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ID Date Author Type Categoryup Subject
  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.

  7128   Thu Aug 9 00:14:02 2012 EricSummaryLockingYARM Locking and Calibration

Today I spent time locking the YARM in order to calibrate the arm cavity. Here's what I did:

1. Misalign all optics other than the beam splitter, ITMY, ETMY and PZT2

2. Restore BS, ITMY, ETMY, and PZT2

3. Open Dataviewer and run /users/Templates/JenneLockingDataviewer/Yarm.xml from the Restore Settings. This opens the signals C1:LSC-POY11_I_ERR (the Pound-Drever-Hall error signal for this measurement) and C1:LSC-TRY_OUT (the light transmitted through ETMY) in the plot window.

4. Adjust ITMY and ETMY pitch and yaw using the video screens looking at AS and ETMYT as a first, rough guide. It can be helpful at first to increase the gain on the YARM servo filter module in the C1LSC control screen to about 0.3 and decrease it back down to 0.1 as the beam becomes better aligned. You know when to decrease this gain when fuzzy, small oscillations appear on the C1:LSC-TRY_OUT signal. If the mode cleaner is locked you should see a bright spot on the AS camera.

5. Tinker with pitch and yaw while looking at the AS screen until you see a reasonably good circular spot without other fringes extending from a bright center.

6. The overall goal is to maximize C1:LSC-TRY_OUT because the power transmitted through EMTY is proportional to the power within the cavity. A decent target value is 0.85 and today I was able to get it to just over 0.80 at best. At first there will probably be small spikes in C1:LSC-TRY_OUT. You want to adjust pitch and yaw until the deviation in the signal from zero is no longer just a spike, but a sustained, flat signal above zero. By this time there should be light showing up on the ETMYT camera as well.

7. Once that happens, continue to successively adjust ITMY and ETMY doing the pitch adjustments on both first, and then the yaw adjustments, or vice versa. You can also tweak the PZT2 pitch and yaw. Once you've got C1:LSC-TRY_OUT as large as possible, you've locked the cavity.

I saved the pitch and yaw settings I ended up with for ITMY, ETMY, BS and PZT2 in the IFO_ALIGN screen. Before the end of the day I think Jenne restored the rest of the previously misaligned optics because they were restored when I got back from dinner.

 

 

I also worked on calibrating the YARM. I opened up DTT using C1:LSC-POY11_I_ERR as the measurement channel and C1:SUS-ITMY_LSC_EXC as the excitation channel. I ran a logarithmic swept sine response measurement with 100 points and an amplitude of 25. The mode cleaner kept losing its lock all day, and if this happened while making this measurement I tried to pause the sweep as quickly as possible. I analyzed the the transfer function and the coherence function that the sweep produced, and thought that some of the odd behavior was due to losing the lock and getting back to a slightly different locked state when resuming the measurement. The measured transfer function and coherence plots are attached below. Both the transfer function and the coherence look good above roughly 30 Hz, but do not look correct at low frequencies. There's also a roll-off in the measured transfer function around 200 Hz, while in the model the magnitude of the transfer function drops only after the corner frequency of the cavity, around several kHz. I have attached a plot of the roughly analogous transfer function from the DARM control loop model (the gains are very large due to the large arm cavity gain and the ADC conversion factor of 2^16/(20 V) ). The measured and the modeled transfer functions are slightly different in that the model does not include the individual mirrors, while the excitation was imposed on ITMY for the measurement.

 

The next steps are to figure out what's happening in DTT with the transfer function and coherence at low frequencies, and to understand the differences between the model and the measurement.

Attachment 1: cal_swept_sine3_tfmag
Attachment 2: cal_swept_sine3_tfph
Attachment 3: cal_swept_sine3_coh
Attachment 4: sensing_func_model.png
sensing_func_model.png
  7130   Thu Aug 9 00:35:53 2012 JenneSummaryLockingYARM Locking and Calibration

Quote:

 Once you've got C1:LSC-TRY_OUT as large as possible, you've locked the cavity.


 Both the transfer function and the coherence look good above roughly 30 Hz, but do not look correct at low frequencies. There's also a roll-off in the measured transfer function around 200 Hz, while in the model the magnitude of the transfer function drops only after the corner frequency of the cavity, around several kHz. I have attached a plot of the roughly analogous transfer function from the DARM control loop model (the gains are very large due to the large arm cavity gain and the ADC conversion factor of 2^16/(20 V) ). The measured and the modeled transfer functions are slightly different in that the model does not include the individual mirrors, while the excitation was imposed on ITMY for the measurement.

 

The next steps are to figure out what's happening in DTT with the transfer function and coherence at low frequencies, and to understand the differences between the model and the measurement.

 The cavity is actually "locked" as soon as the feedback loop is successfully closed.  One easy-to-spot symptom of this is that, as you mentioned elsewhere in your post, TRY is a ~constant non-zero, rather than spikey (or just zero).  Once you've maximized TRY, you've got the cavity locked, and the alignment optimized.

We didn't get to this part of "The Talk" about the birds, the bees, and the DTTs, but we'll probably need to look into increasing the amplitude of the excitation by a little bit at low frequency.  DTT has this capability, if you know where to look for it.

It would be great to see the model and your measurement overlayed on the same plot - they're easier to compare that way.  You can export the data from DTT to a text file pretty easily, then import it into Matlab and plot away.  Can you check and maybe repost your measured plots?  I think they might have gotten attached as text files rather than images.  At least I can't open them. 

  7134   Thu Aug 9 10:09:32 2012 EricSummaryLockingYARM Locking and Calibration

Quote:

Quote:

 Once you've got C1:LSC-TRY_OUT as large as possible, you've locked the cavity.


 Both the transfer function and the coherence look good above roughly 30 Hz, but do not look correct at low frequencies. There's also a roll-off in the measured transfer function around 200 Hz, while in the model the magnitude of the transfer function drops only after the corner frequency of the cavity, around several kHz. I have attached a plot of the roughly analogous transfer function from the DARM control loop model (the gains are very large due to the large arm cavity gain and the ADC conversion factor of 2^16/(20 V) ). The measured and the modeled transfer functions are slightly different in that the model does not include the individual mirrors, while the excitation was imposed on ITMY for the measurement.

 

The next steps are to figure out what's happening in DTT with the transfer function and coherence at low frequencies, and to understand the differences between the model and the measurement.

 The cavity is actually "locked" as soon as the feedback loop is successfully closed.  One easy-to-spot symptom of this is that, as you mentioned elsewhere in your post, TRY is a ~constant non-zero, rather than spikey (or just zero).  Once you've maximized TRY, you've got the cavity locked, and the alignment optimized.

We didn't get to this part of "The Talk" about the birds, the bees, and the DTTs, but we'll probably need to look into increasing the amplitude of the excitation by a little bit at low frequency.  DTT has this capability, if you know where to look for it.

It would be great to see the model and your measurement overlayed on the same plot - they're easier to compare that way.  You can export the data from DTT to a text file pretty easily, then import it into Matlab and plot away.  Can you check and maybe repost your measured plots?  I think they might have gotten attached as text files rather than images.  At least I can't open them. 

 Here's the same plots in pdf format now. I originally posted them as jpg because I couldn't open the resulting pdf from DTT on rosalba, but I could open the jpg. I'll look into overlaying the measured and modeled curves as well.

Attachment 1: cal_swept_sine3_magnitude.pdf
cal_swept_sine3_magnitude.pdf
Attachment 2: cal_swept_sine3_phase.pdf
cal_swept_sine3_phase.pdf
Attachment 3: cal_swept_sine3_coherence.pdf
cal_swept_sine3_coherence.pdf
  7139   Fri Aug 10 09:51:51 2012 EricSummaryLockingYARM Locking and Measurements

I forgot to post this last night, but I locked the YARM again yesterday and misaligned the other optics. I took measurements on ITMY and ETMY with DTT again as well. At the end of the day I aligned the rest of the optics before I left.

  7145   Fri Aug 10 16:39:44 2012 EricSummaryLockingMichelson Locking

I'm working on locking the Michelson now in order to put an excitation on one of the input test masses and measure the resulting error signal at the anti-symmetric port. I aligned the beams from ITMX and ITMY by looking at the AS camera with the video screens, but the fringes were not destructively interfering. Jenne advised that I look at the gain on the MICH servo filter modules in the LSC screen. We flipped the sign on the gain (it was 0.120 and it is now -0.120) and the fringes destructively interfered as desired after this change.

For purposes of documentation, I locked the YARM earlier in the morning before moving on to the Michelson. The purpose of this was to put another excitation on C1:SUS-ETMY_LSC_EXC and then measure the error signal on C1:LSC-POY11_I_ERR.

  7149   Fri Aug 10 19:49:11 2012 EricSummaryLockingMichelson Locking Procedure and Measurements

Today I worked on locking the Michelson. Here's what I did:

 

  1. Open Data Viewer and Restore Settings /users/Templates/JenneLockingDataviewer/MICH.xml. This opens the C1:LSC-ASDC_OUT and C1:LSC-AS55_Q_ERR plots.

  2. Check the LSC screen to verify that the path between the Servo Filter Modules and the SUS Ctrls are outlined in green. If not turn on the OUT button within the Filter Servo Modules, enable LSC mode, and turn on the SUS Ctrls for the BS.

  3. Misalign all optics other than BS and one of ITMX and ITMY. The ITMY was already well-aligned from my work on locking the YARM, so I actually chose to misalign ITMY at first.

  4. Restore BS and ITMX. Use the AS camera on the video screen as your guide when aligning ITMX.

  5. Adjust pitch and yaw of ITMX until a bright, circular spot appears near the middle of the AS camera.

  6. Now restore ITMY and adjust pitch and yaw until a second circular spot appears on the AS camera.

  7. Adjust both ITMX and ITMY until both bright spots occupy the same location. If the spots remain bright when they are in the same location you are locking onto a bright fringe actually, and need to flip the sign of the gain on the MICH servo filter modules. I had to do this today in fact, as discussed in ELOG 7145.

  8. If the sign is correct, the two beams should interfere destructively and the formerly bright spots will form a comparatively dark spot. The shape of the spot will likely be two bright lobes separated by a dark middle.

  9. C1:LSC-ASDC_OUT should be a roughly flat signal, and the goal now is to minimize the magnitude of this signal. The smaller this signal, the darker the AS camera should look. Decent target values for C1:LSC-ASDC_OUT are around 0.10 to 0.05.

 

Once I did this, I made measurements by exciting C1:SUS-ITMY_LSC_EXC and measuring with C1:LSC-AS55_Q_ERR. I ran a logarithmic swept sine response from 1 to 1000 Hz again, with an envelope amplitude dependence. Again I looked at the measured transfer function and coherence. I was able to get good coherence, but it was somewhat erratic in that it dipped low at high frequency multiple times.

  7168   Tue Aug 14 00:42:40 2012 JenneUpdateLockingPOX signal sometimes looks very funny

I'm trying to lock / align the Xarm, and POX 11 I looks funny sometimes.

I attach 2 screenshots so you can see what I mean.  I'm leaving them uncropped so that you can see the only thing that has changed is the LSC enable / disable button. 

The situation:

PRM, SRM, ITMY, ETMY all misaligned.  BS, ITMX, ETMX aligned so that most of the time I can't lock better than 04, bad in yaw, but very occasionally I'll get lucky and catch a 00.  When the LSC enable switch is ON (2nd attachment), the POX signal (green trace in dataviewer in both attachments) looks almost square-ish, and definitely funny.  It doesn't seem to correspond directly to flashing in the cavity (red trace in dataviewer in both attachments).  However when I disable the LSC, POX goes back to looking normal - 1st attachment.  Right around -5 seconds in the 1st attachment, I disabled the LSC.

I don't really know what this means.

Attachment 1: POX_13Aug2012_LSCdisabled_pox_is_normalish.png
POX_13Aug2012_LSCdisabled_pox_is_normalish.png
Attachment 2: POX_13Aug2012_LSCenabled_pox_is_squareish_funny.png
POX_13Aug2012_LSCenabled_pox_is_squareish_funny.png
  7169   Tue Aug 14 04:32:49 2012 rana, yoichiUpdateLockingPOX signal sometimes looks very funny

 The alignment was way off. We moved the PZT, the BS, and the x arm to get it to lock. Along the way we noticed that giving the ETM and POS offsets makes it tilt a lot. The DC coil balancing is no good at all.

After locking, we tuned up the X arm filters in the LSC and activated the filter module triggers.  I would attach a screenshot of the trigger screen, but sadly it has no snapshot button on it.

WE changed the integrator into a double integrator with a complex zero pair. We also replaced the 1:50 boost with a 2nd order complex pole:zero pair. And added a 18 Hz RG. These were all set by looking at the error point spectra and minimizing the RMS. Hopefully, this kind of work will all be obsolete once we get the optimal feedback code. For now, the arm is very stable - we're leaving it locked overnight since the filter triggering seems to work well.

The loop kept oscillating, so we turned the xarm gain down from the 0.3 that we found it at down to 0.045. We measured the loop gain using our old xarm loopgain DTT template (which is in the Templates directory, not in /users/IAmAnAmateur/secret/secret/bozo/). It shows that we are missing ~20 deg of phase at the peak of the phase bubble compared to the old days. We guess that its because of the downsample/upsample digital AA filters which we now have in addition to the 7kHz hardware AA/AI which we still have from the pre-upgrade times). We (Jamie) have to think about how to rationalize this: we cannot survive with double AA/AI.

Another big hindrance in the lock acquisition is that the whitening filters were on. Because the WG is set to 45 dB, the ADCs are getting saturated when the flashes are large. We should have the whitening filters switch after acquiring lock.

Also, why are all the camera views of the ITMs and ETMs different? Steve, please go back and make them all the same (angles, aperture, lenses, etc.). Without them being the same, we cannot compare them.

ETMXF_1028975007.bmp

ETMXT_1028975105.bmpAS_1028975166.bmp

 I have found the video capture scripts in Yuta's personal directory. This is illegal, of course. All useful scripts (even when in development) go into the shared scripts directory. As a punishment, I have added some nasty typos to a couple of his other scripts and then backdated the timestamps so that he cannot find it easily.

 Also, I fixed the "mcup" script. After the ringdown people inserted the pickoff for MC2 trans, no one adjusted the thresholds in the MC autolocker. I've fixed mcup to trigger at 7000 cts. This should be changed back if the pickoff is removed someday. MC WFS now coming on.

Attachment 1: ITMX_1028974969.bmp
  7208   Thu Aug 16 19:12:30 2012 JenneUpdateLockingLong arm lock stretches

YARM_awesome_lock_stretch.png

After Rana and Yoichi tweaked the arm locking filters, we have had some pretty awesome lock stretches. 5-day minute trend.

  7240   Tue Aug 21 01:54:09 2012 JenneUpdateLockingFPMI locked - arms locked with IR

I (for the first time personally) locked the FPMI.  I have data for the POX11I, POY11I, AS55Q error signals for each arm and the Michelson (JenneLockingDTT/FPMI_error_signals.xml), but I haven't calibrated the data yet - Self: do this!  FPMI with arms locked using IR has been happily locked for a long time now - this is good.

From elogs / my old MICH calibration script, I have the plant calibrations of:

POY:  1.4e12 cts/m

POX: 3.8e12 cts/m

AS55: 9.4e9 cts/m

MICH has FM 5 on, Xarm has FM4-10 all on, Yarm has FM3-10 all on. 

Post note: FM 3 - the integrator - for Xarm wasn't triggered.  It turns on just fine, so I've got it triggered just like Yarm.

Also, just remembered - I turned off the XARM TRX power normalization, since it was causing crazy numbers in the xarm servo.  The XARM locked pretty easily after that.

  7246   Tue Aug 21 22:54:47 2012 JenneUpdateLockingRemoved beam dump from POY path

POY was looking funny, and the YARM wasn't locking.  It looked like POY wasn't seeing any light at all.  I went to check, and it looks like a beam dump got accidentally placed in the POY path during oplev adjustments this morning.  POY is back, locking continues.

  7250   Wed Aug 22 16:50:09 2012 JenneUpdateLockingDouble integrator in ARM LSC servos

Last week, Rana changed the integrators in the arm LSC servo filters to be double integrators with complex poles. 

Yesterday, I found that using the "timeout" feature of Foton (at filter ON/OFF request, waits for zero crossing, or T seconds, whichever comes first) is useful for turning on the integrators, but bad for turning them off.  When we're locked, the error signal is oscillating around zero, so there is often a zero crossing.  When we lose lock, we want to turn off the filter immediately.  But, as soon as lock is lost, the input signal gets large, and doesn't often cross zero, so the filter waits 8 seconds until actually turning off.  If the arm flashes any time during that 8 sec, we send a big kick to the optics.

An alternative option could be ramping the filter on.  However, since the double integrator has -180deg phase at low frequencies (until the poles at ~5Hz), the transition between no filter (0deg phase) and integrator on could be problematic.  I simulated this, and find that for the very beginning of the ramping process, we would have a problem. 

The filter is defined as:  NoFilter * (1 - R) + Integrator * (R), so for R=0, the integrator is off, and for R=1, the integrator is fully on.  R can be any value [0,1]. 

The first figure is the time series (1 second, 16kHz), ramp goes from 0->1 or 1->0 in 1 second:

 DoubleIntegrator_timeSeries_LowRes.png

 

The second figure is bode plots for selected values of R:

DoubleIntegrator_Bode_vs_Ramp_LowRes.png

As R gets smaller and smaller, the notch goes to lower frequency, and becomes higher Q.  So perhaps ramping is not a good answer here. 

What if we go for single or triple integrator, to get rid of the (+1) + (-1) problem?

  7334   Tue Sep 4 11:32:58 2012 JenneUpdateLockingFriday in-vac work

Elog re: Friday's work

Adjusted PZT2 so we're hitting the center of PR2. 

Noticed that the beam centering target is too low by a few mm, since the OSEM set screw holes that it mounts to are lower than the center line of the optic.  This meant that while we were hitting the center of PR2, the beam was half clipped by PRM's centering target.  We removed the target to confirm that the beam is really centered on PR2.

Checked the beam on PR3 - it looked fine.  There had been concern last week that PR2 was severely pitched forward, but this turns out to be an effect of the PRM centering target being too low - shoot the beam downward to go through the hole, beam continues downward to hit the bottom of PR2, so beam is falling of the bottom of PR3.  But when we actually centered the beam on PR2, things looked fine on PR3. 

Checked that the beam approximately goes through the beam splitter.  Again, the targets are too low, and these 45 deg targets' holes are smaller than the 0 deg targets, so we don't see any beam going through the target, since the beam is hitting the target higher than the hole.  The beam looked left/right like it was pretty close to the hole, but it was hard to tell since the angle is bad, and I'm not infinitely tall.  We should check again to make sure that the beam is going through properly, and we're not clipping anywhere.  I'll need help from a height-advantaged person for this.

Checked that the beam is hitting the center of the ITMY, as best we can see by using an IR card at the back of the optic.  We didn't try reaching around to put a target on the front side. 

We were debating whether it would be worth it to open ETMY this week, to check that the beam transmitted through the BS hits the center of ETMY.

We also took a quick look around the AS optics, but since that depends on BS/ITMX alignment, we weren't sure how to proceed.  We need a plan for this part.  All suspended optics were restored to their last good alignment, but we haven't tried locking MICH or anything to confirm that the alignment. 

To do list:  Check no clipping on ITMY table of beam between BS and ITMY, clipping on POY optics.  Also, oplev is clipping on cable holder thing on the table - this needs to be moved.  .....other?

  7339   Tue Sep 4 20:06:04 2012 JenneUpdateLockingMC scan input switched to the 11MHz port of EOM

Since the EOM's signal combiner (splitter backwards) is frequency-independent, Koji and Jamie (in the proper turn off, turn on order) put the 55MHz signal back to the EOM, and put the MC mode scan input to the 11MHz port.  This way we can lock the Michelson tomorrow, and we don't have to keep switching cables around when Riju wants to take some scans.

  7514   Wed Oct 10 00:18:58 2012 JenneUpdateLockingREFL camera aligned

I moved some of the REFL optics on the AS table by a teeny bit to accomodate the new place that the REFL beam exits the chamber (none of this was done while we were at air....we were only dealing with the AS beam at the time, and were happy that REFL came out of the vacuum).

The REFL beam is now on the REFL camera (with PRMI aligned), and the beam is going toward the 4 REFL RF PDs, but it's not aligned to any of them.

I have some questions as to mystery optics on in the REFL path.  There is a 90% BS, and I don't know where the 10% reflection goes....is it going to beat against the AUX Stochino laser?

I have to go, and I didn't fix the videocapture script today, so pix tomorrow, I promise.

  7573   Thu Oct 18 03:57:20 2012 JenneUpdateLockingAlignment is really bad??

The goal of the night was to lock the Y arm.  (Since that didn't happen, I moved on to fixing the WFS since they were hurting the MC)

I used the power supplies at 1Y4 to steer PZT2, and watched the face of the black glass baffle at ETMY.  (elog 7569 has notes re: camera work earlier)  When I am nearly at the end of the PZT range (+140V on the analog power supply, which I think is yaw), I can see the beam spot near the edge of the baffle's aperture.  Unfortunately, lower voltages move the spot away from the aperture, so I can't find the spot on the other side of the aperture and center it.  Since the max voltage for the PZTs is +150, I don't want to go too much farther.  I can't take a capture since the only working CCD I found is the one which won't talk to the Sensoray.  We need some more cameras....they're already on Steve's list.

When the spot is a little closer to the center of the aperture than the edge of the aperture (so the full +150V!!), I don't see any beam coming out of AS....no beam out of the chamber at all, not just no beam on the camera.  Crapstick.  This is not good.  I'm not really sure how we (I?) screwed up this thoroughly.  Sigh.  Whatever ghost REFL beam that Kiwamu and Koji found last week is still coming out of REFL.

Previous PZT voltages, before tonight's steering:  +32V on analog power supply, +14.7 on digital.  This is the place that the PRMI has been aligned to the past week or so.

Next, just to see what happens, I think I might install a camera looking at the back (output) side of the Faraday so that I can steer PRM until the reflected beam is going back through the Faraday.  Team K&K did this with viewers and mirrors, so it'll be more convenient to just have a camera.

Advice welcome.

  7579   Fri Oct 19 01:21:42 2012 EvanUpdateLockingAligning PZTs, PRM

[Evan, Jenne]

Tonight we made an attempt at getting the PRM + ITMY aligned with correct input pointing. We steered the good PZT so that the input beam makes it through the aperture in front of ETMY. We then aligned the PRM so that the retroreflection of the input beam makes it back into the Faraday. After that we tried dithering the alignment of ITMY and the beamsplitter to see if we could see a spot flash across the AS port, but we saw nothing.

For the PRM alignment we set up a camera looking into the window at the Faraday in the IOO chamber; it's called FI_BACK. We stole a 50mm lens from the ETMY face camera.

We also tried looking for beam on IP_POS and IP_ANG. When the input beam is aligned to pass through the ETMY aperture, we can see beam on the steering mirrors preceding IP_POS, but it hits a mirror mount. When the input beam is aligned as it was on Monday, it clips on the ETMY aperture but makes it further along the IP_POS optical path.   In both cases, we weren't able to see any beam coming out for IP ANG. 

  7581   Fri Oct 19 16:24:39 2012 ranaUpdateLockingAlignment is really bad??

 

 VENT NOW and FIX ALIGNMENT!

  7730   Tue Nov 20 02:57:24 2012 Ayaka, Den, KojiUpdateLockingred in arms

We aligned and locked x and y arms.

MCL loop makes arms lock unstable, adds a lot of noise at frequencies 60-100 Hz. We'll fix it.

At some point we were not able to lock because of ADC overflows of PO signals. They happened if whitening filters were enabled. So we reduced the gain of POX whitening filters down to 36 dB and POY - to 39 dB. Now cavities can be locked with whitening filters.

Also we changed the pedestal of the lens in the beam path to the POX because the beam was too high.

 

arms.png    arms_psd.png

etmxf.png  etmyf.png

itmxf.png     itmyf.png

etmxt.png    etmyt.png

  7736   Wed Nov 21 01:31:37 2012 Koji, AyakaUpdateLockingalignment on ETMX table

Since the transmission beam on ETMXT camera seemed to be clipped, we checked the optics on ETMX table.

We aligned the lens so that it is orthogonal to the beam, then the beam shape looks fine.

output.nv12.bmp

Also we removed some an-used optics which were used for fiber input.

  7872   Wed Jan 2 15:33:23 2013 JenneHowToLockingWe should retry in-air locking

Immediate things to do include finishing installation of new TTs and re-routing of oplev paths in the BS chamber, but after all that, we should retry in-air locking.

The last time we (I) tried in-air locking, MICH wouldn't lock since there was only ~ 6uW of light on AS55 (see elog 7355).  That was before we increased the power into the MC by a factor of 10 (see elog 7410), so we should have tens of microwatts on the PD now.  At that time, we could barely see some PDH signal hidden in the noise of the PD, so with a factor of 10 optical gain, we should be able to lock MICH.

REFL should also have plenty of power - about 1.5 times the power incident on the PRM, so we should be able to lock PRCL. 

Even if we put a flat G&H mirror after the PRM to make a mini-cavity, and we lose power due to poor mode matching, we'll still have plenty of power at the REFL port to lock the mini-cavity.

For reference, I calculate that at full power, POX and POY see ~13uW when the arms are locked.

 

POX/POY power =  [  (P_inc on ITM) + (P_circ in arm)*(T_itm)  ] * (pickoff fraction of ITM ~ 100ppm)

REFL power = (P_inc on PRM) + (P_circ in PRCL)*(T_prm)     =~ 1.5*(P_inc on PRM)

  7905   Wed Jan 16 18:08:06 2013 JenneUpdateLockingExpected PRC gains

I was calculating the power recycling gains we expect for different versions of the PRC, and I am a little concerned that we aren't going to have much gain with the new LaserOptik mirrors.

I'm using

                       t_PRM^2

G =  -------------------------------------------

       (1 - r_PRM * r_PR2 * r_PR3 * r_end)^2

 

from eqn 11.20 in Siegman.

r_end is either the ITM (for a symmetric Michelson) or the flat mirror that we'll put in (for the PR-flat test case).

r = sqrt( R ) = sqrt( 1 - T ) for mirrors whose power transmission is the quoted value.

 

Some values: 

t_PRM^2 = T_PRM = 0.055   --------->   r_PRM = sqrt( 1 - 0.055 )

T_G&H = 20e-6   ---->   r_G&H = sqrt( 1 - 20e-6 )

T_LaserOptic = 0.015 (see elog 7624 where Raji measured this...1.5% was the best that she measured for P polarization.  Elog 7644 has more data, with 3.1% for 40deg AoI) -------> r_LasOpt = sqrt( 1 - 0.015 ) or sqrt( 1 - 0.031)

T_ITM = 0.014 -----------> r_ITM = sqrt( 1 - 0.014 )

 

Some calculations with 1.5% LaserOptik transmission:

G_PRC_2G&H = 45

G_PRC_G&H_LasOpt = 31

G_PRM_flatG&H = 51

With the 3% LaserOptik transmission:

G_PRC_G&H_LasOpt = 22

G_PRM_flatG&H = 30

More ideal case of just PRM, flat mirror (either ITM or G&H), ignoring the folding mirrors:

G_PRM_ITM = 45

G_PRM_flatG&H = 70

 

Punchline:

If the LaserOptik mirror has 1.5% transmission at ~45 degrees, the regular PRC expected gain goes down to 31, from 45 with both folding mirrors as G&Hs.

  7906   Wed Jan 16 18:52:49 2013 JenneUpdateLockingPRM - Flat mirror cavity plan

Game plan:

* Put 2" G&H mirror into BS chamber, in front of BS.

* Align it, lock cavity using an existing REFL PD.

* Align POP setup so I can use POP camera to take image of transmitted cavity mode, and actually take that image.

* Take image of face of PR2.

* Measure finesse of cavity using POP, or a Thorlabs PD at POP (looking at transmission through PR2) by scanning PRM, and infer cavity gain....compare with values in elog 7905.

* If time / inclination allow, take beam scan measurements of the REFL port.

I will not be able to do as was done in elog 6421 to look at the beam size at POP for non-resonating beams.  I expect ~0.1uW of light at POP in the non-resonant case:  100mW * 5.5% * 20ppm = 0.11microwatts.

 

  7909   Wed Jan 16 20:27:16 2013 ranaUpdateLockingExpected PRC gains

Why would we use such a bad optic in our recycling cavity? Is 1.5% the spec for these mirrors? Is this the requirement that Kiwamu calculated somehow? Did anyone confirm this measurement?

I can't believe that we'll have low noise performance in a RC where we dump so much power.

  7910   Thu Jan 17 00:17:31 2013 JenneUpdateLockingExpected PRC gains

Quote:

Why would we use such a bad optic in our recycling cavity? Is 1.5% the spec for these mirrors? Is this the requirement that Kiwamu calculated somehow? Did anyone confirm this measurement?

I can't believe that we'll have low noise performance in a RC where we dump so much power.

 Yeah, Koji mentioned in response to Raji's measurements several months ago that the LaserOptic mirros were pretty far out of spec. We should probably redo the measurement to confirm.

  7913   Thu Jan 17 15:48:21 2013 JenneUpdateLockingPRM - Flat mirror cavity

 

 2" G&H mirror is installed on a DLC mount just in front of the BS.  I had to remove one of the 4 BS dog clamps, so we must put it back when we are finished with this test.

I aligned the G&H mirror such that the reflected beam is overlapped with the incident beam, and I aligned the PRM such that the regular REFL beam is retro-reflected.  This is the same as getting the beam bouncing off the PRM back to the G&H to be overlapped.

I then saw flashes of the cavity, when I held a card with a hole in the cavity, so the beam was going through a small aperture in the card, but I still saw flashes.  I was not able to see flashes on the IR card transmitted through the G&H mirror.

I also cannot see any flashes or scattered light on the face of PR2 camera.

I do, however, see flashes on the face of the PRM.  Movie saved, will post soonly.

Light is coming out of REFL on the AS table, but it's clipped somewhere....needs investigation/work before we can lock.

I also didn't see anything at the POP port with a card, but I'm hopeful that perhaps with a camera I'll see something.

  7916   Fri Jan 18 00:41:34 2013 JenneUpdateLockingDust?

I was thinking tonight about more possible reasons that our PRC sucks, and I wonder if dust on the BS could create the problem.

Historically, Kiwamu and I found a few dust particle scattering centers every time we inspected the test masses before drag wiping. Sometimes, there would be one frustratingly close to the center of the optic. I'm not sure if we ever made note of how many we saw and where they were, except out loud to the assembled crowd.

Anyhow, the BS is the only IFO optic that was not replaced, so I'm not sure how long it has been since it was cleaned. If the PR-flat cavity looks okay and we take out the BS to do a PRM-ITMY cavity, we should inspect the beam splitter.

Also, the PRM could need cleaning, but at least it has been drag wiped within recent memory.

My question is, could a few scattering centers cause the behavior that we are seeing?

 

EDIT:  List o' elogs....

 

Elog 5301 - Some details on dust seen on ITMs and ETMs, Aug 2011.

Elog 4084 - Kiwamu's in-situ drag wiping how-to, with details on some of the dust we saw. Dec 2010.

Elog 3736 - PRM drag wiped before suspension (Oct 2010)

Elog 3111 - June 2010, BS drag wiped.

  7917   Fri Jan 18 09:54:18 2013 JenneUpdateLockingPRM - Flat mirror cavity

Quote:

I do, however, see flashes on the face of the PRM.  Movie saved, will post soonly.

 Dang it.  I didn't confirm that the movie was good, just that it was there.  It's corrupted or something, and won't play.  I'll just have to make a new movie today after I realign the cavity.

  7918   Fri Jan 18 12:08:08 2013 KojiUpdateLockingDust?

No

Quote:

My question is, could a few scattering centers cause the behavior that we are seeing?

 

  7928   Tue Jan 22 19:53:01 2013 JenneUpdateLockingPR-flat cavity status - not locked

The PR-flat cavity is flashing, although not locked.  I am too hungry to continue right now.

I put the FI_Back camera on a tripod, looking at the back of the Faraday.  The beam that Jamie and I were working with on Friday was clipped going back through the Faraday.  I twiddled the TT2 and PRM pointing such that the beam is retroreflecting, and getting back through the Faraday, and the cavity is still flashing.  I then redid the REFL path on the AS table a little bit.  The beam is currently going to the REFL camera, as well as REFL11 and REFL55. 

Some notes about the AS table:  The Y1 separating the main REFL beam from the REFL camera beam was mounted 90 degrees (rotated about the beam's axis) from what it should be.  I fixed it, so that the straight-through beam that goes to the camera is not clipped by the edge of the mount.  The reason (I think) this mirror was mounted backwards is that when mounted correctly, the back of the mount and the knobs interfere with the AS beam path.  I solved this by rotating the first out-of-vac REFL mirror a small amount so that the REFL and AS beams are slightly more separated. 

I am not seeing any nice PDH signal on dataviewer, so I went to check the signal path for the PDs.  The 11MHz marconi is on and providing RF, the EOM is plugged in to 11, 55 and 29.5 signals (no aux cavity scan cables are plugged in).  Both of the RF Alberto boxes are on.  I measured the RF output of both REFL11 and REFL55, although after the fact I realized that I was BAD, and had not found a 'scope that lets me change the input impedance to 50 ohms.  BAD grad student.  However, since I have numbers, I will post them, despite their being not quite correct:

284mVpp at 11MHz out of REFL11.  This is -6.9dBm

2mVpp at 55MHz out of REFL55, measured by 'scope

So, I can clearly see the 11MHz on the 'scope, and can see a very noisy, small 55MHz signal on the 'scope.  I need to think over dinner about what level of signal we should be sending to the demod boards, and whether or not I need more power coming out of the RFPDs.  There is a wave plate and PBS before beam goes to any of the REFL PDs, presumably to ensure that none of them get fried when we're at high power.  If I need more signal, I suspect I can rotate the wave plate and let more light go to the diodes.

  7931   Wed Jan 23 19:05:16 2013 JenneUpdateLockingPR-flat cavity status - locks!

Status update

I (with help from Q) have redone the POP path on the ITMX table.  1" iris is a little too small, so I took it out.  2" lens moved to be centered on POP beam.  2" Y1 didn't need moving.  Straight refl from the 2" Y1 was aligned on to a PDA10CS (set to 70dB). This PD is blocking the usual POP55 diode.  BS which sends beam to camera was moved to allow room for the new temp DC PD.  Refl from this BS goes to the POP camera, which was moved so that the POP beam takes up most of the camera.  BS that would normally take half of the camera's beam and send it to POP22 (Thorlabs PD) is removed, so no beam to POP22.

Also, I have taken the output of the PDA10CS and hijacked the "POP110" heliax cable.  This was connected to this Thorlabs PD which is used as POP22.  (Kiwamu and I had long-term borrowed the 110 demod board for an AS 110 diode, so the "POP110" heliax was really only serving POP22.) There are yellow labels on the new temp and old regular cables, so we can undo my hack.  Similarly, on the other end of the heliax at the LSC rack, I have taken the heliax's output and sent it to the POPDC input on the whitening board.  Thus, the regular POPDC SMA cable is unplugged, but labeled again with big yellow labels.

In other news - the PR-flat cavity locks!!! 

Koji and I coarsely rotated the REFL11 phase such that the signal is predominantly in the I phase.  We set the LSC input matrix to use REFL11I for PRCL, and the output matrix is set to actuate on PRM.  Then we set the gain to -0.005, and it locked!!!!

 

EDIT:  I turned back on the PRM oplev (after Manasa aligned it and redid the out-of-vac oplev layout a bit), and the motion of the cavity is slightly reduced, although there's still a lot going on.  The cavity is vaguely well aligned, although it's time to go make sure that the beams are still on the REFL and TRANS PDs.  However, it's dinner time.

  7934   Wed Jan 23 20:46:46 2013 Zen MasterUpdateLockingPR-flat cavity status - locks!

Quote:

I (with help from Q)

 Two quadratures working in harmony.

yinYang.png

  7945   Mon Jan 28 17:01:19 2013 DenUpdateLockingVideo of PRM-flat test cavity

What mode will you get if lock the cavity PRM - ITMY/ITMX/TEST MIRROR without PR2, PR3 and BS?

Is it possible to skip MC1, MC3 and lock the laser to this test cavity to make sure that this is not actuator/electronics noise?

  7951   Tue Jan 29 10:50:02 2013 JenneUpdateLockingVideo of PRM-flat test cavity

 

I think Den accidentally edited and overwrote my entry, rather than replying, so I'm going to recreate it from memory:

I aligned the PRM-flat test cavity (although not as well as Jamie and Koji did later in the evening) and took some videos. Note that these may not be as relevant any more, since Jamie and Koji improved things after I left.

 

Also, before doing anything with the cavity, I tuned up the PMC since the pitch input alignment wasn't perfect (we were getting ~0.7 transmission), and also tuned up the MC alignment and remeasured the MC spot positions, to maintain a record.

  7957   Tue Jan 29 19:50:49 2013 JenneUpdateLockingBetter POP layout, no extra PRM motion with locked cavity

[Jenne, Jamie, Manasa]

Today's activities focused on getting the POP layout improved, so that we could get clean data for the mode scan measurement. 

As Jamie and Koji pointed out yesterday, the beam was still a little too big on the POP DC PD, and was falling off the diode when the beam moved a small amount.  We have fixed things so that the PD is now at the focus of the lens, and the camera is at a place where the beam takes up most of the area on the TVs.  The beam no longer falls off the PD with cavity fluctuations.  A key point of this work was also to use an extra 2" optic to steer the beam down the length of the POP table, and then do the 50/50 beam splitting later with a 1" optic.  The 1" BS that we had been using (including with the "real" POP beam) is too small.  We could not find a 2" 50/50 BS, so we opted to do the splitting closer to the focal point.  Also, the BS that was splitting the beam between the PD and the camera was a 33% reflector, but now is a 50/50 BS. When we put back the 'real' POP path, we need to consider using larger optics, or a faster lens. The POP path is now good, hopefully for the duration of the half cavity test.

After getting the POP path taken care of, and tweaking up the cavity alignment a little bit, the transmitted power on POP DC is ~22,000 counts, with occasional fluctuations as high as 25,000 counts. 

Jamie looked at the REFL path, and things look sensible there.  The unlocked REFL power is ~36 counts, and the locked power is ~20 counts.  I'm not sure what the 160 counts that Koji mentioned in his edits to elog 7949 is about.

I looked at the PRM oplev with the cavity locked and unlocked, and with today's alignment, there seems to be no difference in the amount of PRM motion when the cavity is locked vs unlocked. 

HalfPRCL_PRM-flatMirror_RefsAreLocked_OthersUnlocked.png

 It still looks like we might be seeing some clipping in the in-vac POP steering mirrors - we haven't gotten to them yet.

Jamie is currently modifying Yuta's mode scan analysis script to look at the data that we have of the cavity.

 


We need more 2" optics.  There are no mounted 2" spares in the various optic "graveyards" (which, PS, we should consolidate all into the cabinet with doors near the optics bench), and the options for boxes in the drawers is slim pickin's.  We have some S-pol stuff, but no Y1s or BS-50s for P-pol.  Since POP, POX, POY, IPANG, TRX and TRY all come out of the vacuum with large beams, we should have some options for these laying around for this kind occasional temporary thing.  We also need to choose, then purchase better 2" lenses for the pickoffs.

Attachment 1: HalfPRCL_PRM-flatMirror_RefsAreLocked_OthersUnlocked.pdf
HalfPRCL_PRM-flatMirror_RefsAreLocked_OthersUnlocked.pdf
  7959   Tue Jan 29 21:07:48 2013 JenneUpdateLockingPRM coils need diagonalizing

 

 [Jenne, Jamie]

We tried actuating on PRM so that we go through fringes in a known, linear way.  We used C1:SUS-PRM_LSC_EXC and awggui.  It seems that we get a lot of angular motion when we actuate....we need to look into this tomorrow.

EDIT/UPDATE:  Last night we tried several combinations of frequency and amplitude, but just for an idea,  we were using 2Hz, 1000cts.  Using Kiwamu's calibration in elog 5583 for the PRM actuator of 2e-8/f^2 m/cts, this means that we were pushing ~5nm.  But when we pushed much harder (larger amplitude) than that, we saw angular fringing. 

  7961   Wed Jan 30 11:16:32 2013 JenneUpdateLockingMode spacing calc

[Jenne, Jamie]

We did a few pen and paper calculations yesterday to confirm for ourselves that the half PRC should have nicely separated modes.  The half cavity is L=4.34m long, assuming flat mirror is 3.5 inches in front of BS.  That 3.5" is a guess, not a measurement.

Finesse

F = ( pi * sqrt(r1 * r2) ) / (1 - r1*r2) = 111.

Full width at half max

FWHM = c / (2 * L * F) = 311 kHz

FWHM in meters = FWHM * L/f = L*1064nm/c = 4.8 nm

Free spectral range

nu_fsr = F * FWHM = 34.5 MHz

Mode Spacing (eq 19.23 from Siegman)

omega = (n + m) * arccos(\pm sqrt(g1*g2)) / pi     *   (2*pi*c)/(2L)

For our half cavity, g1*g2 = 0.96

For the 01 or 10 modes, n+m = 1

omega = 13.7e6 rad/sec

mode spacing between 00 and 01 = 2.2 MHz

Thus, the modes should be well separated

=>  spacing is 2.2 MHz while FWHM is 0.311 MHz  (cavity fsr = 34.5 MHz)

 

EDIT JCD 31Jan2013:  Fixed mode spacing eqn to be diff between TEM00 mode and HOM, not plane wave and HOM.  Then fixed the factor of 2 error in the mode spacing numbers.

  7966   Wed Jan 30 15:45:09 2013 ZachUpdateLockingMode spacing calc

Quote:

Thus, the modes should be well separated

=>  spacing is 4.3 MHz while FWHM is 0.311 MHz  (cavity fsr = 34.5 MHz)

Something looks fishy. I calculate a transverse mode spacing of 2.21 MHz---is there a factor of two missing somewhere in your analytical calculation?

delta_f = (1/2/pi) * w01 - w00 = (1/2/pi) * acos(±sqrt(0.96)) /pi *2 * pi * c /2 /L = 2.21 MHz

I guess that's still OK, but if you are using 11-MHz sidebands, there is a n+m=5 mode within one linewidth of resonance. Can you use 55?

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

May I suggest my arbcav() tool for things like this? I think it's pretty handy for just this sort of calculations. I'm actually hoping to revamp the I/O to make it much cleaner and more intuitive.

>> T = [0.055 20e-6];

>> L = [4.34 4.34];

>> RoC = [115.5 1e10];

>> theta = [0 0];

>> fmod = 11e6;

>> lambda = 1064e-9;

>> num_pts = 1000;

>> loss = 50e-6;

>> [fin,coefs,df] = arbcav(T,L,RoC,theta,fmod,loss,lambda,num_pts);

>> fmod = 55e6;

>> [fin,coefs,df] = arbcav(T,L,RoC,theta,fmod,loss,lambda,num_pts);

 

HOM11.png HOM55.png

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