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ID Date Authorup Type Category Subject
  6072   Mon Dec 5 19:21:55 2011 kiwamuUpdateLSCcoarse beat note signal : ADC limited above 30 Hz

The signal observed by the coarse frequency discriminator was actually dominated by the ADC noise above 30 Hz.

It means that once increasing the UGF more than 30 Hz the servo will feed the ADC noise to the test mass and shake it unnecessarily.

I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071).

(But still it doesn't fully explain the instability).

 

 To improve the situation I am going to do the following actions:

   (1) Installation of a whitening filter (probably use of SR560s)

   (2) Redesign of the servo filter

 

Here is a brief noise budget of the coarse sensor.

Yarm_ALS_coarse.png

Gray curve: free running noise when no servo is applied

Green curve : in-loop noise when the ALS loop is closed with the coarse frequency-discriminator. The UGF was at 30 Hz.

Red curve : ADC noise of the coarse discriminator

Quote from #6071

 So far I still kept failing to increase the UGF of the ALS servo for some reason (see #6024).

  6074   Tue Dec 6 00:26:00 2011 kiwamuUpdateLSCALS became robust : UGF = 100 Hz

Eventually the instability in the Y end PDH servo turned out to be some kind of an alignment issue.

After carefully realigning the green beam to the Y arm, the UGF of the ALS loop became able to be at more than 50 Hz.

With this UGF it became able to suppress the arm motion to the ADC noise level (few 100 pm in rms).

Now I am scanning the arm length to look for a TEM00 resonance.

 

(the Story)

I have noticed that the spatial fringe pattern of the reflected green light was very sensitive to the pitch motion of ETMY when the green light was locked to the Y arm.

So I realigned the last two launching mirrors to minimize the reflected light. Indeed the misalignment was mainly in the pitch direction.

I basically translated the beam upward by a couple of mm or so.

The amount of the DC reflection is about 2.4 V when it is unlocked and it is now 0.77 mV when the green light is locked.

Quote from #6072

I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071). (But still it doesn't fully explain the instability).

  6076   Tue Dec 6 02:57:44 2011 kiwamuUpdateGreen Locking1st trial of handing off

I succeeded in handing off the servo from that of the ALS to IR-PDH.

However the handing off was done by the coarse sensor instead of the fine sensor because I somehow kept failing to hand off the sensor from the coarse to the fine one.

The resultant rms in the IR-PDH signal was about a few 100 pm, which was fully dominated by the ADC noise of the coarse sensor.

 

Tomorrow I will try :

  (1) Using the fine sensor.

  (2) Noise budgeting with the fine sensor.

 

Here is the actual time series of the handing off.

YarmALS.png

(Upper left ):  intracavity power.
            As the offset was adjusted the power increased to ~ 0.8. Eventually the power becomes close to the nominal value of 1 after the handing off.
(Lower left) : Frequency of the beat-note.
            After the engagement of the ALS servo, I was scanning the arm length and searching for the resonance by changing the error point of this signal.
(Lower right) : IR-PDH signal.
  6079   Wed Dec 7 00:48:58 2011 kiwamuUpdateRF SystemRealigned incindent pointing to MC
Actually it was already in a good place.
I just realigned the zig-zag mirrors on the PLS table to bring the entire beam axis a little bit upward.
The WFS servo still seems fine. The input pzt mirrors are still within their range.

Quote from #6077

Next step:  Kiwamu needs to find his happy mode cleaner place, and we'll realign the PSL beam to the MC.  The PSL-MC axes were mismatched pretty badly according to Suresh anyway, so this had to be done no matter what.

  6080   Wed Dec 7 02:55:38 2011 kiwamuUpdateGreen Lockinglocking activity tonight

No real progress.

Probably I spent a bit too much time realigning the beat-note optical path.

 

(what I did)

 - Switched on a power supply which was supposed to give +/- 15V for the broadband beat-note PD.
   The power supply had been somehow turned off.
 - Realigned the beat-note path. When we installed the new EOM mount today, we moved some of the green steering mirrors to make a space.
   So we had to realign the downstream of the beat-note path. After the realignment the DC output of the PD was about 120 mV and the signal level of the beat-note was at -20 dBm.
 - Took noise spectrum of the beat-note with the arm cavity locked by the IR-PDH
    The noise curve was almost the same as before (i.e. unknown high frequency white noise above 20 Hz and some low frequency noise which has structures at 1 and 3 Hz).
-  Closed the ALS loop with the coarse sensor. But I was too lazy to go further more. 

Quote from #6076
Tomorrow I will try :
  (1) Using the fine sensor.
  (2) Noise budgeting with the fine sensor.

  6091   Thu Dec 8 19:48:23 2011 kiwamuUpdateCDSrestarted c1lsc machine and daqd

Since the c1lsc machine became frozen I restarted the c1lsc machined and daqd.

Then I burtrestored c1lsc, c1ass and c1oaf to this evening. They seem running okay.

  6102   Sat Dec 10 05:27:43 2011 kiwamuUpdateGreen Lockingstatus update of the Y arm green lock

Status update of the Y arm green lock:

  + Recent goal : automation of the single arm green lock

 

(Things done)

  • Implementation of some realtime LOCKIN modules to detect the sign of the error signals.
  • Modification of the realtime control model to accommodate the I/Q MFD signals, which will be available in the near future. (Of course the model file in the svn has been also updated)
  • Update of the medm screens.
  • Scripting of the auto-lock has been 30 % done.
  • Succeeded in automation of closing the ALS loop. (I have tried several times and no failure was observed so far)

(Things to be done)

  • Scripting a routine to detect the sign of the fine sensor signals.
  • Development of a clever length scan algorhythm.
  • Scripting handing off routines.
  • Implementation of some lock-success binary bits to define the ALS state.
  • Implementation of fail-safes.
  6103   Sun Dec 11 17:28:36 2011 kiwamuUpdateGreen Lockingstatus update of the Y arm green lock

Quote from #6102

  + Recent goal : automation of the single arm green lock 

As reported in the previous elog entry #6102, the realtime model and screens have been modified.
Here is a summary about what are new in the realtime model.
 
(What are new ?)
  • The top name of the channels has been changed from GCV to ALS      
    => Although the model name itself is still C1GCV to keep the current relations between other computers.
  • I and Q signals on each sensor.
  • LOCKIN modules to detect the sign of the error signals by shaking suspensions.
  • Offset adjusters, which are combination of a controllable epics value and a low pass filter, to allow a smooth length scan.
  • Input matrix. This branches the input signal to the DOFs as well as the LOCKIN modules.
  • Output matrix to allow some combination of actuation (e.g. DARM, CARM, MCL, etc.,)
  • Output switch to enable/disable any feedbacks to the suspensions
  • Output filters before the suspensions. These filters will be usually flat, but enable us to inject some signals and enable some limiters.
     
    Here is the latest medm screen for the modified realtime controller.
    It gives you the idea of how the latest model works.

 ALSscreens.png

  6106   Mon Dec 12 13:02:08 2011 kiwamuUpdateCDSdaqd restarted

I have restarted the daqd process at 1:01 PM since I have added some new ALS's daq channels.

  6126   Fri Dec 16 13:29:15 2011 kiwamuUpdateGreen LockingY arm noise budget : 60Hz line noise is killing us
Along with development of the automation script, my goals last night were :
 (1) Take a noise budget when the standard ALS configuration is applied
 (2) Take a beautiful time series to show how ALS brings the cavity to the resonance point
 
 However I gave up goal (2) because the resultant time series were very fluctuating at 60 Hz and it wasn't so beautiful enough.
As shown in the noise budget below, the 60 Hz line noise currently dominates the arm displacement.
 

Yarm_ALS_2011DEC16.png

       About Noise Budget       

 The spectra were taken when the arm length was kept at the resonance point using the ALS servo.
So the error signal was taken from the beat-note and was fed back to ETMY.
The servo UGF was at about 100 Hz and the fine frequency discriminator was used.
The red curve in the plot is the arm displacement observed by POY11, which is an out-of-loop sensor in this case.
From the plot it is apparent that the 60 Hz line noise raises the rms to few 100 pm level.
 

       How to improve it ?     

According to my quick calculation if we can exclude the 60 Hz line noise from the rms integration, the rms becomes about 70 pm, which is nice.
I somehow believe this line noise comes from the ALS servo and is injected to the coil-magnet actuator.
So I propose to lower the UGF and make it lower than 60 Hz such that
the servo doesn't react to the 60 Hz line noise and hence no 60 Hz noise injection to the arm displacement.
In any case lowering the UGF is better since our ALS sensor sees only noise above 40 Hz according to the previous noise measurement (#5970)
  6127   Sat Dec 17 00:00:03 2011 kiwamuUpdateGreen Locking60 Hz line nose gone

Quote from #6126
As shown in the noise budget below, the 60 Hz line noise currently dominates the arm displacement.

 The 60 Hz line noise has gone away.

It turned out that the line noise came from an oscilloscope.
The oscilloscope had been connected to a SR560, which amplifies the frequency-discriminated signal before the ADC as a whitening filter.
I still don't have a good explanation for it, but somehow connecting the oscilloscope made the line noise pretty high.
  6129   Sat Dec 17 03:59:32 2011 kiwamuUpdateSUSAborted Hysteresis test

Quote from #6128

To test it, we are shaking all of the suspension biases +/-1.0 with a script.

The hysteresis test has been aborted.

All of the suspensions have accumulated unexpectedly big DC biases of about 5 from their nominal points.

In fact the ITMX and ITMY mirrors started being stacked to their OSEMs.
The script process has been force-quit and I have restored all the DC biases to their nominal points.
They still look okay: MC can be locked at the 00 mode, DRMI fringe is visible at AS, the green beams are resonating the arm cavities
Need another trial.
  6132   Sun Dec 18 16:16:55 2011 kiwamuUpdateSUSAnother trial of Hysteresis test

Koji has modified the script for the hysteresis measurement.

A new test started from 16:05 PT, Dec 18th and takes a couple of hours to finish the measurement.

Do not touch the suspensions until further notice.

Quote from #6129

The hysteresis test has been aborted.

Need another trial.

  6133   Sun Dec 18 18:45:22 2011 kiwamuUpdateGreen LockingY arm ALS : time series and noise budget
As I said in the previous entry (#6126) my current goals were :
 (1) Take a noise budget when the standard ALS configuration is applied
 (2) Take a beautiful time series to show how ALS brings the cavity to the resonance point

Here are the latest plots that I have obtained from the Friday night:

    Time Series   

time_series.png

 The data starts from a point where the cavity is kept away from the resonance point by 200 kHz (in terms of the green laser's frequency).
Then 30 sec after, a cavity sweep started until the main laser becomes resonant for the arm cavity.
After 2.5 minutes the sweep was quit and the arm length was held at this point to show the
stability of the ALS servo.
 
         Noise Budget         

Yarm_ALS_2011DEC17.png

The residual motion in the arm displacements reached 70 pm in rms.

Note that the UGF was at about 100 Hz.
One of the improvements we made in the Friday was the removal of the 60 Hz line noise (#6127).
Currently the rms is dominated by two components:
     (1) A bump around 10 Hz, which is due to lack of the servo gain around there.
         => This can be improved by optimizing the servo filter shape
     (2) High frequency noise above 40 Hz.
         => This can be improved by either decreasing the noise itself or lowering the UGF.
  6134   Sun Dec 18 19:56:00 2011 kiwamuUpdateSUSAnother trial of Hysteresis test

The measurement finished at ~ 21:50 PT.

Quote from #6132

A new test started from 16:05 PT, Dec 18th and takes a couple of hours to finish the measurement.

Do not touch the suspensions until further notice.

  6135   Sun Dec 18 23:00:22 2011 kiwamuUpdateSUSoplve recenterd

I have recentered the oplev beams, including BS, ITMs and ETMs.

  6136   Mon Dec 19 01:54:35 2011 kiwamuUpdateSUSanother trial of hystersis test

Another hysteresis test has begun at 1:50 PT, Dec/19.

It will finish after 3 or 4 hours. During the measurement the PSL mechanical shutter will be kept closed.

Time record                       
   Start:  Dec/19 1:50 PST
   End :  Dec/19  5:30 PST
  6140   Wed Dec 21 03:38:14 2011 kiwamuUpdateGreen LockingY arm ALS : automation script 80 % done

Scripting of the single arm automated lock script is 80% done.

The remaining 20 % is not something immediately needed and I start decreasing the priority on the Y arm ALS.

(Remaining stuff)

  • Automated optimization of I/Q phases at the frequency discriminator's signal.
    • this part will be done after we install Jamie's new beat box
  • A routine function which checks if the beat note is within a reasonable bandwidth
    • This part can be done with the frequency-divided signal and the digital delay line frequency discriminator
    • Another approach is to install a frequency counter, which doesn't have to be so precise
  • A state bit which tells us how far the script goes
  • An exit handler.
    • This should run whenever the script is unexpectedly force-quite, to gently bring the ALS system down.
  • A servo which brings the beat frequency to exactly a point where the infrared light is on a resonance point
    • Currently this part is partially human-aided. I put a little bit of correction in the frequency offset by looking at time series
    • To automate this part, we need another LOCKIN system to shake the arm length and demodulates the transmitted light
  6141   Wed Dec 21 04:29:01 2011 kiwamuUpdateGreen LockingPower Recycled Single Arm

I made the first trial of locking a Power-recycled single arm.

 This is NOT a work in the main stream,

but it gives us some prospects towards the full lock and perhaps some useful thoughts.

 

      Optical Configuration         

  • Y arm and PRM aligned. They become a three-mirror coupled optical cavity
    • Power Recycling Cavity (PRC) is kept at anti-resonance for the carrier when the arm length is off from the resonance point
    • Hence bringing the arm length to the resonance point lets the carrier resonate in the coupled cavity
    • BS behaves as a loss term in PRC and hence results a low recycling gain
  • Everything else are misaligned, including ITMX, ETMX, SRM and BS
    • Therefore there are neither Michelson, X arm nor Signal Recycling Cavity (SRC)

   Lock Acquisition Steps    

  1. Misalign PRM such that there is only Y arm flashing at 1064 nm
  2. Do ALS and bring the arm length to the resonance point
  3. Record the beat-note frequency such that we can go back to this resonance point later
  4. Displace the arm length by 13 nm, corresponding to a frequency shift of 200 kHz in the green beat note
  5. Restore the alignment of PRM.
  6. Lock PRC to the carrier anti-resonance condition using REFL33I. At this point the arm doesn't disturb the lock because it is off from the resonance anyway
  7. Reduce the displacement in the arm and bring it back to the resonance

 

     Actual Time Series     

Below is a plot of the actual lock acquisition sequence in time series.

time_series.png

  • The data starts from the time when the arm length was kept at the resonance point by the  ALS servo.
    • At this point PRM was still misaligned.
  • At 120 sec, the arm length started to be displaced off from the resonance point.
  • At 250 sec, the alignment of PRM was restored and the normalized DC reflection went to 1.
    • Error signals of PRC showed up in both REFL33 and POOY11
  • At 260 sec, PRC was locked to the carrier anti-resonance point using the REFL33_I signal.
    • Both REFL33 and POY11 became quiet.
    • REFLDC started staying at 1, because the carrier doesn't enter to the cavities and directly goes back to the REFL port.
  • At 300 sec, the arm length started to be brought to the resonance point.
  • At 400 sec, the arm length got back to the resonance point.
    • The intracavity power went to 3.5 or so
    • REFLDC went down a bit because some part of the light started entering in the cavities
    • REFL33 became noisier possibly because the Y arm length error signal leaked to it.
  6143   Wed Dec 21 14:41:22 2011 kiwamuSummaryGeneralminutes of 40m meeting : short-term plan

Here is the Gantt chart we discussed in the 40m meeting today.

Based on the discussions we had, I applied a little bit of corrections on the chart but the main stream remains the same.

40mproject.png

  6144   Wed Dec 21 16:55:30 2011 kiwamuUpdateGreen LockingPower Recycled Single Arm
 I did some brief parameter checks for the power-recycled single arm which I have done yesterday.
The purpose is to make sure that the interferometer and I weren't crazy.
So far the measured quantities look reasonable.
  

         Assumptions on the parameter estimations          

   No losses.
   Tprm = 0.05637
   Titm =0.01384
   Tetm = 15 ppm
   Tbs = 0.5
 
        Parameter estimations and comparison with measurement      
   Recycling gain G = Tprm / (1 - ritm * rprm * Tbs) = 0.21 
   Amplitude reflectivity of the arm rarm =   (retm - ritm) / (1 - ritm * retm) = 0.99785
   Effective ITM's amplitude reflectivity ritm' = ( ritm + rprm * Tbs) / (1 + ritm * rprm * Tbs) = 0.9976
   Arm finesse = pi * sqrt (ritm' * retm) / (1 - ritm' * retm) = 1298
 
  + Power build up from single arm to power-recycled arm = G / Tprm = 3.73
      => measured value is 3.8 at maximum
 
  + Reflectance of the coupled cavity R = ( rprm -  rarm * Tbs )2 / (1 - rprm * rarm * Tbs  )2 =  0.841
     => measured value was about 0.85 at minimum
 
 
  + Cavity full linewidth = lambda / arm_finesse / 2 = 0.41 nm
     => narrower than that of the usual single arm by factor of 2.9
     => I guess this was the reason why the intracavity power looked more fluctuating after everything was locked

Quote from #6141

I made the first trial of locking a Power-recycled single arm.

 

  6145   Thu Dec 22 19:15:22 2011 kiwamuUpdateGreen Lockingrearrangement of PSL green optics
 As planed (#6143), rearrangement of the PSL green setup has begun.
It required to move approximately half of the green optics on the PSL table
and I finished displacing and installing the necessary optics coarsely.
So far I just have recovered the Y arm beat-note between the PSL green light.
 
 I will do a fine alignment of the X arm path on the PSL table and try obtaining the X arm beat-note tonight.
  6147   Fri Dec 23 01:07:41 2011 kiwamuUpdateGreen Lockingrearrangement of PSL green optics part II

After I did a fine alignment of the X green beam path on the PSL table, the X arm beat-note was also obtained.

Here is a picture of the latest setup. The blue lines represent S-polarizing green beams.

newLayout.png

During I was working on the PSL table HEPA was at 80 %, and after the work I brought it to 20 %.

Quote from #6145
 I will do a fine alignment of the X arm path on the PSL table and try obtaining the X arm beat-note tonight.

  6149   Mon Dec 26 12:04:41 2011 kiwamuUpdateCDSc1gcy.ini hand edited

I have edited c1scx.ini by hand in order to acquire some green locking related channels.

Somehow c1sus.ini, c1mcs.ini, c1scx.ini and c1scy.ini are not accessible via the daqconfig script.

As far as I remember it had been accessible via daqconfig a week ago when I edited c1scy.ini.

Anyway I had to edit it by hand. They need to be fixed at some point

  6150   Mon Dec 26 14:01:45 2011 kiwamuUpdateLSCmultiple-LOCKIN newly added
The multiple LOCKIN module has been newly added on the LSC realtime model.
The purpose is to demodulate ALL the LSC sensors at once while a particular DOF is excited by an oscillator.
So far the model has been successfully compiled and running okay.
I will make some MEDM screens for this multiple-LOCKIN system.
 

(Some details)

The picture below is a screen shot of the LSC real time model, zoomed in the new LOCKIN part.

multiple-lockin.png

The LOCKIN module consists of three big components:

  1. A Master oscillator
    • This shakes a desired DOF through the LSC output matrix and provides each demodulator with sine and cosine local oscillator signals.
    • This part is shown in the upper side of the screen shot.
    • The sine and cosine local oscillator signals appear as red and blue tags respectively in the screen shot.
  2. An input matrix
    • To allow us to select the signals that we want to demodulate.
    • This is shown in the left hand side of the screen shot.
  3. Demodulators
    • These demodulators demodulate the LSC sensor signals by the sine and cosine signals provided from the master oscillator.
    • With the input matrix fully diagonalized, one can demodulate all the LSC signals at once.
    • The number of demodulators is 27, which corresponds to that of available LSC error signals (e.g. AS55_I, AS55_Q, and etc.).
    • This part is shown in the middle of the screen shot.
  6151   Tue Dec 27 16:56:15 2011 kiwamuUpdateLSCScmitt trigger installed
The old trigger system has been replaced by Schmitt triggers in the c1lsc realtime model.
They seem working correctly.
  

      An example              

Here below is a picture of time series showing how the Schmitt trigger works as an example.
trigger_time_series.png
 
 In order to check the new trigger, I injected a fake sine signal into the TRY path to simulate lock acquisition of the Y arm with TRY used as a trigger.
Then I monitored the trigger signal, called C1:LSC-YARM_TRIG_MON.
This variable is a boolean, and hence it returns zero when the trigger is off and one when it is on.
I set the upper and lower thresholds to be 0.6 and 0.2 respectively.
As shown in the picture, the trigger became on when the TRY sine curve crossed the upper threshold of 0.6.
After that the TRY signal then crossed the lower threshold of 0.2 and the trigger became off.
 

      How to set the thresholds         

The setting procedure is the same as before.
  1. Open the trigger matrix window, which is accessible from the C1LSC overview screen as usual.
  2. Then type the desired upper and lower thresholds into the column.

The below is a screenshot of the trigger matrix screen. The thresholds column is pointed by a big white arrow.

 trig_mat.png

Of course, DO NOT set the upper threshold value to be smaller than that of the lower threshold. Otherwise it won't correctly work.

Also if you want to have the usual trigger rather than the Schmitt trigger, simply put the upper and lower thresholds at the same values.

 

 

      Details         

 Here I explain how the new trigger exactly work.
The attached screen shot below is the actual c1lsc simulink model, zoomed in the blocks of the MICH trigger.
model_trigger_edit.png
 
    The signal flows from the left hand side to the right hand side and the resultant output is always either zero or one.
There are two variables, which you can control via EPICS: TRIG_THRES_ON and TRIG_THRES_OFF.
Those two variables correspond to the upper and lower thresholds respectively.
   An important thing is that there are two key components: "UnitDelay" and "Choice" blocks.
First of all the code checks whether the trigger used to be ON or OFF at the "Choice" block by looking at the TRIG_MON data which is from the past.
The "Choice" block is configured such that if the TRIG_MON value used to be True, it lets the TRIG_THRES_OFF signal go through.
And if the TRIG_MON used to be False, then it lets the TRIG_ON signal go through.
Therefore this procedure breaks the situation into two cases : trigger used be ON and OFF, and depending on the situation it returns a proper threshold.
     After this check, the code does the usual triggering.
The proper threshold from the "Choice" block will be compared with an LSC signal at ">" block.
If the LSC signal is greater than the threshold value then it gives one and enables the feedback.
 
  6152   Tue Dec 27 22:17:56 2011 kiwamuUpdateLSCmultiple-LOCKIN new screens

Some new screens have been made for the new multiple-LOCKIN system running on the LSC realtime controller.

The medm screens are not so pretty because I didn't spend so long time for it, but it is fine for doing some actual measurements with those new screens.

So the basic works for installing the multiple-LOCKIN are done.

 

 The attached figure is a screen shot of the LOCKIN overview window.

As usual most of the components shown in the screen are clickable and one can go to deeper levels by clicking them. 

Untitled.png

Quote from #6150
The multiple LOCKIN module has been newly added on the LSC realtime model.
I will make some MEDM screens for this multiple-LOCKIN system.

  6153   Tue Dec 27 23:03:56 2011 kiwamuUpdatePSLPMC realigned

I have realigned the steering mirrors for PMC because the transmitted light had been at ~ 0.741

After the alignment it went back to ~ 0.850.

  6154   Wed Dec 28 14:13:16 2011 kiwamuUpdateGreen LockingALS feedback on MC2

I added an ALS feedback path on the MC2 suspension and this path will enable us to stabilise the MC length using the ALS scheme.

  The actual digital signal is transmitted from the c1gcv realtime controller to the c1mcs realtime controller through the c1rfm realtime process.
Or in terms of the machines, the signal is transmitted from C1IOO to C1SUS via the reflective memory network.
 
The attached figure is a screen shot of the MC2 position controller screen.  The new ALS path is emphasized by a purple circle in the figure.
MC2_ALS.png

Quote from #5888

Leaving a note on the ALS feedback before I forget:

The MC2 suspension needs to have an input for the ALS feedback in the realtime model like ETMs.

 

  6155   Fri Dec 30 02:16:48 2011 kiwamuUpdateGreen LockingYarm ALS : high frequency noise reduced

The high frequency noise, which has been a dominant noise above 30 Hz in the Y arm ALS (#6133), decreased by a factor of 5.

This reduction was done by increasing the modulation depth at the Y end PDH locking. Now the noise floor at 100 Hz went to 0.2 pm/sqrtHz.

However the noise source is not yet identified and hence it needs a further investigation.

 

 The attached figure is the sensor noises, which were taken from the beat-note signal while the arm was locked by the IR-PDH.
The orange curve is the one before I changed the modulation depth and the red curve is the one taken after I increased the modulation depth.
The high frequency noise went down from 1 pm/sqrt Hz to 0.2 pm/sqr tHz at 100 Hz.
 
Yarm_ALS_2011Dec29.png

 (Increasing the modulation depth)

  Actually I was going to check the RAM noise at the Y end PDH locking as I planed (#6143).
During some preparation for it, I found that there had been a 20 dB attenuator in the modulation LO path.
The reason we have kept it is that somehow a big modulation depth made the reflected DC light noisier.
For curiosity I removed it to see what will happen and took the noise spectra. Then the noise decreased as shown in the plot above.
It means the noise source was like a kind of sensor noise, whose level depends on the responsivity of the sensor.
As far as I can tell, it is not the dark noise or shot noise according to some quick measurements.
  6156   Fri Dec 30 22:05:16 2011 kiwamuUpdateLSCpower normalization in LSC

Now a power normalization is doable for the LSC error signals.

It is working fine, but at some point we may want to have some kind of a saturation filter or limiter to avoid dividing a signal by a small number.

 

 (How to set the normalization)

  •   Click a small matrix panel on the LSC OVERVIEW window (shown in the attached screen shot below).
    •     This will give you a pop-up-window, which shows a matrix to route the normalization signals
POW_NORM_MTRX.png
  •   Choose a numerator channel, which you want to divide, and choose denominator channels, which you want to use as a power normalization factor.
  •   Put some number in the corresponding matrix elements.
  •   Once you put a non-zero element in the matrix, the corresponding numerator channel will be divided by the specified denominator channels.
    •     Otherwise the static normalization factors (e.g. C1:LSC-AS55_POW_NORM, etc.,) will be used for the denominator.
  6158   Tue Jan 3 15:48:39 2012 kiwamuUpdateLSCpower normalization in LSC

It turned out that the power normalization need a modification.

I will work on it tomorrow and it will take approximately 2 hours to finish the modification.

 

     Concept of Power Normalization         

Koji pointed out that the dynamic power normalization, which I have installed(#6156),  should be placed after the LSC input matrix rather than before the matrix.
Now let us review the concept of the power normalization to avoid some confusions.
We will need two kinds of power normalizations as follows:
  1.  Static power normalization, which should be placed before the input matrix.
  2.  Dynamic power normalization, which should be placed after the input matrix.
 The static power normalization will be applied to each I and Q signals in all the LSC signals and also DCPD signals.
This normalization is supposed to cancel the effects from the incident laser power and depths of the phase modulations.
Because the variations in the laser power and modulation depth are expected to be relatively slow, we will apply static normalizations.
 
 The dynamic power normalization will be applied to the DOFs error signals, for example C1:LSC-DARM_IN and so on.
This normalization is supposed to cancel the effect of the internal states of the interferometer, for example alignments.
In addition to it, this dynamic normalization can expand the linear range of the error signals.

Quote from #6156

Now a power normalization is doable for the LSC error signals.

 

  6164   Wed Jan 4 00:43:06 2012 kiwamuUpdateIOOMC became flaky

I don't know what exactly is going on, but MC became flaky and it's been frequently unlocked.

I have turned off the MC WFS servo to check if the WFSs are doing something bad. But it still tends to be unlocked without the WFS servo.

Right now it doesn't stay locked for more than 10 min.

  6166   Wed Jan 4 03:03:24 2012 kiwamuUpdateLSClocking activity tonight and beyond
Last night and tonight, I was doing a kind of rehabilitation -- locking PRMI and DRMI with the new trigger system.
Although MC wasn't so awesome (#6164), I confirmed that the DRMI can stay locked with the conventional RFPD combination (#4760).
Additionally I have modified the IFO configure scripts, such that they also automatically restore the thresholds values for triggering.
The scripts are available in the C1IFO_CONFIGURE screen as usual.

 

       Locking plan            

Here is a plan in my mind and these are basically the details of the gantt chart (#6143):

  • (1 day task) Measurement of the recycling gains of the RF sidebands with the PRMI and DRMI configuration, using POP22/110 RFPD.
    • I need to have confidence that I am really locking the DRMI with SRC resonating to 55 MHz.
    • Also those values will enable us to estimate losses and mode matching again (maybe ?).
  • (3-4 days task) Measurement of the sensing matrix using the multiple-LOCKIN system.
    • Write a script to automatically measure the sensing matrix. This must be easy.
      • The results will enable us to diagonalize the input matrix and therefore it eventually gives more solid lock of the DRMI
      • Also it will give us the optical gains of 3f signals. So this is actually a step toward the 3f signal check.
  • (3-4 days task) Noise budgeting on the 3f signals
    • This is a very important part of the DRMI characterization because the results will tell us whether we can hold the DRMI lock with a sufficient SNR or not.
    • If it turns out that they don't have good SNRs, we then have to come up with some ideas to improve the SNRs.
  • (Extra fun task depending on schedule) 3f DRMI lock + Y arm ALS
    • If the beat-box electronics are not available by the time when the work above are completed, I will do this fun task.
    • Probably it is better to start preparing the common mode servo electronics because it will be needed anyway.

 

  6167   Wed Jan 4 05:02:58 2012 kiwamuUpdateLSCSidebands measurement at POP
Just a quick report:
I did the first attempt to measure the recycling gains of the sidebands in the DRMI configuration (sidebands resonant condition)
by looking at the output of the POP22/110 RFPD.
Because this time what I measured is some absolute values of the sidebands power,
it doesn't tell us anything quantitatively until we calibrate it or compare it with similar data.
So I need to measure the same things in some different configurations (e.g. PRMI, SRMI, etc.)
in order to extract some useful information from the measurement.
 
The attached picture is the display of a power spectrum analyzer looking at the output of the POP22/110 broadband RFPD
while the DRMI (in the sideband resonant condition) was kept locked.
You can see that 111 MHz (twice of 55 MHz) is prominent. Also there are several peaks at 11, 22, 44 and 66 MHz.
SB_DRMI.png
  6170   Wed Jan 4 16:22:30 2012 kiwamuUpdateLSCpower normalization in LSC : modification done

The dynamic power normalization system has been modified such that the normalization happen after the LSC input matrix.

The attached screen shot below tells you how the signals flow.
The red circled region in the picture is the place where the power normalization are performed.
pow_norm.png
 
The dynamic normalization will be activated once you put some numbers into the elements in the matrix.
Otherwise the error signals are always normalized by 1.

Quote from #6158

It turned out that the power normalization need a modification.

I will work on it tomorrow and it will take approximately 2 hours to finish the modification.

 

  6175   Fri Jan 6 01:00:56 2012 kiwamuUpdateCDSc1scx out of sync

Both the c1scx and its IOP realtime processes became out of sync.

Initially I found that the c1scx didn't show any ADC signals, though the sync sign was green.

Then I software-rebooted the c1iscex machine and then it became out of sync.

For tonight this is fine because I am concentrating on the central part anyway.

  6181   Mon Jan 9 13:19:09 2012 kiwamuUpdateSUSETMX damping restored

No we can't do that because the c1scx model is not working properly.

If you look into the real time controller screen you will find what I mean.

Quote from #6180

ETMX sus damping restored

  6182   Mon Jan 9 23:52:15 2012 kiwamuUpdateCDSSUS channels not accessible from dataviewer

[John / Kiwamu]

 We found that some of the suspensions channels (for example C1:SUS-BS_POS_IN1 and etc) were not accessible from dataviewer for some reasons.

So far it seems none of the channels associated with c1sus are accessible from dataviewer.

  6183   Tue Jan 10 00:09:33 2012 kiwamuUpdateLSCspike hunting in REFL33

[John / Kiwamu]

 We tried to figure out what is causing spikes in the REFL33 signal, which is used to lock PRCL.

No useful information was obtained tonight and it is still under investigation.

 


(Background)

 One thing preventing us from doing smooth measurements of the noise budget and the sensing matrix is some sharp spikes in the LSC error signals.

For example when we lock PRMI with REFL33 and AS55 fedback to PRCL and MICH respectively, both the REFL33 and AS55 signals show some spikes in time series.

Those spikes then bring the noise spectra higher than how they should be.

So for the reason, taking the noise budget doesn't give us much information about the interferometer rather than there are spikes.

Also the sensing matrix measurement has been suffered from those spikes, which excite the impulse responses of the low pass filters in the LOCKIN detection systems a lot.

 

(What we did)

 We looked into the actual analog signals to see if there are indeed spikes or not before they are acquired to the ADCs.

But we didn't find any corresponding spikes in the signals that are after the mixers.

It maybe because the signals we looked into didn't have high enough SNR because they were coming out from the monitor lemo outputs on the demod boards.

 Then we thought the spikes are from the whitening circuits, due to some kind of saturation.

We decreased the gain of the whitening filters by a factor of 10, but it didn't help and the spikes were still there.

  6187   Thu Jan 12 03:05:02 2012 kiwamuUpdateLSCOSA installed in AS

[John / Valera / Kiwamu]

 We installed a new weapon, an optical spectrum analyzer in the AS port.

Like we used to do in the old days, two BNC cables were newly laid down and they bring the output of the OSA to the control room to monitor the spectrum with an oscilloscope.

 

(Some notes)

The photo diode of the OSA was replaced by a Thorlab PDA100A to amplify the signals.

The carrier peak is at about 6.9 V and the f1 and f2 sidebands peaks are at about 40 mV when the beam is in straight shot (everything is misaligned except ITMY and BS).

According to a rough calculation, those numbers correspond to a modulation depth of about 0.16 or so.

The depth agree with what Mirko measured before (#5519)

 

  6202   Tue Jan 17 01:02:07 2012 kiwamuUpdateLSCglitch hunting in REFL RFPDs : strange

A very strange thing is going on.

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

This noise shows up even when the beam is single-bounced back from PRM ( the rest of the suspensions are misaligned) and it's very repeatable.

Any idea ?? Am I crazy ?? Is PRM making some fringes with some other optics ??

 

 

(background)

 The most annoying thing in the central part locking is glitches showing up in the LSC error signals (#6183).
The symptom is that when the motion in PRCL at 3 Hz becomes louder, somehow we get glitches in both the MICH and PRCL error signals.
In the frequency domain, those glitches are mostly contribute to a frequency band of about 30 - 100 Hz.
Last Thursday Koji and I locked the half PRM (PRMI with either ITMX or ITMY misaligned) to see if we still have the glitches in this simpler configuration.
Indeed there were the same kind of glitches --a loud 3 Hz motion triggers the glitches.
It was shown particularly in the REFL11 signal but not so much in the REFL33 while AS55 didn't show any glitches.
 
 
(Still glitches even in the single bounce beam)
   We were suspecting some kind of coupling from a beam jitter, so that the 3 Hz motion somehow brings the beam spot to a bad place somewhere in the REFL paths.
I misaligned all the suspensions except for PRM such that the beam directly bounces back from PRM and go to the REFL port.
Indeed there still were glitches in the REFL11 and REFL55 demod signals. It showed up once per 30 sec or so and pushes up the noise floor around 30 - 100 Hz.
There might be a little bit of glitches also in the REFL33, but the ADC noise floor and the expected glitch noise level were comparable and hence it was difficult to see the glitches in REFL33.
 

(Glitch is related to the PRM POS actuation)

 In the single-bounce configuration I started shaking the PIT and YAW motions of PRM at 3 Hz using the realtime LOCKIN oscillator to see if I can reproduce the glitches.
However no significant glitches were found in this test.
Then I started shaking the POS instead of the angular DOFs, and found that it causes the glitches.
At this point it didn't look like a glitch any more, it became more like a stationary noise.
 
 The attached screen shot is the noise spectrum of the REFL11_I.
The red curve is the one taken when I injected the 3 Hz excitation in POS by the LOCKIN oscillator.
The excitation is at 3 Hz with an amplitude of 1000 counts.
As a comparison I plotted the same spectrum when no excitation was injected and it is plotted in pink.
 

 PRMsingle_bounce.png

It seems there is a cut off frequency at 100 Hz.
This frequency depends on the amplitude of the excitation -- increasing the amplitude brings the cut off frequency higher.
This noise spectrum didn't change with and without the oplevs and local damping.
 

(Possible scenario)

A possible reason that I can think of right now is : PRM is interfering with some other optics for some reason.
But if it's true, why I didn't see any fringes in the AS demod signals in the half PRM configuration ?
 

Quote from #6183

 We tried to figure out what is causing spikes in the REFL33 signal, which is used to lock PRCL.

No useful information was obtained tonight and it is still under investigation.

  6203   Tue Jan 17 02:27:49 2012 kiwamuUpdateLSCfringe tests : all the suspensions are innocent

I did a quick test to check a hypothesis that PRM is interfering with some other optics in the single bounce configuration.

I shook all the suspensions (except the MC mirrors) at 3 Hz in POS, PIT and YAW with an amplitude of 1000 counts.

No effects were found in the REFL demod signals.

So it is NOT a fringe effect caused by the other suspended mirrors.

Quote from #6202

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

Is PRM making some fringes with some other optics ??   

 

  6204   Tue Jan 17 02:44:59 2012 kiwamuUpdateCDSawg not working

AWG is not working. This needs to be fixed.

I could set the channel and the parameters in the AWGGUI screen, but it never inject signals to the realtime system.

  6205   Tue Jan 17 03:10:27 2012 kiwamuConfigurationIOOrotated lambda/2 plate

I have slightly rotated the lambda/2 plate, which is used for attenuating the REFL beam's power on the AS table

because the plate had been at an unusual angle for investigation of the glitches since last Thursday.

It means the laser power going to the coating thermal noise setup has also changed. Just keep it in mind.

Quote from #6198

So today we set up the Jenny RC temperature setup to lock the LWE NPRO to the RC and then set up the beat note with the IFO REFL beam on the AS table. By using the 2 laser beat, we are avoiding the VCO phase noise issue which used to limit the PSL frequency noise at ~0.01 Hz/rHz. To do this we have reworked some of the optics on the PSL and AS tables, but I think its been done without disturbing the beams for the regular locking. Beat note has been found, but the NPRO has still not been locked to the RC - next we setup the lockin amp, dither the PZT, and then use the New Focus lock box to lock it to the RC.

  6206   Tue Jan 17 13:47:40 2012 kiwamuUpdateLSCdirty steering mirror in the REFL path

 Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.

Looking at it through an IR viewer, I saw the REFL beam hitting one of the biggest dust particles on that mirror.

This dust particle maybe causing the glitches or maybe not.

Anyway because it's always better to have clean mirrors, I will wipe the steering mirror in this evening and check the presence of the glitches again.

Quote from #6202

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

Is PRM making some fringes with some other optics ??
 

  6207   Tue Jan 17 16:09:20 2012 kiwamuUpdateCDSawg not working on the c1sus machine

Actually awg works fine without any problems when the excitation channels belong to the c1lsc machine.

It seems that the awg doesn't inject signals on the channels of the c1sus machine, for example C1:SUS-BS_LSC_EXC and so on.

Quote from #6204

AWG is not working. This needs to be fixed.

  6209   Wed Jan 18 12:36:26 2012 kiwamuUpdateLSCwiped a steering mirror on the REFL path

I wiped both surfaces of the REFL second steering mirror.

However no improvements. The glitches still remain.

 

(Pic.1 before wiping, Pic.2 after wiping)

DSC_3861_small.jpgDSC_3863_small.jpg

Quote from #6206

 Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.

  6211   Wed Jan 18 14:28:36 2012 kiwamuUpdateLSCestimation of optical length between PRM and scattering object

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 

 (The measurement)

  In order to estimate the optical length between PRM and a scattering body, I swept the frequency of the main laser by actuating on the MC length.
With the sweep, the laser frequency go across some fringes and basically it allows us to estimate the FSR of a very low finesse cavity formed by PRM and the scattering body.
Therefore we get the the optical distance based on the resultant FSR.
 
  The measurement goes as follows:
  1.  Preparation : calibration of the MC2 actuator as a frequency actuator (for more details, see the next section)
  2.  Set the interferometer to the single-bounce configuration such that the beam directly is reflected back from PRM
  3.  Take spectra of REFL11_I without driving any optics. This spectra tells us how quiet the noise normally is.
  4.  Drive MC2_POS at 10 Hz with an amplitude of 10000 counts so that we can see the high frequency up conversion noise
    • The frequency was chosen such that the excitation is out of the local damping bands
    • The amplitude was chosen to be as big as possible until the MC unlocked
    • With this drive, the laser frequency should change by 20 MHz peak-peak at 10 Hz.
  5.  Record the noisy spectrum when the MC2_POS was driven.
  6.  Drive PRM instead of MC2 at 10 Hz.
    • Adjust the amplitude of the excitation such that the cut-off frequency of the up conversion noise matches with that of the MC2 driven case.
    • The amplitude was found to be 1700 - 2000 counts, this uncertainty is currently limiting the precision of the optical distance estimation.
    • With this amount of the drive, PRM moves by 0.8 um peak-peak at 10Hz.
  7. Estimate the optical length based on the amount of the drives for PRM and MC2.
    • Estimate the FSR using the following relation df/FSR = dx/ (lambda/2). => FSR = 17 MHz
    • Since FSR = c/ (2L),  L = c/(2 FSR) = 9.5 m or so
scattering.png

 

 

(Calibration of the MC2 actuator)

 To do the measurement described above, the MC2 actuator must be calibrated in terms of a frequency actuator.
I did the same old technique (#4721): lock a cavity, adjust the UGF as low as possible, and shake an actuator of interest.
This time I used the half-PRM (PRM + ITMY) for this measurement.
The actuator responses are calibrated from that of displacement to frequency by using df/f = dx/L and assumed that L = 6.760 (#4585).
Also the PRM actuator was measured such that we can use this as a reference since we already know the response in displacement (#5637).
 The attached plot below is the actual responses that I measured yesterday. The y-axis is calibrated to Hz/counts.
 

 

calibration.png

 

Quote from #6202

Is PRM making some fringes with some other optics ??

  6212   Wed Jan 18 16:31:10 2012 kiwamuUpdateLSCestimation of optical length between PRM and scattering object

I searched for a scattering body in the REFL path.

According to the result the REFL path on the AS table is innocent.

 

The idea of the search method is given as follows:

  •   Put a 1/10 ND attenuator at the origin of the REFL path on the AS table.
  •   Of course this reduces the signal level by the same factor of 10 in the REFL11_I demod signal.
  •   If the scattering body is in the REFL path the up conversion noise will be smaller by a factor of 100 because the scattered light go across the attenuator twice.

 

 The attached plot below is the spectra of REFL11 with the 1/10 attenuator at the origin of the REFL path when the beam is single-bounced from PRM.
In the measurement PRM_POS was driven at 10 Hz with an amplitude of 1700 all the time. This is exactly the same situation as that explained in the previous elog entry (#6211).
You can see that the up conversion noise level also decreased by the same factor of 10, which suggests there are no scattering object in the REFL path.
Note that the data with the attenuator in place is intentionally scaled by multiplying a factor of 10 for comparison.
ND1atten.png
 

Quote from #6211

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 

ELOG V3.1.3-