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ID Date Author Type Categoryup Subject
  5754   Fri Oct 28 05:17:13 2011 kiwamuUpdateLSClocking activity : PZT1 is still railing

Status update on the LSC activity:

 To see how good/bad the beam pointing is, I locked the Y arm with POY11.
Then I ran the ASS servo to automatically correct the alignment of the ITMY and ETMY suspensions and also the beam pointing.
The result is that the PZT1_X is still railing to the negative side.
Due to it the transmitted light from the Y arm is about 0.6 or so which is supposed to be 1 if the beam pointing is perfect.
The EPICS value of PZT1_X is at the minimum of -10 and the ASS servo tried to push it more negative side.
 
 Tomorrow night I will intentionally introduce offsets in the MC suspensions to avoid the railing.
The goal will be a scan of the incident beam while measuring the recycling gain.
  5760   Fri Oct 28 20:39:19 2011 MIrkoUpdateLSCRFAM monitor in place. ( Uncalibrated ) EPICS troubles

{Suresh, Jamie, Mirko]

We adapted the Stochmon box to include LP filters at 1.8Hz behind the RMS parts.
Then measured the RMS signals for different RF signal levels at 11.0.65, 29.5, 55.325MHz provided by a RF freq. generator.
As you can see in the data below the suppression of the BP filters of neighboring frequencies is only 35-35dB in power (see also manufacturer specs).

We therefor want to substract crosstalk, by calculating it out. We decided to use C-code in CDS. No computer crashing this time :)

We however ran into the problem that the RMS signal channels are acquired by the slow (EPICS) maschine c1iool0. Channels are (C1:IOO-RFAMPD_33MHZ , -"-133MHZ, -"-166MHZ) and we could not access those in the CDS c1ioo model. Using the EpicsIn block we got an CA.Exception stating that the variable was hosted on multiple servers. We then tried to use the EzcaRead to access the variables. Got an compile error, about the compiler not beeing able to connect all parts. It seems that the EzcaRead left behind a "ghost" part in the model (something with M1:SYS-FOO_BAR which is the default naming of the EzcaRead block) even after we deleted that block. We toyed around with the /opt/rtcds/caltech/c1/chans/daq/C1EDU_IOO.ini  and  /cvs/cds/caltech/target/c1iool0/ioo.db  files. We tried to uncomment the "old" (33,133,166) channels there to get rid of the conflict, but that didn't work.

We want to write the outputs to C1:IOO-RFAMPD_11MHZ , -"-29MHZ, -"-55MHZ EPICS channels.

We had to get the model back from the svn to get it running again.

Attachment 1: MC_DC11MHz.m
Pwr=[-60,-55,-50,-45,-40,-35,-30,-25,-20,-10,-5,0,5,10]';
Voltage11=[2.12,2.10,2.03,1.93,1.83,1.71,1.59,1.47,1.35,1.10,0.97,0.85,0.71,0.61]';

Voltage11=spline(Pwr,Voltage11,linspace(-60,10,15));
PwrSmooth=linspace(-60,10,15);

Voltage29=[2.14,2.14,2.14,2.14,2.14,2.14,2.13,2.12,2.09,1.94,1.84,1.73,1.61,1.49];
Voltage29=spline(Pwr,Voltage29,linspace(-60,10,15));

Voltage55=[2.16,2.16,2.16,2.16,2.16,2.16,2.16,2.15,2.14,2.13,2.10,2.04,1.94,1.83];
... 5 more lines ...
Attachment 2: MC_DC29MHz.m
Pwr=[-60,-55,-50,-45,-40,-35,-30,-25,-20,-15,-10,-5,0,5,10]';
Voltage11=[2.16,2.16,2.16,2.16,2.15,2.16,2.15,2.13,2.10,2.03,1.93,1.81,1.70,1.58,1.46]';

Voltage29=[2.12,2.10,2.03,1.93,1.83,1.70,1.59,1.47,1.34,1.22,1.09,0.97,0.84,0.71,0.61]';

Voltage55=[2.16,2.15,2.16,2.16,2.15,2.15,2.14,2.10,2.0,1.97,1.97,1.77,1.65,1.50,1.37]';

%%  Example 55MHz inj.

Voltage11=[2.00];
... 21 more lines ...
Attachment 3: MC_DC55MHz.m
Pwr=[-60,-55,-50,-45,-40,-35,-30,-25,-20,-15,-10,-5,0,5,10]';
Voltage11=[2.16,2.16,2.16,2.16,2.16,2.15,2.15,2.15,2.15,2.15,2.12,2.09,2.00,1.89,1.78]';

Voltage29=[2.14,2.14,2.14,2.13,2.14,2.13,2.11,2.06,1.98,1.88,1.76,1.64,1.52,1.40,1.27]';

Voltage55=[2.14,2.11,2.05,1.96,1.85,1.73,1.61,1.48,1.36,1.23,1.10,0.98,0.84,0.71,0.61]';

plot(Pwr,Voltage55)

%%
... 17 more lines ...
Attachment 4: RFAMPD.c
double x;
double y;
double z;

double temp1;
double temp2;

double Corrx;
double Corry;
double Corrz;
... 49 more lines ...
  5762   Sat Oct 29 05:50:44 2011 kiwamuUpdateLSCMC suspensions misaligned to avid railing for PZTs

I have shifted the alignment of the MC suspensions such that the PZT won't rail.

Since I didn't care of the spot positions on the MC mirrors, currently they are terribly off from the centers.

After the shift, I realigned the Stochmon PD again.

The attachments below shows the alignment of MC and PZTs before shifting the just for a record

 MCalignOct282011.png 

Oct282011.png

Quote from #5754

 Tomorrow night I will intentionally introduce offsets in the MC suspensions to avoid the railing.
The goal will be a scan of the incident beam while measuring the recycling gain.

  5763   Sat Oct 29 22:57:03 2011 MirkoUpdateLSCAM modulation due to non-optimal SB frequency

[Kiwamu, Mirko]

Non-optimal 11MHz SB frequency causes PM to be transformed into AM.
m_AM / m_PM = 4039 * 1kHz / df , with df beeing the amount the SB freq. is off.

Someone might want to double check ths.

Attachment 1: IMC.pdf
IMC.pdf
  5773   Mon Oct 31 21:46:32 2011 kiwamuUpdateLSCDependence of Recycling gain on incident beam pointing

I horizontally swept the translation of the incident beam in order to investigate a possible clipping in Power-recycled Michelson (PRMI).

The recycling gain of PRMI depended on the beam pointing but it did't improve the recycling gain.

I guess the amount of the entire shift I introduced was about +/- the beam diameter = +/- 5 mm or so.

Within the range of about +/- 5mm in the horizontal beam translation I didn't find any obvious sign of a clipping.

 

(Measurement)

 This is the procedure which I did:
  (1) Some amount of offsets were introduced on MC2 in both PIT and YAW such that the PZT1 won't rail (#5762).
      => Every time when I introduced the offset I realigned the zig-zag mirrors on the PSL table to maintain the high transmissivity of MC.
  (2) Fine tuning of the MC offsets so that the PZT1_X EPICS value becomes almost zero when the beam is aligned down to the Y arm.
     => 0.523 in C1:ASC_PZT1_X became a point where the coupling of the beam into the Y arm was maximized.
     => Last time the direction which we investigated was the positive side from this zero point (#5709) in PZT1_X.
  (3) Aligned MICH by steering BS.
  (4) Locked PRMI with carrier resonating and aligned PRM to maximized the power recycling gain which was obtained from POYDC.
  (5) Translated the beam pointing
     => First I shifted PZT1_X by a wanted amount.
    => Then I locked the Y arm and realigned PZT2_X by maximizing the Y arm transmission.
          This procedure should give us a pure translation on the incident beam.
  (6) Repeated the same procedure (3) through (5) in each PZT1 position.
 

(Results)

Here shows the measured recycling gain and the power reflectivity of PRMI as a function of the beam pointing.

beam_scan_PRCL.png

 Upper plot : measured recycling gains (Red) observed maximum values (Black) measured values on average.
 Lower plot : measured power reflectivity of PRMI (Blue) observed minimum values (Black) measured values on average.
 
 As shown in the plots the recycling gain could go up to 8 at some points.
As the PZT went away from 0 it decreased and eventually became about 3 in each side.
The reflectivity showed the minimum value of 0.4 when the PZT1 was at -1 in EPICS value.
One hypothesis to explain this plot can be that : we are just seeing the effect of the incident beam misalignment.

 

  5774   Tue Nov 1 13:41:38 2011 MirkoUpdateLSCAM modulation due to non-optimal SB frequency

Quote:

[Kiwamu, Mirko]

Non-optimal 11MHz SB frequency causes PM to be transformed into AM.
m_AM / m_PM = 4039 * 1kHz / df , with df beeing the amount the SB freq. is off.

Someone might want to double check ths.

 Actually there was an error.

For 11MHz it is:
m_AM / m_PM = 2228 * 1kHz / df

For 55MHz:
m_AM / m_PM = 99.80 * 1kHz / df

see PDF

Attachment 1: IMC.pdf
IMC.pdf
  5788   Wed Nov 2 19:32:20 2011 kiwamuUpdateLSCPOP22/110 installed

[Steve / Kiwamu]

 The POP22/110 RFPD has been installed. It is PDA10A from Thorlabs instead of the usual home-made RFPD.
For an RF cable we rerouted one of the spare Heliax cables for it.
The cable is the one which used to be served for the 166MHz ASC wavefront sensors, picking up the RF source signal at 1X2 and sending it to the LSC rack.
 
 - - Remaining tasks - -
  + Fine alignment
  + Connection at the LSC rack
  + Update of the table diagram

Quote from #5783

They were traced and labeled. One goes to 1X2 and the other to AS-ISCT. They are Andrew Heliax 1/4" od. made by CommScone,  model number FSJ1-50A

  5794   Thu Nov 3 14:25:52 2011 kiwamuUpdateLSCPDA10A as POP22/110 : too small signal

It turned out that the signal was too small with PDA10A to detect the 22 and 110 MHz RF sidebands.

The DC output coming out from it was about half mV or so (corresponding to few uW in laser power) when the PRCL was locked to the carrier.

This is because PDA10A is a silicon detector which is more sensitive to visible light than IR.

The reason we chose PDA10A was that it has relatively a large diode size of 1 mm in diameter.

However according to the data sheet the responsibility at 1064 nm is about 0.05 A/W which is sad.

I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.

Though the diode size will be half mm in diameter, which may require another strong lens in front of it.

Quote from #5788
 The POP22/110 RFPD has been installed. It is PDA10A from Thorlabs instead of the usual home-made RFPD.
  + Fine alignment

  5796   Thu Nov 3 16:31:47 2011 kiwamuUpdateLSCPDA10CF as POP22/110 : better

The POP22/110 RFPD has been replaced by PDA10CF. As a result the 22 and 110 MHz signals became detectable.

However the signal level maybe too low according to a quick look with an RF spectrum analyzer.

The level at 22 and 110 MHz were both approximately -70 dBm although these values were measured when the central part was freely swinging.

Perhaps we need to amplify the signals depending on the actual SNR.

 

 Also I have updated the optical tables' wiki page :

http://blue.ligo-wa.caltech.edu:8000/40m/Optical_Tables

Quote from #5794

I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.

  5801   Thu Nov 3 18:41:36 2011 kiwamuUpdateLSCPOX11 demod board : haven't been modified yet

I pulled out the POX11 demod board and found the power splitter on the board hadn't been modified yet.

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

Quote from #5753
The POX11 demodulation board is broken

  5802   Thu Nov 3 19:58:18 2011 kiwamuUpdateLSCPOX11 demod board : modification done

The modification on the POX11 demod board has been successfully done.

I followed the procedure which had been posted in a past entry (#4554).

The home-made splitter was replaced by PSCQ-2-51W, which has a relatively wide band of 5 - 50 MHz.

The usual orthogonality adjustment will be done in the daytime.

 

 The attached snapshot was taken when an sinusoidal RF signal with a slight frequency offset from LO was injected to the RF input.

It is clear that the I and Q output show healthy signals (i.e. almost the same amplitude and 90 deg phase difference.)

POX11demod.png

Quote from #5801

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

  5804   Fri Nov 4 00:13:24 2011 KojiUpdateLSCXARM locked with POX11

XARM lock was achieved by POX11_I

Summary:

- The  whitening gains of POX11_I and Q are 42dB so that POX11_I have the same amplitude as AS55_I

- The demod phase of POX11 was adjusted to eliminate the PDH signal from the Q phase. The phase is  -100.5deg.

- In order to lock the XARM with POX11_I_ERR, I had to increase the trigger threshold from 0.1 to 0.2 as the arm was
kicked with the threshold of 0.1.


Method

- Lock the X arm with AS55_I at the XARM configuration.

- Adjusted POX11 demod phase so that POX11_Q is minimized.

- POX I&Q whitening gains were adjusted. When they are 42dB, POX11_I_ERR and AS55_I_ERR have almost the same signal amplitude.
(In reality, POX11_I_ERR has +1dB larger amplitude.)

- Adjusted POX11 demod phase again with better precision.

- Measured transfer function between AS55_I_ERR and POX11_I_ERR. As the sign was opposite, the demod phase was -180deg flipped.

- Tried to lock the arm with POX11_I_ERR. It did not acquire the lock. The arm looked kicked by the servo.

- Increased the trigger threshold from 0.1 to 0.2. Now the arm is locked with POX11_I_ERR.

Attachment 1: POX11.pdf
POX11.pdf
  5806   Fri Nov 4 05:24:56 2011 kiwamuUpdateLSCoffset introcuded in MC and IFO-configure script modified

[Offsets in MC]

 I have introduce an offset in MC2 PIT because the PZT1 again started railing.

Right now the PZT1 EPICS value is within the range happily.

Please keep this MC eigen axis as a nominal configuration.

 

[IFO-configure script]

 I have modified the IFO configure scripts such that XARM and YARM are locked with POX11 and POY11 respectively.

A big advantage in use of POX and POY is that we don't need to misalign ITMs when we align each arm.

Those scripts are now available from the C1IFO_CONFIGURE screen as usual.

  5812   Fri Nov 4 15:26:54 2011 JenneUpdateLSCLSC model recompiled

I moved the place where we take the OAF Degree of Freedom signals from - now it's the error point rather than the feedback for DARM, CARM, MICH, PRCL, SRCL, XARM and YARM.  I didn't do anything to MCL.

While trying to compile, there was something wrong with the lockins that were there...it complained about the Q OUTs being unconnected.  I even reverted to the before-I-touched-it-today version of c1lsc from the SVN, and it had the same problem.  So, that means that whomever put those in the LSC model did so, and then didn't check to see if the model would compile.  Not so good.

Anyhow, I just terminated them, to make it happy.  If those are actually supposed to go somewhere, whoever is in charge of LSC lockins should take a look at it.

Also, as Mirko mentioned in the previous elog 5811, we wanted to calculate the effect on the MC without actuating, so we put in a new summing point and a filterbank so we have testpoints.

LSC model recompiled.

OAF model recompiled.

FB restarted because of the new channels added to OAF.

  5832   Mon Nov 7 15:15:21 2011 JenneUpdateLSCLSC model recompiled

Quote:

I moved the place where we take the OAF Degree of Freedom signals from - now it's the error point rather than the feedback for DARM, CARM, MICH, PRCL, SRCL, XARM and YARM.  I didn't do anything to MCL.

While trying to compile, there was something wrong with the lockins that were there...it complained about the Q OUTs being unconnected.  I even reverted to the before-I-touched-it-today version of c1lsc from the SVN, and it had the same problem.  So, that means that whomever put those in the LSC model did so, and then didn't check to see if the model would compile.  Not so good.

Anyhow, I just terminated them, to make it happy.  If those are actually supposed to go somewhere, whoever is in charge of LSC lockins should take a look at it.

Also, as Mirko mentioned in the previous elog 5811, we wanted to calculate the effect on the MC without actuating, so we put in a new summing point and a filterbank so we have testpoints.

LSC model recompiled.

OAF model recompiled.

FB restarted because of the new channels added to OAF.

 After Rana pointed out the errors of our ways, we reverted all of these changes.

  5833   Mon Nov 7 15:43:25 2011 jamieUpdateLSCLSC model recompiled

Quote:

While trying to compile, there was something wrong with the lockins that were there...it complained about the Q OUTs being unconnected.  I even reverted to the before-I-touched-it-today version of c1lsc from the SVN, and it had the same problem.  So, that means that whomever put those in the LSC model did so, and then didn't check to see if the model would compile.  Not so good.

Anyhow, I just terminated them, to make it happy.  If those are actually supposed to go somewhere, whoever is in charge of LSC lockins should take a look at it.

 This was totally my fault.  I'm very sorry.  I modified the lockin part to output the Q phase, and forgot to modify the models that use that part appropriately.  BAD JAMIE!  I'll check to make sure this won't bite us again.

  5849   Wed Nov 9 14:49:07 2011 kiwamuSummaryLSCCharacterization of the Power Recycled Michelson

EDIT by KI:

  The definition of the recycling gain is wrong here.

See the latest entry (#5875)

 

Here is a summary about the Power Recycled Michelson (PRMI).

It seems the mode matching is also one of the greatest contributor on the low recycling gain.

 

 

 (Estimated parameters)

    Loss = 5.3% (or effective reflectivity of  93.28% in Michleson) => Under coupling !!

     +  Mode matching efficiency = 47.4 %  => Really bad !!

   With these values we end up with a recycling gain of 7 and a normalized REFLDC of  0.5 as observed (#5773).

Also according the incident beam scan measurement (#5773) the loss is NOT a local effect like a clipping, it is more like uniformly distributed thing.

As for the mode matching, the number indicates that approximately the half of the incident light is coming back to the REFL port without interacting with PRMI.

This is bad because the non-mode-matched light, which is just a junk light, is entering into the photo detectors unnecessarily.

In the worst scenario, those junk light may create a funny signal, for example a signal sensitive to the alignment of PRM.

 

(Estimation method)

The method to estimate the loss and the MM (Mode-Matching efficiency) is essentially the same as before (#5541).

One difference from the previous estimation is that the I used more realistic parameters on the transmissivity of ITMs and PRM :

     PRM : T = 5.637 %  (see the 40m wiki)

     ITM : T = 1.384 %  (see the 40m wiki)

 

 In addition to the basic calculations I also made plots which are handy for figuring out where we are.

Quantities we can measure are the reflected light from PRMI and the recycling gain using the REFL PD and the POY PD respectively.

So I wanted to see how the loss and MM can be estimated from the measured REFL DC and recycling gain.

The plots below are the ones.

contour_loss.png   contour_MM.png

[Loss map]

 The first figure shows a contour map of the loss as a function of the measured REFL DC and recycling gain.

The white area is a place where no proper solutions can be found (for example MM can get to more than 100 or loss becomes negative).

The star mark in the plot corresponds to the place where we are now. Obviously the loss is about 5%.

If we somehow decrease the amount of the loss the star mark will mostly go up in the plot.

[MM map]
 The second figure shows a contour map of the MM as a function of the measured REFL DC and recycling gain. 

The X and Y axis are exactly the same as that of the first plot. Again the star mark represents the place where we are.

We are currently at MM=47%

 

(Solutions)

Here are some solutions to bring the recycling gain higher.

We don't work on these things immediately since it requires opening of the chambers again and it will take some times.

But we should think about those options and prepare some stuff for a coming vent.

  + Refinement of the position of the mode matching telescopes.  => The Recycling gain can go up to 15.

     => Assuming the loss in the cavity doesn't change, the star mark in the first plot will go to the left hand side along the "0.05" black solid line.

     => However PRMI will be still under coupled.

     => Needs an estimation about which way we move the telescopes.

 + Locate the place of the dominant loss source and reduce it somehow.

    => The recycling gain will be more than 18 if the loss reduces by a factor of more than 5.

    => Needs a clever way to find it otherwise we have to do it in the classical way (i.e. white light and trying to find dirty surfaces)

  5851   Wed Nov 9 16:29:36 2011 KojiSummaryLSCCharacterization of the Power Recycled Michelson

Difficult to understand.

The mode matching does not change the recycling gain. It changes the coupling of the incident light into the cavity.
It changes the reflected and accumulated power, but the recycling gain is not affected.

The recycling gain is determined by the optical configuration and the optical loss in the cavity.

In the actual measurement, of course, we should take both of the loss and the mode matching into account.
But this is the issue of the measurement method.

The essential questions are:
How much is the actual recycling gain? And how does it affect the signal extraction?

  5875   Fri Nov 11 14:55:47 2011 kiwamuSummaryLSCCharacterization of the Power Recycled Michelson : take 2

Quote from #5851

The recycling gain is determined by the optical configuration and the optical loss in the cavity.

How much is the actual recycling gain? And how does it affect the signal extraction?

 As Koji pointed out I made a wrong definition on the recycling gain of PRMI (Power-Recycled Michelson Interferomter).

In the correct definition the estimated recycling gain is 15.
In order to answer Koji's second question,which is about the effect on the signal extraction,
I need to scratch my head for a while.
( Give me some time..)
 
The value what I called "Recycling gain" must have been called "measured power build up" or something like that.
For clarity I put the definitions of the quantities.
    Recycling gain :      rec_gain.png 

   Reflectivity of PRMI (measured by REFLDC): refl.png

    Power build up (measured by POY DC) : pbu.png

    Mode Matching (MM) efficiency :  MM.png

    Loss in the PRMI cavity : loss.png

 


 (Results of Measurement and Estimation)

     Estimated recycling gain = 15

     Estimated MM efficiency = 47.4%

     Estimated Loss = 5.3%

     Measured power build Up = 7

     Measured reflectivity of PRMI = 0.5

  6027   Mon Nov 28 16:51:57 2011 kiwamuUpdateLSCmodulation frequency reset

I reset the modulation frequency to 11065910 Hz (#5530). It had been at 11065399 Hz probably since the power shut down.

  6072   Mon Dec 5 19:21:55 2011 kiwamuUpdateLSCcoarse beat note signal : ADC limited above 30 Hz

The signal observed by the coarse frequency discriminator was actually dominated by the ADC noise above 30 Hz.

It means that once increasing the UGF more than 30 Hz the servo will feed the ADC noise to the test mass and shake it unnecessarily.

I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071).

(But still it doesn't fully explain the instability).

 

 To improve the situation I am going to do the following actions:

   (1) Installation of a whitening filter (probably use of SR560s)

   (2) Redesign of the servo filter

 

Here is a brief noise budget of the coarse sensor.

Yarm_ALS_coarse.png

Gray curve: free running noise when no servo is applied

Green curve : in-loop noise when the ALS loop is closed with the coarse frequency-discriminator. The UGF was at 30 Hz.

Red curve : ADC noise of the coarse discriminator

Quote from #6071

 So far I still kept failing to increase the UGF of the ALS servo for some reason (see #6024).

  6074   Tue Dec 6 00:26:00 2011 kiwamuUpdateLSCALS became robust : UGF = 100 Hz

Eventually the instability in the Y end PDH servo turned out to be some kind of an alignment issue.

After carefully realigning the green beam to the Y arm, the UGF of the ALS loop became able to be at more than 50 Hz.

With this UGF it became able to suppress the arm motion to the ADC noise level (few 100 pm in rms).

Now I am scanning the arm length to look for a TEM00 resonance.

 

(the Story)

I have noticed that the spatial fringe pattern of the reflected green light was very sensitive to the pitch motion of ETMY when the green light was locked to the Y arm.

So I realigned the last two launching mirrors to minimize the reflected light. Indeed the misalignment was mainly in the pitch direction.

I basically translated the beam upward by a couple of mm or so.

The amount of the DC reflection is about 2.4 V when it is unlocked and it is now 0.77 mV when the green light is locked.

Quote from #6072

I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071). (But still it doesn't fully explain the instability).

  6150   Mon Dec 26 14:01:45 2011 kiwamuUpdateLSCmultiple-LOCKIN newly added
The multiple LOCKIN module has been newly added on the LSC realtime model.
The purpose is to demodulate ALL the LSC sensors at once while a particular DOF is excited by an oscillator.
So far the model has been successfully compiled and running okay.
I will make some MEDM screens for this multiple-LOCKIN system.
 

(Some details)

The picture below is a screen shot of the LSC real time model, zoomed in the new LOCKIN part.

multiple-lockin.png

The LOCKIN module consists of three big components:

  1. A Master oscillator
    • This shakes a desired DOF through the LSC output matrix and provides each demodulator with sine and cosine local oscillator signals.
    • This part is shown in the upper side of the screen shot.
    • The sine and cosine local oscillator signals appear as red and blue tags respectively in the screen shot.
  2. An input matrix
    • To allow us to select the signals that we want to demodulate.
    • This is shown in the left hand side of the screen shot.
  3. Demodulators
    • These demodulators demodulate the LSC sensor signals by the sine and cosine signals provided from the master oscillator.
    • With the input matrix fully diagonalized, one can demodulate all the LSC signals at once.
    • The number of demodulators is 27, which corresponds to that of available LSC error signals (e.g. AS55_I, AS55_Q, and etc.).
    • This part is shown in the middle of the screen shot.
  6151   Tue Dec 27 16:56:15 2011 kiwamuUpdateLSCScmitt trigger installed
The old trigger system has been replaced by Schmitt triggers in the c1lsc realtime model.
They seem working correctly.
  

      An example              

Here below is a picture of time series showing how the Schmitt trigger works as an example.
trigger_time_series.png
 
 In order to check the new trigger, I injected a fake sine signal into the TRY path to simulate lock acquisition of the Y arm with TRY used as a trigger.
Then I monitored the trigger signal, called C1:LSC-YARM_TRIG_MON.
This variable is a boolean, and hence it returns zero when the trigger is off and one when it is on.
I set the upper and lower thresholds to be 0.6 and 0.2 respectively.
As shown in the picture, the trigger became on when the TRY sine curve crossed the upper threshold of 0.6.
After that the TRY signal then crossed the lower threshold of 0.2 and the trigger became off.
 

      How to set the thresholds         

The setting procedure is the same as before.
  1. Open the trigger matrix window, which is accessible from the C1LSC overview screen as usual.
  2. Then type the desired upper and lower thresholds into the column.

The below is a screenshot of the trigger matrix screen. The thresholds column is pointed by a big white arrow.

 trig_mat.png

Of course, DO NOT set the upper threshold value to be smaller than that of the lower threshold. Otherwise it won't correctly work.

Also if you want to have the usual trigger rather than the Schmitt trigger, simply put the upper and lower thresholds at the same values.

 

 

      Details         

 Here I explain how the new trigger exactly work.
The attached screen shot below is the actual c1lsc simulink model, zoomed in the blocks of the MICH trigger.
model_trigger_edit.png
 
    The signal flows from the left hand side to the right hand side and the resultant output is always either zero or one.
There are two variables, which you can control via EPICS: TRIG_THRES_ON and TRIG_THRES_OFF.
Those two variables correspond to the upper and lower thresholds respectively.
   An important thing is that there are two key components: "UnitDelay" and "Choice" blocks.
First of all the code checks whether the trigger used to be ON or OFF at the "Choice" block by looking at the TRIG_MON data which is from the past.
The "Choice" block is configured such that if the TRIG_MON value used to be True, it lets the TRIG_THRES_OFF signal go through.
And if the TRIG_MON used to be False, then it lets the TRIG_ON signal go through.
Therefore this procedure breaks the situation into two cases : trigger used be ON and OFF, and depending on the situation it returns a proper threshold.
     After this check, the code does the usual triggering.
The proper threshold from the "Choice" block will be compared with an LSC signal at ">" block.
If the LSC signal is greater than the threshold value then it gives one and enables the feedback.
 
  6152   Tue Dec 27 22:17:56 2011 kiwamuUpdateLSCmultiple-LOCKIN new screens

Some new screens have been made for the new multiple-LOCKIN system running on the LSC realtime controller.

The medm screens are not so pretty because I didn't spend so long time for it, but it is fine for doing some actual measurements with those new screens.

So the basic works for installing the multiple-LOCKIN are done.

 

 The attached figure is a screen shot of the LOCKIN overview window.

As usual most of the components shown in the screen are clickable and one can go to deeper levels by clicking them. 

Untitled.png

Quote from #6150
The multiple LOCKIN module has been newly added on the LSC realtime model.
I will make some MEDM screens for this multiple-LOCKIN system.

  6156   Fri Dec 30 22:05:16 2011 kiwamuUpdateLSCpower normalization in LSC

Now a power normalization is doable for the LSC error signals.

It is working fine, but at some point we may want to have some kind of a saturation filter or limiter to avoid dividing a signal by a small number.

 

 (How to set the normalization)

  •   Click a small matrix panel on the LSC OVERVIEW window (shown in the attached screen shot below).
    •     This will give you a pop-up-window, which shows a matrix to route the normalization signals
POW_NORM_MTRX.png
  •   Choose a numerator channel, which you want to divide, and choose denominator channels, which you want to use as a power normalization factor.
  •   Put some number in the corresponding matrix elements.
  •   Once you put a non-zero element in the matrix, the corresponding numerator channel will be divided by the specified denominator channels.
    •     Otherwise the static normalization factors (e.g. C1:LSC-AS55_POW_NORM, etc.,) will be used for the denominator.
  6158   Tue Jan 3 15:48:39 2012 kiwamuUpdateLSCpower normalization in LSC

It turned out that the power normalization need a modification.

I will work on it tomorrow and it will take approximately 2 hours to finish the modification.

 

     Concept of Power Normalization         

Koji pointed out that the dynamic power normalization, which I have installed(#6156),  should be placed after the LSC input matrix rather than before the matrix.
Now let us review the concept of the power normalization to avoid some confusions.
We will need two kinds of power normalizations as follows:
  1.  Static power normalization, which should be placed before the input matrix.
  2.  Dynamic power normalization, which should be placed after the input matrix.
 The static power normalization will be applied to each I and Q signals in all the LSC signals and also DCPD signals.
This normalization is supposed to cancel the effects from the incident laser power and depths of the phase modulations.
Because the variations in the laser power and modulation depth are expected to be relatively slow, we will apply static normalizations.
 
 The dynamic power normalization will be applied to the DOFs error signals, for example C1:LSC-DARM_IN and so on.
This normalization is supposed to cancel the effect of the internal states of the interferometer, for example alignments.
In addition to it, this dynamic normalization can expand the linear range of the error signals.

Quote from #6156

Now a power normalization is doable for the LSC error signals.

 

  6166   Wed Jan 4 03:03:24 2012 kiwamuUpdateLSClocking activity tonight and beyond
Last night and tonight, I was doing a kind of rehabilitation -- locking PRMI and DRMI with the new trigger system.
Although MC wasn't so awesome (#6164), I confirmed that the DRMI can stay locked with the conventional RFPD combination (#4760).
Additionally I have modified the IFO configure scripts, such that they also automatically restore the thresholds values for triggering.
The scripts are available in the C1IFO_CONFIGURE screen as usual.

 

       Locking plan            

Here is a plan in my mind and these are basically the details of the gantt chart (#6143):

  • (1 day task) Measurement of the recycling gains of the RF sidebands with the PRMI and DRMI configuration, using POP22/110 RFPD.
    • I need to have confidence that I am really locking the DRMI with SRC resonating to 55 MHz.
    • Also those values will enable us to estimate losses and mode matching again (maybe ?).
  • (3-4 days task) Measurement of the sensing matrix using the multiple-LOCKIN system.
    • Write a script to automatically measure the sensing matrix. This must be easy.
      • The results will enable us to diagonalize the input matrix and therefore it eventually gives more solid lock of the DRMI
      • Also it will give us the optical gains of 3f signals. So this is actually a step toward the 3f signal check.
  • (3-4 days task) Noise budgeting on the 3f signals
    • This is a very important part of the DRMI characterization because the results will tell us whether we can hold the DRMI lock with a sufficient SNR or not.
    • If it turns out that they don't have good SNRs, we then have to come up with some ideas to improve the SNRs.
  • (Extra fun task depending on schedule) 3f DRMI lock + Y arm ALS
    • If the beat-box electronics are not available by the time when the work above are completed, I will do this fun task.
    • Probably it is better to start preparing the common mode servo electronics because it will be needed anyway.

 

  6167   Wed Jan 4 05:02:58 2012 kiwamuUpdateLSCSidebands measurement at POP
Just a quick report:
I did the first attempt to measure the recycling gains of the sidebands in the DRMI configuration (sidebands resonant condition)
by looking at the output of the POP22/110 RFPD.
Because this time what I measured is some absolute values of the sidebands power,
it doesn't tell us anything quantitatively until we calibrate it or compare it with similar data.
So I need to measure the same things in some different configurations (e.g. PRMI, SRMI, etc.)
in order to extract some useful information from the measurement.
 
The attached picture is the display of a power spectrum analyzer looking at the output of the POP22/110 broadband RFPD
while the DRMI (in the sideband resonant condition) was kept locked.
You can see that 111 MHz (twice of 55 MHz) is prominent. Also there are several peaks at 11, 22, 44 and 66 MHz.
SB_DRMI.png
  6170   Wed Jan 4 16:22:30 2012 kiwamuUpdateLSCpower normalization in LSC : modification done

The dynamic power normalization system has been modified such that the normalization happen after the LSC input matrix.

The attached screen shot below tells you how the signals flow.
The red circled region in the picture is the place where the power normalization are performed.
pow_norm.png
 
The dynamic normalization will be activated once you put some numbers into the elements in the matrix.
Otherwise the error signals are always normalized by 1.

Quote from #6158

It turned out that the power normalization need a modification.

I will work on it tomorrow and it will take approximately 2 hours to finish the modification.

 

  6183   Tue Jan 10 00:09:33 2012 kiwamuUpdateLSCspike hunting in REFL33

[John / Kiwamu]

 We tried to figure out what is causing spikes in the REFL33 signal, which is used to lock PRCL.

No useful information was obtained tonight and it is still under investigation.

 


(Background)

 One thing preventing us from doing smooth measurements of the noise budget and the sensing matrix is some sharp spikes in the LSC error signals.

For example when we lock PRMI with REFL33 and AS55 fedback to PRCL and MICH respectively, both the REFL33 and AS55 signals show some spikes in time series.

Those spikes then bring the noise spectra higher than how they should be.

So for the reason, taking the noise budget doesn't give us much information about the interferometer rather than there are spikes.

Also the sensing matrix measurement has been suffered from those spikes, which excite the impulse responses of the low pass filters in the LOCKIN detection systems a lot.

 

(What we did)

 We looked into the actual analog signals to see if there are indeed spikes or not before they are acquired to the ADCs.

But we didn't find any corresponding spikes in the signals that are after the mixers.

It maybe because the signals we looked into didn't have high enough SNR because they were coming out from the monitor lemo outputs on the demod boards.

 Then we thought the spikes are from the whitening circuits, due to some kind of saturation.

We decreased the gain of the whitening filters by a factor of 10, but it didn't help and the spikes were still there.

  6187   Thu Jan 12 03:05:02 2012 kiwamuUpdateLSCOSA installed in AS

[John / Valera / Kiwamu]

 We installed a new weapon, an optical spectrum analyzer in the AS port.

Like we used to do in the old days, two BNC cables were newly laid down and they bring the output of the OSA to the control room to monitor the spectrum with an oscilloscope.

 

(Some notes)

The photo diode of the OSA was replaced by a Thorlab PDA100A to amplify the signals.

The carrier peak is at about 6.9 V and the f1 and f2 sidebands peaks are at about 40 mV when the beam is in straight shot (everything is misaligned except ITMY and BS).

According to a rough calculation, those numbers correspond to a modulation depth of about 0.16 or so.

The depth agree with what Mirko measured before (#5519)

 

  6202   Tue Jan 17 01:02:07 2012 kiwamuUpdateLSCglitch hunting in REFL RFPDs : strange

A very strange thing is going on.

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

This noise shows up even when the beam is single-bounced back from PRM ( the rest of the suspensions are misaligned) and it's very repeatable.

Any idea ?? Am I crazy ?? Is PRM making some fringes with some other optics ??

 

 

(background)

 The most annoying thing in the central part locking is glitches showing up in the LSC error signals (#6183).
The symptom is that when the motion in PRCL at 3 Hz becomes louder, somehow we get glitches in both the MICH and PRCL error signals.
In the frequency domain, those glitches are mostly contribute to a frequency band of about 30 - 100 Hz.
Last Thursday Koji and I locked the half PRM (PRMI with either ITMX or ITMY misaligned) to see if we still have the glitches in this simpler configuration.
Indeed there were the same kind of glitches --a loud 3 Hz motion triggers the glitches.
It was shown particularly in the REFL11 signal but not so much in the REFL33 while AS55 didn't show any glitches.
 
 
(Still glitches even in the single bounce beam)
   We were suspecting some kind of coupling from a beam jitter, so that the 3 Hz motion somehow brings the beam spot to a bad place somewhere in the REFL paths.
I misaligned all the suspensions except for PRM such that the beam directly bounces back from PRM and go to the REFL port.
Indeed there still were glitches in the REFL11 and REFL55 demod signals. It showed up once per 30 sec or so and pushes up the noise floor around 30 - 100 Hz.
There might be a little bit of glitches also in the REFL33, but the ADC noise floor and the expected glitch noise level were comparable and hence it was difficult to see the glitches in REFL33.
 

(Glitch is related to the PRM POS actuation)

 In the single-bounce configuration I started shaking the PIT and YAW motions of PRM at 3 Hz using the realtime LOCKIN oscillator to see if I can reproduce the glitches.
However no significant glitches were found in this test.
Then I started shaking the POS instead of the angular DOFs, and found that it causes the glitches.
At this point it didn't look like a glitch any more, it became more like a stationary noise.
 
 The attached screen shot is the noise spectrum of the REFL11_I.
The red curve is the one taken when I injected the 3 Hz excitation in POS by the LOCKIN oscillator.
The excitation is at 3 Hz with an amplitude of 1000 counts.
As a comparison I plotted the same spectrum when no excitation was injected and it is plotted in pink.
 

 PRMsingle_bounce.png

It seems there is a cut off frequency at 100 Hz.
This frequency depends on the amplitude of the excitation -- increasing the amplitude brings the cut off frequency higher.
This noise spectrum didn't change with and without the oplevs and local damping.
 

(Possible scenario)

A possible reason that I can think of right now is : PRM is interfering with some other optics for some reason.
But if it's true, why I didn't see any fringes in the AS demod signals in the half PRM configuration ?
 

Quote from #6183

 We tried to figure out what is causing spikes in the REFL33 signal, which is used to lock PRCL.

No useful information was obtained tonight and it is still under investigation.

  6203   Tue Jan 17 02:27:49 2012 kiwamuUpdateLSCfringe tests : all the suspensions are innocent

I did a quick test to check a hypothesis that PRM is interfering with some other optics in the single bounce configuration.

I shook all the suspensions (except the MC mirrors) at 3 Hz in POS, PIT and YAW with an amplitude of 1000 counts.

No effects were found in the REFL demod signals.

So it is NOT a fringe effect caused by the other suspended mirrors.

Quote from #6202

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

Is PRM making some fringes with some other optics ??   

 

  6206   Tue Jan 17 13:47:40 2012 kiwamuUpdateLSCdirty steering mirror in the REFL path

 Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.

Looking at it through an IR viewer, I saw the REFL beam hitting one of the biggest dust particles on that mirror.

This dust particle maybe causing the glitches or maybe not.

Anyway because it's always better to have clean mirrors, I will wipe the steering mirror in this evening and check the presence of the glitches again.

Quote from #6202

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

Is PRM making some fringes with some other optics ??
 

  6208   Tue Jan 17 19:07:47 2012 ranaUpdateLSCglitch hunting in REFL RFPDs : strange

 Another possibility is that there is some beam clipping of the REFL beam before it gets to the PD. Then there could be a partial reflection from that creating a spurious interference. Then it would only show the fringe wrapping if you excite the scatterer or the PRM.

  6209   Wed Jan 18 12:36:26 2012 kiwamuUpdateLSCwiped a steering mirror on the REFL path

I wiped both surfaces of the REFL second steering mirror.

However no improvements. The glitches still remain.

 

(Pic.1 before wiping, Pic.2 after wiping)

DSC_3861_small.jpgDSC_3863_small.jpg

Quote from #6206

 Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.

  6211   Wed Jan 18 14:28:36 2012 kiwamuUpdateLSCestimation of optical length between PRM and scattering object

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 

 (The measurement)

  In order to estimate the optical length between PRM and a scattering body, I swept the frequency of the main laser by actuating on the MC length.
With the sweep, the laser frequency go across some fringes and basically it allows us to estimate the FSR of a very low finesse cavity formed by PRM and the scattering body.
Therefore we get the the optical distance based on the resultant FSR.
 
  The measurement goes as follows:
  1.  Preparation : calibration of the MC2 actuator as a frequency actuator (for more details, see the next section)
  2.  Set the interferometer to the single-bounce configuration such that the beam directly is reflected back from PRM
  3.  Take spectra of REFL11_I without driving any optics. This spectra tells us how quiet the noise normally is.
  4.  Drive MC2_POS at 10 Hz with an amplitude of 10000 counts so that we can see the high frequency up conversion noise
    • The frequency was chosen such that the excitation is out of the local damping bands
    • The amplitude was chosen to be as big as possible until the MC unlocked
    • With this drive, the laser frequency should change by 20 MHz peak-peak at 10 Hz.
  5.  Record the noisy spectrum when the MC2_POS was driven.
  6.  Drive PRM instead of MC2 at 10 Hz.
    • Adjust the amplitude of the excitation such that the cut-off frequency of the up conversion noise matches with that of the MC2 driven case.
    • The amplitude was found to be 1700 - 2000 counts, this uncertainty is currently limiting the precision of the optical distance estimation.
    • With this amount of the drive, PRM moves by 0.8 um peak-peak at 10Hz.
  7. Estimate the optical length based on the amount of the drives for PRM and MC2.
    • Estimate the FSR using the following relation df/FSR = dx/ (lambda/2). => FSR = 17 MHz
    • Since FSR = c/ (2L),  L = c/(2 FSR) = 9.5 m or so
scattering.png

 

 

(Calibration of the MC2 actuator)

 To do the measurement described above, the MC2 actuator must be calibrated in terms of a frequency actuator.
I did the same old technique (#4721): lock a cavity, adjust the UGF as low as possible, and shake an actuator of interest.
This time I used the half-PRM (PRM + ITMY) for this measurement.
The actuator responses are calibrated from that of displacement to frequency by using df/f = dx/L and assumed that L = 6.760 (#4585).
Also the PRM actuator was measured such that we can use this as a reference since we already know the response in displacement (#5637).
 The attached plot below is the actual responses that I measured yesterday. The y-axis is calibrated to Hz/counts.
 

 

calibration.png

 

Quote from #6202

Is PRM making some fringes with some other optics ??

  6212   Wed Jan 18 16:31:10 2012 kiwamuUpdateLSCestimation of optical length between PRM and scattering object

I searched for a scattering body in the REFL path.

According to the result the REFL path on the AS table is innocent.

 

The idea of the search method is given as follows:

  •   Put a 1/10 ND attenuator at the origin of the REFL path on the AS table.
  •   Of course this reduces the signal level by the same factor of 10 in the REFL11_I demod signal.
  •   If the scattering body is in the REFL path the up conversion noise will be smaller by a factor of 100 because the scattered light go across the attenuator twice.

 

 The attached plot below is the spectra of REFL11 with the 1/10 attenuator at the origin of the REFL path when the beam is single-bounced from PRM.
In the measurement PRM_POS was driven at 10 Hz with an amplitude of 1700 all the time. This is exactly the same situation as that explained in the previous elog entry (#6211).
You can see that the up conversion noise level also decreased by the same factor of 10, which suggests there are no scattering object in the REFL path.
Note that the data with the attenuator in place is intentionally scaled by multiplying a factor of 10 for comparison.
ND1atten.png
 

Quote from #6211

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 

  6224   Thu Jan 26 05:40:10 2012 kiwamuUpdateLSCglitch in the analog demodulated signals

Indeed the glitches show up in the analog demodulated signals. So it is not an issue of the digital processing.

With an oscilloscope I looked at the I/Q monitor outputs of the LSC demodulators, including REFL11, REFL33, REFL55, POY11, AS55 while keep locking the carrier-resonant PRMI.

I saw some glitches in REFL11, REFL55 and AS55. But I didn't see any obvious glitches in REFL33 and PO11 because the SNR of those signals weren't good enough.

 


(some example glitches)

The attached plot below is an example shot of the actual signals when the carrier resonant PRMI was locked.

The first upper row is the spectrogram of REFL11_I, REFL55_I, REFL33_I and AS55_Q in linear-linear scale.

The second row shows the actual time series of those data in unit of counts.

The bottom row is for some DC signals, including REFLDC, ASDC and POYDC.

 

glitch.png

You can see that there are so many glitches in the actual time series of the demod signals (actually I picked up the worst time chunk).

It seems that  most of the glitches in REFL11, REFL33 and AS55  coincide.

The typical time scale of the glitches was about 20 msec or so.

Note that the PRMI was locked by REFL33 and AS55 as usual.

  6231   Fri Jan 27 06:07:47 2012 kiwamuUpdateLSCglitch hunting

I went through various IFO configurations to see if there are glitches or not.

Here is a summary table of the glitch investigation tonight. Some of the cells in the table are still not yet checked and they are just left blank.

IFO configuration  Yarm
Xarm
MICH
Half PRMI
low finesse PRMI
PRMI (carrier)
PRMI (sideband)
DRMI
AS55 NO NO NO   up conversion noise glitch glitch glitch
REFL11 NO NO NO   up conversion noise
glitch glitch glitch
REFL33 NO NO NO   - glitch glitch glitch
REFL55 NO NO NO   up conversion noise
glitch glitch glitch
REFL165 NO NO NO   - glitch glitch glitch
POX11 - NO NO     glitch glitch glitch
POY11 NO - NO     glitch glitch glitch
POP55 - -            
                 

 

        Low finesse PRMI      

The low finesse PRMI configuration is a power-recycled MIchelson with an intentional offset in MICH to let some of the cavity power go through MICH to the dark port.

To lock this configuration I used ASDC plus an offset for MICH and REFL33 for PRCL.

The MICH offset was chosen so that the ASDC power becomes the half of the maximum.

In this configuration NO glitches ( a high speed signal with an amplitude of more than 4 or 5 sigma) were found when it was locked.

Is it because I didn't use AS55 ?? or because the finesse is low ??

Also, as we have already known, the up conversion noise (#6212) showed up -- the level of the high frequency noise are sensitive to the 3 Hz motion.

  6235   Fri Jan 27 17:16:05 2012 kiwamuUpdateLSChypothetical glitch scenario

Here is a hypothetical scenario which could make the glitches in the LSC error signals. It can be considered as a 4 step phenomenon.

        (1) up conversion noise due to a large motion at 3 Hz

   => (2) rms level exceeds the line width (a.k.a. linear range) in some LSC sensors

   => (3) unlocks some of the DOFs  in a moment

   => (4) glitches due to the short unlock.

- - plan  - -

 In order to check this hypothesis the low finesse PRMI must serve as a good test configuration.

What I will do is to gradually decrease the offset in MICH such that the finesse of PRMI becomes higher.

And at each different finesse I will check the spectra, glitch rate, and etc.

Quote from #6231

        Low finesse PRMI      

In this configuration NO glitches ( a high speed signal with an amplitude of more than 4 or 5 sigma) were found when it was locked.

Is it because I didn't use AS55 ?? or because the finesse is low ??

Also, as we have already known, the up conversion noise (#6212) showed up -- the level of the high frequency noise are sensitive to the 3 Hz motion.

  6281   Wed Feb 15 05:29:22 2012 kiwamuUpdateLSCsensing matrix of PRMI

I have measured the sensing matrix of PRMI.

It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control.

The data is coming soon.

  6283   Wed Feb 15 17:15:33 2012 kiwamuUpdateLSCsensing matrix of PRMI

I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts.

Smells like something is very wrong.

 

Measured sensing matrix

The measured matrix are shown in the diagram below.
The lengths of arrows corresponds to the signal strength in unit of V/m. The radial axis in in log scale.
The angle of arrows corresponds to their best demodulation phases.
sensingMAT.png

        Some obvious things:

  •  REFL11 : The separation angle between MICH and PRCL is narrow and it is far from the ideal 90 degree. This doesn't agree with the simulation.
  •  REFL33:  The MICH and PRCL signals are almost degenerated in their demodulation phase.
  •  REFL55 :  It shows non-90 degree separation. This doesn't agree with the simulation.
  •  REFL165 : The separation is close to 90 degree, but the signals are small. And I am not sure if the MICH signal is real or just noise.
  •  AS55 : Somehow it shows a nice 90 degree separation, but this result doesn't agree with the simulation.

 


Expected sensing matrix from a simulation

For a comparison here is a result from an Optickle simulation.
This time the radial unit is W/m instead of V/m, but they are qualitatively the same unit.
The radial axis is in log, so when it says 2, it means 10^2 [W/m].
PRMI_Optickle.png
 
 Simulation setup:
l_PRC  = 6.760 (see #4064)
l_asy  = 0.0364  (see #4821)
loss per optic = 50 ppm
 

Measurement

  •  Locked PRMI with the carrier anti-resonating in PRCL.
  •  Adjusted the control gains for both the MICH and PRCL control to have UGFs at ~ 100 Hz.
  •  Put a 30 dB notch filter  in each control servo at 283.1 Hz where an excitation signal will be.
  •  Excited PRCL and MICH at different time via the realtime lockng in the LSC front end. The amplitude is 1000 counts and the frequency is at 238.1 Hz.
    • For the MICH excitation, I have coherently and differentially excited ITMs
  •  Used DTT to take a transfer function (transfer coefficients at 283.1 Hz) from the lockin oscillator to each LSC demodulated signal.
    • Including AS55I/Q, REFL11I/Q, REFL33I/Q, REFL55I/Q and REFL165I/Q.
  •  Calibrated the obtained transfer functions from unit of counts/counts to V/m using the actuator response (#5637)

Quote from #6281
I have measured the sensing matrix of PRMI.
It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control.
The data is coming soon.

  6284   Thu Feb 16 03:47:16 2012 kiwamuUpdateLSCglitch table

I updated the table which I posted some time ago (#6231). The latest table is shown below.

It seems that the glitches show up only when multiple DOFs are locked.

Interesting thing is that when the low finesse PRMI is locked with a big MICH offset (corresponding to a very low finesse) it doesn't show the glitches.

Qualitatively speaking, the glitch rate becomes higher as the finesse increases.

I will try SRMI tomorrow as this is the last one which I haven't checked the presence of the glitches.

 

 

 Yarm

(POY11 -->

ETMY)

Xarm

(POX11 --> ETMX)

MICH

(AS55-->BS)

or

(AS55 --> ITMs)

Half PRMI

(REFL11 --> PRM)

or

(REFL33 --> PRM)

low finesse PRMI

(ASDC --> ITMs)

(REFL33 --> PRM)

PRMI (carrier)

(AS55 --> ITMs)

(REFL33 --> PRM)

PRMI (sideband)

(AS55 --> ITMs)

(REFL33 --> PRM)

DRMI
AS55 NO NO NO NO glitch (depends on finesse)
glitch glitch glitch
REFL11 NO NO NO NO glitch (depends on finesse)
glitch glitch glitch
REFL33 NO NO NO NO - glitch glitch glitch
REFL55 NO NO NO NO glitch(depends on finesse) glitch glitch glitch
REFL165 NO NO NO - - - - -
POX11 - NO NO NO  - glitch glitch glitch
POY11 NO - NO NO  - glitch glitch glitch
POP55 - - - -  -  - - -
                 

 

 

  6285   Thu Feb 16 04:02:16 2012 kiwamuUpdateLSCinsane REFL165 DC output

I found that the DC monitor of the REFL165 was showing 9 V regardless of how much laser power goes to the diode.

I am worried about whether the RF output is also broken.

It needs to be checked and I will leave this to Suresh as one of his morning tasks.

  6286   Thu Feb 16 04:29:30 2012 kiwamuUpdateLSCupconversion noise from BS motion

Sometimes ago I reported that there have been a kind of upconversion noise when PRM was excited (#6211).

This time I found another one, which showed up when BS was excited.

Assuming this is related to some kind of scattering process and also assuming this is from the same scattering body as that for the PRM driven case,

we may be able to localize and perhaps identify the scattering body.

 

 

(Measurement Condition)

All the suspended optics are intentionally misaligned except for ITMY so that the laser directly goes through to the dark port without any interference.
Then BS_POS is excited at 3 Hz with amplitude of 1000 counts by an oscillator in the realtime lockin system.
 I also excited PITCH and YAW of BS and found that driving the angular motions didn't produce any upconversion noise.
 I didn't excite ITMY to do the same test because I was too lazy.

(Noise spectrum)

The plot below shows the upconversion noise observed at AS55 and REFL11.
The reference curves were obtained when no excitation were applied on BS_POS.
It is obvious that the AS55 signal shows a typical upconversion behavior.
 
Untitled.png

 

  6287   Thu Feb 16 07:38:24 2012 KojiUpdateLSCsensing matrix of PRMI

So why don't you use AS55I and Q for the control of PRMI???

  6289   Thu Feb 16 13:12:30 2012 ranaUpdateLSCsensing matrix of PRMI

Quote:

I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts.

Smells like something is very wrong.

 Those Radar plots are awesome. Even more awesome would be if they were in units of W/m (so that it can be directly compared with Optickle) and so that the numbers are useful even 1 year from now. Otherwise, we will lose the RF transimpedance information and thereby lose everything.

Also, please post the provenance of the counts->V calibration.

  6293   Fri Feb 17 04:45:48 2012 kiwamuUpdateLSCsensing matrix of PRMI

I locked the PRMI with the AS55I and Q combination.

It seems the glitche rate decreased,

but I am not 100 % sure because the rest of the demod signals (i.e. REFL11 and etc) were showing relatively big signals (noise ?), which may cover the glitches.

Also the optical gain of PRCL at AS55I doesn't agree with my expectation based on the obtained sensing matrix (#6283).

It looks too low and lower than the measured sensing matrix by a factor of 50 or so.

I will continue working on this configuration tomorrow and then move on to the SRMI locking as a part of the glitch hunting activity.

Quote from #6287

So why don't you use AS55I and Q for the control of PRMI???

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