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ID Date Author Type Categoryup Subject
  3859   Thu Nov 4 03:13:46 2010 SureshUpdateLockingFibre coupling 1064nm light at the south-end table

[Kiwamu, Suresh]

We decided to use the 1064nm beam reflected from the Y1-1037-45-P mirror after the collimation lens following the doubling crystal for coupling into the optical fiber (ref 3843 and 3847 ).

We replaced a beam dump which was blocking this beam with a Y1-1037-45-P mirror and directed the beam into the fiber coupler with another Y1-1037-45-P.  The power in this beam was about 1W.  This has been stepped down to 10mW by introducing a reflective ND filter of OD=2.  The reflected power has been dumped into a blade-stack beam dump.

Steve has ordered the The Visual Fault Locator from Fluke.  It is expected to arrive within a day or two.

 

 

  3865   Thu Nov 4 19:00:57 2010 SureshUpdateLockingFibre coupling 1064nm light at the south-end table

The Fluke Visual Fault locator (Visifault) arrived and I used it to couple 1064nm light into the single mode fibre at the south-end-table.

Procedure used:

When the output end of the fiber is plugged into the Visifault the light emerges from at the south end (input side for 1064nm).  This light is collimated with the fiber coupler at that end and serves as a reference for the optical axis along which the 1064 light must be directed.  Once the two beams (red and 1064) are overlapped with the beam steering mirrors, the Visifault was disconnected from the fiber and the  fibre output ( 1064 at the PSL table) is maximized by walking the beam at the input end and adjusting the collimation at the input.

The output of the fiber has been collimated with a fiber coupler.

7.5mW are incident on the input end and 1.3mW have been measured at the output.    This output power is adequate for the observing the beats with PSL NPRO.

 

 

 

  3866   Thu Nov 4 19:26:51 2010 SureshUpdateLockingChanges to the Video MUX reversed

All the temporary changes to the video cables and the video MUX ( 3843 ) have been reversed and the system returned to its original state.

  4143   Wed Jan 12 17:22:47 2011 SureshConfigurationLockingMC demod phase adjusted to minimise the I output

[Koji, Suresh]

We wanted to check and make sure that the relative phase of the two inputs ( local oscillator and photodiode signal ) to the demod board is such that the Q output is maximised.   We displayed the I and  Q signals on the oscilloscope in XYmode with I along the X direction.  If Q is maximised (and therefore I is minimised) the oscillocope trace would be perfectly vertical since all the signal would be in Q and none in I. Initially we noted that the trace was slightly rotated to the CCW of the vertical and that a short cable was present in the PD input line.  Removing this rotated the trace CW and made it pretty much vertical.  The screen shot of the oscilloscope is below.

.TEK00000.PNG

  4155   Fri Jan 14 12:29:57 2011 KojiUpdateLockingNext steps for the green

These are the next steps for a better operation of the arm locking. They are suitable for the day time activities

Reconfiguration of the X-End table

- End transmission power monitor (CDS model exists, need to configure the PD)

- IR steering mirror for the transmon

- Restore/align end green beam

- Relocate the end trans CCD

- Connect the video output cable for the X-end CRT monitor

LSC Whitening

- LSC Whitening binary IO connection

 


They are not urgent but also good things to do

MC servo characterization

- Error signal: frequency noise

- Loop characterization

Arm cavity characterization with cavity sweep

- Arm finesse for 1064nm and 532nm

- Arm FSR measurement with 1064 (and optionally with 532nm simultaneously)

- Arm g-factor for 1064nm and 532nm

  4161   Sun Jan 16 02:20:59 2011 SureshUpdateLockingcomparing the PSL with the X-end-NPRO through the green beat

Objective:

      We wish to study the coherence of the two NPROs i.e. PSL and the X-end-NPRO by locking both of them to the X-arm and then observing the green beat frequency fluctuations. 

What we did:

   a) locked the PSL to the X-arm as described in 4153

   b) locked the x-end-NPRO to the X-arm with a PDH lock to the reflected green from the ETMX

   c) Obtained the green beat signal with a spectrum analyser as described in 3771

Observations:

   Please see the attached screen shots from the spectrum analyser.   They are taken with different BW and sweep range settings.  They give a estimate of the width of the green beat signal and the range of the frequency fluctuations of the beat-note.

P1160510.JPGP1160511.JPGP1160515.JPG

P1160516.JPG

 

Estimates:

   a) width of the beat note is less than 6KHz if measured over time scales of a few milli seconds

   b) the frequency fluctuations of the beat note are about 100KHz over time scales longer than 100ms

Next Step:

    We wish to record the beat note frequency as a function of time in order to establish the stability over time scale of a day.

 

 

  4166   Wed Jan 19 03:37:30 2011 SureshUpdateLockingcomparing the PSL with the X-end-NPRO through the green beat

 

 

 [Kiwamu, Suresh]

Today we attempted to convert the beat-note frequency into an analog voltage using the SR620 frequency counter.

First an observation: the stability of the green beat was seen to be much better than the 100kHz fluctuation seen yesterday. Probably because Kiwamu noticed that one of the MC mirrors had a large variance in its motion and changed the  gain and filter parameters to decrease this.  The PSL was therefore more stable and the green peak fluctuation was less than 10kHz over time scales of a few seconds. 

SR620 D/A output resolution given by the manufacturer is 5mV over the -10 to +10V range and this range corresponding to 300MHz.  We, however saw fluctuations of 100mV on the screen which looked as if they corresponded to the  least significant bit.  This would imply a resolution of 1.5MHz at this range.   Even if the manufacturer's claim was true it would lead to a resolution of 75kHz, far in excess of the required resolution a few hundred Hz.

We therefore require to set up the VCO-PLL to obtain a finer frequency resolution.

In the mean time the green beat drifted beyond the 100MHz detection band of the green-PD.  So we changed the x-end-NPRO temperature by -0.05 to bring it back into the detection band.

 

We are also considering, Rana and Koji's suggestion of using a set of 14 flip-flops to divide the ~80MHz beat frequency so that it comes down to about 4kHz.  This could then be sampled by the usual 16-bit, 64kSa/s ADC cards and brought into the digital domain where further digital processing would be needed to extract the the required frequency variations  in the 0 to 10kHz band.  Found a nice paper on this object

Attachment 1: Phase_noise_in_digital_frequency_dividers.pdf
Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf Phase_noise_in_digital_frequency_dividers.pdf
  4177   Thu Jan 20 15:39:59 2011 AidanUpdateLockingUpper limit on frequency noise of ADC

[Aidan, Kiwamu]

Kiwamu and I plugged the output from a DS3456 function generator into the ADC and started recording the data. The func. generator output a 237.8Hz, 1Vpp sine wave. We chose this value because it corresponds to the FSR of a 38.5m cavity (=3.896MHz) divided by 2^14, the frequency divider amount we intend to use.

Since 1 FSR divided down is 237.8Hz and corresponds to a length change of the cavity of 532nm/2 = 266nm, then we can, roughly, say that a frequency change of 1Hz corresponds to a length change in the cavity of approximately 1nm. The width of the 237.8Hz peak in the spectra corresponds to an upper limit on the noise floor due to digitizing the signal (this could be limited by the ADC, or the function generator, or the windowing on the FFT).

The FWHM of the peak in the spectrum was approximately 5mHz, corresponding to an uncertainty in the length of the cavity of about 6pm (we used a Hanning Window, 50% overlap and a BW of 2.92mHz, 7 averages). Regardless of what is the dominant contribution to the width of the peak, this implies that the frequency noise associated with digitizing a signal in the ADC is much smaller than we require and will not limit our performance if we choose to use a frequency divider and digital PLL with the Green Locking.

RA: Here's the previous measurement

Attachment 1: Sine-wave-width-test_of_ADC.pdf
Sine-wave-width-test_of_ADC.pdf
  4178   Thu Jan 20 17:00:39 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

  4182   Fri Jan 21 11:45:01 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

Quote:

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

 Agreed. It doesn't completely rule out the digital PLL. I'll check out Kiwamu's model.

  4822   Wed Jun 15 02:20:00 2011 JenneUpdateLockingMICH noise budget?

I would like to announce my confusion with regard to the MICH noise budget, in hopes that someone else has some inspiration

If you tilt your head sideways, you will notice that in this plot (totally uncalibrated, as yet), the BLACK trace, which is my white-light measurement of the AS55 shot noise is above the AS55Q noise when the Michelson is locked (true only at low frequency).  You will also notice that the same appears to be true for the Whitening Filter + Antialiasing Filter + ADC noise (GRAY trace).  Since Black, Gray, Pink and Green should all have the same calibration factor (a constant), calibrating the plot will not change this.  Brown and Blue are the MICH_OUT (aka MICH_CTRL) for dark and bright fringes, respectively.

I measure 58mV at the DC out of the AS55 PD when the Michelson is locked on the bright fringe.  This (assuming DC transimpedance of 50ohms) gives 1.16mA of DC photo current.

So.  What is going on here?  Am I totally confused??

In other news, assuming (which I'm not 100% confident about right now) that these traces are vaguely correct, the Michelson is limited by shot noise above ~20Hz.  This is...good?  We want to be shot noise limited.  Do we want to be limited at such a low frequency?

(Also, yes I can calibrate the plot to m/rtHz, but no, I won't tonight because something is funny with my calibration for the free running noise and I'll fix it tomorrow.)

MICH_noise_budget_measurements_15June2011.jpg

  4823   Wed Jun 15 12:16:37 2011 JamieUpdateLockingMICH noise budget?

Quote
If you tilt your head sideways, you will notice that in this plot (totally uncalibrated, as yet), the BLACK trace, which is my white-light measurement of the AS55 shot noise is above the AS55Q noise when the Michelson is locked (true only at low frequency).  You will also notice that the same appears to be true for the Whitening Filter + Antialiasing Filter + ADC noise (GRAY trace).  Since Black, Gray, Pink and Green should all have the same calibration factor (a constant), calibrating the plot will not change this.  Brown and Blue are the MICH_OUT (aka MICH_CTRL) for dark and bright fringes, respectively.

Hey, Jenne.  I think there are a couple of things.  First, you're missing a PD dark noise measurement, which would be useful to see.

But I think the main issue is that it sounds like all of your closed loop measurements are done with the in-loop PD.  This means that everything will be suppressed by the loop gain, which will make things look like they have a noise lower than the actual noise floor.

  4893   Tue Jun 28 02:11:47 2011 JenneUpdateLockingLatest MICH noise budget

I have measured / calculated the latest MICH noise budget.  It doesn't really look all that stellar.

MICH_noise_budget_as_of_28June2011.png

As you can see, we are nowhere near being shot noise limited, since there's a huge discrepancy between all of the measured spectra and the teal Shot Noise line. 

One possible suspect is that the analog whitening filters weren't on when I took my measurements.  I didn't actually check to ensure that they were on, so they might not have been.  Right now we're limited by electronics and other boring noises, so I need to make sure we're limited by the noise of the diode itself (we don't have enough light in the IFO to actually be shot noise limited since that takes 2.5mA for AS55 and I only have 1.1mA, but we should be ~within a factor of 2ish).

  5035   Tue Jul 26 03:15:52 2011 JenneUpdateLockingLatest MICH noise budget

[Jenne, Rana]

We had another look at the MICH noise budget tonight. Rana has verified that my techniques / math aren't too ridiculous. 

In the first attachment, you'll notice that the MICH noise is waay above the shot noise of 1mW on the beam splitter.  We don't know why.  One problem is that the modulation depth of the 55MHz is too low by ~a factor of 10.  Kiwamu and his magical resonant circuit are working on fixing this.  This will not, however, fix the huge discrepancy here.  More investigation and meditation is required!  For this measurement, the whitening gain of AS55 was set to 42dB for both I and Q.

In the 2nd attachment, the PSL shutter is closed, so all of these are dark measurements of AS55.  (The input matrix on the LSC screen is AS55Q * 1 -> MICH_IN1, so they're the same).  All we've done is change the whitening gain before the ADC.  For 0dB and 9dB, you can see that the low freq noise didn't change - here we're still limited by the ADC noise.  With 21dB and 42dB we're clear of the ADC, so either is fine.  Unfortunately, the high freq stuff when the loop is on matches up with the high freq part of the dark noise, so that's part of the problem....

Attachment 1: MICHnoise_shotNoise_25July2011.pdf
MICHnoise_shotNoise_25July2011.pdf
Attachment 2: MICH_darkNoise_whiteningGainChanging_25July2011.pdf
MICH_darkNoise_whiteningGainChanging_25July2011.pdf
  5051   Thu Jul 28 02:33:04 2011 JenneUpdateLockingYarm flashing, but not yet locked

Because I'm too lazy to write a cohenrent elog right now, here's my notes that I wrote while working tonight:

Elog notes, 27July2011

Aligned Xarm, just to check on it.  Had to flip sign of TRX in DCPD filter bank (to gain of -1) to make the signal positive.

Restored Yarm, see some slight flashing, but no lock yet.
Adjusted phase rotation of AS55 from 56.5deg to 60deg, just by-eye trying to maximize AS55I, my arm error signal. AS55I goes from ~ -40 to +60 counts

Tried fitzing with Yarm gain, flipping sign, incr gain. No real change in signals, or flashing.


Incr. ETMY oplev gains to -0.4 from -0.2
Engaged ELP35's on Pit and Yaw, to be more similar to other optics.  However, right now all of the optics have different things in their filter banks.  Why??

Arm is flashing pretty reliably now, but still not locking.  The trigger threshold is always satisfied, so that's not it.

  5233   Sun Aug 14 20:04:40 2011 Keiko, Anamaria, Jenne, and KiwamuSummaryLockingcentral part ifo locking plan
GOAL : To lock the central part of ifo

Here is the plan:

Mon - assemble all the cables from PDs and mixers, and check the CDS channels. Prepare the beamsplitters.

Tue - The current paths to REFL11 and REFL55 will be modified to the four paths to REFL11, 33, 55, 165. And the PDs will be placed.
Wed, Thu - during waiting for the ifo available with vacuum, help aligning the POP, POX, POY. In parallel, a simulation to find the PRC length SRC 
length tolerance will be proceeded.

Fri - When the ifo becomes available with vacuum, the sensing signals by 3-f scheme will be obtained with proper demodulation phases.

Sat - Try to lock the central part of the ifo with the new 3-f signals.
  5243   Mon Aug 15 21:43:29 2011 Anamaria and KeikoSummaryLockingcentral part ifo locking project

 REFL33 and REFL165 cables were connected from the AP table to the rack.  Cables on the rack for REFL33I, 33Q, 165I, 165Q ports were connected, too. Connections were confirmed by the data viewer. Two SMA cables which will be used for the two PDs on the AP tabl were built. We will be able to place the two PDs tomorrow. The beamsplitters to split the laser to REFL33 and REFL165 ports were mounted and ready to be placed.

  6421   Thu Mar 15 04:04:23 2012 KojiConfigurationLockingPRC Matching issues

Kiwamu and Koji

We found that the intra-cavity mode of the PRC is not round although it was obvious even with the DARK and REFL port images.
We need to review the mode matching situation.

In order to look at the PRC intra-cavity mode, we reconfigured the POP CCD.

If we look at the beam reflected from the Michelson, the beam is round. However, the PRC intra-cavity mode can never be round
in any resonant conditions. (Pict 1, 2, and 3, for the sideband resonant, carrier resonant conditions and another carrier resonant
one, respactively). Particularly the mode of the carrier resonant case is very unstable and always changing.

P3150902.jpg

P3150906.jpgP3150907.jpg

By misaligning the PRM, we can compare between the spot directly reflected from the Michelson and the one after additional round trip in the PRC (Pic 4).

They looks round, but it was obvious the secondary reflection is dimmer and larger (Pic 5). The intensity difference corresponds to the factor RPRM RMI
(i.e. product of the reflectivities for the PRM and MI). It can be understand if the dimmer spot looks smaller due to the artifact of the CCD. But it is opposite.

This may mean the mode matching is not correct. We are not sure what is not right. This could be just an incorrect incident beam, the curvature error of the PRM,
beam is distortec by the TT mirrors, or some other unknown reasons.

More precise analysis can be done with quantitative analysis of those two spots with Beamscan. This could happen tomorrow.

P3150910.jpgP3150900.jpg

  6437   Thu Mar 22 17:35:59 2012 kiwamuUpdateLockingmode profiles of the POP and POX beams : not bright enough

I tried to measure the beam profiles at the POP and POX ports as Koji mentioned in his entry (#6421).

However it turned out that the beam powers were too small to be measured with our beam scan at those ports.

So I will move on to measurements at the REFL port as Rana suggested because the laser power is much larger than that of POP and POX.

(If the data of the POP and POX beam profiles turn out to be very necessary, we will do the razor blade technique with a more sensitive photo diode)

Quote from #6421

More precise analysis can be done with quantitative analysis of those two spots with Beamscan. This could happen tomorrow.

 

  6532   Thu Apr 12 23:52:49 2012 JenneUpdateLockingPRMI locked - 'bouncy'

I am locking some things, and have the PRM aligned, and it will stay locked for short periods of time, but as Kiwamu warned me, when the PRM alignment is better, the lock is more "crazy" and unstable.  This should go on our list of mysteries.

 

  6596   Thu May 3 13:19:17 2012 JenneUpdateLockingMore success last night

I locked each arm, and the Michelson last night, no problems after I increased the Yarm gain from 0.1 to 0.2 .  I checked the green beam alignment just before going home, and both of the green beams are locking on ~03 or 04 modes, so aligning them is on the list for today.

  6629   Wed May 9 04:47:20 2012 JenneUpdateLockingPRM is really moving when PRMI locked

A few things tonight.  Locked both arms simultaneously (IR only).  Locked MICH, Locked PRMI, although it doesn't like staying locked for more than a minute or so, and not always that long.

Locking PRCL was possible by getting rid of the power normalization.  We need to get some triggering going on for the power norm.  I think it's a good idea for after the cavity is locked, but when PRCL is not locked, POP22 is ~0, so Refl33/Pop22 is ~inf.  The PRCL loop kept railing at the Limit that was set.  Getting rid of the power normalization fixed this railing. 

I took some spectra of PRM's oplev, while PRMI was locked, and unlocked.  The PRM is definitely moving more when the cavity is locked.  I'm not sure yet what to do about this, but the result was repeatable many times (~6 or 7 over an hour or so).  The OpLev spectra when PRMI was locked didn't depend too strongly on the PRM's alignment, although I think that's partly because I wasn't able to really get the PRM to optimal alignment.  I think POP22I is supposed to get to 7 or so...last week with Koji it was at least flashing that high.  But tonight I couldn't get POP22I above 4, and most of the time it wouldn't go above 3.  As I was aligning PRM and the circulating SB power increased, POP22I fluctuations increased significantly, then the cavity unlocked.  So maybe this is because as I get closer, PRM gets more wiggly.  I tried playing 'chicken' with it, and took spectra as I was aligning PRM (align, get some improvement, stop to take spectra, then align more, stop to take spectra....) but usually it would fall out of lock after 1-2 iterations of this incremental alignment and I'd have to start over.  When it relocked, it usually wouldn't come back to the same level of POP22I, which was kind of disappointing. 

In the PDF attached, pink and light blue are when the PRMI is locked, and red and dark blue are no PRCL feedback.  The effect is more pronounced with Pitch, but it's there for both Pitch and Yaw.

Also, I need to relook at my new restore/misalign scripts.  They were acting funny tonight, so I'm taking back my "they're awesome, use them without thinking about it" certification.

Attachment 1: PRM_louder_when_aligned.pdf
PRM_louder_when_aligned.pdf
  6631   Wed May 9 09:19:22 2012 KojiUpdateLockingPRM is really moving when PRMI locked

Is this enhancement of spectrum caused by the lock? Or by the actuation?

If this is also seen with approximately same amount of actuation to PRM POS,
this is just a suspension problem.

If this is only seen with the PRM locked, this is somehow related to the opt-mechanical coupling.

  6701   Tue May 29 14:58:28 2012 JenneUpdateLockingETMX trans camera

...will be helpful for acquiring lock after the vent.  We should install a camera at ETMX.

  6705   Tue May 29 15:49:02 2012 KojiUpdateLockingETMX trans camera

Quote:

...will be helpful for acquiring lock after the vent.  We should install a camera at ETMX.

 Do that.

  6711   Tue May 29 21:50:21 2012 JenneUpdateLockingYarm error spectra

The ~16Hz bounce mode of some optic is showing up in the Yarm error signal. 

MC is kind of 'windy' looking, so maybe it's from that? (Yuta's guess).

We need to make sure that the SUS damping and oplev paths both have notches at the correct bounce mode, not the old, old MOS frequency.  If that doesn't work, may need to put a resgain in Yarm path.

Attachment 1: LSC_POY_11_I_ERR_29May2012.pdf
LSC_POY_11_I_ERR_29May2012.pdf
  6714   Wed May 30 13:24:08 2012 JenneUpdateLockingYarm error spectra

Quote:

The ~16Hz bounce mode of some optic is showing up in the Yarm error signal. 

MC is kind of 'windy' looking, so maybe it's from that? (Yuta's guess).

We need to make sure that the SUS damping and oplev paths both have notches at the correct bounce mode, not the old, old MOS frequency.  If that doesn't work, may need to put a resgain in Yarm path.

 Made the Bounce notch in the BounceRoll filter (ITMY OLPIT, ITMY OLYAW)  wider, so it actually spans the peak we see in the error spectra.  When we next lock the arm later today, I'll retake this spectra to see if the ETMY oplev fix (Koji, Yuta) and this notch fix both helped.

  6729   Thu May 31 11:02:14 2012 steveUpdateLockingETMX 1064 trans camera

Quote:

Quote:

...will be helpful for acquiring lock after the vent.  We should install a camera at ETMX.

 Do that.

 Jenne and Steve

Sony CCD in place needs alignment and ND filter

  6829   Mon Jun 18 16:23:59 2012 JenneUpdateLockingLSC trigger update

The LSC triggers for the individual filter modules in a filter bank now works.  This is handy so that boosts can come on as soon as a cavity is locked, but will turn off when the cavity unlocks.

You choose which filter modules you want to be triggered, and which ones you want to be manually controlled. 

Example:  LSC-YARM    FM4 and FM5 should always be on, but FM2 and FM3 are controlled by the trigger.  You can set the trigger thresholds for the filter modules independently of the main DoF enable trigger thresholds.

  6833   Tue Jun 19 20:26:50 2012 JenneHowToLockingSummer Plan

Jenne and Yuta's Summer Plan

These are the things that we'd like to accomplish, hopefully before Yuta leaves in mid-July

* Yarm mode scan

  ~ Measure residual motion of Yarm cavity when ALS is engaged

* Xarm mode scan

  ~ Align Xarm IR

  ~ Align Xarm green to cavity

  ~ Do mode scan (similar to Yarm)

  ~ Measure residual motion of Xarm cavity when ALS is engaged

* Hold both arms on IR resonance simultaneously (quick proof that we can)

  ~ Modify beatbox so we can use both X and Y at the same time (Jamie will do this Wednesday morning - we've already discussed)

* PRMI + Arms

  ~ Lock the PRMI (which we already know we can do) holding arms off resonance, bring both arms into resonance using ALS

* PRC mode matching - figure out what the deal is

  ~ Look at POP camera with video capture - use software that Eric the Tall wrote with JoeB to measure spot size

* DRMI glitches

  ~ Why can't we keep the DRMI locked stably?

* DRMI + Arms

  ~ Full lock!!

  ~ Make lots of useful diagnostics for aLIGO, measure sensing matricies, etc.

  6838   Wed Jun 20 16:37:11 2012 yutaUpdateLockingETMX 1064 trans camera

[Jenne, Yuta]

We made ETMXT camera working.
We connected the camera to video mux, placed 10% pick off mirror in front of TRX PD, lead the beam go to ETMXT camera.
Transmission to the TRY PD was 23.8 uW, but now, it's 21.3 uW (2.3 uW goes to the camera).
So, we changed C1:LSC-TRX_GAIN from -0.00181818 to -0.00203158 (=-0.00181818*23.8/21.3).

There is a channel for power normalization, C1:LSC-TRX_POW_NORM, but is 1 and it looks like we are using this gain for the normalization. Situation of TRY is the same as TRX.

  6840   Wed Jun 20 18:09:23 2012 yutaUpdateLockingboth arms aligned, ITMX oplev centered

[Jenne, Yuta]

We aligned FPMI. I also centered ITMX oplev because the light was not hitting on QPD.
Alignment procedure we took was;

1. Align Y arm to the Y end green(Y green trans to PSL is now 195 uW with Y end laser measured temperature 34.14 degC).
2. Aligned IR using PZT2 to Yarm(Now, TRY ~ 0.90).
3. Aligned ITMX monitoring AS spots.
4. Aligned X arm so that TRX maximize.
5. Fine adjusted both BS and X arm(Now, TRX ~ 0.82).

Beam spot position on ETMX looks a little too high & left (from ETMXF camera), but we will leave it until ASS scripts is fixed.

FPMIalignment2010620.png

  6847   Thu Jun 21 12:56:49 2012 yutaUpdateLockingETMX 1064 trans camera

Quote:

[Jenne, Yuta]

We made ETMXT camera working.

 Xarm_EndTableLayout_NewTransCamera.png

Here's the new end table layout, for the transmitted IR stuff.

  6849   Thu Jun 21 15:36:51 2012 yutaUpdateLockingX arm alignment

I aligned X arm so that the beam spot comes roughly on the center.

1. Use ITMX and ETMX (mainly ITMX) to make beam spot come on center of the optic using eyeball.

2. Use ETMX and BS to maximize TRX power (reached ~ 0.85)

3. Aligned green optics on X end. Transmission of X green measured at PSL table is now 255 uW and TEM00 has the most power.

It was not easy to increase X green transmission more because beam spot on green transmission PD is wiggly when X end table is opened. When closed, wiggliness is about the same for Y green and X green.
Turning off HEPA on the X end didin't helped, but there must be something bad in the X end table. If we couldn't figure out why, let's wait for PZTs to come for end tables.

Considering the laser power is different(X end 1 W, Y end 700 mW), X green transmission should reach ~400 uW. But I think we should go on to X beat search.

I placed green shutter for X end back for convenience. I put some spacers to adjust its height and avoid beam clipping.


[Steve, Yuta]

What causing wiggly X green transmission was the air flow from the air conditioner. When we turned it off, beam spot motion became quiet. Air flow from HEPA was not effecting much.

  6886   Thu Jun 28 00:50:48 2012 yutaUpdateLockingPRMI work started, commissioning plan

My goal for tonight was to lock PRMI,
 grasp the current situation by my eye,
  and capture some images using Sensoray.

They are done, but what are we going to do to solve the problem? The beam looks terrible than I had expected.


What I did:
  1. DC output of POP55 PD was plugged out from 1Y2 rack, so we plugged it in.

  2. Aligned POP beam to POP25 PD and moved POP camera position at ITMX table.
 
  3. Mis-aligned PRM and SRM, aligned both arms, aligned FPMI as usual.

  4. Mis-aligned PRM and ETMs, aligned MI and locked MI.

  5. Aligned PRM, and carrier locked PRMI. PRM alignment was not saved since June 7, so slider values which give good alignment was pretty much drifted (~0.4 in C1:LSC_PRM_(PIT|YAW)_COMM).

  6. Took some images of POP, REFL, AS during PRMI lock.

POP_1024903948.bmpREFL_1024903929.bmpAS_1024903921.bmp


PRMI commissioning plan:
  From the beam shape at POP, REFL, and AS, the problem clearly comes from the mode-matching, including clipping, longitudinal mismatch, and alignment mismatch. Koji's idea of flipped-PRM seems reasonable, so I think we should better measure something to prove this.
  To prove this,

  1. Simulate what the beam look like in POP, REFL, AS if PRM was flipped. Compare them with actual captured images. I need to study on unstable cavities.
  2. Calculate power recycling gain and compare.
  3. Misalign PRM and capture the image of primary, secondary, ... reflections like Koji did in elog #6421. Measure the beam sizes of these reflections using some image analysis(Python Imaging Library? Is there anyone good at this?) and calculate PRM curvature.
  4. Can we do come characterization by making PRM-ITMY cavity? ITMX will be mis-aligned, BS will be the loss port to PRC.
  5. Beamspot on POP, REFL, AS looks woblby when PRMI is locked. Why?
  6. Open the vaccum chamber and see PRM. Simple.

  Any other ideas? I have to lock PRFPMI, at least, by July 13!

  6887   Thu Jun 28 01:44:57 2012 KojiUpdateLockingPRMI work started, commissioning plan

To be fair, this is Kiwamu's idea. And nothing is reasonable before it is confirmed quantitatively.

Quote:

Koji's idea of flipped-PRM seems reasonable, so I think we should better measure something to prove this.

  6888   Thu Jun 28 15:21:02 2012 ranaUpdateLockingPRMI work started, commissioning plan

 

 Cycling the vacuum is easy. Why not vent starting Thursday evening and pop the doors on Friday morning? Inspect on Friday and pump on Monday morning.

  6889   Thu Jun 28 20:59:28 2012 yutaBureaucracyLockingvent for PRC check, TOMORROW!

Koji, Jamie and I talked together and I decided to VENT TOMORROW MORNING. Main purpose of this vent is to see if PRM is flipped or not.

Vent schedule:
June 28 (Thu)
  Prepare for the vent tonight

June 29 (Fri)
  Start vent in the morning
  Look into PRC in the evening. If PRM was flipped, we will correct them. We'll use REFL to align the PRM. If PRM was not flipped, look into PR2,PR3 and other related optics.

June 30 (Sat)
July 1 (Sun)
  Thinking time. I can work if needed.

July 2 (Mon)
  If we need something else to do, do it.
  If not, start pumping.
  July 4th is the Independence Day. So, I need IFO working before July 4th.

Check List:
 We will just open the BS chamber.
  - PRM flipping
  - PR2, PR3 flipping
  - PRC suspensions
  - Cipping check in PRC

  6890   Thu Jun 28 22:08:57 2012 JenneBureaucracyLockingvent for PRC check, TOMORROW!

Quote:

Check List:
 We will just open the BS chamber.
  - PRM flipping
  - PR2, PR3 flipping
  - PRC suspensions
  - Cipping check in PRC

 What do you mean by PR2, PR3 flipping?  They are (supposed to be) flat mirrors, so obviously they should be installed correctly, but they won't change the mode matching in a huge way if they're backwards, right?

For the PRM, I recommend checking (a) the arrow inscribed on the thinner side of the optic and (b) that the arrow *actually* points to the HR side.  I'm pretty sure I installed all the optics with the arrow pointing away from the OSEMs, but I never did a thorough check that the arrow always actually pointed to the HR coated side.  I don't remember any optics where I said "hmmm, that's funny, the arrow is pointing backwards", but nor did I write down that I had checked.

Also, hopefully the PRM is correct.  If however it's not, that means that all of the magnets are glued onto the HR side, and we'll have to redo all of the magnet gluing.  The guiderods should be fine, but all 6 magnets would need redoing.  If we were very, very careful and didn't break any of the magnets off of the dumbbells, it's a 24 hour turnaround due to drying time.  Since inevitably we break magnets away from dumbbells, conservatively we should think about a 48 hour turnaround. 

  6891   Fri Jun 29 01:49:36 2012 yutaBureaucracyLockingvent for PRC check, TOMORROW!

Quote:

 What do you mean by PR2, PR3 flipping?  They are (supposed to be) flat mirrors, so obviously they should be installed correctly, but they won't change the mode matching in a huge way if they're backwards, right?

We see some ghost beam spots at POP. This may come from the back of PR2 and PR3. Also, they may change mode matching because of thermal lensing, mirror deformation, and other unexpected reasons. I thought we should check every mirrors in PRC, if PRM is not flipped.

We are going to check PRM just because we spent so much time for the PRC problem, and still don't have the solution or evidence.
PRM flipping is kind of the only idea for the root of all evil -- terrible beam shape, low PR gain, unstable PRMI lock.
So, I want to check with my eye during the stay.

I don't think we have to redo magnet gluing. It's okay to leave them on HR side.

  6913   Wed Jul 4 20:13:46 2012 yutaBureaucracyLockingPRC commissioning plan

Issues in PRC:
  1. Power recycling gain is too low (~ 15 instead of 40, according to Kiwamu).
  2. Mode matching to both arms are ~90%(see #6859), but PRC has terrible mode.
       Clipping/flipping in PRC?
  3. From cameras, beam spot moves so much when PRMI is locked.
       Alignment? Mirrors(especially PR2/3) moves too much?
  4. Error signals are glitchy when PRMI is locked.
       Servo design? Mirrors moves too much?

What we have learned from the vent:

  1. PRM, PR2, PR3 was not flipped.
  2. Their suspensions looked OK, too.
  3. We noticed clipping at BS and Faraday. They must be avoided when tip-tilts are installed on next vent.

  4. Took useful photos for next vent. Positions of green optics on optical layout CAD must be updated.
  5. It is not so difficult to recover the IFO state after cycling the vacuum if we use attenuator setup using PBS (see elog #6892).  But, of course, we need plans before cycling.

Commissioning Plan:
  - measure PRMI power recycling gain from POP
  - FPMI using ALS
  - measure PRFPMI power recycling gain from TRY/X
  - correlation between beam spot motion at POP camera and glitch
  - correlation between PR2/PR3 motion and glitch (how can we measure PR2/3 motion? set up oplevs?)
  - mode scan for PRC, using AS AUX laser
  - beam profile measurement at REFL,POP
  - refine servo design of MICH and PRCL

  6914   Wed Jul 4 21:11:53 2012 yutaUpdateLockingFPMI in vacuum is back

I aligned FPMI and greens. There's no recognizable difference between before and after the vent.

What I did:
  1. Aligned Y arm to maximize Y green transmission.
  2. Used PZT1/2 to maximize TRY. But since PZT1 doesn't work so much, I had to align Y arm, too (mostly ETMY). This decreases green transmission, but I will leave it.
  3. Aligned BS and X arm to maximize TRX
  4. Fine tune them to minimize ASDC during FPMI lock, without decreasing TRX
  5. Aligned X end green to get TEM00 transmission.

Now, TRY and TRX are both  ~0.89.
Green transmission from Y and X arm are ~123 uW and ~275 uW respectively. Their max we got so far was ~200 uW and ~255 uW.
I still see clipped beam at AS, which I think is from the Faraday edge, as we found in elog #6897.
Below is the Sensoray capture of some ports, and MEDM screen shots to compare with before vent(see #6893).
There are two AS captures, one is without MI lock and the other is with MI lock. Note that PRM/SRM is misalined.

ALL_1025495266.pngMEDMscreenshotswithCOW_20120704.png


Next:
 - I will check ALS
 - I keep Y end green optics untouched since elog #6776, to use it as a reference. We need to realign them if tip-tilts are installed in vacuum, or PZTs are installed in both ends.

  6916   Thu Jul 5 01:34:11 2012 yutaUpdateLockingMI with X arm ALS

I tried to lock FPMI using ALS, but I could not take care of ALS for both arms + MI. So, I decided to try one arm + MI.
I don't know why, but I couldn't make it. We need investigation.

Procedure I took:

  1. Align FPMI.

  2. Misalign ETMY.

  3. Press CLEAR HISTORY for C1:ALS-BEATY_FINE_PHASE filter module.
    Are there any command to do this?

  4. Stabilize X arm length.
    I made a script for turning on ALS servo nicely. It currently lives in /users/yuta/scripts/easyALS.py. You have to specify the arm(X or Y) and sign of the gain. It needs to be refined.

  5. Sweep the offset and stabilize X arm lenth to IR resonance.
   (Ran /opt/rtcds/caltech/c1/scripts/ALS/findIRresonance.py Xarm)

  6. Tried to lock MI. I tried to do this by feeding back the signal to BS or ITMs. Both worked fine when ALS holds X arm to IR off-resonance, but I couldn't lock MI when ALS holds X arm to IR resonance. This may come from too much phase fluctuation from X arm reflection. We should investigate this.

Handing off the servo from ALS to LSC:

  I made a script to do this. It just decreases ALS gain and increases LSC gain with 30 sec ramp time. It needs to be refined, so it currently lives in /users/yuta/scripts/handofftoLSC.py. It worked fine without loosing IR transmission.

ALS stability:
  Current stabiliy of the ALS servo is not enough. It doesn't stay for more than ~ 10min. I suspect this is from frequency servo of end lasers losing lock, or beat signals being too small for the beat box because of intensity fluctuation of green transmission. We definitely need to align end greens, but it is painful.

  6922   Thu Jul 5 13:38:05 2012 yutaSummaryLockingcavity g-factor from mode scan

Cavity g-factor for X arm is 0.3737 +/- 0.002, Y arm is 0.3765 +/- 0.003.
If ITMs are flat and arm length L = 39 +/- 1 m, this means RoC of ETMX and ETMY is 62 +/- 2 m and 63 +/- 2 m respectively.

Calculation:
  Transverse mode spacing is expressed by

nu_TMS / nu_FSR = arccos(sqrt(g1*g2)) / pi

  where g1 and g2 is g-factor

gi = 1 - L/Ri

 of ITM/ETM.

  For mode-scan, we swept laser frequency nu. Let's assume this sweep was linear and we can replace laser frequency with time. From the mode-scan result, TMS can be derived by

  t_TMS = sum((n_i-n)*(t_i-t)) / sum((n_i-n)^2)

  where n_i is the order of transverse mode, n is average of n_i's, t_i is the time i-th order mode appeared and t is average of t_i's.
  Since I could only recognize up to 3rd order mode, this can be rewritten as

  t_TMS = 1.5/5 * t_0 + 0.5/5 * t_1 - 0.5/5 * t_2 - 1.5/5 * t_3

  FSR is time between TEM00s. So, g1*g2 can be calculated by

g1*g2 = (cos(pi*t_TMS/t_FSR))^2


X arm result:

  From the 8FSR mode-scan data (see elog #6859), X arm HOM positions in sec are;

HOM 0    242.00     214.76     187.22     159.27     131.33    102.96     74.61     46.00     17.51
HOM 1    234.29     206.78     179.20     150.96     122.90     94.58     66.27     38.10
HOM 2    226.36     198.91     170.80     142.92     114.62     86.51     58.05     29.65
HOM 3    218.14     190.65     162.71     134.78     106.68     78.27     49.95     21.25


  Calculated FSR and TMS in sec are;

FSR    27.24     27.54     27.95     27.94     28.37     28.35     28.61     28.49
TMS     7.951     8.020     8.193     8.151     8.223     8.214     8.220     8.270

  Calculated cavity g-factor are;

g1*g2    0.3699     0.3720     0.3662     0.3704     0.3761     0.3765     0.3839     0.3748

  By taking average,

g1*g2 = 0.3737 +/- 0.002  (error in 1 sigma)


Y arm result:
  From 8FSR mode-scan data (see elog #6832), Y arm HOM positions in sec are;

HOM 0    246.70     218.15     190.06     161.87     133.26    104.75     76.01     47.19     18.60
HOM 1    238.83     210.55     181.88     153.47     124.93     96.08     67.51     39.01
HOM 2    230.48     202.21     173.64     144.80     116.43     86.17     59.84     31.43
HOM 3    222.15     193.47     165.33     137.13     108.60     80.04     51.17     22.25


  Calculated FSR and TMS in sec are;

FSR    28.55     28.09     28.19     28.61     28.51     28.74     28.82     28.59
TMS     8.200     8.238     8.243     8.289     8.248     8.404     8.219     8.240


  Calculated cavity g-factor are;

g1*g2    0.3841     0.3657     0.3683     0.3765     0.3778     0.3683     0.3904     0.3811

  By taking average,

g1*g2 = 0.3765 +/- 0.003  (error in 1 sigma)


Conclusion:
  If ITMs are flat and arm length L = 39 +/- 1 m, this means RoC of ETMX and ETMY is 62 +/- 2 m and 63 +/- 2 m respectively. Designed RoC is 57.35 m.
  Error of RoC is dominated by arm length error. So, we need more precise measurement of the length. This can be done when scan is calibrated and we can measure FSR in frequency.
  Also, we need evaluation of linearity of the sweep. This also can be done by calibration.

  6925   Fri Jul 6 01:39:56 2012 yutaUpdateLockingMI + Y arm ALS succeed, but not both

MI with X arm length stabilized off resonance and Y arm length stabilized at resonance using ALS succeed, but I couldn't bring X arm to IR resonance. This maybe because of too much phase fluctuation. I will calculate it later.

What I did:
  1. Brought X arm to IR resonance.
  2. Brought Y arm to IR resonance.
  3. Brought X arm to off-resonance.
  4. Brought Y arm to off-resonance. (1-4 are to play with arms)
  5. Locked MI in dark fringe using AS55_Q as error signal and BS as actuator.
  6. Brought Y arm to IR resonance. This flips sign, so MI lock will be bright fringe.
  7. Brought X arm to IR resonance. This destroys MI lock.

  Below is the plot showing what I did
FPMIALStrial20120706.png

  I also tried to lock MI after both arms are stabilized at resonance, but it failed, too.
  MI + X arm ALS fails. I think this is from too much BS motion to compensate phase fluctuation of arm reflected beam.
  MI + Y arm ALS fails when I want to lock in dark fringe. Only bright fringe works.


New compact MEDM screen for ALS:

  It has (almost) everything you need for ALS. It lives in /opt/rtcds/caltech/c1/medm/c1gcv/master/C1ALS_COMPACT.adl.
  Features;

  - Button for turning on/off ALS. It even does "clear history"!
      (light brown button "ON plus", "ON minus", "OFF"; runs /opt/rtcds/caltech/c1/scripts/ALS/easyALS.py; Currently, you have to guess the sign of gain. Ctrl-C if the sign was wrong. It will be nice if script can handle this. Use lockin to detemrine the sign?)

  - Button for finding IR resonance.
      (pink button "IRres"; runs /opt/rtcds/caltech/c1/scripts/ALS/findIRresonance.py)

  - Button for bringing arm length to off-resonance.
      (pink button "-10", "+10"; steps +/- 10 deg offset)

  - Button for toggling green shutters.
      (green button "shutter"; runs /opt/rtcds/caltech/c1/medm/c1gcv/cmd/toggle(X|Y)Shutter.py)

  - Button for switching monitors.
      (grey button "Video (X|Y)arm"; runs /opt/rtcds/caltech/c1/scripts/general/Video_(X|Y)arm.csh)

  - Slider for changing temperature of end lasers. You can also open temperature servo screens from orange "(X|Y)SLOW" button.

newALSMEDMscreen.png

  6926   Fri Jul 6 02:46:03 2012 yutaUpdateLockingY arm ALS handing off to LSC

Handing off the servo from ALS to LSC for one arm is quite easy because servo filters are pretty much same for ALS and LSC. I demonstrated it Y arm during MI is locked.
We need DARM/CARM-kind of handing off in the near future.

What I did:
  1. Brought both arms to IR resonance.
  2. Brought X arm to off resonance.
  3. Locked MI in bright fringe(why can't I lock in dark fringe, when one arm is on resonance?) using AS55_Q and BS.
  4. Ran /opt/rtcds/caltech/c1/scripts/ALS/handofftoLSC.py Yarm to handoff. It decreases ALS gain and increases LSC gain in 30 sec ramp time. It also turns on some filters for LSC. Make sure you turn off filter triggers for LSC.

 Below is the plot of what I did. You can see LSC feedback signal gradually increasing and TRY getting more stable.
 I was dissapointed with ALS not having any DQ channels for feedback signal. I will make them DQ channels tomorrow.

handofftoLSC20120706.png

  6938   Sun Jul 8 00:27:54 2012 yutaSummaryLockingcalibrating phase tracking mode scan data

FSR for X/Y arm are 3.97 +/- 0.03 MHz and 3.96 +/- 0.02 MHz respectively. This means X/Y arm lengths are 37.6 +/- 0.3 m and 37.9 +/- 0.2 m respectively.
I calibrated the mode scan results using 11MHz sideband as frequency reference.
Calibration factor between the phase of the phase tracker and IR frequency is 9.81 +/- 0.05 kHz/deg for X arm, 9.65 +/- 0.02 kHz/deg for Y arm.

Calculation:
  For the mode scan measurements, we swept the phase of the phase tracker linearly with time. Previous calculation was done without calibrating seconds into actual IR frequency. The first order calibration can be done using modulation frequency as reference. Note that I'm still assuming our sweep was linear here.

  Relation between FSR and modulation frequency can be written in

f_mod = n * nu_FSR + nu_f

  where f_mod is the modulation frequency, n is an integer, nu_f = mod(nu_FSR,f_mod).
  nu_FSR and nu_f are measurable values (in seconds) from the mode scan. We know that f_mod = 11065910 Hz (elog #6027). We also know that nu_FSR is designed to be ~3.7 MHz(=c/2L). So, n = 2.
  We can calculate f_mod in seconds, so we can calibrate seconds into IR frequency.


Calibrating X arm mode scan:
  From the 8FSR mode-scan data (see elog #6859), positions of TEM00 and upper/lower 11 MHz sidebands in seconds are;

TEM00    242.00     214.76     187.22     159.27     131.33     102.96     74.61     46.00     17.51
upper    236.70     209.05     181.36     153.42     125.06      96.86     68.43     40.20
lower    220.35     192.96     165.03     136.98     108.92      80.65     52.25     23.90


  So, FSR and nu_f in seconds are;

FSR    27.24     27.54     27.95     27.94     28.37     28.35     28.61     28.49
nu_f   21.80     21.82     22.14     22.19     22.26     22.28     22.40     22.40


  By using formula above, modulation frequency in seconds are;

f_mod    76.28    76.90    78.04    78.07    79.00    78.98    79.62    79.38

  By taking average, FSR and f_mod in seconds are

FSR    28.1 +/- 0.2
f_mod    78.3 +/- 0.4

  We know that f_mod = 11065910 Hz, so conversion constant from seconds to frequency is

k1 = 0.1413 +/- 0.0007 MHz/sec

  We swept the phase by 3600 deg in 250 sec, so conversion constant from degree to frequency is

k2 = 9.81 +/- 0.05 kHz/deg

  Also, using k1, FSR for X arm is

FSR = 3.97 +/- 0.03 MHz

  This means, X arm length is

L = c/(2*FSR) = 37.6 +/- 0.3 m


Calibrating Y arm mode scan:
  From the 8FSR mode-scan data (see elog #6832), positions of TEM00 and upper/lower 11 MHz sidebands in seconds are;

TEM00    246.70     218.15     190.06     161.87     133.26     104.75     76.01     47.19     18.60
upper    240.86     212.78     184.32     155.73     127.23      98.48     69.78     41.26
lower    224.53     195.73     167.31     139.13     110.81      82.27     53.60     24.50


  So, FSR and nu_f in seconds are;

FSR    28.55     28.09     28.19     28.61     28.51     28.74     28.82     28.59
nu_f   22.44     22.57     22.60     22.61     22.47     22.48     22.50     22.68


  By using formula above, modulation frequency in seconds are;

f_mod    79.54    78.75    78.98    79.825    79.485    79.955    80.14    79.855


  By taking average, FSR and f_mod in seconds are

FSR    28.5 +/- 0.1
f_mod    79.6 +/- 0.2

  We know that f_mod = 11065910 Hz, so conversion constant from seconds to frequency is

k1 = 0.1390 +/- 0.0003 MHz/sec

  We swept the phase by 3600 deg in 250 sec, so conversion constant from degree to frequency is

k2 = 9.65 +/- 0.02 kHz/deg

  (k2 of X arm and Y arm is different because delay-line lengths are different)
  Using k1, FSR for X arm is

FSR = 3.96 +/- 0.02 MHz

  This means, X arm length is

L = c/(2*FSR) = 37.9 +/- 0.2 m


Summary of mode scan results:
X arm
  Mode matching    MMR = 91.2 +/- 0.3 % (elog #6859) Note that we had ~2% of 01/10 mode.
  FSR         FSR = 3.97 +/- 0.03 MHz (this elog)
  finesse    F = 416 +/- 6 (elog #6859)
  g-factor    g1*g2 = 0.3737 +/- 0.002 (elog #6922)

  length        L = 37.6 +/- 0.3 m (this elog)
  ETM RoC  R2 = 60.0 +/- 0.5 m (this elog and #6922; assuming ITM is flat)

Y arm
  Mode matching    MMR = 86.7 +/- 0.3 % (elog #6828) Note that we had ~5% of 01/10 mode.
  FSR         FSR = 3.96 +/- 0.02 MHz (this elog)
  finesse    F = 421 +/- 6 (elog #6832)
  g-factor    g1*g2 = 0.3765 +/- 0.003 (elog #6922)

  length       L = 37.9 +/- 0.2 m (this elog)
  ETM RoC R2 = 60.7 +/- 0.3 m (this elog and #6922; assuming ITM is flat)

  I think these are all the important arm parameters we can derive just from mode scan measurement.

  Every errors shown above are statistical error in 1 sigma. We need linearity check to put systematic error. Also, we need more precise calibration after that, too, if the sweep has considerably large non-linearity. To do the linearity check, I think the most straight forward way is to install frequency divider to monitor actual beat frequency during the sweep.

  6939   Sun Jul 8 00:58:08 2012 KojiSummaryLockingcalibrating phase tracking mode scan data

Quote:

FSR for X/Y arm are 3.97 +/- 0.03 MHz and 3.96 +/- 0.02 MHz respectively. This means X/Y arm lengths are 37.6 +/- 0.3 m and 37.9 +/- 0.2 m respectively.

These aren't so bad. (Look at this entry)

And interestingly the ETM curvatures are closer to ATF measurements than Coastline's measurement. (Look at wiki)

  6940   Sun Jul 8 19:31:53 2012 yutaUpdateLockingcharacterizing LSC arm lock by ALS error signal

RMS of X/Y arm length using POX/POY lock is <160 pm and <120 pm respectively. RMS of free swinging X/Y arm length is both 0.17 um.

I used ALS error signal for out-of-loop evaluation of IR lock. We can even use ALS error signal when arm is free swinging because phase tracking ALS error signal is linear to arm length.
ALS error signal might not be as good as POX/POY. So, this out-of-loop estimation might be not so good.

X arm lock using POX11:
- Openloop transfer function
   I adjusted filter (C1:LSC-XARM) gain and now, UGF ~150 Hz, phase margin ~20 deg.
  570 usec delay (number in the figure is wrong) - Edited by Yuta on July 9
LSCPOXarmIRlockOLTF.png

- Arm length spectra
   Red is the free run spectrum. Measured using C1:ALS-BEATX_FINE_PHASE_OUT, calibration factor in frequency is 9.81 kHz/deg (see elog #6938), so calibration factor is 1.32 nm/deg.
   Green is the out-of-loop spectrum. Measured using C1:ALS-BEATX_FINE_PHASE_OUT.
   Blue is the in-loop spectrum. Measured using C1:LSC-POX11_I_ERR, calibration factor is 3.8e12 counts/m (see elog #6841).
   Black is the expected spectrum from openloop transfer function, such as (free run)/|1+G|.
XarmLengthspectra20120708.png


  Out-of-loop estimation of RMS during POX lock is 160 pm. But since this looks too large, ALS error signal might not see actual arm length change when arm length is locked.
  Also, it is interesting that ALS error signal sees 24 Hz peak, but POX doesn't. Roll mode coupling to green?

Y arm lock using POY11:
- Openloop transfer function
   I adjusted filter (C1:LSC-YARM) gain and now, UGF ~150 Hz, phase margin ~20 deg.
  570 usec delay (number in the figure is wrong) - Edited by Yuta on July 9
LSCPOYarmIRlockOLTF.png

- Arm length spectra
   Red is the free run spectrum. Measured using C1:ALS-BEATY_FINE_PHASE_OUT, calibration factor in frequency is 9.65 kHz/deg (see elog #6938), so calibration factor is 1.30 nm/deg.
   Green is the out-of-loop spectrum. Measured using C1:ALS-BEATY_FINE_PHASE_OUT.
   Blue is the in-loop spectrum. Measured using C1:LSC-POY11_I_ERR, calibration factor is 1.4e12 counts/m (see elog #6834).
   Black is the expected spectrum from openloop transferfunction, such as (free run)/|1+G|.
YarmLengthspectra20120708.png


  Out-of-loop estimation of RMS during POY lock is 120 pm. But since this looks too large, ALS error signal might not see actual arm length change when arm length is locked.
  Also, it is interesting that ALS error signal sees 16.5 Hz peak, but POY doesn't. Bounce mode coupling to green?

Next:
  - Noise budgeting of phase tracking ALS
  - Is it possible to lock MI when RMS of arm length during POX/POY lock increased to ~100pm?

  6941   Mon Jul 9 05:02:58 2012 yutaUpdateLockingadjusted ALS filters, current RMS

I adjusted filters of ALS to give more phase margin.
RMS of stabilized X/Y arm length is 97 pm and 65 pm respectively.

X arm ALS:
- Openloop transfer function
UGF ~160 Hz, phase margin 30 deg
1600 usec delay (LSC-XARM had 1800 usec delay)     500 usec delay (LSC-XARM had 570 usec delay) - Edited by Yuta on July 9

ALSXarmOLTF.png

- Arm length spectra
   Red is the free run spectrum. Measured using C1:ALS-BEATX_FINE_PHASE_OUT. Calibration factor is 1.32 nm/deg.
   Green is the out-of-loop spectrum. Measured using C1:LSC-POX11_I_ERR. Calibration factor is 3.8e12 counts/m.
   Blue is the in-loop spectrum. Measured using C1:ALS-BEATX_FINE_PHASE_OUT.
   Black is the expected spectrum from openloop transfer function, such as (free run)/|1+G|.
ALSXarmLengthspectra20120708.png


   Out-of-loop estimation of RMS during X ALS is 97 pm.
   RMS mostly comes from 1 Hz and 3.3 Hz peak.
   Out-of-loop and in-loop agrees at around 10-20 Hz.

Y arm ALS:
- Openloop transfer function
UGF ~130 Hz, phase margin 20 deg
2400 usec delay (LSC-XARM had 1800 usec delay)     760 usec delay (LSC-XARM had 570 usec delay) - Edited by Yuta on July 9

ALSYarmOLTF.png

- Arm length spectra
   Red is the free run spectrum. Measured using C1:ALS-BEATY_FINE_PHASE_OUT. Calibration factor is 1.30 nm/deg.
   Green is the out-of-loop spectrum. Measured using C1:LSC-POY11_I_ERR. Calibration factor is 1.4e12 counts/m.
   Blue is the in-loop spectrum. Measured using C1:ALS-BEATY_FINE_PHASE_OUT.
   Black is the expected spectrum from openloop transferfunction, such as (free run)/|1+G|.
ALSYarmLengthspectra20120708.png

   Out-of-loop estimation of RMS during X ALS is 65 pm.
   RMS mostly comes from 1 Hz and 3.3 Hz peak.
   Out-of-loop and in-loop agrees at around 3-40 Hz.

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