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ID Date Authorup Type Category Subject
  6900   Sun Jul 1 23:48:15 2012 yutaSummaryGeneralclipping at BS, my plan

[Koji, Yuta]

We aligned PRMI and inspected BS chamber. Last inspection by Jamie and I (see elog #6897) was done when nothing is aligned, so I wanted to see the difference.
Aligning PRMI at low power was difficult for me, because I see no fringe at ASDC PD nor REFLDC PD. I just aligned them by looking at AS/REFL camera. The beam shape at AS looked as bad as when the usual power.

No significant change was found inside the vacuum. We still see clipping at the Faraday, and also, we saw clipping by BS coil holder. Using PZT1, we could make it better, but this might be causing PRC problem -- BS is inside the PRC, too.

We also took some pictures of PR3 and PRM(attached). The arrow pointing HR is correctly pointing inside the PRC. Seeing is believing.

Yuta's plan:
  We might have to avoid clipping at BS (and Faraday) by aligning input optics inside the vacuum. If we are going to align them, I think we should start from centering MC beam spot positions and the whole alignment could take more than a week. I don't want to spend too much time on the alignment. Also, we are going to install tip-tilts on the next big vent, so we have to redo the alignment anyway.
  So, my plan is as follows;

1. Take lots of photos and close the door on Monday(June 2).

2. Pump on Tuesday(June 3).

3. Restart working on ALS. For example, demonstration of FPMI using ALS.

4. We also can do some characterization of PRC, like measuring power recycling gain for PRMI/PRFPMI, mode scan for PRC using AUX laser from AS port, and so on. We need some calculation for clipping tolerance, too.

  Any objections?

  6903   Mon Jul 2 18:27:25 2012 yutaUpdateGeneralBS and ITMX chambers closed

[Koji, Steve, Jamie, Jenne, Yuta]

We opened BS and ITMX chambers, took lots of photos, and closed them with heavy doors.
I turned off high voltage power supplies for PZTs and blocked PSL beam. We are ready for the pumping tomorrow.

Important photos we took:
  - positions of green optics at BS chamber, which was moved on the vent on Aug 2011
  - positions of PZT mirrors and cable connectors at BS chamber, which will be replaced with tip-tilts on the next vent
  - arrow on PR2 pointing HR (it was correct)
  - tried to take photos of clipping IR beam at BS OSEM holder from ITMX chamber
 
 We also took bunch of other photos.


Beam dump needed at BS chamber:
  We also checked some un-dumped beams at BS chamber. We need dumps;
  - behind MMT1, for unwanted transmitted beam
  - behind IPPOSSM3, for unwanted transmitted beam (IPPOSSM3 is the last mirror in BS chamber for IPPOS)

  6910   Tue Jul 3 20:51:06 2012 yutaUpdateIOOMC in vacuum is back

MC came back to the state as it was before the vent.

What I did:
  1. Removed beam attenuating setup on PSL table(see elog #6892).

  2. Removed 100% reflection mirror before the MC reflection PD and put 10% BS back, so that we can have MC WFS. Also, I changed C1:IOO-MC_RFPD_DCMON.HOPR to 5.

  3. Removed autolockMCmain40m_low_power from crontab on op340m, and put autolockMCmain40m again.

  4. Aligned MC and ran /opt/rtcds/caltech/c1/scripts/MC/WFS/WFS_FilterBank_offsets to adjust WFS offsets.

  5. Measured beam spot positions. They looked same as before the vent.

# filename    MC1pit    MC2pit    MC3pit    MC1yaw    MC2yaw    MC3yaw    (spot positions in mm)
./dataMCdecenter/MCdecenter201206290135.dat    2.914584    4.240889    2.149244    -7.117336    -1.494540    4.955329    before vent
./dataMCdecenter/MCdecenter201207011253.dat    3.294659    3.416584    2.620511    -6.691800    -3.164084    4.806517    after vent
./dataMCdecenter/MCdecenter201207032009.dat    3.737099    3.994597    3.087857    -6.442053    -0.992543    4.714607    after pumping (now)

  6. I also turned on high voltage power supplies for input and output PZTs

  7. Below is captured Sensoray images of the current state.
ALL_1025408289.bmp


Next:
  I will go on to check if IFO works as it was before or not, but I think we should center MC beam spot positions and see if we can avoid clipping in the near future.

  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.

  6915   Thu Jul 5 01:20:58 2012 yutaSummaryCDSslow computers, 0x4000 for all DAQ status

ALS looks OK. I tried to lock FPMI using ALS, but I feel like I need 6 hands to do it with current ALS stability. Now I have all computers being so slow.

It was fine for 7 hours after Jamie the Great fixed this, but fb went down couple times and DAQ status for all models now shows 0x4000. I tried restarting mx_stream and restarting fb, but they didn't help.

  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

  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.

  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.

  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.

  6942   Mon Jul 9 05:15:46 2012 yutaUpdateGreen Lockinglocked MI while ALS using ASDC

I locked MI while both arm length are stabilized at IR resonance. This could be done using DC READOUT, in other words, use AS_DC as MICH error signal.
Lock using RF signals are still not successful.

FPMIALStrial20120709.png

  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.

  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
 

  6952   Tue Jul 10 17:47:55 2012 yutaUpdateSUSPRM oplevs fixed

I centetered PRM oplev, lowered gain and PRM oplev servo is not oscillating any more.
It is OK for more than a softball practice.

C1:SUS-PRM_OLPIT_GAIN = 0.15  (was 0.5)
C1:SUS-PRM_OLYAW_GAIN = -0.3  (was 0.7)

Openloop transfer function:
  Oplev Pitch: gain ~ 12 at 0.69 Hz resonance
  Oplev Yaw: gain ~ 18 at 0.83 Hz resonance
PRMoplevpitOLTF.pngPRMoplevyawOLTF.png

  I adjusted the gain so that oplev damps resonance as much as possible, but not introduce additional noise. I did no calculation, but just measured OSEM spectra (SUSPIT and SUSYAW). Below, you can see the noise reduces at resonance when oplev servo is on, and not increasing at other frequencies. It was introducing noise before. Someone should do more systematic adjustment of oplev servos for all the optics.

PRMOplevSpectra20120710.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?

  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

  6960   Wed Jul 11 13:36:58 2012 yutaUpdateSUSOSEM and oplev spectra of optics

Below is angular spectra of every suspended core optics.
As you can see, there's a peak at 3.3 Hz for BS and PRM angular motion. Compared with other optics, they look large.

I briefly checked suspension filters and found that BounceRoll filters and f2a filters are not turned on for BS.
I checked elog and there was no reason for them to be off, so I turned them on. It didn't change angular spectra very much, though.

I'm going to check BS suspension damping and see where 3.3 Hz peak comes from.

Note that oplev quadrant sums are different for every optics, so we can't simply compare angular motion between optics from OLPIT/OLYAW. But for OSEMs, there are "cnt2um" which calibrate sensor outputs into um. and input matrix should be normalized, so we can compare SUSPIT/SUSYAW with other optics.

I centered all oplevs to do this measurement.
Quadrant sum (C1:SUS-XXX_OLSUM) for each optic now is

ITMX   ITMY   ETMX   ETMY     BS    PRM    SRM
2456  14630   1476  14885   3650   4302   2937   (counts)


OLPITYAW.png   SUSPITYAW.png

  6964   Wed Jul 11 16:19:08 2012 yutaUpdateSUSoplev servo phiology

I heard that Steve did great work on oplev in Feb 2012.
Here's summary what happened to oplev since then.
Someone changed oplev filters and gain. I couldn't find elog about it. Does anyone know?

Quadrant sum:
  Quadrant sum (C1:SUS-XXX_OLSUM) for each optic now and in Feb 2012 is

  ITMX   ITMY   ETMX   ETMY     BS    PRM    SRM
  2456  14630   1476  14885   3650   4302   2937   counts (now)
  1300  14500    900   9000   3500   4000   2600   counts (Feb 6, 2012 elog
#6256)
 0.025  0.3    0.2    0.2    0.05   0.06   0.04    mW on QPD (Feb 6, 2012 elog
#6256)
  1350  15000   1500  15500   3500   4000   2600   counts (Feb 23, 2012 elog
#6744)

  ETMX oplev laser was replaced on May 22, 2012, and quadrant sum was 20500 counts at that time (elog #6656).


Oplev servo openloop transfer functions:
  In Feb 2012, gains were adjusted and filter settings are recorded by Steve.
  For all pitch OLTF, see elog #6309.
  For all yaw OLTF, see elog #6323.

  All the filters in Feb is listed in elog #6744.
  Filters now are messed up, as Jamie pointed out in elog #6743.
  Below is the current filter settings.

  I turned ELP and RLP filters on, which wasn't on to cut-off noises at higher frequencies.
  I left resonant gains of ETMs because I don't know what they are for.
  I put ELP35 for ITMs, BS, PRM and SRM. I put RLP80 for BS, PRM and SRM.
  I will leave ELP35 off for BS and SRM because they oscillate currently. ELP50 and ELP40 is on for a substitution. I will readjust them soon.

  I don't know who changed all gains (except for PRM, which I adjusted in elog #6952). It doen't look like it is because of change in quadrant sum.
  I also don't know who deleted 3.3 Hz resonant gain for BS.

  I put all similar filters in same place to make it organized. Now, basic fitlers are organized. We may need some resonant gains for each optics.

OPLEV SERVO 300^2:0 BR ELP RLP RES GAIN QPD counts
filter position FM1 FM5 FM9 FM4 FM3, FM4    
ETMY pit 300^2:0 BR 35 80

0.5 (off)

-0.2 (was -1.5) 14,900
ETMY yaw 300^2:0 BR 35 80 0.6 (off) -0.2 (was -1.0)  
ETMX pit 300^2:0 BR 35 80 0.5 (off) 0.5 1,500
ETMX yaw 300^2:0 BR 35 80 0.6 (off) 0.6 (was 1.0)  
ITMY pit 300^2:0 BR 35 80   2.1 (was 2.0) 14,600
ITMY yaw 300^2:0 BR 35 80   -2.0 (was -4.0)  
ITMX pit 300^2:0 BR 35 80   2.6 (was 1.0) 2,500
ITMX yaw 300^2:0 BR 35 80   -1.6 (was-2.0)  
BS pit 300^2:0 BR 50 (FM10) 80   0.6 (was 0.5) 3,700
BS yaw 300^2:0 BR 50 (FM10) 80 (3.3 is some how deleted) -0.6 (was -1.0)  
PRM pit 300^2:0 BR 35 80 3.3 (off) 0.15 (was 1.0) 4,300
PRM yaw 300^2:0 BR 35 80 3.3 (off),  4 (off) -0.2 (was 0.5)  
SRM pit 300^2:0 BR 40 (FM10) 80   -2.0 2,900
SRM yaw 300^2:0 BR 40 (FM10) 80   2.0  

  I also found Kiwamu's angular motion measurement during PRMI lock (elog #6320). They look different with my measurement yesterday (elog #6954).

  6965   Thu Jul 12 02:12:42 2012 yutaUpdateSUSBS 3.3 Hz motion

I tried to reduce BS 3.3 Hz motion with local damping. 3.3 Hz probably comes from the stack, but I want to reduce this because PRMI beam spot is moving in this frequency.
I tried it by putting some resonant gains to oplev servo and OSEM damping servo, but failed.

What I learned:
  1. BS OSEM input matrix diagonalization looks impressively good. Below is the spectra of oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without damping (REF is without). You can see mechanical resonances are well separated. Also, damping servos don't look like they are adding noise at 3.3 Hz.
BSdam.png

  2. 3.3 Hz motion is not stationary. Amplitude is sometimes high, but sometimes low. Amplitude changes in few seconds. You can even see 3.3 Hz in the dataviewer, too.

  3. I set new oplev gains. I lowered them so that UGFs will be ~ 2.5 Hz. I turned ELP35 on.

C1:SUS-BS_OLPIT_GAIN = 0.2 (was 0.6)
C1:SUS-BS_OLPIT_GAIN = -0.2 (was -0.6)

  4. All OSEM sensors feel about the same amount of 3.3 Hz motion.

  5. OLPIT and OLYAW reduces if you put 3.3 Hz resonant gain to oplev servo, but it is maybe not true since they are in-loop error signals. You can't see the difference from OSEM sensors. Below is oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without 3.3 Hz resonant gain (REF is without).
BSOLSUSresonantgain.png

  6967   Thu Jul 12 13:27:16 2012 yutaUpdateSUSmeasured OLTFs of PRMI optics' SUSPOS

I measured openloop transfer functions of PRM/BS/ITMX/ITMY SUSPOS servo.
They look great. They all have ~50 deg phase margin and damps only POS resonance.
PRMSUSPOSOLTF.pngBSSUSPOSOLTF.pngITMXSUSPOSOLTF.pngITMYSUSPOSOLTF.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?

  6974   Fri Jul 13 15:49:38 2012 yutaBureaucracyGeneral40m Priority Action Items

These are all priority action items need to be done before I come back (in mid-September).
BE PREPARED FOR THE FULL LOCK!

NEXT VENT:
        - Prepare and install tip-tilts -JAMIE
        - Adjust IP-ANG -JAMIE, JENNE, KOJI
        - Make sure there's no clipping. Start from MC centering -JAMIE, JENNE, KOJI

ASS/A2L:
        - Make ASS and A2L work -JENNE, JAMIE
        - Better MC spot position measurement script(see the last sentence in elog #6892) -JENNE
        - Daily beam spot measurements for IFO, just like MC -JENNE
        - ASS for green using PZT steering mirrors on end table -JENNE
        - Modeling of phase tracking ALS -JAMIE

ALS:
        - PZT mounts for PSL and ALS beams -JENNE, KOJI
        - Add temperature sensors for end lasers to CDS slow channels -JENNE
        - Put green trans camera, GTRY PD, and GTRX PD on PSL table -JENNE
        - Better beat box; include comparators, frequency dividers, and whitening filters -JAMIE, KOJI
        - Adjust servo gain/filters of end green PDH lock (reduce frequency noise) -JENNE
        - Add on/off switch, gain adjuster, etc to CDS for end green PDH lock -JENNE, JAMIE

PRC:
        - Find why and reduce 3 Hz motion -JENNE
        - Simulation of PRMI with clipping -YUTA
        - Alignment tolerance of PRMI -YUTA

  7994   Mon Feb 4 19:33:19 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

[Jenne, Yuta]

We redid PRM-PR2 cavity scan because last one (elog #7990) was taken with the sampling frequency of 2 KHz. We have also done TMS measurement.

Method:
 1. Align input TTs and PRM to align PRM-PR2 cavity.
 2. Sweep cavity length using C1:SUS-PRM_LSC_EXC.
 3. Get data using Jamie's getdata and fitted peaks using /users/jrollins/modescan/prc-pr2_aligned/run.py
 4. Calculated cavity parameters

Results:
 Below is the figure containing peaks used to do the calculation.

3peakdata.png

 From 11 MHz sidebands, calibration factor is 462 +/- 22 MHz/sec (supposing linear scan around peaks)
 FWHM is 1.45 +/- 0.03 MHz.
 TMS is 2.64 +/- 0.05 MHz.
 Error bars are statistical errors of the average over 3 TEM00 peaks.

 If we believe cavity length L to be 1.91 m, FSR is 78.5 MHz.
 So, Finesse will be 54 +/- 1 and cavity g-factor will be 0.9944 +/- 0.0002. 0.9889 +/- 0.0004   (Edited by YM; see elog #8056)
 If we believe RoC of PRM is exactly +122.1 m, measured g-factor insists RoC of PR2 to be -187 +/- 4.
 If we believe RoC of PR2 is exactly -600 m, measured g-factor insists RoC of PRM to be 218 +/- 6.

Discussion:
 1. Finesse is too small (expected to be ~100). This time, data was taken 16 KHz. Cut-off frequency of the digital antialiasing filter is ~ 5 kHz (see /opt/rtcds/rtscore/release/src/fe/controller.c). FWHM is about 0.003 sec, so it should not effect much according to my simulation.

 2. I don't know why FWHM measurement from the last one is similar to this one. The last one was taken 2 KHz, this means anti-aliasing filter of 600 Hz. This should double FWHM.

 3. Oscilloscope measurement may clear anti-aliasing suspicion.

  7997   Tue Feb 5 02:04:44 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

I redid PRM-PR2 cavity scan using oscilloscope to avoid anti-aliasing effect.
Measured Finesse was 104 +/- 1.

Method:
 1. Splitted POP DC output into three and plugged two into oscilloscope TDS 3034B. Ch1 and Ch2 was set to 1 V/div and 20 mV/div respectively to take the whole signal and higer resolution one at the same time (Koji's suggestion). Sampling frequency was 50 kHz. Sweeping time through FWHM was about 0.001 sec, which is slow enough.
 2. Took mode scan data from the oscilloscope via network.

Preliminary results:
 Below is the plot of the data for one TEM00 peak.
PRMPR2scan.png

 The data was taken twice.
 Measured FWHM was 0.764 MHz and 0.751 MHz. By taking the average, FWHM = 0.757 +/- 0.005 MHz.
 This gives you Finesse = 104 +/- 1, which is OK compared with the expectation.

What I need:
 I need better oscilloscope so that we can take longer data (~1 sec) with higher resolution (~0.004 V/count, ~50kHz).
 TDS 3034B can take data only for 10 ksamples, one channel by one!  I prefer Yokogawa DL750 or later.

  8000   Tue Feb 5 10:09:08 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

stdev of [0.764, 0.751] is 0.007, but what we need is the error of the averaged number. Statistical error of the averaged number is stdev/sqrt(n).

Quote:

0.764 and 0.751 do not give us the stdev of 0.005.

  8006   Tue Feb 5 19:32:47 2013 yutaSummaryGeneralPR2/PR3 flipping and PRC stability

We are considering of flipping PR2 and/or PR3 to make PRMI stable because PR2/PR3 seems to be convex.
I calculated dependency of the PRC stability on the PR2/PR3 curvature when PR2/PR3 flipped and not flipped.
Flipping looks OK, from the stability point of view.

Assumption:
 PRM-PR2 distance = 1.91 m
 PR2-PR3 distance = 2.33 m
 PR3-ITM distance = 2.54 m
 PRM RoC = +122.1 m
 ITM RoC = Inf

 theta_inc PRM = 0 deg
 theta_inc PR2 = 1.5 deg
 theta_inc PR3 = 41 deg 
          (all numbers from elog #7989)

 Here, RoC means RoC measured from HR side. RoC measured from AR side will be -n_sub*RoC, assuming flat AR surface.
 I also assumed mirror thickness to be negligible.

Method:
  1. I used Zach's arbcav and modified it so that it only tells you your cavity is stable or not.
   (It lives in /users/yuta/scripts/mode_density_PRC/stableornot.m)

  2. Swept PR2/PR3 RoC (1/RoC from -0.005 to 0.005 1/m) to see the stability condition.

Results:
  1. Stability condition of the PRMI when PR2 and PR3 is not flipped is depicted in the graph below. Black region is the unstable region. We all know that current PRMI is unstable, so we are in the black region.
PRMI_PR2HR_PR3HR.png

  2. Stability conditions of PRMI with one of the PR2/PR3 flipped are depicted in the graphs below. If we flip one of them, PRMI will likely to be stable, but if the flipped one is close to flat and the RoC of the other one is  >~ -250 m (more convex than -250 m), PRMI will remain unstable.
PRMI_PR2AR_PR3HR.pngPRMI_PR2HR_PR3AR.png


  3. Stability condition of PRMI with both PR2 and PR3 flipped is depicted in the graph below. If we flip both, PRMI will be stable.
PRMI_PR2AR_PR3AR.png


Discussion:
  1. Flipping one of PR2/PR3 seems OK, but I cannot guarantee. TMS measurement insists RoC of PR2 to be ~ -190 m, if we believe PRM RoC = +122.1 m (elog #7997). We need more precise measurement if we need to be sure before flipping. I prefer PR2 flipping because PR3 flipping gives us longer path in the substrate and larger astigmatism. Also, PR3 RoC is phase-map-measured to be ~ -600 m and PR2 RoC seems to be more convex than -600 m from the TMS measurement.

  2. Flipping both is good from stability point of view. We need calculation of the loss in the PRC (and mode-mismatch to the arms). Are there any requirements?

  3. If we are going to flip PR3, are there any possibilities of clipping the beam at PR3? We need to check.

  4. I need to calculate whether mirror thickness and AR surface curvature are negligible or not.

Conclusion:
  I want to flip only PR2 and lock PRMI.

By the way:
 I don't like matlab plots.

  8012   Wed Feb 6 15:20:55 2013 yutaSummaryGeneralFWHM was wrong

I have to blame Jamie for putting extra 2 randomly.
Measured PRM-PR2 cavity finesse was actually 108 +/- 3 (even if you use digital system to get data).

Lorentzian fit:
  Lorentzian function is;

f(x;x0,gamma,A) = A * gamma**2/((x-x0)**2+gamma**2)

  where x0 is the location of the peak, gamma is HWHM, and A is the peak height.
  Lorentzian fitting function in my original code (/users/yuta/scripts/modescanresults/analyzemodescan.py) was

fitFunc = lambda p,x,m: (m-p[2])*p[0]**4/(4*(x-p[1])**2+p[0]**4)+p[2]

  In this function, p[0] is sqrt(FWHM), not sqrt(HWHM). I doubled gamma to make it FWHM and squared it because they should be positive.
  During Jamie's modification of my code, he doubled p[0]**2 to get FWHM, which is wrong (/users/jrollins/modescan/modescan.py).

  I should have commented that p[0] is sqrt(FWHM).

Redoing the analysis:
  1. I pulled 2 out, and modified Jamie's modescan.py so that you can name each peak with peakdistinguish=True option. I also modified fitpeak function so that it throws away "peaks" which don't look like a peak.

  2. If you run /users/yuta/PRCmodescan/run.py and name each peak, you will get peaks.csv which includes peak position, FWHM, and the type of the peak;

0.065017,0.001458,l
0.070446,0.001463,3
0.075940,0.001509,2
0.081552,0.001526,1
0.087273,0.001565,0
0.112027,0.001911,u
0.278660,0.002211,u
0.306486,0.001658,0
0.312480,0.001576,1
0.313626,2.507910,
0.318486,0.001626,2
0.319730,2.633097,
0.324801,0.001739,3
0.331848,0.001922,l
0.527509,0.001603,l
0.533231,0.001445,3
0.538648,0.001488,2
0.544081,0.001455,1
0.549517,0.001498,0
0.551725,2.422759,
0.570972,0.001346,u


  3. /users/yuta/PRCmodescan/calcmodescanresults.py reads peaks.csv and tells you the results;

Time between TEM00 and sideband  0.0239435  pm  0.00115999887452  sec
Calibration factor is  462.167602898  pm  22.3907907867  MHz/sec
FSR is  78.4797010471  MHz
FWHM is  0.729828720682  pm  0.0174145743828  MHz
TMS is  2.64718671684  pm  0.0538858477824  MHz
Finesse is  107.53166986  pm  2.5658325169
Cavity g-factor is  0.994390582331  pm  0.000228155661075
Cavity g-factor is  0.988812630228  pm  0.000453751681357   (Edited by YM; see elog #8056)
RoC of PR2 is  -187.384503001  pm  4.26100999578  m (assuming PRM RoC= 122.1  m)
RoC of PRM is  217.915890722  pm  5.65451518991  m (assuming PR2 RoC= -600  m)

  8021   Thu Feb 7 10:35:35 2013 yutaUpdateGeneralStore optics in respective cabinets

I'm not the one who opened the ITMX table yesterday, but thanks for reminding me.
I put POP DC oscilloscope and its cables back.

Also, I relocked PMC and MC. It was unlocked since last night.

  8028   Thu Feb 7 19:25:22 2013 yutaUpdateCDSC1ALS filters reloaded

Filters for C1ALS were all gone. So, I copied /opt/rtcds/caltech/c1/chans/C1GCV.txt and renamed it as C1ALS.txt.

I also fixed links in the medm screens; C1ALS.adl and C1ALS_COMPACT.adl.
I'm not sure what happened to C1SC{X,Y} screens.

Quote:

I decided to rename the c1gcv model to be c1als.  This is in an ongoing effort to rename all the ALS stuff as ALS, and get rid of the various GC{V,X,Y} named stuff.

(...snip...)

The above has been done.  Still todo:

  • FIX SCRIPTS!  There are almost certainly scripts that point to GC{V,X,Y} channels.  Those will have to be fixed as we come across them.
  • 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.
  • Fix the C1ALS_COMPACT screen
  • ???

 

 

  8034   Fri Feb 8 12:39:32 2013 yutaUpdateLockingPRMI work

Half-PRC at this time already have two changes from the previous half-PRC; PR2 replaced/flipped and different TM before BS.
PRMI has only one change from the previous PRMI; PR2 replaced/flipped.
This is why I wanted to try PRMI first. But we now recognized that MI alignment (including REFL and AS alignment) is tough without using the arms, I agree that we should try half-PRC first.

I don't exactly know what the situation in the Jamie's calculation, but to make the optical path length the same before and after flipping, PR2 holder have to move about n*t, where n is the substrate refractive index and t is the thickness of the mirror, towards PRM/PR3.

Quote:

The first rule of debugging is to only make one change at a time.

Also, we never talked about moving PR2 to adjust optical path length,

  8036   Fri Feb 8 12:43:26 2013 yutaUpdateComputersvideocapture.py now supports movie capturing

I updated /opt/rtcds/caltech/c1/scripts/general/videoscripts.py so that it supports movie capturing. It saves captured images (bmp) and movies (mp4) in /users/sensoray/SensorayCaptures/ directory.
I also updated /opt/rtcds/caltech/c1/scripts/pylibs/pyndslib.py because /usr/bin/lalapps_tconvert is not working and now /usr/bin/tconvert works.
However, tconvert doesn't run on ottavia, so I need Jamie to fix it.

videocapture.py -h:
Usage:
    videocapture.py [cameraname] [options]

Example usage:
    videocapture.py MC2F -s 320x240 -t off
       (Camptures image of MC2F with the size of 320x240, without timestamp on the image. MUST RUN ON PIANOSA!)
    videocapture.py AS -m 10
       (Camptures 10 sec movie of AS with the size of 720x480. MUST RUN ON PIANOSA!)


Options:
  -h, --help          show this help message and exit
  -s SIZE             specify image size [default: 720x480]
  -t TIMESTAMP_ONOFF  timestamp on or off [default: on]
  -m MOVLENGTH        specity movie length (in sec; takes movie if specified) [default: 0]

  8041   Fri Feb 8 19:29:44 2013 yutaSummaryGeneralarbcav of half PRC with flipped PR2

We need expected finesse and g-factor to compare with mode-scan measurement. Can you give us the g-factor of the half-PRC and what losses did you assumed to calculate the finesse?

Also, flipped PR2 should have RoC of - R_HR * n_sub (minus measured RoC of HR surface multiplied by the substrate refractive index) because of the flipping.
According to Jenne dictionary, HR curvature measured from HR side is;

PRM: -122.1 m
PR2: -706 m
PR3: - 700 m
TM in front of BS: -581 m

Please use these values to calculate expected g-factor so that we don't get confused.

Quote:

Arbcav with half PRC (flat temporary mirror in front of BS), PR2 RoC = 600m, PR3 RoC = -600m:

  8049   Fri Feb 8 23:59:42 2013 yutaUpdateLockingPR2-flipped half-PRC mode scan

I did mode scan of PR2-flipped half-PRC to see if it behaves as we expect.
Measured finesse was 107 +/- 5 and g-factor is 0.98997 +/- 0.00006.
g-factor is 0.9800 +/- 0.0001.  (Edited by YM; see elog #8056)

 
Finesse tells you that we didn't get large loss from flipped PR2.
Since we have convex TM in front of BS, PRC will be more stable than this half-PRC.

Method:
 1. Aligned half-PRC using input TT1 and TT2 by maximizing POP DC during lock. It was not so easy because POP DC fluctuates much at ~ 3 Hz with amplitude of ~ 30 % of the maximum value because of the beam motion (movie on  elog #8039).

 2. Unlocked half-PRC and took POP DC and PRC error signal data;

> /opt/rtcds/caltech/c1/scripts/general/getdata -d 1 -o /users/yuta/scripts/PRCmodescan C1:LSC-POPDC_OUT C1:LSC-REFL11_I_ERR

  Ran again and again until I get sufficiently linear swing through upper/lower sidebands.

 3. Ran modescan analyzing scripts (elog #8012).

Result:
 Below is the plot of POP DC and PRCL error signal (REFL11_I).
halfPRCmodescan.png

 By averaging 5 sets of peaks around TEM00;

Time between TEM00 and sideband  0.0347989  pm  0.00292257322372  sec
Calibration factor is  317.995971137  pm  26.7067783894  MHz/sec
FSR is  34.5383016129  MHz
FWHM is  0.323979022488  pm  0.0145486106353  MHz
TMS is  1.55827297374  pm  0.00439737672808  MHz
Finesse is  106.606598624  pm  4.78727876459
Cavity g-factor is  0.989971692098  pm  5.65040851566e-05
Cavity g-factor is  0.980043951156  pm  0.000111874889586

Discussion:
 Measured finesse is similar to measured PRM-PR2 cavity finesse(108 +/- 3, see elog #8012). This means loss from flipped PR2 and beam path from PR2 to TM is small.

 I'm a little suspicious about measured g-factor because it is hard to tell which peak is which from the mode scan data. Since half-PRC was not aligned well, high HOMs may contribute to POP DC. Astigmatism also splits HOM peaks.

 PRC 3 Hz beam motion was there for long time (see, for example, elog #6954). BS is unlikely to be the cause because we see this motion in half-PRC, too.
 Also, beam spot motion was not obvious in the PRM-PR2 cavity. My hypothesis is; stack resonance at 3 Hz makes PR2/PR3 angular motion and folding by PR2/PR3 makes the beam spot motion.

Next things to do:
 * PRC g-factor
   - Calculate expected half-PRC g-factor with real measured curvatures, with error bar obtained from RoC error and length error (JAMIE)
   - Calculate expected PRC g-factor using measured half-PRC g-factor (JAMIE)
 * PRC 3 Hz beam motion
   - Do we have space to put oplevs for PR2/PR3?
   - Can we fix PR2/PR3 temporarily?
 * PRMI
   - Align incident beam, BS, REFL, AS, and MI using arms as reference
   - lock PRMI
   - PRC mode scan

  8052   Sun Feb 10 17:30:39 2013 yutaUpdateLockingPR2-flipped half-PRC mode scan

I redid half-PRC mode scan by applying mislignment to PRM.
Half-PRC's sagittal g-factor is 0.9837 +/- 0.0006 and tangential g-factor is 0.9929 +/- 0.0005.
sagittal g-factor is 0.968 +/- 0.001 and tangential g-factor is 0.986 +/- 0.001. (Edited by YM; see elog #8056)

Method:
 1. Same as elog #8049, but with small misalignment to PRM.

 2. Algined half-PRC, and misaligned PRM in pitch to get sagittal g-factor.

 3. Restored pitch alignment and misaligned PRM in yaw to get tangential g-factor.

Result:
 Below left is the plot of POP DC and PRCL error signal (REFL11_I) when PRM is misaligned in pitch. Below left is the same plot when misaliged in yaw.
left:modescan_pitmisalign.png    right:modescan_yawmisalign.png

 By averaging 5 sets of peaks around TEM00, I get sagittal/tangential g-factors written above.

Discussion:
  The fact that tangential g-factor is larger than sagittal g-factor comes from astigmatism mainly from PR3. Effective PR3 curvature is

sagittal Re = R/cos(theta) = -930 m
tangential Re = R*cos(theta) = -530 m   (where R = -700 m , theta = 41 deg)

so, PR3 is more convex in tangential plane and this makes half-PRC close to unstable. This is opposite of Jamie's calculation(elog #8022). I'm confused.

  I first thought I don't need to misalign PRM because alignment was not so good - it was hard to align when beam motion is large. Also, this motion makes angular misalignment, so I thought free swinging is enough to make higher order modes. However, misaligning PRM intentionally made it easier to resolve higher order modes. I could even distinguish (10,01) and (20,11,02), as you can see from the plot.

Next:
  We have to compare with expected g-factor before moving on to PRMI.

  8053   Sun Feb 10 18:00:13 2013 yutaSummaryLSCPR2-flipped half-PRC spectra/OLTF

To compare with future PRMI locking, I measured spectra of POPDC and feedback signal. I also measured openloop transfer function of half-PRC locking.
Beam spot motion was at ~ 2.4 Hz, not 3.3 Hz.

Results:
  Below is uncalibrated spectra of POPDC and LSC feedback signal (C1:LSC-PRM_OUT).
POPDCLSCPRM.png

  Below is openloop transfer function of the half-PRC locking loop. UGF is ~ 120 Hz and phase margin is ~ 45 deg. This agrees with the expected curve.
LSCPRCLOLTF.png

  Data was taken when half-PRC was locked using REFL11_I as error signal and actuating on PRM.


Discussion:

  For comparison, POPDC when PRMI was locked in July 2012: elog #6954 and PRCL openloop transfer function: elog #6950.

  Peak in the spectra of POPDC and feedback signal was at ~ 3.3 Hz in July 2012 PRMI, but it is now at ~ 2.4 Hz in half-PRC. The peak also got broader.
  Is it because of the change in the resonant frequency of the BS-PRM stack? How much the load on BS-PRM changed?
  Or is it because of the change in the resonant frequency of PR2/PR3?

  Phase margin is less now because of gain boost ~ 5 Hz and resonant gain at 24 Hz.
 

  8056   Mon Feb 11 13:15:16 2013 yutaUpdateLockingPR2-flipped half-PRC mode scan

I found a mistake in my code (thanks Jamie!).
I forgot to square the g-factor.
I corrected the following elogs;

PRM-PR2 cavity
  elog #7994 : g-factor will be 0.9889 +/- 0.0004
  elog #8012 : g-factor is 0.988812630228 pm 0.000453751681357

half-PRC g-factor
  elog #8040 : g-factor is 0.9800 +/- 0.0001
  elog #8052 : sagittal g-factor is 0.968 +/- 0.001 and tangential g-factor is 0.986 +/- 0.001

I checked that I was correct in July 2012 (elog #6922)

Cavity g-factor formula:
  gm = ( cos(pi*nu_TMS/nu_FSR) )**2

  8064   Mon Feb 11 21:03:15 2013 yutaUpdateLockingPR2-flipped half-PRC mode scan

To estimate the systematic effects to the g-factor measurement, I changed how to analyze the data in multiple ways.
From the estimation, I get the following g-factors for half-PRC;
  tangential: 0.986 +/- 0.001(stat.) +/- 0.008(sys.)
    sagittal: 0.968 +/- 0.001(stat.) +/- 0.003(sys.)


The a la mode/arbcav calculation is not so far from the measurement(elog #8059). So, mirror curvatures and lengths are not far from what we expect.

Method:
  Method I used to analyze the mode scan data is as follows;

  1. Use the spacing between upper sideband and lower sideband to calibrate the data.
  2. Measure the position of 00, 1st, 2nd and 3rd mode.
  3. Used the following formula to get TMS

  nu_TMS = sum((n_i-n)*(nu_i-nu)) / sum((n_i-n)^2)

  where n_i is the order of transverse mode, n is average of n_i's, nu_i is the frequency if i-th order mode and nu is average of nu_i's. This is just a linear fitting.

  But since it is hard to resolve where the higher order mode is, it is maybe better to use only 00, 1st, and 2nd mode. Also, since cavity sweep is not linear enough, it is maybe better to use spacing between 00 and lower sideband (sideband closer to HOMs) to calibrate the data. Changing the analysis will give us information about the effect of peak choosing and linearity.

How the result differ:
  Below are the plots of order of tranverse mode vs measured relative frequency difference from 00 mode. 5 plots on left are when PRM is misaligned in pitch and right are same in yaw. From the plot, you can see using 3rd order mode tend to give larger TMS. Did I picked the wrong one??
left:modespacing_pit.png    right:modespacing_yaw.png

Results:
  Below table is the result when I changed the analyzing method;

PRM misaligned in pitch
  calibration    how many HOMs    measured g-factor
  upper-lower    up to 3rd    0.968
  upper-lower    up to 2nd    0.974
  upper-lower    up to 1st    0.975
  00-lower       up to 3rd    0.952
  00-lower       up to 2nd    0.962
  00-lower       up to 1st    0.963


PRM misaligned in yaw
  calibration    how many HOMs    measured g-factor
  upper-lower    up to 3rd    0.986
  upper-lower    up to 2nd    0.989
  upper-lower    up to 1st    0.991
  00-lower       up to 3rd    0.964
  00-lower       up to 2nd    0.988
  00-lower       up to 1st    0.991


  Using 00-lower calibration tend to give us smaller g-factor. Using less higer order-mode tend to give us higher g-factor.
  By taking standard deviation of these, I roughly estimated the systematic error as above.

Discussion:
  I think it is OK to move on to PRMI now.
  But I wonder how much astigmatism is needed to get this measurement data. If astigmatism is not so crazy, it's OK. But if it's not, I think it is better to do more measurement like PRM-PR2-TM cavity.

  8065   Tue Feb 12 00:14:00 2013 yutaUpdateLockingPRM coil balancing

We tried to lock half-PRC tonight, but we couldn't. Why?? I could lock yesterday.
It locks for ~ 1 sec, but it beam spot motion freaks out mainly in yaw.
I tried to balance PRM coils, but oplev beam was clipped by MMT1......

What I did:
  1. Found elog #5392 and found F2P_LOCKIN.py

  2. Modified F2P_LOCKIN.py because LOCKIN channel names are some how changed like this;

LOCKIN1_I -> LOCKIN1_DEMOD_I
LOCKIN1_Q -> LOCKIN1_DEMOD_Q
LOCKIN1_SIG -> LOCKIN1_DEMOD_SIG

  3. Running

/opt/rtcds/caltech/c1/scripts/SUS/F2P_LOCKIN.py -o PRM

  should adjust (UL|UR|LR|LL)COIL_GAINs by putting some gain imbalance and shaking the mirror in different frequencies. It uses LOCKIN to OL(PIT|YAW).

  4. Since there was no PRM oplev beam coming out from the vacuum, I quickly looked into BS-PRM chamber. Oplev beam was clipped by MMT1. If I adjust PRM slider values to avoid clipping, the beam will be clipped by mirrors on oplev table. What happened to the PRM oplev?

  5. I also made bunch of /opt/rtcds/userapps/trunk/sus/c1/medm/templates/SUS_SINGLE_LOCKIN(1|2)_DEMOD_(I|Q|SIG).adl because there were missing screens.

Next:
 We need to restore the PRM oplev and balance the coils. See, also, elog #7679

  8066   Tue Feb 12 00:50:08 2013 yutaUpdateLockingPR2 oplev spectra

I wanted to see if PR2 motion makes PRC beam motion or not, using temporary oplev to PR2.
I could not measure the coherence between beam motion and PR2 motion, because I couldn't lock half-PRC today.
But I took spectra of PR2 oplev anyway.

Result:

  Below are the spectra of PR2 oplev outputs (taken using C1:SUS-ITMX_OL(PIT|YAW)_IN1). Bottom plot is POP DC during half-PRC locked yesterday.
PR2oplev.png

Discussion:
  We see bump in PR2 oplev output at ~ 2-3 Hz. But we cannot say this is a evidence for PR2 motion making PRC beam motion because no coherence measurement was done. Also, oplev might be just seeing the ITMX stack motion.

  Resonant frequency of TTs measured were at ~ 1.8-1.9 Hz (elog #8054), but we cannot clearly see these peaks in oplev outputs. Did resonant frequency shifted because of different damping condition?

  8073   Tue Feb 12 23:24:17 2013 yutaUpdateAlignmentIFO alignment in prep for in-air PRMI

[Manasa, Yuta]

Lot's of alignment work, still no AS beam. REFL is clipped by Faraday output aperture......
Our guess is that this is because
we skipped MC centering.

Alignment procedure we took:
 1. AM work: Aligned input beam using TT1/TT2
   such that the beam hits ETMY and ITMY at the center.

 2. Coarsely aligned ITMY
   such that the ITMY retro-reflected beam hits BS at the center.

 3. Aligned ETMY (we didn't actually move ITMY)
   such that Y arm flashes.
   This tells you that ITMY is aligned well to the incident beam.

 4. Aligned BS
   such that the beam hits ITMX at the center.

 5. Aligned ITMX
   such that the ITMX retro-reflected beam hits BS at the center.
   At this point, we saw MI fringes at AS port.

 6. Fine alignment of ITMX:
   MI reflected beam was not overlapping in front of BS after it was reflected by PRM.
   We used this longer REFL path to tune alignment of ITMX to ITMY reflected beam.
   We saw MI fringe at REFL port coming out of the chamber, but it was clipped.

 7. Aligned PRM
   by looking at REFL beam from PRM on the back face of Faraday (video FI_BACK).
   We fine tuned the alignment such that PRM retro-relfected beam hits BS at the center and REFL beam from PRM overlaps with the MI fringes at the back face of Faraday.

 8. Clipping of REFL at the Faraday output aperture:
   We confirmed that the shape of the REFL beam from PRM was OK at the back face of Faraday. But some how, it was clipped at the output aperture. So, REFL beam coming out of the chamber is clipped now.

 9. Tried to get AS beam out of the chamber:
   We tweaked steering mirrors after SRM to get AS beam out of the chamber. But, we lost the AS beam between the very last folding mirrors (OMPO and OM6) in the OMC chamber......


Discussion:
 1. Why clipping at the Faraday output aperture?
   In principle, if PRM reflects the incident beam at normal incidence, it should pass the Faraday unclipped. But it's not!
   Our guess is that the incident beam does not go well centered through the apertures of the Faraday. I think we have to do MC centering to get good pointing to the Faraday.
   We also see that MI fringe at the back face of the Faraday is at the edge of its aperture, after all of these alignment work (we even used Y arm!). This tells you that some thing is wrong.

 2. Why did you guys lose the AS beam?
   AS beam is too weak after reflecting off of OMPO. The beam was neither visible on IR cards nor IR viewers. The beam is weaker than usual because PMC transmission is ~0.7 and MC REFL is getting high (~ 0.7). We didn't want to realign MC after all of this work today.


Tomorrow (my suggestion):
  1. Align PMC (for higher power).
  2. MC centering.
  3. Input beam steering using TTs and redo the same alignment procedure (it shouldn't take longer than today).
      ==> Center beam on PR2  (Added by Manasa)
  4. Maybe we should better check PRM reflection at REFL port after the Faraday, before doing the full alignment work.
  5. Align AS, REFL, POP PDs/cameras.
  6. Setup PRM/BS/ITMX/ITMY oplevs.
  7. Balance the coils on these mirrors.
  8. Lock PRMI.


What needs to be done before pumping down:
  1. PRMI characterization: PR gain and g-factor
   How can we do the g-factor measurement? Use additional laser? Kakeru method (elog #1434; we need to calibrate mirror tilt to do this)?
  2. Glitch study in PRMI locking. If still glitchy, we have to do something. How is beam spot motion? (elog #6953)
  3. Fine alignment of the flipped PR2.
  4. Fine alignment of IFO using both arms.

  8074   Wed Feb 13 01:26:08 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

Koji was correct.

When you estimate the variance of the population, you have to use unbiased variance (not sample variance). So, the estimate to dx in the equations Koji wrote is

dx = sqrt(sum(xi-xavg)/(n-1))
   = stdev*sqrt(n/(n-1))


It is interesting because when n=2, statistical error of the averaged value will be the same as the standard deviation.

dXavg = dx/sqrt(n) = stdev/sqrt(n-1)

In most cases, I think you don't need 10 % precision for statistical error estimation (you should better do correlation analysis if you want to go further). You can simply use dx = stdev if n is sufficiently large (n > 6 from plot below).
unbiased.png



Quote:

Makes sense. I mixed up n and n-1

Probability function: X = (x1 + x2 + ... + xn)/n, where xi = xavg +/- dx

Xavg = xavg*n/n = xavg

dXavg^2 = n*dx^2/n^2
=> dXavg = dx/sqrt(n)

Xavg +/- dXavg = xavg +/- dx/sqrt(n)

 

  8078   Wed Feb 13 19:09:32 2013 yutaSummaryGeneralpossible explanations to oval REFL beam

[Jenne, Manasa, Jamie, Yuta]

The shape of the REFL beam reflected from PRM is oval after the Faraday.
We tried to fix it by MC spot position centering and by tweaking input TT1/TT2/PRM. But REFL still looks bad (below).

REFL_1044844506.bmp

What has changed since:
  REFL looks OK in mid-Dec 2012. Possibly related things changed are;

  1. New active input TTs with new mirrors installed
  2. Leveling of IMC stack changed a little (although leveling was done after installing TTs)

Possible explanations to oval REFL:
  A. Angled input beam:
    Input beam is angled compared with the Faraday apertures. So, beam coming back from PRM is angled, and clipped by the Faraday aperture at the rejection port.

  B. Mode mis-match to PRM:
    New input TTs have different curvatures compared with before. Input mode matching to PRM is not good and beam reflected from PRM is expanding. So, there's clipping at the Faraday.

  C. Not clipping, but astigmatism:
    New input TTs are not flat. Incident angle to TT2 is ~ 45 deg. So, it is natural to have different tangential/sagittal waist sizes at REFL.

How to check:
  A. Angled input beam:
    Look beam position at the Faraday apertures. If it doesn't look centered, the incident beam may be angled.
   (But MC centering didn't help much......)

  B. Mode mis-match to PRM:
    Calculate how much the beam size will be at the Faraday when the beam is reflected back from PRM. Put some real numbers to curvatures of input TTs for calculation.

  C. Not clipping, but astigmatism:
    Same calculation as B. Let's see if REFL is with in our expectation or not by calculating the ratio of tangential/sagittal waist sizes at REFL.

  8080   Wed Feb 13 19:41:07 2013 yutaSummaryGeneralpossible explanations to oval REFL beam

We checked that REFL beam is already oval in the vacuum. We also centered in-air optics, including lens, in the REFL path, but REFL still looks bad.

By using IR card in vacuum, PRM reflected beam looks OK at MMTs and at the back face of the Faraday. But the beam looks bad after the output aperture of the Faraday.

  8082   Thu Feb 14 00:10:12 2013 yutaSummaryAlignmentREFL is not clipped

Let's wait for astigmatism calculation.
In either case(clipping or astigmatism), it takes time to fix it. And we don't need to fix it because we can still get LSC signal from REFL.
So why don't we start aligning input TTs and PRMI tomorrow morning.

Take the same alignment procedure we did yesterday, but we should better check REFL more carefully during the alingment. Also, use X arm (ETMX camera) to align BS. We also have to fix AS steering mirrors in vacuum. I don't think it is a good idea to touch PR2 this time, because we don't want to destroy sensitive PR2 posture.


Calculations need to be done in in-air PRMI work:
  1. Explanation for REFL astigmatism by input TTs (Do we have TT RoCs?).
  2. Expected g-factor of PRC (DONE - elog #8068)
  3. What's the g-factor requirement(upper limit)?
    Can we make intra-cavity power fluctuation requirement and then use PRM/2/3 angular motion to break down it into g-factor requirement?
    But I think if we can lock PRMI for 2 hours, it's ok, maybe.
  4. How to measure the g-factor?
    To use tilt-and-measure-power-reduction method, we need to know RoC of the mirror you tilted. If we can prove that measured g-factor is smaller than the requirement, it's nice. We can calculate required error for the g-factor measurement.

  8091   Fri Feb 15 20:07:28 2013 yutaUpdateAlignmentPOP path set up but AS55 is broken

[Manasa, Yuta]

We set up POP camera and POPDC PD, and centered REFL PDs.
We also tried to center AS55 PD, but AS55 seems to be broken.

What we did:
 1. POP path alignment:
   Shot green laser pointer from ITMX table at where POPDC PD was sitting and centered green beam at optics in the POP path. Steered POPM1/M2 mirrors in the ITMX chamber to make green laser overlap with the PRM-PR2 beam as far as I can reach from ITMX chamber. We removed some ND filters and a BS for attenuating POP beam because POP power was somehow so low. Currently, POP is pick-off of the beam which goes from PRM to PR2.

 2. POP camera and PD:
   We first used camera to find the beam at where POPDC PD was sitting because it is much easier to find focused beam. Put an iris in front of the camera, and put POP DC behind it. Steered a mirror in front of PD to maximize DC output.

 3. REFL PDs:
   Steered mirrors in the REFL path to center the beam and maximized DC outputs, as usual.

 4. AS55:
   AS55 was not responding very much to the flashlight nor AS beam. C1:LSC-ASDC_OUT looked funny. By swapping the ribbon cables of AS55, REFL55, and REFL165, I confirmed that AS55 PD itself is broken. Not the ribbon cable nor PD circuit at LSC rack. I don't know what happened. AS55 was working on Feb 8 (elog #8030).

Result:
  We aligned PRMI coarsely. POP(right above) looks much better than before. REFL (left below) still looks elliptic, but ellipticity differs with the position on the camera. Some astigmatism is happening somewhere. AS (right below) looks pretty nice with MI aligned.


Next:
  1. Fix AS55? Or replace it with POP55 PD, which is currently unused.
  2. Confirm we are getting the right error signals or not, and lock PRMI.

ELOG V3.1.3-