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ID Date Authorup Type Category Subject
  5788   Wed Nov 2 19:32:20 2011 kiwamuUpdateLSCPOP22/110 installed

[Steve / Kiwamu]

 The POP22/110 RFPD has been installed. It is PDA10A from Thorlabs instead of the usual home-made RFPD.
For an RF cable we rerouted one of the spare Heliax cables for it.
The cable is the one which used to be served for the 166MHz ASC wavefront sensors, picking up the RF source signal at 1X2 and sending it to the LSC rack.
 - - Remaining tasks - -
  + Fine alignment
  + Connection at the LSC rack
  + Update of the table diagram

Quote from #5783

They were traced and labeled. One goes to 1X2 and the other to AS-ISCT. They are Andrew Heliax 1/4" od. made by CommScone,  model number FSJ1-50A

  5794   Thu Nov 3 14:25:52 2011 kiwamuUpdateLSCPDA10A as POP22/110 : too small signal

It turned out that the signal was too small with PDA10A to detect the 22 and 110 MHz RF sidebands.

The DC output coming out from it was about half mV or so (corresponding to few uW in laser power) when the PRCL was locked to the carrier.

This is because PDA10A is a silicon detector which is more sensitive to visible light than IR.

The reason we chose PDA10A was that it has relatively a large diode size of 1 mm in diameter.

However according to the data sheet the responsibility at 1064 nm is about 0.05 A/W which is sad.

I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.

Though the diode size will be half mm in diameter, which may require another strong lens in front of it.

Quote from #5788
 The POP22/110 RFPD has been installed. It is PDA10A from Thorlabs instead of the usual home-made RFPD.
  + Fine alignment

  5796   Thu Nov 3 16:31:47 2011 kiwamuUpdateLSCPDA10CF as POP22/110 : better

The POP22/110 RFPD has been replaced by PDA10CF. As a result the 22 and 110 MHz signals became detectable.

However the signal level maybe too low according to a quick look with an RF spectrum analyzer.

The level at 22 and 110 MHz were both approximately -70 dBm although these values were measured when the central part was freely swinging.

Perhaps we need to amplify the signals depending on the actual SNR.


 Also I have updated the optical tables' wiki page :


Quote from #5794

I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.

  5801   Thu Nov 3 18:41:36 2011 kiwamuUpdateLSCPOX11 demod board : haven't been modified yet

I pulled out the POX11 demod board and found the power splitter on the board hadn't been modified yet.

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

Quote from #5753
The POX11 demodulation board is broken

  5802   Thu Nov 3 19:58:18 2011 kiwamuUpdateLSCPOX11 demod board : modification done

The modification on the POX11 demod board has been successfully done.

I followed the procedure which had been posted in a past entry (#4554).

The home-made splitter was replaced by PSCQ-2-51W, which has a relatively wide band of 5 - 50 MHz.

The usual orthogonality adjustment will be done in the daytime.


 The attached snapshot was taken when an sinusoidal RF signal with a slight frequency offset from LO was injected to the RF input.

It is clear that the I and Q output show healthy signals (i.e. almost the same amplitude and 90 deg phase difference.)


Quote from #5801

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

  5806   Fri Nov 4 05:24:56 2011 kiwamuUpdateLSCoffset introcuded in MC and IFO-configure script modified

[Offsets in MC]

 I have introduce an offset in MC2 PIT because the PZT1 again started railing.

Right now the PZT1 EPICS value is within the range happily.

Please keep this MC eigen axis as a nominal configuration.


[IFO-configure script]

 I have modified the IFO configure scripts such that XARM and YARM are locked with POX11 and POY11 respectively.

A big advantage in use of POX and POY is that we don't need to misalign ITMs when we align each arm.

Those scripts are now available from the C1IFO_CONFIGURE screen as usual.

  5817   Sat Nov 5 00:04:23 2011 kiwamuUpdateASCASS scripts gone

Did somebody delete all the scripts in /opt/rtcds/caltech/c1/scripts/ASS ?

  5820   Sat Nov 5 04:30:21 2011 kiwamuUpdateGreen LockingRe:Passive summing box modifications

I think you also should check the PZT's capacitance of the 700mW LightWave because 2.36 nF is the one for the 1W Innolight laser.

Quote from #5807

To combat this, I propose we simply change the resistor in the modulation path from 1M to 10k. This leaves the feedback path TF unchanged, and changes the mod path into a sort of bandpass filter for the modulation frequency. The fact that the phase is near zero at fmod means we don't have to come up with some way to phase shift the signal for demodulation.

  5838   Mon Nov 7 22:20:18 2011 kiwamuUpdateGreen LockingRe:YARM length fluctuation

A nice plot !

Can you put another y-axis on the right hand side of the same plot  in terms of the cavity displacements ?

And can you also measure a more important spectrum, namely the suppressed error signal ?

Quote from #5837

I measured the power spectrum of channel C1:GCY_SLOW_SERVO1_IN1, which is the PZT driving voltage.

  5849   Wed Nov 9 14:49:07 2011 kiwamuSummaryLSCCharacterization of the Power Recycled Michelson


  The definition of the recycling gain is wrong here.

See the latest entry (#5875)


Here is a summary about the Power Recycled Michelson (PRMI).

It seems the mode matching is also one of the greatest contributor on the low recycling gain.



 (Estimated parameters)

    Loss = 5.3% (or effective reflectivity of  93.28% in Michleson) => Under coupling !!

     +  Mode matching efficiency = 47.4 %  => Really bad !!

   With these values we end up with a recycling gain of 7 and a normalized REFLDC of  0.5 as observed (#5773).

Also according the incident beam scan measurement (#5773) the loss is NOT a local effect like a clipping, it is more like uniformly distributed thing.

As for the mode matching, the number indicates that approximately the half of the incident light is coming back to the REFL port without interacting with PRMI.

This is bad because the non-mode-matched light, which is just a junk light, is entering into the photo detectors unnecessarily.

In the worst scenario, those junk light may create a funny signal, for example a signal sensitive to the alignment of PRM.


(Estimation method)

The method to estimate the loss and the MM (Mode-Matching efficiency) is essentially the same as before (#5541).

One difference from the previous estimation is that the I used more realistic parameters on the transmissivity of ITMs and PRM :

     PRM : T = 5.637 %  (see the 40m wiki)

     ITM : T = 1.384 %  (see the 40m wiki)


 In addition to the basic calculations I also made plots which are handy for figuring out where we are.

Quantities we can measure are the reflected light from PRMI and the recycling gain using the REFL PD and the POY PD respectively.

So I wanted to see how the loss and MM can be estimated from the measured REFL DC and recycling gain.

The plots below are the ones.

contour_loss.png   contour_MM.png

[Loss map]

 The first figure shows a contour map of the loss as a function of the measured REFL DC and recycling gain.

The white area is a place where no proper solutions can be found (for example MM can get to more than 100 or loss becomes negative).

The star mark in the plot corresponds to the place where we are now. Obviously the loss is about 5%.

If we somehow decrease the amount of the loss the star mark will mostly go up in the plot.

[MM map]
 The second figure shows a contour map of the MM as a function of the measured REFL DC and recycling gain. 

The X and Y axis are exactly the same as that of the first plot. Again the star mark represents the place where we are.

We are currently at MM=47%



Here are some solutions to bring the recycling gain higher.

We don't work on these things immediately since it requires opening of the chambers again and it will take some times.

But we should think about those options and prepare some stuff for a coming vent.

  + Refinement of the position of the mode matching telescopes.  => The Recycling gain can go up to 15.

     => Assuming the loss in the cavity doesn't change, the star mark in the first plot will go to the left hand side along the "0.05" black solid line.

     => However PRMI will be still under coupled.

     => Needs an estimation about which way we move the telescopes.

 + Locate the place of the dominant loss source and reduce it somehow.

    => The recycling gain will be more than 18 if the loss reduces by a factor of more than 5.

    => Needs a clever way to find it otherwise we have to do it in the classical way (i.e. white light and trying to find dirty surfaces)

  5850   Wed Nov 9 16:03:21 2011 kiwamuSummaryGeneralGoal this week

Goal of this week :  ALS on the Y arm

Minimum success : Detection of the green beatnote between the freq-doubled PSL and the Y arm transmitted light

  5852   Wed Nov 9 16:49:17 2011 kiwamuUpdateGreen LockingY end laser temperature with slow input connected

Indeed it is strange. I took a quick look at it.

In order to recover the same condition (e.g. the same amount of the reflected DC light and the same temperature readout),

it needed to have +8.9V in the slow input from the DAC through EPICS.

Obviously applying an offset in the slow input to maintain the same condition is not good.

It needs another solution to maintain the sweet frequency where the frequency of the PSL and the Y end laser is close in a range of 200 MHz.

Quote from #5797

Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.


  5860   Thu Nov 10 05:54:23 2011 kiwamuUpdateGreen LockingBeat-note detected : PSL vs Y arm

[Katrin / Kiwamu]
The beat-note between the PSL green laser and the Y end green laser was successfully detected.
The detection was done by the new broad-band RFPD.
The next step will be an extraction of the frequency fluctuation signal using the delay-line-mixer frequency discriminator.


Here is a picture of the RF spectrum analyzer displaying the direct output signal from the broad-band RFPD.
The beat-note was moving around 100 MHz with an RF power of -36 dBm. The frequency fluctuation was about +/- 7MHz in a time scale of 1 sec or so.

(What we did)
 + Connected a BNC cable which goes from the c1iscey's DAC to the laser slow input
    => this enables a remote control of the laser frequency via the temeperature actuation
 + Realigned the beam pointing of the Y end green laser
 + Installed all the necessary optics on the PSL table
     => currently the PSL green light is adjusted to completely S-polarization
 + readjusted the mode matching telescopes
     => the Y green beam becomes the one with a long Rayleigh range
 + Health check on the broad-band RFPD to see if it is working
 + Installed the BB-RFPD with a +/-15V power supply
 + Fine alignment of the beam combining path
 + Fine tuning of the Y end laser temperature
     => T_PSL = 31.72 deg when the slow FSS feedback is zero.
     => Based on Bryan's measurement (see #elog) the Y end laser temperature was adjusted to 34.0 deg by applying an offset to the slow input.
 + Found the beat note at 100 MHz or so.
     => optimizing the alignment of the beam combining path by maximizing the peak height of the beat-note.
     => maximum peak height observed with an RF spectrum analyzer was about -36 dBm.

  5875   Fri Nov 11 14:55:47 2011 kiwamuSummaryLSCCharacterization of the Power Recycled Michelson : take 2

Quote from #5851

The recycling gain is determined by the optical configuration and the optical loss in the cavity.

How much is the actual recycling gain? And how does it affect the signal extraction?

 As Koji pointed out I made a wrong definition on the recycling gain of PRMI (Power-Recycled Michelson Interferomter).

In the correct definition the estimated recycling gain is 15.
In order to answer Koji's second question,which is about the effect on the signal extraction,
I need to scratch my head for a while.
( Give me some time..)
The value what I called "Recycling gain" must have been called "measured power build up" or something like that.
For clarity I put the definitions of the quantities.
    Recycling gain :      rec_gain.png 

   Reflectivity of PRMI (measured by REFLDC): refl.png

    Power build up (measured by POY DC) : pbu.png

    Mode Matching (MM) efficiency :  MM.png

    Loss in the PRMI cavity : loss.png


 (Results of Measurement and Estimation)

     Estimated recycling gain = 15

     Estimated MM efficiency = 47.4%

     Estimated Loss = 5.3%

     Measured power build Up = 7

     Measured reflectivity of PRMI = 0.5

  5885   Mon Nov 14 11:32:02 2011 kiwamuSummaryGeneralGoal this week

Goal of this week : Noise budgeting on the Y arm ALS

Minimum success : bring the Y arm to the resonance by using ALS  NOISE BUDGETING!!!

 => as a preparation the incident beam pointing needs to be fixed by steering the MC suspensions.

Quote from #5850http://nodus.ligo.caltech.edu:8080/40m/5850

Goal of this week :  ALS on the Y arm (DONE)

  5888   Mon Nov 14 17:01:14 2011 kiwamuUpdateGreen LockingALS feedback on MC2

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.

  5890   Mon Nov 14 22:56:31 2011 kiwamuUpdateGreen LockingY end PDH lock : UGF at 17 kHz

[Tomotada / Kiwamu]

  The open loop transfer function of the Y end PDH loop was remeasured : the UGF was found to be at 17 kHz.

The phase margin at the UGF was about 27 deg.



While the measurement we noticed that the modulation onto the laser PZT was too big

and it was creating a big AM on the reflected light with an amplitude of a few mV.

So we put a 20 dB attenuator to decrease the modulations and the reflected light became much quitter.

Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).

  5894   Tue Nov 15 12:25:38 2011 kiwamuUpdateGreen LockingY arm ALS : beat-note free run fluctuation

Locking activity last night :

  The free run beat-note in 532 nm has been measured.

However I couldn't close the ALS loop somehow.

Every time I tried closing the loop it broke the Y end PDH lock in a couple of minutes.




 (Things to be done)

   1.  Optimization of the Y end PDH servo loop

      1.1 Measurement of the arm fluctuation => to allow re-designing the servo shape
      1.2 Preparation of PDH box, and temporary SR560 servo
      1.3 Sanity checks on the modulation depth, reflectivity, PD dark noise and etc.,
      1.4 Make the servo more robust
      1.5 Some modifications on the medm screens
      1.6 Activation of the temperature feedback through the realtime digital control

   2. Refinement of the broadband RFPD setup

      2.1 Investigation of the peak source => there was a relatively big peak around 50 MHz or so.
      2.2 Noise characterization of the frequency detection system
      2.3 Nicer routing of some cables.
      2.4 Make two-more ADC channel connectors
      2.5 Power budget on the PSL beat-note setup => estimate the expected RF level of the beat-note
      2.6 Realignment of the PSL doubling and resetting of the doubling oven temperature
  3. Noise budgeting
     3.1 IR locked condition  => measure the noise in the green beat-note system.
     3.2 ALS engaged condition
          3.2.0 shot noise
          3.2.1 ADC noise
          3.2.2 PD dark noise
          3.2.3 freq. discriminator noise
          3.3.4 DAC noise through the coil-magnet actuators
          3.3.5 End laser suppression
          3.3.6 Intensity noise
          3.3.7 Thermo-elastic noise
          3.3.8 Thermo-refractive noise


  5895   Tue Nov 15 15:16:04 2011 kiwamuUpdateCDSdataviewer doesn't run

Dataviewer is not able to access to fb somehow.

I restarted daqd on fb but it didn't help.

Also the status screen is showing a blank white form in all the realtime model. Something bad is happening.



  5914   Wed Nov 16 17:29:46 2011 kiwamuUpdateGreen LockingSome updates on the Y end green PDH
Quote from #5894

 (Things to be done)

   [DONE]   1.1 Measurement of the arm fluctuation => to allow re-designing the servo shape
   [DONE]   1.2 temporary SR560 servo
   [ONGOING]1.3 Sanity checks on the modulation depth, reflectivity, PD dark noise and etc.,
   [DONE]  1.4 Make the servo more robust
   [DONE]  1.5 Some modifications on the medm screens
   [NOTYET]   1.6 Activation of the temperature feedback through the realtime digital control

Some updates on the Y end green PDH lock

(Measurement of the Y arm fluctuation)

In order to design the PDH box's servo shape we wanted to measure the Y arm fluctuation.
Here is the spectrum taken by looking at the control signal before the laser PZT.
 The scale of the Y axis is calibrated by using the PZT response of 5 MHz/V.
Above 10 Hz the spectrum shows 1/f noise which I believe the laser frequency noise.

(Temporary servo setup)

 We have found that the servo shape was not enough (#5890) to well-suppress the fluctuation shown above.
 Since the Newfocus fast servo box only makes 1/f shape, the error signal wasn't suppressed within the linear range.
So I have added an SR560 in the other input of the Newfocus servo box to make the filter shape 1/f^2.
Then the lock became more solid and the reflected DC light in time series is now much flat if the alignments are good.
I will post the servo shape and diagram later.

(Sanity checks)

 I looked at the reflected DC light when the laser was kept locked.
The reflectivity of the Y arm cavity went down to about 30% and this is good because it is supposed to be 27.5% when it is locked according the spec.
This means the mode-matching is not so bad.
  5920   Thu Nov 17 03:46:52 2011 kiwamuUpdateGreen LockingPSL doubling had been diabled

I found that the temperature controller of the PSL doubling oven had been disabled.

Because of that I took a little bit long time to recover the beat-note.
I have no idea why its been disabled.
I turned it on to make the PSL green beam bright,
Also the I-parameter of the PID temperature control was too big
and because of that a big overshoot in the temperature happened (overshoot of ~ 5 deg !).
So I decreased the I-parameter from 175 to 85 (250 is the maximum).
Now the intensity of the green light seems reasonably bright and stable.
  5929   Thu Nov 17 17:21:22 2011 kiwamuUpdateGreen LockingY end green PDH servo : it's okay

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.

The Y arm green PDH servo is working fine with a sufficient amount of suppression.

(Servo filters)

 As reported on the previous elog entry (#5914) an SR560 was installed to provide one more pole-zero combination in the servo filter.
Here is a plot showing the transfer function of the latest servo filter.

And the servo configuration looks like this :


 The demodulated signal is split into two path; one goes directly to the Newfocus servo box and the other goes through SR560.
With the SR560 the two way summing path makes a pole at 1 Hz and zero at 100 Hz with when the SR560 has a gain of 100.
The overall gain is adjustable from a knob on the Newfocus servo box.

(the Error signal)

 One of the reasons we wanted to increase the servo gain was that :
the laser frequency has to be tightly locked to the Y arm motion because the laser frequency must represent the arm motion in our scheme.
Our requirement for allowing a successful ALS is : RMS < 10 pm (1/100 of the cavity linewidth)

I took a spectrum of the error signal when the laser was locked to the Y arm and found that it meets the requirement.


 In the plot I also put a dark noise from the PD to make sure the in-loop noise is above the dark noise.
Right now the power lines at 60 Hz and 180 Hz are lifting the RMS up.
Note that the UGF was at 20-30 kHz.
  5930   Thu Nov 17 18:20:26 2011 kiwamuUpdateGreen LockingY arm ALS : 1st trial of noise budget

The noise budget on the Y arm ALS has begun.

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

(Though I feel I made a wrong calibration ... I have to check it again)



(Measurement condition)

 + The Y arm is locked to the PSL laser by acting o ETMY.
 + The end green laser is locked to the Y arm.
 + The fine resolution MFD (Mixer-base Frequency Discriminator) is used to observe the beat-note fluctuation
   (We have two MFDs : fine resolution and coarse resolution.)
  5942   Fri Nov 18 02:50:10 2011 kiwamuUpdateIOORF generation box : power switch malfunction

[Suresh / Kiwamu]

 The power switch button of the RF generation box is not properly working

For tonight we are leaving it as it is but it needs to be fixed at some point.


(the Story)

While I was working around the green broad-band RFPD, I noticed that the RFPD was detecting the 25 MHz modulation signal.
To confirm if it really comes from the modulation source, I switched OFF the RF generation box by pressing the blue LED power button on the rear side of it.
The 25 MHz signal in the RFPD disappeared. So it was indeed the 25 MHz modulation signal.
Then I pressed the LED button again to bring it ON, but the switch didn't stay in the clicked position.
Keeping pressing the button could make it ON but once I released my finger from it it became OFF.
So the mechanical thing in the LED button is not properly working.
I removed the box from the 1X2 rack to take a look at it.
With a help from Suresh we somehow managed to keep it ON after several trials of pressing it.

The temporary solution we decided is to leave it ON so that we can survive tonight.

The box was back in place. The MC is find and 11 MHz and 55 MHz seem okay.


Please be aware of it.



This is a picture showing the rear view of the RF generation box. The red arrow is pointing the blue LED switch button.

  5947   Fri Nov 18 15:35:18 2011 kiwamuUpdateIOORF generation box : power switch malfunction

Jenne gave me a spare LED power switch .

I will replace the broken one on Monday.

By the way here is a picture album of the RF generation box which I took last night.


Quote from #5942

 The power switch button of the RF generation box is not properly working

  5963   Sun Nov 20 14:48:55 2011 kiwamuUpdateGeneralrecovery from the power shutdown

Recovery from the power shutdown

 - Turned on the raid disk of linux1.

 - Woke linux1 up. No fsck this time.

 - Woke up all the lab machines.

 - Turned on all the electronics racks' AC powers

 - Woke up fb and then front end machine (the raid for fb had been already up as I turned on the AC powers)

 - Turned on all the electronics racks' DC powers (Sorensens, Kepcos, and etc.)

 - Turned on the Marcnois which is driving the RF generation box.

 - Woke up all the lasers (PSL and End lasers)

 - Some burtrestoring (c1ioo, c1sus, c1susaux, c1msc, c1psl, c1iool0, c1auxey, c1auxex, c1oaf, c1pem)

 - Ran autolockMC scripts on op340m => After relocking of PMC a lock of MC was acquired immediately.

 - Turned on the PZT HV drivers.


Some issues

 - 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.

 - C1SCX is not properly running. Rebooting the machine didn't help. This needs to be fixed.

       The symptom is : (1) all the values are frozen in the screens. (2) the c1scx status screens shows NO SYNC sign. (3) however the timing board looks blinking happily.

 - One of the VME rack on 1X3 is not showing the +/-15V green LED lights.

   This is the one on very upper side of the rack, which contains the old c1lsc machine and c1iscaux2. If we are still using c1iscaux2, it needs to be fixed.

  5964   Sun Nov 20 15:11:09 2011 kiwamuUpdateIOORFAM monitoring test


Plus, MC has to be kept locked with the WFS.


An RFAM measurement is ongoing


 Since the Stochmon turned out to be tricky to calibrate the outputs, Koji and I decided to monitor the RFAMs using REFL11 and REFL55 RFPDs while the beam is single-bounced from PRM.
This is, of course, not a permanent RFAM monitor, but at least it gives us a long-term continuous RFAM information for the first time.
Before the measurement I ran the offset zeroing scripts, therefore any offsets from electronics must be tiny in the acquired REFL signals.
The measurement has begun from approximately 3:00 pm.
 Also I found C1LSC.ini file again became default (no channels had been acquired).
So I replaced it with an archived ini file and then restarted fb.
  5968   Mon Nov 21 14:35:28 2011 kiwamuUpdateIOORFAM monitoring test


 This is a trend for a day long showing the REFL11/55 demod signals, REFLDC (corresponding to the MC transmitted power) and the PSL booth temperatire.

There are sudden jumps in the REFL55_I and REFL11_Q signals around 5:00 AM this morning, also at the same time the temperature suddenly went up.

But the quality of the signal turned out to be not so good because the fluctuation is still within 1 bit of the ADCs,

we have to try it again with a bigger gain in the analog whitening circuit.


An RFAM measurement is ongoing

  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.


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

  5974   Tue Nov 22 00:19:10 2011 kiwamuUpdateSUSc1auxey hadware rebooted

I found that the slow machine c1auxey, which controls and monitoring the ETMY suspension things, were not responding.

The machine responded to ping but I wasn't able to telnet to it.

I went down there and power-cycled it by keying the power of the VME rack, and then it came back and seems working properly.

I have no idea why it ran into such condition.

  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.

  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).

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