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ID Date Author Type Categoryup Subject
  5401   Wed Sep 14 01:19:20 2011 AnamariaConfigurationLSC3f PD Install in Progress

I have reconfigured the refl beam path on the AP table to include REFL33 and REFL165. Would be done if we hadn't prepared P BSs instead of S, which required some serious digging to find two others. And if someone hadn't stolen our two 3m SMA cables that Keiko and I made on our previous visit and I had left with the 3f PDs. I don't expect them to reappear but if they do, it would be grand.

Note: Refl beam from ifo looks a bit high, ~1cm on the lens 20'' from output port. Not sure what that means about ifo alignment change, I've left it as is. When we know we have a good alignment, we should be able to easily realign the beam path if necessary. If it remains the same, we might want to change the lens height.


1) REFL11 and REFL55 are now hooked up and aligned in a low power beam. (I set the power as low as I could by eye to not risk burning the PDs during alignment)

2) The required BSs and REFL33 and REFL165 are in place, powered.

3) I have set them in a configuration such that the beam is the same distance from the main beam, to adjust beam size easily for all 4.

4) Camera has been moved from main beam to behind a steering mirror, ND filters removed, centered on camera.

To Do:

1) Find one more longish SMA cable.

2) Align beam on REFL33 and REFL165.

3) Check beam size carefully. (I get a plateau on the scope, and I can "hide" the beam on the PD, but it could be better. The path has become longer by ~5-8inches.)

4) Adjust power.

5) Redo layout diagram, post in wiki.

  5406   Wed Sep 14 15:00:00 2011 kiwamuUpdateLSCmeasurement of spot position on Y arm

Forgot to attach a picture of the ITMY's face camera when it was locked.

The horizontal position of the spot looks good, but the vertical position is apparently too low, which agrees with the A2L result.


Quote from #5400
  amount of off-centering [mm]
ETMY_PIT  0.0032
ETMY_YAW  -0.13
ETMY_YAW  0.91



  5410   Wed Sep 14 21:18:45 2011 kiwamuUpdateLSCY arm locking prep

Although we did some of the Input Matrix diagonalization, we have not yet actually used this knowledge. As a result all of the optics are shaking all over the place.

Sunshine Task: Set the input matrices to their calculated values and then adjust the OSEM damping gains for all optics so as to get a Q ~ 5.

  5412   Thu Sep 15 01:06:20 2011 KeikoUpdateLSC3f demodulation board check

In addition to REFL 33 ans 165, I checked the orthogonality for the other existing three channels.



ABS = 1.025035  PHASE = -93.124929 [deg]


ABS = 0.920984  PHASE = -88.824691 [deg]


ABS = 1.029985 , PHASE = -90.901123 [deg]

- - - - - - - - - - - - - - - - - -


The demodulated signal was set as 50 Hz (for example LO 11MHz and RF 11MHz+50Hz from function generators.) These AS11, REFL11, REL55, REFL33m REFL165 are the current available channels in terms of the connection to the data system from the demodulation board. I am going to estimate the error next.



ABS = 1.070274, PHASE = -81.802479 [deg]

- - - - - - - - - - - - - - - - - -


ABS = 1.016008 PHASE = -89.618724 [deg]


  5413   Thu Sep 15 01:17:10 2011 KeikoUpdateLSCMICH locked and attempt to lock PRCL

 Anamaria, Keiko

- We aligned MICH and were successfully locked MICH using AS55Q. The other mirrors were misaligned so that the other degrees of freedom didn't exist. AS55 was fed back to BS. The f2a filters on BS suspension were required to lock, because the pos feedback was unbalanced to angle degrees of freedom.

- We tried to lock PRCL next, however, because we aligned the MICH and the REFL beam paths were changed, REFL PDs didn't have the light anymore. The REFL paths were modified now, so we will try the PRCL locking next.

- We couldn't confirm REFL55 signals although we alined the REFL paths to REFL55 PD.

  5414   Thu Sep 15 02:18:19 2011 AnamariaUpdateLSCMICH locked and attempt to lock PRCL

Kiwamu, Keiko, Anamaria


We were able to lock PRC using REFL11I after improving the MICH dark fringe a bit (moving BS) and rotating AS55 and REFL11 such that the signal was maximized in the phases we were using. The dark port is not so dark... but the lock is stable.

I had finished the whole REFL path alignment, but I didn't have a good input beam reference at the time, which is why we had to realign the PDs and the camera. We only had strength to realign 11 and 55. Otherwise, we just need to tweak and center beam on 33 and 165, figure out what's up with 55 and be done with the AP table mods. I hope.



 Anamaria, Keiko

- We aligned MICH and were successfully locked MICH using AS55Q. The other mirrors were misaligned so that the other degrees of freedom didn't exist. AS55 was fed back to BS. The f2a filters on BS suspension were required to lock, because the pos feedback was unbalanced to angle degrees of freedom.

- We tried to lock PRCL next, however, because we aligned the MICH and the REFL beam paths were changed, REFL PDs didn't have the light anymore. The REFL paths were modified now, so we will try the PRCL locking next.

- We couldn't confirm REFL55 signals although we alined the REFL paths to REFL55 PD.


  5420   Thu Sep 15 17:12:29 2011 MirkoUpdateLSCRF modulation depth measurement

[Mirko, Kiwamu]

Put up a temp. setup on the laser table to measure the RF modulation depths using the optical spectrum analyzer. First with a pickoff beam with about 2mW => SNR of 8 of 1 peak per FSR.

Then with a beam with about 100mW. Much better SNR on the single peak but still no sidebands visible. Modematching not too good in either case. Shouldn't matter.

  5425   Thu Sep 15 20:30:52 2011 MirkoUpdateLSCPlan for long term optical spec. analyzer setup

Just to give some heads up on how the setup on the PSL table does / will look. We start out with one of the two reflections of a window. Power about 2mW.


  5430   Fri Sep 16 03:22:11 2011 AnamariaUpdateLSCMore Refl PDs Work and Attempt at DRMI

Kiwamu, Keiko, Anamaria

I started today with a different input beam, so I had to realign the REFL path again. Then we measured the RF signal out of the 4 REFL PDs and found them to be too low. We increased the power to around 10mA for each diode, and we can see the right modulation frequency on each diode, though REFL165 is way too weak so we might need an RF amplifier on it. We will measure demod board noise tomorrow.

We had an issue with REFL165 not giving the right DC level, low by a factor of 10, even though it was receiving the same optical power as the others. We fifteen-checked clipping and alignment, then pulled it out and measured it on the test stand - found it to be ok. So I uplugged its power cable at the rack and connected it to the AS165 slot. Problem sloved. Not sure what was wrong with the other power slot.

Then we found REFL55 to be clipping on its black glass, we fixed that. But the REFL55 DC power still changes a lot with seemingly not huge motions of the PRM. We'll investigate more tomorrow.

We added a lens in the path to REFL165 because unlike the others it is a 1mm diode. All diodes have about half a turn to a full turn flatness of maximum (on tiny steering mirror).

We set the whitening gain on all four diodes to 21 db.

Not sure if we should set the power to be different on these diodes since their sensitivity is different to RF, and now REFL11 sees huge signal.

We continued the DRMI locking attempt and brought in the SRC, using AS55I to control it. It kind of works/stays locked. We did manage to get MICH and PRC better controlled than last night, but with SRC in the mix, something is wrong. We have to redo f2a filters on SRM and hopefully things will be better after Jenne's suspension work tomorrow. Oplevs not optimized yet either.

We intend to realign POY beam path so we can monitor power in cavities.

  5440   Fri Sep 16 21:26:12 2011 KeikoUpdateLSC3f demodulation board check

The demodulation phases and gains for the all existing channels, AS11, REFL11,REFL55, REFL165, and REFL33, were adjusted by the command "ezcawrite" commands. 

Scripts are: 

REFL165 ezcawrite C1:LSC-REFL165_Q_GAIN 0.934340 && ezcawrite C1:LSC-REFL165_PHASE_D -81.802479


ezcawrite C1:LSC-REFL33_Q_GAIN 0.984244 && ezcawrite C1:LSC-REFL33_PHASE_D -89.618


ezcawrite C1:LSC-REFL11_Q_GAIN 1.173418 && ezcawrite C1:LSC-REFL11_PHASE_D -442.882697

ezcawrite C1:LSC-AS11_Q_GAIN 0.975576 && ezcawrite C1:LSC-AS11_PHASE_D -93.12492


ezcawrite C1:LSC-AS55_Q_GAIN 0.999164 && ezcawrite C1:LSC-AS55_PHASE_D -89.300986
  5441   Fri Sep 16 21:36:25 2011 KeikoUpdateLSCPOY11 and POY55 were added

 New channels, POP55 and POY11 are connected to the rack and now available on the data system.

POX11 I is not working. I didn't investigate what was wrong. Please make sure when you come to need POX11.

The orthogonalities of POY11 and POP55 were measured and already adjusted. The results are below:


ABS = 0.973633 

PHASE = 92.086483 [deg]

ezcawrite C1:LSC-POY11_Q_GAIN 1.027081 && ezcawrite C1:LSC-POY11_PHASE_D 92.086483


ABS =  1.02680579

PHASE =  88.5246 [deg]

ezcawrite C1:LSC-POP55_Q_GAIN 0.973894 && ezcawrite C1:LSC-POP55_PHASE_D 88.524609



  5445   Sat Sep 17 01:53:41 2011 KeikoUpdateLSCPOY and POP beams clipped

 Keiko, Paul, Kiwamu

We found that POP beam is clipped by the steering mirrors inside the tank. POY beam is also likely to be clipped inside. Also the hight of POY beam is too high (about 5 cm higher than the normal paths) at the first lens. These imply the input pointing is bad.

  5453   Mon Sep 19 01:38:00 2011 kiwamuUpdateLSCtoday's locking activity

[Anamaria / Kiwamu]

 The incident beam pointing was improved by using PZT1 and PZT2. 

With some triggers the lock of PRMI became smoother.

For the DRMI lock, the MICH and SRCL signals on AS55 are not quite decoupled, so we should find cleaner signals for them.


(what we did)

 + locked the Y arm

 + aligned incident beam by using PZT1(#5450) and PZT2. The spot positions on ITMY and ETMY are now well-centered.

 + tried activating C1ASS but failed. It needs some gain changes due to the new PZT1 response.

 + locked the X arm

 + aligned the TRX PD (Thorlab signal PD) and set the trigger.

 + C1ASS also doesn't work for the X arm

 + realigned the PRM and BS oplevs. the PRM oplev was clipped at a steering mirror on the optical bench

 + locked PRMI and aligned the PRM mirror such that the optical gain was maximized

 + optimized the demod phase of AS55 and REFL11

 + checked the UGF of the MICH and PRCL lock. The UGF of MICH is about 100Hz with gain of -20, and the UGF of PRCL was 85 Hz with gain of 0.1

 + adjusted the output matrix such that the MICH control doesn't couple into the PRCL control.

 + set the triggers for the MICH and PRCL control to make the lock acquisition smoother.

 + tried locking DRMI and it was sort of locked. However the SRCL signal showed up a lot in AS55_Q, where the MICH signal is extracted.

  5454   Mon Sep 19 02:08:24 2011 kiwamuUpdateLSCfixed POP clipping

Actually the clipping of POP wasn't in the chamber but it was on the first lens on the optical bench.

So I repositioned the lens to avoid the clipping and now there are no clipping on POP.

Quote from #5445

We found that POP beam is clipped by the steering mirrors inside the tank.


  5462   Mon Sep 19 15:44:32 2011 MirkoUpdateLSCRF modulation depth measurement

Earlier measurements of the modulation index were less than optimal because we had too low transmission through the cavity. Contrary to what was believed you actually need to modematch onto the cavity.

Earlier transmitted power was about 8.5uW.

With a 250mm lens we archived 41uW.

Impinging power on the cavity is 1.7mW.

PD TF approx 0.1V / uW.

Carrier power: 4.1V => 41uW

41uW/1.7mW = 2.4 % transmission. Manufacturer clain for peak transmission: 20-30%.

11MHz SB: 28.8mV => m=0.17

55MHz SB:36mV => m=0.19

As you can see on the pic the SNR of the SBs is not too good.


  5463   Mon Sep 19 16:20:35 2011 kiwamuUpdateLSCAS55 whitening gain decreased

The gain of whitening filters on AS55 was decreased from 21 dB to 0 dB for the Y arm locking.


- - (Background)- -

Since the modulation depths became bigger from the past (#5462), the PDH signal from Y arm was saturated in the path of AS55.

Due to the saturation the lock of the Y arm became quite difficult so I decreased the gain of of the whitening filter from 21 dB to 0 dB.

In this condition, a required gain in C1:LSC-YARM_GAIN is about -0.3, which is 10 times bigger from the default number.

For the MICH locking tonight, it may need to be back to a big gain.

  5464   Mon Sep 19 16:44:16 2011 KeikoHowToLSCProcedure for the demodulation board check

 Here I note the procedure for the demodulation board orthogonality check for the future reference.

1. prepare two function generators and make sure I an Q demodulation signals go to the data acquisition system.

2. sync the two generators

3. drive the function generator at the modulation frequency and connect to the LO input on the demod board

4. drive the other function generator at the modulation frequency + 50Hz  the RF in

5. run "orthogonality.py"  from a control computer scripts/demphase directory. It returns the amplitude and phase information for I and Q signals. If necessary, compensate the amplitude and phase by the command that  "orthogonality.py" returns.


If you want to check in the frequency domain (optional):

1. 2. 3 are the same as above.

4. drive the function generator at the LO frequency + sweep the frequency, for example from 1Hz to 1kHz, 50ms sweep time. You can do it by the function generator carrier frequency sweep option.

5. While sweeping the LO frequency, run "orthogonality.py"

6. The resulting plot from "orthogonality.py" will show the transfer function from the RF to demodulated signal. The data is saved in "dataout.txt" in the same directory.

  5473   Tue Sep 20 02:21:10 2011 KojiUpdateLSCLSC MEDM screen cleaning up

I have made some cleaning up of the LSC-related MEDM screens.

- LSC overview screen: ADC OVFL and WFAA indicators are now correctly matched to it associated PD signals.

- Whitening screens now have the correct indication of the associated PD signals.

- LSC Ctrl screen, which is invoked from the overview screen by clicking the servo filters, now has the switches of the servo filters.

- LSC tab of the sitemap was cleaned up by removing the broken links.

  5474   Tue Sep 20 03:02:23 2011 KeikoUpdateLSClocking activity tonight

 Keiko, Anamaria, Koji

We were not able to establish the stable DRMI tonight. We could lock MICH and PRCL quite OK, and lock the three degrees of freedom at somewhere strange for several seconds quite easily, but the proper DRMI lock was not obtained.

When MICH and PRC are locked to the carrier, REFL DC PD reading dropps from ~3000 counts to 2600~2700 counts as REFL beam is absorbed to PRC. We'll try to lock PRC to sidebands - but flipping gain sign didn't work today, although it worked a few days ago. 

POP beam (monitor) is useful to align PRM.

  5489   Tue Sep 20 20:58:35 2011 AnamariaConfigurationLSCNew AP Table Drawing

As promised, I have made a final AP table drawing, including the MC camera relocation changes by Kiwamu. I have posted it in the wiki on the tables list, and on the AP table page I've attached the inkscape .svg I used to make it, if someone needs to do small modifications.

Attached is a pdf version of it.

Big changes:

1) REFL beam has been split into 4, to go in equal powers and equal beam size to the now 4 REFL RFPDs, 11, 33, 55 and 165. A lens had to be added for REFL165 because it's a 1mm PD instead of 2mm like the other 3.

2) MC camera has moved.

3) I've cleaned up most of the random components on the table, put them away, and tidied up the cabling.


Attachment 1: APtableSep20th.pdf
  5492   Tue Sep 20 23:59:53 2011 KojiSummaryLSCPlan to update the LSC code for multiple lock-ins

DRMI team needs to use at least three lockins on LSC

  • Increase the number of the lockin matrix  done
  • Duplicate lockin modules in the LSC code  done
  • modify the main LSC screen done
  • modify the lockin screen done
  • modify the lockin matrix screen done
  5495   Wed Sep 21 02:49:39 2011 KeikoSummaryLSCLSC matrices

I created 3 kinds of LSC matrices, PRMI condition with carrier resonant in PRC, PRMI condition with SB resonant in PRC, and DRMI with SB resonant in PRC. The matrices are with AS55 and REFL11 which are used for locking right now. The signal numbers are written in log10, and the dem phases are shown in degrees.

From CR reso PRMI to SB reso PRMI, demodulation phases change  ----


PRMI - Carrier resonant in PRC


            PRCL      MICH  SRCL

REFL11 7.7079 2.9578 0
REFL33 5.2054 3.2161 0
REFL55 7.7082 2.9584 0
REFL165 3.9294 2.5317 0
AS11 1.0324 3.5589 0
AS33 1.0286 1.6028 0
AS55 1.1708 4.2588 0
AS165 1.1241 0.9352 0
POP11 2.8015 -1.3331 0
POP33 0.2989 -1.6806 0
POP55 2.8017 -0.6493 0
POP165 -0.9769 -2.3708 0
POX11 3.7954 -0.3363 0
POX33 1.293 -0.7058 0
POX55 3.796 0.355 0
POX165 0.0187 -1.3837 0
Dem Phase      
REFL11 3 179 0
REFL33 165 -172 0
REFL55 13 170 0
REFL165 86 177 0
AS11 -32 73 0
AS33 176 -72 0
AS55 -41 12 0
AS165 -7 146 0
POP11 -11 -116 0
POP33 124 147 0
POP55 -54 -146 0
POP165 -117 -25 0
POX11 -87 15 0
POX33 -105 -80 0
POX55 -76 16 0
POX165 180 -91 0

PRMI - SB resonant in PRC

SB reso PRMI    
REFL11 7.6809 5.2777 0
REFL33 5.2465 3.1565 0
REFL55 7.2937 5.589 0
REFL165 4.3892 2.6857 0
AS11 1.3123 3.545 0
AS33 0.9331 1.6022 0
AS55 1.7425 4.0514 0
AS165 1.5838 1.1344 0
POP11 2.7745 0.3791 0
POP33 0.3401 -1.7392 0
POP55 2.3872 0.6904 0
POP165 -0.5171 -2.2279 0
POX11 3.7684 1.3574 0
POX33 1.3341 -0.7664 0
POX55 3.3815 1.6688 0
POX165 0.4785 -1.2163 0
Dem Phase
REFL11 155 -115 0
REFL33 -8 3 0
REFL55 91 -178 0
REFL165 -62 28 0
AS11 109 62 0
AS33 -39 99 0
AS55 13 -38 0
AS165 -155 168 0
POP11 141 -128 0
POP33 -48 -38 0
POP55 24 115 0
POP165 95 -176 0
POX11 65 155 0
POX33 83 95 0
POX55 2 92 0
POX165 32 123 0

DRMI - SB resonant in PRC

REFL11 7.6811 5.0417 4.2237 
REFL33 5.2751 4.1144 3.7766
REFL55 7.2345 7.0288 6.6801
REFL165 4.3337 4.1266 3.7775
AS11 1.1209 3.512 0.9248
AS33 0.9159 1.6323 0.7971
AS55 2.6425 5.3915 2.5519
AS165 2.6423 2.4881 2.3272
POP11 2.7747 0.1435 -0.6846
POP33 0.3687 -0.7849 -1.122
POP55 2.3244 2.1302 1.7815
POP165 -0.5833 -0.8 -1.1548
POX11 3.7676 3.261 0.8086
POX33 1.3896 0.2372 0.2333
POX55 3.4619 3.0097 3.1326
POX165 0.782 0.6668 0.4357
Dem Phase
REFL11 154 -16 4
REFL33 -5 12 51
REFL55 129 -166 -123
REFL165 -23 40 83
AS11 132 79 69
AS33 -92 -127 -83
AS55 -33 -55 -5
AS165 154 179 -144
POP11 141 -29 -9
POP33 -46 -27 12
POP55 62 127 170
POP165 135 -161 -117
POX11 64 -102 -83
POX33 85 143 118
POX55 57 103 124
POX165 99 155 -164



  5498   Wed Sep 21 14:28:25 2011 KojiSummaryLSCThe LSC code/screen modification for LSC LOCKINs

The LSC code has been modified

- The code was modified, compiled, and installed.

- The code is now running. FB was restarted to deal with the change of the channel names.

- Now we have LOCKIN1, 2, and 3. This required the change of the names from C1:LSC-LOCKIN_.... to C1:LSC-LOCKIN1_...


- The LSC screen has also modified. It has three lockins on the screen.

- The corresponding matrix screens have been modified/created and linked from the main screen.

- I need to make the screens more cool but the locking team can start to use those lockins.

  5512   Thu Sep 22 01:45:41 2011 KeikoUpdateLSCLocking status update

Keiko, Anamaria

Tonight we want to measure the LSC matrix for PRMI and compare the simulation posted last night (#5495).

First. we locked MICH and PRCL, and measured the OLT to see how good the locking is. The following rough swept sine plots are the OLTs for MICH and PRCL. The gain setting was -10 and 0.5 for MICH and PRCL, respectively. Integrators were off. Looking at the measured plots, MICH has about 300 Hz UGF, when the gain is -20, and PRCL has about 300 HZ UGF, too, when the gain is 0.8.



As these lokings seemed good, so we tried the LSC matrix code written by Anamaria. However it is not working well at this point. When the script add excitations to the exc channels, they kick the optics too much and the lockings are too much disturbed...

Also, we have been trying to lock PRC with the SB resonant, it doesn't work. Looking at the simulated REFL11I (PRCL) signal (you can see it in #5495 too), the CR and SB resonances have the opposite signs... But minus gain never works for PRCL. It only excites the mirror rather than locking.

  5513   Thu Sep 22 04:49:14 2011 AnamariaUpdateLSCLocking status update - Some Scripts, No Louck

The scripts I wrote can be found in /users/anamaria/scripts/sensemat/

]There are two of them:

- one that sets all the switches, gains, frequencies, etc, then cycles through the various RFPDs I and Q into the LOCKIN signal, so as to see the sensing matrix.

- the second one is a matlab script that takes the crappy file tdsavg outputs and makes it into a cute mag/phase matrix.

They're quite primitive at this point, I've forgotten a lot of tcsh... may improve later. But could be useful later to someone else at least.

I don't think it's particularly the fault of the script that we can't measure the sensing matrix. We can slam on the excitation by hand, and it holds for a little while. I set a wait time for lock to adjust, and most times it just oscillates a bit for a few seconds. Also, the script turns on the excitation and it's done, the rest is just measurement, then turns it off at the end. So during the script, there's not much to deal with, except keeping the lowpass filters quiet when switching the signal to demod; but that doesn't go anywhere, so it definitely doesn't disturb the ifo. Turns out pressing the RSET clear history button needs a 2 to make it happen.

I think I might prefer to set the excitation to run, and then do the old retrieve-data-later-nds-matlab thing. I do not trust these measurements without coherence and a bit of variance study, given instabilities.

Point is... Even on carrier, the PRC lock is not stable by any means. Can barely turn on low freq boosts, every other lock. Until we fix the lock stability issue, there's not much to measure I guess.

Unfortunately, I don't know how to make that happen. Before we leave on Friday we could do a few sanity checks such as measuring the noise of the RFPDs vs ADC+whitening, which I may have said I would do; and perhaps setting up a couple OSAs, one on REFL, one on AS, to make sure we know what the sidebands are doing. Both of which Rana suggested at some point.

(There used to be a quote here from Keiko here but I got mad when it reformated my entire log to be one cluster- hence the look)

  5515   Thu Sep 22 11:49:05 2011 kiwamuUpdateLSCsome LSC scripts don't run on pianosa

Found some LSC scripts didn't run on pianosa. Particularly all the scripts on the C1:IFO_CONFIGURE screen don't run.

They need to be fixed.

  5516   Thu Sep 22 11:50:37 2011 KojiUpdateLSCLocking status update

Both loops basically have no phase margins. i.e. unstable. How can you lock PRMI with these servos?


The following rough swept sine plots are the OLTs for MICH and PRCL. The gain setting was -10 and 0.5 for MICH and PRCL, respectively. Integrators were off. Looking at the measured plots, MICH has about 300 Hz UGF, when the gain is -20, and PRCL has about 300 HZ UGF, too, when the gain is 0.8.


  5519   Thu Sep 22 15:53:37 2011 MirkoUpdateLSCRF modulation depth measurement again

Toyed around with the modematching some more today.

The outermost glass elements of the OSA are about 28cm apart.

With the OSA beeing a confocal cavity that should mean that the ROC of every mirror is 28cm on the cavity side. If the input surface is flat we need a 28cm focusing lens for good MM. If it's not we shouldn't need any MM.

Tried a f=250mm lens on different positions first. Got at best about 570mV (PD gain=10) in transmission of the OSA.

Then tried a f=1000mm lens. Best transmission 1.22V (7.2% transmission). SB were (PD gain =100) 11MHz: 87.2mV (m=0.17) , 55MHz: 59.2mV (m=0.14)

Lost the position while toying around. Left it then at 1.0V transmisison at 15:15 local time. Let's see how much it drifts. SBs for this were 11MHz: 52.8mV (m=0.17), 55MHz: 73.8mV (m=0.14)

[Ed by KA: If the carrier transmission was really 1.22V and 1.0V the modulation depths calculated are inconsistent with the measurement.]

Spacing between carrier 11MHz and 55MHz SBs seems consistent, and leads to a FSR measurement of 1.5GHz, also fine.


Update: After 90mins no change in carrier transmitted power. Next morning: Carrier transmission down by 10%.




  5522   Thu Sep 22 18:33:01 2011 KojiSummaryLSCThe LSC screen modification

As per the request of Anamaria, I have added the slider of the demodulation phase for each RF PD screens.

Attachment 1: PD_screen.png
  5525   Thu Sep 22 22:55:01 2011 AnamariaUpdateLSCPOX channel = POY PD connected + Bad Rack

Keiko, Anamaria

We decided we needed a DC channel to sense the gain in the PRC, so we set to align POY55. It took a while because the beam was very weak, and it comes in upwards, so we used a couple of mirrors to bring to a reasonable flat level, and put it on the PD. Then we went to read the DC out and we got 1.3V stationary! Nonsense. We also realized there is no LO for this PD, or any other 55MHz PD, aside from REFL55. Oh well, we only wanted the DC for now. POY55 is aligned (decently).

Koji told me to try swapping the power cable, so I unplugged it at the rack and plugged it in another power card. And it worked! I then moved the DC out (back of rack) to follow the front, and it turns out POY55 diode is read on the POXDC channel. I plugged and unplugged it in disbelief, but it is what it is. At least we have a readout on the power level in PRC.

I attach a picture of the power cards for the LSC RFPDs, with the 3 I found to be bad, and showing current config. I had to move REFL11 and POY55 from their assigned spot.

The two on the lower left are bad in the sense that they put an offset on the PD and make the DC readout be 1.3V for no reason (when working, for example, POY55 read 60mV). The one on the lower right I had trouble with some time ago, it made the PD not read any voltage at all (when working it would read at least 100mV). Beyond that I have not investigated what is up, since I could find working plugins.

Attachment 1: RFPDpowerRack2.pdf
  5528   Thu Sep 22 23:18:51 2011 KojiSummaryLSCThe LSC screen modification


C1LSC_RFPD.adl screen was modified to have more information.

Attachment 1: C1LSC_RFPD.png
  5530   Fri Sep 23 16:56:07 2011 MirkoUpdateLSCDesired MC modulation frequency measurement, tuning of modulation frequency

[ Mirko, Koji, Suresh ]

Looked into the modulation frequency that should pass the input MC. With a locked MC looked at the RF output of the PD in refl of the MC. Looked at the beat between 11MHz and 29.5MHz. Minimizing it by fine-tuning the 11MHz freq. ( which means maximizing the 11MHz transmission).

SB freq. [MHz]     Beat power [dBm]

11.065650          -75

11.065770          -80 (diving into spec. analyzer instrument noise)

11.066060          -80 (surfacing out of spec. analyzer instrument noise)

Set the freq. to the middle of the last two points: 11.065910MHz at 16:26.

ToDo: How big a problem is the AM?

  5539   Sat Sep 24 17:12:54 2011 KojiUpdateLSCRealignment of REFL / Some 3f PRMI locking / Recycling Gain

[Koji Suresh]

Activity on Friday evening

- The REFL path has been thoroughly aligned
As I did not like the REFL spot misaligned on the REFL CCD, we went to the AP table.
Many optics had the spots not on the middle of the optic, including the PBS whose post was not fixed on the post holder.
We aligned the optical paths, the RF PDs, and the CCD. The alignment of the PD required the use of the IR viewer.
One should not trust the DC output as a reference of the PD alignment as it is not enough sensitive to the clipping.

We aligned the optical paths again after the reasonable alignment of PRM is established with the interferometer.
"Next time when you see REFL spot is not at the center of the camera, think what is moved!"

- The REFL165 PD is disconnected from the power supply
I found that the REFL165 PD is producing 7.5V output at the DC monitor no matter how the beam is blocked.
As I could not recover this issue by swapping the power connector at the LSC rack, I disconnected the cable
at the RFL165 PD side. I need to go through the PD power supply circuit next week.

- PRMI alignment policy of the night

Kiwamu has aligned Y-arm some time ago (Thursday evening?). I decided not to touch ITMY.
So the Michelson is aligned by ITMX, PRC is aligned by PRM.

- Michelson locking

The short Michelson was locked with AS55Q and the MICH filter. We could use the gain of +/-20 for locking,
and could increase it up to ~+/-250. At the max gain, the all three integrators and the two resonant gains
could be activated. The sign depends on which fringe you want at the AS port (bright or dark).

In this condition, the output of the POXDC channel (which is actually the POY DC out -- c.f. This entry
is used to determine the internal power. It was ~70cnt.

- PRMI locking

Then the PRMI was locked. There was some confusion of the gains because of the limitters at the servo filters
(which yielded the locking with 1bit outputs no matter how much the gains were....)

After all, I decided to use REFL33I for the PRCL for the test. The PRCL gain was -0.3~-1.0 for the carrier lock, but
was highly dependent on the alignment. i.e. if accidentally hit the high power recycling gain, it oscillated easily
and the lock was lost. Probably this was the first 3f locking at the 40m in the current optical config, if
Kiwamu did not do that secretly. The SB lock was also obtained by flipping the sign of the PRCL servo.

The difficulty we had was the instability when the recycling gain became big. We were monitoring the POXDC
(i.e.DCout of the POY PD). When this exceeds 5000, many glitches appears in the LSC signals and disturbs the lock.
This was not the fringes from neither the arms nor the SRC.

The observed POY DC with the carrier resonant PRMI was 5000~8000vcnt (momentary).

  5541   Sat Sep 24 20:14:36 2011 KojiUpdateLSCRough estimation of the PR gain


POXDC (i.e. POY DCout)
PRM misaligned: 70cnt
CA resonant PRMI: ~8000cnt (max)


PRMI antiresonant = 5200cnt
PRMI resonant = ~3000cnt
==> Visivility = 0.6

Transmissivity: TR=0.0575, tR=sqrt(TR)

Rough estimation of the power recycling gain (assuming perfect mode matching)

PPRM_mialign = Pin tR2
PPRM_resonant = Pin [tR/(1-rR rMI)]2

G = tR2 PPRM_resonant / PPRM_mialign = 8000/70*0.0575 = 6.5

This is way too low compared with the design (G>40)
This corresponds to rMI2=0.885 (loss of 10%) in the power recycling cavity.
But this yields visibility of 16%, instead of 60% which we saw. This is inconsistent.

If mode matching is not perfect, effective incident power of PRMI decreases
and this discrepancy may be explained

Pin = Pjunk + (Pin-Pjunk)

PPRM_mialign = Pin tR2
PPRM_resonant = (Pin-Pjunk) [tR/(1-rR rMI)]2

PREFL_antires ~ Pin
PREFL_resonant = Pjunk+(Pin-Pjunk)[-rR+(tR2 rMI)/(1-rR rMI)]2


PPRM_resonant / PPRM_mialign = (1-Rmm) /(1-rR rMI)2=8000/70
PREFL_resonant /PREFL_antires= Rmm+(1-Rmm)[-rR+(tR2 rMI)/(1-rR rMI)]2=0.6

here Rmm= Pjunk/Pin is the mode matching ratio

Solving the last two equations, we obtain

rMI2= 0.939 (loss of 4-5%)

Can we believe that the mode matching is 60% and the loss is 5%???

  5545   Mon Sep 26 15:15:45 2011 AnamariaUpdateLSCRealignment of REFL / Some 3f PRMI locking / Recycling Gain

A few comments on REFL table alignment and REFL165.

Last time we realigned the table was after the PZT work by Koji/Kiwamu; we made sure that the beam was going through optics satisfactorily and that we were reading reasonable numbers. I did use primarily a viewer to align onto PD, after which we used the voltage reading to center better around that spot. As desired, I could not see the beam once it was centered on the PD. I never touched the PBS unfortunately, so I never noticed it was not fixed. Sad.

I am very surprised to hear the reading from REFL165, since I was reading around 400mV from it a few days before. Something strange happened in the mean time. I hope not when I was plugging and unplugging at the power rack for the POY work. But I would not have needed to touch REFL165. Those cables should get some strain relief at the rack, by the way.

I thought about it, and I must admit that after we centered camera on REFL (paired with an alignment), we did not check the beam path later, even after we saw that the REFL beam had moved. We only did a quick by-viewer check that the beams were not off of the PDs.


[Koji Suresh]

- The REFL path has been thoroughly aligned
Many optics had the spots not on the middle of the optic, including the PBS whose post was not fixed on the post holder.
We aligned the optical paths, the RF PDs, and the CCD. The alignment of the PD required the use of the IR viewer.
One should not trust the DC output as a reference of the PD alignment as it is not enough sensitive to the clipping.

We aligned the optical paths again after the reasonable alignment of PRM is established with the interferometer.
"Next time when you see REFL spot is not at the center of the camera, think what is moved!"

- The REFL165 PD is disconnected from the power supply
I found that the REFL165 PD is producing 7.5V output at the DC monitor no matter how the beam is blocked.
As I could not recover this issue by swapping the power connector at the LSC rack, I disconnected the cable
at the RFL165 PD side. I need to go through the PD power supply circuit next week.


  5553   Tue Sep 27 04:13:22 2011 kiwamuUpdateLSCtonight's locking activity

The lock of PRMI wasn't so robust although it could stay locked for more than 10 minutes.

There have been 2-3Hz spikes in everywhere. It needs to be investigated.


(to do)

 + Diagnosis on the suspensions.

 + Check the beam centering on the RFPDs.

 + Check the f2a filters on PRM and BS.

 + Health check of the suspensions by locking some cavities and measuring the noise spectra for comparison.

 + Trying to use another signal port other than AS55.



 The attached picture below is an example of the REFLDC and POXDC signals in time series.

This was when PRCL and MICH were locked by REFL33_I and AS55_Q respectively.


Note that when PRMI is unlocked, REFLDC goes to ~ 5000 counts and POXDC goes within ADC noise of ~ 1 counts.

According to the POP camera it looked like something was oscillating in the YAW direction which coincided with the spikes.

I tried finding any suspicious angular motions in the ITMs, BS and PRM olevs, but none of them showed the 2-3 Hz feature.

  5582   Fri Sep 30 05:35:42 2011 kiwamuUpdateLSClength fluctuations in MICH and PRCL

The MICH and PRCL motions have been measured in some different configurations.

According to the measurements :

      + PRCL is always noisier than MICH.

      + MICH motion becomes noisier when the configuration is Power-Recycled Michelson (PRMI).

The next actions are :

      + check the ASPD

      + check the demodulation phases

      + try different RFPDs to lock MICH


 The lock of PRMI have been unstable for some reason.
One thing we wanted to check was the length fluctuations in MICH and PRCL.

Four kinds of configuration were applied.
     (1) Power-recycled ITMX (PR-ITMX) locked with REFL33_I, acting on PRM.
     (2) Power-recycled ITMY (PR-ITMY) locked with REFL33_I, acting on PRM.
     (3) Michelson locked with AS55_Q, acting on BS.
     (4) Power-recycled Michelson locked with REFL33_I and AS55_Q, acting on PRM and BS.

In each configuration the spectrum of the length control signal was measured.
With the measured spectra the length motions were estimated by simply multiplying the actuator transfer function.
Therefore the resultant spectra are valid below the UGFs which were at about 200 Hz.
The BS and PRM actuator responses had been well-measured at AC (50 - 1000 Hz)
For the low frequency responses they were assumed to have the resonances at 1 Hz with Q of 5.

The below plot shows the length noise spectra of four different configurations.
There are two things which we can easily notice from the plot.
    + PRCL (including the usual PRCL and PR-ITMs) is always noisier than MICH.
    + MICH became noisier when the power recycling was applied.
In addition to them, the MICH noise spectrum tended to have higher 3 Hz bump as the alignment gets improved.
In fact everytime when we tried to perfectly align PRMI it eventually unlocked.
I am suspecting that something funny (or stupid) is going on with the MICH control rather than the PRCL control.


   BS actuator = 2.190150e-08 / f2
   PRM actuator = 2.022459e-08 /  f2
  5583   Fri Sep 30 06:25:20 2011 kiwamuUpdateLSCCalbiration of BS, ITMs and PRM actuators
The AC responses of the BS, ITMs and PRM actuators have been calibrated.
 To perform some interferometric works such as #5582, the actuator responses must be measured.
     BS = 2.190e-08 / f2     [m/counts]
     ITMX  = 4.913e-09 / f2   [m/counts]
     ITMY  = 4.832e-09 / f2   [m/counts]
     PRM   = 2.022e-08 / f2  [m/counts]
The same technique as I reported some times ago (#4721) were used for measuring the BS and ITMs actuators.
In order to measure the PRM actuator, power-recycled ITMY (PR-ITMY) was locked and the same measurement was applied.
The sensor response of PR-ITMY was calibrated by exciting the ITMY actuator since the response of the ITMY had been already measured.
  5584   Fri Sep 30 08:40:02 2011 KojiUpdateLSClength fluctuations in MICH and PRCL

Tip-Tilts has almost no isolation up to 3Hz, and isolation of about 0.5 up to 10Hz.
They have vertical resonances at around 20Hz.

See Nicole's entry




  5595   Sun Oct 2 02:33:32 2011 kiwamuUpdateLSCsomething funny with AS55

Just a quick report.

The AS55 signal contains more noise than the REFL signals.

Why ? Is this the reason of the instability in PRMI ?


 I locked the Power-Precycled ITMY with REFL33.

As shown in the plot above, I compared the in-loop signal (REFL33) and out-of-loop signals (REFL11 and AS55).

All the signals are calibrated into the displacements of the PR-ITMY cavity by injecting a calibration peak at 283 Hz through the actuator of PRM.

AS55 (blue curve) showed a structure around 3 Hz and higher flat noise below 1 Hz.

Quote from #5582
I am suspecting that something funny (or stupid) is going on with the MICH control rather than the PRCL control.


  5598   Mon Oct 3 04:43:03 2011 kiwamuUpdateLSCsideband-resonance PRMI locked

My goal of today was to lock PRMI without using AS55 and it is 50% successful.

The sideband-resonance PRMI (SB-PRMI) was locked with REFL33_I and REFL55_Q for the PRCL and MICH control respectively.

The carrier-resonance PRMI wasn't able to be locked without AS55.

     (it looked no clean MICH signals at the REFL ports.)



 The motivation of not to use AS55 came from the suspicion that AS55 was injecting some noise into MICH (#5595).

So I wanted to try another RFPD to see if it helps the stability or not. 


(locking activity)

  The lock of SB-PRMI was quite stable so that it stayed locked more than 30 minutes (it ended because I turned off the servos.)

Then I briefly tried DRMI while PRCL and MICH kept locked by the same control loops, namely REFL33_I and REFL55_Q.

The lock of MICH and PRCL looked reasonably robust against the SRCL fringes, but wasn't able to find a good signal for SRCL.

I think I am going to try locking DRMI tomorrow.

 - - settings

    Demod phase for REFL55 = -45.3 deg

    Demod phase for REFL33 = -14.5 deg

    Whitening gain for REFL55 = 4 (12 dB)

    Whitening gain for REFL33 = 10 (30 dB)

    MICH gain = 100

    PRCL gain = 8



 + I removed an iris on the ITMY table because it was in the way of POY. See the picture below.



  + I found that burtrestore for the ETMX DC coil forces were not functional.

  => currently ETMX's "restore" and "mislalign" buttons on the C1IFO_ALIGN screen are not working.

  => According to the error messages, something seemed wrong on c1auxex, which is a slow machine controlling the DC force.

  5624   Thu Oct 6 05:18:20 2011 kiwamuUpdateLSCNoise in AS55 was from clipping : fixed

It turned out the noise in AS55 was due to a clipping.  After fixing the clipping the noise successfully went down.

I was going to briefly check the clipping and go ahead locking DRMI, but for some reason I couldn't stop myself from working on this issue.

Here is a plot of the noise spectra taken before and after fixing the clipping.

The configuration of this measurement is exactly the same as that I did before (#5595)


(what I did)

 + Locked power-recycled ITMY so that the AS beam is bright enough to work with.

 + Shook BS at 1 Hz in the YAW direction

 + Looked around the AP table with an IR viewer and searched for a clipping moving at 1Hz.

 + Found the first lens in the AS beam path has clipped the beam at the upper side. A tiny portion of the beam was clipped.

 + Corrected the beam height to 4 inch by steering the very first mirror.

 + Raised the height of the lens because it was about 3.5 inch or so.

 + Found the lens had a scratch (~1 mm size ) at 1 cm blow the center on the surface.

   => I tried finding a spare 2 inch lens with a long focul length, but I couldn't find it,

        So I left the lens as it is, but we should buy some 2 inch lenses just in case like this.

 + Replaced the 1 inch beam splitter by 2-inch 99% BS so that most of the light goes into the RFPD and a little bit goes into the camera.

Quote from #5595

The AS55 signal contains more noise than the REFL signals.

  5626   Thu Oct 6 15:40:57 2011 JenneUpdateLSCArm absl length data taken

[Katrin, Jenne]

We took the data for the new absolute length measurement of both arms, after the latest vent and move.  We will analyze soonly.  We had done a round of analysis,  but then Koji pointed out that our data wasn't so clean because the whitening filters were on (and saturated the ADC).  We now have the data (but not the analysis) for the better data with the WF off.

So our dirty-data preliminary number for the X arm is 37.73meters, which is 14cm different from our old length.  We were supposed to move by ~20cm, so....either this measurement is bad because the data sucked (which it did), or we are 6cm off.  Or both.

I'll do another analysis with the clean data for both arms later today/tomorrow.

  5627   Fri Oct 7 04:42:24 2011 kiwamuUpdateLSCDRMI locked and some plans

DRMI has been locked using the same RFPD selection as the old days (i.e. AS55_I, AS55_Q and REFL_I).(#4760)

But remember : this is just a beginning of several measurements and tests to characterize the central part.


Here is a list of the measurements and actions :

  - 3f locking related

      + Listing up the necessary RFPDs and their installations.

      + Calibration of the SRM actuator  => this is necessary to convert the sensing matrix into unit of [counts/m] or [W/m].

      + Measurement of the sensing matrix => check the performance of 3f signals. Also diagonalization of the LSC sensing matrix

      + Diagonalization of the output matrix.

      + Noise characterization of 3f PDs => confirm the noise are low enough to keep the lock of the central part

 - Power-recycling gain issue related (#5541)

     + Estimation of the mode matching efficiency => maybe we can use power-recycled ITMs to estimate it (?)

     + Implementation of auto alignment servos and scripts for MICH, PRCL and SRCL. => integrate it to the existing ASS model

     + Search for a possible loss factor

  5628   Fri Oct 7 11:45:24 2011 KojiSummaryLSCPOY11 installed, 55MHz PD at POY removed

POY11 PD was installed last night. The lock of the Y arm was confirmed with the POY11I signal.

- The DC transimpedance was modified to be 1010V/A as the incident power is tiny.

- The demodulation phase of the roughly adjusted (148deg) to have PDH signal at the I-phase.
The comparison with AS55I signal exhibits that POY11I have ~150 times weaker signal with 45dB whitening.
(In total 25000 times weaker.)

On the way to make POY11 functioning, there were many fixes at the LSC rack...


- The PD interface cards (power supply for the RFPDs) were checked:
So far the two card at the right hand side were checked. 

Desipite the previous entry reported the issues on those boards, they did not show any problem yesterday.

One hypothetical possibility is the enabling switches that is controlled from the old slow epics targets.

- POY55 was removed

This 55MHz PD is supposed to be installed at POP.
The PD, an RF cable, an RF amp, the power supply of the RF amp were removed.

- POY11 was installed

The PD was placed where the 55MHz was placed.

The beam was aligned on the diode using the IR viewer and the digital multimeter.

The power supply cable and the RF cable for POY on the ITMY table were used.

There were an ND filter on the POY beam path. It was removed.

- On the LSC rack
The PD RF was connected to the patch panel at the top of the rack.

There were loose connectors on the patch panel. Some connectors were tightened on the panel.

I found that POY11 and POX11 had I&Q signal reversely connected to the whitening board.
   ==> These were fixed but
require the orthogonality test again for those channels.

The I phase output of the AS11 demod board had a broken connector. 

The onboard SMA has got disintegrated because of too much twist on the connector.
The board was once removed from the rack and the connector was fixed using a heat gun and soldering.

The DC signals were checked. POYDC was not correctly connected. POYDC were correctly connected to the POYDC channel.

c1lsc was found with the RFM frozen.
The c1lsc machine was soft-rebooted after stopping all of the RT processes.

Once the RT processes came back, they were all burtrestored.

- PDH locking
Restored Y-arm. Locked it with AS55Q.
Ran ASS alignment for Y-arm.
100cnt 150Hz sinusoidal signal is applied to ETMY

Measured the PSD of AS55Q, POY11I, and POY11Q.
Adjusted the demod phase so that the excitation could be minimized in POY11Q.

  5629   Fri Oct 7 11:53:47 2011 KojiUpdateLSCDRMI locked and some plans

- REFL165 PD to be fixed (shows constant high voltage at the DC out)

- Make POP22/110 PD

- Install AS11? or use it as POX11?

- Install POP55

  5637   Sat Oct 8 00:44:42 2011 kiwamuUpdateLSCcalibration of SRM actuator

The AC response of the SRM actuator has been calibrated.

(Summary of the calibration results)
     BS = 2.190e-08 / f2     [m/counts]
     ITMX  = 4.913e-09 / f2   [m/counts]
     ITMY  = 4.832e-09 / f2   [m/counts]
     PRM   = 2.022e-08 / f2  [m/counts]
     SRM   = 2.477e-08 / f2  [m/counts]    ( NEW ! ) 
The same technique as I reported some times ago (#4721) were used.
The Signal-Recycled ITMY was locked for measuring the actuator response.
Since the ITMY actuator had been already calibrated, first the sensor was calibrated into [counts/m] by exciting the ITMY actuator and then calibrated the SRM actuator with swept sine measurement.
 - - notes to myself
   SRCL GAIN = 2.2
   Sensor = REFL11_I
   Demod. phase = 40 deg
   Resonant condition = Carrier resonant
   Gain in WF = 0 dB

Quote from #5583
The AC responses of the BS, ITMs and PRM actuators have been calibrated.


  5638   Sat Oct 8 04:41:07 2011 kiwamuUpdateLSClength fluctuations in SRCL

For a comparison, the length fluctuation of Signal-Recycled ITMX (SRX) and ITMY (SRY) have been measured.

Roughly speaking the length motion of SRX and SRY are as loud as that of PRCL.

Some details about the measurement and data analysis can be found in the past elog entry (#5582).

In the process of converting the raw spectra to the calibrated displacements the SRM actuator was assumed to have a resonance at 1Hz with Q = 5.


(Notes on SRX/Y locking)

     Sensor = REFL11_I
     Actuator = SRM
     Demod. phase = 40 deg
     SRCL_GAIN = 20
     UGF = 100 - 200 Hz
     Resonant condition = Carrier resonance
     Whitening gain = 0 dB
     ASDC = 360 counts

Quote from #5582

The MICH and PRCL motions have been measured in some different configurations.

      + PRCL is always noisier than MICH.

  5639   Sun Oct 9 17:13:46 2011 kiwamuUpdateLSCFirst attempt to estimate mode matching efficiency using interferometer

The efficiency of the mode matching (MM) to PRC (Power-Recycling Cavity) has been estimated by using the interferometer.

The estimated MM efficiency is about 74 % when losses in the cavity are assumed to be zero.



 There had been an issue that the recycling gain didn't go to the designed high value of about 42  (#5541).
One of the possibilities is a low efficiency in the MM to PRC (also see #5541).
Although the MM efficiency had been measured using a beam scan ( see a summary on the wiki) a long time ago, it haven't been verified.
Therefore the MM has to be reviewed by using the real interferometer.


 The concept of this measurement is observe the amount of the reflected light from a power-recycled cavity and estimate the MM efficiency based on the measured reflectivities.
 Since using the real PRC (consisting of BS, ITMs and PRM) could be a too complicated system for this measurement,
simpler cavities, namely Power-Recycled ITMX and ITMY (PRX and PRY), were used to examine the MM efficiency.
 The measurement goes in the following order :
    (1) Measurement of the amount of the single-bounce reflection from PRM with BS and ITMs misaligned.
    (2) Lock PRX or PRY to carrier resonance.
    (3) Alignment of PRX/Y to maximize the intracavity power. This time ASDC was used as a monitor of the intracavity power.
    (4) Measurement of the amount of the reflected light when the cavity is in resonance. The value in REFLDC was averaged in 100 sec.
     => done by tdsavg 100 C1:LSC-REFLDC_OUT
The same measurement was performed for both PRX and PRY.
 - locking parameters -
  Sensor = REFL11_I
  Whitening gain = 10 (30 dB)
  UGF ~ 200 Hz


In order to estimate the relation between the MM efficiency vs. the reflected light, two models are considered:
   (1) simple model => no loss and no sidebands
   (2) sideband-included model => no loss but sidebands are taken into the account of the reflection.
(1) In the simple model the reflectivity Prefl / Pin is expressed by
         [Reflectivity]  = Prefl / Pin = Z * Rcav +  (1- Z) * Rprm
where Z is MM efficiency and Rprm is the reflectivity of PRM
and Rcav is the reflectivity of PRX/Y when it's resonance and it is defined by
         Rcav = | rprm - ritm t2BS|2 / |1 -rprm ritm t2BS |2
Tprm = 5.75% and Titm = 1.4 % are assumed in all the calculations.
In the first equation the first term represents the mode matched light and hence it couples with the cavity through Rcav.
The second term is the non-mode-matched light and because they are not interacting with the cavity they will be simply reflected by PRM through Rprm.
(2) In reality two phase-modulated light (11 MHz and 55 MHz) will behave differently from the carrier.
For example when the carrier is in resonance the sidebands will be anti-resonance against the cavity.
So that the amount of REFLDC will be slightly bigger because of the reflection of the sidebands.
      Prefl = Z * Rcav * Pc + Z * Ranti * Ps +  (1- Z) * Rprm * (Pc + Ps)
where Pc and Ps are the power in the carrier light and the sidebands respectively.
And Ranti is the reflectivity of the anti-resonance PRX/Y, which can be obtained by replacing the minus sign by the plus sign in the equation of Rcav shown above.
It is assumed that the sum of the carrier power and sidebands power is the incident power Pin = Pc + Ps.
The power in the carrier and the sidebands were estimated based on the OSA measurement (#5519), so that
          Pc / Pin = |J0(0.14)|2 * |J0(0.17)|2 =  0.976
          Ps / Pin = 2 * |J1(0.14)|2 + 2 * |J1(0.17)|2 =  0.024


Here are the measured values in REFLDC

 -- Measurement 1 : PRX
    Single bounce from PRM = 4802.27 counts
       ==> the incident power = 5095.25 counts
    Reflected light from PRX = 4433.88 counts
      ==> Reflectivity = 0.8702
-- Measurement 2 : PRY
    Single bounce from PRM = 4833.05 counts
       ==> the incident power = 5127.05 counts
    Reflected light from PRX = 4444.48 counts
      ==> Reflectivity = 0.86672
On average the reflectivity of power-recycled ITM cavity was 0.868 with a standard deviation of  0.001744.
Actually the standard deviation estimated here is not fair because the measurement was done by only twice,
but my intention was that I wanted to see how the error can affect the estimation of the MM efficiency.
Here is a plot comparing the model curves and the measured values with 5 sigma error box (5 times of measured standard deviation).


It is shown that the mode matching efficiency is 73.7 % when the sideband-included model is considered.
With the 5 sigma deviation it can go from 65% to 82% but it is still low and lower than the beam scan measurement ( see a summary on the wiki). 

Anyways the estimated MM efficiency with the sidebands effect included and without loss effect is

        MM efficiency = 73.7 +/- 1.7 % (1 sigma error)  or +/- 8.7 % (5 sigma error)

  5640   Mon Oct 10 00:01:26 2011 KojiUpdateLSCFirst attempt to estimate mode matching efficiency using interferometer

"^2"s are missing in the second equation, but the calculation results seem correct.

PRX and PRY have different mode matching because of the Michelson asymmetry.
Are individually estimated mode matching indicates any sign of reasonable mode mismatch?
(The difference can be very small because the asymmetry is not so big.)

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