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  17503   Fri Mar 10 16:42:16 2023 TomohiroUpdateIMCStep response test on MC1, MC2, and MC3 YAW


  • We compared the new output matrix with old one by the step response test.
  • We focused on the off-diagonal components of the step response result to compare the output matrix.
  • We found that the old one is relatively good to WFS1/2 and MC2_TRANS whereas the new one is useful only to WFS1.
  • Also we found that the new output matrix made from the sensing matrix was not significantly better than the original one.


Alex, Anchal, and I did the experiment to find out the better output matrix. We got the new output matrix from the step response test in 40m/17500, so we checked whether the output matrix is good or not.


We used the following method to check the output matrix. In the previous step response test, we applied the step offset to ``ExciteIn'' points, and measure the step response at ``SensOut'' points. These points are defined in Attatchment 4. From the test, we got the matrix A. Thus, we derived the new output matrix O_1 from taking the inverse of AO_1 = A^{-1}. If the new output matrix is well derived, the matrix can diagonalize the product of A and O_1A O_1 = \bf{I}, where \bf{I} is the identity matrix. AO_1 can be measured by the step response test from ``SensIn'' to ``SensOut.'' Therefore we checked the output matrix by measuring AO_1. We call the measured matrix S_1 (\equiv A O_1) as a sensing matrix.

To evaluate that S_1 is diagonalized, we computed the sum of the absolute values of the off-diagonal components in S_1

D_1 \equiv \sum_{j \neq k} \left| S_1 (j, k) \right| .

Note that each column of the matrix was normalized by its diagonal component.

We tried to find out the better output matrix as the following method. We created new output matrix O_2 from O_2 \equiv O_1 {S_1}^{-1}, and did the same step response test with O_2. Then we got the new sensing matrix S_2. We computed the sum of the absolute values of the off-diagonal components in S_2D_2. We can get the relation D_1 > D_2 if O_2 is better than O_1. Therefore we compared D_2 with D_1.

Note: If D_n and D_{n+1} have the relation D_n > D_{n+1} (\geq 0), the output matrix O_n \equiv O_{n-1} {S_{n-1}}^{-1} will get better and better.

We also did the step response test with O_0, which is defined as the output matrix now used. Then we compare D_0 with D_{1, 2}.


Before doing each step response test, we did the following processes:

  • MC WFS relief for 60 secs with closed loops,
  • turn off the WFS servo,
  • turn off all the filters (WFS1/2: FM3, 4, 6; MC2-TRANS: FM1, 3, 4, 6),
  • change the output matrix,
  • set all the gain as unity,
  • adjust each step offset.

We used the python script, toggleWFSoffsets.py, for testing the step response. The script is stored in /opt/rtcds/caltech/c1/Git/40m/scripts/MC/WFS/. The time appling each step offset is set as 120 secs. O_i~(i = 0, 1, 2) are specifically the following matrix:

O_0 = \begin{pmatrix} -4.0940 & -3.0383 & 34.0917 \\ -0.1259 & 0.27008 & -16.081 \\ -7.1811 & 0.74271 & 28.9458 \end{pmatrix}  O_1 = \begin{pmatrix} 0.342 & 0.117 & 1.967 \\ -0.016 & 0.036 & 2.82 \\ 0.732 & -0.042 & 1.873 \end{pmatrix}  O_2 = \begin{pmatrix} 0.812 & -0.819 & -2.289 \\ -0.036 & 0.761 & 2.998 \\ 0.085 & 0.386 & 2.835 \end{pmatrix}

Note: O_1 is different from [-0.188, -0.009, ...] in 40m/17500 because the previous calculation had a mistake.

The step response data is analyzed for making plot and calculating O_{1, 2} and D_{0, 1, 2} by the python script, /opt/rtcds/caltech/c1/Git/40m/scripts/MC/WFS/IOO_WFS_YAW_RESPONSE_TEST_100323.ipynb. 


The step response results for S_{1, 2, 0} are represented in Attachment 1, 2, 3, respectively. In each plot, upper left shows all the data for WFS1 (solid green), WFS2 (solid blue), and MC2_TRANS (solid brown). Also upper right, lower left, and lower right shows the result of WFS1, WFS2, and MC2_TRANS, respectively. The plots except for the upper left have the applied step offset drawed by dashed line. The three step offsets were applied in the order of WFS1 (dashed green in the upper right), WFS2 (dashed blue in the lower left), and MC2_TRANS (dashed brown in the lower right). The high-frequency components of all the plots are removed with a second-order Butterworth low-pass filter and then plotted. Dotted line and its surrounding area show the mean value for each step response or existing offset without the step offset, and its standard deviation, respectively.

We summarize each plot:

  • S_1

The matrix of S_1 is written from Attachment 1:

S_1 = \begin{pmatrix} -140 \pm 10 & 90 \pm 10 & 290 \pm 10 \\ 2 \pm 1 & -32 \pm 1 & 28 \pm 1 \\ -9 \pm 7 & -40 \pm 7 & -234 \pm 7 \end{pmatrix} .

Focusing on each column in S_1 and the plot, only the step response for WFS1 is well diagonalized. The result of D_1 is D_1 = 5.6 \pm 0.8. Note that all the sign of the step offset in Attachment 1 is negative because we set each gain of the filter as -1.

  • S_2

The matrix of S_2 is written from Attachment 2:

S_2 = \begin{pmatrix} 140 \pm 10 & 206 \pm 9 & -102 \pm 7 \\ 50 \pm 20 & 360 \pm 10 & -340 \pm 10 \\ -11 \pm 3 & -55 \pm 2 & 84 \pm 2 \end{pmatrix} .

The output matrix O_2 has worse normalization to WFS1 than O_1 from comparing S_2 with S_1D_2 also gets worse value than D_1D_2 = 6.4 \pm 0.4.

  • S_0

The matrix of S_0 is written from Attachment 3:

S_0 = \begin{pmatrix} -1700 \pm 100 & -130 \pm 120 & 2100 \pm 100 \\ -240 \pm 80 & -1100 \pm 70 & 1440 \pm 60 \\ 110 \pm 160 & 200 \pm 100 & -1400 \pm 100 \end{pmatrix} .

Although S_0 has relatively better normalization to WFS1 and 2 than S_{1, 2}, it is characterized by a large overall error. D_0 has minimum value with relatively large uncertainty: D_0 = 3.1 \pm 0.7.


We compare each value D_{1, 2, 0}, which is plotted in the left of Attachment 5. From the figure, we can find D_1 and D_2 agree within the margin of error, and D_0 is significantly smaller than D_1 and D_2. Also we compare D_{1, 2, 0} focusing on WFS1 column shown in the right of Attachment 5. D_{1, 0} have almost the same value, and D_2 has slightly larger value than other. This result shows O_0 is relatively good to WFS1/2 and MC2_TRANS whereas O_1 is useful only to WFS1.

Attachment 1: step_response_YAW_S1_100323.pdf
Attachment 2: step_response_YAW_S2_100323.pdf
Attachment 3: step_response_YAW_S0_100323.pdf
Attachment 4: Mar10_FlowDiagram.pdf
Attachment 5: Mar10_Dfactor.pdf
  17504   Mon Mar 13 14:48:37 2023 AnchalUpdateIMCDiagonalizing YAW output matrix using a different method

I tried a different method today to see if it works. Following are the steps:

  • Run WFS relief.
  • Turn off the WFS loops.
  • Calculate the effective current YAW matrix by transferring C1:IOO-MC#_YAW_GAIN to respective rows of the matrix read from C1:IOO-OUTMATRIX_Y. No need to change the matrix itself.
    • This step should not be required. We should move these gains to the matrices as soon as we can.
  • Put in the first column (corresponds to WFS1_YAW controller output) of this effective current YAW matrix to C1:IOO-LKIN_OUT_MTRX_4_1, C1:IOO-LKIN_OUT_MTRX_5_1, C1:IOO-LKIN_OUT_MTRX_6_1.
    • This is the output matrix of LOCKIN in WFS screens.
    • We are trying to actuate on what we think only affects WFS1_YAW and see if it is crosscoupled to WFS2_YAW or MC2_TRANS.
    • Then we can cancel coupling to the other two sensors by changing our couple vector.
  • Turn on locking at 0.5 Hz with gain 1.
  • Turn on BLP0.3 filter module. This is a 8th order 0.3 Hz butterworth filter.
  • Adjust phases to get all signal in the I quadratures.
  • Using ratio of C1:IOO-WFS_LKIN_I5_OUT16 to C1:IOO-WFS_LKIN_I4_OUTPUT, subtract or add this much factor of the WFS2_YAW column (the second column) of the effective YAW matrix to the column that is put in the LOCKIN output matrix.
    • I was able to subtract to less than 10% cross coupling with the intial matrix I started with.
  • Repeat until no cross-coupling is seen between WFS1_YAW and WFS2_YAW.
  • Repeat the above steps for WFS2_YAW column by putting that into the LOCKIN output matrix. Use the column calculated in last step for adding or subtracting WFS1 actuation.
    • I was able to make WFS2 column very clean with less than 1% measurable crosscoupling to other sensors.
  • I repeated the step for WFS1 column again to remove the cross coupling to WFS2 further to less than 1%.
  • For doing the above steps for MC2_TRANS column, the initial effective matrix column was very bad. The outputs were higher in WFS1 and WFS2 then MC2_TRANS output itself.
  • So I made the first guess by taking a cross-product between the obtained WFS1_YAW and WFS2_YAW columns estimated earleir.
  • Then I repeated the above steps to minimize coupling to WFS1 or WFS2 sensors to less than 10% of MC2_TRANS.
  • THe three column vectors obtained represent the new outpute YAW matrix. I removed the normalization that would be applied by C1:IOO-MC#_YAW filter gains from the rows of this amtrix to get the output matrix that can be put into C1:IOO-OUTMATRIX_Y

Once this matrix was in, I quickly tested it by closing the loop and making gain sign flips if required. Then I took quick swept sine transfer functions to estimate UGFs and scaled the columns of the output matrix to get UGF of 2.5 Hs for WFS1_YAW and WFS2_YAW loops and 0.1 Hz for MC2_TRANS YAW loop when all filter gains are 1 and overall gain C1:IOO-WFS_GAIN is 4. See attached plots.

Old matrix:

-4.094  ,  -3.0383 ,  34.0917
-0.1259 ,   0.27008, -16.081  
-7.1811 ,   0.74271,  28.9458

This was used with gains: 0.5 for WFS1_YAW loop, 0.6 for WFS2_YAW loop and 0.3 for MC2_TRANS_YAW loop.

New matrix:

-1.48948, -1.3029 , -4.93096
-0.05839,  0.15206, -3.66245
-2.82285,  0.92391, -4.68009

All loop gains 1.

Alex and Tomohiro are characterizing this matrix with step response and UGF measurements.

Attachment 1: WFS_YAW_OLTF_Measurements.pdf
WFS_YAW_OLTF_Measurements.pdf WFS_YAW_OLTF_Measurements.pdf WFS_YAW_OLTF_Measurements.pdf WFS_YAW_OLTF_Measurements.pdf WFS_YAW_OLTF_Measurements.pdf
  17505   Mon Mar 13 15:37:13 2023 AlexUpdateIMCStep Response of newly diagonalizing YAW output matrix

From the work that Anchal has completed for diagnolizing the YAW ouput matrix, a step response was taken of this new matrix using our previous methodolgies and the following results:

The step response can be seen plotted in attachment 1. The off diagonal terms of this new matrix sum to 1.24, which is a large decrease from the current matrix and the matrices that were tested from our previous step responses. 

Tomohiro and I are now currently working futher to configure the UGF's for YAW given this new output matrix.


Tomohiro and I have completed testing the YAW Sensor outputs with broadband noise injection and have confirmed that gains currently set on each filter module (which is 1.0 for WFS1, WFS2, and MC Trans) provides us with adequate UGF's. As seen bellow in attachment 2-3, WFS1 and WFS2 have UGF's between 2 and 3 Hz. MC Trans can be seen in attachment 4 and has been confirmed to have a UGF around 0.1 Hz.

Finally, attachment 5 displays the off diagnolized sums and uncertainties for each of our previous step response results and the newest result (labeled "new") for Anchal's OUTPUT YAW matrix. The first graph in blue displays the overall sum and uncertainty related to each step response taken. Then in the following 3 plots, the sum's and uncertaintes for each sensor are displayed individually for each step response test.

For reference:

New: corresponds to Anchal's YAW OUPUT MATRIX

D0: refers to the previously implemented matrix, prior to any testint or updates

D1: refers to the matrix that was computed based off of the first test Tomohiro and I performed

D2: refers to the matrix computed as a secondary result from D1. This matrix was thought to provide a lower off diagonal sum, but did not.

This thoroughly displays our results such that the newly computed matrix from Anchal is much more diagnolized then that of the step response matrices Tomohiro and I have computed.


Attachment 1: step_response_YAW_130323.pdf
Attachment 2: WFS1_YAW_OLTF_NI.pdf
Attachment 3: WFS2_YAW_OLTF_NI.pdf
Attachment 4: MC2_YAW_OLTF_NI.pdf
Attachment 5: Mar13_Dfactor.pdf
  17508   Tue Mar 14 11:38:44 2023 AnchalUpdateIMCTurned on 6:3lead FM7 on WFS1 and WFS2 YAW loops

I realized that for more phase margin, rana added 6:3lead filter on WFS PIT loops. Since we have increased the UGF on YAW loops too, I turned these on the YAW loops as well. The loops remain stable unlike with the previous matrix. Attachment 1 is the repeat of teh emasurement done by rana earlier but with the new matrix and updated gains in PIT loops. The dark green traces are the references from last measurment with higher gain and HEPA off. The remainging colored traces were measured today.

Attachment 1: Screenshot_2023-03-14_11-57-34.png
  17509   Tue Mar 14 13:59:11 2023 AnchalUpdateIMCIMC WFS aligned and offsets reset

The WFS loops were not maximizing the IMC transmission. The transmission counts remained stuck at around 12500 counts. The reflection DCMON from IMC had reached above 0.35 while nominally it had been around 0.2. So today, I manuaaly aligned the IMC to best transmission and lowest reflection, then unlocked IMC and reset the offsets on WFS1 and WFS2 RF readouts. After the offsets were changed, the error singals were fluctuating around 0 in best algined state. Then turning on the WFS loops made the transmissions slighlty higher to 13250 counts.

  17510   Tue Mar 14 15:46:06 2023 TomohiroUpdateIMCDiagonalizing YAW output matrix using a different method

Alex, Anchal, and I adjusted the number of the MC2-TRANS column in the YAW output matrix. We used the same method in 40m/17504 but the amplitude of oscillator for Lock In Amplifier is increased from 1 to 4.

The corrected numbers of the column in the output matrix is as follows:

MC1 -5.5196
MC2 -2.8778
MC3 -5.2232

We did the step response test for the corrected output matrix. The sum of off-diagonal terms was 0.62, which is the minimum value. Attachment 1 is the step response test result. From the figure, the reduction of the sum is because the column MC2_TRANS can diagonalize better. We can find out the property from Attachment 2.

Attachment 1: step_response_YAW_140323.pdf
Attachment 2: Mar14_Dfactor.pdf
  17512   Thu Mar 16 13:31:25 2023 TomohiroUpdateIMCDiagonalizing YAW output matrix using a different method


  • To adjust the components of the WFS2 column in the YAW output matrix.
  • To check the value of the off-diagonal components of the WFS1 column.


Alex, Anchal, and I used the same method in 40m/17504 to adjust the components of the WFS2 column. And we did the same step response test to check the value of the off-diagonal components in the YAW output matrix.

Used script & file

All the scripts & files are stored in /opt/rtcds/caltech/c1/Git/40m/scripts/MC/WFS/ directory.

  • DiagnoalizatingMethod.ipynb: for adjusting the components and replacing the new output matrix,
  • toggleWFSoffsets.py: for doing the step response test,
  • IOO_WFS_YAW_STEP_RESPONSE_TEST.py: for analyzing the step response result.


We changed the WFS2 column as follows

  From To
MC1 -1.3029 -1.8548
MC2 0.15206 -0.1357
MC3 0.92391 0.40158

We can successfully diagonalize the WFS2 column. The sum of the off-diagonal components is slightly reduced. However, WFS1 has worse diagonalization.

The same step response test should be performed on a different day to see if the results change. It is because the multiple causes could exist: the influence of the changed other columns, the long time drift, the day to day change, and so on.

Attachment 1: step_response_YAW_160323.pdf
Attachment 2: Mar16_Dfactor.pdf
  17513   Fri Mar 17 17:27:58 2023 Alex, TomohiroUpdateIMCArm Cavity Noise injection with WFS1/2 PIT and YAW

Tomohiro and I performed some tests under Rana's guidance to find cross corelations between WFS1 and WFS2 output signals in both pitch and yaw. We performed this test to further understand the degree to which our output matrices have been diagonolized.

Seen in attachment 1 is our base level with no injected noise source. In each figure, we also have inlcuded the coherence plot which compares each control signal to the overalll YARM power signal.

Attachments 2-5 display our results for injecting noise into each control signal individually.

We found the following corelations for each respective test:

Control Signal with Noise Corelated signals (order)
WFS1 PIT WFS1 YAW, WFS2PIT, WFS2 YAW (all equally corelated)
WFS1 YAW WFS1 PIT, WFS2 YAW, WFS2 PIT (most to least)
WFS2 PIT WFS1 PIT, WFS2 YAW, WFS1 YAW (most to least)
WFS2 YAW WFS2 PIT, WFS1 YAW (all equally corelated)

We judged our corelated signals by the peaks seen from out noise injection on the power spectrum as well as by their coherence at the same frequencies of our noise (20Hz-30Hz) compared to the overall power spectrum of YARM.


Performing this measurement was done using diaggui and awggui. The diaggui files for each test are saved at: "users/Templates/singleArmCal/ArmCavityNoise_230317_2_WFS1_PIT"

To properly fix each of the control signals to the same magnitude plotted for YARM output, we callibrated each plot using the settings seen in Attachment 7. First the units were changed on the plots to represent the true scale of each measurement:

We found that the ETMY actuation strength is 10.843e-9 / f^2 (from 17376) and used this to clibrate the plots to the nanometer scale. Next the gain was adjusted such that each plot would align over the YARM output when noise was injected onto it, setting a basis for all four measurements.

Finally, some filtering poles were added to the callibration for each plot such that it resembled that of the filters seen by the YARM ouput signal. (RXA: this is the 28 Hz ELP filter to simulate the dewhitening filters)

The measurements were taken with the settings seen in Attachment 8, and noise injected using the parameters seen in attachment 9.

RXA: Some edits/comments:

The noise was injected as band-limited random noise with a Normal distribution. We used noise rather than lines so as to capture the linear and bilinear noise contributions. In the case where the coupling is mostly bilinear, we would not expect to see much coherence.

The first attachment is a ASC noise budget for the single arm - in the high gain mode, the noise does not limit the noise as seen by the arm. Next is to see if its due to the MC dewhitening filters being on/off?

Attachment 1: ArmCavityNoise_230317_2.pdf
Attachment 2: ArmCavityNoise_230317_2_WFS1_PIT.pdf
Attachment 3: ArmCavityNoise_230317_2_WFS2_PIT.pdf
Attachment 4: ArmCavityNoise_230317_2_WFS1_YAW.pdf
Attachment 5: ArmCavityNoise_230317_2_WFS2_YAW.pdf
Attachment 6: Screenshot_2023-03-17_17-23-34.png
Attachment 7: Screenshot_2023-03-17_17-24-47.png
Attachment 8: Screenshot_2023-03-17_17-24-00.png
  17515   Tue Mar 21 18:41:12 2023 AlexUpdateIMCDither Lines set on MC1, MC2, MC3 for the night

With Anchal's help, I have setup dither lines for Rana on MC1,2,3 that will be running overnight. The oscilations were set on MC1,2,3, oscillator screens.
The following table describes the current setup:

Mirror Frequency Amplitude
MC1 21.12 Hz 2000
MC2 25.52 Hz 1000
MC3 27.27 Hz 2500

These frequencies and amplitudes were set on LOCKIN1 for each MC1,2,3. The output filters matrix for MC1,2,3 was also updated to reflect the degree of freedom being tested: PITCH.

The frequencies were picked to avoid the dewhitening frequency: 28Hz, and the Bounce/Roll frequencies: 16 Hz & 24 Hz. Furthermore, decimal value frequencies were utilized to avoid the multiples of 1 Hz.

The oscilators were originally started at 1363480200 and will be turned off at 1363535157.

See attachment 1 for the plot of the power spectrum. This test is done to find the beam offset for pitch.

Attachment 1: 21032023_Dither_lines_plot
  17516   Wed Mar 22 15:51:44 2023 AlexUpdateIMCBeam offset calculation for MC1,2,3 from dither results

I have organized the resulting data from running dither lines on MC1,2,3. The data has been collected from diaggui as shown in attachment 1.

Mirror f_l Avg Re (+/- 1000) Avg Im (+/- 1000) Peak Power (\delta f) Cts/urad
MC1 21.12 7000 4000 8062 12.66
MC2 25.52 13000 10000 16401 6.83
MC3 27.27 4000 -600 4044 11.03

Next using the following equations we can find \Delta Y:

\Delta L = \Delta Y \cdot \theta_{AC}

Where \Delta L is the change in length in result of the dithering and \Delta Y is the overall change in beam spot position

Delta L can be calculated by:

\Delta L = \frac{\delta f}{v_{laser}} \cdot L_{IMC}

where \delta f is the peak power of the line frequency and is found by taking the square root of the magnitude of the Real and imaginary terms, v_{laser} is frequency the laser light is traveling at (281 THz) and L_{IMC} is the lenght of the IMC (13.5 meters).

\theta_{AC} can then be calculated by:

\theta_{AC} = \theta_{DC}/f_l^2

where  \theta_{AC} is the angle at which the mirror was shaken at a given frequency. We can find \theta_{DC} by converting the amplitude of the frequency that the mirror was shaken at and converting it into radians using the conversion constants found here: 17481.

\theta_{AC} is then shown to be found by this angle diveded by the line frequency.

The final values are calculated and displayed bellow:

Mirror \theta_{DC} \theta_{AC} \Delta L \Delta Y
MC1 157.9 urad 0.35 urad 0.38 nm 1.08 mm
MC2 146.4 urad 0.23 urad 0.78 nm 3.39 mm
MC3 226.7 urad 0.31 urad 0.19 nm 0.61 mm


Attachment 1: 22032023_Dither_lines_demod_MC1_21-12.pdf
22032023_Dither_lines_demod_MC1_21-12.pdf 22032023_Dither_lines_demod_MC1_21-12.pdf
  17519   Thu Mar 23 16:21:10 2023 ranaUpdateIMCBeam offset calculation for MC1,2,3 from dither results

I have changed the MC SUS output matrices by a few % for some A2L decoupling - if it causes trouble, please feel free to revert.

Anchal came to me and saiddevil, "I think those beam offsets are a bunch of stinkin malarkey!", so I decided to investigate.cool

Instead of Alex's "method" of trusting the actuator calibration, I resolved to have less systematics by adjusting the SUS output matrices ot minimize the A2L and then see what's what vis a vis geometry.

The attached screenshot shows you the measurement setup:

  1. copy the DoF vector from DoF column into the LOCKIN1 column.
  2. Turn on the OSC/LOCKIN for the optics / DoF in question (in this example its MC2 PITCH)
  3. Monitor the peak in the MC_F spectrum
  4. Also monitor the mag and phase of the TF of MC_F/LOCKIN_LO
  5. use the script stepOutMat.py to step the matrix

Next I'm going to modify the script so that it can handle input arguments for optic/ DOF, etc.

FYI, the LOCKIN screens do have a TRAMP field, but its not on the screens for some reason surprise. Also the screens don't have the optic name on them.crying :


After finishing the tuning of all 3 IMC optics, I have discovered that 27.5 Hz is a bad frequency to tune at: the Mc1/MC3 dewhtiening filters have a 28 Hz cutoff, so they all have slightly different phase shifts at 27-28 Hz due to the different poles due to tolerances in the capacitors (probably).

*Also, I am not able to get a real zero coupling through this method. There always is an orthogonal phase component that can't be cancelled by adjusting gains. On MC3, this is really bad and I don't know why.

Attachment 1: TuninMC2OutMat-A2L-beaucoup.png
Attachment 2: IMC-A2Lnomore_cawcaw.png
  17552   Wed Apr 19 17:32:11 2023 AlexUpdateIMCBeam offset calculation for MC1,2,3 from dither results

Today, we ran dither lines on the MC1,2,3 mirrors in YAW from 136598007 to 1365981967 and similarly on PIT from 1365982917 to 1365984618.

The following frequencies and amplitudes were recorded for each dither line:

optic freq amp YAW amp PIT
MC1 21.21 3000 6000
MC2 26.62 6000 9000
MC3 23.10 3000 6000


The urad conversions used to calculate theta DC and AC can be found at 17481


The dither lines were then demodulated in python and the steps shown in 17516 were followed to calculate the beam offset that each dither line represented in pitch and yaw. 

The following results were found:

Optic Delta Y (mm)
MC1 YAW 1.42
MC2 YAW 1.6
MC3 YAW 1.78
MC1 PIT 2.72
MC2 PIT 2.33
MC3 PIT 2.83


Attatched bellow is the power spectrums for both yaw and pitch.

Attachment 1: 19042023_Dither_Lines_YAW.pdf
Attachment 2: 19042023_Dither_Lines_PIT.pdf
  17559   Mon Apr 24 18:33:22 2023 AlexUpdateIMCBeam offset movement for MC1,2,3 in PIT and YAW from dither results

Mayank and I worked on finalizing the plots for the beam offset from the dithering test done in 17552. Plotted in attachment 1 are the beamspot demodulated signals from MC_F_DQ which are averaged over 1 second each (blue) for YAW and PIT in MC1,2,3. The yellow line over each plot shows the 3 Hz lowpassed signal of the beamspot movement.

Additionally, we have seen no direct correlation to the WFS1 or 2 sensors due to the MC movements. This may be because the WFS display a complete signal that includes all changes in the cavity length due to the shaking of the mirrors. Thus, the signal (shown in red) of the WFS sensors will show a combined average of movement from all 3 dither lines.

Attachment 1: beam_spot_time_series.png
  17561   Tue Apr 25 15:51:21 2023 JcUpdateIMCIMC has been tripping

It has happened multiple times today that IMC has tripped on its own. Yehonathan and I have had to come back to manually lock IMC multiple times.

Wed Apr 26 10:24:07 2023 [EDIT]

[Paco] I aligned the MC by hand, let it run locked for 30 minutes without angular controls, and then switched on the WFS loops yesterday at ~ 6 PM. IMC has been locked ever since.

Attachment 1: Screenshot_2023-04-25_15-55-33.png
  17573   Mon May 1 08:57:45 2023 JCConfigurationIMCBad Alignment

I had to realign the IMC today. When I came in, it was very bad, not much flashing at all, I had to do it from scratch. CH01 Camera on MON7 in the control room is completely white. Did the camera go out over the weekend? I will come back to poke around later, I have headed over to WB for a moment and will be back soon. sitemapsi

Attachment 1: Screenshot_2023-05-01_15-55-33.png
  17577   Tue May 2 10:39:49 2023 JCConfigurationIMCBad Alignment

It took a while, but I was finally able to align IMC. It seems like WFS has been getting really whacky lately when we arent in the lab watching it angry. The picture attached has an arrow of where the beam spot was at this morning

Attachment 1: BB26DF83-5B6A-4BC1-A2A0-6E18E1A2B91E.jpeg
  18   Fri Oct 26 16:19:29 2007 Tobin FrickeRoutineIOOMC resonances
We would like to measure the absorption of the mode cleaner optics. The plan is to repeat <a href="http://ilog.ligo-wa.caltech.edu:7285/mLIGO/Cleaning_the_Mode_Cleaner">Valera's experiment</a> in which we track the MC's thermal resonances to infer their power absorption. Last night Rana and I hooked up a lock-in amplifier to heterodyne the MC servo signal by 28 kHz and piped the output into an ADC using the MC_AO channel. We did not find any resonances.

Valera recommends we drive the POS of the three MC optics with bandlimited noise to excite the resonances.
  22   Sun Oct 28 03:03:42 2007 ranaConfigurationIOOThree Way Excitement
We've been trying to measure the MC mirror internal mode frequencies so that we can measure
their absorption before and after drag wiping.

It looked nearly impossible to see these modes as driven by their thermal excitation level;
we're looking at the "MC_F" or 'servo' output directly on the MC servo board.

Today, I set up a band limited noise drive into the 'Fast POS' inputs of the 3 MC coil
driver boards (turns out you can do this with either the old HP or the SR785).

MC1     28.21625 kHz
MC2     28.036   kHz
MC3     28.21637 kHz

I don't really have this kind of absolute accuracy. These are just numbers read off of the SR785.

The other side of the setup is that the same "MC_F" signal is going into the SR830 Lock-In which
is set to 'lock-in' at 27.8 kHz. The resulting demodulated 'R" signal (magnitude) is going into
our MC_AO channel (110B ADC).

As you can see from the above table, MC1 and MC3 are astonishingly and annoyingly very close in
frequency. I identified mirrors with peaks by driving one at a time and measuring on the spectrum
analyzer. I repeated it several times to make sure I wasn't fooling myself; it seems like they
are really very close
but distinct peaks. I really wish we had chipped one of these mirrors
before installing them.

Because of the closeness of these drumhead modes, we will have to measure the absorption by making long
measurements of this channel.
  29   Tue Oct 30 00:47:29 2007 ranaOtherIOOMC Ringdowns
I did a bunch of MC ringdown measurements using the PD that Rob set up. The idea is to put a fast PD (PDA255)
looking at the transmission through MC2 after focusing by a fast lens. The input to the MC is turned off fast
by flipping the sign of the FSS (Andri Gretarsson's technique).

With the laptop sitting on the MC can, its easy to repeat many ringdowns fast:
- Turn off the MC autolocker. Relock the MC with only the acquisition settings; no boosts
  and no RGs. This makes it re-acquire fast. Turn the MC-WFS gain down to 0.001 so that
  it keeps it slowly aligned but does not drift off when you lose lock.

- Use low-ish gain on the FSS. 10 dB lower than nominal is fine.

- Setup the o'scope (100 MHz BW or greater) to do single shot trigger on the MC2 trans.

- Flip FSS sign.

- Quickly flip sign back and waggle common gain to get FSS to stop oscillating. MC
  should relock in seconds.

Clearly one can scriptify this all just by hooking up the scope to the ethernet port.

Attached are a bunch of PNG of the ringdowns as well as a tarball with the actual data. A sugar
napoleon to whomever can explain the 7 us period of the wiggle before the vent!
Attachment 1: tek00000.png
Attachment 2: tek00001.png
Attachment 3: tek00004.png
Attachment 4: MC2ringdown.tar.gz
  30   Tue Oct 30 13:58:07 2007 ajwConfigurationIOOMC Ringdowns
Here's a quick fit-by-eye to the latter part of the data from tek00000.xls.

The prediction (blue) is eqn 41 of

T1 = T2 = 0.002. Loss1 = Loss2 = 150 ppm.
MC3 assumed perfectly reflecting.
Velocity = 320 um/s (assumed constant), 2 usec into the ringdown.

OK, there's one little fudge factor in the prediction:
I multiplied D by 2.
Attachment 1: CavityRingdown.png
Attachment 2: CavityRingdown.m
% CavityRingdown.m
% Eqn 41 of 
% "Doppler-induced dynamics of fields in Fabry–Perot
% cavities with suspended mirrors", Malik Rakhmanov (2000).
% http://www.ligo.caltech.edu/docs/P/P000017-A.pdf

clear all

% read in ringdown timeseries:
at = importdata('tek00000.csv');
... 121 more lines ...
  35   Wed Oct 31 08:34:35 2007 ranaOtherIOOloss measurements
In the end, we were unable to get a good scatter measurement just because we ran out of steam. The idea was to get a frame
grab image of MC2 but that involves getting an unsaturated image.

In the end we settle for the ringdowns, Rob's (so far unlogged) cavity pole measurement, and the MC transmission numbers. They
all point to ~100-150 ppm scatter loss per mirror. We'll see what happens after wiping.
  36   Wed Oct 31 08:38:35 2007 ranaProblem FixedIOOMC autolocker
The MC was having some trouble staying locked yesterday. I tracked this down to some steps in the last
half of the mcup script; not sure exactly which ones.

It was doing something that made the FAST of the PSL go to a rail too fast for the SLOW to fix.
So, I broke the script in half so that the autolocker only runs the first part. We'll need to
fix this before any CM locking can occur.

We also need someone to take a look at the FSS Autolocker; its ill.
  39   Wed Oct 31 15:02:59 2007 tobinRoutineIOOMode Cleaner Mode Tracking
I processed the heterodyned mode cleaner data yesterday, tracking the three 28 kHz modes corresponding to MC1, MC2, and MC3. Unfortuntately the effect of our MC power chopping is totally swamped by ambient temperature changes. Attached are two plots, one with the tracked mode frequencies, and the other containing dataviewer trends with the MC transmitted power and the room temperature. Additionally, the matlab scripts are attached in a zip file.
Attachment 1: mode-track.pdf
Attachment 2: trends.pdf
Attachment 3: mcmodetrack.zip
  40   Wed Oct 31 15:22:59 2007 robConfigurationIOOMode Cleaner transfer function
I measured the transfer function of the input mode cleaner using a PDA255 and the ISS. First I put the PD in front of the ISS out-of-loop monitor diode and used an SR785 to measure the swept sine transfer function from the Analog IN port of the ISS to the intensity at the PD. Then I moved the PD to detect the light leaking out from behind MC2, using ND filters to get the same DC voltage, and measured the same transfer function. Dividing these two transfer functions should take out the response of the ISS and the PD, and leave just the transfer function of the MC. A plot of the data, along with a single-pole fit, are attached.

The fit is pretty good for a single pole at 3.79 kHz. There's a little wiggle around 9kHz due to ISS weirdness (as Tobin has not been giving it the attention it requires), but this shouldn't affect this result too much. Using the known MC length of 27.0955m, and assuming that MC1 and MC3 have a power transmissivity of 2000ppm and MC2 is perfectly reflecting, the total round trip loss should be about 300ppm. The fitted finesse is 1460.
Attachment 1: MCtf.pdf
  45   Thu Nov 1 11:45:30 2007 tobinConfigurationIOOMode cleaner drag-wiping
Andrey, Bob, David, John Miller, Rana, Rob, Steve, Tobin

Yesterday we vented the vacuum enclosure and opened up the chamber containing MC1 & MC3 by removing the access connector between that chamber and the OMC chamber. Rana marked MC1's location with dogs and then slid the suspension horizontally to the table edge for easy drag-wiping access. The optic was thoroughly hosed-down with the dionizer, in part in an effort to remove dust from the cage and the top of the optic. Drag-wiping commenced with Rob squirting (using the 50 microliter syringe) and Tobin dragging (using half-sheets of Kodak lens tissue). We drag-wiped the optic many (~10) times, concentrating on the center but also chasing around various particles and a smudge on the periphery. There remains one tiny speck at about the 7:30 position, outside of the resonant spot area, that we could not dislodge with three wipes.

Today we drag-wiped MC3. First we slid MC1 back and then slid MC3 out to the edge of the table. We disconnected the OSEM cables in the process for accessibility, and MC1 is perched at an angle, resting on a dog. We did not blow MC3 with the deonizer, not wanting to blow particles from MC3 to the already-cleaned MC1. We drag-wiped MC3 only three times, all downward drags through the optic center, with Steve squirting and Tobin dragging. Some particles are still visible around the periphery, and there appears to be a small fiber lodged near the optic center on the reverse face.

Andrey and Steve have opened up MC2 in preparation for drag-wiping that optic after lunch.
  61   Sun Nov 4 23:55:24 2007 ranaUpdateIOOFriday's In-Vac work
On Friday morning when closing up we noticed that we could not get the MC to flash any modes.
We tracked this down to a misalignment of MC3. Rob went in and noticed that the stops were
still touching. Even after backing those off the beam from MC3 was hitting the east edge of
the MC tube within 12" of MC3.

This implied a misalignment of MC of ~5 mrad which is quite
large. At the end our best guess is that either I didn't put the indicator blocks in the
right place or that the MC3 tower was not slid all the way back into place. Since there
is such a strong stickiness between the table and the base of the tower its easy to
imagine the tower was misplaced.

So we looked at the beam on MC2 and twisted the MC3 tower. This got the beam back onto the
MC2 cage and required ~1/3 if the MC3 bias range to get the beam onto the center. We used
a good technique of finding that accurately: put an IR card in front of MC2 and then look
in from the south viewport of the MC2 chamber to eyeball the spot relative to the OSEMs.

Hitting MC2 in the middle instantly got us multiple round trips of the beam so we decided
to close up. First thing Monday we will put on the MC1/MC3 access connector and then
pump down.

Its possible that the MC length has changed by ~1-2 mm. So we should remeasure the length
and see if we need to reset frequencies and rephase stuff.
  62   Mon Nov 5 07:29:35 2007 ranaUpdateIOOFriday's In-Vac work
Liyuan recently did some of his pencil beam scatterometer measurements measuring not the
BRDF but instead the total integrated power radiated from each surface point
of some of the spare small optics (e.g. MMT, MC1, etc.).

The results are here on the iLIGO Wiki.

So some of our loss might just be part of the coating.
  67   Tue Nov 6 10:42:01 2007 robConfigurationIOOmode cleaner locked
Increased the power exiting the PSL by turning the half-wave plate after the MOPA, opened the PSL shutter, and aligned the mode cleaner to the input beam. It wasn't that hard to find the beam with the aperture open all the way on the MC2 camera. The transmitted power is now 2.9 arbitrary units, while the input power is 1.2 arbitrary units. Not sure yet if that's an increase or decrease in efficiency, since no one posted numbers before the vent. Also turned on the input-steering PZTs and saw a REFL beam on the camera.
  68   Tue Nov 6 14:51:03 2007 tobin, robUpdateIOOMode cleaner length
Using the Ward-Fricke variant* of the Sigg-Frolov method, we found the length of the mode cleaner to be 27.0934020183 meters, a difference of -2.7mm from Andrey, Keita, and Rana's measurement on August 30th.

The updated RF frequencies are:
3  fsr =  33 195 439 Hz
12 fsr = 132 781 756 Hz
15 fsr = 165 977 195 Hz
18 fsr = 199 172 634 Hz
* We did the usual scheme of connecting a 20mVpp, 2 kHz sinusoid into MC AO. Instead of scanning the RF frequency by turning the dial on the 166 MHz signal generator ("marconi"), we connected a DAC channel into its external modulation port (set to 5000 Hz/volt FM deviation). We then scanned the RF frequency from the control room, minimizing the height of the 2 kHz line in LSC-PD11. In principle one could write a little dither servo to lock onto the 15fsr, but in practice simply cursoring the slider bar around while watching a dtt display worked just fine.
  74   Wed Nov 7 00:51:33 2007 andrey, rob, tobinConfigurationIOOMC ringdowns
We completed several ringdown measurements this afternoon; Andrey is currently processing the data.
  75   Wed Nov 7 02:14:08 2007 AndreyBureaucracyIOOMore information about MC2 ringdown
As Tobin wrote two hours ago, we (Andrey, Tobin, Robert) made a series of ringdown measurements for MC2
in the spirit of the measurement described by Rana -> see
entry from Mon Oct 29 23:47:29 2007, rana, Other, IOO, MC Ringdowns.

I attach here some pictures that we saw on the screen of the scope, but I need to admit that I am not experienced enough to present a nice fit to these data, although I attach fits that I am able to do today.

I definitely learned a lot of new Matlab functions from Tobin - thanks to him!, but I need to learn two more things:

Firstly, I do not know how to delete "flat" region (regions before the ringdown starts) in Matlab ->
I needed to delete the entries for times before the ringdown ("negative times") by hand in the text-file, which is extremely non-elegant method;

Secondly, I tried to approximate the ringdown curve by a function ydata=a*exp(b*xdata) but I am not exactly sure if this equation of the fitting curve is a good fit or if a better equation can be used.

It seems, in this situation it is better for me to ask more experienced "comrades" on November 7th.

P.S. It seems I really like the type of message "Bureaucracy" - I put it for every message. As Alain noted, maybe that is because some things are very bureacratized in the former USSR / Russia. By the way, when I was young, November 7th was one of two most important holidays in the USSR - I liked that holiday because I really liked military parades on the red square. I attach a couple of pictures. November 7 is the anniversary of the Revolution of 1917.
Attachment 1: image-attempt_1.png
Attachment 2: image-attempt_2.png
Attachment 3: image-attempt_3.png
Attachment 4: image-attempt_4.png
Attachment 5: image-attempt_5.png
Attachment 6: Fit-1st_attempt.jpg
Attachment 7: Fit-5th_attempt.jpg
Attachment 8: 7_Nov_1941-parad-na-krasnoy-ploschadi.jpg
Attachment 9: parad1984-moskva.jpg
  78   Wed Nov 7 13:54:44 2007 robConfigurationIOOMode Cleaner transfer function
I performed the same procedure described here, and re-measured the transfer function of the mode cleaner to see the effect of the drag-wiping. The results are attached in a pdf. We don't seem to have done any damage, but the improvements are barely measurable.

pole frequency3.789kHz3.765kHz
loss per optic99ppm91ppm
Attachment 1: mctf.pdf
  80   Wed Nov 7 14:05:59 2007 tobinConfigurationIOOMC ringdown
Modeling the mode cleaner as a simple cavity with all losses lumped together, we expect the cavity power to be
attenuated by a factor (1-L) after each interval (2l/c)=1/fsr. Therefore we can get the cavity loss L
(including power lost through transmission) from the ringdown time constant tau as:

L = 1 - exp[ - 1/(tau * fsr) ]

From this we have to subtract the 2000 ppm transmission for each of MC1 and MC3, and divide by three to spread
the losses across the three optics.

I get 168 ± 39 ppm loss per optic based on a very simple exponential fit to the tails (t>0) of four of Andrey's data files.

By comparison, I get 154 ± 37 ppm from Rana's data files from before the vent.
  125   Tue Nov 27 15:47:17 2007 robConfigurationIOOMC loop
After the FSS running pretty quick, I checked the MC loop. I used TPA 1&2.

MC loop
UGF: 70kHz
Input Gain: 29dB
Boost Level: 2
phase: 40 deg
Attachment 1: MCsmall.jpg
  126   Tue Nov 27 16:18:58 2007 robConfigurationIOOMC loop
Reduced the common gain to 22dB in the mcup script, so that the WFS would not blow the lock. The above measure of the OLG was done without the mcWFS running, so may be a low estimate as compared to when the alignment is perfect.
  154   Sun Dec 2 21:02:12 2007 ranaConfigurationIOOMC SUS re-alignment
The spot on MC2 was not centered, so I put it back in the center:

  • Made sure MC trans was high with the WFS off.
  • Moved the Sliders on the MC Align screen until spot was centered (by eye)
  • Moved some more until power was maximized.
  • Unlock MC
  • Center spots on McWFS
  • Re-enable autolocker and McWFS loops.
  155   Sun Dec 2 21:07:39 2007 ranaConfigurationIOOMC SUS re-alignment
you asked for:   diff 2007/12/01,4:58:48 2007/12/03,4:58:48 utc 'MC.*COMM'
LIGO controls: differences, 2007 12/01 04:58:48 utc vs. 2007 12/03 04:58:48 utc
__Epics_Channel_Name______   __Description__________   __value1____     __value2____
C1:SUS-MC1_YAW_COMM                                    -0.273460        -0.503460
C1:SUS-MC2_PIT_COMM                                     3.624020         3.632020
C1:SUS-MC2_YAW_COMM                                    -0.936800        -1.038800
C1:SUS-MC3_YAW_COMM                                    -3.129000        -3.369000
  156   Sun Dec 2 21:13:16 2007 ranaConfigurationIOOMC SUS re-alignment
Attachment 1: e.png
  178   Fri Dec 7 00:02:26 2007 ranaSummaryIOOMC/FSS Frequency Noise
The FSS frequency noise is not very bad.

I compared the MC_F spectra between Hanford and the 40m using DTT and its 'User NDS' option.
After Sam, Jenne, and DavidM installed the new MC Servo some time ago, the MC_F spectrum here
has had some whitening before it goes into the DAQ (on board; same as LLO & LHO). The tuning
coefficient of the VCO is also basically the same between all PSLs since everyone has the same
chip in the VCO driver.

Therefore, at the frequencies where the MC gain is more than ~4, the MC_F signal calibration is
the same here as anywhere. Since its the servo control signal, its basically a measure of the
frequency noise incident on the MC -- its just what comes out of the FSS with the table noise on
top. At low frequencies (< 100 Hz) its a measure of the motion of the MC mirrors.

Above 200 Hz ours is the same as theirs; except for the enormous power line spikes. I think that's
either all on the light. But our acoustics are better and the noise above 1 kHz levels off at the
same flat floor (the phase noise of the VCO) as H1. The huge lump around 100 Hz is the MC2 DAC noise and
it goes down to the H1 levels when we flip on the dewhites. The giant excess from 5-50 Hz is just the fact
that our stacks don't do much until 20-30 Hz.

So we can stop blaming the FSS and move on with life as soon as Tobin gets the ISS back in shape.
Attachment 1: fly.pdf
  304   Sat Feb 9 13:05:48 2008 JohnSummaryIOOPMC camera/ HEPA
I replaced the Gig-E camera on the PMC trans beam. The PZT was close to railing and I wanted to adjust it. I just did a quick job, there is a little scattered light on the image. If Joe is finished with the Gig-E I'll take another look at it.

The HEPA in the PSL table was turned off for some reason. I turned it back on.
  307   Sun Feb 10 21:43:16 2008 robConfigurationIOOMC alignment tweaked

I adjusted the alignment of the free hanging mode cleaner to best transmit the PSL beam.
  357   Tue Mar 4 20:14:02 2008 ranaConfigurationIOOMC Alignment
The MC alignment was pretty far off. We were getting TEM01 mode locks only.
Rather than inspect what happened I just aligned the MC suspensions to get
the transmission higher. Now Matt should be able to lock the X arm and collect
adaptive filter data.
  361   Wed Mar 5 17:35:24 2008 ranaUpdateIOORFAM during MC lock
I used an ezcaservo command to adjust the offsets for Alberto's StochMon channels. They are all
at +2 V with no light
on the RFAM PD (MC unlocked).

Then I looked at 5 minutes of second trend around when the MC locks. Since Alberto has chosen
to use +2V to indicate zero RF and a negative gain, there is a large RF signal when the StochMon
channels approach zero

From the plot one can see that the RFAM for the 133 & 199 MHz channels is much worse than for the 33 and 166.
Its also clear that the turn on of the WFS (when the RFAMPD's DC light level goes up) makes the single demod
signals get better but the double demod get worse.
Attachment 1: rfam.pdf
  372   Wed Mar 12 23:05:44 2008 ranaUpdateIOOMC WFS
they are bad, somewhat

please fix
  437   Tue Apr 22 17:08:04 2008 CarynUpdateIOOno signal for C1:IOO-MC_L
C1:IOO-MC_L signal was at zero for the past few days
  439   Tue Apr 22 22:51:30 2008 ranaConfigurationIOOMcWFS Status
I've been working a little on the MC WFS in the last few days. I have made many
changes to the sensing matrix script and also to the MCWFSanalyze.m script.

The output matrix, as it was, was not bad at low frequencies but was making noise in
the ~1 Hz band. Turning the gain way down made it do good things at DC and not make
things work higher.

The output matrix generating script now works after Rob fixed the XYCOM issue. Not sure
what was up there. As Caryn mentioned the SUS2.ini channels were all zero after Andrey's
PEM power cycle a few days ago. Rob booted c1susvme to get the SUS1 channels back and
today we did c1susvme2 to get the IOO-MC_L et. al. back.

Even after doing the matrix inversion there is some bad stuff in the output matrix. I
checked that the sensing matrix measurement has good coherence and I measured and set the
MC WFS RF phases (they were off by ~20-30 deg.). Still no luck.

My best guess now is that the RG filters I've used for POS damping and the movement of the
beam on the MC mirror faces has made a POS<->YAW instability at low frequencies. My next
move is to revert to velocity damping and see if things get better. Should also try redoing
the A2L on the MC1-3.
  451   Fri Apr 25 20:53:02 2008 ranaConfigurationIOOMC WFS with more gain
Quick update: we found that the reason for the MC WFS instability was that the digital anti-whitening was one but not the analog whitening.

We turned off the digital filters and were able to increase the gain by a factor of ~30. It is left like this, but if it hampers IFO locking then best to just turn it back down to an overall gain of 0.1 or 0.05.
  454   Sun Apr 27 02:11:11 2008 ranaConfigurationIOOMC WFS Notes
As noted in the elog from Friday, the WFS has been bad ever since someone switched on the digital whitening filters (FM1 & FM2)
in the MC WFS I&Q filter banks.

On Friday evening, John, Alan, and I went to the rack and verified that although the drawing shows a hookup for the whitening
filters, there is actually no such thing and so we can't have the whitening. So the anti-whitening turns on two lag filters
(2 poles at 4 Hz) and without the hardware this makes the servos unstable by adding 90 deg of phase lag at 4 Hz.

There are still several problems in this system:
- AD797 is used after the mixer. This is an unreliable, noisy part. We need to change this out
  with some OP27s so that this becomes reliable and has a more reasonable noise figure.

- Hard wire the whitening filters ON. We never want these to be off. Then we can turn on the
  anti-whitening. This will give us a factor of 100 better noise without filtering.

- The AD602 on the front of the whitening board has a 100 Ohm internal impedance and the 
  resistor between the demod board and the AD602 is 909 Ohms. This results in dividing the
  signal by 10.

- The signal at the ADC is ~100 cts peak-peak. The full ADC range is, of course, 65000 cts. So
  we could use a lot more gain. The mean quadrant signals are also ~100 cts so we could easily
  up the analog DC gain by a factor of 30 on top of the whitening filter increase.

- The AD602 at the input and the AD620 on the output are both variable gain stages but because
  of our lack of control are set to ambiguous gain levels. We should set the AD602 on the input
  to its max gain of 30 dB. With the -20 dB from the x10 voltage division, this will give us
  an overall gain of 3 for the puny demod signals.

  455   Sun Apr 27 05:09:30 2008 ranaConfigurationIOOMC WFS Whitening turned on
I hardwired on the MC WFS whitening filters.

The MAX333A switches which choose between whitening and bypass on that board were in the bypass position
because the Xycom220 connections are not there. So the control switch gets +15V but there is no pull
down to set it to the whitened mode.

The least invasive (easiest) change I could do was to tie all of those inputs to ground. This pulls a few mA
through the pull-down resistors but is otherwise innocuous. All of these control lines come in on the A-row
of the P1 connector, so I was able to solder a single wire across all of them to ground them all.

The WFS2 board had a blown electrolytic capacitor on the -15 V line and so there was probably some extra noise
getting in that way. I couldn't find any extra SMD to replace it so I cut the legs off of a 22 uF polarized
tantalum and stuck it in there. Its even close to being the same color. I checked out the other caps, and they were all
close to 68 uF as spec'd. This one had luckily blown open and so didn't suck down the Sorensen and destroy everything.

Plugged everything back in switched the WFS servos back on. Looks good. Took before and after spectra.

In the plot:

GREEN: Open loop dark noise before changes
RED: Open loop bright (MC locked but MCWFS off)
BLUE: Closed loop, MC locked

BLACK: Dark noise after whitening
ORANGE:Closed loop after whitening

The cursor is at 16.25 Hz, the SOS bounce mode.

The I ran the new setMCWFSgains script which uses pzgain to set the UGFs of the 4 loops to 4.01 Hz.
We have in the past had problems with high WFS gains causing instabilities with the CM servo around 10-30 Hz. If this happens we should
just lower the gain by a factor of ~5.
Attachment 1: mcnoise.png
  489   Tue May 20 18:33:01 2008 Andrey, JohnConfigurationIOOMode Cleaner is locked again

It was noticed by Mr.Adhikari earlier today that the MC became unlocked at about 11AM.

There is no clear understanding what caused the problem.

Trying to restore the modecleaner locking, we noticed with John that the beam was not centered on the wavesensors (WFS1. WFS2 on the screen "C1IOO_LockMC.adl"). We decided to adjust the beam position moving slightly the bias sliders for pitch and yaw degrees of freedom for MC1.
This allowed to make the MC locked.

Old positions for the MC1 sliders: Pitch = 2.9934, Yaw = -0.6168;
New positions --------//---------: Pitch = 3.0604, Yaw = -0.7258.

At the same time, FSS for PSL is still showing the values in the range 0.720 - 0.750 which is lower than the usual values. The indicator for FSS value is yellow when it is below 0.750.
ELOG V3.1.3-