed the name of the OFSFILT variable, and the check which arm logic around line 37.  Again, both of those lines have comments on how to revert the changes.)

  9656   Wed Feb 19 14:14:46 2014 ericqUpdateLSCSome Simulation Efforts

 Q EDIT: THIS IS WRONG. I LOCKED PRC ON THE CARRIER

Koji noted oddities in the sensing matrix results I had gotten; namely that the plots showed REFL33 not changing at all, when we know for a fact that this should not be the case. 

Gabriele lent his eyes to my code, and came up with the idea that the modulation depths I was using were maybe not ideal (.1 for both 11 and 55). This affects REFL33 in that it is not simply Carrier * 33Mhz + 11Mhz * -22Mhz but also 22MHz * 55MHz, etc. 

I got more realistic values from Jenne (0.19 for 11MHz and .26 for 55Mhz) and re-ran the code, with more realistic results. The behavior for 165 has remained the same, but the other signals are more well behaved. 

Moral of the story: the modulation depths affect the 3f signals in a complicated way.

PRMISensingAsIs.pdf

PRMISensingCoinc.pdf

MICHvPRCLangle.pdf

 

 

  9657   Wed Feb 19 16:42:08 2014 ericqUpdateLSCSome Simulation Efforts

Disregard previous ELOGs, I had the PRC locked on carrier 

Locked on the sideband, the MICH / PRCL angle is much less sensitive to the PRC length, and shouldn't in fact be as degenerate as we've seen in reality. 

SBLOCK_PRMISensingAsIs.pdfSBLOCK_MICHvPRCLangle.pdf

So, my simulations no longer provide any reason for the 3F signals to be so degenerate. 

  9658   Wed Feb 19 18:21:33 2014 manasaUpdateLSCScripts for ALS modified

Quote:

We need to change several scripts for use with the new ALS-in-the-LSC paradigm:

* Watch arms (to turn off ALS if we lose the beatnote, before pushing optics too hard)

* Find IR resonance

* Offset from resonance

None of these should be difficult, just changing the filter bank names to match the new ones (ex. LSC-XARM rather than ALS-XARM, and LSC-ALSX rather than ALS-OFFSETTER1). 

So far, I have changed the "find resonance" script (ALSfindIRresonance.py).  I believe, in principle, to first order, that my modifications should work, however I have not yet tested the script.  So.  If you use it, watch the output of the script and ensure it's doing what it ought.  I'll check it after the lunch meeting and update this log entry.  (I changed the name of the "OFSFILT" variable, line 26, and also modified line 114.  Both of those lines have comments on how to revert the changes).

I have also changed the "offset from resonance" script (ALSchangeOffset.py).  Again, since I'm not locking right now, I have not tested this script either.  So, pay attention if you need to use it, before I check it.  (I changed the name of the OFSFILT variable, and the check which arm logic around line 37.  Again, both of those lines have comments on how to revert the changes.)

Watch arms script (ALSdown.py) has been modified and now watches the LSC-$ARM filter module instead of the ALS-$ARM filter module. Threshold has been kept the same +/-5000 counts to the ETM suspensions. The script has been tested and works just fine. It exists in the same place scripts/ALS/.

Jenne's modified versions of ALSfindResonance.py and ALSchangeOffset.py were tested and work just fine.

  9659   Wed Feb 19 22:47:26 2014 JenneUpdateLSCALS locked using LSC model, Common & Diff transitioned to IR transmission signals

[Jenne, Koji, Manasa, EricQ]

Today we successfully locked the ALS using the LSC system, with filters that are good for both the IR PDH and the ALS locking.  We tried PRFPMI, but were unable to hold PRMI lock while the arms were held with ALS.  We combined the ALS signals into common and differential signals, and successfully transitioned over to a combined set of 1/sqrt(TRANS) signals for the common mode part of the lock (differential stayed with ALS). 


Locking the ALS using filters in the LSC system that are also good for IR PDH

The biggest difference between the ALS and LSC filters were the ones used for lock aquisition. At Koji's suggestion, I made FM5 of the LSC servos (for X and Y arms) the filter needed for ALS locking.  Then, I made FM4 into a combination of old LSC FM4 and FM5, as well as an inverse of the new FM5, so that when both FM4 and FM5 are engaged, the servo shape is the same as the old LSC.  I left the other LSC filters where they were.  I replaced the FM1 +6dB with the combined integrators (really, just gentle DC boosts) for the ALS, since we were never using this +6dB filter module.  The LSC resonant gain filter for the bounce mode also included a resgain for 18.5 Hz.  I don't know what that was for, and it was eating into phase that I needed, so I removed it.

The other filter that changed significantly was the Boost filter.  The ALS system had been using more DC gain than the LSC had.  However, the current ALS boost filter (in FM10 of the old ALS servos) was eating too much phase near my UGF.  So, I scooted the whole boost filter to lower frequencies, to give myself some extra phase margin.  The boost was set to "zero history", "zero crossing", with 0.01 tolerance and an 8 second timeout.  Setting it to zero crossing with a low tolerance, rather than just ramping it on, was the key to engaging the boost.

ALS_newVSoldBoosts.pdf

I had to be so careful about phase margin, since I lost ~15 degrees of phase at 200 Hz from the lag of going through the RFM network.  This was pretty frustrating, but I don't have a better plan yet, save moving the c1als model and ADC to the SUS machine, which has Dolphin access to the LSC.  I may back off my safety margin, and give myself some gain in the boost back at 10Hz, since we are now seeing too much noise at 10Hz in the closed-loop spectra.  I also "cheated" and lowered my UGF from the ~150Hz it used to be in the ALS model, to 100Hz, where I was closer to the top of the new phase bubble.

With the new filter situation, I was able to lock the Xarm (the one I was using for design work) with both IR and ALS.  To lock IR, the "restore" script still works. For the ALS, we should put in a separate "restore" script into the IFO_CONFIGURE screen. 

The ALS locking procedure is as follows:

* Prepare ALS and green locking.  Green locked to 00 mode, alignment all nice, etc, etc.  Beatnote within 100MHz on spectrum analyzer.  If doing both arms, try to get beatnotes on opposite sides of PSL, to keep crossbeatnotes at higher frequencies, and out of the way.

* Turn on Watch script.

* Set LSC parameters (this is where a new restore script will come in handy): 

       * Zeros in RFPD columns of input matrix (i.e. POX and POY).

       * Ones in AUX input matrix elements.

       * Zeros in power normalization matrix rows for arms.

       * All FM triggers for arms set to "Man" for manual.

       * Override main trigger, so that signals are always going through to the servo.

       * Only FM5 engaged in arm servo.

       * Gain of servo set to zero, output on, then engage main LSC master switch.  ETM output on.

* Clear history in phase tracker.

* Check sign of gain using + or - 0.1 in the servo.  You'll know if you got it wrong (the ETM will be kicked, and the beatnote will fly around).  If you didn't get it wrong, you probably got it right.

* Increase gain to about 12 (with correct sign).

* Engage FM1 (gentle DC boost), FM6,7,8 (resonant gains for stack, bounce, roll)

* Wait a few seconds for filters to settle, then engage FM9 (boost).

* Run find IR resonance script.

* Move off resonance by ~36 counts (12 times the +3 script).  This number comes from trying to be completely off the IR resonance, even when the PRMI was locked.

* Do whatever locking (ex. PRMI) you set out to do.


 PRFPMI attempt

After locking both arms with ALS using the LSC system, we attempted to lock the PRMI.  We were able to lock PRMI on REFL55 I&Q, REFL33 I&Q, and REFL55 I&AS55Q before the arms were locked, so we were hoping that we wouldn't have too much trouble.

We found the IR resonance for both arms, then moved off resonance.  Then, restored the PRM.  For REFL55, Koji coarsely turned the REFL 55 demod phase from 16 degrees to 87, while we were locked on the carrier.  After this, I stepped farther and farther from the IR resonance, since at first I found that our transmitted powers were something like 4, rather than almost zero, so the demod phase may not be totally correct.  

We were having trouble, so we locked the PRMI on carrier using REFL55 I and AS55 Q, with 1's in both elements in the input matrix.  MICH gain was about -10, PRCL +0.010.  We used this time to tweak up the alignment of the PRMI.  At some point, Koji tweaked the REFL33 demod phase from 124 to 134 degrees.  Then we switched back to sideband locking.  After some trials with REFL55 I&Q, and REFL55/AS55, we went to REFL33 I&Q.  REFL33I->PRCL was 1.556 in the input matrix, and REFL33Q->MICH was -0.487.  No other elements in the input matrix.  MICH gain was reduced to -6, PRCL gain to -0.020.  MICH FMs 3,6,9 triggered, PRCL FMs 2,3,6,8,9 triggered.  We were able to keep short locks on the order of ~10 seconds, but not longer. We played with every parameter we could think of (alignment being good is one of the most important!), but were not able to keep better lock.  The POP spot is moving around a lot, so the PRCL ASC needs to be examined, hopefully tomorrow.

We started losing the Xarm lock fairly regularly, I'm not sure why, but the Yarm was locked for almost 2 hours straight, held off resonance with ALS!


 ALS Common and Differential, transition to IR control

We set PRMI aside for the rest of the night, and looked at using ALS to control the arms in common and differential modes. 

Regular ALS locking procedures were used (see above), with the exception of the AUX input matrix:

  1/sqrt(TRX) 1/sqrt(TRY) ALSX ALSY
XARM (common) 0 0 +1 -1
YARM (differential) 0 0 +1 +1

 Since the beatnotes were on opposite sides of the PSL frequency, the common and differential modes look opposite of what you'd expect. 

We then used the regular find IR resonance scripts running simultaneously, which worked really well to find both arms' IR resonance points.

I put a 1 count offset in the Xarm servo (which was our proxy for common mode), although in retrospect this should have been +0.5 in ALSX, and -0.5 in ALSY, so that our signals going through the input matrix were at their zero crossings.  Anyhow, this offset put us at about half fringe on both arms (transmissions were about 0.6). 

Koji set the offsets in the 1/sqrt(trans) filter banks before the input matrix so that they would have zero crossings at this point (avg the IN1, put negative of that value into the offset). 

We then stepped the input matrix values until our common mode (Xarm) row was:

  1/sqrt(TRX) 1/sqrt(TRY) ALSX ALSY
XARM (common) -0.7 -0.7 0 0

We left the differential (YARM) row alone, so that the ALS system would still be controlling the differential degree of freedom.  The values and sign for the 1/sqrt(trans) signals came from a transfer function of dividing the spectra of each error signal and noting the relative gain and sign.

After we swapped the error signals, we realized that we had to remove the offset from the XARM servo, which is why we should have put the offsets elsewhere in the first place.

Then, Koji took a spectrum, which is attached to this entry.  We note that the ALS signals are strongly correlated, and mostly common. 


To Do List

Going forward, we need to figure out what is going on with the PRMI, and why we're having trouble keeping lock.

We need to redo the PRCL ASC servo, with the anti-oplev trick that Rana mentioned a week or two ago.

We need to investigate the degeneracy of REFL165, now that Q's simulation doesn't justify / explain it. 

Attachment 1: common_diff_ALS.pdf
common_diff_ALS.pdf
  9660   Fri Feb 21 12:45:57 2014 ericqUpdateLSCEquivalent Displacement Noise from QPD Dark Noise in SQRTINV

EQ UPDATE: Measured it wrong the first time, fixed now.

I measured the spectra of the SQRTINV channels from dark QPDs, with offsets adjusted to imitate various transmission levels. (While the dark noise stays constant in terms of, say, TRX counts, 1/sqrt(TRX) isn't linear, and so the noise coupling depends on the TRX offset). 

SQRTINVspectra.pdf

I did some calculations to turn this into the equivalent displacement noise when using SQRTINV as an error signal. This depends on where on the fringe you are locking, since the slope of SQRTINV vs. position is not constant, and can only really be treated as linear down to about 1/3 of a line width away from full resonance. In my calculations, I assumed a coupled arm line width of 38pm, and a full transmission of 700 counts in TRX/Y. 

The QPD dark noise RMS when two line widths away (TR = 40) is about 5fm, and only goes down from there. 

SQRTINV_DarkNoise.pdf

  9668   Tue Feb 25 00:00:01 2014 rana, jenneUpdateLSCreasons that the REFL signals may be degenerate now

We're exploring some effects which may give some funny macroscopic detuning and cause a near phase degeneracy in the REFL RF signals (see radar plot from Jenne below).

1) Alignment: we centered the oplevs to reduce fluctuations and then tweaked the BS and PRM alignment to build up the power. No significant change in the RF phases of the DOFs.

2) Measuring RAM: we set the dark offsets (by hand since the Masayuki script doesn't really work well anymore) to with 1 counts. We then locked the MC, misaligned the ITMs, and looked at the REFLOUT16 channels using the following command line:

z avg 12 C1:LSC-REFL11_I_OUT16 C1:LSC-REFL11_Q_OUT16 C1:LSC-REFL33_I_OUT16 C1:LSC-REFL33_Q_OUT16 C1:LSC-REFL55_I_OUT16 C1:LSC-REFL55_Q_OUT16 C1:LSC-REFL165_I_OUT16 C1:LSC-REFL165_Q_OUT16
C1:LSC-REFL11_I_OUT16     -12.04
C1:LSC-REFL11_Q_OUT16     -14.34
C1:LSC-REFL33_I_OUT16       0.43
C1:LSC-REFL33_Q_OUT16      -0.28
C1:LSC-REFL55_I_OUT16       2.84
C1:LSC-REFL55_Q_OUT16       5.64
C1:LSC-REFL165_I_OUT16      4.40
C1:LSC-REFL165_Q_OUT16      0.10

So these offsets are small in counts. In meters this corresponds to....less than 3 pm for any of the I signals.

Refl11I = 2.06e-12 meters

Refl11Q = 2.94e-10 meters

Refl33I = 5.28e-13 meters

Refl33Q = 1.07e-11 meters

Refl55I = 2.71e-12 meters

Refl55Q = 3.55e-11 meters

Refl165I = 3.07e-13 meters

Refl165Q = 8.63e-14 meters

 

 

3) Next we want to put large offsets into the error points of the loops

4) Change modulation depth

5) Check IMC length (todo for Q/Manasa for Tuesday - Wednesday)

  9669   Tue Feb 25 02:46:38 2014 rana, jenneUpdateLSCChanging PRCL offset changes REFL 165 degeneracy

[Jenne, Rana]

We put offsets in the PRCL and MICH loops, and measured sensing matrices for each condition. 

What we found was that PRCL offsets of order 1/20th a linewidth (calibration to be checked tomorrow) would give significant changes in the angles of the REFL signal sensing matrix elements.  We broke MICH lock before we were able to put in a significant enough offset to see the demod phases change.

Because there are so many plots, I've put them together in a pdf. Each page has a set of radar plots for sensing matrix elements.  On the bottom of each page I note what our MICH and PRCL offset values were, and where the data is saved (in the 40m scripts directory). To see the differences, make sure your pdf viewer is set to single-page, not scrolling.

PRC_offsetCheck_24Feb2014.pdf

One major thing that we noted was that putting in a PRCL offset also changed the MICH offset.  When we increased the PRCL offset, we saw the AS port get brighter (but not as bright as when we were putting in large MICH offsets). 

Tomorrow, I need to check the calibrations we were using, to see how many meters we were moving the optics.  Also, Q, Gabriele and I need to meditate and do some modelling to figure out why the length offset could be affecting the degeneracy so strongly. 

  9670   Tue Feb 25 14:48:49 2014 ericqUpdateLSCChanging PRCL offset changes REFL 165 degeneracy

After speaking with Jenne and Gabriele, I did a little bit of simulating based on my earlier code that looked at the angle of MICH vs. PRCL, just with cavity detuning instead of macroscopic length change.

The zero point in the following plots is with the PRC locked on the sideband. The PRC detuning was done by changing the PRM-BS microscopic length (in terms of phase), and the MICH detuning was done by adding half of the detuning to the BS-ITMY distance, and subtracting half of it from the BS-ITMX distance. 

MICHvPRCLangle_wOffset.pdf

 

This plot is in terms of radians, so to roughly relate it to line width, here's a plot of the POP powers as a function of the PRC detuning. 

SBprclPeaks.pdf 

  9671   Tue Feb 25 16:07:33 2014 ericqUpdateLSCChanging PRCL offset changes REFL 165 degeneracy

 And glossing over the MICH offset, here's the PRC offset plots in displacement, rather than radians.

The simulation is actually slightly different now. I now use nominal ITM T values (T=.014) instead of the random R=.99 I had in place. 

MICHvPRCLangle_wOffset.pdfMICHvPRCLangle_wOffset_fullscale.pdf

(correction: Field Power should be Field Amplitude in the first plot)

  9673   Tue Feb 25 17:27:41 2014 JenneUpdateLSCREFL signals calibrated

I have recalibrated the REFL signals.

I first adjusted the demod phases until the I-signals lined up with the I-phase in the sensing matrix plot:

SensMat_25Feb2014.png

I then balanced the ITM drives by pushing on -1*ITMX and +1.015*ITMY, and seeing a minimum of MICH actuation in the I-phase of REFL55 (the PD I was locking with).

I then took a nice long measurement with DTT, and measured the peak heights in I and Q for each REFL diode.  I was driving PRM with 100 cts at 675.1Hz, and ITMX with 1000 cts at 452.1 Hz (and matching ITMY drive, to make pure MICH).  Knowing these numbers, and the actuator calibrations (PRM elog 8255, ITMs elog 8242), I know that I was driving PRCL by ~4.3 pm, and MICH by ~23 pm. 

For the I-phase calibrations, I find the peak height at the PRCL drive frequency, and divide 4.3 pm by that height.  For the Q-phase calibrations, I find the peak height at the MICH drive frequency, and divide 23 pm by that height.

This gives me the following calibrations:

  Calibration [picometers / count]
REFL 11 I    0.15
REFL 11 Q   21.6
REFL 33 I    1.06
REFL 33 Q  209
REFL 55 I    0.9
REFL 55 Q   27       
REFL 165 I    0.1
REFL 165 Q   11.6

 My calibrated REFL spectra then looks like:

Calibrated_25Feb2014.pdf

  9674   Tue Feb 25 18:16:22 2014 JenneSummaryLSCEven more violin filters

A new violin mode at 1303 Hz was ringing up this afternoon.  Rana and I added a notch for this.

RXA: while the mode at 1303.6 Hz was ringing down, I used the narrowband DTT technique to measure the Q (after turning on the notch in SUS-PRM_LSC). So its another frequency in the PRM (not the BS).

The time that it takes for 2 -foldings is 652 s, which implies that Q = pi*f*tau = 1.3e6. This seems too high by a factor of ~10, so my guess is that there is still some feedback path happening. The previous bandstop filter was centered around 1285 Hz and seems also weird that the PRM would have 2 violin modes with such different frequencies. Is the mirror rotated around the optic axis such that the standoffs are not at the same height?

Attachment 1: PRMvio2.png
PRMvio2.png
  9676   Wed Feb 26 01:49:08 2014 JenneUpdateLSCChanging PRCL offset changes REFL 165 degeneracy

I have measured the sensing matrix at a variety of PRCL offset values.

DemodPhaseSeparation.pdf

During this each measurement, I also took a 20 second average of the POP 2f signals and the ASDC signal:

POP_AS_PDvalues.pdf

All of this data was taken during a single lock stretch. 

If / when I do this again, I want to go out to larger offsets.  I won't take as many points, but I do want to see how far I can go before I lose lock, and what the phase separation looks like at larger offset values (this time, I stopped at +700 counts which is about 0.7nm, to start checking the negative values. MC has been unhappy, so I wasn't able to take very many negative offset values.) 

I conclude that these sensing matrix measurements do see changes in the phase separation with PRCL length offset (what we saw / said yesterday), but that they do not line up with Q's simulation from this afternoon in elog 9671.

The simulation says that we shouldn't be seeing large phase changes until we get out to several nanometers, however the measurement is showing that we get large phase chnages with picometer scale offsets.  Yesterday, Rana and I said that the offsets due to RAM were small (of order picometer), and that they were therefore likely not important (elog 9668).  However, now it seems that the RAM is causing significant length offsets which then cause poor MICH/PRCL phase separation.

To Do List:

* Confirm MIST simulation with Optickle.

* Look at sensing matrix data pre-lockins (in the raw sensors).

* Check that there is no clipping anywhere in the REFL path (at least out of vacuum), and that the beam is sufficiently small on all 4 REFL diodes.

* Calculate the new PRC g-factor with the new length.

  9685   Mon Mar 3 17:35:10 2014 KojiUpdateLSCVarious demod phase measurement

I wanted to check how the refl signals looked like.
I decided to measure the demod phase where PRCL and MICH appear, one by one.

The method I used is to actuate PRCL or MICH at a fixed frequency and rotate the demod phase such that
the signal at the actuating frequency disappears.

For the PRCL actuation, PRM was actuated by the lock-in oscillator with the amplitude of 100cnt.
For MICH, the ITMX and ITMY was actuate at the amplitude of 1000cnt and 1015cnt respectively.

The script I used was something like this

ezcaread C1:LSC-REFL11_PHASE_R
ezcaservo -r C1:CAL-SENSMAT_CARM_REFL11_Q_I_OUTPUT C1:LSC-REFL11_PHASE_R -g 100 -t 60
ezcaread C1:LSC-REFL11_PHASE_R

"11" should be changed according to the PD you want to test.
"Q" should be changed to "I" depending on form which quadrature you want to eliminate the signal

The option "-g" specifies the servo gain. This specifies which slope (up or down) of the sinusoidal curve the signal is locked.
Therefore, it is important to flip the signal angle 180degree if a negative gain is used.


Note: Original phase settings before touching them

REFL11  - 19.2
REFL33   135.4
REFL55    48.0
RELF165 -118.5

 

Here in the measurement PRMI was locked with AS55Q (MICH) and REFL55I (PRCL)


Without no serious reason I injected a peak at 503.1Hz. This peak is not notched out by the servo. There may have been
some residual effect of the feedback loops.

PRCL: By elliminating the peak from the Q quadrature, we optimize the I phase for PRCL.

REFL11,   minimize PRCL in "Q", gain, -1, -19.3659 deg
REFL33,   minimize PRCL in "Q", gain, -1, 132.813 deg
REFL55,   minimize PRCL in "Q", gain, -1, 20.9747 deg
REFL165, minimize PRCL in "Q", gain, -1, -119.004 deg

MICH: By elliminating the peak from the I quadrature, we optimize the Q phase for MICH.
If PRCL and MICH appears at the same phase, the resulting angles shows an identical number.

REFL11,   minimize PRCL in "I", gain, -1, -28.4526 deg
REFL33,   minimize PRCL in "I", gain, -1, 65.9148 deg
REFL55,   minimize PRCL in "I", gain, -1, 12.4051 deg
REFL165, minimize PRCL in "I", gain, -0.1, -143.75 deg


Then, the signal frequency was changed to 675Hz where the notch filters in the servo is active.

PRCL: By elliminating the peak from the Q quadrature, we optimize the I phase for PRCL.

REFL11,   minimize PRCL in "Q", gain, 1, -19.5224 deg
REFL33,   minimize PRCL in "Q", gain, -1, 135.868 deg
REFL55,   minimize PRCL in "Q", gain, 1, 48.5716 deg
REFL165, minimize PRCL in "Q", gain, 1, -122.398 deg

MICH: By elliminating the peak from the I quadrature, we optimize the Q phase for MICH.
If PRCL and MICH appears at the same phase, the resulting angles shows an identical number.

REFL11,   minimize PRCL in "I", gain, -10, -73.7153 deg
REFL33,   minimize PRCL in "I", gain, -10, 135.5 deg
REFL55,   minimize PRCL in "I", gain, 10, -2.55868 deg
REFL165, minimize PRCL in "I", gain, -5, -156.135 deg


 

 

This is just a test of the REFL channels for the arms signals. ETMX or ETMY were actuated.

YARM

REFL11, minimize ETMY in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = 145.694
REFL55, minimize ETMY in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = -60.1512

XARM

REFL11, minimize ETMX in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = 142.365
REFL55, minimize ETMX in "Q", gain 100 => C1:LSC-REFL55_PHASE_R = -68.6521

  9687   Mon Mar 3 22:21:43 2014 KojiSummaryLSCPRMIsb locked with REFL165I&Q

Successful PRMIsb locking with REFL165I/Q

My previous entry suggested that somehow the REFL165 signals show reasonable separation between PRCL and MICH, contrary to our previous observation.
I don't know what is the difference now. But anyway I took this advantage and tried to lock sideband resonant PRMI.

REFL165I was adjusted so that the signal is only sensitive to PRCL. Then REFL165I and Q were mixed so that the resulting signal shows.
(Next time, we should try to optimize the Q phase to eliminate PRCL and just use the I phase for PRCL.

At first, I used AS55Q for lock acquisition and then switched the MICH input matrix to REFL165.
Later I found that I can acquire PRMI just turning on AS55Q without turning off REFL165.

The REFL165 MICH signal had an offset of 15cnt. The lock was more robust and the dark port was darker once the MICH input offset was correctly set.


MICH OFS = 0
Turn on AS55Q only / or AS55Q + REFL156I/Q
Once it is locked and all of the FMs are activated, give -15.0OFS to MICH.
Turn off AS55Q.

Input ports:
AS55       WHTN: 21dB  demod phase -5.5deg
REFL165 WHTN: 45dB demod phase -156.13deg

Input matrix:
AS55Q x1.00 MICH
REFL165I x-0.035 + REFL165Q -0.050 MICH

REL165Q x+0.14

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/6/7/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS -15.0 / Gain -10 / Limitter ON
PRCL OFS 0 / Gain -0.02 / Limitter ON

Output matrix:
MICH ITMX -1.0 / ITMY +1.0
PRCL PRM 1.0

 

  9688   Mon Mar 3 23:16:06 2014 ranaUpdateLSCY Arm Loop Shape found to be weird: changed now

 I was getting the Y Arm ready for Eric Q's loss measurements and so I looked at the noise and loop shape. The loop shape was strange:

Yarm_sweep_140303.pdf

You can see that the gain margin is too low at high frequencies. That's why we have >15 dB of gain peaking. Way too much! I think this is from Masayuki and Manasa increasing the phase margin at some point in the past. I lowered the gain by 3 dB from 0.1 to 0.07 and now the awful gain peaking is less. But what about the low frequency gain? Is there enough?

Yarm_sweep_140303b.pdf

yarm.pdf

I calibrated the OUT channel with 14 nm/count (1/f^2) with a Q = 10 pole pair at 1 Hz. The error signal is done to cross over at 180 Hz. It looks like the resonant gain at 25 Hz is a little too much and the in-loop RMS is 10 pm. Jenne says the linewidth is ~1 nm, so this seems sort of OK. Except that the LIGO-I DARM RMS had to be <0.1 pm for ~the same linewidth. Do we need to do better before trying to bring the arms into resonance?

I've remove FM1 and FM8. I put the RollRG of FM8 into the BounceRG and renamed it BounceRoll. Also changed the Y-arm restore so that RollRG and the 5,5:0,0 are no longer triggered automatically since the double integrator was overkill and we already have a 1:0 in FM2. I also lowered the peak gain for the roll mode RG from 30 to 10 dB because it was also overkill. We've gained a few more degrees at the UGF.

  9691   Wed Mar 5 11:33:10 2014 KojiSummaryLSC2 arm ALS->LSC transition - road map

Step by step description of transition from 2arm ALS to Common/Differential LSC for FPMI

- Step 0: Place the frequencies of the arm green beams at the opposite side of the carrier green.

- Step 1: Activate stablization loops for ALSX and ALSY simultaneously.
  (Use LSC filter modules for the control. This still requires correct handling of the servo and filter module triggers)

- Step 2: Activate stablization loops for ALS Common and Differential by actuating ETMX and ETMY

- Step 2 (advanced): Activate stabilization loops for ALS Common by actuating MC2 and ALS Differential by ETMX and ETMY

- Step 3: Transition from ALS Common to 1/SQRT(TRX)+1/SQRT(TRY). Make sure that the calibration of TRX and TRY are matched.
  The current understanding is that the offset for 1/SQRT(TRX)+1/SQRT(TRY) can't be provided at the servo filter. Figure out
  what is the correct way to give the offsets to the TR signals.

- Step 4: Lock Michelson with AS55Q and then POP55Q (PD not available yet) or any other PD, while the arms are kept off-resonant using ALS.

- Step 5: Reduce the TR offsets. Transition to RF CARM signals obtained from POP55I or REFL11I in the digital land.

- Step 5 (advanced): Same as test6 but involve the analog common mode servo too.

- Step 6: Transition from ALS Differential to AS55Q


Independent test: One arm ALS (To be done everyday)

- ALS resonance scan

- Measurement of out-of-loop displacement (or frequency) stability 

- Check openloop transer function


Independent test: Common Mode servo for one arm

- Reproduce Decmber CM servo result of transition from one arm ALS to CM servo
  Insert 1/sqrt(TRY) servo in between?

- How can we realize smooth transition from ALS to POY11?

  9692   Wed Mar 5 16:27:51 2014 ericqUpdateLSCPreliminary Arm Loss Measurements

I measured the arm cavity losses as Kiwamu did way back in ELOG 5074.

I used the same logic as the ../scripts/LSC/armloss script, but did it manually. This meant:

  1. Lock and ASS-Align both arms. 
  2. Misalign the ITM of the arm that I'm not measuring, to get its spot off of AS
  3. Take 10 seconds of ASDC_OUT data while the arm is locked. 
  4. Unlock, misalign ETM of arm of interest, take another 10 seconds of ASDC_OUT
  5. Relock, run ASS, goto #3

Analysis was done similar to ../scripts/LSC/armloss.m. This uses the nominal T values (.014 and 15e-6) to estimate the input power from the unlocked ASDC data, and the cavity reflectivity from the locked ASDC / input power. Then, loss is calculated by:

  • Pin = ASDC(unlocked) / R1
  • Rc = ASDC(locked) / Pin
  • rc=sqrt(Rc), etc.
  • Loss = 1 - (( 1 / r1r2)) * ( 1 - t1^2 r2 / (r1 - rc)) ^2

I did this for pairs of locked / unlocked data stretches. (Subsequent pairs maybe have slightly different things going on, but each pair was taken within a minute or so of each other)

Unfortunately, during the X Arm measurements, the MC was misbehaving with large REFL fluctuations, so I don't have confidence the results.

The Y Arm data seems fine, however. 

The Y arm loss is 123.91 +/- 10.47 ppm 

(Trial-to-Trial fluctuations dominate the fluctuations within each trial by far, and their standard deviation is what I report as the random error above)

This seems roughly in agreement with old values I've seen in the ELOG. I'll remeasure the x arm tomorrow during the day. Here's a plot showing the ASDC values of the Y Arm measurements. 

Yarm.pdf

  9693   Wed Mar 5 18:04:36 2014 ericqUpdateLSCEquivalent Displacement Noise from QPD Dark Noise in SQRTINV

At today's meeting, it was suspected that these noise levels were far too low. (ELOG 9660)

I've attached the math I did to get the conversions, as well as the dark noise SQRTINV spectra at various imitated transmission values and the python script that does the converting. 

I've gone over my calculations, and think they're self-consistent. However, a potential source of misestimation is the treatment of the Lorentzian profile simply existing with the coupled arm line width (38pm). The conversion to m/rtHz is directly proportional to the line width of the transmission peak, so if it is much broader in practice (because of imperfect PRC buildup or something), the noise will be that much worse.

I'm open to any other feedback about what I may have done wrong!

 

Attachment 1: calc1.jpg
calc1.jpg
Attachment 2: calc2.jpg
calc2.jpg
Attachment 3: SQRTINVspectra.dat.zip
Attachment 4: darkTransmonSpec.py
#! /usr/bin/env python
import numpy as np
import matplotlib.pyplot as plt

data = np.loadtxt('./SQRTINVspectra.dat')

# Coupled arm linewidth
w = 38e-12
# Lorentzian value at full resonance
I0 = 700
... 21 more lines ...
  9694   Wed Mar 5 19:15:39 2014 JenneSummaryLSCALS offset moving script modified

Quote:

- Step 3: Transition from ALS Common to 1/SQRT(TRX)+1/SQRT(TRY). Make sure that the calibration of TRX and TRY are matched.
  The current understanding is that the offset for 1/SQRT(TRX)+1/SQRT(TRY) can't be provided at the servo filter. Figure out
  what is the correct way to give the offsets to the TR signals.

 I have modified the script ALSchangeOffsets.py (in ..../scripts/ALS/) to also handle a "CARM" situation.  There is a new button for this on the ALS in LSC screen.  This script takes the desired offset, and puts half in the ALSX offset, and half in the ALSY offset.  Whatever offset you ask for is given the sign of the input matrix element in the ALS->CARM row of the input matrix.  For example, if you ask for a CARM offset of 1, and the matrix elements are ALSX->CARM=+1 and ALSY->CARM=-1 (because your beatnotes are on opposite sides of the PSL), you will get an offset of +0.5 in ALSX and -0.5 in ALSY, which should be a pure CARM offset. The offsets get set as expected, but I haven't had a chance to test it live while the arms are locked. 

I also want to write a script that will average the IN1 of the 1/sqrt(TR) signals, and put that number into the 1/sqrt(TR) offsets.  If this is run when we are at about half fringe, this will set the zero point of the 1/sqrt(TR) signals to the half fringe (or where ever we are).  Then, we need a script similar to the ALS CARM one, to put offsets into the CARM combination of 1/sqrt(TR)s. 

I think that putting the offsets in before the servo filters will mean that the signals coming out of the input matrices will already be at their zero points, so we won't have as much trouble shifting from ALS to IR.

  9696   Wed Mar 5 22:32:21 2014 manasaUpdateLSCStuck at step 2

Quote:

Step by step description of transition from 2arm ALS to Common/Differential LSC for FPMI

- Step 0: Place the frequencies of the arm green beams at the opposite side of the carrier green.

- Step 1: Activate stablization loops for ALSX and ALSY simultaneously.
  (Use LSC filter modules for the control. This still requires correct handling of the servo and filter module triggers)

- Step 2: Activate stablization loops for ALS Common and Differential by actuating ETMX and ETMY

I locked the arms using ALS error signals and the LSC filter modules. But when I try to acquire CARM and DARM using ALS, the arms lose lock when the matrix elements ALSX to Yarm and ALSY to X arm reach -/+0.9

What I did:

1. ALS locking of arms
(i) Found arm beat notes
(ii) Input matrix POX and POY elements set to '0'
(iii) Aux matrix elements ALSX to Xarm and ALSY to Y arm set to '1'
(iv) Power normalization matrix elements for TRX and TRY set to '0'
(v) Triggers for arm lock over ridden and the FM triggers were set to 'manual'
(vi) Arm servo gains set to '0'
(vii) All but FM5 were disabled
(viii) Phase tracker history reset and servo actuation set to ETMs
(ix) Servo gain increased in steps (+/-10 for the arms)
(x) FM1, FM6, FM7 enabled (see note 1 below)
(xi) FM9 enabled

Arms were locked with ~2000Hz rms

2. CARM and DARM locking
(i) Scanned the arms for IR resonance
(ii) Moved off-resonance (Stepped arm servo offsets by 30 counts)
(iiI) Stepped matrix elements ALSY to X arm and ALSX to Y arm ezcastep C1:LSC-PD_DOF_MTRX_6_29 +-0.1 C1:LSC-PD_DOF_MTRX_7_28 +0.1

Whenever the matrix elements reached -/+0.9, the arms were kicked out of lock. I don't see anything obvious as to why this is happening even after nearly 10+times of redoing.

Notes:
1. I found the filters for the arm servos different for X and Y. FM1 and FM8 were missing in one of the filter modules. Jenne remembered Rana modifying and removing the unnecessary filters in one arm. We put back FM1 (low pass filter) which might not be necessary for PDH lock but is necessary for ALS. FM8 is now added to FM7.
2. To self : Check ALS Y arm power outlets (60Hz frequency comb seen in the error signal)

  9698   Thu Mar 6 11:15:32 2014 KojiSummaryLSCStuck at step 2

You don't need to make transition from ALS X/Y to ALS C/D. Just stabilize the arms with ALS C/D from the beginning.

  9702   Fri Mar 7 00:43:34 2014 manasaUpdateLSCALS C&D locked (on MC2 and ETMs) and IR resonance obtained

[EricQ, Manasa]

ALS common locked by actuating on MC2 and ALS Differential locked by actuating on ETMX and ETMY (Stable lock acquired for over an hour).

Common and Differential offsets were swept to obtain IR resonance in both the arms (arms stayed on resonance for over 15 minutes).

Procedure:

1. Configured LSC settings to allow locking using ALS error signals.

2. Locked common and differential using ALS error signals

Aux matrix
              ALSX    ALSY
------------------------------
XARM    1            -1
YARM    1              1
-----------------------------
X arm servo settings:
FIlters: FM1, FM5, FM6, FM7, FM9
Gain = -8.0

Y arm servo settings:
Filters: FM1, FM5, FM6, FM7, FM9
Gain = +8.0

Out matrix
    XARM    YARM
------------------------
ETMX    1    0
ETMY    0    1
------------------------

3. Transitioned CARM control output to actuate on MC2 instead of ETMX

SUS-MC2_LSC servo gain = 1.0
The transition was done in very small steps : actuating on MC2 in -0.01 steps at the outmatrix upto -1.0 while reducing the ETMX actuation to 0 simultaneously.

DARM still stayed locked only with actuation on ETMY.

4. Transitioned DARM control to ETMX and ETMY.

Used ezcastep to step up DARM control (Y arm output) actuation on ETMX and step down the actuation on ETMY.

Final output matrix
    Xarm    Yarm
-----------------------
ETMX      0    -0.5
ETMY      0     0.5
MC2    -1.0      0
-----------------------

Noise plot in attachment.

5. Finding arm resonance

Used ezcastep to gradually build up offsets in CARM (LSC-XARM_OFS) to find IR resoance in one arm (Y arm).
Introducing a small (order of 0.5) DARM offset (LSC-YARM_OFS) shifted the Y arm off-resonance.
Used CARM offset to get back the Y arm to resonance.
Changing CARM and DARM offsets alternately while tracking the Y arm resonance got us to a point where we had both the arms resonating for IR.

6. At this point the MC decided to give up and we lost lock.

Notes:
1. We found that the WFS2 YAW output filterbank had the output switched OFF (probably accidentally by one of us). This was reenabled. Please be careful while manually turning ON and OFF the MC WFS servos.

Attachment 1: ALS_MC2CARM.pdf
ALS_MC2CARM.pdf
  9708   Mon Mar 10 21:12:30 2014 KojiSummaryLSCComposite Error Signal for ARms (1)

The ALS error (i.e. phase tracker output) is linear everywhere, but noisy.
The 1/sqrt(TR) is linear and less noisy but is not linear at around the resonance and has no sign.
The PDH signal is linear and further less noisy but the linear range is limited.

Why don't we combine all of these to produce a composite error signal that is linear everywhere and less-noisy at the redsonance?

This concept was confirmed by a simple mathematica calculation:

The following plot shows the raw signals with arbitorary normalizations

1) ALS: (Blue)
2) 1/SQRT(TR): (Purple)
3) PDH: (Yellow)
4) Transmission (Green)

The following plot shows the preprocessed signals for composition

1) ALS: no preprocess (Blue)
2) 1/SQRT(TR): multiply sign(PDH) (Purple)
3) PDH: linarization with the transmission (If TR<0.1, use 0.1 for the normalization). (Yellow)
4) Transmittion (Green)

The composite error signal

1) Use ALS at TR<0.03. Use 1/SQRT(TR)*sign(PDH)*(1-TR) + PDH*TR at TR>0.03
2) Transmittion (Purple)
 

Attachment 1: composite_linear_signal.nb.zip
  9709   Mon Mar 10 21:13:43 2014 nicolasSummaryLSC Composite Error Signal for ARms (2)

In order to better understand how the composite signal would behave in the presence of noise, I decided to do a simple analysis of the cavity signals while sweeping through resonance.

My noise model was to just assume that a given signal has some rms uncertainty (error bars) and use linear error propagation to propagate from simple signals to more complicated ones.

I used the python package uncertainties to do the error propagation.

I assumed that the ALS signal, the cavity transmission, and the cavity PDH error signal all have some constant noise that is independent of the cavity detuning. Below is a sweep through resonance (x axis is cavity detuning in units of radians).

rawsigs.png

The shaded region represents the error on each signal.

Next I calculated the 'first order' calculated error signals. These being a raw PDH, normalized PDH, an inverse square root trans, and the normal ALS again. I tuned the gains so they match appropriately.

Here, one can see how the error in the trans signal propagates to the normalized and trans signals and becomes large are the fractional error in the trans signal becomes large.

errorsigs.png

Next I did some optimization of linear combinations of these signals. I told the code to maximize the total signal to noise ratio, while ensuring that the overall signal had positive gain. I did this again as a function of the cavity detuning.

Each curve represents the optimized weight of the corresponding signal as a function of detuning.

optimalweights.png

So this is roughly doing what we expect, it prefers ALS far from the resonance, and PDH close to the resonance, while smoothly moving into square root trans in the middle.

It's a little fake, but it gives us an idea of what the 'best' we can do is.

Finally I used these weights to recombine the signals into a composite, to get an idea of the noise of the overall signal. At the same time, I plot the weighting proposed by Koji's mathematica notebook (using trans and 1-trans, and a hard switch to ALS).

compositenoise.png

So as one can see, at least for the noise levels I chose, the koji weighting is not much worse than the 'optimal' weighting. While it is much simpler.

The code for all this is in the svn at 40mSVN/nicolas/workspace/2014-03-06_compositeerror

  9710   Mon Mar 10 21:14:58 2014 ericqSummaryLSCComposite Error Signal for ARms (3)

Using Koji's mathematica notebook, and Nic's python work, I set out to run a time domain simulation of the error signal, with band-limited white noise added in. 

model.png

Basically, I sweep the displacement of the cavity (with no noise), and pass it to the analytical formulae with the coefficients Koji used, with some noise added in. I also included some 1/0 protection for the linearized PDH signal. I ran a sweep, and then compared it to an ALS sweep that Jenne ran on Monday; reconstructing what the CESAR signal would have looked like in the sweep. 

The noise amounts were totally made up. 

They matched up very well, qualitatively! [Since the real sweep was done by a (relatively) noisy ALS, the lower noise of the real pdh signal was obscured.]

simSweep.pdfalsSweep.pdf

Given this good match, we were motivated to start trying to implement it on Monday. 

At this point, since we've gotten it working on the actual IFO, I don't plan on doing much more with this simulation right now, but it may come in handy in the future...

  9711   Mon Mar 10 21:16:13 2014 KojiSummaryLSCComposite Error Signal for ARms (4)

The LSC model was modified for CESAR.

A block called ALSX_COMBINE was made in the LSC block. This block receives the signals for ALS (Phase Tracker output), TRX_SQRTINV, TRX, POX11 (Unnormalized POX11I).
It spits out the composite ALS signal.

Inside of the block we have several components:

1) a group of components for sign(x) function. We use the PDH signal to produce the sign for the transmission signal.

2) Hard triggering between ALS and TR/PDH signals. An epics channel "THRESH" is used to determine how much transmission
we should have to turn on the TR/PDH signals.

3) Blending of the TR and PDH. Currently we are using a confined TR between 0 and 1 using a saturation module. When the TR is 0, we use the 1/SQRT(TR) signal for the control,
    When the TR is 1, we use the PDH signal for the control.

4) Finally the three processed signals are combined into a single signal by an adder.


It is important to make a consideration on the offsets. We want all of ALS, 1/SQRT(TR), and PDH to have zero crossing at the resonance.
ALS tends to have arbitorary offset. So we decided to use two offsets. One is before the CESAR block and in the ALS path.
The other is after the CESAR block.
Right now we are using the XARM servo offset for the latter purpose.

We run the resonance search script to find the first offset. Once this is set, we never touch this offset until the lock is lost.
Then for the further scanning of the arm length, we uused the offset in the XARM servo filter module.

Attachment 1: ss1.png
ss1.png
Attachment 2: ss2.png
ss2.png
Attachment 3: CESAR_OFFSETS.pdf
CESAR_OFFSETS.pdf
  9712   Mon Mar 10 21:16:56 2014 KojiSummaryLSCComposite Error Signal for ARms (5)

After making the CDS modification, CESAR was tested with ALS.

First of all, we run CESAR with threshold of 10. This means that the error signal always used ALS.
The ALS was scanned over the resonance. The plot of the scan can be found in EricQ's elog.
At each point of the scan, the arm stability is limited by the ALS.

Using this scan data, we could adjust the gains for the TR and PDH signals. Once the gains were adjusted
the threshold was lowered to 0.25. This activates dynamic signal blending.

ALS was stabilized with XARM FM1/2/3/5/6/7/9. The resonance was scanned. No glitch was observed.
This is some level of success already.

Next step was to fully hand off the control to PDH. But this was not successfull. Everytime the gain for the TR was
reduced to zero, the lock was lost. When the TR is removed from the control, the raw PDH signal is used fot the control
without normalization. Without turning on FM4, we lose 60dB of DC gain. Therefore the residual motion may have been
too big for the linear range of the PDH signal. This could be mitigated by the normalization of the PDH signal by the TR.

  9713   Tue Mar 11 14:49:01 2014 KojiSummaryLSCImportant notice on the XARM servo

The nominal gain of the XARM for the POX11 error signal is 0.03 (instead of previous 0.3)

This is due to my increase of the gain in FM4 by 20dB so that we can turn of FM4 without changing the UGF when it is at 150Hz.

The YARM servo was not yet touched.

  9715   Tue Mar 11 15:14:34 2014 denSummaryLSCComposite Error Signal for ARms (1)

Quote:

The composite error signal


 

 Very nice error signal. Still, I think we need to take into account the frequency shape of the transfer function TR -> CARM. 

  9717   Tue Mar 11 15:21:08 2014 KojiSummaryLSCComposite Error Signal for ARms (1)

True. But we first want to realize this for a single arm, then move onto the two arms case.
At this point we'll need to incorporate frequency dependence.

  9718   Tue Mar 11 18:33:21 2014 KojiUpdateLSCComposite Error Signal for ARms (6)

Today we modified the CESAR block.

- Now the sign(X) function is in a block.

- We decided to use the linearization of the PDH.

- By adding the offset to the TR signal used for the switching between TR and PDH, we can force pure 1/sqrt(TR) or pure PDH to control the cavity.

Attachment 1: 14.png
14.png
  9719   Tue Mar 11 18:34:11 2014 JenneUpdateLSCComposite Error Signal for ARms (7)

[Nic, Jenne, EricQ, and Koji]

We have used CESAR successfully to bring the Xarm into resonance.  We start with the ALS signal, then as we approach resonance, the error signal is automatically transitioned to 1/sqrt(TRX), and ramped from there to POX, which we use as the PDH signal.

In the first plot, we have several spectra of the CESAR output signal (which is the error signal for the Xarm), at different arm resonance conditions.  Dark blue is the signal when we are locked with the ALS beatnote, far from IR resonance.  Gold is when we are starting to see IR resonance (arm buildup of about 0.03 or more), and we are using the 1/sqrt(TRX) signal for locking.  Cyan is after we have achieved resonance, and are using only the POX PDH signal.  Purple is the same condition as cyan, except that we have also engaged the low frequency boosts (FM 2, 3, 4) in the locking servo.  FM4 is only usable once you are at IR resonance, and locked using the PDH signal.  We see in the plot that our high frequency noise (and total RMS) decreases with each stage of CESAR (ALS, 1/sqrt(TR) and PDH). 

To actually achieve the gold noise level of 1/sqrt(TR), we first had to increase the analog gain by swapping out a resistor on the whitening board. 

 

spectra-ungarble.pdf

The other plots attached are time series data.  For the python plots (last 2), the error signals are calibrated to nanometers, but the dark blue, which is the transmitted power of the cavity, is left in normalized power units (where 1 is full IR resonance). 

In the scan from off resonance to on resonance, around the 58 second mark, we see a glitch when we engage FM4, the strong low frequency boosts.  Around the 75 second mark we turned off any contribution from 1/sqrt(TR), so the noise decreases once we are on pure PDH signal. 

In the scan through the resonance, we see a little more clearly the glitch that happens when we switch from ALS to IR signals, around the 7 and 12 second marks. 

We want to make some changes, so that the transition from ALS to IR signals is more smooth, and not a discrete switch.

 

Attachment 2: Screenshot-1.png
Screenshot-1.png
Attachment 3: ScanFromOffToOnResonance.pdf
ScanFromOffToOnResonance.pdf
Attachment 4: ScanThroughResonance.pdf
ScanThroughResonance.pdf
  9724   Thu Mar 13 01:18:00 2014 JenneUpdateLSCComposite Error Signal for ARms (8)

[Jenne, EricQ]

As Koji suggested in his email this afternoon, we looked at how much actuator range is required for various forms of arm locking:  (1) "regular" PDH lock aquisition, (2) ALS lock acquisition, (3) CESAR cooling.

To start, I looked at the spectra and time series data of the control signal (XARM_OUT) for several locking situations.  Happily, when the arm is at the half fringe, where we expect the 1/sqrt(TRX) signal to be the most sensitive (versus the same signal at other arm powers), we see that it is in fact more quiet than even the PDH signal.  Of course, we can't ever use this signal once the arm is at resonance, so we haven't discovered anything new here.

XARM_OUT_VariousErrorSignals_ungarb.pdf

EricQ then made some violin plots with the time series data from these situations, and we determined that a limit of ~400 counts encompasses most of the steady-state peak-to-peak output from locking on the PDH signal.

xarmOutViolinPlot.pdfxarmOutViolinSub.pdf

[ericq: What's being plotted here are "kernel density estimates" of the time series data of XARM_OUT when locked on these signals. The extent of the line goes to the furthest outlier, while the dashed and dotted lines indicate the median and quartiles, respectively]

I tried acquiring ALS and transitioning to final PDH signals with different limiters set in the Xarm servo.  I discovered that it's not too hard to do with a limit of 400 counts, but that below ~350 counts, I can't keep the ALS locked for long enough to find the IR resonance.  Here's a plot of acquiring ALS lock, scanning for the resonance, and then using CESAR to transition to PDH, with the limit of 400 counts in place, and then a lockloss at the end.  Even though I'm hitting the rails pretty consistently, until I transition to the more quiet signals, I don't ever lose lock (until, at the end, I started pushing other buttons...).

LimiterAt400cts.pdf

After that, I tried acquiring lock using our "regular" PDH method, and found that it wasn't too hard to capture lock with a limit of 400, but with limits below that I can't hold the lock through the boosts turning on.

noLimitPDHAcq.pdfwithLimitPDHAcq.pdf

Finally, I took spectra of the XARM_OUT control signal while locked using ALS only, but with different limiter values. Interestingly, I see much higher noise between 30-300 Hz with the limiter engaged, but the high frequency noise goes down.  Since the high frequency is dominating the RMS, we see that the RMS value is actually decreasing a bit (although not much).

XARM_OUT_VariousLimits_ungarb.pdf

We have not made any changes to the LSC model, so there is still no smoothing between the ALS and IR signals.  That is still on the to-do list.  I started modifying things to be compatible with CARM rather than a single arm, but that's more of a daytime-y task, so that version of the c1lsc model is saved under a different name, and the model that is currently compiled and running is reverted as the "c1lsc.mdl" file.

  9726   Fri Mar 14 09:44:34 2014 SteveUpdateLSCmorning lock
Attachment 1: 2hrsMorningLock.png
2hrsMorningLock.png
  9728   Fri Mar 14 12:18:55 2014 KojiUpdateLSCComposite Error Signal for ARms (9)

Asymptotic cooling of the mirror motion with CESAR was tested.

With ALS and the full control bandwidth (UGF 80-100Hz), the actuator amplitude of 8000cnt_pp is required.

Varying control bandwidth depending on the noise level of the signal, the arm was brought to the final configuration with the actuator amplitude of 800cnt_pp.

Attachment 1: asymptotic_cooling.pdf
asymptotic_cooling.pdf
  9740   Wed Mar 19 21:37:45 2014 manasaSummaryLSCAttempt to lock PRMIsb with REFL165I&Q

I tried to repeat Koji's PRMI lock using REFL165I/Q. I was not able to lock PRMI stably. All I could get was momentary PRMI sb locks (few seconds) using AS55Q for MICH and REFL165Q for PRMI. I tried to transition MICH locks from AS55Q to REFL165I/Q and this did not work well; I lost even the momentary locks.

The demod phases for both AS55 and REFL165 were also very different. 

Input ports:
AS55       WHTN: 21dB  demod phase -78.7deg
REFL165 WHTN: 45dB demod phase -80.7deg

Input matrix:
AS55Q x1.00 MICH

REL165Q x+0.14

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/6/7/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS 0.0 / Gain -10 / Limiter ON
PRCL OFS 0 / Gain -0.023 / Limiter ON

Output matrix:
MICH ITMX -1.0 / ITMY +1.0
PRCL PRM 1.0

 

  9742   Fri Mar 21 01:54:32 2014 ericqUpdateLSCSome early CARM modeling

 I've been getting a simulation going with the eventual goal of simulating CESAR-type signals for CARM. So for I've only been using MIST, though I'm still thinking about what to do for a fully time domain approach. (For example, maybe a mixture of simulink and analytical equations? We'll see how painful that gets...)

Anyways, with the parameters I have for the 40m, I've set up a simulation, where I can do things like a "static" CARM scan.

(i.e. PRMI perfectly locked. Ask what different PDs see if the arms were just statically sitting at some CARM offset)

staticCarmSweep.pdf

PDH signals are there in the REFL diodes. The coupled line width here looks smaller than the ~40pm number I've heard before, so I should check my parameters. (Likely culprit, I'm using nominal R and T for the arm cavities)

I've also done the slightly more sophisticated thing of looking at the transfer function from CARM motion to different PDs, at different CARM offsets. For TRX and REFLDC, these seem to match up qualitatively to some plots that Kiwamu has done for aLIGO, with frequencies shifted by the relative arm length factor of 100. (Q's left, K's right, Y-axis on mine are W/m with 1W input the IFO)

carm2TRX.pdfCARM_TFs_TRXDC.pdf

 

carm2reflDC.pdf CARM_TFs_REFLDC.pdf

 

We can also look at the PDH diodes (revised from my initial post. Had an error in my code): 

 carm2refl11.pdfcarm2refl55.pdf

 

That's where I've gotten so far!

 

  9744   Sun Mar 23 14:20:07 2014 ranaHowToLSCBLRMS screens

 We should make screens like this for the LSC signals, errors, ALS, etc.

Attachment 1: blrms.png
blrms.png
  9751   Wed Mar 26 11:16:59 2014 ericqSummaryLSCComposite Error Signal for ARms (3)

Extending the previous model, I've closed a rudimentary CESAR loop in simulink. Error signals with varying noise levels are combined to bring a "cavity" to lock.  

simlink.pdf

There are many things that are flat out arbitrary at this point, but it qualitatively works. The main components of this model are:

  • The "Plant": A pendulum with f0 = 2Hz, Q = 10
  • Some white force noise, low passed at 1Hz before input to the plant.
  • The Controller: A very rough servo design that is stable...
  • ALS signal: Infinite range Linear signal, with a bunch of noise
  • Transmission and PDH signals are computed with some compiled C code containing analytic functions (which can be a total pain to get working), have less noise than ALS
  • Some logic for computing linearized PDH and SqrtInv signals
  • A C code block for doing the CESAR mixing, and feeding to the servo

And it can lock! 

simulatedCESARLock.pdf

 

Right now, all of the functions and noise levels are similar to the previous simulation, and therefore don't tell us anything about anything real...

However, at this point, I can tune the parameters and noise levels to make it more like our interferometer, and thus maybe actually useful. 

  9753   Wed Mar 26 14:54:32 2014 KojiSummaryLSCPRMIsb locked with REFL165I&Q again

[Manasa, Eric, Koji]

PRMIsb was locked with REFL165I&Q.


- Aligned the arms with ASS. The misaligned ETMX and ETMY

- Configured PRMIsb with IFO_Configure screen

- Immediately PRMIsb was locked with REFL55I&Q

- Checked the REFL165 phase in terms of the REFL165Q vs PRCL. It was already well adjusted at -82.5deg. We tuned the phase a bit more and got -83.5deg.

- With DTT, relative gain between REFL55I and REFL165I was measured. REFL165I is about x10 higher than REFL55I and has the same sign.

- The transition of PRCL with the input matrix was just easy.

- With DTT, relative gain between REFL55Q and REFL165Q was measured. REFL165Q is about x3 higher than REFL55Q and has the same sign.

- The transition of MICH was flakey, but after careful adjustment of the PRM alignment, ~10s lock was achieved. It seemed that the PRM alignment fluctuation
  was bug enough to unlock the interferometer.

- Eric went into the lab and aligned all of the oplevs except for the SRM's one.

- Now the lock with REFL55 and also with REFL165 became more robust. Less MICH offset and darker AS port.


Input ports:
REFL55   WHTN: 45dB demod phase +45.0deg
REFL165 WHTN: 45dB demod phase -83.5deg

Input matrix: for acquisition:
REFL55I x 1.0 -> PRCL
REFL55Q x 1.0 -> MICH

Input matrix: PRCL Transition:
REFL55I x 1.0 + REFL165I x 0.0 -> x0.5 + x0.0 -> x0.5 + x0.05 -> x0.3 + x0.05 -> x0.2 + x0.05 -> x0.1 + x0.05 -> x0.0 + x0.05

Input matrix: MICH Transition:
REFL55Q x 1.0 + REFL165Q x 0.0 -> x0.5 + x0.0 -> x0.5 + x0.3 -> x0.3 + x0.3 -> x0.2 + x0.3 -> x0.1 + x0.3 -> x0.0 + x0.3

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS 0 / Gain 1.3 / Limitter ON
PRCL OFS 0 / Gain -0.04 / Limitter ON

Output matrix:
MICH PRM -0.2625 / BS 0.5
PRCL PRM 1.0

  9754   Wed Mar 26 21:51:42 2014 ericqSummaryLSCPRMIsb locked with REFL165I&Q again

Incidentally, while messing around with transfer functions and sensing matrix elements this evening, I was able to sideband lock straight onto REFL33 I&Q.  The settings were all identical to Koji's ELOG, with the following differences:

Input ports:
REFL33   WHTN: 30dB demod phase +125.5deg (tweaked from 135.5 to minimize MICH in I)

Input matrix:

REFL33I x +1.0 -> PRCL
REFL33Q x +3.0 -> MICH

Servo:
MICH OFS 0 / Gain 1/ Limitter ON (Oscillations occurred at 1.3)
PRCL OFS 0 / Gain -0.04 / Limitter ON

Output matrix:

MICH ITMX -1.0 / ITMY 1.0
PRCL PRM 1.0

 

  9758   Fri Mar 28 17:22:55 2014 KojiSummaryLSCPRMIsb locked with REFL165I&Q again

While I'm looking at the PRM ASC servo model, I tried to use the current servo filters for the ASC
as Manasa aligned the POP PDs and QPD yesterday. (BTW, I don't find any elog about it)

I found no issue for locking PRMIsb with the REFL165I&Q signals if the PRM ASC is employed.
See this entry for the IFO settings.

It is just stable. The IFO is ready for the arm scanning.

=== ASC setting ===

PRCL_PITCH: FM1/3/9 x-0.004
PRCL_YAW: FM1/3/9 x-0.001

The PRM OPLEV has to be off when the PRM ASC is engaged. Actually, it turned out that we don't need OPLEV for locking.

  9765   Mon Mar 31 13:15:55 2014 manasaSummaryLSCAlignment update

Quote:

While I'm looking at the PRM ASC servo model, I tried to use the current servo filters for the ASC
as Manasa aligned the POP PDs and QPD yesterday. (BTW, I don't find any elog about it)

 Guilty!!

POP path

The POP PD was showing only ~200 counts which was very low compared to what we recollect from earlier PRMI locks (~400 counts). Also, the POP ASC QPD was also not well-aligned.
While holding PRMI lock on REFL55, I aligned POP path  to its PD (maximize POP DC counts) and QPD (centered in pitch and yaw).

X and Y green

The X green totally lost its pointing because of the misaligned PZTs from last week's power failure. This was recovered.
Y arm green alignment was also recovered.

  9766   Mon Mar 31 13:26:23 2014 manasaUpdateLSCLSC model modified

I have included Yarm CESAR to the LSC model. It was just a copy paste of the Xarm CESAR. Since we are now meditating about implementing CCESAR and DCESAR, I did not run or install the model as yet.

  9767   Mon Mar 31 17:47:57 2014 ericqSummaryLSCMICH sensing oddities in REFL 3F

Last week, while I had the PRMI locked on REFL33, I did some poking around with mirror excitation to RFPD quadrature transfer functions. I got some indication of weird things with sensing MICH with the 3F REFL signals, but it should be explored more before taken as a real thing. I just figured I would show what I saw. 

With that disclaimer out of the way, here's what I did:

  • Locked PRMI on PRCL:REFL33_I and MICH:REFL33_Q, as detailed in my earlier ELOG
  • Created PRCL and MICH excitations at two different frequencies, notched said frequencies out of the control filters
  • Took transfer functions from mirror LSC output signals to 33 I, 33 Q, 165 I, 165 Q in DTT
  • For each DOF, look at the measured transfer functions only at the excitation frequency. (Assuming good coherence, which was there)

The basic idea was, some PRCL motion (for instance), has a transfer function to both the I and Q quadratures at a given PD. As the PRCL excitation sine wave goes through one cycle, the REFL signals at the excitation frequency go through some coherent cycle. Thus, the excitation traces out some trajectory in the I vs. Q plane. I believe this is analogous to the typical "radar plot" that we make for sensing matrix elements. 

However, the straight line that we normally plot in the radar plots assumes a certain phase relationship between the DOF-> I and DOF->Q transfer functions that results in a straight line. Here are the trajectories I actually measured, normalized by the excitation amplitudes.

REFL_33_traj.pdfREFL_165_traj.pdf

The plotted traces are (x,y) = (H_prcl->I * prcl, H_prcl->Q * prcl) and  (x,y) = (H_mich->I * mich, H_mich->Q * mich) where H_prcl->I is the measured complex transfer function from prcl to REFL I, for instance, and prcl and mich are the excitation signals, normalized to unit amplitude.

PRCL looks like a nice straight line in both of these, and pretty well phased, but not only is MICH not very orthogonal to PRCL, there is quite a bit of ellipticity present, which means we can't fully decouple the two DOFs, even if they were nominally orthogonal. 

I'm not sure what may cause this. To back up this measurement/interpretation, I tried to take measurements of these transfer functions across different excitation frequencies via swept sine DTT, but seismic activity kept me from staying locked long enough...

ELOG V3.1.3-