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ID Date Author Type Categorydown Subject
  6535   Sat Apr 14 00:19:35 2012 SureshOmnistructureLSCOptical Fibers for insitu RFPD characterisation

   I have worked out the fibers we need to get for the following distribution scheme:

1) We have a laser placed at the 1Y1 rack.  A part of the power is split off for monitoring the laser output and sent to a broadband PD also placed in the same rack.  The RF excitation applied to the laser is split and sent to LSC rack (1Y2) and used to calibrate the full PD+Demod board system for each RFPD.

2) A single fiber goes from the laser to a 11+ way switch located in the OMC electronics cabinet next to the AP table.  From here the fibers branch out to three different tables.

Table / Rack   RF PDs on the table Number of PDs Fiber Length from OMC
The AP table AS11,AS55,AS165,REFL11,REFL33,REFL55,REFL165 7 6 m
The ITMY table POY11 1 12 m
The ITMX table POX11, POP22/110 and POP55 3 20 m

 

Cable for the laser source to the OMC table:

The 1Y1 Rack to OMC rack AM Laser Source to Switch 25 m

We also require a cable going from PSL table to the ETMY table:   This is not a part of the RFPD characterisation.  It is a part of the PSL to Y-end Aux laser lock  which is a part of the green locking scheme.  But it is  fiber we need and might as well order it now along with the rest.

PSL Table to ETMY Table PSL to ETMY Aux laser 75m

 

If you would like to add anything to this layout / scheme, please comment.  On Monday Eric is going to take a look at this and place orders for the fibers.

(I have included the lengths required for routing the fibers and added another 20% to that ) 

 

  6598   Thu May 3 17:15:38 2012 KojiUpdateLSCc1iscaux2 rebooted/burtrestored

[Jenne/Den/Koji]

We saw some white boxes on the LSC screens.
We found c1iscaux2 is not running.

Once the target was power-cycled, these epics channels are back.
Then c1iscaux2 were burtrestored using the snapshot at 5:07 on 4/16, a day before the power glitch.

  6716   Wed May 30 18:08:40 2012 JamieUpdateLSCc1lsc: add error point pick-offs, moved ctrl pick-offs after feedforward

I made some modifications to the c1lsc model in order to extract both the error and control signals.

I added pick-offs for the error signals right before IFO DOF filter modules.  These are then sent with GOTOs to outputs.

I also modified things on the control side.  The OAF stuff was picking off control signals before feedforward in/outs.  After discussing with Jenne we decided that it would make sense for the OAF to be looking at the control signals after feedforward.  It also makes sense to define the control signal after the feedforward.  These control signals are then sent with GOTOs to another set of outputs.

Finally, I moved the triggers to after the control signal pickoffs, and right before the output matrix.  The final chain looks like (see attachment):

input matrix --> power norm --> ERR pickoff --> DOF filters --> FF out --> FF in --> CTRL pickoff --> trigger --> output matrix

The error pickoff outputs in the top level of the model are left terminated for the moment.  Eventually I will be hooking these into the new c1cal calibration model.

The model was recompiled, installed, and restarted.  Everything came up fine.

Attachment 1: LSCchain.png
LSCchain.png
  6717   Wed May 30 18:16:44 2012 JamieUpdateLSCskeleton of new c1cal calibration model created

[Jamie, Xavi Siemens, Chris Pankow]

We built the skeleton of a new calibration model for the LSC degrees of freedom.  I named it "c1cal".  It will run on the c1lsc FE machine, in CPU slot 4, and has been given DCUID 50.

Right now there's not much in the model, just inputs for DARM_ERR and DARM_CTRL, filters for each input, and the sum of the two channels that is h(t).

Tomorrow we'll extract all the needed signals from c1lsc, and see if we can generate something resembling a calibrated signal for one of the IFO DOFs.

 

  6735   Thu May 31 23:53:00 2012 JenneUpdateLSCLSC trigger update

I modified the lsc model (after Jamie finished) to use a new triggering scheme.  It HAS NOT yet been compiled and tested, since it's way past time for us to start beatnote-ing.  I will compile, test, debug, etc. tomorrow. Don't compile the LSC model tonight. 

Now we also have (assuming no bugs.....) triggering capability for the filter modules in the filter banks.  Yay!  Testing, etc will commence tomorrow.

  6749   Mon Jun 4 17:14:31 2012 JenneUpdateLSCLSC recompiled several times today

As of now, the regular LSC DoF triggers work, just as they used to.  There is a problem with the filter module triggers that I haven't figured out yet. 

We can't send integers (like control words for the filter banks) through Choice blocks, since those pass doubles by default.  I fixed that by removing the choice block, but the triggering still isn't happening properly.

  6831   Mon Jun 18 23:38:39 2012 JenneUpdateLSCAdded LSC channels to frames

Since the .ini files get overwritten every time a model is compiled now, we need to put all channels we want saved to frames in the DAQ Channels list inside the model.

I added the _ERR channels for all RFPDs (I and Q for each), as well as the _OUT channels for the DCPDs.  I also added the _OUT channels for the DoF servos (ex. C1:LSC-DARM_OUT).  I don't remember off the top of my head what else we used to save from the LSC model, but those all seemed like ones we'll possibly want access to later. 

We need to go through and do this to all the models we use regularly.

Since SUS hasn't been recompiled in a while, all those channels are saved (until such time as someone does a recompile).  Den has gone through and edited the PEM and OAF .ini files by hand each time he recompiles, so we have that data, although we need to put it into the model (which is the new proper way to acquire channels).

  6834   Tue Jun 19 23:36:19 2012 yutaUpdateLSCcalibrated POY error signal

[Jenne, Yuta]

We calibrated POY error signal(C1:LSC-POY11_I_ERR). It was 1.4e12 counts/m.

Modeling of Y arm lock:
  Let's say H is transfer function from Y arm length displacement to POY error signal. This is what we want to measure.
  F is the servo filter (filter module C1:LSC-YARM).
  A is the actuator TF using ITMY. According to Kiwamu's calibration using MICH (see elog #5583),

  A_ITMY  = 4.832e-09 Hz^2*counts/m / freq^2

  We used ITMY to lock Y arm because ITMY is already calibrated.

What we did:
  1. Measured openloop transfer function of Y arm lock using POY error signal using ITMY (G=HFA). We noticed some discrepancy in phase with our model. If we include 1800 usec delay, phase fits well with the measurement. I think this is too big.
LSCyarmTF_usingITMY.png


  2. Measured a transfer function between actuator to POY error signal during lock. This should give us HA/(1+G).
LSCyarm_HAover1plusG.png

  4. Calculated H using measurements above. Assuming there's no frequency dependance in H, we got

  H = 1.4e12 counts/m

POYerrorcalibration.png

 For sanity check; Peak to peak of the POY error signal when crossing the IR resonance is about 800 counts. FWHM is about 1 nm, so our measurement is not so crazy.

  6835   Wed Jun 20 00:01:04 2012 JenneUpdateLSCcalibrated POY error signal

[Yuta, Jenne]

We have measured the out of loop residual motion of the Yarm while locked with the ALS.  We see ~70pm RMS, as compared to Kiwamu's best of ~24pm RMS.  So we're not yet meeting Kiwamu's best measurement, but we're certainly not in crazy-land.

The Yarm ALS was locked, I took a spectrum of POY11_I_ERR, and used the calibration that we determined earlier this evening.  For reference, I attach a screenshot of our ALS loop filters - we had on all the boosts, and both resonant gain filters (~3Hz and ~16Hz).

A large part of the RMS is coming from the 60Hz power line and the 180Hz harmonic....if we could get rid of these (how were they eliminated from the measurement that Kiwamu used in the paper?? - plotted elog 6780) we would be closer. 

Also, it looks like the hump (in our measurementf ~100Hz, in Kiwamu's ~200Hz) is not quite an order of magnitude higher in amplitude in our measurement vs. Kiwamu's.  We have ~5e-11 m/rtHz, Kiwamu had ~7e-12 m/rtHz.  This increase in noise could be coming from the fact that Yuta and Koji decreased the gain in the Ygreen PDH loop to prevent the PDH box from oscillating. 

While we should still think about why we can't use the same gain that Kiwamu was able to ~6 months ago, we think that we're good enough that we can move on to doing mode scans and residual motion measurements of the Xarm.

 

Attachment 1: LSC_POY_11_I_ERR_calib_19June2012.pdf
LSC_POY_11_I_ERR_calib_19June2012.pdf
Attachment 2: POY_calib_19June2012_FiltBankSettings.png
POY_calib_19June2012_FiltBankSettings.png
  6841   Wed Jun 20 18:43:57 2012 yutaUpdateLSCcalibrated POX error signal

[Jenne, Yuta]

We did the same calibration for POX. It was 3.8e12 counts/m. See elog #6834 for the details of calibration we did.

According to Kiwamu's calibration, actuator response of ITMX is;

A_ITMX  = 4.913e-09 Hz^2*counts/m / freq^2

Plots below are results from our calibration measurement.

LSCxarmTF_usingITMX.pngLSCxarm_HAover1plusG.pngPOXerrorcalibration.png

  6931   Fri Jul 6 14:10:31 2012 yutaSummaryLSCcalculation of FPMI using ALS

From calculation, phase fluctuation of reflected beam from length stabilized arm is not disturbing MI lock.

Easy calculation:
  The phase PD at AS port sense is

phi = phi_x - phi_y = 2*l_MICH*omega/c + (phi_X - phi_Y)

  where l_MICH is the Michelson differential length change, omega is laser frequency, phi_X and phi_Y are phase of arm reflected beam. From very complicated calculation,

phi_X ~ F/2 * Phi_X

  at near resonance. Where F is arm finesse, Phi_X is the round trip phase change in X arm. So,

phi = 2*l_MICH*omega/c + F/2 * 2*L_DARM*omega/c

  Our ALS stabilizes arm length in ~ 70 pm(see elogs #6835#6858). Finesse for IR is ~450. Considering l_MICH is ~ 1 um, MICH signal at AS port should be larger than stabilized DARM signal by an order of magnitude.

Length sensing matrix of FPMI:
  Calculated length sensing matrix of 40m FPMI is below. Here, I'm just considering 11 MHz modulation. I assumed input power to be 1 W, modulation index 0.1i, Schnupp asymmetry 26.6 mm. PRM/SRM transmissivity is not taken into account.

[W/m]     DARM      CARM      MICH
REFL_I    0         1.69e8    0
REFL_Q    7.09e1    0        -3.61e3
AS_I      0         0         0
AS_Q      1.04e6    0         3.61e3


  Maybe we should use REFL_Q as MICH signal, but since IQ separation is not perfect, we see too much CARM. I tried to lock MI with REFL11_Q yesterday, but failed.

  6947   Mon Jul 9 23:18:09 2012 yutaUpdateLSCPRMI got more stable a bit

I modified filiters for LSC_MICH and LSC_PRCL.
Although modes we can see at POP and AS look still bad, error signals are less glitchy than I see before (elog #6886).

Measured power recylcing gain for PRMI was 1.6 (??)

Openloop transfer function for LSC_MICH:
  UGF ~130Hz, phase margin ~30 deg
  550 usec delay
LSCMICHOLTF.png

APOLOGIES: I forgot "pi" in previous delay calculation. (I put notes on elogs #6940 and #6941)

Openloop transfer function for LSC_PRCL:
  UGF ~130Hz, phase margin ~30 deg
  550 usec delay
  A bump cam be seen in ~200 Hz. Coupling of DOFs?
LSCPRCLOLTF.png

Beam shape and motion:
   Below left is the Sensoray capture of AS/REFL/POP when PRMI is carrier locked.
ALL_1025928219_PRMIlocked3.pngPRMIbeammotion20120709.png

  Beam spot motion looks less bouncy than before, but it still shows motion mostly at ~3.3Hz. This might be from PRM motion. Above right is uncalibrated spectra of POPDC and REFLDC. You can see 3.3 Hz peak. This peak has some coherence with PRM motion measured by oplevs. I centered BS/PRM oplev to do this measurement.

Power recycling gain:
 - Definition and designed value
  Power recylcing gain is

G = (PRC intracavity power) / (incident power)

  When MI is perfectly symmetric, this can be written as

G  = (t_PRM/1-r_PRM*r_ITM)**2

  where t_i, r_i is amplitude transmissivity, reflectivity. Inserting the designed values;

 t_PRM = sqrt(0.0575)
 r_ITM = sqrt(1-0.014)

  designed power recycling gain for PRMI is

G = 44

 - Measurement
  POP power when PRM is misaligned and MI is locked at dark fringe is

P_mis = P_in * T_PRM * (1-T_PR3) * (1-T_ITM) * T_PR3

  POP power when PRMI is locked is

P_PR = P_intra * T_PR3

  So,

G = P_intra / P_in = (P_PR / P_mis) * T_PRM * (1-T_PR3) * (1-T_ITM) ~ (P_PR / P_mis) * 0.06

  I measured power of POP using C1:LSC-POPDC_OUT. It was 268 when PRM is misalined and MI is locked at dark fringe. Also, it was ~850 when PRMI is carrier locked. When closing PSL shutter, it was ~246. So,

G_PR = (850-246)/(268-246) * 0.06 = 1.6

  It looks too small.

  6949   Tue Jul 10 01:52:47 2012 KojiUpdateLSCPRMI got more stable a bit

The phase margins looks still too small.

Do You need such high gain at LF? This is not a high finesse cavity so can we sacrifice
some DC gain while gaining more phase around UGFs?

Otherwise, the gain fluctuation should be nicely compensated (i.e. fancy normalization).

  6950   Tue Jul 10 03:16:17 2012 yutaUpdateLSCPRMI got more stable a bit

I modified filiters for LSC_MICH and LSC_PRCL again to cope with power recycling gain fluctuation.
After some more alignment, power recycling gain increased (but still ~3.7). It fluctuates more than a factor of 2, and I began to see glitches again. So I needed more gain margin, as Koji pointed out.

I played around with filters, but I couldn't remove all the glitches. Gain margin now look OK in principle.
It looks like PRM motion is related. Since PRM doesn't have oplev now, I will see PRM oplev tomorrow.

New openloop transfer function:
 LSC_MICH
   UGF ~100 Hz, phase margin ~ 50 deg
   no phase flip in less than factor of ~5 gain change
   550 usec delay
 LSC_PRCL
   UGF ~100 Hz, phase margin ~ 70 deg (phase bump at UGF)
   no phase flip in less than factor of ~5 gain change
   550 usec delay
LSCMICHOLTF.pngLSCPRCLOLTF.png

Power recylcing gain:
  It is now ~3.7. It fluctuates pretty much. See time series data below when I locked PRMI. MICH and PRCL locks at the same time.

G = (1600-244)/(266-244)*0.06 = 3.7

PRMI20120709_2.png
 

  6953   Tue Jul 10 21:37:05 2012 yutaUpdateLSCPRMI glitch study

PRMI glitch certainly comes from power recylcing gain fluctuation.
I confirmed this by
  - Reading the value of POPDC at the time when there's glitch in error signals
      -> There was some threshold for POPDC to make a glitch
  - Look closer to the glitch
      -> It was oscillation in ~400Hz, where we have phase flip in PRCL/MICH servo

Next is to find why we have power recycling gain fluctuation. I want to see the correlation between alignment fluctuation of optics and POPDC.

Glitch analysis:
  Below is the plot of
   Red   PRCL error signal (C1:LSC-REFL33_I_ERR)
   Green MICH erorr signal (C1:LSC-AS55_Q_ERR)
   Blue  PRC intra-cavity power (C1:LSC-POPDC_OUT)
  when PRMI is carrier locked.

PRMIgilitch20120709.pngPRMIgilitch20120709_closer.png

  Time when there is a glitch in error signal is marked. Value of POPDC at that time is also marked. It looks like there's some threshold (dotted blue line).
  It sometimes doesn't show glitch even if POPDC is above the "threshold". It is maybe because of alignment fluctuation. Intra-cavity power gets high, but power at PDs get low, or vice versa.

  Right plot is closer look. Glitch is a sudden oscillation at ~400 Hz. It is the frequency where we have phase flip in PRCL/MICH openloop transfer function now(see elog #6950).

  6954   Wed Jul 11 02:25:11 2012 yutaUpdateLSCPRMI beam spot motion might be from PRM/BS motion

My hypothesis from the measurements below, to explain PRMI beam spot motion is;

  Stack motion at 3.3 Hz largely couples to BS and PRM angular motion.
  LSC for PRMI try to compensate this 3.3 Hz motion because they appear in the error signal.
  But since it's not length, failing and even adding more angular motion.

Some plots:
  1. Uncalibrated spectra of POPDC and ASDC when PRMI is locked. This tells you that beam motion seen at POP is 3.3 Hz.

  2. Uncalibrated spectra of feedback signal to BS and PRM. This tells you that LSC is actuating BS and PRM mainly at 3.3 Hz. I think this is because beam spot on PD moves at 3.3 Hz and so faking the error signal.

  3. Below left is uncalibrated spectra of BS, ITMX, ITMY, PRM (and ETMY) angular motion measured using oplevs. I centered oplevs on these optics (except ETMY, which was mis-aligned during PRMI lock). It looks like BS and PRM motion at 3.3 Hz is larger than other optics. Also, there's some coherence between POPDC and BS/PRM motion. We see some coherence with ITMs and even with ETMY, which is completely independent from PRMI. I think this is because 3.3 Hz motion is originated from the ground (stack) motion.

  left:  OLPITYAWandPOPDC4.png          right: OLPITYAWandPOPDCunlocked.png

  4. Above right is the same spectra, but when PRMI is not locked. It looks like there's no big change compared with PRMI locked. When locked, there's some excess for BS and PRM at ~1-3 Hz. I think this is from LSC feedback, which in principle, doesn't affect any angular motion.

Next:
  - Why BS and PRM has large 3.3 Hz peak compared with other optics?
  - Is 3.3 Hz peak effecting MI lock or arm lock?
  - How can we monitor PR2/3 angular motion?

Attachment 1: POPDCASDC4.png
POPDCASDC4.png
Attachment 2: Feedback4.png
Feedback4.png
  6955   Wed Jul 11 03:53:41 2012 yutaUpdateLSCBS 3.3 Hz motion on MI

It is not as dramatic as PRMI, but I could see BS 3.3 Hz motion at AS and REFL when MI is locked at dark fringe.
Below is uncalibrated spectra of REFLDC and ASDC when
  Red: MI is locked at dark fringe
  Blue: there's no light (PSL shutter closed)

We have to do something to get rid of this.

REFLDCASDCMIlocked.png

  6972   Thu Jul 12 23:15:34 2012 yutaUpdateLSCPRMI LSC is making PRM motion worse

It looks like PRMI LSC is making PRM motion (and BS motion) at ~3Hz worse.
I concluded this from measuring feedback signal of suspension servo and LSC servo.

Mechanism:
 1. BS and PRM moves alot at ~3 Hz.
 2. LSC senses fake signal at ~3Hz from beam spot motion on PD
 3. LSC feedback this motion to position of PRM
 4. Suspension damping servo try to cancel this because ~3 Hz motion is not actual length signal

Calculation:
x:   Orignal longitudinal motion of PRM
n_L: Sensing noise in LSC (including ITM motion, fake ~3Hz motion)
n_S: Sensing noise in suspension damping (OSEM sesor noise, fake ~3Hz motion)
G_L: Openloop transfer function of PRCL LSC
G_S: Openloop transfer function of suspension damping (PRM SUSPOS)
H:   LSC sensor transferfunction (PDH signal on REFL_33_I)
F_S: Filter for suspension damping
A:   Actuator transfer function (PRM OSEM coils)

  Since G_L >> G_S and G_L >> 1 for below 100Hz (see elogs #6950 and #6967), feedback signal of LSC and suspensiton damping can be written as

f_L = x - A*F_S*n_S - (1+G_S)/H*n_L
f_S = 1/G_L*x - A*F_S*n_S - G_S/H*n_L 

  So, basically, LSC supresses PRM motion but puts n_L to PRM. Suspension servo try to surpress n_L, which was not there when LSC is off.

Measurement:
 1. Below left is uncalibrated spectra of

Red:  suspension damping feedback to PRM/BS when PRMI is locked
Blue: LSC feeed back to PRM/BS when PRMI is locked
Pink: suspension damping feedback to PRM/BS when PRMI is not locked

  As you can see, PRM suspension damping feed back increases at ~ 1.5-3 Hz because of LSC. This is the same for BS at ~1 Hz and ~3 Hz.

PRMBSPRMIonoff.png    ITMXITMYPRMIonoff.png

 2. Above right is same spectra for ITMX/ITMY. There's no change in suspension damping feedback. This means, radiation pressure coupling or something is not related in this issue. LSC servo is not engaged for ITMs.

 3. Below is oplev spectra for PRM/BS

Red:  Oplev pitch error signal of PRM/BS when PRMI is locked
Blue: Oplev yaw error signal of PRM/BS to PRM/BS when PRMI is locked
Pink:  Oplev pitch error signal of PRM/BS when PRMI is not locked
Cyan: Oplev yaw error signal of PRM/BS to PRM/BS when PRMI is not locked

  You can see the increase in pitch/yaw motion at ~ 1.5-3 Hz for PRM, and ~1Hz/~3Hz for BS. They are consistent with measurement of feedback spectra.

OplevPRMIonoff.png



By the way:

  I adjusted oplev servo gains for ITMX. They were crazy this evening. They now have UGF ~ 2.5 Hz.

C1:SUS-ITMX_OLPIT_GAIN = 1.0 (was 2.6)
C1:SUS-ITMX_OLYAW_GAIN = -0.5 (was -1.6)


Next questions:
  - Can we notch ~3 Hz feedback so that LSC doesn't feedback this motion?
  - Why ~3 Hz motion is high for BS/PRM? Too much load on BS chamber stack?
  - Can we reduce ~3 Hz motion?
  - If BS chamber stack is bad, PR3 might have ~3 Hz motion, too. Does this make PRMI beam spot motion crazy?
  - How about PR2?

  6976   Sun Jul 15 16:25:15 2012 ranaUpdateLSCPRMI LSC is making PRM motion worse

As stephanie did a few years ago, the idea should be to match the damping between the DRMI optics so as to minimize the differential motion. No notching is necessary. Read her SURF report about the IMC.

 

  7029   Wed Jul 25 15:33:55 2012 janoschUpdateLSCringdown measurement

We did our first ringdown measurement on the Y arm. First we tried to keep the arm locked in green during the ringdown, but for some reason it was not possible to get the cavity locked in green. So we decided to do the first measurement with infrared locked only.

For the measurement we had to change the LSC model to acquire the C1:LSC-TRY_OUT_DQ at higher sampling frequency. We changed the sampling frequencies of C1:LSC-{TRX,TRY}_OUT_DQ from 2048Hz to 16384Hz.

The measurement was done at GPS 1027289507. The ringdown curve looks very clean, but there seem to be two time constants involved. The first half of the curve is influenced by the shutter speed, then curvature is changing sign and the ringdown is likely taking over. We will try to fit a curve to the ringdown part, but it would certainly be better to have a faster shutter and record a more complete ringdown.

Rindown1.png

 

  7030   Wed Jul 25 16:31:01 2012 JenneUpdateLSCYarm green locking to arm - PDH box saturating

Quote:

... it was not possible to get the cavity locked in green. So we decided to do the first measurement with infrared locked only. 

 When we sat down to align the Yarm to the green, the green light was happy to flash in the cavity, but wouldn't lock, even after Jan had tweaked the mirrors such that we were flashing the TEM00 mode.  When we went down to the end to investigate, the Universal PDH box was saturating both negative and positive.  Turning down the gain knob all the way to zero didn't change anything, so I put it back to 52.5.  Curiously, when we unplugged the Servo OUT monitor cable (which was presumably going to the rack to be acquired), the saturation happened much less frequently.  I think (but I need to look at the PDH box schematic) that that's just a monitor, so I don't know why that had to do with anything, but it was repeatable - plug cable in, almost constant saturation....unplug cable, almost no saturation.

Also, even with the cable unplugged, the light wouldn't flash in the cavity.  When I blocked the beam going to the green REFL PD (used for the PDH signal), the light would flash.

Moral of the story - I'm confused.  I'm going to look up the PDH box schematic before going back down there to investigate.

  7033   Wed Jul 25 22:16:36 2012 KojiUpdateLSCringdown measurement

Is this the step response of the single pole low pass???
It should have an exponential decay, shouldn't it? So it should be easier to comprehend the result with a log scale for vertical axis...

I think you need a fast shutter. It is not necessary to be an actual shutter but you can use faster thing
which can shut the light. Like PMC or IMC actuators.

Another point is that you may like to have a witness channel like the MC transmission to subtract other effect.

  7038   Thu Jul 26 13:10:51 2012 janoschUpdateLSCmodelled ringdown

We fitted shutter and ringdown functions to the ringdown data. It is not perfectly clear how the power change due to the shutter is handed over to the power change due to ringdown. The fit suggests that the ringdown starts at a later time, but this does not necessarily make sense. It could be that the slow power decrease when the shutter starts clipping the TEM00 beam is followed by the cavity, but then the power decrease becomes too fast when the shutter reaches the optical axis and the ringdown takes over. Also, the next measurement should be taken with adjusted DC offset.

Ringdown.png

  7039   Thu Jul 26 15:43:03 2012 ranaUpdateLSCmodelled ringdown

You cannot use the digital system for this. You hook up a scope to the transmitted light as well as the incoming light (after the MC, perhaps at IP_POS). Then you acquire the data from both places simultaneously using an ethernet equipped scope. The step response of the PDs used for this has to be calibrated separately.

  7073   Wed Aug 1 18:20:58 2012 JamieUpdateLSCYarm recovered

[Jenne, Jamie]

We recovered lock and alignment of the Y arm.  TRY_OUT is now at ~0.9, after tweaking {I,E}TMY pit/yaw and PZT2.  YARM_GAIN is 0.1.

I saved ITMY, ETMY, and PZT2 alignments in the IFO_ALIGN screen with the new alignment save/restore stuff I got working.

Working on getting Yarm ASS working now...

  7078   Thu Aug 2 11:09:52 2012 EricSummaryLSCFree-Swinging Michelson Measurements

To take the free swinging Michelson measurements for the interferometer calibration Jamie aligned the beam splitter with ITMX and ITMY. I recorded the GPS time (1027827100 and for several hundred seconds later) when the Michelson was aligned in order to look at the correct data. I then copied the python script nds-test.py from Jamie, and modified it to take and plot data from C1:LSC-AS55_Q_ERR_DQ offline. I used dataviewer to verify that C1:LSC-AS55_Q_ERR_DQ and C1:LSC-AS55_Q_ERR were recording the same signal, and to check that I was taking the correct data with NDS. Taking data online worked as well, but it was easier to use a time when the Michelson was known to be free-swinging and take data offline. Attached is some sample data while free-swinging, with time in GPS time.

Attachment 1: free_swing_MICH.png
free_swing_MICH.png
  7170   Tue Aug 14 04:37:06 2012 YoichiSummaryLSCXARM Open Loop Gain

Yoichi, Rana

Here is the open loop gain of the XARM loop.

The reference is from the pre-upgrade era. We get the extra phase delay because we have two anti-aliasing filters. One is the hardware filter at about 7kHz for 16kHz sampling. This filter should have been replaced to the one for 64kHz sampling but it has not yet happened. The second one is the software anti-aliasing filter applied when down sampling from 64kHz to 16kHz. So we have double AA filters, which are the culprits for the extra phase delay.

We should either replace the hardware AA filter to the 64kHz one (preferred way), or change the software AA filter to a less aggressive one (easier temporary fix).

Attachment 1: xarm-opltf.png
xarm-opltf.png
  7171   Tue Aug 14 04:53:45 2012 YoichiSummaryLSCX-Arm noise spectrum

Yoichi, Rana

Here is the noise spectrum of the X-arm error signal along with the TRX DC power fluctuations.

The spectra were taken while the whitening filters for POX11 were OFF.

EDIT (Integrity Fairy): Shall we assume these units are "Intergalactic translational qubits/sqrt(Hz)"?

Attachment 1: xarm-spectrum.png
xarm-spectrum.png
  7184   Tue Aug 14 22:16:46 2012 JenneUpdateLSCLSC whitening triggers

I'm ~30% of the way through implementing LSC whitening filter triggers.  I think that everything I have done should be compile-able, but please don't compile c1lsc tonight.  I haven't tested it, and some channel names have changed, so I need to fix the LSC screen when I'm not falling asleep.

Also, Rana pointed out that we may not want the whitening to trigger on immediately upon acquiring lock - if there are other modes ringing down in the cavity, or some weird transients, we don't want to amplify those signals.  We want to wait a second or so for them to die down, then turn on analog whitening.  Jamie - do you know how long the "unit delay" delays things in the RCG?  Do those do what I naively think they do?  I'll ask you in the morning.

  7187   Wed Aug 15 04:03:55 2012 ranaSummaryLSCY-Arm Locking

0) Did a bunch of alignment to get beams roughly centered on ETMY and ITMY and maximize power. Adjusted the aperture and focus on ETMY camera to get nice image. Camera needs to be screwed in tightly and cables given some real strain relief, Steve.

1) snapshots not working on many MEDM screens. Who's on top of this?

2) save/restore not working for PZT2 sliders

3) changed power and filter triggers on yarm to match xarm

4) yarm filters copied from xarm (need to handtune RGs)

5) DTT wasn't working on rossa. Used the Date/Time GUI to reset the system time to match fb and then it stopped giving 'Test Timed Out'. Jamie check rossa ntpd.

6) Removed the high 3.2 Hz RG filter. We don't have any sharp features like that in the spectrum.
   ---then added it back. The 3.2 Hz comes and goes depending on what Yoichi is doing over in the MC area. Leaving it in by default, but lowering the Q from 2 to 1.5.

7) Attached is the noise spectra, coherence, and loop gain model for this yarm condition. For the plant model, I assume a pendulum (f=1 Hz, Q = 9) and a cavity pole of 1600 Hz. Gain is scaled to set the UGF at 165 Hz (as guessed by looking at the servo gain peaking frequency). This cheezy model doesn't include any of the delays from DAC, AA, or AI. Eric and Sasha should have something more useful for us by Friday.

8) Change the DQ channels: need XARM and YARM IN1 at 16k. e.g. XARM_ERR, etc.

9) To get the DTT plots to make thumbnails in the elog, I print a .ps file and then use 'epstopdf' to make the PDF.

Attachment 1: yArmNoise_120815.png
yArmNoise_120815.png
Attachment 2: yarm.pdf
yarm.pdf
  7188   Wed Aug 15 09:09:45 2012 jamieUpdateLSCLSC whitening triggers

Quote:

I'm ~30% of the way through implementing LSC whitening filter triggers.  I think that everything I have done should be compile-able, but please don't compile c1lsc tonight.  I haven't tested it, and some channel names have changed, so I need to fix the LSC screen when I'm not falling asleep.

Also, Rana pointed out that we may not want the whitening to trigger on immediately upon acquiring lock - if there are other modes ringing down in the cavity, or some weird transients, we don't want to amplify those signals.  We want to wait a second or so for them to die down, then turn on analog whitening.  Jamie - do you know how long the "unit delay" delays things in the RCG?  Do those do what I naively think they do?  I'll ask you in the morning.

The unit delay delays for a single cycle, so I think that's not what you want.  I'm not sure that there's an existing part to add delays like that.

We also need to be a little clever about it, though, since we'll want it to flip off if we loose lock during the delay.

  7191   Wed Aug 15 11:44:35 2012 jamieSummaryLSCntp installed on all workstations

Quote:

5) DTT wasn't working on rossa. Used the Date/Time GUI to reset the system time to match fb and then it stopped giving 'Test Timed Out'. Jamie check rossa ntpd.

ntp is now installed on all the workstations.  I also added it to the /users/controls/workstation-setup.sh script

  7211   Fri Aug 17 00:16:30 2012 EricSummaryLSCYARM Calibration

I modified my Simulink model of the YARM to match the new filter modules Rana installed on YARM. I also scaled the open loop transfer function of the model to fit the measured open loop transfer function at the unity gain frequency, as shown in the figure below. From this I produced the length response function correctly scaled, also shown below.  Then I applied the calibration factor to the YARM data measured in /users/Templates/Y-Arm_120815.xml. Both the uncalibrated and calibrated spectra are included below.

 

 

Attachment 1: olg_model_meas.png
olg_model_meas.png
Attachment 2: length_response_model.png
length_response_model.png
Attachment 3: yarm_uncal_power_spec.pdf
yarm_uncal_power_spec.pdf
Attachment 4: yarm_cal_power_spec.pdf
yarm_cal_power_spec.pdf
  7213   Fri Aug 17 04:54:01 2012 Yoichi, KojiSummaryLSCPRMI Locking

 To taste the strangeness of the current 40m PRC, I locked the PRMI with the guide of Koji.

We first aligned MICH by mostly tweaking ITMX, assuming that ITMY is in a good place as the Y-arm locks. MICH lock was stable.

Then we restored the IFO to the PRM_SBres mode. With a bit of alignment work on PRM and gain tweaking, the PRMI locked.

Yes, the beam spots look UGLY !

Also the PRMI was not so stable. Especially, when the alignment fluctuates, the optical gain changes and the loop becomes temporarily unstable. We took POP_DC as the guide for the gain change and normalized the PRCL error signal with it. To do this smoothly, we first changed the input matrix to route the PRCL error signal, which is REFL33_I, so that the signal also goes to the MC filter bank. Then with dtt, we monitored the spectra of the PRCL_IN1 and MC_IN1. We tweaked the value of the element in the normalization matrix for the MC path until the two spectra look the same (at this moment, the normalizing factor for the PRCL path was still zero). During this process, we noticed that the MC path signal (normalized by POP_DC) is noisier at above 500Hz. This was because the POP_DC has a large noise at high frequencies. So we put a low pass filter (100Hz 2nd order Butterworth) to the POP_DC filter bank to reduce the noise. Then the two spectra looked almost the same. The correct normalization factor found in this way was 0.03. So we put this number in the normalization matrix for PRCL. It did not break the PRMI lock.

 

After the normalization is turned on, the PRMI lock became somewhat more stable. However, the POP_DC was still fluctuating a lot, especially when the alignment is good. So I made a boost filter: 5Hz pole Q=2, 15Hz zero Q=1.5. I also made this filter automatically triggered when the PRMI is locked. This made the PRMI lock acquisition quicker. However, still the POP_DC fluctuation is large. It seems that the alignment of PRC is really fluctuating a lot.

 The current UGF of PRMI is about 150Hz with the phase margin over 50deg.

 

 

 

 

Attachment 1: AS_1029238601.jpg
AS_1029238601.jpg
Attachment 2: POP_1029238616.jpg
POP_1029238616.jpg
Attachment 3: REFL_1029238629.jpg
REFL_1029238629.jpg
Attachment 4: PRMI-OPLG.png
PRMI-OPLG.png
  7224   Sat Aug 18 03:55:12 2012 YoichiSummaryLSCX-arm locking again

Tonight, I worked on the X-arm locking again. I did not have any significant progress, but observed several issues and will give some suggestions for future work here.

What I did tonight was basically re-alignment of the X-arm (because Rana touched the PZT mirrors for the Y-arm alignment, the X-arm alignment was screwed up). Then I measured the open loop gain. Of course it was almost identical to the one posted in this entry. It reminded myself of how small the phase bubble is. This means we have to finely adjust the gain to set the UGF at the right frequency, i.e. 100Hz. So I decided to do the signal normalization using the TRX power. Using the MC path method described here,  the appropriate normalization coefficient was determined to be 1.6, when the XARM gain is set to 0.05. Using burtgooey, I updated the burt snapshot used by the X-arm restore script.

Now I observed the following things:

When the normalization is used, the lock itself is stable, but the lock acquisition takes loner (i.e. fails more often).

I don't know the exact reason, but here is my guess: Usually, the error signal is divided by the square root of the transmitted power to widen the linear range of the PDH error signal. However, what I'm doing here is dividing the error signal with the power itself, not the sqrt. This might distort the error signal in a not-friendly-for-lock way ? I don't know.

I checked the c1lsc FE code. There seems to be the sqrt(TRX) and sqrt(TRY) signals computed in the code. However, these are not used for the normalization. 

Now, there are two requirements. When dragging the mirrors into the resonance, we want to normalize the error signal with sqrt(TRX). When the mirrors reach the resonance, the gain of the loop must be normalized by TRX. How do we smoothly connect those two states ? Someone should spend some time on this. Maybe I will work on this in Japan.  

We really need a time delay in the filter trigger

The automatic filter trigger is awesome. However, the [0^2:5^2] filter, which is an integrator, takes time to switch on and off. Every time the cavity passes by a resonance, this filter gets turned on and off slowly, giving some large transients. This transient combined with the bad coil balance of ETMX sometimes made the optical lever of ETMX crazy. This can be avoided by turning on this filter a few seconds after the power reaches the threshold. As Rana suggested, we should be able to put an arbitrary time delay to the filter trigger.

Someone should balance the coils

The coil balance of ETMX is bad and causing the above mentioned problem. I tweaked the coil balance by injecting a sinusoidal signal (10Hz) into ETMX pos and trying to minimizing the spectral peak in the optical lever signals. Of course, this is a cheesy work. Someone should put more serious effort on this.

A civilized interferometer should have an auto-alignment capability

After my alignment work, the X-arm power got to about 0.7. (This is probably because the MC transmission power has been low for the past 5 hours or so (attachment 1)).

In anyway, after the cavity locked to the TEM00 mode, the alignment has to be automatically improved by dithering. It is anachronism to sit down and click on the MEDM screen until the power gets big enough.

 

 

Attachment 1: MC_Trans.png
MC_Trans.png
  7274   Fri Aug 24 21:00:40 2012 KojiUpdateLSCX end green investigation

I checked and fixed the X end green situation. Now the X green beam is locked with TEM00.

There are various reasons it did not lock nicely.

  • The IR beam axis was changed by Yoichi and Rana (ELOG #7169). So the green axis also had to be changed.
  • The end green optics is really "BS". Anytime I see it, I feel disgusted. Because of 3D steering mirrors, cross couplings
    between yaw and pitch are big. This makes the alignment hard.
  • Even with acceptable alignment, the lock was only momentarily. I found the slow control was on. This pushed the frequency
    too much and made the lock unstable.
  • The slow control screen was broken as Jamie changed the model names but did not fix the slow screens.
    • Jamie saids (ELOG #7011): Fix the c1sc{x,y}/master/C1SC{X,Y}_GC{X,Y}_SLOW.adl screens. 
      I need to figure out a more consistent place for those screens.

Now some action items are left:

- IR TRX is not aligned.
- X end green needs precise alignment.
- PSL GR TRX is not aligned.

These will be checked on Sunday.

- End green setup is horrible. => Manasa and I should work on this together.

  7311   Wed Aug 29 19:28:41 2012 Elli KingUpdateLSCSetup for a cavity scan or the input mode cleaner

 Riju, Elli

Today we prepared our experimental setup to take a cavity scan of the input mode cleaner, which we want to measure in the next day or so.  Attached is a diagram of our setup.

What we want to do is to inject a set of sidebands into the PSL and sweep their frequency from 32-45 MHz (a range just over one fsr of the mode cleaner- vfsr=11MHz).  We will measure the power transmitted out of the MC using a photo-diode and demodulate this signal with our input signal from the Marconi.  From this we should be able to see the resonant frequencies of the carrier and the higher order modes.

One aspect we spent some time thinking about; whether we would be able to inject a signal into an EOM given the EOM and the Marconi are not perfectly impedance matched.  Based on Kiwamu’s previous e-log entries designing the EOM, we decided that injecting a signal in 32-45 MHz region at 15dBm is similar to injecting the 29.5MHz sideband (at the same power level with very similar input impedance.) Fingers crossed we don’t blow anything up first week on the job.

Attachment 1: 40m_cavity_scan_diagram.jpg
40m_cavity_scan_diagram.jpg
  7360   Fri Sep 7 12:28:09 2012 KojiUpdateLSC11&55MHz modulations turned off

11MHz modulation source was turned off (disabled) at Marconi at 12:00.

  7445   Thu Sep 27 13:05:55 2012 Eric GustafsonUpdateLSC40 meter photodiode frequency response measurement system installation

Jenne, Mike and I installed all of the post holders we could today including: REFL11, REFL33, REFL55, AS55, MCRef, POX11 and POP55.  We did not install AS110, POY or REFL165 because there are interferences that will require moving stuff around. We also did not mount POP22 because it is a peely wally ThorLabs PD that will be replaced by a strong, straight and right thinking LIGO PD in the fullness of time.  We did move it out of the way however which is no more than it deserves. Next step this afternoon Mike and I will install all of the telescopes and launching hardware.  Then with the help of Steve we will begin routing the fibers.  The splitter module will be here by next Monday, the laser by the following Friday and then we will light up the fibers. 

  7447   Thu Sep 27 16:26:11 2012 SteveUpdateLSCRF fibre protection in cable trays

Quote:

Jenne, Mike and I installed all of the post holders we could today including: REFL11, REFL33, REFL55, AS55, MCRef, POX11 and POP55.  We did not install AS110, POY or REFL165 because there are interferences that will require moving stuff around. We also did not mount POP22 because it is a peely wally ThorLabs PD that will be replaced by a strong, straight and right thinking LIGO PD in the fullness of time.  We did move it out of the way however which is no more than it deserves. Next step this afternoon Mike and I will install all of the telescopes and launching hardware.  Then with the help of Steve we will begin routing the fibers.  The 1x16 splitter module will be here by next Monday, the laser by the following Friday and then we will light up the fibers. 

 I'm proposing split loom tubing that would run in the cable tray  to protect the fibers  inside of it.  This tubing diameter in the cable tray can be 1.5-2"  and out of the tray 0.75"

 

  7448   Thu Sep 27 17:00:41 2012 Eric GustafsonUpdateLSC40 meter photodiode frequency response measurement system installation

Mike and I installed all of the telescopes and launching hardware for REFL11, REFL33, REFL55, AS55, MCRef, POX11 and POP55. On Monday afternoon Steve will work with us on the fiber routing.  Steve is buying some protective covers for the fibers.

  7513   Tue Oct 9 23:12:56 2012 JenneUpdateLSC11MHz reconnected to EOM

Riju hasn't been in the lab in a long time to do any measurements, so I put the signals back to how they should be. 

I turned off / confirmed off the things which were sending signal to the EOM:  the network analyzer, the RF generator box, and the Marconi which supplies the 11MHz. 

I removed the cavity scanning cable, and terminated it, and put the regular 11MHz cable back on the splitter.

I then turned on the RF gen box and the Marconi.  The Marconi had been off, so we were not getting any 11MHz or 55MHz out of the RF gen. box.  This is why I couldn't lock any cavities last night (duh). 

On to locking!

----------------- In other news,

While swapping out the EOM cable, I noticed that the DC power supply sitting under the POX table was supplying a weird value, 17 point something volts.  I checked on the table to remind myself why that power supply is there...it's powering an RF amplifier right after the commercial PD that is acting as POP22.  The amplifier wants +15 and GND, so I reset the power supply to 15V.  We should add this to the list of things to fix, because it's dumb.  Either we need to put in the real POP22 (long term goal), or we need to get this guy some rack power, and do the same for any amplifiers for the Beat setup.  It's a little hoakey to have power supplies littering the lab.

  7515   Wed Oct 10 02:15:14 2012 ranaUpdateLSC11 MHz reconnected to EOM

 Absolutely hokey. What are our requirements for this RFPD? What are the power levels and SNR that we want (I seem to remember that its for 22 as well as 110 MHz)? Perhaps we can test an aLIGO one if Rich has one sitting around, or if the aLIGO idea is to use a broadband PD I guess we can just keep using what we have.

  7554   Tue Oct 16 00:33:29 2012 JenneUpdateLSCPOP lens placed on POX table, 2 PRMI movies

[Evan, Jenne]

We aligned the PRMI.  We definitely can lock MICH, but we're not really sure if PRCL is really being locked or not.  I don't think it is.

Anyhow, we found 2 different places on the AS camera that we can align the PRMI.  One (middle, right hand side of the camera), we see the same weird fringing that we've been seeing for a week or two.  The other (lower left side of the camera), we see different fringing, almost reminds me more of back in the day a few months ago when the beam looked like it was expanding on each pass.  As I type, Evan is uploading the movies to youtube.  I *still* don't know how to embed youtube videos on the elog!

Also, we found both forward-going and backward-going POP beams coming out onto the POX table.  We placed the 2" lens in the path of the backwards beam, so that we can find it again.  We can't see it on an IR card, but if we put some foil where we think the beam should be, we can use a viewer to see the spot on the foil.  Poking a hole in the foil made an impromptu iris.

Youtube videos:

Lower left on camera

Middle right on camera

  7555   Tue Oct 16 02:34:38 2012 KojiUpdateLSCPOP lens placed on POX table, 2 PRMI movies

How can you lock the PRMI without the REFL beams? c.f. this entry by Kiwamu
Which signals are you using for the locking?

I think the first priority is to find the fringes of the arms and lock them with POX/POY.

As for the POP, make sure the beam is not clipped because the in-vac steering mirrors
have been supposed to be too narrow to accommodate these two beams.

  7556   Tue Oct 16 11:38:17 2012 JenneUpdateLSCMore PRMI notes from last night

Quote:

How can you lock the PRMI without the REFL beams? c.f. this entry by Kiwamu
Which signals are you using for the locking?

I think the first priority is to find the fringes of the arms and lock them with POX/POY.

As for the POP, make sure the beam is not clipped because the in-vac steering mirrors
have been supposed to be too narrow to accommodate these two beams.

I was using AS55I for PRCL, and AS55Q for MICH.  I snuck that into the last line of an unrelated elog, since I did both things at the same time: see elog 7551.  Kiwamu's measurements (elog 6283) of the PRMI sensing matrix show that the PRCL and MICH signals are almost orthogonal in AS55 (although the optickle simulation doesn't agree with that...)  He was able to lock PRMI with AS55 I&Q (elog 6293), so I thought we should be able to as well.  Locking the PRMI was supposed to help tune the alignment of the PRM, not be the end goal of the night.  Also, we only tried locking PRCL in the "middle right" configuration, not the "lower left" configuration, but we were seeing what looked like recycling flashes only in the "lower left" configuration.

I agree in principle that we should be working on the arms. However, since we can't use the old steer-the-beam-onto-the-cage trick to find the beam, I was hoping that we could steer the beam around and see some light leaking out of the ETM, onto the end table.  However, with the 1% transmission of the ITMs and ~10ppm transmission of the ETMs, there's not a lot of light back there.  I was hoping to align the PRMI so that I get flashes with a gain of 10 if I'm lucky, rather than just the 5% transmission of the PRM.  With the PRMI aligned, I was expecting:

(1W  through Faraday) * (10 PR gain) * (0.5 BS transmission) * (0.01 ITM transmission) * (10ppm ETM transmission) = 0.5uW on the ETM tables during PRCL flashes

I was hoping that things would be well enough aligned that I could just go to the end table, and see the light with a viewer, although as I type this, I realize that if the beam was not on the end table (or even if it was...) any time I move the PZTs, I'd have to completely realign the PRMI in order to see the flashes.  This seems untenable, unless there are no other options.

We then got sidetracked by trying to see the POP beam, and once we saw the POP beam we wanted to put something down so we could find it again.  POP is also small, but not as small as expected at the end:

(1W  through Faraday) * (10 PR gain) * (20ppm PR2 transmission) = 0.2mW on POP during PRCL flashes.

POP was very difficult to see, and we were only able to see it by putting the foil in the beam path, and using a viewer.  I think that we once were able to see it by looking at a card with the viewer, but it's much easier with the foil.  I'd like to find an iris that is shiny (the regular black iris wasn't helpful), to facilitate this alignment.  Since we were just looking at the reflection off of the foil, I have no comment yet about clipping vs. not clipping.  I do think however that the forward-going beam may have been easier to find....when the PRMI alignment drifted, we lost the beam, but I could still see the forward-going beam.  Probably I should switch to that one, since that's the one that was lined up with the in-vac optics. 

Summary:

Ideas are welcome, for how to align the beam to the Yarm (and later to the Xarm), since our old techniques won't work.  Aligning the PRMI was a distraction, although in hopes of getting flashes so we could see some light at the end tables.  I'm going to go see if I can look through a viewport and see the edges of the black glass aperture, which will potentially be a replacement for the steering-on-the-cage technique, but if that doesn't work, I'm running out of ideas.

  7738   Wed Nov 21 21:06:13 2012 AyakaUpdateLSCcalibration of arms

Motivation

In order to estimate whether we can see acoustic coupling in arms or not, we have to calibrate signals to phase noise.

Method

I used the same method as Yuta and Jenne did (6834).
I switched from ETM locking to ITM locking since only ITM actuators are calibrated (5583), and measured the open loop transfer function and the transfer function from ITM excitation to POX/POY error signal. Then I can estimate the calibration value H [counts/m] from POY/POX error signal to displacement.

Results

Yarm; H = 9.51 x 1011 counts/m
  OL_y.pngerr_exc_y.pngPOY_disp_y.png

Xarm; H = 6.68 x 1011 counts/m
OL_x.pngerr_exc_x.pngPOX_disp_x.png

Phase noise in arms:
XY_phase.png
blue; Xarm, green; Yarm

 

Next Step

I will calibrate the acoustic signal and see if it is reasonable that we can see the acoustic coupling signal in the arms.
But I guess it is difficult. Actually I have not seen coherence between ETM feedback signals and acoustic sounds yet. (I measured acoustic noise near POX and in PSL table.)

If I find that it is hopeless, I will create some sounds and try to measure transfer function from acoustic sound to arm cavity signals.
I am interested in how the transfer function calculated by wiener filtering is different from the measured transfer function.

 

Note

I found that we do not have enough phase margin. This is why the arm locking is not so stable.

  7739   Sat Nov 24 13:58:07 2012 ranaUpdateLSCcalibration of arms

For the loop diagnosis, its best to use the method of "IN1/IN2", rather than manipulate the close loop gain. In this way, you can directly plot the swept sine measurement from DTT as the open loop gain.

Also, for reporting calibration, we should all try to record the current settings better. Anything that may change the loop gain should be recorded along with the Bode plot and the DATA must be posted to the elog - no more of just posting plots.

We need to know, e.g.

  1. what is the power in the arms?
  2. are the LSC whitening filters on?
  3. are the SUS dewhitening filters on?
  4. What normalization is being used in the LSC?
  5. What digital filters are on in the X/YARM loop filter bank?

Resistance is feudal.

  7743   Mon Nov 26 10:42:06 2012 AyakaUpdateLSCcalibration of arms

I uploaded a zip file that contains data files used for the calibration.

OLTF_x/y.txt: the open loop transfer function (measured by IN1/IN2 in arm servo filter bank).
coh_x/y.txt: coherence of OLTF. I used the data where coherence > 0.98.
ext_err_x/y.txt: the transfer function from ITM excitation signal to POX/POY error signal.
coh_x2/y2.txt: coherence of ext_err. I used the data where coherence > 0.98.

The LSC whitening filter was off because the xarm was unlocked when the POX Q whitening filter was turned on. (We have to study what was wrong.)
The SUS whitening filters were on.
The all digital filters except +6dB filter were on.

Attachment 1: armcalib.zip
  7800   Sat Dec 8 04:12:38 2012 DenUpdateLSCprcl

 Today I wanted to check that AS and REFL beams are real and contain proper information about interferometer. For this I locked YARM using AS55_I and REFL11_I. Then I compared spectrum with POY11_I locking. Everything is the same. I've also adjusted phase rotations of AS55 (0.2 ->24) and REFL11 (-34.150 -> -43).

Then I've locked MICH and aligned EMTs such that ASDC was close to zero. Then I locked PRCL and aligned PRM. Power buildup was 50. 

IMG_0118.JPG

ELOG V3.1.3-