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ID Date Authorup Type Category Subject
  5690   Wed Oct 19 04:23:58 2011 kiwamuUpdateSUSSRM free swinging test

The following optics were kicked:
Wed Oct 19 04:22:53 PDT 2011

  5691   Wed Oct 19 05:15:44 2011 kiwamuUpdateSUStaking care of SRM

I made some efforts to fix the situation of SRM but it is still bad.

The POS motion wasn't well damped. Something is wrong either (maybe both) sensing part or actuation part.

I am going to check the sensing matrix with the new free swinging spectra (#5690)



 When I was trying to lock SRMI I found that the fringes observed at the AS camera didn't show spatial higher order modes, which is good.

So I thought the SRM suspension became quiet, but it actually wasn't. Because the RMS monitor of the SRM OSEMs already went to about 30 counts.

At the same time the opelev error signals were well suppressed. It means some DOFs which were insensitive to the oplev were ringing up, namely POS and SIDE.

According to the LSC error signal and the ASDC signal, I believe that the POS was going wild (although I didn't check the OSEM spectra).

(Some efforts)

 + Readjusted the f2a filters (see the attachment).

 + Tried to eliminate a coupling between the POS and SIDE drives by tweaking the output matrix.

    => In order to eliminate the coupling from the POS drive to SIDE sensor, I had to put a comparable factor into an element.

     So it might be possible that the POS sensor was showing the SIDE signal and vice versa.

      In order to check it I left SRM free swinging (#5690).

Quote from #5684

The main reason why I couldn't lock DRMI was that the suspensions were touchy and especially the SRM suspension wasn't good.

Attachment 1: f2pSRM.png
  5694   Wed Oct 19 10:49:35 2011 kiwamuUpdateSUSSRM oscillation removed


The SRM oplevs were found to be oscillating because of a small phase margin.

I reduced the gains to the half of them. The peak which Steve found today maybe due to this oscillation.

Quote from #5630

The SRM bounce peak 18.33 Hz. Suresh helped me to retune filter through Foton, but we failed to remove it. 

 Kiwamu removed the 18.3 Hz ocsillation by turning down the oplev servo gain.

Attachment 1: SRMoplevKWMtune.png
  5698   Wed Oct 19 14:03:41 2011 kiwamuUpdateGeneralvent prep : dichroic mirrors

Status update on dichroic mirror:

 I got the specification sheet of an aLIGO 2" dichroic mirror from Lisa.


This is the one from ATF. It has low loss, a high R for 1064 nm and high T for 532 nm. So it matches our needs.

Based on this sheet we may reset some of the parameters in the specification (e.g. incident angle and etc.,) and will get a quote from ATF.

We will buy 3 of them, including 1 spare. First I need to review the specification.

  5699   Wed Oct 19 15:46:49 2011 kiwamuUpdateSUStaking care of SRM

Quote from #5691

I am going to check the sensing matrix with the new free swinging spectra (#5690)


The SRM input matrix has been readjusted.

However still there is the unwanted coupling from the POS drive to SIDE signal and from the SIDE drive to POS signal.

  SRM  SRM.png       pit     yaw     pos     side    butt
UL    0.871   0.975   1.115  -0.295   1.096  
UR    1.015  -1.025   1.128  -0.140  -1.053  
LR   -0.985  -0.984   0.885  -0.088   0.831  
LL   -1.129   1.016   0.872  -0.243  -1.020  
SD    0.084   0.061   3.534   1.000  -0.018  


  5702   Wed Oct 19 16:53:38 2011 kiwamuUpdateCDSsome screens need labels


Some of the sub-suspension screens need labels to describe what those row and column are.

  5704   Wed Oct 19 17:33:07 2011 kiwamuUpdateGreen LockingETMY mechanical shutter : fully functional

The mechanical shutter on the Y end is now fully functional.


 It is newly named to 'C1AUX_GREEN_Y_Shutter' in the EPICS world.

It uses the same binary output channel which had been served for the POY shutter.

To change the EPICS name I edited a db file called ShutterInterLock.db, which resides in /cvs/cds/caltech/target/c1aux.

After editing the file I rebooted the c1aux machine, by telnet and the reboot command in order to make the change effective.

Also I added this new shutter on the ALS overview screen (see the attachment below)


Quote from #5701

The ETMY  shutter can be remotely switched from medm screen POY of mechanical shutters.

The new cable from ETMY controller goes to east vertex EV-ISCT where it is connected to POY shutter hook up BNC cable.

  5709   Thu Oct 20 04:47:37 2011 kiwamuUpdateLSCclipping search round 1

[Koji / Kiwamu]

  We tried finding a possible clipping in the vertex part.

We couldn't find an obvious location of a clipping but found that the recycling gain depended on the horizontal translation of the input beam.

We need more quantitative examination and should be able to find a sweet spot, where the recycling gain is maximized.


(what we did)

  + locked the carrier-resonant PRMI.

  + with IR viewers we looked at the inside of ITMX, ITMY and BS chambers to find an obvious clipping.

    => found two suspicious bright places and both were in the ITMY chamber.

      (1) POY pick off mirror : looked like a small portion of a beam was horizontally clipped by the mirror mount but not 100% sure whether if it is the main beam or a stray beam.

      (2) The top of an OSEM cable connectors tower : although this is in the way of the SRC path and nothing to do with PRC.

 + Made a hypothesis that the POY mirror is clipping the main beam.

 + To reject/prove the hypothesis we shifted the translation of the incident beam horizontally such that more beam hits on the suspicious mirror

 + Realigned and relocked PRMI.

    => Indeed the recycling gain went down from 6 to 0.8 or so. This number roughly corresponds to a loss of about 50%.

         However the MICH fringe still showed a very nice contrast (i.e. the dark fringe was still very dark).

         Therefore our conclusion is that the POY mirror is most likely innocent.

  5744   Wed Oct 26 23:03:03 2011 kiwamuUpdateLSCRF distribution box : two more 55MHz available

The RF distribution box has been modified so that it generates two more 55 MHz LO signals.

After the modification I put the box back in place.

Then I checked the MICH and YARM locking quickly as a working test of the distribution box and it is working fine so far.

I will update the diagram of the RF distribution box (#4342) tomorrow.



  Since we newly installed POP55 (#5743) an LO signal was needed for the demodulation.

However the RF distribution box didn't have any extra LO outputs.

Therefore we had to make a modification on the RF distribution box so that we can have a 55MHz LO signal for POP55.

Eventually I made two more 55MHz outputs including one spare.



The box actually had two extra output SMAs which had been just feed-thru connectors on the front panel without any signals going through.

In the box the modules consist of two categories; the 11MHz system and 55MHz system. I modified only a part of the 55MHz system.

The modification was done in this way:

  * split two branches of 55MHz into four branches by installing two new power splitters (ZMSC-2-1).

  * made and installed some SMA cables whose length were adjusted to be nicely fit in the box.

  * readjustment of the RF levels to 0-2 dBm at the outputs by replacing some attenuators.

  * checked the signals if all of them were happily coming out or not.

Also I found that the POX11 and POY11 demod boards were connected to the whitening filters in a wrong way.

The I and Q signals were in a wrong order. So I corrected them so that the upper inputs in the whitening filter is always the I signal.


(RF levels on 55MHz LO outputs)

Since the demod board requires a certain level of the RF signal as as LO, the LO signals have to be 0-2 dBm.

Here are the RF level in each 55MHz output after the adjustment of the level.

     AS55 =  0.76 dBm

     REFL55 = 0.76 dBm

     POP55 = 0.79 dBm

     spare = 0.83 dBm

Those numbers were measured by an oscilloscope and the oscilloscope was configured to measure the rms with the input impedance matched to 50Ohm.

In the measurement I used the actual input seed 55MHz signal from the RF generation box to drive the distribution box.

  5746   Thu Oct 27 16:09:37 2011 kiwamuUpdateLSCRF distribution box : two more 55MHz available

The diagram of the RF distribution box has been updated according to the modification ( #5744).

Both pdf and graffle files are available on the 40m svn : https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/

Here shows the latest version of the diagram.


Quote from #5744

I will update the diagram of the RF distribution box (#4342) tomorrow.

  5747   Thu Oct 27 18:00:38 2011 kiwamuSummaryLSCOffsets in LSC signals due to the RFAMs : Optickle simulation

The amount of offsets in the LSC signals due to the RFAMs have been estimated by an Optickle simulation.

The next step is to think about what kind of effects we get from the RFAMs and estimate how much they will degrade the performance.


  We have been having relatively big RFAM sidebands (#5616), which generally introduce unwanted offsets in any of the LSC demodulated signals.
The motivation was that we wanted to estimate how much offsets we've been having due to the RFAMs.
The extreme goal is to answer the question : 'How big RFAMs do we allow for operation of the interferometer?'.
Depending on the answer we may need to actively control the RFAMs as already planed (#5686).
Since the response of the interferometer is too complicated for analytic works, so a numerical simulation is used.

(Results : Offsets in LSC error signals)





  Figure: Offsets in unit of meter in all the LSC demodulated signals.  Y-axis is the amount of the offsets and the X-axis represents each signal port.
In each signal port, the signals are classified by color.
(1) Offsets in the PRCL signal. (2) Offsets in the MICH signal. (3) Offsets in the SRCL signal.
Roughly the signals showed offsets at a 0.1 nm level.
The numerical error was found to be about 10-10 nm by running the same simulation without the AM sidebands.
Here is a summary of the amount of the offsets:
    offsets [nm] (1f signal port)  offsets [nm] (3f signal port)  biggest offsets [nm] (signal port)
PRCL       0.3 (REFL11)       0.2 (REFL33)     1 (REFL55)
MICH      0.00009 (AS55)       0.8 (REFL33)     7 (POP11)
SRCL      0.1 (REFL55)       0.1 (REFL165)     40 (POX11)
In the SRCL simulation  REFL11I, REFL11Q, POP11I, POP11Q and POX11I didn't show any zero crossing points within 100 nm range around the resonance.
It is because that the SRCL doesn't do anything for the 11MHz sidebands. So it is the right behavior.
However POX11 was somewhat sensitive to the SRCL motion and showed a funny signal with a big offset.

(Simulation setup)

I applied the current PM/AM ratio according to the measurement (#5616, #5519)
The modulation indices used in the simulation are :
    + PM index in 11MHz = 0.17
    + PM index in 55MHz = 0.14
    + AM index in 11MHz = 0.17 / 200 = 8.5x10-4
    + AM index in 55MHz = 0.14 / 200 = 7.0x10-4
Note that the phases of the AM and PM sidebands are the same.

For clarity, I also note the definition of PM/AM ratio as well as how the first order upper sideband looks like.



The optical parameters are all at ideal length although we may want to check the results with more realistic parameters:
    + No arm cavities
    + PRCL length = 6.75380
    + SRCL length = 5.39915
    + Schnupp asymmetry = 3.42 cm
    + loss in each optic = 50 ppm
    + PRCL = resonant for 11 and 55MHz
    + MICH = dark fringe
    + SRCL = resonant for 55 MHz
The matlab script will be uploaded to the cvs server.

Quote from #5686
  8. In parallel to those actions, figure out how much offsets each LSC error signal will have due to the current amount of the RFAMs.
    => Optickle simulations.

  5749   Fri Oct 28 01:13:17 2011 kiwamuUpdateSUSITMX oplev : iris fully opened

I found that the sum of the ITMX oplev signals had gone down to zero yesterday.

I checked the ITMX table and found two iris on the He-Ne laser path were blocking the beam on their apertures.

I guess this is because we were working around there for installation of POP/POX and may have touched some of the oplev optics.

Then I fully opened the apertures of those two iris and the sum went back to nominal of 600 counts.

  5752   Fri Oct 28 03:42:50 2011 kiwamuUpdateLSCITMX table needs to be refined


The POX beam had been 80% clipped at a black glass beam dump of the POX11 RFPD.

I steered the first mirror in the POX path to fix the clipping. Then the beam was realigned onto the RFPD.

However the beam is still very close to the black glass, because the incident angle to the second mirror is not 45 deg .

We need to refine the arrangement of the POX11 optics a bit more so that the beam will never be clipped at the black glass.



 The POP optics also need to be rearranged to accommodate one more RFPD.

Additionally Rana, Suresh and I discussed the possible solutions of POP22/110 and decided to install a usual PD (PDA10A or similar) instead of a custom-made.

So a plan for the POP detectors will be something like this:

        + design an optical layout.

        + buy a 2 inch lens whose focul length is long enough (#5743)

        + rearrange the optics and install POP22/110

        + lay down a long SMA cable which sends the RF signal from POP22/110 to the LSC rack.

        + install a power splitter just before the demod board so that the signal is split into the 22MHz demoad board and 110MHz demod board.

           => make sure we have a right splitter for it.

        + install a band pass filter after the power splitter in each path.

           => A 22MHz band pass filter is already in hand. Do we have 110MHz band pass filter somewhere in the lab ?

The picture here shows the latest configuration on the ITMX table.


Quote from #5743

RF photo diodes POP55 and POX11 are installed. The beams are aligned to the photo diodes. 

  5753   Fri Oct 28 04:57:00 2011 kiwamuUpdateLSCPOX11 demod board broken
The POX11 demodulation board is broken. It needs to be fixed in the daytime tomorrow.
It only outputs the Q signal and nothing is coming out from the I output.

(Some stuff checked)
 [OK] ADCs
 [OK] Whitening filters looked fine. Their gains were controllable from EPICS.
 [OK] Connection between the POX11 RFPD and demodulator box
 [OK] The Q signal showed the PDH signal of the X arm with an amplitude of about 200 counts, which almost is the same as that of POY11.
 [NOT GOOD] The I signal from the demod board
 [OK] Outputs cables, which send the I and Q signals from the demod board to WFs are fine.
(Test on the POX11 demod board)
 As usual, a test signal whose frequency is shifted by a little bit from that of LO was injected to the RF input of the board to see if the circuit is working.
The I signal didn't show up and there were no signals even in the monitor LEMO output.
Something is wrong in the I signal demodulation path on the circuit board.

Here is an actual time series of the I and Q signals in dataviewer. The I signal outputs just junk while the Q showed a nice sine curve.

  5754   Fri Oct 28 05:17:13 2011 kiwamuUpdateLSClocking activity : PZT1 is still railing

Status update on the LSC activity:

 To see how good/bad the beam pointing is, I locked the Y arm with POY11.
Then I ran the ASS servo to automatically correct the alignment of the ITMY and ETMY suspensions and also the beam pointing.
The result is that the PZT1_X is still railing to the negative side.
Due to it the transmitted light from the Y arm is about 0.6 or so which is supposed to be 1 if the beam pointing is perfect.
The EPICS value of PZT1_X is at the minimum of -10 and the ASS servo tried to push it more negative side.
 Tomorrow night I will intentionally introduce offsets in the MC suspensions to avoid the railing.
The goal will be a scan of the incident beam while measuring the recycling gain.
  5762   Sat Oct 29 05:50:44 2011 kiwamuUpdateLSCMC suspensions misaligned to avid railing for PZTs

I have shifted the alignment of the MC suspensions such that the PZT won't rail.

Since I didn't care of the spot positions on the MC mirrors, currently they are terribly off from the centers.

After the shift, I realigned the Stochmon PD again.

The attachments below shows the alignment of MC and PZTs before shifting the just for a record



Quote from #5754

 Tomorrow night I will intentionally introduce offsets in the MC suspensions to avoid the railing.
The goal will be a scan of the incident beam while measuring the recycling gain.

  5773   Mon Oct 31 21:46:32 2011 kiwamuUpdateLSCDependence of Recycling gain on incident beam pointing

I horizontally swept the translation of the incident beam in order to investigate a possible clipping in Power-recycled Michelson (PRMI).

The recycling gain of PRMI depended on the beam pointing but it did't improve the recycling gain.

I guess the amount of the entire shift I introduced was about +/- the beam diameter = +/- 5 mm or so.

Within the range of about +/- 5mm in the horizontal beam translation I didn't find any obvious sign of a clipping.



 This is the procedure which I did:
  (1) Some amount of offsets were introduced on MC2 in both PIT and YAW such that the PZT1 won't rail (#5762).
      => Every time when I introduced the offset I realigned the zig-zag mirrors on the PSL table to maintain the high transmissivity of MC.
  (2) Fine tuning of the MC offsets so that the PZT1_X EPICS value becomes almost zero when the beam is aligned down to the Y arm.
     => 0.523 in C1:ASC_PZT1_X became a point where the coupling of the beam into the Y arm was maximized.
     => Last time the direction which we investigated was the positive side from this zero point (#5709) in PZT1_X.
  (3) Aligned MICH by steering BS.
  (4) Locked PRMI with carrier resonating and aligned PRM to maximized the power recycling gain which was obtained from POYDC.
  (5) Translated the beam pointing
     => First I shifted PZT1_X by a wanted amount.
    => Then I locked the Y arm and realigned PZT2_X by maximizing the Y arm transmission.
          This procedure should give us a pure translation on the incident beam.
  (6) Repeated the same procedure (3) through (5) in each PZT1 position.


Here shows the measured recycling gain and the power reflectivity of PRMI as a function of the beam pointing.


 Upper plot : measured recycling gains (Red) observed maximum values (Black) measured values on average.
 Lower plot : measured power reflectivity of PRMI (Blue) observed minimum values (Black) measured values on average.
 As shown in the plots the recycling gain could go up to 8 at some points.
As the PZT went away from 0 it decreased and eventually became about 3 in each side.
The reflectivity showed the minimum value of 0.4 when the PZT1 was at -1 in EPICS value.
One hypothesis to explain this plot can be that : we are just seeing the effect of the incident beam misalignment.


  5776   Tue Nov 1 16:02:15 2011 kiwamuUpdateSUSRe: SUS input matrix diagonalizer REMOVED from crontab


It turns out that nodus doesn't know how to NDS2, so I can't run diagAllSUS as a cron job on nodus. To further complicate things, no other machines can run the elog utility, so I am going to have to do something shifty...

 Actually in the last 40m meeting we discussed the SUS diagnosis and decided not to post the results on the elog.

Alternatively we will have a summary web page which will contain all the information (sensitivity, UGF monitors, etc.,) and will be updated everyday like GEO.

This will be a place where we should post the SUS results every week.

So we don't need to worry about the cron-elog job, and for running the scripts you can simply use one of the lab machines as a cron host.

Once you get the scripts running on a machine as a cron job, it will be the point where we should quit developing the SUS diagonalizer and pass it to the web summary people.

  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.

ELOG V3.1.3-