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.

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.

 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.

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

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

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.

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

[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.

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):

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

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

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

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.

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

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.

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.

No real progress.

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

(what I did)

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.

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.

• 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.

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

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

       About Noise Budget       

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.

The hysteresis test has been aborted.

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

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.

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

    Time Series   

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

The measurement finished at ~ 21:50 PT.

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

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.

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

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.

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.

         Assumptions on the parameter estimations          

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 %.

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

(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.

      An example              

      How to set the thresholds         

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.

      Details         

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. 

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.

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 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.

 (Increasing the modulation depth)

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.

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         

1.  Static power normalization, which should be placed before the input matrix.
2.  Dynamic power normalization, which should be placed after the input matrix.

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.

       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.

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

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.

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.