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ID Date Author Type Categoryup Subject
  5937   Fri Nov 18 00:36:23 2011 ZachUpdateGreen LockingY-Arm PDH box modified

I modified the Y-Arm PDH box (S/N 17) to have the same TF as the one of the temporary setup described in Kiwamu's earlier entryNote that the TF below was taken with the gain knob set to 0, so that the proper DC gain is achieved with a setting of ~4. This is desirable because it gives us wiggle room.

The changes were:

  • R14: 25 -> 50
  • R29: 1k -> 10.5k
  • R30: 1k -> 20k
  • R28: 102 -> OMIT
  • C20: 84nF -> OMIT
  • R31: SHORT -> 475
  • R16: 10k -> 48.7k
  • R24: 10 -> 5

Below is the TF along with the LISO model. They are different at low frequencies because the box must have been railing internally (though the phase shows that the result is as expected), and there is a feature around 60 kHz that probably arises from some op amp instability. I will see if adding a small cap somewhere does the trick, and then take a new TF with a lower source voltage.

pdh17_tf_vs_liso_11_17_11.png

I'll try to lock the arm with the box tomorrow.

  5945   Fri Nov 18 11:28:39 2011 ranaUpdateGreen LockingY end green PDH servo : it's okay

Quote:

Quote from #5914
So I have added an SR560 in the other input of the Newfocus servo box to make the filter shape 1/f^2.
I will post the servo shape and diagram later.

 Another way to make a 1:100 pole:zero boost is to use resistors and capacitors in a Pomona box 

mixer -> LB box -> Pomona box -> PZT

Pomona Box =     R1 = 7.2 kOhm, C2 = 22 uF, R2 = 72 Ohms     (sr560 = $2400, pomona ~ $50)

 

For the RMS calculation, it would be good to notch out the harmonics. They don't matter since our ALS feedback will have notches at those frequencies.

  5946   Fri Nov 18 12:11:24 2011 ZachUpdateGreen LockingY end green PDH servo : it's okay

Quote:

 

 Another way to make a 1:100 pole:zero boost is to use resistors and capacitors in a Pomona box 

mixer -> LB box -> Pomona box -> PZT

Pomona Box =     R1 = 7.2 kOhm, C2 = 22 uF, R2 = 72 Ohms     (sr560 = $2400, pomona ~ $50)

 

For the RMS calculation, it would be good to notch out the harmonics. They don't matter since our ALS feedback will have notches at those frequencies.

I wouldn't bother...

  5956   Sat Nov 19 00:47:24 2011 ZachUpdateGreen LockingY-Arm locked with PDH Box #17

I installed the newly modified PDH box #17 and locked the Y-Arm.

I wasn't able to bring the REFL level down to the 30% that Kiwamu claimed to get, despite readjusting the alignment---I got ~40-45%. I attained a UGF of ~8 kHz, lower than the 20 kHz that Kiwamu said he got with the temporary setup, probably because the PDH box just isn't as fast. Despite that, it looks like the error suppression is actually better than before...

Here is an error spectrum:

error_sig_m_11_18_11.png

I have to admit that this calibration is worthy of suspicion and should be done more rigorously. I simply used the measured UGF frequency and known servo TF and PZT actuator gain to estimate the optical response. I am pretty confident that it's accurate to within a factor of 3 or so.

  5970   Mon Nov 21 16:08:04 2011 kiwamuUpdateGreen Locking2nd trial of Y arm ALS noise budget : broad band noise gone

Quote from #5930

Right now the fluctuation of the green beat-note seems mostly covered by unknown noise which is relatively white.

The 2nd trial of the Y arm ALS noise budgeting :

(Removal of broad band noise)

  + The broad band noise decreased somewhat after I fixed a broken connection in the discriminator.
  + I took a look at the frequency discriminator setup and found one of the SMA-BNC adapter was broken.
     This adapter was attached to one of the outputs of the 4-way power splitter, which splits the signal into the coarse and find discriminator paths.
     And this broken adapter was in the coarse path, which actually I am not using for the noise budget.
     Depending on the stress acting on the adapter it was creating broadband noise, even in the fine path.
     So I threw it away and put another SMA-BNC adapter.
 
Here is a plot of the latest noise : high frequency noise is still unknown.

Yarm_ALS_2011Nov19.png

I will add the dark noise of the broad-band beat-note PD  and the MFD read out noise on the budget.

  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
  5983   Wed Nov 23 00:00:53 2011 ZachSummaryGreen LockingSome issues on the Y end green PDH locking

Quote:

(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.

What is meant by the "average response of 50 dB"? Is this dB[ RIN / Hz ] or something? Also, do you mean the average over a broad band or the average response at the chosen modulation frequency over several trials? I don't really understand what measurement was done.

  5987   Wed Nov 23 13:53:36 2011 ZachUpdateGreen LockingSensor noise

The in-loop Y-Arm error signal looks equal to the beat note noise divided by the Y-Arm OL gain in the broadband-noise region (>20 Hz), which would be the case if the loop was dominated by sensor noise here.

I would re-check the Y-Arm dark noise, or at least check for coherence between the Y-Arm error signal and the beat signal above 20 Hz. The input-referred PDH box noise should not be flat there according to the LISO model, but that might be worth checking, too.

Yarm_ALS_2011Nov19_marked.png

  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.

AMTF_lightwave.png

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.

  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.

  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.
  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.

  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

  6120   Wed Dec 14 14:40:53 2011 steveUpdateGreen Lockingdelay line bnc cable specs

The existingly used used Pasternack Enterprices RG58 C/U cable lenght ~ 140 ft and the specs are here at Atm1

 

Atm2 The performance grade RG58-P coaxial cable specs.

  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.
  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.
  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.
  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.

  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.
  6214   Fri Jan 20 15:59:02 2012 kiwamuUpdateGreen LockingY arm ALS noige budget

One of my goals in this week is : measurement of the current best ALS noise budget.

Last night I took a new noise spectra of the Y arm ALS, which is shown in the attached figure below.

The displacement of the arm cavity observed from the IR PDH is at 66 pm in rms. In the measurement the arm length was stabilized with the ALS technique.

 

Yarm_ALS_2012Jan19.png

 

  6215   Fri Jan 20 16:24:50 2012 kiwamuUpdateGreen LockingY arm ALS : time series

Here is a new time series plot showing how stably ALS can control the arm length.

In the middle of the plot the cavity length was held at the resonance point for ~ 2 min. and then it passed through the resonance point to show the full shape of the PDH signal.

Apparently the PDH signal is now quieter than before (#6133)

time_series.png

Quote from #6214

One of my goals in this week is : measurement of the current best ALS noise budget.

 

  6216   Fri Jan 20 17:05:59 2012 ranaUpdateGreen LockingY arm ALS : time series

                        One of my goals this week is to get people to make plots with physical units:

That ALS plot would be 5x cooler if the POY11 signal could be in meters instead of counts or cubits.

  6220   Tue Jan 24 18:11:13 2012 kiwamuUpdateGreen LockingY arm ALS noise budget

I did some more stuff for the Y arm ALS and updated the noise budget:

After the works, the rms displacement improved a little bit, so it is now at 24 pm in rms.

Though, it turned out that the MFD's ADC is now limiting the noise in a frequency band of 200 mHz - 5 Hz.

So tonight I will increase the gain of the whitening filter to push down the ADC noise more.

 

Yarm_ALS_2012Jan19.png

 

(What I did)

 + added the DAC noise and comparator noise based on measurements.

 + redesigned the servo filter shape to suppress the seismic noise below 10 Hz.

 The attached plot below shows the newly designed open loop transfer function together with the old one for a comparison.

UGF is at 120 Hz and the phase margin is about 27 deg.

  newservo.png

  • FM7 = resonant gain (17)
  • FM6 = resonant gain (3)
  • FM5 = zero(1) * pole(500)
  • FM4 = pole(1) * zero(40.) * 40.
  • FM3 = pole(1) * zero(40.) * 40.
  • FM2 = pole(0.001)*zero(1)*1000.
  6221   Wed Jan 25 02:59:46 2012 kiwamuUpdateGreen LockingY arm ALS noise budget

Surprisingly increasing the gain of the whitening filter didn't improve the noise curve.

It suggests that the ADC noise is not the limiting factor below 10 Hz.

Quote from #6220

Though, it turned out that the MFD's ADC is now limiting the noise in a frequency band of 200 mHz - 5 Hz.

So tonight I will increase the gain of the whitening filter to push down the ADC noise more.

 

  6223   Wed Jan 25 17:32:03 2012 steveUpdateGreen Lockinggeen pointing into y arm is misaligned

I  placed an other Y2-LW-1-2050-UV-45P/AR steering mirror into the beam path of the green beam launching in order to avoid the ~30 degrees use of the 45 degrees mirror. The job is not finished.

  6225   Thu Jan 26 06:09:52 2012 kiwamuUpdateGreen Lockingnoisy AS55

During the Y arm ALS I found that the noise of the AS55 demod signal was worse than that of POY11 in terms of the Y arm displacement.

There is a bump from 500 mHz to 100 Hz in the AS55 signal while POY11 didn't show such a structure in the spectrum.

 

The plot below is the noise spectra of the Y arm ALS. The arm length was stabilized by using the green beat-note fedback to ETMY.

In this measurement, POY11 and AS55 were served as out-of-loop sensors, and they were supposed to show the same noise spectra.

In the plot It is obvious that the AS55 curve is louder than the POY curve.

Yarm_ALS_2012Jan25.png

  6227   Thu Jan 26 10:17:01 2012 steveUpdateGreen Lockinggeen pointing into y arm is realigned

Quote:

I  placed an other Y2-LW-1-2050-UV-45P/AR steering mirror into the beam path of the green beam launching in order to avoid the ~30 degrees use of the 45 degrees mirror. The job is not finished.

 The alignment is finished after the realization that the 3rd steering mirror had to be adjusted too.

The input power increased from 1.2 to 1.4 mW

  6230   Fri Jan 27 05:21:43 2012 kiwamuUpdateGreen Lockingfine alignment of the Y end green setup

I did a fine alignment on the Y end green setup. The green light became able to be locked again.

Quote from #6227

 The alignment is finished after the realization that the 3rd steering mirror had to be adjusted too.

  6234   Fri Jan 27 16:55:28 2012 JenneUpdateGreen LockingY-green realigned

The Yarm green laser really wanted to lock on a 01/10 mode, so Kiwamu suggested I go inside and realign the green beam to the arm.  I did so, and now it's much happier locked on 00 (the Yarm is resonating both green and IR right now).

  6299   Tue Feb 21 08:33:16 2012 steveUpdateGreen Lockingperiscope adapter plate

Two extender plates ready for cleaning. The existing optical table tops have 38" OD. Using two of these the OD will be 44"

  6301   Tue Feb 21 18:39:11 2012 kiwamuUpdateGreen LockingNew BBPDs installed

Two new BBPDs have been installed on the PSL table.

The first one was installed by Koji a few days ago, and I stalled the second one today.

They will serve as beat-note detectors for the green locking.

Next step : I have to lay down a long SMA cable which goes from the BBPD to the IOO rack.

  6324   Mon Feb 27 14:35:37 2012 JenneUpdateGreen LockingPSL Beat Setup

Xarm is aligned for both IR and green. 

Here is a photo of the beam paths of the PSL beat setup.  I want to make sure that the X-green BBPD sees a nice beam from both the PSL and the Xarm, without disturbing the currently working Y setup.  I keep getting confused with all the beamsplitters, especially the green PBSes, which operate at ~56deg, not 45deg, so I made a diagram.

BeatPSLlayout_27Feb2012.png

  6326   Mon Feb 27 18:35:45 2012 JenneUpdateGreen LockingX Beat Search

Meh.  I've searched in steps of 20 counts in C1:GCX-SLOW_SERVO2_OFFSET units (16 bit +\- 10V DAC, and 1GHz/V coeffecient for the Xgreen aux laser means this is ~0.6MHz per 20 count step).  I went from -400cts to +800 cts and haven't found the beatnote yet.  Meh. 

Both PSL green and Xgreen beams are going to the Xgreen BBPD.  Both beams are easily visible, so while I didn't actually measure the power, it should be sufficient.  The arm is being re-locked in green for each step, but it's not locked in IR, but that doesn't matter for just finding the beatnote.

I've got the output of the BBPD directly connected to the 50 ohm input of the HP8591E spectrum analyzer, with the freq span from 10MHz to 120MHz.  The BBPD is supposed to be good up to ~100MHz, so I should catch any beatnote that's there.  I have to head out, so I guess I'll continue the search tomorrow. 

One of Kiwamu's suggestions was that, since no one is using the Ygreen concurrent with my fiddling, I rotate the waveplate after the PSL doubling oven so that max power goes to the Xgreen path, thus giving myself a bigger signal.  I'll try that tomorrow.  Today, I didn't ever touch the waveplate.

  6342   Wed Feb 29 20:27:00 2012 JenneUpdateGreen LockingX green beat - found it!

Found it!

The actual temperature of the Xend laser is 0.02 C higher than anticipated based on the formula in elog 3759.  Both the PSL and the Xend laser are at their nominal diode currents (2.100 A for the PSL, 2.003 A for Xend), so the curves should be used as they are.  The PSL temp (when the slow servo offset is ~0) is 31.71 C.  Using curve 2 from elog3759, the Xend laser should be 37.78, which I found was +10 counts on the Xgreen slow servo offset. 

Right now the Xend laser is at 37.80 C, and the beat is around 30 MHz.  This is +80 counts on the Xgreen slow servo.  +60 counts gave me ~80 MHz.  When (a few minutes ago) the MC unlocked and relocked, it came back to a slightly different place, so the temp of the Xend laser had to go up a few 10's of counts to get the same beat freq.  Right now the PSL slow servo offset is 0.076 V. 

The HP8591E is set with ResBW=100kHz, Ref Level= -39dBm (so I'm not attenuating my input signal!).  The largest peak I see for the beatnote is -66dBm.  The nose floor around the peak is -83dBm.  Trace (trace button!) A is set to MaxHoldA, and Trace B is set to ClearWriteB, so B is giving me the actual current spectrum, while A is remembering the peak value measured, so it's easier to see if I went past the peak, and just didn't see it on the analyzer. 

Also, I went back and realigned the beams earlier, to ensure that there was good overlap both near the BS which combines the PSLgreen and Xgreen beams, and at the PD.  The overlap I had been looking at was okay, but not stellar.  Now it's way better, which made the peak easier to see.  Also, also, the waveplate after the doubling oven on the PSL table is still rotated so that I get max power on the Xgreen side of things, and not much at all on the Ygreen side.  I'll need to rebalance the powers, probably after we make sure we are seeing the beatnote with the BeatBox.

Next Steps:

Lay a cable from the BBPD to the BeatBox in 1X2, make the BeatBox do its thing.

Use the dichroic locking to do a sweep of the Xarm.

  6371   Wed Mar 7 11:44:29 2012 JenneUpdateGreen LockingXgreen beatnote cable made, laid

The Xgreen PD now has a cable going over to the beatbox. Once beatbox characterization is done I can re-find the beat, and we can do some stuff with the beatbox.

  6395   Fri Mar 9 16:00:46 2012 steveUpdateGreen Lockinglaser emergency shut down switch replaced at the south end

Over-sized local laser emergency switch was held by large C clamp at the south end. This was replaced by a smaller one and it is mounted with magnets.

The Innolight laser was turned off, while the interlock was wired.

  6413   Wed Mar 14 10:06:26 2012 steveUpdateGreen Lockingdichroic mirror quotes

Dichroic mirror quotes are in the wiki.

ATF is pricy.

We got a good price from Laseroptik, but the wedges are 5 arcminutes. The fused silica grade is 0F, meaning the  homogeneity is 5 ppm instead of 1ppm.  I requested an other large wedge quote on the substrates.We may have to get substrates from somebody else and ship it to Germany

MLT quote is outrageously high

REO is not interested in this low volume job.

 

  6435   Thu Mar 22 08:14:21 2012 steveUpdateGreen Lockingdichroic mirror quotes with large wedge

Quote:

Dichroic mirror quotes are in the wiki.

ATF is pricy.

We got a good price from Laseroptik, but the wedges are 5 arcminutes. The fused silica grade is 0F, meaning the  homogeneity is 5 ppm instead of 1ppm.  I requested an other large wedge quote on the substrates.We may have to get substrates from somebody else and ship it to Germany

MLT quote is outrageously high

REO is not interested in this low volume job.

 

 The Laseroptik quote is here.The 2 degrees wedge cost is $40 on each optics!  See wiki

  6603   Fri May 4 17:46:46 2012 JenneUpdateGreen LockingPSL doubling oven back on

While walking past the PSL, I noticed that the PSL's doubling oven's heater was still disabled from the power outage.  As with the ETMY heater, I hit the Enable button, and it started warming up (according to the front panel at least).

  6713   Wed May 30 01:35:15 2012 yutaUpdateGreen Lockingaligned Y arm green beam

[Jenne, Yuta]

We aligned the Y arm for IR (C1:LSC-TRY_OUT is now ~ 0.9), and aligned the green beam from the ETMY table. The Y arm green is now resonating in TEM00 mode, but we need some monitors (green trans or green refl) to maximize the coupling.

We noticed that the MC beam spot are oscillating at ~ 1 Hz, mostly in YAW.  This wasn't observable before the PMC realignment (elog #6708). We should find out why and fix it.

  6724   Thu May 31 01:27:16 2012 yutaUpdateGreen LockingPSL and Y arm green beams aligned

[Jenne, Yuta]

We aligned the PSL green optics so that the PSL green beam and Y arm green beam interfere. 2 beams are now hitting the Y arm beat PD. The DC level from the beat PD is about 13 mV.

We didn't try to see the beat signal for today, because the temperature of the doubling crystal seemed funny. We need to look into it tommorow.

Currently, the temperature control is enabled and the set point is 36.9 deg C, but the temperature is stuck at 33.0 deg C.

  6725   Thu May 31 01:36:17 2012 yutaUpdateGreen LockingGREEN_TRX/GREEN_TRY PDs

I did the cabling for monitoring DC transmission of the green beam from the end table.
The two PDs are called GREEN TRX and GREEN TRY, and the channel names are C1:GCV-GREEN_TRX and C1:GCV-GREEN_TRY.
The two signal from the PDs go to the ADC_0 card of the c1ioo computer.

Now, C1:GCV-GREEN_TRX/Y are actually connected to the respective PDs, but green beams are not hitting on the PD. We need two pickoff mirrors.

  6731   Thu May 31 16:19:07 2012 yutaUpdateGreen Lockingtemperature setting for PSL doubling crystal

I fixed the temperature control of the oven for the PSL doubling crystal.
The PID settings were not good, and also, TC200 was beging DETUNED. So, I activated TUNE function and adjusted PID settings.
I'm not sure what the DETUNE function is for. The manual can be found here;
   http://www.thorlabs.com/thorproduct.cfm?partnumber=TC200

Current settings for Thorlabs TC200 are (Red ones are what I changed from the previous setting);

parameters Xend Yend PSL
TEMP SET (deg C) 37.5 35.7 36.9
P 250 250 250
I 60 60 200 (was 117)
D 25 25 40 (was 19)
(DE)TUNE on? TUNE TUNE TUNE (was DETUNE)
TMAX (deg C) 200 200 170
PMAX (Watts) 18 18 18
temperature sensor PTC100 PTC100 PTC100
ELOG V3.1.3-