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ID Date Author Type Category Subjectup
  1820   Mon Aug 3 14:15:50 2009 JenneUpdateIOOWFS recentered

I am (was) able to get the mode cleaner mostly locked, but because WFS2 wasn't centered, the MC would drift, then lose lock.  I recentered both the WFS (after unlocking the MC and the MZ), and am now about to commence relocking both of those.

 

/end{quick update}

 

Note to self:  WFS get centered based on the direct reflection from MC1.  Once the MC is close enough, the WFS are enabled, and they twiddle all 3 MC mirrors to minimize their error signal.  Moral of the story: make sure the WFS are centered.

  12900   Wed Mar 22 16:58:25 2017 gautamUpdateIMCWFS sensing matrix measurements

I've taken a bunch of transfer function measurements from the MC ASC PIT and YAW channels to the WFS error signals using the same set of DTT templates Koji used while characterizing the WFS loops a couple of months ago, before the IMC RF changes. Analysis is underway and I will post the results here shortly...

As an aside, Rana had added 10dB and 20dB gains to all of the WFS filter banks yesterday. I tried engaging the 10dB gains on the two MC2_TRANS PD loops, and this did not seem to induce any instability. I stepped both loops and saw that as expected, the 1/e times for both of these loops is about 45 seconds now (compared to ~150 seconds at the nominal gain). These have been running all day today, and the IMC seems well behaved, so I am going to leave these on for now... Jacking up the gain on the MC2_TRANS_QPD loops by 20dB induced instability - same story for the 4 WFS loops with 10dB additional gain...

  12901   Thu Mar 23 01:44:53 2017 gautamUpdateIMCWFS sensing matrix measurements

Thanks to Koji's nice MATLAB script using DttData functions, I was able to quickly analyze the TF data. Essentially, this measurement was a repetition of what was done here. The difference is that the modulation depth has been increased by ~25x compared to that measurement from December 2016. Here are the measured TFs (before accounting for the 1/f^2 normalization) for the various quadrants and the PIT/YAW channels:

  

The plots above are just to illustrate that the measurement was clean between the band over which the averaging will be done to compute the TF amplitude - i.e. 7-15Hz. The full summary of TF amplitudes, standard deviations, and the sensing matrix in the style of the referenced elog (the actual excel spreadsheet is Attachment #4, minus some of the graphics Koji had on his excel sheet):

Inverting those matrices, we get the matrices that diagonalize the sensor-actuator chain:

PITCH:

\begin{pmatrix} -0.00518 & -0.00305 & -639.6\\ 0.00354 & -0.00281 & 198.8\\ 0.00102 & 0.00672 & -756.6 \end{pmatrix}

YAW:

\begin{pmatrix} 0.00523 & -0.00276 & -856.7\\ 0.000318 & 0.00010 & -366.4\\ 0.00039 & -0.00548 & -851.9 \end{pmatrix}

I will try implementing these matrices tomorrow and take a look at the step responses of the loops - the idea is that perhaps the system wasn't optimally diagonalized before and perhaps we can now improve the bandwidths of all the loops.

 

Attachment 1: IMC_WFS_segment_TF.pdf
IMC_WFS_segment_TF.pdf
Attachment 2: IMC_WFS_channels_TF.pdf
IMC_WFS_channels_TF.pdf
Attachment 3: TFsummary.pdf
TFsummary.pdf
Attachment 4: IMC_WFS_170322.xlsx.zip
  12902   Thu Mar 23 08:43:11 2017 ranaUpdateIMCWFS sensing matrix measurements

For sensing matrix, better to use single frequency sine response. We don't want to measure around the bounce or above the 28 Hz cutoff filters in the MC SUS.

  12867   Sun Mar 5 12:41:23 2017 gautamUpdateIMCWFS servo-steppin

I've been sitting on some data for a while now which I finally got around to plotting. Here is a quick summary:

Attachment #1: I applied a step input to the offset of each of the six WFS loops and observed the step response. The 1/e time constant for all 4 WFS loops is <10s suggesting a bandwidth a little above 0.1Hz. However, the MC2 P and Y loops have a much longer time contant of ~150s. Moreover, it looks like the DC centering of the spot on the QPD isn't great - the upper two quadrants (as per the MEDM screen) have ~3x the cts of the lower pair.
I did not (yet) try increasing the gain of this loop to see if this could be mitigated. I accidentally saved this as a png, I will put up the pdf plot

Attachment #2: This is a comparison of the WFS error signals with the loops engaged (solid lines) vs disabled (dashed lines). Though these measurements were taken at slightly different times, they are consistent with the WFS loop bandwidths being ~0.1Hz.

Attachment #3: Comparison of the spectra of the testpoint channels and their DQ counterparts at the same time which are sampled at 512Hz. It does not look like there is any dramatic aliasing going on, although it is hard to tell what exactly is the order of the digital AA filter implemented by the RCG. Further investigation remains to be done... For reference, here are some notes: T1600059, T1400719

GV 7 March 2017 6pm: It looks like we use RCG v2.9.6, so it should be the latter document that is applicable. I've been going through some directories to try and find the actual C-code where the filter coeffs are defined, but have been unsuccessful so far...

Quote:

I will update with the in-loop error signal spectra, which should give us some idea of the loop bandwidth.


I will look into lowering the sampling rate, and how much out-of-band power is aliasing into the 0-256 Hz band and update with my findings.

 

Attachment 1: WFS_stepping.png
WFS_stepping.png
Attachment 2: WFS_comparisons.pdf
WFS_comparisons.pdf WFS_comparisons.pdf
Attachment 3: WFSdigitalAA.pdf
WFSdigitalAA.pdf WFSdigitalAA.pdf
  15965   Thu Mar 25 15:31:24 2021 gautamUpdateIOOWFS servos

The servos are almost certainly not optimal - but we have the IFO sort of working, so before we make any changes, let's make a strong case for it. Once the loop TFs and noises (e.g. the sensing noise reinjection you maybe saw) are fully characterized and a new loop is shown to perform better, then we can make the changes, but until then, let's continue using the "nominal" configuration and keep all the WFS loops on wink. I turned everything back on.

BTW, MC2_ASCPIT_IN1 isn't the correct channel to measure the sensing noise re-injection, you need some other sensor, e.g. is the MC transmission (de)stabilized. 0-20 Hz is where I expect the WFS is actually measuring above the sensing noise.

  12838   Fri Feb 17 20:10:18 2017 gautamUpdateIMCWFS servos turned back on

[Koji, gautam]

Turns out the "problem" with WFS2 and the apparent offset accumulation on the IMC Servo board is probably a slow machine problem.

Today, Koji and I looked at the situation a little more closely. This anomalous behaviour of the C1:IOO-MC_SUM channel picking up an offset seems correlated with light being incident on WFS2 head. Placing an ND filter in front of WFS 2 slowed down the rate of accumulation (though it was still present). But we also looked at the in-loop error signal on the IMC board (using the "Out 2" BNC on the front panel), and this didn't seem to show any offset accumulation. Anyways, the ability of the Autolocker doesn't seem to be affected by this change, so I am leaving the WFS servo turned on.

The new demod phases (old +45degrees) and gains (old gains *0.2) have been updated in the SDF table. It remains to see that the WFS loops don't drag the alignment over longer timescales. I will post a more detailed analysis here over the weekend...

Also, we thought it would be nice to have DQ channels for the WFS error signals for analysis of the servo (rather than wait for 30 mins to grab live fine resolution spectra of the error signals with the loop On/Off). So I have added 16 DQ channels [recorded at 2048 Hz] to the c1ioo model (for the I and Q demodulated signal from each quadrant for the 8 quadrants). The "DRATE" for the c1ioo model has increased from ~200 to 410. Comparing to the "DRATE" of c1lsc, which is around 3200, we think this isn't significantly stretching the DAQ abilities of the c1ioo model...

 

  12839   Sat Feb 18 14:09:06 2017 ranaUpdateIMCWFS servos turned back on

Yikes. Please change the all teh WFS DQ channels sample rates from 2048 down to 512 Hz. I doubt we ever need anything about 180 Hz.

There is sometimes an issue with this: if our digital AA filters are not strong enough, the noise about above 256 Hz can alias into the 0-256 Hz band. We ought to check this quantitatively and make some elog statement about our AA filters. This issue is also seen in DTT when requesting a low frequency spectrum: DTT uses FIR filters which are sometimes not sharp enough to prevent this issue.

 

  12840   Sat Feb 18 21:50:48 2017 gautamUpdateIMCWFS servos turned back on

Here is a comparison of the error signal spectra after increasing the IMC modulation depth, to the contribution with RF inputs / whitening inputs terminated (which I borrowed from Koji's characterization of the same in Dec 2016, these shouldn't have changed).

Some general observations:

  1. This data was taken with the WFS servos disabled, but with the IMC hand-aligned to a good state (MC_TRANS ~15,000). The error signal spectra are from the new DQ channels (but still sampled at 2048Hz, I had not implemented the change to 512Hz).
  2. The error signals seem to have increased by ~25x yes, which is consistent with how much we expect the modulation depth to have increased
  3. The bump around 1 Hz is now cleaerly visible in all 16 channels, as is the bounce peak at 16Hz (relative to Dec 2016). In general, between 0.1Hz and 5Hz, there is now a fair bit of daylight between the error signals and the electronics noise contribution. 

I will update with the in-loop error signal spectra, which should give us some idea of the loop bandwidth.


I will look into lowering the sampling rate, and how much out-of-band power is aliasing into the 0-256 Hz band and update with my findings.

Quote:

Yikes. Please change the all teh WFS DQ channels sample rates from 2048 down to 512 Hz. I doubt we ever need anything about 180 Hz.

There is sometimes an issue with this: if our digital AA filters are not strong enough, the noise about above 256 Hz can alias into the 0-256 Hz band. We ought to check this quantitatively and make some elog statement about our AA filters. This issue is also seen in DTT when requesting a low frequency spectrum: DTT uses FIR filters which are sometimes not sharp enough to prevent this issue.

 

 

Attachment 1: WFS_error_noise.pdf
WFS_error_noise.pdf
  4148   Thu Jan 13 03:00:01 2011 JenneUpdateIOOWFS shenanigans

My goal this afternoon was to measure the quantum efficiency of the MC WFS.  In the process of doing this, I discovered that when I reverted a change in the MCWFS path (see elog 4107 re: this change), I had not checked the max power going to the WFS when the MC unlocks.

Current status:

MC locks (is locked now).  No light going to WFS at all (to prevent MC WFS french-fry action).  Quantum Efficiency measured.

The Full Story:

Power to WFS:

Rana asked me to check out the quantum efficiency of the WFS, so that we can consider using them for aLIGO.  This involves measuring the power incident on the PDs, and while doing so, I noticed that WFS1 had ~160mW incident and WFS2 had ~240mW incident while the mode cleaner was unlocked.  This is bad, since they should have a max of ~10mW ever.  Not that 200mW is going to destroy the PD immediately, but rather the current out, with the 100V bias that the WFS have, is a truckload of power, and the WFS were in fact getting pretty warm to the touch.  Not so good, if things start melting / failing due to extended exposure to too much heat.

The reason so much power was going to the WFS is that it looks like Yuta/Koji et. al., when trying to use the WFS as a MC1 oplev, changed out 2 of the beam splitters in the MC WFS / MC Refl path, not just one.  Or, we've just been crispy-frying our WFS for a long time.  Who knows?  If it is option A, then it wasn't elogged.  The elog 3878 re: BS changeout only mentions the change of one BS.

Since the MC Refl path has a little more than ~1W of power when the MC is unlocked, and the first BS (which was reverted in elog 4107) is a 10% reflector, so ~100mW goes to the MC Refl PD, and ~900mW goes to the MC WFS path.  In front of a Black Hole beam dump was sitting a BS1-33, so we were getting ~300mW reflected to be split between the 2 WFS, and ~600mW dumped.  The new plan is to put a W2 window in place of this BS1-33, so that we get hopefully something like 0.1% reflected toward the WFS, and everything else will be dumped.  I could not find a W2-45S (everything else is S, so this needs to be S as well).  I found a bunch of W2-0deg, and a few W2-45P.  Does anyone have a secret stash of W2-45S's???  To avoid any more excessive heat just in case, for tonight, I have just left out this mirror entirely, so the whole MC WFS beam is dumped in the Black Hole.  The WFS also have aluminum beam dumps in front of them to prevent light going in.  None of this affects the MC Refl path, so the MC can still lock nice and happily.

Quantum Efficiency Measurement:

I refer to Jamie's LHO elog for the equation governing quantum efficiency of photodiodes: LHO 2 Sept 2009

The information I gathered for each quadrant of each WFS was: [1] Power of light incident on PD (measured with the Ophir power meter), [2] Power of light reflected off the PD (since this light doesn't get absorbed, it's not part of the QE), and [3] the photo current output by the PD (To get this, I measured the voltage out of the DC path that is meant to go to EPICS, and backed out what the current is, based on the schematic, attached). 

I found a nifty 25 pin Dsub breakout board, that you can put in like a cable extension, and you can use clip doodles to look at any of the pins on the cable.  Since this was a PD activity, and I didn't want to die from the 100V bias, I covered all of the pins I wasn't going to use with electrical tape.  After turning down the 100V Kepco that supplies the WFS bias, I stuck the breakout board in the WFS.  Since I was able to measure the voltage at the output of the DC path, if you look at the schematic, I needed to divide this by 2 (to undo the 2nd op amp's gain of 2), and then convert to current using the 499 Ohm resistor, R66 in the 1st DC path.  

I did all 4 quadrants of WFS1 using a 532nm laser pointer, just to make sure that I had my measurement procedure under control, since silicon PDs are nice and sensitive to green.  I got an average QE of ~65% for green, which is not too far off the spec of 70% that Suresh found.

I then did all 8 WFS quadrants using the 1064nm CrystaLaser #2, and got an average QE of ~62% for 1064 (58% if I exclude 2 of the quadrants....see below).  Statistics, and whatever else is needed can wait for tomorrow.

Problem with 2 quadrants of WFS2?

While doing all of this, I noticed that quadrants 3 and 4 of WFS2 seem to be different than all the rest.  You can see this on the MEDM screens in that all 6 other quadrants, when there is no light, read about -0.2, whereas the 2 funny quadrants read positive values.  This might be okay, because they both respond to light, in some kind of proportion to the amount of light on them.  I ended up getting QE of ~72% for both of these quadrants, which doesn't make a whole lot of sense since the spec for green is 70%, and silicon is supposed to be less good for infrared than green.  Anyhow, we'll have to meditate on this.  We should also see if we have a trend, to check how long they have been funny.

Attachment 1: D990249-B-1_MCWFS_schematic.pdf
D990249-B-1_MCWFS_schematic.pdf
  4149   Thu Jan 13 12:56:57 2011 ranaUpdateIOOWFS shenanigans

Actually, I just found out that there are different flavors of 'YAG-444'.

There's a YAG-444AH and also a YAG-444-4AH. I'm not sure which one we have or even which is better. The diode's internal resistance is not listed.

They also say explicitly that he 'YAG Enhancement' is just using thicker Silicon. Since the absorption of 1064 nm light in Silicon is very small, most of the light just goes in and then comes back out without depositing much of the power.

Attachment 1: PerkinElmerQPDs.pdf
PerkinElmerQPDs.pdf PerkinElmerQPDs.pdf
  5042   Wed Jul 27 10:04:29 2011 SureshUpdateIOOWFS transfer function measurements

This is part of the WFS activity.  So far I have completed the following tasks:

1)  I fixed the MEDM screens up to a point where they can be used for locking.  There are still some buttons which invoke non-existing screens and some blank fields.  But the basic filter banks and input  and output matrices are fixed.

2) I copied all the old filter banks into the new screens both in the WFS head and in the WFS Master, where the servo filters are located.  The I and Q filter banks in the WFS heads have been switched on.

3) I <=> Q phase settings in the WFS head for each quadrant:  We have assumed that the I and Q are orthogonal so D=90 for all cases.  I set the R phase to minimise the signal in all the Q lines.  So the signal is largely in the I phase.  I used Sine Response feature in DTT while supplying an excitation signal to MC2_ASCPIT_EXC.  At times I used the YAW instead of PIT if I did not get enough coherence.  This was set manually by watching the Q phase signal and minimising that by adjusting the R angle.  It was in general possible to get this correct to a deg.   There are several old scripts to do this in the MC/WFS but they do not work since most of them are based on the ezlockin or ezcademod functions.    I will try to fix the ezWFS1phase and ezWFS2phase scripts to automate this.  Some channel names have to be changed in these.

4) I measured the transfer function between the mirror motions [(MC1, MC2, MC3) x (PIT, YAW)] and the sensor DoF [(WFS1, WFS2) x (PIT, YAW)].  The measurements are reported below.  The plan is to invert this matrix and use it as the Out_Matrix.

WFS_TF_Phase_Sheet1.png

I list here the various steps I took in making this measurement.

a) Set the DC offsets on the individual quadrants to zero using an old script (which I updated with the new channel names).  The script is called McWFS_dc_offsets and is located in the $scripts$/MC/WFS directory.   Note that before doing this the PSL shutter was closed.  This script sets a basic EPICS parameter called AOFF for each channel.  These are listed in cvs/cds/caltech/target/c1iool0 .

b) Then the PSL beam into the MC was steered to optimise coupling into MC (described in my earlier post today).  This is because we use the input beam as a reference while setting up the WFS.

c) Unlock the MC and center the directly reflected beam from the MC on the WFS.  We use the DC monitors on the C1IOO_WFS_QPD.adl screen to center the spot on the WFS head. 

d) Then used the WFSoffsets script to set the offsets in the I and Q filter banks to zero.  This script uses the ezcaservo to look at the OUT16 channels and zeroes them by setting an appropriate offset.  I took care to switch off all slow filters in the I and Q filter banks before this operation was carried out .  Only the 60Hz comb filter was on.

e) Opened the PSL shutter and relocked the MC

f) Then I measured the transfer co-efs by oscillating the optic (exciting a specific degree of freedom) and observing the response in the WFS sensor degrees of freedom.   These are tabulated above.

Next

   I plan to use this matrix and prepare the Output matix and then close the WFS servo loops. 

 

 

  10431   Tue Aug 26 23:46:55 2014 ericqUpdateIMCWFS tuneup

 I decided to see what I could do with the new WFS setup. 

First, I adjusted the WFS digital demod angles. Once I ensured that the static MC alignment and DC alignment onto the WFS was good, I drove MC2 in pitch with the WFS output off. I then did the usual thing of making the Q peak at the excitation frequency go away. Here are the changes:

  • WFS1 Q1: 7 -> -24 (-31)
  • WFS1 Q2: 6.5 -> -9.5 (-16)
  • WFS1 Q3: -6.5 -> -26.5 (-20)
  • WFS1 Q4: 47 -> 30 (-17)
  • WFS2 Q1: -51 -> -39 (-12)
  • WFS2 Q2: -39 -> -21 (-18)
  • WFS2 Q3: -32 -> -20 (-12)
  • WFS2 Q4: -120 -> -108 (-12)

I then drove each MC mirror in pitch and yaw respectively, and measured the TF from excitation to the WFS signal (dB Magnitude, sign):

 

Mirror DoF WFS1 Pitch WFS1 Yaw WFS2 Pitch WFS2 Yaw
MC1 Pit -67.7,+ -81.9,+ -58.9,- -83.7,+
  Yaw -82.5,- -48.7,- -83.7,+ -112.3,-
MC2 Pit -50.4,- -77.1,- -54.2,- -67.9,+
  Yaw -82.1,- -52.9,+ -59.6,- -44.0,-
MC3 Pit -59.7,- -97.3,+ -62.0,+ -83.9,-
  Yaw -78.0,+ -52.9,+ -67.3,+ -51.4,+

 

I looked through some old ELOG's of Suresh's and used similar logic to scripts/MC/WFS/wfsmatrix2.m to generate a new output matrix. (This involves creating a null sensing vector that is orthogonal to the measured ones, and inverting that matrix) 

Old:

Pitch WFS1 WFS2 MC2T   YAW WFS1 WFS2 MC2T
MC1 -1 0.044 0   MC1 -1 -0.294 0
MC2 0.19 1 1   MC2 -0.26 -0.045 -1
MC3 0.5 -0.681 0   MC3 -.9 1 0

 

New:

 

Pitch WFS1 WFS2 MC2T   YAW WFS1 WFS2 MC2T
MC1 0.835 -1 0   MC1 -1 -0.229 0
MC2 -0.948 -0.433 1   MC2 0.317 -1 -1
MC3 -1 0.865 0   MC3 0.743 0.628 0
 

 

I had to flip a gain or two to keep things stable, then measured the WFS error signal spectra to see if this made anything better. The WFS1 spectra look better, but WFS2 not so much. 

newWFSmatrix.pdf

The loops would need a more thorough investigation, but for now, they're at least a little calmer. The MC is stabler than immediately after the upgrade, but there's still room for improvement. 

 

  10432   Wed Aug 27 09:12:47 2014 KojiUpdateIMCWFS tuneup

I'm sure that the 1~3Hz motion comes from the mirror motion, but not 100% sure what is causing
the broad stochastic noise. If this is the beam jitter, this penetrates to the IFO via the WFS servos.
Is there any way to characterize this noise in order to compare it with the actual (estimated) motion of the mirrors?

  17168   Sat Oct 1 13:09:49 2022 AnchalUpdateIMCWFS turned on

I turned on WFS on IMC at:

PDT: 2022-10-01 13:09:18.378404 PDT
UTC: 2022-10-01 20:09:18.378404 UTC
GPS: 1348690176.378404

The following channels are being saved in frames at 1024 Hz rate:

  • C1:IOO-MC_TRANS_PIT_ERR (Same as C1:IOO-MC_TRANS_PIT_OUT)
  • C1:IOO-MC_TRANS_YAW_ERR (Same as C1:IOO-MC_TRANS_YAW_OUT)
  • C1:IOO-MC_TRANS_SUM_ERR (Same as C1:IOO-MC_TRANS_SUMFILT_OUT)

We can keep it running over the weekend as we will not use the interferometer. I'll keep an eye on it with occasional log in. We'll post the time when we switch it off again.


The IMC lost lock at:

UTC    Oct 03, 2022    01:04:16    UTC
Central    Oct 02, 2022    20:04:16    CDT
Pacific    Oct 02, 2022    18:04:16    PDT

GPS Time = 1348794274

The WFS loops kept running and thus took IMC to a misaligned state. Between the above two times, IMC was locked continuously with very brief lock loss events, and had all WFS loops running.

  9389   Fri Nov 15 09:24:41 2013 SteveUpdateIOOWFS with beam dumps

This is a proposal to move WFSs such way that their reflected beam can be trapped.

Later ps: Nic will take care of the Gouy phase telescopes.

Attachment 1: MCwfsRefTraped.jpg
MCwfsRefTraped.jpg
  9390   Fri Nov 15 09:27:58 2013 KojiUpdateIOOWFS with beam dumps

Unfortunately this does not work. These WFSs are not the detectors which we can move freely.
In order to move the WFS detectors, we need the precise design of the Gouy phase for each WFS heads.
Without the design, we can't move the detectors.

  16862   Wed May 18 09:02:52 2022 AnchalUpdateBHDWFS1 PD centered

I centered WFS1 PD so that IMC WFS Servo does not go out of range.

 

  4883   Sat Jun 25 04:40:43 2011 SureshUpdateASCWFS1 Transimpedance measurement

WFS1 Transimpedance

The attached plots show the location of the ~29.5 MHz pole and the 59 MHz notch for each quadrant of the WFS1 Sensor head.

 

WFS1 Pole (MHz) Z(Ohms) Notch (MHz) Z(Ohms)
Q1 28.89 598 60.38 0.83
Q2 29.20 513 57.70 0.57
Q3 29.63 681 59.63 0.89
Q4 28.89 609 58.13 0.78

 

As may be seen from the above table, these frequencies will need to be adjusted in some cases.

From the plots we can see that, when there is no attenuation set on the attenuator AT65-0263 (ref D990249-A),  the MAX4107  oscillations are seen in Q2,Q3,Q4 quadrants at around 200 MHz.  

Rana suggested, from his previous encounter with this circuit, that the solution is to remove the second MAX4106 and the attenuator on the RF line to avoid this oscillation.

 

WFS1_transimpedance.pdf

A look at the circuit board shows that some of the inductors have not been mounted.  That explains the presence of only one notch though the schematic shows two. 

P6250224.JPG         P6250223.JPG

  4995   Wed Jul 20 06:36:39 2011 SureshUpdateIOOWFS1 and 2 gains

Gains of individual quadrants in both the WFS

As a simple check of the gains on all the quadrants I hooked up the AM (Jenne) laser to put FM modulated light on to the WFS heads and observed the FM modulation frequency , 105 Hz, show up on a power spectrum of the RF outputs.   The plots below show the peak at 105Hz in all the quadrants.

WFS1_7kHz_105Hz.pdf

WFS2_7kHz_105Hz.pdf

 

However I should have put in AM modulation rather FM modulation.  I will do that using the digital system today.  The first version above was done wth a Marconi driving the AM laser modulation.

 

 

  4860   Wed Jun 22 18:51:47 2011 SureshUpdateIOOWFS2 RF response

I have shifted the Jenne laser back to the small table where we do RF PD characterisation (RFPD table).  I found several 25pin D-type connector cables, connected them in tandem and am using that to power the WFS2 sensor head at the RFPD table. 

The set up is ready for looking at the RF response of the  WFS sensors.  Will continue tonight.

 

  4895   Tue Jun 28 09:50:03 2011 SureshUpdateIOOWFS2 RF response

The WFS2  Transimpedance has been measured to determine if it also suffers from the same 200MHz oscillations seen in WFS1 sensor head

The attached plots (pdf attached) show that the 29.5 MHz peak needs tweaking in Q2 and Q1 seems to have a much lower transimpedance than other quadrants.  The table below summarises the resonances and notches of the ckt

 

WFS2 Pole(MHz) Z(Ohms) Notch (MHz) Z(Ohms)
Q1 29.63 576 59.25 0.76
Q2 28.5 862 59.0 1.41
Q3 29.8 766 59.25 1.05
Q4 29.8 704 59.0 1.09

 

The peak at 10MHz is much sharper than the similar peak at 13MHz in the case of WFS1.  Is this a matter for some concern? 

The 200MHz oscillation once again exists in Q2, Q3 and Q4.  This sensor head will also require the same treatment as WFS1.

 

 

 

Quote:

I have shifted the Jenne laser back to the small table where we do RF PD characterisation (RFPD table).  I found several 25pin D-type connector cables, connected them in tandem and am using that to power the WFS2 sensor head at the RFPD table. 

The set up is ready for looking at the RF response of the  WFS sensors.  Will continue tonight.

 

 

Attachment 1: WFS2_transimpedance.pdf
WFS2_transimpedance.pdf WFS2_transimpedance.pdf WFS2_transimpedance.pdf WFS2_transimpedance.pdf
  15670   Tue Nov 10 14:30:06 2020 gautamUpdateIOOWFS2 broken

While proceeding with the interferometer recovery, I noticed that there appeared to be no light on WFS2. I confirmed on the AP table that the beam was indeed hitting the QPD, but the DC quadrants are all returning 0. Looking back, it appears that the failure happened on Monday 26 October at ~6pm local time. For now, I hand-aligned the IMC and centered the beams on the WFS1 and MC2T QPDs - MCT is ~15000 cts and MC REFL DC is ~0.1, all consistent with the best numbers I've been able to obtain in the past. I don't think the servo will work without 1 sensor without some retuning of the output matrix.

It would appear that both the DC and RF outputs of WFS2 are affected - I dithered the MC2 optic in pitch (with the WFS loop disabled) at 3.33 Hz, the transmission and WFS1 sensors see the dither but not WFS2. It could be that I'm just not well centerd on the PD, but by eye, I am, so it would appear that the problem is present in both the DC and RF signal paths. I am not going into the PD head debugging today.

Quote:

Looking back through the elog, 1mtorr is the pressure at which it is deemed safe to send the full power beam into the IMC. After replacing the HR mirror in the MCREFL path with a 10% reflective BS, I just cranked the power back up. IMC is locked. With the increased exposure on the MC2T camera, lots of new scattered light has become visible.

Attachment 1: WFS2broken.png
WFS2broken.png
Attachment 2: WFS2broken_RF.png
WFS2broken_RF.png
  15708   Fri Dec 4 15:58:22 2020 KojiUpdateIOOWFS2 broken

I checked the backplane connection for IMC WFS2  and found that the cables for IMC WFS2 and the IMC demod were swapped during my IMC noise hunting activities. I reverted it just now.

But we need to check if this damaged anything such as the WFS2 head, the WFS2 demod, etc, once the IMC locking is back.

  4819   Wed Jun 15 00:49:34 2011 SureshUpdateIOOWFS2 has been fixed.

 

The WFS2 sensor head had a damaged Quadrant PIN diode (YAG-444-4A).  This has been replaced by a   YAG-444-4AH  which has a responsivity of 0.5 A/W. 

P6150121.JPG     P6150124.JPG

The responsivity of each quadrant was measured at normal incidence.  A diagram of the set up with the relevant power levels is attached.  The precision of these measurement is about 5% .  Largely because the power levels measured are sensitive to the position of the laser beam on the power meter sensor head (Ophir with ND filter mask taken off).  Putting the mask back on did not solve this problem.

The incident power was 0.491mW  of which about 0.026mW was reflected from the face of the QPD.  The beam was repositioned on the QPD to measure the response of each quadrant.  In each case the beam was positioned to obtain maximum DC output voltage from the relevant quadrant.  A small amount of spill over was seen in the other quadrants.  The measurements are given below

WFS2 DC output measurements (mV)
  Position 1 Position 2 Position 3 Position 4 Dark
Q1 244 6.7 5.4 6.9 4
Q2 5.9 238 8.4 5 5
Q3 9 6.6 236 7.3 6
Q4 7.5 7 7 252 7

WFS_QE_measurement.png

To measure these DC outputs of from the sensor-head a breakout board for the 25-pin D-type connector was used as in the previous measurements.  The results are given below

 

WFS2 Quantum Efficiency measurement

  DC out (mV)

Responsivity

A/W

Quantum Efficiency (%)
Q1 238 0.52 0.60
Q2 233 0.50 0.59
Q3 230 0.50 0.58
Q4 244 0.53 0.61

 

The measured responsivity agrees with the specification from the manufacturer.  It is to be noted that the previous QPD is reported to have a slightly smaller responsivity 0.4 A/W at 1064 nm.  The data sheet is attached. 

Since the new QPD may have a slightly different capacitance the RF transfer function of the WFS2 needs to be examined to verify the location of the resonances. 

 

Quote:

[Larisa and Jenne]

A few weeks ago (on the 28th of January) I had tried to measure the quantum efficiency of one quadrant of the WFS as a function of angle.  However, Rana pointed out that I was a spaz, and had forgotten to put a lens in front of the laser.  Why I forgot when doing the measurement as a function of angle, but I had remembered while doing it at normal incidence for all of the quadrants, who knows?

Anyhow, Larisa measured the quantum efficiency today.  She used WFS2, quadrant 1 (totally oil-free), since that was easier than WFS1.  She also used the Jenne Laser (with a lens), since it's more stable and less crappy than the CrystaLasers.  We put a 50 Ohm terminator on the RF input of the Jenne Laser, since we weren't doing a swept sine measurement.  Again, the Ophir power meter was used to measure the power incident on the diode, and the reflected power, and the difference between them was used as the power absorbed by the diode for the quantum efficiency measurement.  A voltmeter was used to measure the output of the diode, and then converted to current as in the quote below. 

Still on the to-do list:  Replace the WFS2 diode.  See if we have one around, otherwise order one.  Align beams onto WFS so we can turn on the servo.

QE = (h*c)/(lambda*e) * (I/P)

Where I = (Volts from Pin1 to GND)/2 /500ohms
P = Power from laser - power reflected from diode.
h, c, e are the natural constants, and lambda is 1064nm.
Also, I/P = Responsivity


Larissa is going to put her data and plots into the elog shortly....

Quote:

Quantum Efficiency Measurement:

I refer to Jamie's LHO elog for the equation governing quantum efficiency of photodiodes: LHO 2 Sept 2009

The information I gathered for each quadrant of each WFS was: [1] Power of light incident on PD (measured with the Ophir power meter), [2] Power of light reflected off the PD (since this light doesn't get absorbed, it's not part of the QE), and [3] the photo current output by the PD (To get this, I measured the voltage out of the DC path that is meant to go to EPICS, and backed out what the current is, based on the schematic, attached). 

I found a nifty 25 pin Dsub breakout board, that you can put in like a cable extension, and you can use clip doodles to look at any of the pins on the cable.  Since this was a PD activity, and I didn't want to die from the 100V bias, I covered all of the pins I wasn't going to use with electrical tape.  After turning down the 100V Kepco that supplies the WFS bias, I stuck the breakout board in the WFS.  Since I was able to measure the voltage at the output of the DC path, if you look at the schematic, I needed to divide this by 2 (to undo the 2nd op amp's gain of 2), and then convert to current using the 499 Ohm resistor, R66 in the 1st DC path.  

I did all 4 quadrants of WFS1 using a 532nm laser pointer, just to make sure that I had my measurement procedure under control, since silicon PDs are nice and sensitive to green.  I got an average QE of ~65% for green, which is not too far off the spec of 70% that Suresh found.

I then did all 8 WFS quadrants using the 1064nm CrystaLaser #2, and got an average QE of ~62% for 1064 (58% if I exclude 2 of the quadrants....see below).  Statistics, and whatever else is needed can wait for tomorrow.

Problem with 2 quadrants of WFS2?

While doing all of this, I noticed that quadrants 3 and 4 of WFS2 seem to be different than all the rest.  You can see this on the MEDM screens in that all 6 other quadrants, when there is no light, read about -0.2, whereas the 2 funny quadrants read positive values.  This might be okay, because they both respond to light, in some kind of proportion to the amount of light on them.  I ended up getting QE of ~72% for both of these quadrants, which doesn't make a whole lot of sense since the spec for green is 70%, and silicon is supposed to be less good for infrared than green.  Anyhow, we'll have to meditate on this.  We should also see if we have a trend, to check how long they have been funny.

 

 

Attachment 2: SensorsBrochure-p12.pdf
SensorsBrochure-p12.pdf
  4224   Fri Jan 28 18:19:21 2011 JenneUpdateIOOWFS2 has some kind of oil on it

Mystery solved!

I removed WFS2 from the AP table (after placing markers so I can put it back in ~the same place) so that I could take some reflectivity as a function of angle measurements for aLIGO WFS design stuff.

I was dismayed to discover, upon glancing at the diode itself, that half of the diode is covered with some kind of oil!!!.  The oil is mostly confined to quadrants 3 and 4, which explains the confusion with their quantum efficiency measurements, as well as why the readback values on the MEDM WFS Head screen for WFS2 don't really make sense. 

The WFS QPD has a piece of glass protecting the diode itself, and the oil seems to be on top of the glass, so I'm going to use some lens tissue and clean it off.

Pre-cleaning photos are on Picasa.

Update:  I tried scrubbing the glass with a Q-tip soaked with Iso, and then one soaked in methanol.  Both of these failed to make any improvement.  I am suspicious that perhaps whatever it is, is underneath the glass, but I don't know.  Rana suggested replacing the diode, if we have spares / when we order some spares.

Oily_WFS2.jpg

Quote:

Problem with 2 quadrants of WFS2?

While doing all of this, I noticed that quadrants 3 and 4 of WFS2 seem to be different than all the rest.  You can see this on the MEDM screens in that all 6 other quadrants, when there is no light, read about -0.2, whereas the 2 funny quadrants read positive values.  This might be okay, because they both respond to light, in some kind of proportion to the amount of light on them.  I ended up getting QE of ~72% for both of these quadrants, which doesn't make a whole lot of sense since the spec for green is 70%, and silicon is supposed to be less good for infrared than green.  Anyhow, we'll have to meditate on this.  We should also see if we have a trend, to check how long they have been funny.

 

  4927   Fri Jul 1 07:01:23 2011 SureshUpdateIOOWFS2 resonances and installation

This was the WFS whose photodiode was repaced as the old one was found to be damaged. 

I retuned the resonances and the notches of all the quadrant and have attached a pdf file of my measurements.

 

Some notes:

a)  The variable inductor on WFS2Q2 quadrant may need to be changed. The ferrite code has come of the solinoid and is just held in place due to friction..  It may be easily disturbed.    So though i chose to leave it in place for now,  it will need to be replace in case the Q3 misbahaves..

b) In general the frequencies have shifted a bit when I closed the lid of tne WFS sensor head.

 

WFS1 and 2 have been installed on the AP table and are functional. I am shifting attention to the software.

 

Attachment 1: WFS2new.pdf
WFS2new.pdf WFS2new.pdf WFS2new.pdf WFS2new.pdf
  4928   Fri Jul 1 11:47:25 2011 ranaUpdateIOOWFS2 resonances and installation

What is implicit in Suresh's entry is that we decided to run the WFS with the 10 dB internal attenuation set to ON as the nominal. In the past, we have always had all the attenuation OFF for max gain. The layout of the WFS is such that we get that nasty 200 MHz oscillation due to crosstalk between the 2 MAX4106 opamps for each quadrant. The 10 dB attenuator is able to reduce the positive feedback enough to damp the oscillation.

In principle, this is still OK noise-wise. I think the thermal noise of the resonant circuit should be ~2-3 nV/rHz. Then the first opamp has a gain of 5, then the -10 dB attenuator, then another gain of 5. The noise going to the demod board is then ~10-15 nV.

The real noise issue will be the input noise of the demod board. As you may recall, the output of the AD831 mixer goes to a AD797. The AD797 is a poor choice for this application. It has low noise only at high frequencies. At 10 Hz, it has an input voltage noise of 10 nV/rHz and a current noise of 20 pA/rHz. If we wanted to use the AD797 here, at least the RC filter's resistor should be reduced to ~500 Ohms. Much better is to use an OP27 and then choose the R so as to optimize the noise.

We should also be careful to keep the filter frequency low enough so as not to rate limit the OP27. From the schematic, you can see that this circuit is also missing the 50 Ohm termination on the output. There ought to be the usual high-order LC low pass at the mixer output. The simple RC is just not good enough for this application.

As a quick fix, I recommend that when we next want to up the WFS SNR, we just replace the RC with an RLC (R = 500 Ohms, L = 22 uH, C = 1 uF).

 

Attachment 1: Screen_shot_2011-07-01_at_11.13.01_AM.png
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  5761   Sat Oct 29 02:35:39 2011 SureshUpdateIOOWFS_MASTER screen and lockin screens fixed

I have fixed the WFS_MASTER screen and several of the subscreens such as the MCASS and MC_WFS_LKIN.

Since MC_WFS_LKIN uses six demodulators and single oscillator I could not use the automatically built Lockin screens. 

I built one using the compact filter banks mentioned earlier

The phases in the WFSlockins have yet tp be set.

  13305   Mon Sep 11 09:47:53 2017 SteveUpdateGeneralWIMA caps refilled

Instock WIMA caps refilled to a minimum 50 pieces each.

Attachment 1: WIMA.png
WIMA.png
  3592   Tue Sep 21 15:33:02 2010 steveMetaphysicsTreasureWagonga alart

John Miller has arrived from Australia with 3 bags of  Wagonga Coffee. Trade bargaining has started on

250 mgs of Sumatran Mandehling, Timur and Papua New Guine.

Attachment 1: P1060866.JPG
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Attachment 2: P1060872.JPG
P1060872.JPG
  11150   Fri Mar 20 12:42:01 2015 JenneUpdateIOOWaking up the IFO

I've done a few things to start waking up the IFO after it's week of conference-vacation.

PMC trans was at 0.679, aligned the input to the PMC, now it's up at 0.786.

MC transmission was very low, mostly from low PMC transmission.  Anyhow, MC locked, WFS relieved so that it will re-acquire faster.

Many of the optics had drifted away. AS port had no fringing, and almost every optic was far away from it's driftmon set val.  While putting the optics back to their driftmon spots, I noticed that some of the cds.servos had incorrect gain.  Previously, I had just been using the ETMX servo, which had the correct gain, but the ITMs needed smaller gain, and some of the optics needed the gain to be negative rather than positive.  So, now the script ..../scripts/SUS/DRIFT_MON/MoveOpticToMatchDriftMon.py has individually defined gains for the cds.servo. 

Next up (after lunch) will be locking an aligning the arms.  I still don't have MICH fringing at the AS port, so I suspect that the ASS will move some of the optics somewhat significantly (perhaps the input tip tilts, which I don't have DRIFT_MON for?)

  11151   Fri Mar 20 13:29:33 2015 KojiUpdateIOOWaking up the IFO

If the optics moved such amount, could you check the PD alignment once the optics are aligned?

  11152   Fri Mar 20 16:44:49 2015 ericqUpdateIOOWaking up the IFO

X arm ASS is having some issues. ITMX oplev was recentered with ITMX in a good hand-aligned state. 

The martian wifi network wasn't showing up, so I power cycled the wifi router. Seems to be fine now. 

  11153   Fri Mar 20 23:37:46 2015 JenneUpdateSUSWaking up the IFO

In addition to (and probably related to) the XARM ASS not working today, the ITMX has been jumping around kind of like ETMX sometimes does.  It's very disconcerting. 

Earlier today, Q and I tried turning off both the LSC and the oplev damping (leaving the local OSEM damping on), and ITMX still jumped, far enough that it fell off the oplev PD. 

I'm not sure what is wrong with ITMX, but probably ASS won't work well until we figure out what's up.

I tried a few lock stretches (after realigning the Xgreen on the PSL table) after hand-aligning the Xarm, but the overall alignment just isn't good enough.  Usually POPDC gets to 400 or 450 while the arms are held off resonance, but today (after tweaking BS and PRM alignment), the best I can get POPDC is about 300 counts. 

Den and I are looking at the ASS and ITMX now.

  10941   Mon Jan 26 21:10:04 2015 JenneUpdateModern ControlWaking up the OAF

I had a look at the OAF model today. 

Somehow, the screens that we had weren't matching up with the model.  It was as if the screens were a few versions old.  Anyhow, I found the correct screens in /userapps/oaf/common/medm, and copied them into the proper place for us, /userapps/isc/c1/medm/c1oaf.  Now the screens seem all good.

I also added 2 PCIE links between the OAF and the SUS models.  I want to be able to send signals to the PRM's pitch and yaw.  I compiled and restarted both the oaf model and the sus model.

The OAF model isn't running right now (it's got the NO SYNC error), but since it's not something that we need for tonight, I'll fix it in the morning.


My thought for trying out the OAF is to look at the coherence between seismic motion and the POP DC QPD when the PRMI is locked (no arms).  I assume that the PRM is already handled in terms of angular damping (local and oplev), so the motion will be primarily from the folding mirrors.  Then, if I can feedforward the seismometer signal to the PRM to compensate for the folding mirrors' motion, I can use the DC QPD as a monitor to make sure it's working when we're PRMI-only locked, or at low recycling gain with the arms.  But, since I'm not actually using the QPD signal, this will be independent of the arm power increase, so should just keep working.

Anyhow, that's what my game plan is tomorrow for FF.  Right now the T-240 is settling out from its move today, and the auto-zero after the move.

  11014   Thu Feb 12 12:23:21 2015 manasaUpdateGeneralWaking up the PDFR measurement system

[EricG, Manasa]

We woke up the PDFR measurement setup that has been sleeping since summer. We ran a check for the laser module and the multiplexer module. We tried setting things up for measuring frequency response of AS55.
We could not repeat Nichin's measurements because the gpib scripts are outdated and need to be revised. 

PDFR diode laser was shutdown after this job.

  11132   Wed Mar 11 15:35:38 2015 manasaUpdateGeneralWaking up the PDFR measurement system

I was around the 1Y1 rack today. Trials were done to get the PDFR of AS55.

Quote:

[EricG, Manasa]

We woke up the PDFR measurement setup that has been sleeping since summer. We ran a check for the laser module and the multiplexer module. We tried setting things up for measuring frequency response of AS55.
We could not repeat Nichin's measurements because the gpib scripts are outdated and need to be revised. 

PDFR diode laser was shutdown after this job.

 

  11209   Wed Apr 8 21:10:55 2015 manasaUpdateGeneralWaking up the PDFR measurement system

I was poking around with the PDFR hardware today.

I moved the Agilent which had its screen projected on the monitor. I have put it back...but please verify the settings before using it for tonight.

  11493   Tue Aug 11 11:56:36 2015 Ignacio, JessicaUpdatePEMWasps obliterated maybe...

The wasp terminator came in today. He obliterated the known wasp nest.

We discovered a second wasp nest, right next to the previous one...

Jessica wasn't too happy the wasps weren't gone!

  11512   Mon Aug 17 17:48:12 2015 KojiUpdatePEMWasps obliterated maybe...

We found the same wasp in the 40m. Megan found it walking behind Steve desk!

  3473   Thu Aug 26 13:08:03 2010 josephbUpdateCDSWatch dogs for Vertex optics turned off

We are in the process of doing a damping test with the real time code and have turned off the vertex optics watchdogs temporarily, including BS, ITMs, SRM, PRM, MCs.

  3479   Fri Aug 27 14:03:43 2010 kiwamuUpdateCDSWatch dogs for Vertex optics turned off

For a futher damping test, I again turned off the vertex optics watchdogs temporarily, including BS, ITMs, SRM, PRM, MCs.

  14564   Tue Apr 23 19:31:45 2019 JonUpdateSUSWatchdog channels separated from autoBurt.req

For the new c1susaux, Gautam and I moved the watchdog channels from autoBurt.req to a new file named autoBurt_watchdogs.req. When the new modbus service starts, it loads the state contained in autoBurt.snap. We thought it best for the watchdogs to not be automatically enabled at this stage, but for an operator to manually have to do this. By moving the watchdog channels to a separate snap file, the entire SUS state can be loaded while leaving just the watchdogs disabled.

This same modification should be made to the ETMX and ETMY machines.

  5559   Tue Sep 27 20:02:19 2011 KojiUpdateSUSWatchdog rearmed

I came to the control room and found the PMC and IMC were unlocked. ==> Relocked
I found the watch dogs of the vertex suspensions are tripped.

I checked the data for the past 6 hours and found they are independent events.
The unlock of the MCs occured 4 hours ago and the watchdogs tripped 2 hours ago.

The suspension damping was restored at around 7:50PM PDT.

  5560   Wed Sep 28 00:06:21 2011 JenneUpdateSUSWatchdog rearmed

Quote:

I came to the control room and found the PMC and IMC were unlocked. ==> Relocked
I found the watch dogs of the vertex suspensions are tripped.

I checked the data for the past 6 hours and found they are independent events.
The unlock of the MCs occured 4 hours ago and the watchdogs tripped 2 hours ago.

The suspension damping was restored at around 7:50PM PDT.

 Oops, I should have noticed all of those things.  Several hours of computer-battle exhausted me.  Thanks Koji.

  15862   Thu Mar 4 11:59:25 2021 Paco, AnchalSummaryLSCWatchdog tripped, Optics damped back

Gautam came in and noted that the optics damping watchdogs had been tripped by a >5 magnitude earthquake somewhere off the coast of Australia. So, under guided assistance, we manually damped the optics using following:

  • Using the scripts/SUS/reEnableWatchdogs.py script we re-enabled all the watchdogs.
  • Everything except SRM was restored to stable state.
  • Then we clicked on SRM in SUS-> Watchdogs, disabled the Oplevs, shutdown the watchdog.
  • We changed the threshold for watchdog temporarily to 1000 to allow damping.
  • We enabled all the coil outputs  manually. Then enabled watchdog by clicking on Normal.
  • Once the SRM was damped, we shutdown the watchdog, brought back the threshold to 215 and restarted it.

Gautum also noticed that MC autolocker got turned OFF by me (Anchal), we turned it back on and MC engaged the lock again. All good, no harm done.

  15863   Thu Mar 4 15:48:26 2021 KojiSummaryPEMWatchdog tripped, Optics damped back

EQs seen on Summary pages
https://nodus.ligo.caltech.edu:30889/detcharsummary/day/20210304/pem/seismic_blrms/

  2532   Tue Jan 19 16:21:18 2010 AlbertoUpdateABSLWatchdogs not working and then fixed

This afternoon the watchdogs stopped working: they didn't trip when the suspension positions crossed the threshold values.

I rebooted c1susaux (aka c1dscl1epics0 in the 1Y5 rack), which is the computer that runs the watchdog processes.

The reboot fixed the problem.

  7576   Thu Oct 18 15:36:57 2012 SteveUpdateCamerasWatec cameras & Tamron lenses

I purchased 3x  1/2" ccd cameras and 3x  F  50 mm lenses for the lab.

The spectral sensitivity plot is for an older model 902H. This new model has better sensitivity

Attachment 1: 10181201.PDF
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