Daytime tasks :

 - PRM & BS oplev (Steve)

 - LSC binary outputs (Joe/Jamie)

 - installation of the REFL55 RFPD (Suresh/Jamie)

 - Adjustment of demodulation phases (Kiwamu)

 - Bounce-Roll filters on BS and PRM (Suresh/Joe)

 - Suspension diagnostic using the free-swinging spectra (Leo)

 - PMC alignment (Jenne/Koji)

I think the installation of the PD DC signals are quite important. What to do
1) Connect the DC signals to the right top whitening board (be aware that there may be the modification of the whitening circuit).
2) Reconfigure the LSC model such that the DC signal is passed to the right channels (modify the left top part of the model)

Done. C1:PSL-PMC_PMCTRANSPD was improved from ~0.75 to 0.87.

Here are some details about the PRMI locking done last night.

(REFL11 installation)

 REFL11 has been installed on the AP table. The RF signal from the RFPD is sent by a heliax cable which has been called ASDD133.

Before the beam goes into the RFPD a HWP and PBS are installed such that we can adjust the amount of light entering to the photo diode.

One thing I didn't like was that I had to introduce a big amount of the light into the PD to get a reasonably big RF signal.

I was trying to look for an RF signal by looking at a spectrum analyzer, then I realized that the RF signal at 11 MHz was quite tiny when the DC_MON was less than 1.5 V.

After I increased the amount of the light up to 1.9 V in DC_MON, which sounds already too much, I then got able to see the 11 MHz signal on the analyzer.

Note that I decreased the amount of the light down to 0.5 V after I finished locking the PRMI.

We should make sure what is going on with the 11 MHz modulation.

(Locking)

First I started locking the MIchelson with AS55. The demodulation phase was already somewhat optimized to the I-signal port.

So I decided not to touch the demodulation phase matrix because it may take some times.

After I eliminated electrical offsets in the digital side, I was easily able to lock the Michelson. The control sign was plus.

Then I started playing with the PRC control too. The demodulation phase in REFL11 looked nearly 45 deg although I didn't carefully measure it.

I made a 45 deg rotational matrix to maximize the I-port signal and tried to lock the PRC. Then immediately I was able to lock PRC as well as MICH.

 GAIN_MICH = 100

 GAIN_PRC = 100

Also GAIN_PRC = -100 gave a carrier resonant lock.

The control filters are the same in MICH and PRC. I used my favorite filters as usual.

 FM1 = 1000 : 10

 FM6 = 0.1 : 1

 FM7 = 1 : 50

Somehow I frequently failed to engage the boost filters (i.e. FM6 and FM7) it looks offsets in the control path kicks either BS or PRM.

[Rana/Jamie/Kiwamu]

 Since we've got the PRMI locked we now should be able to do more qualitative measurements.

Here is a task list that we will measure/develop in the PRMI condition.

 - Optical gain measurements

 - Characterization of control loops

 - MICH and PRC calibrations

 - Noise budget

 - Development of automatic noise budget scripts

 - Arm loss measurement 

 - Shnupp asymmetry measurement

Last night I was trying to calibrate the MICH error signal and the actuators on BS and ITMs.

However I gave up taking the data because the MC locking was unstable. MC3 drifted a lot.

I modified C1LSC.mdl to use the CDSphase blocks, which automatically calculate the R and D phase rotation for us.  Now each of the RFPDs has 2 channels in place of the old IQ_MTRX channels:  C1:LSC-RFPD_PHASE_R and C1:LSC-RFPD_PHASE_D.

I have not yet compiled / rebooted / done CDS magic to actually make these installed.  So far the change is only in the simulink model.

I was going to wait until morning to compile/reboot/magic, so I can do it under Joe's supervision.

In the meantime, I also modified the RFPD screens.  They have white boxes for the _R and _D channels just now, but that's because the new model hasn't been put in.  They now look like phase rotators, instead of Koji's temporary matrix.

Still to do:  Find the EPICS database where the phase rotation calculation is done (you give it an angle, it gives you sin(angle) and cos(angle) ).  I want to put a "90-angle" in the database so that we can type in the measured relative phase between I and Q, and it will calculate how many more degrees it needs to get to 90deg. 

Comparison between Hamamatsu S3399 and Perkin Elmer FFD-100

These are the candidates for the BB PD for the green beat detection as well as aLIGO BB PD for 532nm/1064nm.

FFD-100 seems the good candidate.

Basic difference between S3399 and FFD-100

- S3399 Si PIN diode: 3mm dia., max bias = 30V, Cd=20pF

- FFD-100 Si PIN diode: 2.5mm dia., max bias = 100V, Cd=7pF

The circuit at the page 1 was used for the amplifier.

- FFD-100 showed 5dB (= x1.8) larger responsivity for 1064nm compared with S3399. (Plot not shown. Confirmed on the analyzer.)

- -3dB BW: S3399 180MHz, FFD-100 250MHz for 100V_bias. For 30V bias, they are similar.

Joe helped me compile the lsc simulink model, and now we have R&D phase rotation.

Right now, we have to do our own math, and figure out what relative phase to put in.  Soonly, I'll figure out how to do subtraction, and we can put in the measured value.

More details when I'm not running around like crazy...

--------------------------------------------------------------------------------------------

Okie dokie.  Last night I had modified the c1lsc.mdl to accommodate the R & D phase rotation.  I also made pretty new screens.  This morning however, the adventures began.....

Under Joe's supervision, I ran "make c1lsc".  The error that came up was something about things not being connected.  Joe assures me that this is a temporary problem, that Rolf is already working on.  The reason is that right now the LSC model is "flat", i.e. it doesn't have a bunch of sub-boxes and sub-screens in the simulink model.  Somehow this causes badness.  Joe stuck all the guts of the LSC model into a sub-model.  He then enabled "top_names", which makes the channels use the name of the sub-model, not the sub-model AND the main model (so since the sub-model is called LSC, our channels are just C1:LSC-OTHER_STUFF, rather than C1:LSC-LSC_OTHER_STUFF).  This fixed things so that the compiling worked (when we did "make c1lsc").  The one other thing that we changed was to delete all of the little "Outs" that were attached to EPICS readouts.  These are unneccessary and don't go anywhere, and when we made the sub-model, they made a bunch of empty outputs (unconnected outs on the main simulink model).  So, after doing that, we were able to compile, and do "make install-c1lsc", and all was good in the world.  Mostly.

Joe then noticed that I was using the CDS part "cdsPhase", which only takes one phase input.  I wanted "cdswfsPhase", which actually does the R&D phase rotation that we want.  Perhaps Alex/Rolf/whoever should change the name of that CDS part.  We switched all of the cdsPhase blocks to be cdswfsPhase, and recompiled.  All was still good in the world.  Mostly.

The last thing that was funny was that when I wanted to execute the medm screens, they would still look at the old _IQ_MTRX_1_1 and _IQ_MTRX_2_1 values, rather than the newly defined _PHASE_R and _PHASE_D channels, even though while editing the medm screen, it looked like it was pointing to the right place.  Anyhow, I opened the text file version of the C1LSC_PDX.adl, and changed the channel names to the _R and _D versions by hand.  I don't know if we edit the screens and run generate_screens.py again, if we'll have to re-edit the .adl text files.

After fixing this, all really was good in the world. 

Perhaps though, this making a subsystem business broke the filters somehow?  Foton is looking at the wrong text file now?  Something?  The filters are all still there, they just got moved down a level.  Joe said that he and Rolf are on it, and he should be able to put the LSC model back to being "flat" in the next few days.

Foton doesn't correctly display the LSC filter bank file : C1LSC.txt.

Foton tells a lie that they all are empty.

The file itself looks fine to me i.e. I can find correct filters in text format.

Looks like someone (maybe Joe and Jenne ?) updated the file. I am not sure if this is the reason or not.

allegra:chans>ls -al | grep LSC
-rw-r--r--  1 controls controls   20659 May  5 11:46 C1LSC.txt

NEEDS TO BE FIXED SOON

EDIT by KI on 15/5/2011:

The calibration of MICH error signal was wrong by a factor of 2.

The open loop transfer functions of the Michelson locking have been measured.

The purpose of this excise is to calibrate the coil-magnet actuators on BS and ITMs.

The estimated actuation coefficients are :

 BS = 3.69e-08 [m/counts]
 ITMX = 8.89e-09 [m/counts]
 ITMY = 9.22e-09 [m/counts] 

I guess the accuracy is something like 5 % because the calibration of the MI optical gain relies on a peak-to-peak measurement.

A next step is to calibrate the PRM actuator and the PRC optical gain.

(measurement)

The Michelson was locked with different actuators in every measurement. I locked the Michelson to the dark fringe with BS, ITMX and ITMY in each time.

The measured peak-to-peak value in the error signal was 20.2 counts, corresponding to a sensor gain of 5.96e+07 [counts/m]. Note that I used AS55_Q for the locking.

After locking the MI I took the open loop transfer function by injecting broadband noise from DTT.

Then the data were fitted coarsely.  In the fitting I used the resonant frequencies that Leo reported recently (http://blue.ligo-wa.caltech.edu:8000/40m/Mechanical_Resonances).

The Q-values are assumed to be 5 because of the local dampings. As a result the fitting gives us the actuator coefficients.

Here is a plot showing the measured open loop transfer functions. The solid lines represent the fittings.

(by the way)

- The delay time including ADC/DAC and RFM looks quite big. According to the fitting the delay is something like 600 usec.

This is about two times larger than the one reported before (see this entry). I will re-measure it with empty filters.

I've got confused

1) Are these the DC responses of the coils? If that is true, we need to specify the resonant frequency of each suspension to get the AC response.

2) Are these the AC responses well above the resonant freqs? In that case, The responses should be x.xxx / f^2 [m/counts]

 See my updated elog 4636 for what Joe and I did this morning, and what a possible problem is (making the LSC model into a sub-model).

They are the DC responses.

I put the resonant frequencies that Leo reported in the wiki to obtain the DC response.

The resonant frequencies I used are :

  f_BS = 0.957 Hz

  f_ITMX = 0.966 Hz

  f_ITMY = 0.988 Hz

Also I assumed that all the Q-values are 5 due to the damping.

 This was because of a bug in the RCG for foton filter module naming when top names is being used.  Rebuilding the LSC front-end model with top_names (which was needed to get around another bug in the RCG) broke the filter file.  I manually fixed the file, so it should work now.

[Suresh / Kiwamu]

 We installed the TRY photo diode (Thorlabs one) and the ETMYT CCD camera in place on the ETMY table.

Now we can see a signal on the TRY digital channel.

It will be quite useful for the Y arm locking, for instance we can do a triggered locking and the maximization of the intracavity power.

Someone has to install the EMTY trans QPD at some point.

I found that C1:LSC-TRIG_MTRX has a wrong matrix size. It needs to be fixed.

It is designed to have a 11x8 matrix in the simlink model file, but it's been compiled as a 6x8 matrix.

I recompiled c1lsc but it didn't fix the issue. Here below is the matrix statement in the C file :c1lsc.c. Indeed it is 6x8 matrix ....

// MuxMatrix:  LSC_TRIG_MTRX
for(ii=0;ii<8;ii++)
{
  lsc_trig_mtrx[ii] =
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][0] * lsc_imux_trigger[0] +
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][1] * lsc_imux_trigger[1] +
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][2] * lsc_imux_trigger[2] +
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][3] * lsc_imux_trigger[3] +
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][4] * lsc_imux_trigger[4] +
          pLocalEpics->lsc.LSC_TRIG_MTRX[ii][5] * lsc_imux_trigger[5];
 }

[Joe, Kiwamu]

There is a feature/bug of the RCG code that you can only have 1 receiving tag for every sending tag.  There were 5 tags which were being received by two tags each, for two different matrices.  Only the first tag was receiving, the second was apparently ignored.

This has been fixed temporarily by putting in direct lines in place of these 5 tags.

I made a new medm screen for the triggering logics. Have fun.

I put a button on C1LSC.adl to invoke this screen.

Aux- rack _1Y2 is just behind 1Y3  It contains Kepco Analoge DC power supplies for +- 5, 15 and 24V

Placing these power supplies away from the LSC rack was an effort to minimize pick up from them.

Rana forced me to write this entry for summary because he didn't come to the 40m meeting today.

Status update :

    Interferometer Input Beam alignment with the PZTs.

     60 % done. The rest of the 40 % is to make the procedures automated.

     The beam spots on ITMY and ETMY are centered within ~1 mm accuracy.

     PRM, BS, ITMX, & ITMY actuator calibrations and PRC/MICH error calibrations

    Ongoing: First we will do it by hand, then some scripts will be made for the calibraion and resultant noise budget.

     F2A Suspension filter calculations.

      ETMY and ITMY are done. Need volunteer for ETMX, ITMX, BS, PRM, & SRM !!

      Bounce-Roll notch filters

      Leo is working on it. 25% complete...

     DC signal from RFPDs

      The RFPDs have a local SMA DC output as well as a DC output from their PD Interface cards in the LSC rack. We have hooked up some of the PD Interface DC outputs to the LSC ADCs but not tested??

Next steps:

  Installation of a temporary (Thorlabs) DCPD on either POY to see the intra-cavity power in the PRC. It would be ridiculous to put detectors on POX or POP since they're still clipped.

  D-phase and amplitude imbalance adjustment of the demod baords.

          make a script which uses pynds.

  Alignment of the full interferomter, starting from the X arm

  Loss measurements for the arms

  Schnupp asymmetry measurement

[Valera / Kiwamu]

 We are able to lock each arm smoothly.  It is ready for the Schnupp asymmetry measurement.

( to be done )

 - Manual D-phase adjustment of the AS55 channel.

 - A script to adjust the D-phase.

 - Trigger logic for the boost filters.

 - Modification of some old alignment scripts to adopt them to the new LSC channels

Incidentally, a blown fuse on 5V line at 1Y2 rack was found during the intallation of Sorensens.
The fuse (5A 125V) has been replaced and fixed.

When I plugged the fuse in, I heard some sound like relays were switched. Are there any relays in the LSC rack?

It was a 9th fuse from the top as seen in the picture.

The AC response of the actuators on BS, ITMX and ITMY were re-measured by another technique.

Last time I estimated them by measuring the open-loop transfer functions, but this time the responses were measured in a more direct way.

The measured AC responses (60 Hz - 200 Hz) are :

      BS   = 1.643e-98 / f2  [m/counts] (corrected based on the plot below - Manasa)


     ITMX = 3.568e-9 / f2 [m/counts]

     ITMY = 3.542e-9 / f2 [m/counts]

Next : measurement of the PRM actuator response

(The technique) 

 This time a technique that Rana told me a week ago was used.

This technique allows us to directly measure the response of an actuator at high frequency without any loop corrections.

First of all, MICH has to be locked to keep MICH within the linear range of the error signal. So now MICH is a linear sensor to the mirror motions.

In the MICH control a steep low pass filter should be inserted in order to avoid unwanted effects from the control loop at the high frequencies.

For example I put a low pass filter composed of an elliptical filter whose cut-off frequency is at 50 Hz such that the control loop doesn't push the mirrors above the cut-off frequency.

Hence the error signal of MICH above 50 Hz directly corresponds to the motion of the mirrors including BS, ITMX and ITMY.

Taking a transfer function from an actuator to the MICH error signal directly gives the actuator response.

In my measurements MICH was locked by feeding the signal back to BS. The plot below is the expected open-loop transfer function for the MICH control.

You can see that the open loop TF suddenly drops above 50 Hz. The UGF was at about 20 Hz, confirmed by looking at the loop oscillation on DTT.

(Measurement)

 In the technique the error signal has to be calibrated to [m]. This time AS55_Q was used and calibrated based on a peak-to-peak measurement.

The peak to peak value in the MICH error signal was 8 counts, which corresponds to the sensor efficiency of 4.72e+07 [counts/m].

Then I took transfer functions from each suspension (i.e. C1:SUS-XXX_LSC_EXC) to the error signal at AS55_Q over a frequency range from 60 Hz to 200Hz.

For the transfer function measurements I ran the swept sine on DTT to get the data. Note that the PD whitening filters were on.

The plot below is the results of the measurements together with the fitting lines.

In the fitting I excluded the data pints at 60 Hz, because their coherence was low due to the power line noise.

I re-centered beams on several PDs and a camera including :

  AS55, ETMY_QPD, TRY and ETMYT_CCD.

The most important one was AS55.

When I was locking each arm I found that the error signal from AS55 was very coupled to the angular motion of the arms.

I checked the beam on the AS55 RFPD and found the beam on the edge of the photo diode. This is possibly because Valera and I had been touching the input beam alignment.

At that time the DC signal from AS55 without aligning PRM and SRM was about 5 mV.

Adjusting the beam position by a steering mirror brought the DC signal up to 20 mV.

Then the lock of each arm became more stable.

I added a lockin to the LSC model, and added it's corresponding control to the LSC screen.  Here's is what I added to the LSC model:

On the left are the froms from the normalized RF PD outputs. Those go into a matrix, whose single row goes into the lockin signal input. The clock output from the lockin goes into the LSC output matrix (last row).

Here is what I added to the LSC master screen:

I also modified the lockin overview screen:

I think this new screen looks a lot cleaner.  Maybe we could start using this one as a template for lockin screens.

 This is OK....but, the input matrix should come from the same place as the regular input matrix: i.e. it should be just another row like CARM, DARM, etc. rather than have its own screen.

Also, I think a nice mod to all the matrices would be if the ORANGE triangle was only visible when there's a signal flowing through it.

According to Suresh's LSC rack design I rearranged the input channels of the c1lsc model such that the analog signals and the ADC channels are nicely matched.

Also I updated the c1lsc model in the svn with a help from Joe. The picture below is a screen shot of the input channels in the model file after I edited it.

(PRMI locking)

Since REFL11 has gone I tried locking the PRMI with combination of REFL55 and AS55.

Without any pain the lock of PRMI was achieved successfully. AS55 was used to sense MICH and REFL55 was used for PRC.

(scripting)

Additionally I was modifying several scripts which are invoked from C1IFO_CONFIGURE.adl. Some details about the scripts will be uploaded on the wiki later.

An important thing is that now we are able to use the "restore" commands for the Y arm, X arm, Michelson and PRM locking.

The scripts will automatically acquire the lock of each DOF.  The image below is just a screen shot of the medm screen where you can call the scripts.

( Still to do)

   * PRM actuator response measurement

   * PRC noise budget

   * MICH-PRC actuator decoupling

I will try with POY55 that Koji prepared today.

Eventually the DRMI was locked.

I was struggling to find a good signal port for SRC over the weekend and finally found AS55_I worked somehow. I used :

   REFL11_I --> PRC

   AS55_Q   --> MICH

   AS55_I    --> SRC

A configuration script was prepared such that someone can try this configuration by clicking a button on the C1IFO_CONFIGURE.adl screen.

I don't think this signal extraction scheme is the best, but now we can find better signal ports by shaking each DOF and looking at each signal port.

More details will be reported in the morning.

(PRMI locking with slightly misaligned SRM)

 First I tried locking PRC and MICH with a little bit misaligned SRM. This condition allowed me to search for a good signal port for SRC.

In this locking, REFL11_I was used to lock PRC and AS55_Q was used for MICH. This is the same scheme as the current PRMI locking.

Since the alignment of SRM was close to the good alignment, I expected to see fringes from SRC in some signal ports (i.e. REFL55, POY55 and so on).

Sometimes a fringe of SRC disturbed AS55_Q and broke the MICH locking, so I had to carefully misalign SRM so that the SRC fringes are small enough to maintain the lock of MICH.

(Looking for a good signal port for SRC)

 After I locked the PRMI with slightly misaligned SRM, I started looking for a good signal port for SRC.

At the beginning I tried finding a good SRC port by shaking SRM at 100 Hz and looked at the power spectra of all the available LSC signals.

I was expecting to see a 100 Hz peak in the spectra, but this technique didn't work well because SRC wasn't within the linear range and hence didn't produce linear signals.

So I didn't see any strong signals at 100 Hz and finally gave up this technique.

Then I started looking for a PDH-like signal in time series and immediately found AS55_I showed large PDH-like signals.

So I started using the AS55_I for the SRC locking and eventually succeeded.
 

(Two tips for the DRMI locking)

During the locking of DRMI, I found two tips that made the locking quite smooth.

 - Triggered locking

   Since every LSC signal ports showed large signals from PRC somehow, feeding back the signals made the suspensions crazy.

   So I used triggered locking for the PRC and MICH locking to avoid unwanted kicks on BS and PRM.

   If  the DC of REFL goes above a certain level, the control of  PRC starts. Also if the DC of AS goes below a certain level the control of MICH starts.

  These triggers make the lock smoother.

 - Do not use resonant gain filters

  This is really a stupid tip. When I was trying to lock MICH, the lock became quite difficult for some reasons.

  It looked there was an oscillation at 3 Hz every time the MICH control started. It turned out that a 3 Hz resonant gain filter had been making it difficult.

  All the resonant gain filters should be off when a lock acquisition is taken place.

Last Saturday the POY55 RFPD (see this entry) was installed on the ITMY optical bench for the trial of the DRMI locking.

Since the amount of the light coming into the diode is tiny, the DC monitor showed ~ 3 mV even when the PRC was locked to the carrier.

In order to amplify the tiny RF signal from the photo diode a ZHL amplifier was installed next to the RFPD. The RF amp is sitting on delrin posts for insulation from the table.

During the DRMI trial I noticed that the f2p filters on PRM is not quite effective (i.e. pushing PRM in POS direction makes misalignments).

I checked the f2p filters in an easy way. I pushed POS at 0.01 Hz with an amplitude of 1000 counts and looked at the oplev error signals with / without the f2p filters.

The picture below is a time series of the POS excitation, the oplev's PITCH and YAW error signals.

You can see there still is a big coupling from POS to YAW after the f2p filters were enabled. (Its supposed to be like this)

I will redo the f2p measurement on PRM.

The DC Transimpedance of POP55 was increased from 50 Ohm to 10010 Ohm. There is the offset of 46mV. This should be cancelled in the CDS.

 You're absolutely right.  That was a brain-fart oversight.  I fixed the model so that the input from the lockin comes from another output row in the RFPD input matrix.  I then fixed the C1LSC medm screen accordingly:

This is obviously much simpler and more straight-forward.

A future improvement would be to modify the DCPD input matrix to be able to route those signals to the lockin as well.  This is actually currently possible since the DCPD input matrix is just a subset of the full input matrix, but it's not available via medm yet.

 I went ahead and added the lockin output to the DCPD input matrix.

LSC rack 1Y2 cables are strain relieved and labeled. Spare and/or obsolete cables are laid out on the top of the beam tube and on the outside of the rack.

The POY 110 MHZ demodboard has a very touchy position in the VME crate. Watch out for it! It has to be fixed.

I changed optics in the ETMX transmon path to remove clipping (which made a false QPD signal).

During the weekend I found that there was an offset in X arm c1ass pitch servo, which derives the signal by demodulating the arm cavity power, coming from the beam clipping in the transmon path.

The clipping was on the pair of the 1" mirrors that steer the beam after the 2" lens (see attached picture). The beam is about 5-6 mm in diameter at this distance from the lens and was not well centered.

I moved the steering mirrors downstream by about 8" where the beam is about 2-3 mm (the attached picture shows the mirrors in the new location). The Y arm layout is different from X arm and I didn't find any obvious clipping in transmon path.

The max X arm buildup went up from 1.3 to 1.5. I changed the TRX gain from -0.003 to -0.002 to obtain the normalized X arm power of 1 in this state. The MC refl DC is 1.6 out of 4.9 V and the Y arm buildup is ~0.9 so the TRX(Y) gains will have to be adjusted once the MC visibility is maximized.

Approximately two weeks ago I diagonalized the LSC output matrix for the DRMI locking.

Since actuation on the position of BS changes not only MICH but also PRC and SRC, we needed to diagonalize the output matrix.

- What I did :

 (1) The DRMI was locked. At this point PRC, MICH and SRC was controlled by PRM, BS and SRC actuators respectively.

 (2) I injected excitation signal on C1:LSC-MICH_EXC by awg. The excitation was at about 200 Hz, which is above the UGF of all the LSC loops.

    At this point the excitation only shakes the position of BS.

 (3) I looked at spectra of REFL11_I, AS55_Q, AS55_I, that were used to sense PRC, MICH and SRC respectively.

   At the beginning I was able to see the peak due to the excitation in those spectra. This means BS shakes the other DOFs (i.e. PRC and SRC) as well as MICH.

 (4) To minimize the coupling from MICH to PRC (or SRC), I tuned a number on an element of the output matrix, which transfers the signal from MICH to PRM (or SRM).

   This business was done by looking at the peak on REFL11_I (or AS55_I) and minimizing it. Since this technique was too naive the tuning was done only in second decimal place.

[Koji Jamie]

The new c1lsc code has been installed. The LSC screens have also been updated (except for ASS screen).

The major changes are:

1. Naming of the RFPD channels. Now the PD signals were named like:

REFL11_I_IN1, REFL11_I_IN2, REFL11_I_OUT ....

instead of REFL11I_blah

2. NREFL11, etc has been removed. We now have the official error signals
named like

REFL11_I_ERR

We can't use the name "REFL11_I" for the error signal as this name is
occupied by the name of the filter module.

After a couple of hickups, I was able to compile and install Koji's rework of the LSC model.

The main changes are that the model now use an RF_PD library part, and the channel names were tweaked to be more in line with what we expect.

I found a couple of small bugs in the model that were preventing it from compiling.  Those were fixed and it compiled with no further problems.

There was also some rearrangement of signal inputs to the PD_DOF matrix.  The matrix screen was updated to reflect the proper inputs.  However, this also meant that the burt restore scripts for the IFO configurations were setting the wrong elements in the matrix.  I fixed the settings for X and Y arm locking, and updated the burt snapshots using the burt/c1ifoconfigure/C1save{X,Y}arm scripts.  NOTE: burt settings will need to be updated for the MICH, PRM, DRM, and FULL IFO configurations as well.

During the build/install process, Joe and I also found a bug in the feCodeGen that was causing the filter screens to be created with the wrong names.  Joe sent out a patch that will hopefully be merged soon.  Building the model with Joe's patch fixed the screen names, so the screens are currently named correctly.

We are now locking the arms reliably, with reasonable transmitted power.  We zeroed the LSC offsets with script, since they were apparently not being reset with either the overall burt restore or the arm restore scripts.

We have lost a bit of power through the mode cleaner.  However, we have opted not to tweak it up just yet, so that we don't have to realign to the arms.

Measurement of Schnupp asymmetry

This was done by measuring the relative phase between the sidebands reflected from the two arms while the arm cavities are locked.

The Schnupp asymmetry is measured to be:   L_sa = 3.64 ± 0.32 cm

Description:

As a phase reference we use the zero crossing of the response function for the out-of-phase control signal for the single arm cavity lock [0]. The difference in the RD rotation phase of the response zero crossings indicates the phase difference in the sideband signals reflected from the arms. Assuming the asymmetry is less than half the RF modulation wavelength [1], the asymmetry is given by the following formula:

       \Delta \phi   c   1 
L_sa = ----------- ----- -
           360     f_RSB 2

We use a LSC digital lock-in to measure the response of the arm cavity at a single-frequency drive of it's end mirror.

[0] The locations of the zero crossings in the out-of-phase components of the response can be determined to higher precision than the maxima of the in-phase components.

[1] f_RSB = 55 MHz,     c/f_RSB/2 = 2.725 m

Procedure:

1. Lock/tune the Y arm only.
   
   • We use AS55_I to lock the arms.
2. Engage the LSC lock-in.
3. Tune the lock-in parameters:

lock-in freq: 103.1313 Hz
I/Q filters:  0.1 Hz low-pass
phase:        0 degrees

4. Set as input to the lock-in the out-of-phase quadrature from the control RFPD.  In this case AS55_Q->LOCKIN.
5. Drive the arm cavity end mirror by setting the LOCKIN->Y_arm element in the control matrix.
6. Note the "RD Rotation" phase between the demodulated signals from the control PD (AS55)
7. For some reasonable distribution of phases around the nominal "RD Rotation" value, measure the amplitude of the lock-in I output.
   • Assuming the Q output is nearly zero, it can be neglected.  In this case the Q amplitude was more than a factor of 10 less than the I amplitude.
   • Here we take 5 measurements, each separated by one over the measurement bandwidth (as determined by the lock-in low pass filter), in this case 10 seconds.  The figure above plots the mean of these measurements, and the error bars indicate the standard deviation.

The data and python data-taking and plotting scripts are attached.

Error Analysis:

To to determine the parameters of the response (which we know to be linear) we use a weighted linear least-squares fit to the data:

y = b X

where:

X_0j = 1
X_1j = x_j              # the measurement points
y = y_i                 # the response
b = (b₀, b₁)     # line parameters

The weighting is given by the inverse of the measurement covariance matrix. Since we assume the measurements are independent, the matrix is diagonal and W_ii = 1/\sigma_i² The
estimated parameter values are given by:

\beta  =  ( X^T W X )^-1 X^T W y  =  ( X'^T X' )^-1 X'^T y'

where X' = w X, y' = w y and w_ii = \sqrt{W_ii}.

The X' and y' are calculated from the data and passed into the lstsq routine. The output is \beta.

The error on the parameters is described by the covariance matrix M^\beta:

M^\beta = ( X^T W X)^-1 = ( X'^T X')^-1

with correlation coefficients \rho_ij = M^\beta_ij / \sigma_i / \sigma_j.

The x-axis crossing is then given by:

X(Y=0) = - \beta₁ / \beta₀

References:

Valera's LLO measurement
http://en.wikipedia.org/wiki/Weighted_least_squares
http://en.wikipedia.org/wiki/Linear_least_squares_(mathematics)#Weighted_linear_least_squares
http://en.wikipedia.org/wiki/Error_propagation

Some updates of the LSC screen

- Signal amplitude monitor for the PD signals (--> glows red for more than 1000)

- Kissel Buttons for the main matrices

- Trigger display at the output of the DOF filters

- Signal amplitude monitor for the SUS LSC output (--> glows red for more than 10000)

ADC Over flow monitor is showing some unknown numbers (as ADCs are handled by IOPs).
I asked Joe for the investigation (and consideration for the policies)

[Suresh, Koji]

   I used a matlab code written by Koji to analyse the transimpedance and current noise data  of REFL55.  The details are in the attached pdf file.

Resonance is at 55.28 MHz:

Q of 4.5, Transimpedance of 615 Ohms

shot noise intercept current = 1.59 mA

current noise =21 pA/rtHz

Notch at 110.78 MHz:

Q of 54.8 Transimpedance of 14.68 Ohms.

Last night I was making a script which will measure the sensing matrix using the realtime LOCKIN module.

The script is a kind of expansion of Jamie's one, which measure the asymmetry, to more generic purpose.

It will shake a suspended optic of interest and measure the response of each sensor by observing the demodulated I and Q signals from the LOCKIN module.

I will continue working on this.

  (current status)

 - made a function that drives the LOCKIN oscillator and get the data from the I and Q outputs.

 - checked the function with the MICH configuration.

   ITMX, ITMY and BS were shaken at 100 Hz and at different time.

   Then the response of AS55_Q showed agreement with what I got before for the actuator calibration (see this entry).

   It means the function is working fine.

I am now measuring the sensing matrix in the DRMI configuration.

A goal of tonight is to measure the sensing matrix as a test of the script.

The result will be updated later.

The sensing matrix was measured in the DRMI configuration for the first time.

The measurement was done by an automatic script and the realtime LOCKIN module built in the c1lsc model.

The resultant matrix is still too primitive, so I will do some further analysis.

(Measurement of sensing matrix)

 The quantities we want to measure are the transfer functions (TFs) from displacement (or change in optical phase) of each DOF to sensors in unit of [counts/m].

So essentially the measurement I did is the same as the usual TF measurement. The difference is that this measurement only takes TFs at a certain frequency, in this case 283 Hz.

 The measurement goes in the following order :

  (1) Lock DRMI

  (2) Shake an optic of interest longitudinally with an amplitude of 1000 counts at 283.103 Hz, where no prominent noise structures are present in any spectra of the sensor signals.

  (3) Put a notch filter at the same frequency of 283.103 Hz in each DOF (MICH, PRC and SRC) to avoid unwanted suppression due to the control loops.

       (This technique is essentially the same as this one, but this time the control loops are shut off only at a specific frequency )

       The notch filter I put has a depth of 60 dB and Q of 20. The filter eats the phase of ~10 deg at 200 Hz, which still allow servos to run with a high UGF up to 200Hz.

  (4) Take the output signal from a signal port of interest (i.e. REFL11_I, etc.,) and then put it into the realtime LOCKIN module.

  (5) Measure the resultant I and Q signals coming out from the LOCKIN module.

  (6) Repeat the procedure from (2) through (5) for each optic and sensor.

(Results)

 Again, the resultant sensing matrix is still primitive, for example the optic-basis should be converted into the DOF basis.

The values listed in the matrix below is the absolute values obtained by operation of sqrt( I^2 + Q^2) plus the polarity according to the output from I and Q of LOCKIN.

Therefore they still contain the actuator response, which is not desired. i will calibrate them into [counts/m] later by using the calibration factor of the actuator responses.

All the raw data showed the relative phase between I and Q either ~ 127 deg or ~ -53 deg.

In my definition, the one has 127 deg is plus polarity and the one has -53 deg is minus polarity.

Technically speaking the polarity depends on the polarity of the actuator and also the direction of the actuator against the DOFs.

Without any excitation the absolute values fluctuated at about 10^-4 - 10^-5, so the excitation amplitude was big enough to observe the sensing matrix.

Though, I still need to estimate the statistical errors to make sure the SNR is reasonably big.

  Fig.1 Measured sensing matrix from optic to sensors.

(Things to be done)

  - convert the optic-basis (i.e. BS, ITMs, PRM and SRM) to the DOF-basis (i.e. MICH, PRC and SRC) so that the matrix is understandable from point of view of the interferometer control.

  - estimate the optimum demodulation phase for each DOF at each sensor port.

  - add some statistical flavors (e.g. error estimations and so on.)

  - edit the script such that it will keep watching the ADC overflows and the coherence to make sure the measurement goes well.

  - add some more signal ports (e.g. REFL55, POY55 and etc.)

  - compare with an Optickle model

I was trying to measure the sensing matrix in the PRMI configuration, but basically gave up.

It is mainly because the lock of PRMI wasn't so stable and it didn't stay locked for more than a minute.

It looked like an angular motion fluctuated a lot around 1- 3 Hz. The beam spot on the AS camera moved a lot during the lock.

I have to figure out who is the bad suspension and why.