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ID Date Authorup Type Category Subject
  5975   Tue Nov 22 04:02:47 2011 kiwamuUpdateIOOchanged MC alignment

I have changed the MC2_YAW DC bias because the PZT1_YAW was railing.

I also realigned the steering mirrors in zig-zag path since the mode cleaner tended to resonate with higher order modes after I have changed the MC2 bias.

  C1:SUS-MC2_YAW_COMM =  -1.1548    => -1.1208

  5978   Tue Nov 22 15:18:18 2011 kiwamuUpdateGreen Lockingbroad band noise depends on the gain of Y green PDH. and comaprator broken

Quote from #5970
Here is a plot of the latest noise : high frequency noise is still unknown.

(The broad-band noise vs. gain of the Y end green PDH)

 Last night I was trying to identify the broad band noise which is white and dominant above 20 Hz (#5970).

I found that the level of the noise depended on the servo gain of the Y end green PDH loop.

Decreasing the servo gain lowers the noise level by a factor of 2 or so. This was quite repeatable.

(I changed the gain knob of the PDH box from the minimum to a point where the servo starts oscillating)


(Malfunction in the comparator)

  However I had to give up further investigations because the comparator signal suddenly became funny: sometimes it outputs signals and sometimes not.

It seems the comparator circuit became broken for some reason. I will fix it.

  5980   Tue Nov 22 18:42:10 2011 kiwamuSummaryGreen LockingSome issues on the Y end green PDH locking

[Rana / Kiwamu]

 As a part of the ALS noise budgeting we took a look at the Y end PDH setup to see if we are limited by an effect from the Amplitude Modulation (AM).

Then we found two issues :
 (1) a big variation in AM transfer function from the laser PZT to the intensity of the frequency-doubled laser. We haven't figured out the reason yet,
 (2) some of the optics and their mounts need to be refined.


(AM transfer function)

 One of the suspicious noise source of the Y arm ALS was an AM effect in the Y end green PDH locking.
A possible scenario is that: there is some amount of the offset in the PDH signal due to the AM at the modulation frequency,
and it allows the intensity noise to couple to the laser frequency, which we want to suppress.
 So we wanted to check if the measured AM (#2799) at 1064 nm  is still true at 532 nm.
The problem right now is that : every time we measured the AM transfer function by exciting the laser PZT with swept sine,
the transfer function varied by 20 dB, with average response of 50 dB. And there was no repeatability.
We were using the PD which is for the green PDH signal and the single-bounced light from ETMY.
The measurement was done in a frequency band of 100 - 400 kHz where we expect a couple of sharp notches.
Perhaps we should try the same measurement with IR first to make sure we are doing a right thing, and then do it with the frequency-doubled laser.


(Y table setup needs more improvements)

  We found some optics and their mounts which need to be refined.
Here is a list which we briefly made at the time.
  • Use washers
  • Beam clipping in Green Faraday and the very last mirror
  • Use two screws and wide base plate
  • Tune PPKTP PID parameters
  • Remove flipper mirror
  • Move the mechanical shutter to where the beam size is smaller
  • Put a beam damp for the reflected light from the PD
  • Cable rack
  • Improve the incident angle on the last two launching mirrors
  5982   Tue Nov 22 23:06:13 2011 kiwamuUpdateSUSMC watchdogs

[Rana / Mirko / Kiwamu]

 The watchdogs on the MC suspensions are not working.

Switching off the watchdogs doesn't stop feeding signals to the suspensions.

For tonight, we will leave the controller of the MC suspensions switched off so that the computer won't smash the optics accidentally.

  5993   Thu Nov 24 01:28:09 2011 kiwamuUpdateGeneral1X8 sorensen came back

Quote from #5963

 - One of the Sorensens in 1X8 rack is showing the current limit sign. This is exactly the same situation as we saw before (#5592).

       Currently it's off. It needs an investigation to find who is drawing such a large amount of current.

 The 1X8 Sorensen's issue has been solved somehow.

 To investigate what is going on with the Sorensen in the 1X8 rack, I turned on the Sorensen.
Then this time it didn't show the current limit sign, the voltage went up to 15.0, where it is supposed to be.
Surprisingly this is exactly the same recovery process as we saw before (#5592).
  6002   Thu Nov 24 15:27:15 2011 kiwamuUpdateCDSc1iscey hardware rebooted
The c1iscey machine crashed around 1:00 AM last night and I did a hard-ware reboot by pressing a button on the front panel of the machine.
After the reboot its been running okay so far.
The crash happened after I pressed the "Diag Reset" button on the CDS status screen.
  6018   Sat Nov 26 19:07:40 2011 kiwamuSummaryGreen LockingAM trnasfer function of the Y end laser with doublin crystal

Quote from #5980

 As a part of the ALS noise budgeting we took a look at the Y end PDH setup to see if we are limited by an effect from the RF Amplitude Modulation (AM).

The AM transfer function of the Y end laser has been measured again, but using the frequency-doubled laser this time.

Here is the latest plot of the AM transfer function. The Y-axis is calibrated to RIN (Relative Intensity Noise) / V.

IFBW (which corresponds to a frequency resolution) was set to 100 Hz and the data was averaged about 40 times in a frequency range of 100 kHz - 400 kHz.

Also the zipped data is attached.


It is obvious that out current modulation frequency of 179 kHz (178850 Hz) is not at any of the notches.

It could potentially introduce some amount of the offset to the PDH signal, which allows the audio frequency AM noise to couple into the PDH signal.

Currently I am measuring how much offset we have had because of the mismatched modulation frequency and how much the offset can be reduced by tuning the modulation frequency.

Attachment 2: AMTF_cailbrated.bod.zip
  6020   Mon Nov 28 06:53:30 2011 kiwamuUpdateCDSc1sus shutdown

I have restarted the c1sus machine around 9:00 PM yesterday and then shut it down around 4:00 AM this morning after a little bit of taking care of the interferomter.

Quote from #6016

c1sus has been shutdown so that the optics dont bang around.  This is because the watch dogs are not working.

  6024   Mon Nov 28 15:00:20 2011 kiwamuUpdateGreen LockingY arm ALS engaged
Quote from #5894

  However I couldn't close the ALS loop somehow.

 Locking activity last night:

  It became able to close the ALS loop (beat-note signal was fed back to ETMY).

The UGF was about 60 Hz, but somehow I couldn't bring the UGF higher than that.

Every time when I increased the UGF more than 60 Hz, the Y end PDH was unlocked (or maybe ETMY became crazy at first).

Perhaps it could be a too much noise injection above 60 Hz, since I was using the coarse frequency discriminator.

Anyway I will try a cavity sweep and the successive noise budgeting while holding the arm length by the beat-note signal.

Another thing : I need a temperature feedback in the Y end green PDH loop, so that the PZT voltage will be offloaded to the laser temperature.

  6026   Mon Nov 28 16:46:55 2011 kiwamuUpdateCDSc1sus is now up

I have restarted the c1sus machine and burt-restored c1sus and c1mcs to the day before Thank giving, namely 23rd of November.

Quote from #6020

I have restarted the c1sus machine around 9:00 PM yesterday and then shut it down around 4:00 AM this morning after a little bit of taking care of the interferometer.

  6027   Mon Nov 28 16:51:57 2011 kiwamuUpdateLSCmodulation frequency reset

I reset the modulation frequency to 11065910 Hz (#5530). It had been at 11065399 Hz probably since the power shut down.

  6028   Mon Nov 28 18:19:53 2011 kiwamuUpdateIOOStochmon seems working

Here is a 48 hours trend of the RFAM monitor (a.k.a StochMon):


The upper plot is the DC output from the StochMon PD and the lower plot shows the calibrated RIN (Relative Intensity) at each modulation frequency.

I have downloaded minutes trends of StochMon for 48 hours staring from 6:00AM of Nov/24.

I followed Koji's calibration formula (#6009) to get the actual peak value (half of the peak-peak value) of the RF outputs and then divided them by the DC output to make them RIN.

It looks the RINs are hovering at ~ 4 x 10-4 and fluctuate from 1x10-4 to 1x10-3. Those numbers agree with what we saw before (#5616)

So it seems the StochMon is working fine.

Quote from #6009

 New RFAM mon calibration

  6033   Tue Nov 29 04:47:49 2011 kiwamuUpdateCDSc1sus shut down again

I have shut down the c1sus machine at 3:30 AM.

  6042   Tue Nov 29 18:54:29 2011 kiwamuUpdateCDSc1sus machine up

[Zach / Kiwamu]

 Woke up the c1sus machine in order to lock PSL to MC so that we can observe the effect of not having the EOM heater.

  6044   Tue Nov 29 22:10:18 2011 kiwamuUpdateRF SystemRFAM fluctuation reduced

Quote from #6035

I left the EOM stabilization running overnight, so we can finally see how the EOM temperature stabilization does over long periods of time.

The controller was turned on at ~8:40 UTC, and you can see that the Stochmon signals quiet down a lot right at that time. 

Indeed the fluctuation of the RFAM became quieter with the temperature control ON.

However the absolute value of the RFAMs stayed at relatively high value.

I guess we should be able to set the right temperature setpoint such that the absolute value of the RFAM is smaller.

Here is the calibrated RFAM data (for 5 hours around the time when Zach activated the temperature control last night):


  6050   Wed Nov 30 03:01:55 2011 kiwamuUpdateRF SystemRFAM fluctuation reduced

Okay I have turned ON the temperature control at 2:40 AM and will leave it ON for a while.

Quote from #6047

I was hesitant to claim that this is definitely true without the control data we were taking after the heater was turned off today. This is because before I replaced the malfunctioning op amp last night, the heater was actually ON and injecting temperature noise into the system that would not be there with it off. I think the best idea is to compare the data from today (heater on vs. heater off, but with functioning circuit).


  6060   Thu Dec 1 17:33:18 2011 kiwamuUpdateSUSwatchdogs fixed

The watchdogs' issue has been solved and they are now working fine.

It was just because one of the Sorensens had been off.

The Sorensen is the one supplying +5 V in the 1X5 rack.
This +5 V is actually used as a pull-up-current to properly drive the MAX333As (CMOS analog switch) in the coil drivers (D010001).
So this was it.

Quote from #6010

Tonight we noticed that, in fact, the watchdogs don't work for any of the corner optics (I confirmed that they do work for the ETMs).

  6071   Mon Dec 5 17:44:41 2011 kiwamuUpdateGeneralmy plan tonight

I am going to try handing off the ALS servo to the IR PDH servo on the Y arm and measure the noise.

 - first I need to investigate why the Y end PDH servo becomes unstable when the ALS is engaged with a high UGF.


(some notes)

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

Every time when I increased the UGF more then 50 Hz, the Y arm PDH lock became unlocked. It needs an explanation and a solution.

Another thing: During several trials in this evening I found the ETMY_SUSPOS_GAIN had been set to 1, so I reset it to 20, which gives us the damping Q of about 5.


(Temperature feedback activated)

 As planed in #6024 I have activated the temperature feedback, so that the PZT control signal is offloaded to the temperature. And it seems working fine.

Currently the gain is set to 0.03, which gives us a time constant of ~30 sec for offloading the control signal.

  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.


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.


(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.


  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.


       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   


 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         


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.


  • 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.


  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.


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.


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.
 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.


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.




 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.
    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. 


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.

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.

 (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
  •   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.


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