Continued to work on the WFS repair
Demod phase adjustment:
- Use the PDH signal to adjust the demodulation phase to have uniform signals between the segments.
- Excited laser frequency at 1234Hz by injecting 10mVpp into IMC Servo Board IN2. The input was enabled on the MC Servo screen and given the input gain of 0dB.
- Looked at the ~real time spectrum in WFS1/2 SEG1/2/3/4 I&Q after the phase rotators. Changed the demod phases 1) to have ~0deg transfer function between C1:IOO-MC_F to C1:IOO-WFSi_Ij 2) to minimize the freq signal in Q phases.
(See Attachment 1)
- Resulting change of the demod phases:
WFS1 SEG1 52.0 -> 38.0deg
WFS1 SEG2 54.0 -> 53.0deg
WFS1 SEG3 16.6 -> 33.2deg
WFS1 SEG4 103.9 ->-37.1deg
WFS2 SEG1 17.0 -> 57.8deg
WFS2 SEG2 26.6 -> 51.5deg
WFS2 SEG3 24.5 -> 44.0deg
WFS2 SEG4 -58.0 ->103.7deg
SEG4 of both WFSs had significant phase rotation. A quick check of the power spectrum indicates that the Q signals have significantly (<x1/10) lower signals (Attachment 2/3/4). So that's good.
Transfer function measurement
Now the ASCPIT/ASCYAW of the MC1/2/3 suspension were excited and the transfer functions to WFS1/2 SEG1/2/3/4 and MC Trans P/Y were measured. The analysis will come later.
Again here the Q signals have significantly lower sensitivity to the mirror motion. So it is consistent with the above observation of the spectra.
However, the quick check of the transfer functions indicated that the conventional input matrices result in the flipped dependence of the combined error signals in pitch and yaw.
This might indicate that some of the cables were not inserted into the demod board properly although the cables at the demod boards show no indication of anomaly. (See the photos in ELOG 17048)
It might be the case that the cable had been inserted with a special unusual arrangement.
In any case, this can be fixed at the input matrix. Native change of the input matrix made WFS1PIT/WFS1YAW/WFS2PIT/WFS2YAW/MC2Trans YAW servos running (after some adjustment of the servo signs).
The MC2TRANS PIT servo didn't seem to settle and run away no matter which sign is used.
It's probably better to look at the sensing matrix and figure out the proper input/output matrix carefully. So at this moment, no WFSs are working.
Note that I left the new demod phases in the system
During the transfer function measurement some filters were turned off to make the shaking smoother:
IMC ASC filters were turned off to make the FResp flat:
- MC1 ASCP/Y FM1/FM5 OFF
- MC2 ASCP/Y FM1/FM5/FM6 OFF
- MC3 ASCP/Y FM1/FM5 OFF
60Hz comb OSEM Input filters were also turned off to make the transfer functions simpler:
- MC1 INPUT FM2 OFF (60Hz comb)
- MC2 INPUT FM2 OFF (60Hz comb)
- MC3 INPUT FM2 OFF (60Hz comb)
cf. Past IMCWFS commissioning http://nodus.ligo.caltech.edu:8080/40m/12684 |
Last week, we could find an alignment which realizes LO beam and AS beam both unclipped, but it was not consistent with an alignment which realize BHD fringe (40m/17046).
Today, we tweaked the alignment of SR2, AS1, AS4 to have BHD fringe with reduced LO and AS beam clipping.
AS beams on AP table and BHD both still look clipped, but much better now.
Ideally, SR2 and AS1 will unclip AS beam, and LO1, LO2, AS4 would make BHD fringe, but it is hard right now since LO beam seem to have little room and LO2 have little actuation range.
BHD optics on ITMY table, including camera, and AS55/ASDC were realigned after the aglinment work (Note that DCPD_A path have a pick-off for camera path, and this pick-off mirror have quite significant incident angle dependence of R/T ratio).
Current alignment scheme:
Current alignment scheme I figured out is the following.
- Check Y green. If it is transmitted at good spot on GTRY camera, Yarm is OK. If not, tweak ITMY/ETMY. alignment.
- Align TT1, TT2, LO1 to have DCPD_A_OUT of ~130 and DCPD_B_OUT of ~125.
- Align PR3, PR2 to maximize TRY_OUT to ~1.05.
- Tweak ITMY/ETMY if the beam spot on them are not good.
- Align BS, ITMX to have good MICH fringe and TRX_OUT to ~1.1.
- Tweak ITMX/ETMX if the beam spot on them are not good.
- Misalign ETMY, ETMX, ITMY to have LO-ITMX fringe in BHD DCPDs, and align AS beam with SR2 and AS4 differentially, with ratio of AS4/SR2=3.6.
DC PD values in various configurations:
Both arms locked with POX/POY, MICH free, PRM/SRM misaligned
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14088.57 13947.52 14167.04
C1:LSC-ASDC_OUT16 : 0.16 -0.02 0.34
C1:LSC-POPDC_OUT16 : 369.34 -74.88 854.34
C1:LSC-REFLDC_OUT16 : 0.03 -0.00 0.06
C1:LSC-TRY_OUT16 : 1.00 0.95 1.04
C1:LSC-TRX_OUT16 : 1.07 1.04 1.08
Only LO beam to BHD DCPDs
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14121.32 14057.71 14159.38
C1:HPC-DCPD_A_OUT16 : 129.80 128.37 130.68 (Consistent with, 40m/17046. Power as expected within 20%. Squashed shape)
C1:HPC-DCPD_B_OUT16 : 123.42 121.92 124.48
ITMX single bounce (ITMY, ETMX, ETMY, PRM, SRM, LO misalgined)
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14105.13 14000.89 14171.91
C1:HPC-DCPD_A_OUT16 : 92.54 91.45 93.30 (Consistent with 40m/17040, Power as expected within 40%. Clipped to the left in camera)
C1:HPC-DCPD_B_OUT16 : 137.70 136.55 138.53 (Note that DCPD_A/B ratio is different from LO, due to BHD BS R/T unbalance; 40m/17044)
C1:LSC-ASDC_OUT16 : 0.10 0.09 0.10 (Power as expected 40m/16952. Clipped to the right in camera)
C1:LSC-POPDC_OUT16 : 309.19 288.93 327.10 (Power as expected within 30% 40m/17042.)
C1:LSC-REFLDC_OUT16 : 0.02 0.01 0.02
ITMY single bounce (ITMX, ETMX, ETMY, PRM, SRM, LO misalgined)
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14112.09 14025.37 14154.51
C1:HPC-DCPD_A_OUT16 : 92.58 92.01 93.26
C1:HPC-DCPD_B_OUT16 : 137.68 136.81 138.27
C1:LSC-ASDC_OUT16 : 0.10 0.09 0.10
C1:LSC-POPDC_OUT16 : 308.48 290.49 319.73
C1:LSC-REFLDC_OUT16 : 0.02 0.01 0.02
MICH fringe only (ETMX, ETMY, PRM, SRM, LO misalgined)
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14090.34 13979.15 14143.86
C1:HPC-DCPD_A_OUT16 : 325.60 91.92 714.57
C1:HPC-DCPD_B_OUT16 : 400.27 18.37 762.57
C1:LSC-ASDC_OUT16 : 0.19 -0.05 0.41
C1:LSC-POPDC_OUT16 : 595.66 -119.21 1334.11
C1:LSC-REFLDC_OUT16 : 0.03 -0.01 0.07
LO-ITMX fringe only (ITMY, ETMX, ETMY, PRM, SRM misalgined)
Mean Max Min
C1:IOO-MC_TRANS_SUM : 14062.58 13968.05 14113.67
C1:HPC-DCPD_A_OUT16 : 224.31 89.57 371.66
C1:HPC-DCPD_B_OUT16 : 259.74 85.37 421.86
Next:
- Measure contrast (40m/17020) and estimate mode-matching of LO-AS again (40m/17041)
- Now that we have better LO-AS fringe, lock LO phase in MICH (40m/17037)
- Now that Dolphin issue was fixed, try double-demodulation to lock LO phase |
Sensing matrix measurement
MCx_ASCyyy_EXC was shaken with the amplitude of 3000 cnt. Measure the transfer functions to each segment of the WFS I&Q demod outputs.
- Pitch excitations consistently indicated WFS1 SEG2&3 / SEG1&4, and WFS2 SEG 1&2 / SEG 3&4 are the pairs.
- Yaw excitations consistently indicated WFS1 SEG1&2 / SEG3&4, and WFS2 SEG 1&4 / SEG 2&3 are the pairs.
---> WFS1P matrix {1,-1,-1,1}, WFS1Y matrix {1,1,-1,-1}, WFS2P matrix {1,1,-1,-1}, WFS2Y matrix {-1,1,1,-1}
Now look at the servo input. The following lists show the important numbers for the actuation to sensor matrices. The numbers were the measured transfer function between 7~10Hz and the unit is 1/f^2 [cnt/cnt].
CHA:, C1:SUS-MC1_ASCPIT_EXC, CHB:, C1:IOO-WFS1_I_PIT_OUT, -77.4602 +/- 18.4495
CHA:, C1:SUS-MC1_ASCPIT_EXC, CHB:, C1:IOO-WFS2_I_PIT_OUT, -22.6042 +/- 5.289
CHA:, C1:SUS-MC1_ASCPIT_EXC, CHB:, C1:IOO-MC_TRANS_PIT_OUT, -0.0007949 +/- 0.00019046
CHA:, C1:SUS-MC1_ASCYAW_EXC, CHB:, C1:IOO-WFS1_I_YAW_OUT, -60.5557 +/- 14.1008
CHA:, C1:SUS-MC1_ASCYAW_EXC, CHB:, C1:IOO-WFS2_I_YAW_OUT, -206.3526 +/- 47.1332
CHA:, C1:SUS-MC1_ASCYAW_EXC, CHB:, C1:IOO-MC_TRANS_YAW_OUT, 0.00027094 +/- 6.6131e-05
CHA:, C1:SUS-MC2_ASCPIT_EXC, CHB:, C1:IOO-WFS1_I_PIT_OUT, 57.8636 +/- 35.3874
CHA:, C1:SUS-MC2_ASCPIT_EXC, CHB:, C1:IOO-WFS2_I_PIT_OUT, -185.079 +/- 104.679
CHA:, C1:SUS-MC2_ASCPIT_EXC, CHB:, C1:IOO-MC_TRANS_PIT_OUT, 0.00089367 +/- 0.00052603
CHA:, C1:SUS-MC2_ASCYAW_EXC, CHB:, C1:IOO-WFS1_I_YAW_OUT, -349.7898 +/- 202.967
CHA:, C1:SUS-MC2_ASCYAW_EXC, CHB:, C1:IOO-WFS2_I_YAW_OUT, -193.7146 +/- 111.2871
CHA:, C1:SUS-MC2_ASCYAW_EXC, CHB:, C1:IOO-MC_TRANS_YAW_OUT, 0.003911 +/- 0.0023028
CHA:, C1:SUS-MC3_ASCPIT_EXC, CHB:, C1:IOO-WFS1_I_PIT_OUT, 65.5405 +/- 14.305
CHA:, C1:SUS-MC3_ASCPIT_EXC, CHB:, C1:IOO-WFS2_I_PIT_OUT, 78.8535 +/- 17.1719
CHA:, C1:SUS-MC3_ASCPIT_EXC, CHB:, C1:IOO-MC_TRANS_PIT_OUT, -0.00087661 +/- 0.00020837
CHA:, C1:SUS-MC3_ASCYAW_EXC, CHB:, C1:IOO-WFS1_I_YAW_OUT, -130.7286 +/- 29.6898
CHA:, C1:SUS-MC3_ASCYAW_EXC, CHB:, C1:IOO-WFS2_I_YAW_OUT, 129.0654 +/- 28.6328
CHA:, C1:SUS-MC3_ASCYAW_EXC, CHB:, C1:IOO-MC_TRANS_YAW_OUT, -0.00024944 +/- 5.9112e-05
Put these numbers in the matrix calculation and take the inverse for pitch and yaw separately.
We obtained
WFS1P WFS2P MCTP
-4.017 -4.783 -7.306e5 MC1P
3.611 -5.252 -2.025e5 MC2P
7.323 -1.017 -6.847e5 MC3P
WFS1Y WFS2Y MCTY
-3.457 -4.532 -5.336e5 MC1Y
-0.1249 0.3826 2.635e5 MC2Y
-5.714 1.076 -4.578e5 MC3Y
Basically we can put these numbers into the output matrix. The last column corresponds to the spot position servo and we want to make this slow.
So used x1e-5 values (i.e. removed e5) instead of these huge numbers.
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