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ID Date Author Type Categoryup Subject
  8642   Fri May 24 14:40:22 2013 JenneUpdateLSCPRMI sensing matrix: now what?


It's hard to believe but is AS55Q really almost insensitive to MICH?

Well, anyway, now it is the time to use the automatic demod phase (and input matrix) adjustment.

 I am also wondering if I understand / am using the demod phase from the screen correctly.  This plot is indicating that MICH is entirely in I, and not at all in Q.

Currently, I take the demod phase, and plot that as the "I" line, then plot the "Q" line 90 degrees away from the I line.  Maybe it should be the other way around?

Re: the auto-demod phase, I was starting to wonder about that.  For each sensor, can I declare what degree of freedom I want in which quadrature to take priority (ex. MICH goes to REFL55 Q), and set the demod phase to the value that makes that true?

  8644   Fri May 24 22:18:33 2013 JenneUpdateLSCPRMI sensing matrix: Got it!

Okay, I think I am finished with the sensing matrix scripts!  

I had the syntax for atan2() wrong, so I was calculating the demod phase wrong.  Do not trust the phase in any previous elogs!!

Also, the theta=0 axis of the plots are for 0 degree demod phase, but our PDs are not at 0 deg.  The measured sensing matrix phase is relative to the current demod phase, not 0 (unless the demod phase for that PD is currently 0degrees).  So, now I take that into account.  I add the current PD demod phase to the measured sensing matrix phase, so that the plot is actually true.

For interested parties, I have made all of the sensing matrix scripts, and the data folder a subdirectory of the /scripts/LSC folder, since it was starting to get crowded in there.  I have moved the 2 data sets that have been collected (21May, 23May) into the new place.

Future thoughts: 

* Save the amplitude and modulation frequency and the current demod phases in the data file.  Right now the ampl and mod freqs are included in the title of the data file, but there is no record of what the demod phase was at the time.  I need to fix this.


So, really, really, the Sensing Matrix:

Sensing Matrix, units = counts/meter, phase in degrees
            PRCL Mag   PRCL Phase    MICH Mag   MICH Phase  
AS55         5.485E+08   -43.424      2.679E+09    93.392    
REFL11       1.126E+13    -7.168      1.618E+11   135.296    
REFL33       2.658E+11   164.973      8.910E+09    -2.226    
REFL55       3.012E+11   -75.216      1.210E+10   172.764


  8648   Tue May 28 14:52:56 2013 JenneUpdateLSCPRMI sensing matrix: Got it!

Just so we have it, here is the re-analysis with the correct plot and phases for the May 21st data, taken near the violin mode:

Sensing Matrix, units = counts/meter, phase in degrees
            PRCL Mag   PRCL Phase    MICH Mag   MICH Phase  
AS55         9.048E+11   -22.880      2.927E+12   107.071    
REFL11       2.954E+16   -21.628      3.670E+14   123.857    
REFL33       2.757E+14  -192.608      9.186E+12    -4.037    
REFL55       2.868E+14   -82.690      1.186E+13   170.097 


Even though this data was taken near the violin mode (oops!), it is fairly consistent with the stuff taken a few days later at 580Hz (elog 8644). 

Neither of these is at all similar to what Kiwamu had measured a year ago (elog 6283), but we have changed many, many things since then.  He also includes an Optickle simulation, which is fairly similar to the Koji simulation in the wiki, but neither his measurements nor mine are particularly close to the simulated version.  I should think about why this is.

Also, I have fixed up the measurement scripts so that they record all of the relevant current settings / information:  Current actuator calibration, current PD demod phases, drive amplitude and drive frequency.  The "Analyze Saved Data" script has been updated to read all of this info from the files.  If you want to plot / look at any old data, open up SensMatAnalyzeSavedData in /scripts/LSC/SensingMatrix/ and put in the relevant filename that you want (which should be saved in /scripts/LSC/SensingMatrix/SensMatData/)

  8650   Tue May 28 17:06:04 2013 KojiUpdateLSCPRMI sensing matrix: Got it!

- We want to add POX11/POY11 in the collection. They may indicates some abnormal asymmetry between two arms (for PRMI).

- We also want to PRCL/MICH after the input matrix. This will be useful when we want to adjust the input matrix to give the optimul
demod phase for the two signals from a single port.

  8667   Mon Jun 3 22:36:07 2013 ranaUpdateLSCALS-TRY_OUT needs anti-whitening

 After working some more on the EY table, we are getting some TEM00 flashes for the Y arm green. We have had to raise the height of one of the MM lenses to prevent clipping.

We used a function generator to apply a ~300 mV 10 Hz triangle wave to scan the laser frequency while aligning.

We tried to use the C1:ALS-TRY_OUT channel to help us in our alignment but there are a couple problems:

1) It seems that there is an uncompensated whitening filter before the ADC - Annalisa is making a compensation filter now.

2) The data delay is too much to use this for fast alignment. We might need to get a coax cable down there or mount a wired ethernet computer on the wall.

3) We need to make DQ channels for the TRY and TRX OUT. We need long term data of these, not just test points.

Attachment 1: try.pdf
  8671   Tue Jun 4 16:04:34 2013 AnnalisaUpdateLSCALS-TRY_OUT needs anti-whitening


 After working some more on the EY table, we are getting some TEM00 flashes for the Y arm green. We have had to raise the height of one of the MM lenses to prevent clipping.

We used a function generator to apply a ~300 mV 10 Hz triangle wave to scan the laser frequency while aligning.

We tried to use the C1:ALS-TRY_OUT channel to help us in our alignment but there are a couple problems:

1) It seems that there is an uncompensated whitening filter before the ADC - Annalisa is making a compensation filter now.

2) The data delay is too much to use this for fast alignment. We might need to get a coax cable down there or mount a wired ethernet computer on the wall.

3) We need to make DQ channels for the TRY and TRX OUT. We need long term data of these, not just test points.

 I made the anti-whitening filter for the C1:ALS-TRY_OUT channel. But then I forgot to make an ELOG because I am bad.

  8672   Tue Jun 4 17:28:09 2013 AnnalisaUpdateLSCC1:ALS-TRY_OUT filter and green progress

 [Annalisa, Gautam, Rana]

I made the anti-whitening filter for the C1:ALS-TRY_OUT channel.

zpk [[150],[15],1] Hz

Now we can look at the picks of this signal to align the green into the cavity.

We already had some 00 flash, but a better alignment has to be done.


- put the shutter along the beam path

- check the polarization (we have a new PBS for visible)


Attachment 1: green.JPG
Attachment 2: QUAD1_1054358327.mp4
  8674   Tue Jun 4 21:50:23 2013 AnnalisaUpdateLSCC1:ALS-TRY_OUT filter and green progress


 [Annalisa, Gautam]

 The green beam alignment has been improved, so we see much more 00 bright flashing. We checked the polarization and the Ygreen shutter is back in place.

A mirror is already in place to steer the rejected beam from the green Faraday into a PD, tomorrow morning we'll put a lens and the PD to take the signal for PDH locking.


  8677   Wed Jun 5 14:01:37 2013 ranaUpdateLSCC1:ALS-TRY_OUT filter and green progress

The rejected beam from this Faraday comes out at a tiny, tiny angle and so its tough to pick it off without clipping the main beam.

Some care must be taken in setting this up - Steve may have some good ideas on what kind of mount can be placed so close to the beam.

Why did we ever order this terrible Faraday? Let's never get a Faraday with a tiny angle between the beams again.

  8679   Wed Jun 5 14:43:42 2013 AnnalisaUpdateLSCALS-TRY_OUT DQ channels


 After working some more on the EY table, we are getting some TEM00 flashes for the Y arm green. We have had to raise the height of one of the MM lenses to prevent clipping.

We used a function generator to apply a ~300 mV 10 Hz triangle wave to scan the laser frequency while aligning.

We tried to use the C1:ALS-TRY_OUT channel to help us in our alignment but there are a couple problems:

1) It seems that there is an uncompensated whitening filter before the ADC - Annalisa is making a compensation filter now.

2) The data delay is too much to use this for fast alignment. We might need to get a coax cable down there or mount a wired ethernet computer on the wall.

3) We need to make DQ channels for the TRY and TRX OUT. We need long term data of these, not just test points.

 [Jenne, Annalisa]

DQ channels have been created in the C1ALS model for TRX and TRY. They are called TRX_OUT and TRY_OUT and the sampling rate is 2048 Hz.

  8680   Wed Jun 5 15:03:42 2013 AnnalisaUpdateLSCC1:ALS-TRY_OUT filter and green progress


The rejected beam from this Faraday comes out at a tiny, tiny angle and so its tough to pick it off without clipping the main beam.

Some care must be taken in setting this up - Steve may have some good ideas on what kind of mount can be placed so close to the beam.

Why did we ever order this terrible Faraday? Let's never get a Faraday with a tiny angle between the beams again.

The rejected beam from the Faraday is steered with a mirror into the PDA32A PD  and a 75mm fl lens is used to focus the beam into it.

The main beam is a few millimeters away from the mirror mount (maybe 2mm), and I think it should be fine as long as the main beam is not supposed to move.


Attachment 1: faraday_rejected_beam.JPG
  8700   Thu Jun 13 15:04:16 2013 JenneUpdateLSCNew modeled sensing matrix

Using all of the latest parameters that I can find, I have re-modeled the 40m sensing matrix.  Also, I have it output the data in a format that can be used by the same plotting function as the measured sensing matrix, so they are nice and easy to compare.

The newly modeled 40m sensing matrix:


To compare, here is the measured sensing matrix from elog 8644:


Notice that (a) the units are different, so don't focus too much on the amplitudes of the lines, and (b) all of the measured and modeled matrix elements are pretty similar, except for the REFL11.  REFL11 (top right in model plot, top center in measured plot) looks like it's flipped, as well as rotated.  The new model doesn't match up too well with the Kiwamu/Koji models (which matched eachother okay), but I like that the new model matches the measurements fairly well.  The Koji sensing matrix: on the 40m wiki

EDIT: I have replaced the modelled plot with a new version.  The data and numbers are the same, but I have switched the labels on the individual radar plots, and forced them to be in the same order as they are in the measured plot.

  8702   Thu Jun 13 16:13:08 2013 nicolasUpdateLSCNew modeled sensing matrix

I'd repeat the measurement for REFL11. The PRC arrow has some big error bar on it, and maybe the true error is even bigger.

Also, please make the placement of the plots the same for modeled and measured so it's easy to compare.

  8705   Fri Jun 14 00:32:43 2013 JenneUpdateLSCNew modeled sensing matrix

I put in a new version of the modelled plot.  I figured out a different way to keep things generic so the same script can be used for other sites, but writes the names in the same format as the measured matrix, so the correct order is preserved.

The REFL11 measurement is consistent with the one in elog 8648 (data taken a few days earlier), within the error bars.  My goal for tonight is to hopefully get the POP path back in order, so that I can lock the PRMI again, and can measure again if I want.

The error bars for each sensor are only taken once (with no drive, so it's the noise in the "dark" sensor).  I take 6 "dark" measurements for each sensor, and get the stdev.  Then I use that and propagate it through for each measured sensing matrix element.  So, the PRCL and MICH error bars for REFL11 were created from the same standard deviation, and propagated in the same way, but the values plugged into the partial derivative of the function were different for PRCL and MICH. 

s_f = \sqrt{ \left(\frac{\partial f}{\partial {x} }\right)^2 s_x^2 + \left(\frac{\partial f}{\partial {y} }\right)^2 s_y^2 + \left(\frac{\partial f}{\partial {z} }\right)^2 s_z^2 + ...}(wikipedia - propagation of uncertainties)


Also, to answer an emailed question via the elog, the "0 degree" axis of the plots is the 0 demod phase axis, which corresponds to the I output of the demod boards (the I input to the RFPDs, before the phase rotation).  The "I" axis that I've drawn is the current demodulation phase that we have, which corresponds to the I_ERR output of the RFPDs after the phase rotation, which is the PD_I signal that goes into the LSC input matrix.  I draw this to help us see if our current demod phase is well tuned or not.

Yes, the MICH and PRCL signals are not at all orthogonal in the REFL33 sensor.  I think this is because our modulation frequency was chosen to be good in the case of the full DRFPMI IFO, not the corner IFO cavities.  As I calculated in elog 8538, the ideal frequency for the PRMI is 18kHz larger than our current modulation frequency. 

For the plots below, note that 11.066134 MHz is our current actual modulation frequency, and 11.0843 MHz is my calculated ideal modulation freq

Model, using our current modulation frequency, and the designed PRCL cavity length (same as elog earlier today):


Model, using the "ideal" PRMI modulation freq, and the PRCL cavity length used in elog 8538, where I calculated that number (a few cm different than the design PRCL length):


You can see that if we could use a better frequency, we would get much, much better signal separation.  Since our modulation frequency choice is related to our vacuum envelope constraints (we can't make the arms of a length that will have the sidebands exactly antiresonant when the arms are locked on the carrier), I hope that this will not be a significant issue in aLIGO. 

  8706   Fri Jun 14 02:38:07 2013 ranaUpdateLSCNew modeled sensing matrix

 This is nice - how about figuring out how to plot the measurement and model on the same plot? I guess we need to figure out how to go from counts to Watts.

  8711   Mon Jun 17 16:34:15 2013 JenneUpdateLSCSensing Matrix vs. Schnupp Asymmetry

I have made some plots of the sensing matrix (PRCL / MICH amplitude ratio, and relative angle) versus Schnupp asymmetry for all the configurations that involve the power recycling cavity.  I am still meditating on what they mean for us, in terms of whether or not we should be changing our Schnupp asymmetry.

The Schnupp asymmetry scan starts at 1mm, rather than 0.  Also, recall that our current Schnupp asymmetry is 3.9cm.















  8712   Mon Jun 17 17:51:43 2013 JenneUpdateLSCPOP QPD cables laid

Power not on to the POP QPD yet though.  Also, still need to reconnect POPDC.

  8713   Mon Jun 17 21:10:25 2013 JenneUpdateLSCSensing Matrix vs. Schnupp Asymmetry

The plots, with a log y axis









  8716   Tue Jun 18 07:22:20 2013 KojiUpdateLSCSensing Matrix vs. Schnupp Asymmetry

What's the reason why the PRMI/MICH ratio gets worse (larger) for 55MHz and 165MHz for the DRMI compared to the PRMI case?

  8730   Wed Jun 19 23:50:44 2013 JenneUpdateLSCPRCL locking again

This is a mid-evening update, so I don't forget all the stuff I've already done.

Aligned PRMI, no nice flashes on POP110.  Aligned and locked PRM-ITMY half-cavity on the carrier, and used that POP beam to center the beam on the POP110 PD.  I also turned on the new QPD and centered the beam on it.

Notes about QPD setup:  The "zero/cal" switch is OFF, so none of the small knobs on the front (basically, everything but the gain knob) should be bypassed.  The gain knob is set to position 3.  This is the highest gain that I can have without the "too much light" saturation light blinking on the front panel.  (During this time, POP110I is flashing around 200 counts).

I made a super hacky ASC screen, which is accessible from the ASC button on the sitemap.  While there is a pitch path in the model, I only put in the yaw elements (except for the QPD readouts) in the screen, since that's what I'll be using for now. 

I added filter banks to the front side of the ASC subblock in the ASS model, so that I have a place to monitor the QPD signals on the screen and with striptool. 

Using the settings that Koji recorded in elog 8521 in the "Locking with SQRT(POP110I)" section (and no ASC engaged so far), I can lock the PRMI for ~10 or 20 seconds, at 150 or 200 counts on POP110I.  So, I'm doing well so far, and next up is to copy the ASC filters Koji made in elog 8562, and try the new ASC.

  8731   Thu Jun 20 01:13:18 2013 JenneUpdateLSCPRCL locking again - no ASC success

I didn't have any success with the ASC tonight.  I copied over the filters that Koji had used in elog 8562, and put them in the new ASC filter banks (and turned them off in the SUS-PRM_ASCYAW bank).  I also moved all the old scripts that were in .../scripts/ASC to an OLD subdirectory (the most recent edit is from 2009 sometime).  I then copied over the up and down scripts that Koji had written for his ASC test into the ..../scripts/ASC directory, and modified them to work with my new channels. 

I then tried locking, and wasn't very successful.  Actually, my best lock, ~4 minutes, including tweaking up the PRM alignment, was when the ASC path was off (even though I thought it was on).  After discovering my mistake, I tried locking for another hour or so, but haven't really gotten anywhere.  The lock stretches I'm getting are rarely long enough for me to get to the terminal and run my up script, and the maybe ~6 or 7 times I've been able to run it, I haven't converged toward finding a good gain value for the PRC yaw loop.  At some point, I redid the MICH alignment since it had drifted away a bit, but that didn't really help.

I think that one of the next things I might try is carrier-locking the PRMI, to find okay loop gain settings for the ASC path.  Since the QPD output is already normalized (I'd have to custom-make some electronics to make it non-normalized), I think the gain should be the same for both carrier and sideband lock cases.


Once I finally get a good, stable, PRMI sideband lock, I think I need to take the following measurements:

* CTRL and ERR spectra for MICH and PRCL

* TFs for MICH and PRCL loops

* Sensing matrix, including AS55, REFL11, REFL33, REFL55, POX and POY.

---->> Are there any others?

  8737   Mon Jun 24 11:51:23 2013 JenneUpdateLSCNew modeled sensing matrix


 This is nice - how about figuring out how to plot the measurement and model on the same plot? I guess we need to figure out how to go from counts to Watts.

I haven't done a units conversion for the measured vs. modelled plot,  but at least we can compare the separation between the different degree of freedom signals.  Figuring out why the REFL11 measurement and models are so different is still high on my to-do list.  But at least the measurements that were taken last month are consistent with one another. EDIT:  The separation angles match up pretty well between the 2 sets of measurements, but the overall rotation isn't really consistent.  I do not believe that the phase rotation values that we're using online changed between the measurements, so the I&Q lines should be the same for both seets of measurements....however, I did not write down the phase rotation values at the time of the first measurement, so there's a chance that they were different.  Also, something that I need to monitor is the coherence of my measurement, to make sure I'm really driving and measuring something.


2 measurements, with overall rotation arbitrarily rotated to make MICH lines match up:


Same 2 measurements, without the arbitrary overall rotation:


Measurement vs. Model, with the *modelled* phase arbitrarily rotated:


  8741   Tue Jun 25 00:28:52 2013 rana, manasaUpdateLSCArm Cavity scan with X-ALS after ALS servo upgrade

[Rana, Manasa]

ALS noise suppressed to 1KHz/rtHz. 1kHz RMS.

Plot 1: Scan of X arm by changing offset into Phase Tracker -> Xarm loop. Filter bank ramp time set to 120 s + using a 30 mHz low pass filter. IR beam is aligned to x arm, but not well.

Plot 2: ALS error signal with loop open (BLUE), closed with old filters (PURPLE), and with new, better boost (RED).

Plot 3: Bode plot of new boost (FM10), v. old, sad boost (1:50 pole:zero). RMS is now less than 1 kHz or ~50 pm. (in your face, Kiwamu!)

Changes made to the ALS servo:


ALS-TRX has been calibrated to read from 0-1 instead of counts in 1000 s. Calibration factor = 1/4500 = 0.00022


Old antiwhitening filter has been removed. Added LPF at 1000Hz to remove glitches at high frequencies.


No changes made.


FIlter FM5 modified. 1000:1 changed to 3000:1

5. Offset for ALS scan were given through C1ALS_OFFSETTER1 with LPF50m enabled.


The filter modules of the servo were:






Check PZT out range for ALS. Figure out what the deal is with ALS SLOW servos.

Add DQ channels for ALS.

Automatic ALS up script (enable and disable phase tracker included).



Attachment 1: scan.png
Attachment 2: als-x-err.pdf
Attachment 3: FM10.pdf
  8742   Tue Jun 25 10:18:34 2013 Mystery ManUpdateLSCArm Cavity scan with X-ALS after ALS servo upgrade


RMS is now less than 1 kHz or ~50 pm. (in your face, Kiwamu!)

 Isn't this still a factor of 2 away from the limit in the paper?

  8744   Tue Jun 25 11:39:13 2013 KojiUpdateLSCArm Cavity scan with X-ALS after ALS servo upgrade

My understanding is that that number is an in-loop evaluation of the loop so far (as the first step of the loop evaluation).
This is not what we can directly compare with the number in the paper.

Basically the entry 8741 is telling us that the new filter suppresses the error signal better than before.
That's clearly shown in the attachment 2.



RMS is now less than 1 kHz or ~50 pm. (in your face, Kiwamu!)

 Isn't this still a factor of 2 away from the limit in the paper?


  8753   Wed Jun 26 04:38:02 2013 JenneUpdateLSCPRCL locking again - ASC success

With Rana's help/supervision/suggestions, I have closed the loop on the PRMI ASC servo with the new QPD.  I think I've had it locked for ~30+ minutes now.  It was locked for ~45 minutes, but then the MC momentarily lost lock.  I immediately recovered the PRMI+ASC (after small PRM yaw tweaking, since the ASC isn't triggered yet, so the MC lockloss caused a big yaw step function to go to the PRM, which displayed a bit of hysteresis.).

My biggest problem was that I didn't really understand Koji's servo filter choices, so I wasn't using the right ones / doing good things.  In particular, I need to compensate for the oplev servo filters.  The oplev servo shape is something like ^, so the 1/(1+G) shape is something like =v= (ignoring the lower horizontal lines there).  For tonight, we just turned off the PRM oplevs, but clearly this isn't a permanent solution.  (Although, after Rana went in and roughly centered the PRM oplev, we noticed that turning the oplev on and off doesn't make a huge difference for the PRM....we should investigate why not.  Also, we turned off the FM2 3.2Hz resonant gains in the PRM oplevs, since the Q of those filters is too high, much higher than our actual stacks). 

Rana and I also locked the PRM-ITMY half cavity, and used that beam to realign the beam onto the POP QPD, POP110 PD, and the camera. 

The POP QPD pitch and yaw signals with the half cavity have some noise, that looks like 60Hz crap.  Since this goes away (rather, is much less noticeable) with the regular sideband-locked PRMI, we suspect this is a problem with perhaps the normalization, with the sum very low, and having some noise on it.

Once we had our ASC filters set up (not the 10Hz boost yet though, I think), if I increased the gain from -0.02 to -0.03, we start to get some gain peaking.  With a gain of -0.04, the peak is very noticeable around 250Hz.  We aren't sure where this is coming from, since it shouldn't be coming from the ASC loop.  The UGF of that loop is much lower (I measured it, to check, and the UGF is ~5Hz). Anyhow, this is still a mystery, although the gain of -0.02 holds the cavity pretty well.

I measured the power spectra of the POP QPD pit, yaw, sum, as well as POPDC and POP110I, with the ASC loop on and off (dashed lines are with the loop on.  You can see that the yaw motion as seen on the QPD was reduced by almost 2 orders of magnitude below 1Hz.  It also looks like we can win some more by turning on the equivalent pitch ASC servo (this is also something we see when looking at the dataviewer traces).

I also tried to measure the PRMI sensing matrix, but I get some weird results, even after I double the drive actuation.  I need to be checking whether or not my drive is actually coherent with the error signals that I'm seeing, because right now I'm not sure that I believe things. I'm going to leave that on the to-do list for tomorrow night though.

Next up:

* Engage POP QPD -> pitch loop, copying yaw loop.

* enable ASC triggering

* model PRMI sensing matrix and error signals, bringing one arm into resonance

* Lock the PRMI, and bring the Xarm into IR resonance using the ALS system.


Here are some numbers and plots from the night:

Right now, I'm locking the LSC with:

MICH LSC with AS55Q, FMs 4 and 5 on, FM 3 is triggered, gain = -40.0, normalized by sqrt(POP110I)*0.1

PRCL LSC with REFL33I, FMs 4 and 5 on, FM 9 is triggered, gain = +2.5, normalized by sqrt(POP110I)*10

(FM3 of MICH and FM9 of PRCL are the same, just in different spots).

The ASC (only POP yaw -> PRM yaw right now) has:

FMs 1,2,5,6 on (1 = integrator [0:0.1], 2 = 3.2 res gain, 5 = [1000,1000:1 and gain of 0.01], 6 = 10Hz boost).  Gain = -0.020,  Limit=5000.

Turn off the input, turn on the output and the gain, clear the histories (to clear out the integrator in FM1), then turn on the input.

PRM oplev is OFF. (need to put in a filter to compensate for it in the ASC servo, but for tonight, we just turned it off.)

We measured the spectra of the POP QPD signals with the ASC loop on and off:


I also measured the ASC loop (with the PRM oplev still off):




(sorry about the separate plots - I can't make DTT give me more than 2 plots on a page at a time right now, so I'm giving up, and just making 3 separate pages)

Weird sensing matrix, unsure if I'm really getting good coherence:


  8767   Thu Jun 27 17:09:41 2013 JenneUpdateLSCPRCL locking again - POP PIT work

Last night before dinner, I copied over the ASC yaw servo filters to the ASC pitch filter bank.  Using ASC gain of +0.001, I was getting the ~250Hz oscillations that Rana and I had seen with yaw. 

Rana pointed out to me that my measured TF of the yaw loop doesn't look right up in the several hundred Hz region:


As you can see on the right side, which is all of the PRCL ASC yaw filter banks, multiplied by a simulated pendulum filter, the magnitude should just keep decreasing.  However, on the measured plot on the left, you can see that I have a little gain hump.  I'm not sure what this is from yet.

  8772   Thu Jun 27 19:17:03 2013 manasaUpdateLSCXarm ALS out-of-loop noise

Measured frequency noise is ~10Hz/rtHz @100Hz. 

Measure the out-of-loop noise of Xarm ALS:

1. The X-arm was locked for IR using PDH error signal.

2. 'CLEAR HISTORY' of the phase tracker filters.

3. Measured the power spectrum of the phase tracker output. I have used the newly created calibrated channel "PHASE_OUT_DQ. So the phase tracker output now reads in Hz.


The measurement was done with beat note frequency at ~40MHz. The flat noise level of 10Hz/rtHz from 20-100Hz (in plot 2) is not good. We should investigate as to what sets this noise level. The spike at 60Hz is because the 60Hz frequency comb filter was not enabled.

I plan to the following to get a clearer outlook
1. Connecting the beat box to an RF source and measure the noise levels for a range of frequency inputs to the beatbox.
2. Measure the noise at C1:ALS-BEATX_FINE_I_IN1 (before the antiwhitening filters) and check whether the new whitening filters has done anything good with respect to minimizing the DAQ noise.


Attachment 1: ALS_OoL.pdf
Attachment 2: ALS_OoL1.pdf
  8779   Fri Jun 28 02:12:21 2013 manasaUpdateLSCPRMI + X arm ALS

X arm stabilized using ALS while PRMI stayed locked

[Rana, Lisa, Jenne, Manasa]

Attachment 1

Time series : ALS enabled at t = 0 and disabled at t = 95s


What we did:
1. Jenne will elog about ASC (POP QPD) updates.
2. Found the beat note between Xarm green and PSL green.
3. Stabilized arm fluctuation by enabling ALS servo.
4. Scanned the arm for carrier resonance by ramping on the offset and set the offset such that we had IR resonating (TRX fluctuated between 0.1 and 0.8 counts).
5. Disabled the ALS servo and locked PRMI using AS55 for MICH and REFL33 for PRCL.
6. Enabled ALS.

Enabling ALS to detune the arm out of resonance kept PRMI locked  (currently for a span of few tens of seconds). However we could not see PRMI locked as stably compared to when the arms are misaligned. Everytime the offset was set IR to resonate, the PRMI was kicked out of lock.

Also there is some leakage at the arm transmission when PRMI was locked. The leakage was visible at ETMX transmission as flashes in different higher order modes indicating the not-so sufficient ALS stability. The leakage sets an offset at TRX measuring 0.01-0.05 counts.

To do list:
The ALS_OFFSETTER1 has to be calibrated in FSR. We were giving random offsets to do the offset scan.

Installed a filter before ETMXT camera to remove the refl green. (Note to myself: The filter needs to go on a better mount/adapter).

  8780   Fri Jun 28 02:12:41 2013 JenneUpdateLSCPRCL locking again - ASC work

Rana had the epiphany that I didn't have any antiwhitening for my POP QPD.  Ooops. 

We looked at the schematic for the Pentek Generic board (pdf), and saw that it has a Zero @ 15Hz, and Poles @ 150Hz and 1500Hz, times 2 stages.  We determined from the TF that I posted that probably both stages are engaged, so I made an antiwhitening filter consisting of the inverse (so, 2 poles at 15Hz, 2 zeros at 150Hz and 2 zeros at 1500Hz).  [Rana points out that for this low frequency system we may not want to include the 1500Hz compensation, since it is probably just enhancing ADC noise].  The ASC system worked really well, really easily, after that.

Another note though, the AA stage of the Pentek Generic boards have 4 poles at 800Hz, which are not compensated.

Rana also added a 60Hz comb to the filter bank with the AntiWhitening, since the QPD has an unfortunately large amount of 60Hz noise.  Also, the 60Hz lowpass in the ASC loop was engaged for both pitch and yaw.

Rana, Lisa and Manasa also found that the ASC system was *more* stable with the PRM oplev ON. 

So, the ASC locking situation is:

PRM oplev loops on.

AS-POP_QPD_[PIT/YAW] filter banks with FM1, FM6 on.

ASC-PRCL_[PIT/YAW] filter banks with FM1, FM5, FM6 and FM9 on.



(No triggering yet).

The ASC Up and Down scripts (which are called from the buttons on the ASC screen) have all of these gain settings, although they assume for now that all the filters are already on.

Here's a screenshot of the power spectra showing the angular motion suppression. The PDF is attached so you can zoom in and see some details.  The dashed lines are the "PRMI locked, ASC off" case, and the solid lines are the "PRMI locked, ASC on" case.  You can see that according to the QPD, we do an excellent job suppressing both the pitch and yaw motion (although better for yaw), but there isn't a huge effect on POPDC or POP110I.  While we could probably do better if we had a 2 QPD system with the QPDs at differet gouy phases, this seems to be good enough that we can keep the PRMI locked ~indefinitely. 


I would like to compile the ASC model, so that I can implement triggering.  For tonight, we did not have the ASC engaged during our PRMI+Xarm tests (see Manasa's elog), but I think it'll make things a little easier if we can get the ASC going automatically.

Attachment 1: PRMI_ASC_powerSpectra_27June2013.pdf
  8781   Fri Jun 28 02:23:00 2013 JenneUpdateLSCNeed to measure sensing matrix at REFL165

[Lisa, Rana, Jenne]

Lisa asked to see a model of the PRMI sensing matrix with REFL165 included, in the hopes that it wouldn't be as degenerate as REFL33.


The conclusion, immediately after looking at this, is that I should make sure the REFL beam is nicely aligned onto the REFL165 PD (Koji did some tests, swapping out the REFL165 resonant PD with a broadband PD, and I don't remember if he aligned beam back onto the REFL165 PD).  Then, I need to measure the PRMI sensing matrix, including REFL165.  Hopefully, it is similar to the model, and we can use it as our 3f diode for locking.

  8783   Fri Jun 28 12:15:09 2013 KojiUpdateLSCNeed to measure sensing matrix at REFL165

There is no sensible REFL165 PD in the lab. I am supposed to prepare a new version of REFL165 using prototype BBPD.

  8788   Mon Jul 1 23:27:07 2013 JenneUpdateLSCSensing Matrix vs. Xarm sweep

I have modeled the PRMI sensing matrix as I bring the Xarm into resonance.  In optickle, I have the PRMI on sideband resonance, the ETMY is artificially set to have a transmission of 1, and the ETMX has it's nominal transmission of 15ppm.  I start with the ETMX's microscopic position set to lambda/4 (antiresonant for IR in the arm), and take several steps until the ETMX's microscopic position is 0 (resonant for IR in the arm).

Xarm antiresonant:

Modeled sensing matrix, units = W/m, Offset = 2.66e-07, phase in degrees
            MICH Mag   MICH Phase    PRCL Mag   PRCL Phase  
AS55         3.348E+04   142.248      5.111E+03    70.571    
POX11        3.968E+01   -66.492      1.215E+04    54.312    
REFL11       3.231E+05    24.309      9.829E+07   144.311    
REFL165      9.946E+03  -159.540      4.540E+05   -64.710    
REFL33       1.963E+04  -168.530      1.573E+06    -2.744    
REFL55       1.160E+06    -6.755      5.429E+07    86.895 


Xarm resonant:

Modeled sensing matrix, units = W/m, Offset = 0, phase in degrees
            MICH Mag   MICH Phase    PRCL Mag   PRCL Phase  
AS55         1.647E+06    57.353      3.676E+06   -81.916    
POX11        3.927E+02  -118.791      2.578E+04  -102.158    
REFL11       7.035E+05    61.203      1.039E+08   167.149    
REFL165      1.602E+04  -144.586      5.971E+05   -49.802    
REFL33       2.157E+04   171.658      1.940E+06    -9.133    
REFL55       1.822E+06     7.762      6.900E+07   101.906 


For REFL55, the MICH magnitude increases by a factor of 1.6, while the PRCL  magnitude increases by 1.3 .  The MICH phase changes by 15 degrees, while the PRCL phase also changes by 15 degrees.  Just eye-balling (rather than calculating), the other REFL PDs look to have similar-ish magnitude and phase changes.  Certainly none of them are different by orders of magnitude.

Movies forthcoming.

  8790   Tue Jul 2 02:29:47 2013 JenneUpdateLSCSensing Matrix vs. Xarm sweep

Here is the Sensing Matrix movie (sorry for the iffy quality - my movies usually come out better than this):


This is the sensing matrix for the sideband locked on PRMI, bringing the Xarm into resonance from anti-resonance, in 20 equally-spaced steps.  You can see the microscopic ETMX offset (units of meters) in the title of the figures.

I was surprised to see some of the 'jumps' in the sensing matrix that happen near the end, when the arm is almost in resonance.  I'm in the process of making movies of the error signals as the Xarm is brought into resonance.  I'll have to post those in the morning, since they're taking a long time to produce and save, however when I looked at a few, there is some weird stuff going on as we get close to resonance, even with the 3f signals. 

The modeling phone call is in the morning, but if anyone who is not regularly on the call has thoughts, I'm all ears.

  8797   Wed Jul 3 14:33:46 2013 KojiSummaryLSCTest result for the REFL165 photodetector

P.1 Circuit diagram

Added components are indicated by red symbols.

- The diode on the board is HAMAMATSU S3399. It is a Si PIN diode with φ3.0 mm.

- Based on prototype version of aLIGO BBPD D1002969-v8 (although the board says v7, It is v8.)

- The input impedance of the MAR-6SM amplifier (50Ohm) provides the transimpedance.

- The first notch (Lres and Cresa/b) is actually not notch but a LF rejection with DC block.

- The second and third notches are tuned to 11MHz and 55MHz.

- Another notch is implemented between the RF amps. The 33MHz signal is weak so I expected
to have no saturation at the first amplifier.

- As you see from the DC path, the transimpedance of the DC path is 2k V/A. If this is too high,
  we need to replace R9 and R11 at the same time. TP1 is providing +10V such that the total
  reverse bias becomes 25V without bringing a special power supply.

P.2 Transimpedance

The transimpedance is measured with an amplitude modulated diode laser.

The transimpedance is 1k V/A ish. It is already at the edge of the bandwidth.
If we need more transimpedance at 165MHz, we should replace
the PD with FFD-100 (I have one) and apply 100V of reverse bias.

P.3 Current noise spectrum

The measured dark noise voltage spectrum was converted to the equivalent current noise at the diode.

The measured transimpedance is ~1.2kV/A.
The reduction of the transimpedance above 100MHz has been seen as 165MHz is already at the edge of the bandwidth.
If we need more transimpedance at 165MHz, we should replace the diode with FFD-100 (I have one) and apply 100V of reverse bias.

P.4 Shot-noise intercept current

Shot-noise intercept current was measured with a white light from a light bulb.
This measurement suggests the shot-noise intercept current of 1mA, and transimpedance of 1.5kV/A.

Attachment 1: REFL165_response_130702.pdf
REFL165_response_130702.pdf REFL165_response_130702.pdf REFL165_response_130702.pdf REFL165_response_130702.pdf
  8801   Thu Jul 4 01:09:33 2013 Annalisa, KojiUpdateLSCPRMI locked with REFL165


- The new REFL165 PD was installed on the AP table
- The REFL165I/Q signals are now showing sensible and robust PRCL/MICH signals
- PRMIsb was locked only with these REFL165 signals


- Installation of the REFL165 PD

We prepared the REFL165 PD for the 4" optical height. The actual issue was the power supply for the PD.
We soldered wires between the PD and the RF PD interface break-out board. Then the PD interface
cable for the old REFL165 (iLIGO style) was connected.

At the REFL port, most of the light is rejected by the first beam splitter (R=90%?). We attenuated the beam by a factor of 10
using an ND filter. The new PD showed the DC output of ~10V. This corresponds to the photocurrent of 5mA.
(cf. the shot-noise intercept current is ~1mA)

The output of the REFL165 PD was checked with the RF spectrum analyzer. It was a bit surprising but we had a forest of
RF signals betwen 11MHz and 178MHz.
We tried to use a high-pass filter with fc=100MHz (SPH-100) but still the rejection
was not enough. We ended up with using SPH-150 (fc=150MHz).

- Whitening / Demodulation phase

Then we connected the RF output to the SMA cable to the LSC rack. We immediately saw the nice signals from REFL165I/Q
channels, namely sensible structure of pendulum resonances (1/3/16Hz peaks) and floor level.

The whitening level was changed from 21dB to 45dB (max). The DC offsets in the I/Q channels (of the order of 2000~4000)
were removed by the ./LSC/LSCoffset script.

Firstly we locked the PRMI with the usual signals (REFL33I and AS55Q).
The demodulation phase was roughtly tuned (1deg precision) such that the Q phase signal is minimized,
assuming most of the signal is coming from PRCL. Our choise is 74deg.

In this configuration, PRCL shows same quality of signal as our prefered PRCL (i.e. REFL33I) in the amplitude and the sign.

- Locking

We switched to the REFL165 signal by handing off at the input matrix. The input matrix element for REFL165_I was gradually
increasded up to 0.8 while the element for REFL33I was gradually reduced to 0. We did the same for REFL165_Q with the element of 0.2.

Now we tried locking with REFL165I/Q from the beginning. Once the alignment is adjusted, the lock was immediately obtained
only with REFL165I/Q.
Today we did not adjusted the ASC stuff (OPLEVs and PRM ASC) so the lock was not long (<1min). Particularly
ITMX poiting kept drifting and it made the lock difficult. We should check the oplev setup carefully.

- LSC summary

Signal source: REFL165I (74deg) / Whitening gain 45dB
Normalization sqrt(POP110I x 0.1) / Trigger POP110I 100up 3down
Servo: input matrix 0.80 -> PRCL Servo FM3/4/5 Always ON G=+2.50
Actuator: output matrix 1.00 -> PRM

Signal source: REFL165Q (74deg) / Whitening gain 45dB
Normalization sqrt(POP110I x 10.0) / Trigger POP110I 100up 3down
Servo: input matrix 0.20 -> MICH Servo FM4/5 Always On G=-40
Actuator output matrix -1.00 -> ITMX / +1.00 -> ITMY

To Do:

- Refine the PRM asc servo (AC coupled)
- Align oplevs
- ITMX oplev is drifting quickly (~1min time scale)





Attachment 1: 130703_PRMI.pdf
Attachment 2: Screenshot.png
  8816   Tue Jul 9 23:27:17 2013 KojiSummaryLSCMICH: ITMX/Y <=> PRM/BS

The MICH actuation with PRM/BS was investigated again.

(ITMX -1 / ITMY +1) is equivalent to (PRM -0.267 and BS +0.50).

- PRMIsb was locked with REFL33I&AS55Q.

- Using the locking module in the LSC model, actuate ITMX (-1) and ITMY (+1) at 580.1Hz. Note that the notch filters in the MICH/PRCL servos were on.

- Look at the peak in the AS55Q spectrum. Tune the BS element in the output matrix of the lock-in to minimize the peak height.
=> The peak was minimized at BS = -0.50.

- Look at the peak in the REFL33I spectrum. Tune the PRM element in the output matrix of the lock-in to minimize the peak height.
=> The peak was minimized at PRM = +0.267

- These measurement leads to the conclusion mentioned above.

  8825   Thu Jul 11 03:14:19 2013 JenneUpdateLSCYarm held nicely on IR resonance with ALS, PRMI+arm attempt

[Annalisa, Jenne, Nic]

After having troubles with the Xarm earlier (maybe Manasa can write/say something about this?  Something about perhaps seeing the phase tracker jump, and cause it to lose lock?), we moved on to the Y arm. 

Annalisa locked the Yarm green, and closed the ALS loop.  I believe that earlier today, she tuned the gain such that we don't start getting gain peaking at a few hundred Hz.  We would like to get a script going, so that it's not so labor intensive to reclose the ALS loop after an MC lockloss....but that's a daytime task.

We then found the IR resonance, using only the Yarm ALS system.  After Manasa's work yesterday, the Yarm was very stable while locked with the ALS.  We took a power spectrum of POY11_I_ERR, which I have calibrated using the number in elog 6834 of 1.4e12 cts/m, or 7.14e-13 m/ct.  See the figure below.

After that, we changed the offsetter2 offset such that the arm was off resonance, but not so far off that we crossed any significant resonances (in particular, we wanted to not go as far as the 55MHz resonance). 

Then, I tried to lock the PRMI for a while, but the alignment wasn't very good.  We knew that the Yarm was well aligned, since our IR resonance was > 0.98, but it had been a while since we had aligned the X arm.  I tweaked the ITMX position to make the Michelson dark, and then tried acquiring PRMI lock.  At first, I tried with REFL165 I and Q, but with the non-ideal alignment and the offset in the 165 diode (LSC offsets was not run this evening), I wasn't catching any locks.  I then switched to AS55Q and REFL33I, but wasn't able to catch lock there either. 

The MC lost lock, which made us lose the ALS loop, but the ALS had been locked for more than 30 minutes, at least.  I tried locking the PRMI with the current alignment (after having misaligned ETMY), but was only able to get lock stretches of 1 second at maximum.

We are calling it a great success for the night, since we have confirmed that, at least for the Yarm, Manasa's beatbox work has improved things.  Also, we have a pretty solid plan for trying the PRMI+arm tomorrow, even though it didn't work out tonight.

Attachment 1: Yarm_onIRresonance_noPRMIyet_POYcalibrated.pdf
  8826   Thu Jul 11 07:34:42 2013 manasaUpdateLSCYarm held nicely on IR resonance with ALS, PRMI+arm attempt


We knew that the Yarm was well aligned, since our IR resonance was > 0.98, but it had been a while since we had aligned the X arm. 

 The X arm was locked with TRX>0.98 earlier last night while I was measuring the out of loop noise of the phase tracker.

  8833   Fri Jul 12 00:12:41 2013 KojiUpdateLSCPRMI + Y arm trial

[Koji, Manasa, Annalisa]

I made several trials to scan the arm on the IR TEM00 resonance while the PRMI was held with REFL165I&Q.
It was so hectic to keep multiple systems running correctly. We talked about how it should be automated.
We'll gradually offload the switching works on scripts.

In a good alignment condition, when I swept on the resonance, everytime the PRMI lost the lock. It reacquired
once the arm passed the resonance.

Lately I got difficulty to acquire lock of the PRMI while the arm is waiting at its off resonance.
If I change the ALS offset I got a stable lock in a certain offset, and did not get in another offset
so there could be something systematic. (The arm was in between the carrier resonance and the next sideband (55MHz) resonance).




- Run LSCoffset script.

- Misalign PRM. Lock and align the arms with ASS.

- Go into the tables. Align the oplevs for ETMX/Y, ITMX/Y, and BS. (Very important for alignment stability)

- Align PRMI and lock PRMI. Unlock once.

- Go into the BS/PRM table. Align the oplev for PRM.


- Misalign PRM by -0.2

- Find the beat note at around 50MHz by changing the Yarm SLOW control. Today the PSL SLOW was ~0.24, and the Yarm SLOW was -10981.

- Reset Phase Tracker History (Important)

- Engage Yarm ALS with FM5. Tested the sign of the servo by giving 0.01 or -0.01. In my case, the negative number worked fine.
  Gradually increase the gain up to -10. Turn on FM2/3/6/7/10.

- Use Filter module "C1ALS-OFFSETTER2" to give the ALS sweep. I used FM1 (30mHz LPF). Change the offset while looking at the IR TRY and POY11 error signal.

- Once the resonance is found, shift the beat note by giving +10 or -10 offset.


- While the arm is kept off resonance, align PRM.

- Lock PRMI with REFL33I and AS55Q. Turn on PRM ASC.

- Once the stable lock is obtained, switch the input signals to REFL165I&Q. I used REF33I x1.0->REFL165I x0.8 and AS55Q x1.0 -> REFL165Q x0.5

[PRMI + one arm]

- Revert the ALS offset by 10 to bring the arm on the resonance the see what happens.


  8837   Fri Jul 12 12:51:16 2013 manasaUpdateLSCPRMI + ALS automation


We talked about how it should be automated.

We'll gradually offload the switching works on scripts.

 Here is the list of automations that we need to work on for less hectic PRMI+ALS trials.

1. Enable/Disable ASC when PRMI is locked/unlocked.

2. Smooth transfer from REFL33/AS55 to REFL165 when PRMI is locked.

3. Change actuation from the ITMs to BS and PRM after PRMI lock.

4. Enable ALS.

5. IR resonance scan using ALS.

  8867   Thu Jul 18 02:21:41 2013 KojiUpdateLSCPRMI+Y arm ALS success!

[Koji, Jenne, Manasa, Annalisa, Rana, Nic]

PRMI locked using 3f signals and Y arm brought to resonance using ALS



- After we checked the functionarity of the Yarm ALS, both arms were locked with the IR, and aligned by ASS.

- Disengaged the LSC feedback. Approximately aligned the PRM.

- Recorded the current alignment biases. Turned off all of the oplevs.

- Went into the lab, aligned all of the oplevs on the QPDs (except for the SRM).

- Check the locking of the PRMI.

- Once it is locked, go into the lab again and align the POP QPD.

- Check everything of the PRMI LSC/ASC works.

- Misalign PRM by 0.2

- Lock the arm again. Run ASS again.

- Miaslign ETMX.


- Lock the Xarm with green. Adjust the beat freq between 30-50MHz.

- Reset Phase Tracker history.

- Check if there is any offset for the ALS. If there is, adjust it to zero.

- Stabilize the arm with the ALS. We should check the sign of the servo before it is cranked up to the nominal.

- Confirm if the offset FM has LPF (30mHz LPF).

- Run excastep for the ALS offset until we find the TEM00 resonance of the IR

- Record the offset at the resonance.

- Step back by 5 count (=100kHz)


- Started from the offset of -5.

- Aligned the PRM and the PRMI was locked by REFL165I(x0.8)nadQ(x0.2).

- PRM ASC engaged

- Moved the offset to -4 by ezcastep C1:ALS-OFFSETTER2_OFFSET +0.01,100 -s 0.1

- Moved to -3, -2, -1.5, -1. During the sweep PRCL/MICH gain was tweaked so that the gain is reduced.
  Nominal locking gain was PRCL x+2.5/MICH -30 . During the sweep they were +2.2 / -12
  PRCL FM2/4/5 ON, Later FM3/6 turned on and no problem.

- Moved to -0.9, .... , and finally to 0.


- Automation of the PRMI+one arm

- PRMI locking with BS/PRM

- Better sensing matrix

- PRMI+two arms

- Use of the DC signals form the transmission monitors. (High power /low power transmon).



Attachment 1: Screenshot-Untitled_Window1.png
Attachment 2: PRMI_Yarm.pdf
  8868   Thu Jul 18 10:47:21 2013 JamieUpdateLSCPRMI+Y arm ALS success!

AWESOME!  You guys rock.

  8869   Thu Jul 18 10:50:54 2013 LisaUpdateLSCPRMI+Y arm ALS success!


[Koji, Jenne, Manasa, Annalisa, Rana, Nic]

PRMI locked using 3f signals and Y arm brought to resonance using ALS

Fantastico! :-)

  8871   Thu Jul 18 15:55:31 2013 JenneUpdateLSCPRMI+Y arm ALS Sensing Matrices

Last night, I took sensing matrix data at various different offsets for the Yarm.  The sensing matrices I measured were of the PRMI, while the Yarm was (a) Held off resonance, (b) Held at ~50% peak power, and (c) Held on resonance.

The dither lines were clear in the MICH and PRCL spectrum, so I think I'm driving hard enough, but something else seems funny, since clearly the REFL165 I and Q signals were not completely overlapping last night.  If they were, we wouldn't have been able to lock the PRMI using REFL 165 I&Q.

Anyhow, here's the data that was taken.  Data folder is ...../scipts/LSC/SensingMatrix/SensMatData/

Yarm off resonance, SensMat_PRMI_1000cts_580Hz_2013-07-18_012848.dat


Yarm at ~50% resonance, SensMat_PRMI_1000cts_580Hz_2013-07-18_013937.dat


Yarm on resonance, SensMat_PRMI_1000cts_580Hz_2013-07-18_013619.dat



  8872   Thu Jul 18 16:30:08 2013 KojiUpdateLSCPRMI+Y arm ALS Sensing Matrices

Hmm. I agree that something was funny.
Let's take the matrix without the arms and confirm the measurement is correct.

  8879   Fri Jul 19 12:02:18 2013 manasaUpdateLSCPRMI+Y arm ALS success!

Data retrieved using getdata (30 minutes trend) saved at


  8882   Fri Jul 19 22:35:06 2013 KojiSummaryLSCVarious Arm signal (Yarm)

The StripTool plot attached below shows various arm signals measured with the Y arm cavity swept using ALS.

Yellow: TRY

Blue: ALS additive OFFSET to the error signal

Red: Raw PDH error signal (POY11I)

Purple: Linearized PDH error (POY11/TRY)

Green: 1/Sqrt(TRY)-5 (No normalization)

Inverse Sqrt of the TRY had been implemented when this LSC controller was first coded.
It is confirmed that the calculation is working correctly.

Attachment 1: various_arm_signal.png
  8885   Fri Jul 19 23:35:52 2013 KojiSummaryLSCTRY DC locking

The Y arm was locked with the TRY DC signal.

The handing off process is too complicated because there is no path from ALS to the LSC error.

 The TRY DC error signal & the gain determination

- The error signal was produced by the operation 1/SQRT(TRY) - OFFSET. The initial offset was -5.

- The sign of the TRY DC error signal depends on which side of the resonance the arm is.
  By looking at the strip chart, I determined that the sign is opposite of the ALS.
  The ALS had the gain of -25, so the TRY control gain was to be positive.

- From the strip chart on the previous entry , the slope difference between the PDH error and the TRY DC error was x500.
  The arm control with POY11 PDH had the gain of 0.2. So the target gain for the TRY DC was determined to be +100.

Handing off

- The arm was stabilized by ALS. The ALS gain was -25 with FM2/3/5/6/7/10

- YARM configuration: no trigger / no FM trigger / gain =+0 / FM5 ON / OFFSET -5

- Start handing off:
  YARM: Turned up the gain to +50

- ALS: Turned off FM6/7

- YARM: Turned on FM6/7

- ALS: Turned off FM2

- YARM: Turned on FM4

- ALS: Turned off FM3/10

- YARM: Turned on FM2/3/8/9 ON

- ALS: Reduced the gain to -15

- YARM: Increased the gain to +70

- ALS: Reduced the gain to 0

- YARM: Increased the gain to +100


Changing the offset

The offset of -5 gave the TRY of <0.1.

The detuning was reduced by giving the offset of -4. TRY went up to ~.1

The offset of -3 made TRY 0.13

The offset of -2 made TRY 0.25

The offset of -1.5 made TRY 0.4. And the arm could not be held by this error signal anymore.



Attachment 1: TRY_locking.png
  8974   Tue Aug 6 19:53:15 2013 JenneUpdateLSCArms locked in IR, aligned. IFO at nominal power

[Koji, Manasa, Jenne]

The Y arm was locked in IR, and we saw flashing in the Xarm (Gautam had the Xarm for green work when we began).  I checked IPANG, and the beam was beautifully unclipped, almost perfectly centered on the first out of vacuum mirror.  I aligned the beam onto the QPD.

We then swapped out the MC Y1 that we use at low power, and replace the usual 10% BS, so that we wouldn't crispy-fry MC REFL.  Manasa adjusted the half wave plate after the laser, to maximize the power going toward the PMC.  We relocked the PMC, and see transmission of ~0.84, which is at the high side of what we usually get.  The beam was aligned onto MC REFL and centered on the WFS, and the MC was locked at nominal power.  Koji tweaked up the alignment of the MC, and ran the WFS offset script.  I aligned beam onto POP QPD and POP110 coarsely (using a flashing PRC, not a locked PRM-ITMY cavity, so the alignment should be rechecked).  The arms have both been locked and aligned in IR....the green beams need to be steered to match the current cavity axis. 

The AS beam, as well as REFL and POP, are all coming out of the vacuum nicely unclipped. 

Notes:  When Koji was aligning the SRM to get the SRC cavity roughly aligned (the AS flashes all overlapping), we noticed that there is some major pitch-yaw coupling.  Serious enough that we should be concerned that perhaps some connector is loose, or an actuator isn't working properly.  This should be checked.

Moral of the story:  Coarse alignment of all mirrors is complete after pump-down and we have IR locked and aligned to both arms at nominal power.


Still to do:

* Restore PRM, align beam onto the REFL PDs. 

* Lock PRM-ITMY cavity, align beam onto POP PDs.

* Align AS beam onto AS55. 

* Recenter all oplevs.

* Recenter IPPOS and IPPANG at nominal power.

* Start locking!!

ELOG V3.1.3-