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ID Date Author Type Category Subjectup
  2323   Tue Nov 24 18:24:54 2009 SanjitConfigurationAdaptive FilteringASS channels added to framebuilder

 

[Sanjit, Jenne, Rob, Joe]

 

We added and tested the following channels from "/cvs/cds/gds/param/tpchn_C3.par" to "/cvs/cds/caltech/chans/daq/C1ASS.ini" appending a "_2048" extension to the channel name (as the name of a channel in .ini and .par files must be different):

[C1:ASS-TOP_CORR_IN1_2048]
[C1:ASS-TOP_ERR_EMPH_IN1_2048]
[C1:ASS-TOP_PEM_10_IN1_2048]
[C1:ASS-TOP_PEM_11_IN1_2048]
[C1:ASS-TOP_PEM_12_IN1_2048]
[C1:ASS-TOP_PEM_15_IN1_2048]
[C1:ASS-TOP_PEM_16_IN1_2048]
[C1:ASS-TOP_PEM_17_IN1_2048]
[C1:ASS-TOP_PEM_18_IN1_2048]
[C1:ASS-TOP_PEM_19_IN1_2048]
[C1:ASS-TOP_PEM_20_IN1_2048]
[C1:ASS-TOP_PEM_24_IN1_2048]
[C1:ASS-TOP_PEM_2_IN1_2048]
[C1:ASS-TOP_PEM_3_IN1_2048]
[C1:ASS-TOP_PEM_4_IN1_2048]
 

These five-line entries for each channels in the .par file were manually copy pasted from the .ini file, should think about a smarter way...

The old .par file is kept as: /cvs/cds/caltech/chans/daq/C1ASS.ini.20Nov2009

The current one is also saved as: /cvs/cds/caltech/chans/daq/C1ASS.ini.24Nov2009

And, the current one is committed to the svn.

 

NOTE: In the first attempt, the channel names were mistakenly kept the same in both the .ini and .par files and this caused DAQ daemon to crash badly. It could only be recovered by hard reboot of the frame builder.  Important info here: Jenne's elog 2316

  383   Sun Mar 16 17:03:32 2008 robConfigurationCDSASS code change

I've updated the ass.mdl file in the directory:

/cvs/cds/caltech/users/alex/cds/advLigo/src/epics/simLink/

to get us started in the adaptive PEM noise subtraction.

After several iterations of remote help from Alex, the code compiles and runs, receives signals from the LSC, PEM, and MC2, and communicates with the suspension controllers. I've also adapted the .par file from the code generator, but haven't got the testpoints working with the new ASS code. There are no MEDM screens yet, and Matt's adaptive filter code has not been installed (there's a matrix as a placeholder).

Putting in the adaptive code should be simple, building the MEDM screens tedious, and getting the testpoints working uncertain. I noticed that the new testpoint.par file starts at a different channel number than the previous (working) version, which is strange. I probably have a script somewhere to change all these numbers by a constant offset, but I don't know if that's the actual problem--maybe stuff just needs to be rebooted.

The code receives as input the first 24 channels from the PEM ADCU, the eight suspension control signals from the LSC, and the output of the MCL filter from MC2. It outputs to the MCL filter input of each suspension (except MC2).
  740   Fri Jul 25 17:32:46 2008 SharonUpdate ASS computer
So, it seems a bit too complicated getting the coefficients the way I wanted it to happen (simulink-.ini...).
I returned everything to the way it was and it's all working. The new plan is to choose the specific channel I want to find its instantanous coefficients, let the adaptive code run for a while, setting mu and tau to zero (freezing the coefficients), and exciting the noise signal channel taking the transfer function. This way I can find the filter I want to simulate with an IIR filter.
Once I have the mode cleaner to myself, I'll start posting results.
  6723   Thu May 31 01:20:41 2012 JenneUpdateASSASS filter outputs are non-zero with no input

I was looking a little at ASS, while Yuta was doing some Green transmitted DC PD work, and I find that the output of some filters is totally insane with no deliberate input or excitation signals.

Note in the figure that the filter (which is a 2nd order butter bandpass in the C1:ASS-LOCKIN29_SIG filter bank) is ringing a lot - this needs fixing.  But, more disconcertingly, sometimes (not every time) the arm flashes, the input to the filter bank gets a ~1 sample long spike that is ~9,000,000 counts.  9 million is a lot of counts.  This is then making the filter go crazy.

Any ideas on how this can happen, and how we can stop / fix it?  It's certainly a CDS issue, but I'm not sure where or how.

Attachment 1: ASS_Yarm_crazyOutputs_30May2012.png
ASS_Yarm_crazyOutputs_30May2012.png
  10719   Fri Nov 14 19:28:33 2014 JenneUpdateSUSASS gain reduced for Yarm

[Koji, Jenne]

We noticed last night that the yarm couldn't handle the old nominal gain for the ASS servos.  We were able to run the ASS using about 0.3 in the overall gain.  So, I have reduced the gain in each of the individual servos by a factor of 3, so that the scripts work, and can set the overall gain to 1.

  6979   Tue Jul 17 02:17:50 2012 JenneUpdateASCASS gains wrong?
I was checking on the ASS system, and I think that the gains on some of the loops may not be correct. An old symptom was that the commands in the script were not being executed when we changed over to Ubuntu. Now it seems that each command is working fine, but the loops are pushing the optics more out of alignment than anything. I flipped the sign on some of the loops and it helped, others it didn't. I need to measure some transfer functions and meditate on what they should look like. It will be really nice to have the alignment system working again.
  12869   Mon Mar 6 12:34:30 2017 johannesSummaryASSASS light injection scenarios

What we want from the light source for the AS port light injection:

  • Frequency control for locking and maintaining known offset from arm cavity resonances -> see below
  • Fast extinguishing light in the IFO -> AOM first order switching

We have four possible laser sources that we can use for the injection of 1064 nm from the back:

  • There are ~65 mW of IR power coming from the PSL doubling oven, of which ~2mW are used for the fiber beat box. The remaining light is currently dumped on the PSL table and would be available. It is picked off after the PMC and does not have any of the sidebands.
  • There is a ~200 mW Lightwave NPRO on the PSL table that is currently unused.
  • Koji said he has a ~500mW NPRO in the OMC lab that has no PZT actuation. I contacted a couple companies about fiber-coupled variable AOM frequency shifters that we can pair with this laser.
  • I don't think using the high power beam of the PSL itself is a good idea, especially if we want to map the loss on the optics, because' we'll need it for the dither locking

I think for maximum flexibility it's best to fiber-couple whichever source we choose on the PSL table and then just collimate it out of a fiber on the AS table. This way if we want to add fiber-coupled modulators of any kind it's a plug-and-play modification.

Different frequency control schemes are:

  • Modulate sidebands on the light and stabilize directly to the arm, using POX/Y or back-reflection at AS
    • Free-space resonant EOM
    • Free-space broadband EOM with Rich's resonant amplifier attachment
    • Fiber-coupled EOM
  • Offset phaselock:
    • PSL IR: Transfer mode-cleaner stability
      • Can lock arms while measurement in progress, but will have PSL IR light on PDs
    • Green from the end;
      • Broadly tunable laser frequency and no interference from IR.

Either way we'll need a few things:

  • Faraday Isolator
    • required for PDH locking, optional if we phaselock instead
  • AOM
    • We have free-space available, looking into fiber-coupled ones with frequency tuning
    • Fast switching electronics
  • Various fiber stuff
    • We have enough to set up the fiber coupling of one light source. I'm starting with the 200 mW NPRO but this is technically interchangable.

I'm working on how to best set this up at the AS port and interfere with normal operation as little as possible. Ideally we use a Faraday just like for squeezed light injection, but this requires some modification of the layout, although nothing that involves mode-matching.

 

 

  7137   Thu Aug 9 23:50:09 2012 JenneUpdateASSASS matrix measured, first ASS test

Koji pointed out that I was being silly, and rather than actually misaligning the optics (by, say, changing their IFO Align sliders) I was changing the location of the actuation node by changing the coil output gains.  Now I see nice signals at the I_OUT of each of the demodulators (so far I've only looked at the YARM).

I've measured and inverted the matrix by taking the nominal values of the demodulator outputs when the optics are all by-hand optimally aligned, then one-by-one misaligning an optic's angle (pitch or yaw), and looking at the demod outputs that result.  Repeat with each misalignment DoF for each of the 4 rows of the matrix.  Then I set the pit/yaw coupling elements of the matrix to zero.  Then invert the matrix, put it in, and see what happens.  So far, the yaw DoFs converged to zero, but the pitch ones didn't.  I'll play with it more and think some more tomorrow.

  12140   Mon May 30 18:19:50 2016 JohannesUpdateCDSASS medm screen update

I noticed that the TRY button in the ASS main screen was linking to LSC_TRX instead of LSC_TRY. Gautam fixed it.

  8657   Thu May 30 11:33:26 2013 JamieConfigurationComputer Scripts / ProgramsASS medm/model changes need to be committed to SVN

There are a lot of changes to the ASS stuff that have not been committed to the SVN:

controls@rossa:/opt/rtcds/userapps/release/isc/c1 0$ svn status | grep -v '?'
M       medm/c1als/C1ALS_X_SLOW.adl
D       medm/c1ass/C1ASS_TRY_YAW_LOCKIN.adl
D       medm/c1ass/ASS_SERVOS.adl
D       medm/c1ass/ctrl_yaw_mtrx.adl
D       medm/c1ass/C1ASS_QPDS.adl
D       medm/c1ass/C1ASS_SEN_YAW_MTRX.adl
M       medm/c1ass/C1ASS_XARM_SEN_MTRX.adl
D       medm/c1ass/SITEMODEL_LOCKINNAME.adl
D       medm/c1ass/C1ASS_TRX_YAW_LOCKIN.adl
D       medm/c1ass/C1ASS_LOCKIN1.adl
D       medm/c1ass/C1ASS_LOCKIN2.adl
D       medm/c1ass/C1ASS_LOCKIN3.adl
D       medm/c1ass/C1ASS_LOCKIN4.adl
D       medm/c1ass/C1ASS_LOCKIN5.adl
D       medm/c1ass/C1ASS_LOCKIN6.adl
D       medm/c1ass/C1ASS_LOCKIN7.adl
D       medm/c1ass/C1ASS_LOCKIN8.adl
D       medm/c1ass/C1ASS_LOCKIN9.adl
D       medm/c1ass/C1ASS_REFL11I_PIT_LOCKIN.adl
M       medm/c1ass/C1ASS.adl
D       medm/c1ass/C1ASS_LOCKIN10.adl
D       medm/c1ass/C1ASS_LOCKIN11.adl
D       medm/c1ass/C1ASS_LOCKIN12.adl
D       medm/c1ass/C1ASS_LOCKIN13.adl
D       medm/c1ass/C1ASS_LOCKIN14.adl
D       medm/c1ass/C1ASS_LOCKIN15.adl
D       medm/c1ass/sen_yaw_mtrx.adl
D       medm/c1ass/C1ASS_LOCKIN16.adl
D       medm/c1ass/C1ASS_LOCKIN17.adl
D       medm/c1ass/C1ASS_DOF_YAW.adl
D       medm/c1ass/C1ASS_LOCKIN18.adl
D       medm/c1ass/C1ASS_LOCKIN19.adl
D       medm/c1ass/C1ASS_TRY_PIT_LOCKIN.adl
D       medm/c1ass/ctrl_pit_mtrx.adl
D       medm/c1ass/C1ASS_SEN_PIT_MTRX.adl
D       medm/c1ass/C1ASS_LOCKIN20.adl
D       medm/c1ass/C1ASS_LOCKIN21.adl
D       medm/c1ass/C1ASS_LOCKIN22.adl
D       medm/c1ass/C1ASS_LOCKIN23.adl
D       medm/c1ass/C1ASS_LOCKIN24.adl
D       medm/c1ass/C1ASS_LOCKIN25.adl
D       medm/c1ass/C1ASS_LOCKIN26.adl
D       medm/c1ass/C1ASS_LOCKIN27.adl
D       medm/c1ass/C1ASS_TRX_PIT_LOCKIN.adl
D       medm/c1ass/C1ASS_LOCKIN28.adl
D       medm/c1ass/C1ASS_LOCKIN29.adl
D       medm/c1ass/C1ASS_XARM_QPDS.adl
D       medm/c1ass/C1ASS_YARM_QPDS.adl
M       medm/c1ass/C1ASS_XARM_OUT_MTRX.adl
D       medm/c1ass/ASS_SEN_MTRX.adl
D       medm/c1ass/ASS_LOCKINS.adl
D       medm/c1ass/sen_pit_mtrx.adl
D       medm/c1ass/C1ASS_REFL11I_YAW_LOCKIN.adl
D       medm/c1ass/C1ASS_LOCKIN30.adl
D       medm/c1ass/C1ASS_DOF_PIT.adl
M       models/c1ass.mdl
controls@rossa:/opt/rtcds/userapps/release/isc/c1 0$
  7135   Thu Aug 9 12:31:36 2012 JenneUpdateASSASS rebuilt again
I was (in between Eric's measurements) driving the YARM ASS dithers, and noticed that instead of driving ITMY PIT, I was driving ITMX PIT. I looked in the model, and when I re-did the model after an svn revert a few days ago, it looks like I got the shmem parts for the ITM PIT signals backwards. I have fixed that, rebuilt, installed and restarted the ass model.
  9081   Wed Aug 28 06:26:28 2013 manasaUpdateComputer Scripts / ProgramsASS req and snap files edited

[From yesterday] ASS for X arm was behaving slightly funny over the last couple of days. ASS could not correct the BS misalignment. Jenne pointed out that the LSC output matrix on the ASS medm screen set itself to zeroes whenever we ran the ASS_dither_ON script. I checked the burt request file: ASS_DITHER_ON.req  in /opt/rtcds/caltech/c1/scripts/ASS and found that the LSC output matrix channels were not added to it. I added these channels for both the X and Y arm. Following this, I also edited the corresponding snap file as well. This should now set the LSC matrix to the right values everytime we run the script.

  13033   Fri Jun 2 01:22:50 2017 gautamUpdateASSASS restoration work

I started by checking if shaking an optic in pitch really moves it in pitch - i.e. how much PIT to YAW coupling is there. The motivation being if we aren't really dithering the optics in orthogonal DoFs, the demodulated error signals carry mixed information which the dither alignment servos get confused by. First, I checked with a low frequency dither (~4Hz) and looked at the green transmission on the video monitors. The spot seemed to respond reasonably orthogonally to both pitch and yaw excitations on either ITMY or ETMY. But looking at the Oplev control signal spectra, there seems to be a significant amount of cross coupling. ITMY YAW, ETMY PIT, and ETMY YAW have the peak in the orthogonal degree of freedom at the excitation frequency roughly 20% of the height of the DoF being driven. But for ITMY PIT, the peaks in the orthogonal DoFs are almost of equal height. This remains true even when I changed the excitation frequencies to the nominal dither alignment servo frequencies.

I then tried to see if I could get parts of the ASS working. I tried to manually align the ITM, ETM and TTs as best as I could. There are many "alignment references" - prior to the coil driver board removal, I had centered all Oplevs and also checked that both X and Y green beams had nominal transmission levels (~0.4 for GTRY, ~0.5 for GTRX). Then there are the Transmon QPDs. After trying various combinations, I was able to get good IR transmission, and reasonable GTRY.

Next, I tried running the ASS loops that use error signals demodulated at the ETM dither frequencies (so actuation is on the ITM and TT1 as per the current output matrix which I did not touch for tonight). This worked reasonably well - Attachment #1 shows that the servos were able to recover good IR transmission when various optics in the Y arm were disturbed. I used the same oscillator frequencies as in the existing burt snapshot. But the amplitudes were tweaked.

Unfortunately I had no luck enabling the servos that demodulate the ITM dithers.

The plan for daytime work tomorrow is to check the linearity of the error signals in response to static misalignment of some optics, and then optimize the elements of the output matrix.

I am uploading a .zip file with Sensoray screen-grabs of all the test-masses in their best aligned state from tonight (except ITMX face, which for some reason I can't grab).

And for good measure, the Oplev spot positions - Attachment #3.

Quote:

While Gautam is working the restoration of Yarm ASS, I worked on Xarm.

 

Attachment 1: ASS_Y_recovery.png
ASS_Y_recovery.png
Attachment 2: ASS_Repairs.zip
Attachment 3: OLs.png
OLs.png
  10789   Fri Dec 12 04:33:49 2014 JenneUpdateASCASS retuned

[Rana, Jenne]

We decided that tonight was the night for ASS tuning. 

We started from choosing new frequencies, by looking at the transmission and the servo control signals spectra to find areas that weren't too full of peaks.  We chose to be above the OpLev UGF by at least a factor of ~2, so our lowest frequency is about 18Hz.  This way, even if the oplevs are retuned, or the gains are increased, the ASS should still function. 

We set the peak heights for the lowest frequency of each arm to have good SNR, and then calculated what the amplitude of the higher frequencies ought to be, such that the mirrors are moving about the same amount in all directions. 

We re-did the low pass filters, and eliminated the band pass filters in the demodulation part of the servo.  The band passes aren't strictly necessary, as long as you have adequate lowpassing, so we have turned them off, which gives us the freedom to change excitation frequencies at will.  We modified the lowpass filter so that we had more attenuation at 2Hz, since we spaced our excitation frequencies at least ~2.5 Hz apart.

The same lowpass filter is in every single demodulator filter bank (I's and Q's, for both length and transmission demodulation).  We are getting the gain hierarchy just by setting the servo gains appropriately. 

We ran ezcaservos to set the demodulation phase of each lockin, to minimize the Q-phase signal. 

We then tuned up the gains of the servos.  Rana did the Y arm, but for the X arm I tried to find the gains where the servos went unstable, and then reduced the gain by a factor of 2.  The Xarm is having trouble getting good alignment if you start with something less than about 0.7, so there is room for improvement.

Rana wrote a little shell script that will save the burt snapshot, if the gains need adjusting and they should be re-saved. 

The scripts have been modified (just with the new oscillator amplitudes - everything else is in the burt snapshots), so you should be able to run the start from nothing and the start from frozen scripts for both arms.  However, please watch them just in case, to make sure they don't run away.

  10807   Wed Dec 17 01:51:44 2014 rana, jenneUpdateASCASS retuned

Did a big reconfig to make the Y-arm work again since it was bad again.

  1. Undid Koji's topology change. The A2L loops now feedback to the arm mirrors to adjust the cavity axis. The cavity transmission signals now feedback to the input beam.
  2. The UGF of the Trans->Input beam servos is ~5-10x higher than the A2L servos.
  3. The Trans loops have a ~10-15 s settling time.
  4. The Input Matrix has been adjusted to fit with our intuition:The ETM tilt moves the beam equally on the ITM and ETM faces.
  5. The Output Matrix has also been adjusted to do like this: we're using an intuitive matrix inverse rather than one based on measurement. It turns out to be a reasonable guess and we can tune this later.
  6. Seems stable with many kinds of steps and misalignments. Seems not reliable if the arm power is less than ~0.5.
  7. Reducing the dither amplitudes to make the power fluctuation less than 5% made it much more stable.

With the arm aligned and the A2L signals all zeroed, we centered the beam on QPDY (after freezing the ASS outputs). I saw the beam going to the QPD on an IR card, along with a host of green spots. Seems bad to have green beams hitting the QPD alogn with the IR, so we are asking Steve to buy a bunch of the broad, dielectric, bandpass filters from Thorlabs (FL1064-10), so that we can also be immune to the EXIT sign. I wonder if its legal to make a baffle to block it on the bottom side?

P.S. Why is the Transmon QPD software different from the OL stuff? We should take the Kissel OL package and put it in place of our old OL junk as well as the Transmons.

Attachment 1: ASSconfig_141217_0205.png
ASSconfig_141217_0205.png
  10812   Wed Dec 17 19:04:12 2014 jenneUpdateASCASS retuned

I made the Xarm follow the new (old) topology of Length -> test masses, and Trans -> input pointing.

It takes a really long time to converge (2+ min), since the input pointing loops actuate on the BS, which has an optical lever, which is slow.  So, everything has to be super duper slow for the input pointing to be fast relative to the test mass motion.

Also, between last night and this afternoon, I moved the green ASX stuff from a long list of ezca commands to a burt file, so turning it on is much faster now.  Also, I chose new frequencies to avoid intermodulation issues, set the lockin demodulation phases, and tuned all 4 loops.  So, now the green ASX should work for all 4 mirrors, no hand tuning required.  While I was working on it, I also removed the band pass filters, and made the low pass filters the same as we are using for the IR ASS.  The servos converge in about 30 seconds.

  10813   Wed Dec 17 19:31:55 2014 KojiUpdateASCASS retuned

I wonder what to do with the X arm.

The primary purpose of the ASS is to align the arm (=transmission), and the secondary purpose is to adjust the input pointing.

As the BS is the only steering actuator, we can't adjust two dof out of 8 dof.
In the old (my) topology, the spot position on ITMX was left unadjusted.

If my understanding of the latest configuration, the alignment of the cavity (=matching of the input axis with the cavity axis)
is deteriorated in order to move the cavity axis at the center of the two test masses. This is not what we want as this causes
deterioration of the power recycling gain.

  10946   Tue Jan 27 21:33:39 2015 KojiUpdateASCASS retuned

I checked the situation of ASS. I wanted to know how much we are away from the maximum transmittion.

Conclusion:
ASS makes the X arm shifted from the maximum transmission. This causes the contrast degraded by ~3%.
We need to fix the Xarm ASS so that it can maximize the transmission and ignor the spot centering at ITMX.


Conditioning before the measurement:

- ASDC offset was removed
- X&Y arm was aligned by ASS

With ASS:

Average transmission: 0.86
Pmax = 1045 +/- 9 cnts
Pmin = 22 +/- 4 cnts

==> Contrast = (Pmax - Pmin)/(Pmax+Pmin) = 0.960+/-0.007

After manual alignment of the X arm (ignoring spot centering):

Average transmission: 0.88
Pmax = 1103 +/- 11 cnts
Pmin = 5 +/- 1 cnts

==> Contrast = (Pmax - Pmin)/(Pmax+Pmin) = 0.991+/-0.002

  5817   Sat Nov 5 00:04:23 2011 kiwamuUpdateASCASS scripts gone

Did somebody delete all the scripts in /opt/rtcds/caltech/c1/scripts/ASS ?

  5818   Sat Nov 5 00:24:13 2011 SureshUpdateASCASS scripts gone

Quote:

Did somebody delete all the scripts in /opt/rtcds/caltech/c1/scripts/ASS ?

 I have moved all the MC_ASS scripts to a directory called MC under ASS

 

  5821   Sat Nov 5 14:54:59 2011 KojiUpdateASCASS scripts gone

In any case, the daily backup of the scripts are found in /cvs/cds/caltech/scripts_archive

Quote:

Quote:

Did somebody delete all the scripts in /opt/rtcds/caltech/c1/scripts/ASS ?

 I have moved all the MC_ASS scripts to a directory called MC under ASS 

 

  6677   Thu May 24 16:13:05 2012 yutaUpdateComputersASS scripts on new ubuntu machines

[Den, Yuta]

Background:
 ASS and many other scripts don't work on new ubuntu machines.

What we did:
1. Installed C-shell on rossa and rosalba(Ubuntu machine).
  sudo apt-get insall csh

2. Find out that
  /opt/rtcds/caltech/c1/scripts/AutoDither/alignY

runs, but
  /opt/rtcds/caltech/c1/scripts/medmrun /opt/rtcds/caltech/c1/scripts/AutoDither/alignY

doesn't run. It gives us the following error messages.

ezcawrite: error while loading shared libraries: libca.so: cannot open shared object file: No such file or directory
ezcaswitch: error while loading shared libraries: libca.so: cannot open shared object file: No such file or directory

Result:
 ASS scripts run on rossa and rosalba, but not with medmrun.
 At least ASS scripts run on pianosa(ubuntu machine) with medmrun. So we decided to wait for JAMIE to fix it.

  6684   Fri May 25 17:50:38 2012 JamieUpdateComputersASS scripts on new ubuntu machines

Quote:

[Den, Yuta]

Background:
 ASS and many other scripts don't work on new ubuntu machines.

What we did:
1. Installed C-shell on rossa and rosalba(Ubuntu machine).
  sudo apt-get insall csh

2. Find out that
  /opt/rtcds/caltech/c1/scripts/AutoDither/alignY

runs, but
  /opt/rtcds/caltech/c1/scripts/medmrun /opt/rtcds/caltech/c1/scripts/AutoDither/alignY

doesn't run. It gives us the following error messages.

ezcawrite: error while loading shared libraries: libca.so: cannot open shared object file: No such file or directory
ezcaswitch: error while loading shared libraries: libca.so: cannot open shared object file: No such file or directory

Result:
 ASS scripts run on rossa and rosalba, but not with medmrun.
 At least ASS scripts run on pianosa(ubuntu machine) with medmrun. So we decided to wait for JAMIE to fix it.

Apparently the environment was not being properly inherited by the scripts launched from medmrun.  We modified the medmrum script so that it executes things with an interactive shell ("bash -i -c ...") and this fixed the problem (by assuring that it sources all the interactive environment configs (i.e. ~/.bashrc)).  I'm still not sure why we were seeing different behavior on pianosa, but at least the solution we have now should be robust.

As a reminder, all scripts launched from MEDM should use medmrun:

/opt/rtcds/caltech/c1/scripts/medmrun
  8977   Wed Aug 7 15:32:37 2013 KojiUpdateASCASS setting up accelerated (slightly)

I moved bunch of ezcawrite from the ASS Dither On script to a snapshot file.

This accelerated a half of the "up" time but still switching part is not in the snapshot.

If you find anything wrong with ASS, please notify me.

  8980   Wed Aug 7 19:16:20 2013 JenneUpdateASCASS setting up accelerated more

I have furthered Koji's work, and moved the filter on/off state for all the filter banks also to the burt snapshot.  

Turning on the ASS is now much faster than it was originally, with the ezcawrites in series.

  7100   Tue Aug 7 03:20:56 2012 JenneUpdateASSASS setup, on, off scripts written

I wrote new setup, on and off scripts for the arm ass.  They take the arm as an argument, so it's the same script for both arms.  Scripts are in ...../scripts/ASS/ , and have been checked in to the 40m svn.

So far the on script doesn't really do anything, since I haven't chosen values for the CLKGAINs of the lockins.  The old values were 30 for lockins 12, 14, 27, 29 and 250 for lockins 7, 9, 22, 24.  Unfortunately, I have no memory of which lockin means what in the old numbered system.  I'll have to look that up somehow.  Or, just dither the optics using some value and look at the spectrum to see the resulting SNR and just pick something that gives me reasonable SNR.

I modified the ASS model slightly:

* Added an overall gain to the ASS_DOF2 library part, between the matrix and the servo inputs so we can do soft startups.  Self - remember that the main ASS screen needs to be modified to reflect this!

* Rearranged the order that the demodulated signals go into the matrix.  I hadn't paid attention, and the old ordering had the transmission (TRX/TRY) demod signals interleaved with the LSC demod signals.  I've changed it to be all the TR signals, then all the LSC signals.  I think this makes more sense, since we will use these inputs separately, so now they're on different halves of the matrix.

  8982   Wed Aug 7 22:18:43 2013 KojiUpdateASCASS update

While Gautam is working on the Xarm green ASS...

The EPICS monitor points for the ASS actuators were added to the ASS model.

This will be used for the offloading the ASS actuations to the alignment biases.
As this modification allowed us to monitor the actuation apart from the dithering,
now we can migrate the ASS actuation to the fast alignment offset on the suspension.
This modification to the offset moving scripts were also done.

Screenshot-Untitled_Window.png

  9018   Fri Aug 16 13:25:50 2013 KojiUpdateASSASX model/screen cleaning up

[Koji Manasa]

Yesterday we cleaned up the ASX model and screens to have more straight forward structure of the screen
and the channel names, and to correct mistakes in the model/screens.

The true motivation is that I suspect the excess LF noise of the X arm ALS can be caused by misalignment
and beam jitter coupling to the intensity noise of the beat. I wanted to see how the noise is affected by the alignment.
Currently X-end green is highly misaligned in pitch.

- Any string "XEND" was replaced by "XARM", as many components in the system is not localized at the end table.

- The name like "XARM-ITMX" was changed to "XARM-ITM". This makes easier to create the corresponding model for the other arm.

- There was some inconsistency between the MEDM screens and the ASX model. This was fixed.

- A template StripTool screen was created. It is currently saved in users/koji/template as ASX.stp.
  It will be moved to the script directory once it's usefulness is confirmed.


The next step is to go to the end table and manually adjust M2 mirror while M1 is controlled by the ASX.
The test mass dithering provides the error signal for this adjustment but the range of the PZT is not enough
to make the input spot position to be controlled. In the end, we need different kind of matching optics
in order to control the spot position. (But is that what we want? That makes any PZT drift significantly moves the beam.)

  14716   Mon Jul 1 20:27:44 2019 gautamUpdateASCASX tuning

Summary:

To practise the dither alignment servo tuning, I decided to make the ASX system work again (mainly because it has fewer DoFs and so I thought it'd be easier to manage). Setup is: dither PZT mirrors on EX table-->demodulate green transmission at the dither frequencies-->Servo the error signals to 0 by an integrator.

Details:

  1. Started by checking the dither lines are showing up with good SNR in GTRX. They are, see Attachment #1. The dither lines are at 18.23 Hz, 27.13 Hz, 53.49 Hz and 41.68 Hz, and all of them show up with SNR ~100.
  2. Hand-aligned the beam till I got a maximum of GTRX ~ 0.35. This is lower than the usual ~0.5 I am used to - possibilities are (i) in the process of plugging in the BNC cable to the rear of the EX laser for my PLL investigations, I disturbed the alignment into the SHG crystal ever so slightly and I now have less green light going into the cavity or (ii) there is an iris on the EX table just before the green beam goes into the vacuum on which it is getting clipped. IIRC, I had centered the GTRX camera view such that the spot was well centered in the field of view, but now I see substantial mis-centering in pitch. So the cavity alignment for IR could also be sub-optimal (although I saw TRX ~1.15). Anyways, I decided to push on.
  3. Introduced a deliberate offset in a given DoF, e.g. M1 PIT. Then I looked at the demodulated error signals (filtered through an RLP0.5 filter post demodulation, so the 2f component should be attenuated by 100 dB at least), and tuned the demod phase until most of the signal appeared in the I-phase, which is what is used for servoing. The Q-phase signals were ~x10 lower than their I-phase counterparts after the tuning.
  4. Checked the linearity of the error signal in response to misalignment of a given DoF. I judged it to be sufficiently linear for all four DoFs about the quadratic part of the GTRX variation.
  5. Tweaked the overall servo gains to have the error signals be driven to 0 in ~10 seconds.
  6. There was quite significant cross-coupling between the DoFs - why should this be? I can understand the PIT->YAW coupling because of imperfect mounting of the PZT mounted mirror in a rotational sense, but I don't really understand the M1->M2 coupling.
  7. Nevertheless, the servo appears to work - see Attachment #2.

The adjusted demod phases, servo gains were saved to the .snap file which gets called when we run the "DITHER ON" script. Also updated the StripTool template.

I plan to repeat similar characterization on the IR dither alignment servos. I think the tuning of the ASS settings can be done independently of figuring out the mystery of why the TRY level is so low.

Attachment 1: ASX_ditherlines.pdf
ASX_ditherlines.pdf
Attachment 2: ASX.png
ASX.png
  15316   Fri May 1 22:44:17 2020 gautamUpdateALSASY M2 PZT damaged

I went to EY and saw that the HV power supply was only putting out 50 V and had hit the current limit of 10 mA (nominally, it should be 100 V, drawing ~7mA). This is definitely a problem that has come up after the power shutdown event, as when I re-energized the HV power supply at EY, I had confirmed that it was putting out the nominal values (the supply was not labelled with these nominal numbers so I had to label it). Or maybe I broke it while running the dither alignment tests yesterday, even though I never drove the PZTs above 50 Hz with more than 1000cts (= 300 mV * gain 5 in the HV amplifier = 1.5 V ) amplitude.

The problem was confirmed to be with the M2 PZT (YAW channel) and not the electronics by driving the M2 PZT with the M1 channels. Separately, the M1 PZT could be driven by the M2 channels. I also measured the capacitance of the YAW channels and found it to be nearly twice (~7 uF) of the expected 3 uF - this particular PZT is different from the three others in use by the ASX and ASY system, it is an older vintage, so maybe it just failed? 😔 

I don't want to leave 100 V on in this state, so the HV supply at EY was turned off. Good GTRY was recovered by manual alignment of the mirror mounts. If someone has a spare PZT, we can replace it, but for now, we just have to live with manually aligning the green beam often.

Quote:

Could be that the power outage busted something in the drive electronics. 

  15317   Sat May 2 02:35:18 2020 KojiUpdateALSASY M2 PZT damaged

Yes, we are supposed to have a few spare PI PZTs.

  15315   Fri May 1 01:49:55 2020 gautamUpdateALSASY commissioning

Summary:

It appears that the EY green steering PZTs have somehow lost their bipolar actuation range. I will check on them the next time I go to the lab for an N2 switch.

Details:

  • Yuki installed the EY green PZTs and did some initial setup of the RTCDS model. 
  • But we don't have a functional dither alignment servo yet, which is mildly annoying. So I thought I'll finally finish my SURF project.
  • There were several problems with the signal flow, MEDM screens etc.
  • I rectified these, and set up some operational scripts, burt snapshots etc in $SCRIPTS/ASY. The c1asy and c1als models were also modified, recompiled and restarted, everything appears to have come back online smoothly.
  • The LO frequencies/amplitudes, demod filter gains and demod phases were chosen to have a signal mostly in the _I quadrature of the demodulated signal when the alignment is slightly disturbed from optimal (monitored after the post-demod LPF).
  • While trying to close the integrator loops, I found that I appear to only have monopolar actuation ability (positive DAC output changes the alignment, negative DAC output does nothing).

Could be that the power outage busted something in the drive electronics. 

  8495   Fri Apr 26 10:50:07 2013 AnnalisaUpdateABSLATF laser on PSL

The ATF NPRO auxiliary laser has been moved on the PSL table. All the optics for beat note measurement are in place and alignment has been done.

The setup for this measurement is the same as described in elog 8333.

  3442   Thu Aug 19 11:38:48 2010 AlastairUpdateComputersATF wiki

The ATF wiki page doesn't seem to be working any more.  Does anyone know where this is held so we can try to get it back online?  Thanks

  3443   Thu Aug 19 12:06:07 2010 AlastairUpdateComputersATF wiki

Quote:

The ATF wiki page doesn't seem to be working any more.  Does anyone know where this is held so we can try to get it back online?  Thanks

 I phoned Phil Ehrens and found out that all these wikis have been moved to a new wiki site

The ATF wiki can now be found here

I have updated the link from the 40m wiki to reflect this

  14035   Tue Jul 3 11:59:10 2018 JonUpdateAUXAUX Carrier Scan of Y-Arm Cavity

I made the first successful AUX laser scan of a 40m cavity last night.

Attachment #1 shows the measured Y-end transmission signal w.r.t. the Agilent drive signal, which was used to sweep the AUX carrier frequency. This is a distinct approach from before, where the carrier was locked at a fixed offset from the PSL carrier and the frequency of AM sidebands was swept instead. This AUX carrier-only technique appears to be advantageous.

This 6-15 MHz scan resolves three FSR peaks (TEM00 resonances) and at least six other higher-order modes. The raw data are also enclosed (attachment #2). I'll leave it as an excercise for the SURFs to compute the Y-arm cavity Gouy phase.

Attachment 1: yarm_carrier_trans.pdf
yarm_carrier_trans.pdf
Attachment 2: AG4395A_02-07-2018_185504.txt
# AG4395A Measurement - Timestamp: Jul 02 2018 - 18:55:04
#---------- Measurement Parameters ------------
# Start Frequency (Hz): 6000000.0, 6000000.0
# Stop Frequency (Hz): 15000000.0, 15000000.0
# Frequency Points: 801, 801
# Measurement Format: LOGM, PHAS
# Measuremed Input: AR, AR
#---------- Analyzer Settings ----------
# Number of Averages: 16
# Auto Bandwidth: Off, Off
... 807 more lines ...
  10360   Sun Aug 10 00:54:54 2014 HarryUpdateGeneralAUX Couping

The Y End laser dumped SHG light has been coupled into the yellow fiber that terminates at the PSL table.

It's not super stably coupled, and only at 5mW. I'll be interested to see what it is on monday.

  10349   Thu Aug 7 17:09:53 2014 HarryUpdateGeneralAUX Coupling In Progress

 I'm currently in the process of coupling dumped SHG light from the Y arm end table into fibers for FOL.

The main point is that the NPRO at that end in shuttered, because I wasn't sure whether or not leaving it open would've set anything on fire.

  13994   Thu Jun 21 09:33:02 2018 JonUpdate AUX Mode Scans of YARM, PRC cavities

[Jon, Keerthana, Sandrina]

Yesterday we carried out preliminary proof-of-concept measurements using the new AS-port-injected AUX laser to resolve cavity mode resonances.

At the time we started, I found the beat note levels consistent with what Johannes had reported the night before post-realignment. Hence we did not change the AUX alignment.

Test 1: YARM Mode Scan

  • IFO locked in YARM configuration on carrier.
  • Confirmed the presence of a -80 dBm beat note on the temporary YEND broadband PD (i.e., at the cavity transmission).
  • Slowly canned the RF offset of the AUX laser from 50 MHz (nominal) to 60 MHz in 10 kHz steps.
  • Attachment 1 shows the measured scan in "max hold" mode. The bottom panel is the transmission spectrum and the top panel is the reflection, with the AUX/PSL carrier-carrier beat note visible to the far left. In addition to the FSR, it looks to me like the scan resolves at least two HOMs.

Test 2: PRC Mode Scan

  • IFO locked in PRMI configuration on carrier.
  • Moved the temporary 150 MHz PDA10CF from the YEND to an unused pickoff of the REFL33 beam (i.e., the PRC transmission of the AUX beam). There was an existing 50-50 beamsplitter just before REFL33 whose reflected beam was directed onto a beam dump. The PD is now placed in that location. The modification to the AS table is shown in Attachment 2.
  • We made a similar slow scan of the AUX RF offset over ~35 MHz in 10 kHz steps.
  • We resolve the 22 MHz FSR, but it is apparent that an incoherent "max-hold" analyzer measurement is inadequate. The problem is that in max-hold mode, because the 11 MHz-spaced PSL sidebands also beat with the AUX subcarrier, we measure a messy superposition of the PSLcarrier-AUXcarrier beat AND all of the PSLsideband-AUXcarrier beats. The next step is to use the AOM to make a coherent measurement at only the frequency of PSL/AUX carrier-carrier beat.

The SURFs have the data from last night's scans and will be separately posting plots of these measurements. We'll continue today with mode scans using AM sidebands rather than the AUX RF offset.

Attachment 1: YARM_AUX_RF-offset_scan.pdf
YARM_AUX_RF-offset_scan.pdf
Attachment 2: temp_broadband_refl33.pdf
temp_broadband_refl33.pdf
  11351   Wed Jun 10 03:19:58 2015 ericqUpdateLSCAUX PDH error measured in CDS

Looking over the old noise budget in the green locking paper, it seems the main technical noise sources were the AUX PDH error and DFD noise. I'm working on quantifying the current state of these noises. 

Rather than lugging out the analyzers every time I wanted to make a measurement of the AUX PDH error signals, I set out to make the existing digitized channels (ALS-[X/Y]_ERR_MON) usable for easier, and continuous, monitoring. Sadly, up until now the signals were poorly conditioned, and drowning in ADC noise. (When locked, the Y error signal was only +-10 counts!)

Of course, given the bandwidth of the green servos (10kHz), this won't tell us the full story of the what the green PDH lock is doing, but does indicate how much residual frequency noise exists in the ALS control band. 

I'm currently using SR560s at G=20 at each end to amplify the ERR MON outputs of the uPDH boards before sending them to the ADCs; now that I've found a gain that works, I'll modify the error point monitor buffer opamps inside the uPDH boards themselves during the daytime. 

The AUX Y error signal was going into an AA board with some funky filtering going on that I didn't want to mess with. Instead, I've moved the signal to the pentek generic board whose first four channels are used for the oplev segments, and the second quartet are unused, save for the TST channel I hooked up yesterday. 

On the pentek board, I changed the 4th order 800Hz lowpass to a 4th order 8kHz lowpass on the last three channels through some resistor swapping. (At first it was just the last two, but I found I was getting weird signals in the 32nd channel; and if I recall correctly from my cymac work, the 32 ADC channel is used for some timing signal or something...). I also turned off the 1:10 whitening filters on the last four channels via PCB jumper. 

I then unhooked the PZT drive and let the PDH error signals swing around, to calibrate the ADC counts into HZ. Now, the ALS-[X/Y]_ERR_MON_OUT_DQ are calibrated in green Hz! Here are the spectra.

As we've seen in the past (ELOG 10464), the X green is limited by the dark noise of the PD from 10-100Hz. This isn't so great. The RMS noise from 300Hz downwards (which is maybe the band where the ALS control would inject noise into the mirror motion) is about Y:10Hz X:40Hz.

During this time, the test masses were not under any longnitudinal control, so I'm not sure why there is such a difference in the height of the suspension resonance peaks, unless there's some differene in the low frequency PDH TFs that I've forgotten about. 

Now, with these references, we can easily check if the PDH loops change qualitatively over longer time periods.

I'll be including the effect of these noises in the upcoming revised ALS noise budget.

Attachment 1: AUXspectra.png
AUXspectra.png
  11715   Mon Oct 26 19:10:59 2015 gautamUpdateGreen LockingAUX PDH loop characterization

I began my attempts to characterize the PDH loops at the X end today. My goal was to make the following measurements:

  • Dark noise and shot noise of the PD
  • Mixer noise
  • Servo electronics noise 

which I can then put into my simulink noise-budget scheme for the proposed IR beat setup.

I've made an Optickle model of a simple FP cavity and intend to match the measured PDH error signal from the X end to the simulated error signal to get the Hz/V calibration. I'll put the plots up for these shortly.

With regards to the other measurements, I was slowed down by remote data-acquisition from the SR785 - I've only managed to collect the analyzer noise floor data, and I plan to continue these measurements during the day tomorrow. 

  16152   Fri May 21 12:12:11 2021 PacoUpdateNoiseBudgetAUX PDH loop identification

[Anchal, Paco]

We went into 40m to identify where XARM PDH loop control elements are. We didn't touch anything, but this is to note we went in there twice at 10 AM and 11:10 AM.

  16933   Tue Jun 21 14:59:22 2022 CiciSummaryGeneralAUX Transfer Function Loop Exploration

[Deeksha, Cici]

We learned about the auxillary laser control loop, and then went into the lab to identify the components and cables represented by our transfer functions. We connected to the SR785 inside the lab so that we can use it to insert noise next time, and measure the output in various parts of the control loop.

  11908   Tue Jan 5 02:54:38 2016 ericqUpdateLSCAUX X Freq Noise attempt

[ericq, Gautam]

We set out to lock a marconi to the IR fiber beat of PSL + AUX X to measure some frequency noise, and failed.

In short, the Marconi's 1.6MHz max external FM isn't enough oomph to stabilize the PLL error signal. It's actually evident on the Agilent that the beat moves around a few times more than that, which I should've noticed sooner... We could briefly "lock" the PLL for a few tenths of a second, but weren't able to get a spectrum from this.

We also tried using the digital phase tracker temperature servo for some help at ~DC; this worked to the extent that we didn't have to twiddle the Marconi carrier frequency to stay on top of the fringes as the beat wandered, but it didn't otherwise stabilize the beat enough to make a difference in locking the PLL.

I suppose one more thing to try is to lock the PSL laser itself to each AUX laser in turn via PLL, and look for different / excess noise.

The Green and IR beat electronics are a in a little bit of disarray at the moment, but it's not like anyone else is going to be using them for the time being...

  11910   Tue Jan 5 13:17:06 2016 ranaUpdateLSCAUX X Freq Noise attempt

The problem here is that the MC displacement noise is leading to large frequency excursions of the PSL beam. Options

  1. Feed back the low frequency PLL control signal to the MC2 length to suppress the excursion required by the Marconi. This is better than driving the laser, since the drive to the laser would be squashed by the MC locking loop.
  2. Put the beat signal through a divider? Don't know if this makes the Marconi more able to handle it.
  3. Turn on the MCL path. this will make the low frequency MC error signal go to the MC length, thereby reducing the low frequency feedback to the NPRO.
  11912   Tue Jan 5 16:33:45 2016 ericqUpdateLSCAUX X Freq Noise attempt

Turning on the MCL path (in addition to the MCL FF we always have on) let me lock the PLL for multiple seconds, but low frequency excursions still break it in the end. I was able to briefly observe a level of ~50Hz/rtHz at 1kHz, which may or may not be real. Tomorrow we'll send the PLL control signal to MC2, which should lock it up just fine and give us time to twiddle laser diode current, measure the PLL loop shape, etc. 

  11917   Thu Jan 7 04:28:39 2016 ericqUpdateLSCAUX X Freq Noise measured

[ericq, Gautam]

Brief summary of tonights work:

  • Locked Marconi to AUX X vs PSL beat at around 320MHz, PSL shutter closed (i.e. both lasers free running)
  • Measured control signal spectrum at various laser diode currents, crystal temperatures. Oddly, spectra remained consistent across these variables. 
  • Measured OLG of PLL to calibrate into open-loop frequency noise of the beat, found UGF ~30kHz

Our "requirement" for the end laser is as follows: We expect to (and have in the past) achieved ALS sensitivity of 1Hz/rtHz at 100 Hz. If the end PDH loop is 1/f from 100Hz-10kHz, then we have 40dB of supression at 100Hz, meaning the free running AUX laser noise should be no more than 100Hz/rtHz at 100Hz.

So, if we expect both the PSL and AUX lasers to have this performance when free running, we would get the green curve below. We do not. frown


I'll post more details about the exact currents, temperatures and include calibrated plots for the >30kHz range later. Here's the OLG for kicks. 

Attachment 1: PLLspec.pdf
PLLspec.pdf
Attachment 2: PLL_OLG.pdf
PLL_OLG.pdf
  11919   Thu Jan 7 16:52:32 2016 ericqUpdateLSCAUX X Freq Noise measured

Here is some of the promised data. As mentioned, changing diode current and crystal temperature didn't have much effect on the frequency noise spectrum; but the spectrum itself does seem too high for our needs. 

At each temperature, we started measuring the spectrum at 1.8A, and stepped the current up, hoping to reach 2.0 A.

At 47.5 C, we were able to scan the current from 1.8 to 2.0 A without much problem. At 49.0C, the laser mode would hop away above 1.95A. At 50.4C it would hop away above 1.85A. The spectra were not seen to change when physically disconnecting the PZT actuation BNC from the rear of the laser. 

The flattening out at the upper end is likely due to the SR560 output noise. I foolishly neglected to record the output spectrum of it, but with the marconi external modulation set to 3.2MHz/V, the few Hz/rtHz above 20k translates to a signal on the order of uV/rtHz, which seems reasonable. 

Data and code attached. 

Attachment 1: AUXfreqnoise.pdf
AUXfreqnoise.pdf
Attachment 2: auxXmeasurements.zip
  11920   Thu Jan 7 19:04:25 2016 KojiUpdateLSCAUX X Freq Noise measured

The next step is to compare this data with the same measurement with the PSL and the AUX laser on the PSL table (or the end Y laser). If these show a lot lower noise level, we can say 1) the x-end laser is malfunctioning and 2) the y-end and AUX laser on the PSL are well low noise.

  13325   Thu Sep 21 01:32:00 2017 gautamUpdateALSAUX X Innolight AM measurement running

[rana,gautam]

We set up a measurement of the AUX X laser AM today. Some notes:

  • PDA 55 that was installed as a power monitor for the AUX X laser has been moved into the main green beam path - it is just upstream of the green shutter for this measurement.
  • AUX X laser power into the doubling crystal was adjusted by rotating HWP upstream of IR Faraday (original angle was 100, now it is 120), until the DC level of the PDA 55 output was ~2.5V on a scope (high impedance).
  • BNC-T was installed at the PZT input of the Innolight - one arm of the T is terminated to ground via 50 ohms. The purpose of this is to always have the output of the power splitter from the network analyzer RF source drive a 50 ohm load.
  • The output of the Green PDH servo to the Innolight PZT was disconnected downstream of the summing Pomona box - it is now connected to one output of a power splitter (borrowed from SR function generator used to drive the PZT) connected to the RF source output of the AG4395.
  • Other output of power splitter connected to input R of AG4395.
  • PDA55 output has been disconnected from CH5 of the AA board. It is connected to input A of the AG4395 via DC block.

Attachment #1 shows a preliminary scan from tonight - we looked at the region 10kHz-10MHz, with an IF bandwidth of 100Hz, 16 averages, and 801 log-spaced frequencies. The idea was to get an idea of where some promising notches in the AM lie, and do more fine-bandwidth scans around those points. Data + code used to generate this plot in Attachment #2.

Rana points out that some of the AM could also be coming from beam jitter - so to put this hypothesis to test, we will put a lens to focus the spot more tightly onto the PD, repeat the measurement, and see if we get different results.

There were a whole bunch of little illegal things Rana spotted on the EX table which he will make a separate post about.

I am running 40 more scans with the same params for some statistics - should be done by the morning.

Quote:

I borrowed the HP impedance test kit from Rich Abbott today. The purpose is to profile the impedance of the NPRO PZTs, as part of the AUX PDH servo investigations. It is presently at the X-end. I will do the test in the coming days.
 


Update 12:00 21 Sep: Attachment #3 shows schematically the arrangement we use for the AM measurement. A similar sketch for the proposed PM measurement strategy to follow. After lunch, Steve and I will lay out a longish BNC cable from the LSC rack to the IOO rack, from where there is already a long cable running to the X end. This is to facilitate the PM measurement.

Update 18:30 21 Sep: Attachment #4 was generated using Craig's nice plotting utility. The TF magnitude plot was converted to RIN/V by dividing by the DC voltage of the PDA 55 of ~2.3V (assumption is that there isn't significant difference between the DC gain and RF transimpedance gain of the PDA 55 in the measurement band) The right-hand columns are generated by calculating the deviation of individual measurements from the mean value. We're working on improving this utility and aesthetics - specifically use these statistics to compute coherence, this is a work in progress. Git repo details to follow.

There are only 23 measurements (I was aiming for 40) because of some network connectivity issue due to which the script stalled - this is also something to look into. But this sample already suggests that these measurement parameters give consistent results on repeated measurements above 100kHz.

TO CHECK: PDA 55 is in 0dB gain setting, at which it has a BW of 10MHz (claimed in datasheet).


Some math about relation between coherence \gamma_{xy}(f) and standard deviation of transfer function measurements:

\mathrm{SNR}(f) = \sqrt{\frac{\gamma_{xy}^{2}(f)}{1-\gamma_{xy}^{2}(f)}}

\sigma_{xy}^{2} = \frac{1-\gamma_{xy}^{2}(f)}{2N\gamma_{xy}^{2}(f)}|H(f)|^2  --- relation to variance in TF magnitude. We estimate the variance using the usual variance estimator, and can then back out the coherence using this relation.

\sigma_{\theta_{xy}} = \mathrm{tan}^{-1}\left [ \sqrt{\frac{1-\gamma_{xy}^{2}(f)}{2N\gamma_{xy}^{2}(f)}} \right ] --- relation to variance in TF phase. Should give a coherence profile that is consistent with that obtained using the preceeding equation.

It remains to code all of this up into Craig's plotting utility.

Attachment 1: Innolight_AM.pdf
Innolight_AM.pdf
Attachment 2: Innolight_AM.tar.gz
Attachment 3: IMG_7599.JPG
IMG_7599.JPG
Attachment 4: 20170921_203741_TFAG4395A_21-09-2017_115547_FourSquare.pdf
20170921_203741_TFAG4395A_21-09-2017_115547_FourSquare.pdf
ELOG V3.1.3-