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ID Date Authordown Type Category Subject
  3766   Fri Oct 22 21:28:27 2010 AidanUpdateLockingGreen era: found a green beat note finally

Nice work!

Quote:

finally we found it !

 green_beatnote.jpg

 

  3907   Fri Nov 12 11:36:06 2010 AidanConfigurationComputersFixed the PERL PATH errors from the scripts directory change

 I've been trying to get a PID loop running for the green locking and I've discovered that some of the directories in the path for the Perl Modules are now obselete. Specifically, since the scripts directory has been moved from /cvs/cds/caltech/scripts to /cvs/cds/rtcds/caltech/c1/scripts the following locations in the Perl @INC path list need to be changed:

  • /cvs/cds/caltech/scripts/general
  • /cvs/cds/caltech/scripts/general/perlmodules

I've added the above directories to the PERL5LIB path in /cvs/cds/caltech/cshrc.40m.

 

 

setenv PERL5LIB /cvs/cds/caltech/scripts/general:

/cvs/cds/caltech/scripts/general/perlmodules:

/cvs/cds/caltech/libs/solaris9/usr_local_lib/perl5/5.8.0/:

/cvs/cds/rtcds/caltech/c1/scripts/general:

/cvs/cds/rtcds/caltech/c1/scripts/general/perlmodules

 This seems to fix the problem .. at least, you no longer get an error if you try nodus:~>perl -e 'user EpicsTools'

 

  3908   Fri Nov 12 12:06:11 2010 AidanConfigurationGreen LockingPID script working - now it needs to be tuned

 I've set up a PID script that senses the EX-PSL Green Beat note (from the frequency counter) and actuates on the temperature of the end laser to drive the beat note to a given setpoint.

  • I've added the necessary EPICS channels to c1iscaux and rebooted it so that the channels are live. They are listed in a new database file slow_grnx_pid.db
  • This database was added to the list of those loaded by startup.cmd.  
  • The PID script, GRNXSlowServo, is just a modified version of FSSSlowServo.
  • The version I've been running is currently in /cvs/cds/caltech/users/abrooks/.
  • There's also an MEDM screen in this directoy, C1LSC_EX_GRN_SLOW.adl, there that shows the PID settings.

Right now the script only passes the initial sanities checks, that is:

  1. It runs.
  2. You can enable/disable it without any errors and it starts actuating.

The settings all need to be tuned up - e.g. maximum_increment, hard_stops, time_step, PID constants.

Additionally, the units in the whole thing are pretty useless - some of the channels are in VOLTS, others in WATTS. I'd like to change all these to be in Hz. 


EPICS channels added:

  • grecord(ao,"C1:LSC-EX_GRN_SLOWKD")
  • grecord(ao,"C1:LSC-EX_GRN_SLOWKP")
  • grecord(ao,"C1:LSC-EX_GRN_SLOWKI")
  • grecord(ao,"C1:LSC-EX_GRN_PID_SETPT")
  • grecord(ao,"C1:LSC-EX_GRN_TIMEOUT")
  • grecord(stringin,"C1:LSC-EX_GRN_SLOWVERSION")
  • grecord(bi,"C1:LSC-EX_GRN_SLOWLOOP")
  • grecord(bi,"C1:LSC-EX_GRN_DEBUG")
  • grecord(bi,"C1:LSC-EX_GRN_SLOWBEAT")
 

 

Attachment 1: Screen_shot_2010-11-12_at_12.05.01_PM.png
Screen_shot_2010-11-12_at_12.05.01_PM.png
  3922   Mon Nov 15 14:42:01 2010 AidanUpdatePSLC1PSL rebooted?

Yeah. Joe and I rebooted c1psl a couple of times this morning. I didn't realize the burtrestore wasn't automatic.

 

Quote:

Has C1PSL rebooted? Has burtrestore been forgotten? Even without elog?

We found some settings are wrong and the PMC has pretty low gain.

 

  3930   Tue Nov 16 09:02:54 2010 AidanUpdateGreen LockingPID loop - calibration of SR620 output

 [Aidan, Kiwamu]

Kiwamu and I roughly calibrated the analogue output from the SR620 frequency counter yesterday. The input channel, intuitively named C1:PSL-126MOPA_126MON, now reads the measured frequency in MHz with an error of about 0.1MHz - this is, I think, due to the bit noise on the D/A conversion that Kiwamu discovered earlier. That is, the output range of the SR620 corresponds to around 100MHz and is digitized at 10-bit resolution, and ...

100MHz/(10^2) ~= 0.098MHz. [Sad Face]

Calibration:

We set the EPICS range to [-100, 100] (corresponding to [-5V, 5V]), connected a Marconi to the Freq Counter, input a variety of different frequencies and measured the counts on the EPICS channel.

The linear fit to the calibration data was F = 2.006*EPICScount - 0.2942. From this we worked out the maximum and the minimum for the range settings that give the channel in MHz: EGUF = -200.8942 and EGUL = 200.3058. The previous range was [-410, 410]

 

Calibration of SR620 analogue output
Input Frequency (MHz) Measured EPICS Value
10  5.191
20  9.98
30 15.21
40 20.00
50 25.18
60 29.99
70 35.18
71 35.565
72 35.9894
73 36.3861
74 37.17
75 37.576
76 37.9669
77 38.3575
78 39.166
79 39.5691
80 39.978
   

 

  3931   Tue Nov 16 10:47:45 2010 AidanUpdateGreen LockingRebooted c1psl - added new GRNBEAT_FREQ channel

I restored C1:PSL-126MOPA_126MON to its original settings (EGUF = -410, EGUL = 410) and added a new calc channel called C1:LSC-EX_GRNBEAT_FREQ that is derived from C1:PSL-126MOPA_126MON. The calibration in the new channel converts the input to MHz.

grecord(calc, "C1:LSC-EX_GRNBEAT_FREQ")
{
        field(DESC,"EX-PSL Green Beat Note Frequency")
        field(SCAN, ".1 second")
        field(INPA,"C1:PSL-126MOPA_126MON")
        field(PREC,"4")
        field(CALC,"0.4878*A")
        }

I rebooted c1psl and burtrestored.

  3932   Tue Nov 16 12:47:30 2010 AidanUpdateGreen LockingPID loop but no green

The PID loop is ready to be run on the green beat note but, since the tanks are open, there is no green transmission from the end getting to the PSL table. Nevertheless, here's the screen for the PID loop. The loop script is still in my directory /cvs/cds/caltech/users/abrooks/GRNXSlowServo

The medm screen is attached. It shows the current beat note frequency in MHz ()

In c1auxey/ETMYaux.db I added a couple of channels. These are all displayed on the MEDM screen. I added them to autoBurt.req as well.

  • C1:LSC-EX_GRNLSR_TEMP_NOM: the zero-volt setpoint temperature of the end laser (as set on the front panel of the Mephisto controller). This must be entered manually in EPICS as there is no way to read it remotely. [Sad Face]
  • C1:LSC-EX_GRNLSR_TEMP_CALC: the sum of the zero-volt set point temperature and the offset temperature set by the input voltage from C1:LSC-EX_GREENLASER_TEMP

I rebooted c1auxey to get these to work.

Once we get the green beat back again, the PID loop should servo on the end laser temperature to drive the Beat Frequency to the Frequency Setpoint, C1:LSC-EX_GRN_PID_SETPT, which can be set by the pink slider.

RA: All MEDM screens must be in the proper MEDM directory!! Also, all perl scripts must have a .pl extension!!! Also, all scripts must be in the scripts directory even if they are in development!!! And all scripts should use 'env' rather than have absolute pathnames for the location of perl, csh, tcsh, python, etc.

Attachment 1: Screenshot-C1LSC_EX_GRN_SLOW.adl.png
Screenshot-C1LSC_EX_GRN_SLOW.adl.png
  3934   Tue Nov 16 16:00:26 2010 AidanUpdateGreen LockingPID loop but no green

Quote:

RA: All MEDM screens must be in the proper MEDM directory!! Also, all perl scripts must have a .pl extension!!! Also, all scripts must be in the scripts directory even if they are in development!!! And all scripts should use 'env' rather than have absolute pathnames for the location of perl, csh, tcsh, python, etc.

 That's not unreasonable. But if we try 

 grep "perl" /cvs/cds/rtcds/caltech/c1/scripts/*/* 

you can see that we've got a fair amount of housekeeping to attend to. We might want to think about tidying up the scripts directory as part of the cds upgrade.

 

 

 

 

  4040   Fri Dec 10 09:58:57 2010 AidanUpdateSUSbeam pointing has been done

Good news. I feel multi-chromatic-locking success is just around the corner.

By the way, there's a new presentation on the DCC from the ANU group where they've locked a short single cavity with both colors - G1000735:

https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=14040

 

 

Quote:

[Koji, Osamu and Kiwamu]

 We aligned the beam axis pointing down to both X and Y arm.

Now the beams are hitting the centers of both ETMX and ETMY.

Amazingly Osamu made X arm flashing by aligning the cavity.


 

  4177   Thu Jan 20 15:39:59 2011 AidanUpdateLockingUpper limit on frequency noise of ADC

[Aidan, Kiwamu]

Kiwamu and I plugged the output from a DS3456 function generator into the ADC and started recording the data. The func. generator output a 237.8Hz, 1Vpp sine wave. We chose this value because it corresponds to the FSR of a 38.5m cavity (=3.896MHz) divided by 2^14, the frequency divider amount we intend to use.

Since 1 FSR divided down is 237.8Hz and corresponds to a length change of the cavity of 532nm/2 = 266nm, then we can, roughly, say that a frequency change of 1Hz corresponds to a length change in the cavity of approximately 1nm. The width of the 237.8Hz peak in the spectra corresponds to an upper limit on the noise floor due to digitizing the signal (this could be limited by the ADC, or the function generator, or the windowing on the FFT).

The FWHM of the peak in the spectrum was approximately 5mHz, corresponding to an uncertainty in the length of the cavity of about 6pm (we used a Hanning Window, 50% overlap and a BW of 2.92mHz, 7 averages). Regardless of what is the dominant contribution to the width of the peak, this implies that the frequency noise associated with digitizing a signal in the ADC is much smaller than we require and will not limit our performance if we choose to use a frequency divider and digital PLL with the Green Locking.

RA: Here's the previous measurement

Attachment 1: Sine-wave-width-test_of_ADC.pdf
Sine-wave-width-test_of_ADC.pdf
  4178   Thu Jan 20 17:00:39 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

  4182   Fri Jan 21 11:45:01 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

Quote:

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

 Agreed. It doesn't completely rule out the digital PLL. I'll check out Kiwamu's model.

  4205   Wed Jan 26 10:11:47 2011 AidanUpdateGreen Lockingcavity scan

Quote:

cavity_scan.png

 

Whether or not it's as clean as we'd like, it's really nice to see this result with real data.

  4209   Wed Jan 26 14:49:48 2011 AidanUpdateEnvironmentTurned on Control room AC

80 degrees is too uncomfortable in the control room so I turned on the AC. The set point is 74F.

  4217   Fri Jan 28 09:03:38 2011 AidanSummaryGreen LockingDigital Frequency Discriminator

Quote:

That's some pretty fast work! I thought we would be taking up to a week to get that happening. I wonder what's the right way to measure the inherent frequency noise of this thing?

Also, should the comparator part have some hysteresis (ala Schmidt trigger) or is it best to just let it twirl as is? Is it sensitive to DC offsets on the input or is there a high pass filter? What's the correct low pass filter to use here so that we can have a low phase lag feedback to the ETM?

 

We could try inputing a 4kHz carrier modulated width a depth of a few Hz at a modulation frequency of F1. Then we could take an FFT of the output of the discriminator and measure the width of the peak at F1 Hz. This seems like an arduous way to measure the frequency noise at a single frequency though.

It'll definitely be sensitive to DC offsets but there is already a filter bank on the INPUT filter so we can shape that as necessary. We could probably band-pass that from [4.5 - 5.3kHz] (which would correspond to a range of [73,87] MHz into a 2^14 frequency divider.

 

  4227   Sun Jan 30 17:15:09 2011 AidanSummaryGreen LockingDigital Frequency discriminator - frequency noise

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

Attachment 1: _Untitled_(modified).png
_Untitled_(modified).png
  4229   Mon Jan 31 07:03:59 2011 AidanSummaryGreen LockingDFD - noise spectra

Quote:

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

 Here is the spectrum of the input into the DFD (a 234.5Hz sine wave, 0.5 Vpp) and the spectrum and RMS of the LP output. The linewidth of the input signal is clearly much less than 0.1Hz, where as the RMS noise (above 2mHz) is approximately 0.2Hz and the main contributions are clearly the harmonics of the 234.5Hz signal.

Attachment 1: DFD-bandwidth_noise.pdf
DFD-bandwidth_noise.pdf
  4230   Mon Jan 31 07:41:23 2011 AidanUpdateGreen LockingDFD - medm screen

I added an MEDM screen for the DFD to the GREEN screen. It is displayed in the attached screen shot.

This screen is located in: /cvs/cds/rtcds/caltech/c1/medm/c1gfd/C1GFD_DFD.adl

Attachment 1: Screenshot-3.png
Screenshot-3.png
  4234   Mon Jan 31 18:25:25 2011 AidanUpdateGreen LockingDFD - results from the new filters (and running with AWG)

Quote:

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

Joe injected a 234.567 etc. Hz sine wave into the excitation channel in the DFD INPUT filter. The spectrum of the output of the LP filter with the new filter is shown below with the RMS calculated from 300Hz down to 1mHz - see first attachment. The RMS is equal to about 2.5Hz. (Incidentally, the RMS is very much higher (slightly less than 400Hz - see second attachment) if you calculate it from 7kHz down to 1mHz). 

Attachment 1: DFD-bandwidth_noise_CLP500_to_300Hz.pdf
DFD-bandwidth_noise_CLP500_to_300Hz.pdf
Attachment 2: DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
DFD-bandwidth_noise_CLP500_to_7000kHz.pdf
  4245   Thu Feb 3 16:08:06 2011 AidanUpdateComputer Scripts / ProgramsRCG VCO frequency error

Joe and I were looking at the RCG VCO algorithm to determine if we could adapt it to run at a faster rate (you can currently change its frequency at 1Hz). I noticed that the algorithm that is used to calculated the values of sine and cosine at time T1  is a truncated Taylor series which uses the values of sine and cosine calculated at time T1 - Delta t . I was concerned that there would be an accumulating phase error so I tested the algorithm in MATLAB and compared it to a proper calculation of sine and cosine. It turns out that at a given 'requested' frequency there is a constantly accumulating phase error - which means that the 'actual' frequency of the RCG VCO is incorrect. So I have plotted the frequency error vs requested VCO frequency. It gets pretty bad!

 Here's the code I used:

dt = 1/16384;

diffList = [];
% set the frequencies

flist = 1:5:8192;
for f = flist;
   
    % get the 'accurate' values of sine and cosine
    tmax = 0.05;
    time1 = dt:dt:tmax;
    sineT = sin(2.0*pi*f*time1);
    cosineT = cos(2.0*pi*f*time1);
   
    % determine the phase change per cycle
    dphi = f*dt*2*pi;
    cosT1 = 1:numel(time1);
    sinT1 = 0*(1:numel(time1));
   
    % use the RCG VCO algorithm to determine the values of sine and cosine
    for ii = 1:numel(time1) - 1;                 
        cosNew = cosT1(ii)*(1 - 0.5*dphi^2) ...
                      - (dphi)*sinT1(ii);
        sinNew = sinT1(ii)*(1 - 0.5*dphi^2) ...
                      + (dphi)*cosT1(ii);
                 
       
        cosT1(ii+1) = [ cosNew];
        sinT1(ii+1) = [ sinNew];
       
    end
    % extract the phase from the VCO values of sine and cosine
    phaseT = unwrap(angle(cosineT + i* sineT));
    phaseT1 = unwrap(angle((cosT1 + i*sinT1)));
   
    % determine the phase error for 1 cycle
    diff = phaseT1 - phaseT;
    % determine the frequency error
    slope = (diff(2) - diff(1))/(dt);
   
    diffList = [diffList, slope];
    disp(f)
    pause(0.001)
end

% plot the results

close all
figure
orient landscape
loglog(flist, abs(diffList/(2.0*pi)))
xlabel('Requested VCO Frequency (Hz)')
ylabel('Frequency error (Hz)')
grid on

print('-dpdf', '/users/abrooks/VCO_error.pdf')

Attachment 1: VCO_error.pdf
VCO_error.pdf
  4259   Tue Feb 8 10:23:02 2011 AidanSummaryGreen LockingDigital Frequency Discriminator - reference

 

Here's the reference for the self-reference frequency detection idea. See Figure 2.

http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/mixers.pdf

  4260   Tue Feb 8 13:26:11 2011 AidanSummaryGreen LockingTemperature dependence of phase change of green on reflection

 I did a quick back of the envelope calculation of the expected green phase change on reflection from the aLIGO ITM.

The phase change per nm, K1 = delta phi/delta Lambda, around 532nm is ~1.5 degrees/nm (from the LMA data) [this number is approximately 100x smaller at 1064nm]

I assumed that very small changes in the thickness of the coating appear equivalent to shifting the spectra for reflection/transmission/phase-change-on-reflection up or down by delta lambda, where

delta Lambda/Lambda = delta h/h

where h is the total thickness of the coating and delta h is the change in the thickness of the coating.

Assume that delta h/h = alpha deltaT, where alpha is the coefficient of thermal expansion and delta T is the change in temperature. (approximately 1K)

Then delta phi = K1* Lambda * alpha * delta T = 1.5 degrees/nm * 532nm * 10^-5 K^-1 * 1.0 K =  8 * 10^-3 degrees.

Assume that 360 degree phase change corresponds to one FSR.

Therefore, the frequency shift due to temperature change in the coating = 8*10^-3/360 * FSR = 2.2 *10^-5 * FSR.

Therefore, the expected frequency shift per degree temperature change = 2.2*10^-5 * FSR [Hz/K]

  4271   Thu Feb 10 14:52:36 2011 AidanHowToComputersAdding filenames in MATLAB plots

The following code is incredibly useful when creating  MATLAB plots as it adds the filename of the script to the plot itself. I think it should be used for all MATLAB plots that go on the elog.

For example, I have no idea where the data/script is that was used to generate these plots.

 

orient landscape

xposn = 0.0;

yposn = -0.13; % you sometimes have to tweak this value depending on the page size and the number of subplots

text(xposn,yposn,[filename('fullpath'), '.m'], ...

     'Units', 'normalized', ...

     'Interpreter', 'none', ...

     'FontSize', 6)

print('-dpdf', [filename('fullpath'), '.pdf'])

  4351   Thu Feb 24 17:42:00 2011 AidanUpdateGreen Locking15% of end laser sideband power transmitted through cavity

I did a quick calculation to determine the amount of sideband transmission through the FP cavity.

The modulation frequency of the end PDH is 216kHz. The FSR of the cavity is about 3.9MHz. So the sidebands pick up about 0.17 radians extra phase on one round trip in the cavity compared to the carrier.

The ITM reflectance is r_ITM^2 = 98.5% of power, the ETM reflection is r_ETM^2 = 95%.

So the percentage of sideband power reflected from the cavity is R_SB = r_ITM*r_ETM*(exp(i*0.17) - 1)^2 / (1 - r_ETM*r_ITM exp(i*0.17) )^2 = 0.85 = 85%

So about 15% of the sideband power is transmitted through the cavity. The ratio of the sideband and carrier amplitudes at the ETM is 0.05

So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.

Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.

 

 

  4362   Sun Feb 27 09:43:59 2011 AidanUpdateGreen Lockingsidebands on beatnote

Can we set up a fiber-PD on the end table to look at the beat between the "end laser IR beam" and the "PSL IR beam fiber-transmitted end beam"? 

We should see the same thing on that PD that we see on the green PD (plus any fiber noise and I'm not really sure how much that'll be off the top of my head). If we unlock the lasers from the arm cavity then the free-running noise of the lasers wrt to each other will probably swamp the 50kHz and 150kHz signals. Maybe we could lock the end laser to the free-running PSL by demodulating the beat note signal from the fiber-PD and then we could look for the extra sidebands in the IN-LOOP signal. Then we could progressively lock the PSL to the MC and arm cavity and see if the sidebands appear on the fiber-PD at some point in that process. 

It's possible that the 216kHz drive of the PZT on the Innolight is somehow driving up some sub-harmonics in the crystal. I think this is unlikely though: if you look at Mott's measurements of the Innolight PZT response, there are no significant PM resonances at 50 or 150kHz.

 

Quote:

Other than the +/-216 kHz sidebands, we can see some funny peaks at +/- 50 kHz and +/-150 kHz.

 

Quote: #4351 by Aidan

So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.

Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.

 

  4365   Tue Mar 1 08:42:18 2011 AidanUpdateelogRestarted the elog this morning

 The elog was dead this morning. I reanimated it. It is now undead.

Attachment 1: Zombie.gif
Zombie.gif
  4368   Wed Mar 2 17:19:58 2011 AidanConfigurationGreen LockingMoved PDH PD on end table

As previously noted, there are multiple beams coming back from the ETM surface onto the PDH PD on the end table. They are spread out in a vertical pattern. All the spots swing together (as the ETM moves?).

I moved the PDH Green PD on the end table so that it was further away from the Faraday and I added an iris in between the Faraday and the PD. Now only the principle reflection from the ETM is incident on the PD. See attached photos. In order to sneak past the neighbouring optics, I had to steer the beam down a bit, so the PD is now lower than it previously was.

Just FYI: the angle between the returning beams is about 5 or 6 mrad at the PD. Before the beams get to the PD they go through a telescope that de-magnifies the beam by about 5 or 6 times. This implies that the angle between adjacent returning beams from the ETM is around 1 mrad at the ETM.

This does make the position of the spot on the PD more susceptible to the alignment of the ETM - we should use a short focal length lens and image the ETM plane onto the PD.

 

First image - overview of table

Second image - the three returning beams immediately before the IRIS

Third image - a close up of the IRIS and PDH PD. 

 

 

 

Attachment 1: P1000223-a.jpg
P1000223-a.jpg
Attachment 2: P1000218.jpg
P1000218.jpg
Attachment 3: P1000224.jpg
P1000224.jpg
  4369   Wed Mar 2 18:08:43 2011 AidanUpdateGreen LockingGhost beams on green

Kiwamu and I noticed that there is a ghost beam on the green beam going into the ETM. What we see is some interference fringes on the edge of the transmission of the green beam through the dichroic beam splitter (DCBS). If we look at the reflection from the dichroic beam splitter these are much more pronounced.

The spacing of the fringes (about 2 per 10mm) indicates an angle between the fields of around 0.1 mrad.

We were able to cause significant motion of the fringes by pushing on the knobs of the steering mirrors that steer the beam into the DCBS. A rough calculation of the derivative of optical path difference between the ghost and the primary beam as a function of input angle gives about 15 microns per mrad. What filtering the effect the arm cavity will have on the ghost beam is not immediately clear, but the numbers shouldn't be too difficult to determine.

 

Attachment 1: Ghost_Beam_at_ETM_DCBS.pdf
Ghost_Beam_at_ETM_DCBS.pdf
  4428   Wed Mar 23 08:50:36 2011 AidanUpdateGreen Lockingservo handig off

Nicely done!

 

Quote:

Succeeded in handing off the servo from the green to the red.

stripTransit_edit.png

 

 

 

Attachment 1: green-to-red.jpg
green-to-red.jpg
  4435   Wed Mar 23 19:16:17 2011 AidanSummaryGreen LockingY-END green equipment is all available

With the exception of a 2" mirror mount, I've confirmed that we have everything for the Y-end green production and mode-matching.

We need to calculate a mode-matching solution for the Lightwave laser so that it gives the correct beam size in the doubling crystal.

Additionally, Rana has suggested that we change the pedestals from the normal 1" diameter pedestal+fork combo  to the 3/4" diameter posts and wider bases that are used on the PSL table (as shown in the attached image).

Attachment 1: three-quarter_inch_pedestal.jpg
three-quarter_inch_pedestal.jpg
  4443   Fri Mar 25 08:58:38 2011 AidanUpdateTreasureCleared stuff off SP table

I tidied up some of the stuff that was on the SP table. The ISS box that has been sitting on there for months is now underneath the X-arm on top of the spare Marconi which is stored there.

 

 

Attachment 1: ISS_box.JPG
ISS_box.JPG
  4460   Wed Mar 30 16:32:29 2011 AidanConfigurationComputer Scripts / ProgramsAdded a sitemap alias

I added an alias to the sitemap MEDM screen in /cvs/cds/caltech/target/cshrc.40m

Now you can enjoy launching sitemap from a terminal.

alias sitemap 'medm -x /cvs/cds/rtcds/caltech/c1/medm/sitemap.adl'

  4479   Thu Mar 31 20:37:10 2011 AidanSummaryGreen LockingRF amplitude source

 I gutted one of the $2 red laser pointers to build a laser source whose amplitude we could modulate at RF frequencies. Basically, I cut off the bulk of the housing from the pointer and soldered a BNC connection into the two terminals that the 2x 1.5V batteries were connected to. When I applied 3V across this BNC connector the diode still worked. So far so good.

Next I added a bias tee to the input. I put 3V across the DC input of the bias tee and added a -3dBm signal into the RF port of the tee. The laser beam was incident on a PDA100A (bandwidth of 1.7MHz) and, sure enough, Kiwamu and I could see a flat response in the amplitude at a given drive frequency out to around 1.7MHz.

We should check the response on a faster PD to see how fast the laser diode is, but we should be able to use this now to check the RF response of the green beat note PD. 

TO DO:

1. Add some capacitors across the DC input of the bias tee.

2. Do something about the switch on the laser diode.

3. Attach some labels to the laser that specify what is the required DC voltage and the maximum acceptable RF modulation amplitude.

Attachment 1: P1000543.jpg
P1000543.jpg
Attachment 2: P1000544.jpg
P1000544.jpg
Attachment 3: P1000545.jpg
P1000545.jpg
  4480   Thu Mar 31 20:46:11 2011 AidanSummaryGreen LockingGreen beat note PD DC response

I measured the DC response of the Green PD


Power into PD at DC (green laser pointer) = 285 uW
Voltage out of PD = 552mV/(100x SR560gain) = 5.52mV
Photocurrent = 5.52mV/(241 Ohms)*3 = 68.7uA
Responsivity = 68.7/285 = 0.24 A/W

Therefore, since the responsivity is in the correct range for a Silicon PD at 532nm, the DC output is giving us sensible response to an input signal.


But, there is a 2.12MHz, 328mV oscillation on the DC output irrespective of the incident power.
 

  4494   Wed Apr 6 19:36:32 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I moved the Hartmut Green PD to the Jenne laser bench to try to determine if the response at RF was reasonable or somehow very much smaller than it should be. It was set up as shown in the attached diagram. The first pass at this was by comparing the ratio of the RF photocurrent of the green PD to the RF photocurrent of the New Focus 1611 InGaAs PD. That ratio (at a sufficiently low frequency) should be the same as the ratio the DC photocurrents of the two PDs.

Using the network analyzer I measured the ratio of the voltages of the two RF signals (and then scaled each of these by the respective transimpedances of the PDs: 700 Ohms for the 1611 and 240 Ohms for the Harmut PD). The resulting ratio is shown in the attached plot.

I measured the DC voltages from each PD and scaled those by the transimpedances to get the photocurrent (10 kOhm for the 1611 and 80 Ohm effective for the Harmut PD). The ratio of the DC photocurrents was 0.37. This is roughly 3x the ratio of the RF photocurrents at 500kHz (=0.14). This discrepancy is uncomfortably large.

 The full set of measurements is given in the table below:

Measurement Value
DC voltage from Hartmut PD 6.5mV (checked by turning laser on and off and measuring the difference)
DC voltage from 1611 InGaAs PD 2.20V
Transimpedance of Harmut PD at DC 80 Ohm (effective)
Transimpedance of Harmut PD at RF 240 Ohm
Transimpedance of 1611 InGaAs at DC 10 KOhm
Transimpedance of 1611 InGaAs at RF 700 Ohm
Incident Power on Hartmut PD (100% on PD area) 0.28mW (measured by Ophir power meter)
Incident Power on 1611 InGaAs (<100% on PD area) 0.64mW
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W
   

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

Attachment 1: PD_measurement.png
PD_measurement.png
Attachment 2: plot_PD_RF_ratios.pdf
plot_PD_RF_ratios.pdf
  4500   Thu Apr 7 16:09:17 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I think I had underestimated the responsivity of the Silicon PD at 1064nm. The previous value was based on a rough search online for the responsivity of Silicon (I couldn't find the product number of the actual PD we are using). For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm. 

If we calculate the responsivity of the Hartmut PD from the measurements I made today (input power = 0.300mW, output voltage = 5.56mV, effective transimpedance = 80 Ohms), then the responsivity at 1064nm is 0.23 A/W which is not an unreasonable number given the response of the Thorlabs detector.

Quote:

Measurement Value
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W
   

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

 

  4502   Thu Apr 7 21:58:57 2011 AidanSummaryGreen LockingBeat note amplitude

Having convinced myself that the green Hartmut PD is giving an acceptable response at RF frequencies I decided to double-check the beatnote at IR (fiber transmission from the X-end beating with the PSL). This took a while because I had to realign the beam into the fiber at the X-end (I had a PD monitoring the output from the fiber on the PSL table and 40m of BNC cable giving me the signal from it at the X-end).

Eventually, I managed to get a beatnote on the PD. At first there was no signal at the temperature calculated using Koji and Suresh's calibration, but it turned out that the mode-overlap wasn't good enough on the PD. Now I can clearly see beats between a couple of modes, one of which is much stronger than the other. I think we should use a frequency discriminator on the output from the IR PD to servo the end laser and keep the strong beat note within <100MHz of DC.

 

  4575   Wed Apr 27 20:14:16 2011 AidanSummaryelogRestarted with script ...
  4584   Thu Apr 28 22:38:38 2011 AidanUpdateGreen LockingElectronics schematic for vertex beatbox

 With some assistance from Kiwamu and Koji, I've drawn up the electronics design for the Beat Box for the vertex green locking. The Omingraffle schematic is posted on the Green Locking Wiki page. It's also attached below. Some final touches are necessary before we can Altium this up.

 Attachment 1: Schematic of beatbox

Attachment 2: Front and back panel designs.

Attachment 1: Canvas_1.png
Canvas_1.png
Attachment 2: Canvas_2.png
Canvas_2.png
  4741   Wed May 18 18:33:46 2011 AidanUpdateelogrestarted elog with script
  6162   Tue Jan 3 18:40:08 2012 AidanSummaryComputer Scripts / Programsmedm directory clean-up

 I moved the following old and obsolete MEDM directories to an archive /cvs/cds/rtcds/caltech/c1/medm

  • c1vga
  • c1vgl
  • c1gpt
  • c1gpv
  • c1nio
  • c1spy
  • c1spx

None of these models were present in /cvs/cds/rtcds/caltech/c1/target

  7495   Sun Oct 7 12:11:00 2012 AidanUpdateComputersRebooted cymac0

I rebooted cymac0 a couple of times. When I first got here it was just frozen. I rebooted it and then ran a model (x1ios). The machine froze the second time I ran ./killx1ios. I've rebooted it again.

  15945   Fri Mar 19 15:26:19 2021 AidanUpdateComputersActivated MATLAB license on megatron

Activated MATLAB license on megatron

  15946   Fri Mar 19 15:31:56 2021 AidanUpdateComputersActivated MATLAB license on donatella

Activated MATLAB license on donatella

  161   Mon Dec 3 19:44:58 2007 Accelerometers on new mountsConfigurationPEMAndrey

I (Andrey) continued today working with new accelerometer mounting. (see entry #151 about my Friday work).

I bought screws/washers and attached those mounts with accelerometers to metallic frames which are firmly cemented to the floor.

One such mount with three accelerometers (in X-, Y-, Z-directions) is installed near the ITMX (in the previous location, but NOT on top of the unused stack as before Friday), the other mount with three accelerometers in three orthogonal directions is installed near ETMX in the east end of the room (this set of accelerometers was installed between MC and BS before Friday). I uncoiled the cables, put them into the cable tray towards the ETMX, and hooked-up the three accelerometers near ETMX in the east end of the room.

Now all six accelerometers are hooked-up (that is, connected to power supply board with cables).

We decided with Steve Vass to put red cones (similar to those that are on highways in the road construction zones) in order to prevent people from bumping into accelerometers. Please use caution when walking along the X-arm.

I took several pictures of the new accelerometer setup. Picture "DSC_0194.JPG" shows the mount with accelerometers near the the ITMX and the beamsplitter chamber,
picture "DSC_0195.JPG" is the "zoomed-in" view of the same accelerometers, while picture "DSC_0196.JPG" shows the mount with accelerometers near ETMX in the east end of the room.

Many thanks to Mr. Steve Vass for his thorough explanation/showing me how to drill the metal and put threads in the holes.
Attachment 1: DSC_0194.JPG
DSC_0194.JPG
Attachment 2: DSC_0195.JPG
DSC_0195.JPG
Attachment 3: DSC_0196.JPG
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  3484   Sat Aug 28 08:17:51 2010 AbertoUpdateElectronicsFSS Frequency Generation Box under test

I've taken the FSS frequency generation box out of the 1Y1 rack. It's sitting on one of the electronics benches. I'm measuring its phase noise.

  12153   Tue Jun 7 17:21:13 2016 AakashUpdateGeneralSURF 2016

Hi!

I am Aakash Patil. I will be working at the 40m lab as a SURF student with Gautam Venugopalan on enclosures for seismometers to shield them from thermal and magnetic fluctuations. This week I will be working on the development of hardware for four probe measurement along with a constant current source. It will effectively help us in accurate temperature measurement throughout the development of enclosure.

 

  12160   Thu Jun 9 09:57:06 2016 AakashUpdateGeneralSeismometer Enclosure Development
Me and Gautam yesterday opened the tilt-free seismometer enclosure to see if we could use the thermocouples and
other things previously used by Megan. But we are planning to get new four-wire RTDs for our work.
For the next day or two, I will be trying to set up Acromag Busworks terminal so that the data logging during
this enclosure development experiment becomes perfect and easy. Johannes has sent me the wiki page URL for the same.
  12163   Thu Jun 9 18:54:40 2016 AakashUpdateGeneralAbout Acromag | SURF 2016

Today I tried to setup Acromag Busworks card. I was able to calibrate and test it over USB but I couldn't test it over ethernet. I'll utilize a few hours tomorrow to test it over ethernet and see if I can make it work. I have also found a few RTDs which I want to use for temperature sensing via four probe method. So, tomorrow I'll get these RTD details revived by Gautam and Steve.

I was wondering if we have a basic DAQ card with maybe 4 channels which is simple to setup like NI DAQ cards.

  12172   Mon Jun 13 19:30:58 2016 AakashUpdateGeneralEPICS Installation | SURF 2016

About acquiring data: Initially I couldn't start with proper Acromag setup as the Raspberry pi had a faulty SD card slot. Then Gautam gave me a working pi on which I tried to install EPICS. I spent quite a time today but couldn't setup acromag over ethernet.  But, it would be great if we have a USB DAQ card. I have found a good one here http://www.mccdaq.com/PDFs/specs/USB-200-Series-data.pdf It costs around 106$ including shipping (It comes with some free softwares for acquiring data) . Also, I know an another python based 12bit DAQ card (with an inbuilt constant current source) which is made by IUAC, Delhi and more information can be found here http://www.iuac.res.in/~elab/expeyes/Documents/eyesj-progman.pdf  It costs around 60$ including shipping.

About temperature sensing: The RTD which I found on Omega's list is having a temperature resolution of 0.1 deg C. I have also asked them for the one with good resolution. Also according to their reply, they have not performed any noise characteristics study for those RTDs.

 

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