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ID Date Author Type Category Subject
4639   Thu May 5 14:40:14 2011 KojiUpdateLSCMI locking : calibration of BS and ITMs actuators

I've got confused

1) Are these the DC responses of the coils? If that is true, we need to specify the resonant frequency of each suspension to get the AC response.

2) Are these the AC responses well above the resonant freqs? In that case, The responses should be x.xxx / f^2 [m/counts]

 Quote: The open loop transfer functions of the Michelson locking have been measured. The purpose of this excise is to calibrate the coil-magnet actuators on BS and ITMs. The estimated actuation coefficients are :  BS = 3.69e-08 [m/counts]  ITMX = 8.89e-09 [m/counts]  ITMY = 9.22e-09 [m/counts]

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.

10503   Fri Sep 12 15:10:09 2014 JenneUpdateASCMICH ASS

During the Sim meeting today, I added parts to the ASS model so that we can also dither the BS and minimize the power at AS.

ASS screen has been updated.

Model changes required a new sender from LSC for ASDC, so both LSC and ASS were compiled, installed and restarted.  Also on LSC, I added AS110 I&Q to DQ channels, since we haven't been recording them in the past.

I have done a quick trial in MICH-only lock, and it seems to work.  Gain of 10 for both Pit and Yaw servos.

12979   Wed May 10 01:56:06 2017 gautamUpdateGeneralMICH NB - OL coupling

### Last night, I tried to estimate the contribution of OL feedback signal to the MICH length error signal.

In order to do so, I took a swept sine measurement with a few points between 50 Hz and 500 Hz. The transfer function between C1:LSC-MICH_OUT_DQ and the Oplev Servo Output point (e.g. C1:SUS-BS_OL_PIT_OUT etc) was measured. I played around with the excitation amplitude till I got coherence > 0.9 for the TF measurement, while making sure I wasn't driving the Oplev error point too hard that side-lobes began to show up in the MICH control signal spectrum.

#### The Oplev control signal is not DQ-ed. So I locked the DRMI again and downloaded the 16k data "live" for ~5min stretch using cdsutils.getdata on the workstation. The Oplev error point is DQ-ed at 2k, but I found that the excitation amplitude needed for good SNR at the error point drove the servo to the limiter value of 2000cts - so I decided to use the control signal instead. Knowing the transfer function from the Oplev *_OUT* channel to C1:LSC-MICH_IN1_DQ, I backed out the coupling - the transfer function was only measured between 50 Hz and 500 Hz, and no extrapolation is done, so the estimation is only really valid in this range, which looks like where it is important anyways (see Attachment #2, contributions from ITMX, ITMY and BS PIT and YAW servos added in quadrature).

I was also looking at the Oplev servo shapes and noticed that they are different for the ITMs and the BS (Attachment #1). Specifically, for the ITM Oplevs, an "ELP15" is used to do the roll-off while an "ELP35" is employed in the BS servo (though an ELP35 also exists in the ITM Oplev filter banks). I got lost in an elog search for when these were tuned, but I guess the principles outlined in this elog still hold and can serve as a guideline for Oplev loop tweaking.

Coil driver noise estimation to follow

 Quote: I think the most important next two items to budget are the optical lever noise, and the coil driver noise. The coil driver noise is dominated at the moment by the DAC noise since we're operating with the dewhitening filters turned off.

GV 10 May 12:30pm: I've uploaded another copy of the NB (Attachment #3) with the contributions from the ITMs and BS separated. Looks like below 100Hz, the BS coupling dominates, while the hump/plateau around 350Hz is coming from ITMX.

Attachment 1: OL_BS_ITM_comp.pdf
Attachment 2: C1NB_disp_40m_MICH_NB_8_May_2017.pdf
Attachment 3: C1NB_disp_40m_MICH_NB_10_May_2017.pdf
12981   Wed May 10 16:53:38 2017 ranaUpdateGeneralMICH NB - OL coupling

That's a good find.

1. The OL control signal can be gotten from the DQ error signal. You just need to multiply it by the digital filters and the gain. The state of the filters and the gain can be gotten using matlab tools like getFotonFilt.m. For python ChrisW wrote a tool called foton.py which is in the GDS SVN. You should ask him for it. It requires access to some ROOT libraries to run.
2. We should have sub budgets for everything like OL and thermal, etc. They should be automatically produced each time you run the main budget and should be separate pages in the same PDF file. Jamie / Chris may have something going along these lines so check to see if they are already on it.
12974   Fri May 5 10:13:02 2017 ericqUpdateGeneralMICH NB questions
Is suspension thermal noise missing? I take it "Thermal" refers just to thermal things going on in the optic, since I don't see any peaks at the bounce/roll modes as I would expect from suspension thermal noise.

What goes into the GWINC calculation of seismic noise? Does it include real 40m ground motion data and our seismic stacks?

I'm surprised to see such a sharp corner in the "Dark Noise" trace, did you apply the OLG correction to a measured dark noise ASD? (The OLG correction only needs to be applied to the in-lock error signals to recover open loop behavior, there is no closed loop when you're measuring the dark noise so nothing to correct for.)
12975   Fri May 5 12:10:53 2017 gautamUpdateGeneralMICH NB questions

 Quote: Is suspension thermal noise missing? I take it "Thermal" refers just to thermal things going on in the optic, since I don't see any peaks at the bounce/roll modes as I would expect from suspension thermal noise. What goes into the GWINC calculation of seismic noise? Does it include real 40m ground motion data and our seismic stacks? I'm surprised to see such a sharp corner in the "Dark Noise" trace, did you apply the OLG correction to a measured dark noise ASD? (The OLG correction only needs to be applied to the in-lock error signals to recover open loop behavior, there is no closed loop when you're measuring the dark noise so nothing to correct for.)

I've included the suspension thermal noise in the "Thermal" trace, but I guess the GWINC file I've been using to generate this trace only computes the thermal noise for the displacement DoF. I think this paper has the formulas to account for them, I will look into including these.

For the seismic noise, I've just been using the seis40.mat file from the 40m SVN. I think it includes a model of our stacks, but I did not re-calculate anything with current seismometer spectra. In the NB I updated yesterday, however, I think I was off by a factor of sqrt(3) as I had only included the seismic noise from 1 suspended optic. I've corrected this in the attached plot.

For the dark noise, you are right, I had it grouped in the wrong dictionary in the code so it was applying the OLG inversion. I've fixed this in the attached plot.
Attachment 1: C1NB_disp_40m_MICH_NB_30_April_2017.pdf
12976   Sat May 6 21:52:11 2017 ranaUpdateGeneralMICH NB questions

I think the most important next two items to budget are the optical lever noise, and the coil driver noise. The coil driver noise is dominated at the moment by the DAC noise since we're operating with the dewhitening filters turned off.

13984   Mon Jun 18 19:47:02 2018 gautamUpdateGeneralMICH actuator calibration

Summary:

The actuator (pendulum) gains for the Beam Splitter and the two ITMs were measured to be:

BS: 9.54 +/- 0.05 nm/ct [100 ohm series resistor in coil driver board]

ITMX: 2.44 +/- 0.01 nm/ct [400 ohm series resistor in coil driver board]

ITMY: 2.44 +/- 0.02 nm/ct [400 ohm series resistor in coil driver board]

Counts here refers to DAC counts at the output of the coil filter banks (as opposed to counts at the LSC servo output). The dominant (systematic) uncertainty (which isn't quoted here) in this measurement is the determination of the peak-to-peak swing of the dark port sensor, AS55_Q. I estimate this error to be ~1ct/33cts = 3%. These values are surprisingly consistent with one another once we take into account the series resistance.

Details:

The last time this was done, we used ASDC to do the measurement. But I don't know what signal conditioning ASDC undergoes (in PD or in readout electronics). In any case, in my early trials yesterday, ASDC was behaving unpredictably. So I decided to do redo the measurement.

[Attachment #1]- Flowchart describing the calibration procedure.

[Attachment #2] - AS55_Q output while the Michelson was freeswinging. I had first aligned the ITMs using ASS. The peak-to-peak value of this corresponds to $\lambda/4$. So we know AS55_Q in terms of cts/m of MICH displacement.

[Attachment #3] - Magnitudes of transfer function from moving one of the MICH optics, to the now calibrated AS55_Q. Fits are to a shape $a/f^2$, with $a$ being the fitted parameter. Coherence during the measurement is also plotted.

• Note that the excitation is applied to the channels C1:SUS-<optic>_LSC_EXC, for <optic> in [BS, ITMX, ITMY]. But since my de-whitening board re-work to remove the analog x3 gain, there is a digital x3 gain in the coil driver filter banks. So while the calibration numbers given above are accurate, be aware that when using them for sensing matrix measurements etc, you have to multiply these by x3.
• Furthermore, moving the BS by $x$ results in a Michelson length change of $\sqrt{2}x$, and this has been factored into the above number.

Next Steps:

1. Now that I have a calibration I trust more, re-analyze my DRMI sensing matrix data. Actually the sensing response numbers aren't significantly different from what I have been assuming. It's just that in terms of counts applied at the LSC input of a suspension, there is a digital x3 gain that has to be explicitly factored in.
2. Calibrate POX and POY by locking the arms and driving the now calibrated ITMs by a known number of counts.
3. Calibrate the ETMs, and MC1/MC2/MC3 by looking at calibrated POX/POY.
4. Lock DRMI, and calibrate SRM and PRM.

Reference:

Attachment 1: AS55cal_process.pdf
Attachment 2: AS55cal.pdf
Attachment 3: MICH_act_calib.pdf
9317   Wed Oct 30 03:36:51 2013 JenneUpdateLSCMICH and PRCL UGFs change with ALS enabled

Masayuki was able to hold both arms off-resonance with ALS long enough for me to lock the PRMI (arms still held off resonance), and take a set of transfer functions.

MICH gain is still -2.0, PRCL gain is still 0.070, which, with the ETMs misaligned, gave me UGFs of 70 for MICH and 180 for PRCL.

Now, however, with the ETMs aligned, but arms held off resonance with ALS, the UGFs have been lowered by a factor of 2 in frequency!  What is doing this??  MICH is now 40 Hz, and PRCL is now 80 Hz.

We measured the MICH and PRCL loops for several arm powers, and there was no change, at least until the arms were both resonating with powers of ~4 .

After misaligning the ETMs, I remeasured the loops, and the UGFs went back up to where they started.

9314   Wed Oct 30 01:44:13 2013 JenneUpdateLSCMICH and PRCL gains adjusted (Config file saved)

 Quote: I am now taking transfer functions of the MICH and PRCL loops to make sure that we have the gains about right.

I have set the PRCL UGF to be about 180Hz, and the MICH UGF to be about 70 Hz.

This is with locking on REFL165 I&Q, with MICH gain of -2.0 and PRCL gain of 0.70 .

The PRCL loop only has about 30 degrees of phase margin, and is not near the top of its phase bubble.  During the day, I need to look at why we don't have more phase near 200 Hz.

6334   Tue Feb 28 16:39:25 2012 kiwamuUpdateLSCMICH and PRCL signals in a simulation

I briefly ran a Optickle code to see how the PRC macroscopic length screws up the sensing matrix in the PRMI configuration.

Especially I focused on the optimum demodulation phases for the MICH and PRCL signals to see how well they are separated in different PRC length configuration.

It seems that the demod phases for MICH and PRCL are always nicely separated by approximately 90 degree regardless of how long the PRC macroscopic length is.

If this is true, how can we have such a strange sensing matrix ??

(Simulation results)

The plots below show the simulation results. The x-axis is the macroscopic length of PRC in a range from 6.3 meter to 7.3 meter.
The y-axis is the optimum demodulation phases for MICH (blue) and PRCL (black).
The red line is the difference between the MICH and PRCL demodulation phases.
The left plot is for the REFL11 signals and the right plot is for the REFL55 signals.
When the difference is 90 degree, it means we can nicely separate the signals (i.e. REFL11I for PRCL and REFL11Q for MICH).
Obviously they are always nicely separated by ~ 90 deg.

 Quote from #6330 The lock of the PRMI doesn't look healthy, especially the sensing matrix doesn't make sense at all (#6283). A very staring thing in the sensing matrix is that the REFL11 and REFL55 didn't show the 90 degree separation between MICH and PRCL.

6335   Tue Feb 28 16:44:56 2012 ranaUpdateLSCMICH and PRCL signals in a simulation

### Like I said, this is possible if you fail to set up the OSA to look at the sidebands at BOTH the AS and REFL ports at all times. Don't waste your time - set up an OSA permanently!

9118   Mon Sep 9 20:46:28 2013 MasayukiUpdateLSCMICH calbration

[Manasa, Masayuki]

We took a bunch of measurements. Transfer function and power spectrum using DTT. They will be used to obtain calibrated MICH in-loop and free-running noise. Detail Elog with plots will follow very soon.

9121   Tue Sep 10 17:35:50 2013 Masayuki, ManasaUpdateLSCMICH calbration

 Quote: [Manasa, Masayuki] We took a bunch of measurements. Transfer function and power spectrum using DTT. They will be used to obtain calibrated MICH in-loop and free-running noise. Detail Elog with plots will follow very soon.

[Masayuki, Manasa]

Estimation of free-running MICH displacement noise:

Method 1. Assuming AS55_Q_err to be a linear sensor, as shown in (1) of figure below, free-running MICH noise (V_d) can be estimated by measuring V_err and the OLTF G. H can be estimated by using method explained in elog

Method 2. Considering that the AS55_Q signal might be distorted or saturated, method 1 may not be precise. In method 2, we will use the ASDC as the sensor (S' in (3)) instead and lock MICH using ASDC in mid-fringe to calibrate the ITM actuators.

Figure:1

Schematic:

What we did:

1. Estimate H' from free-running ASDC signal (bright to dark fringe).
2. With MICH locked on ASDC, give an excitation signal to C1:LSC-SUS_XXXX_EXC (XXXX could be ITMX or ITMY) and measure R'. [(3) of schematic]
3. Measure OLTF of MICH locked on ASDC (hence estimate L). [(3) of schematic]
4. With MICH locked on AS55_Q, give an excitation signal to C1:LSC-SUS_XXXX_EXC (XXXX could be ITMX or ITMY) and measure R1. [(2) of the schematic]

Results/Plots:

Figure:2

OLTF of MICH locked on ASDC

Figure2:

Actuator excitation to MICH transfer function (MICH locked using ASDC)

* y axis (no units)

Figure 3:
Actuator excitation to MICH transfer function (MICH locked using AS55Q)

* y axis (no units)

Figure 4:
Free-running MICH noise

Discussion:

1. By using the second sensor, we also eliminate the effect of the MICH servo loop locked on AS55_Q (Estimated V_d does not depend on G but only on G').

2. The free-running MICH noise is still suppressed at 1Hz. This should be coming from the effect of the UGF of the loop at ~10Hz and the vicinity to the pendulum frequency at 1Hz.

Edit/Masayuki// This noise curve is not collect, especially in low frequency region. We used the measured OLTF for compensating the free running noise, but that is not collect in low frequency region. So we should model the OLTF and fit that into the measured OLTF. We will fix this soon.

9127   Thu Sep 12 23:36:25 2013 MasayukiUpdateLSCMICH calbration

For Modelling of the OLTF, I measured the response of the BS suspension. I used the OSEM sensor for measurement. The attatchment1 is the measured TF from C1:SUS-BS_LSC_EXC to C1:SUS-BS_SUSPOS_IN1 with exciting with random force. The measured data was fitted and the resonant frequency is 1.029(±0.005) Hz and quality factor is 12.25 (± 0.2).  Additionally I did same measurement for ITMX and ITMY. The attachment 2 and 3 are the results for ITMX and ITMY. Each eigenfrequency and Q are 1.063 (±0.008) Hz and 7.33 (±0.13) (ITMX), 1.022 (±0.005) Hz and 9.41 (±0.09) (ITMY).

After that, I locked the MICH with AS55, and measured the PSD of error signal. I compensated the that PSD by the modelled OLTF with this suspension TF and the servo TF. The result is in attachment 4. Above 1 Hz it is quite close to the previous data by Keiko (elog#6385) But below 1 Hz there is a large dip. The error signal has also this dip. I looked for a integral filter between 0.2 Hz and 1 Hz, but I connot find a such filter. And when I locked MICH with using ASDC, there was same dip at same frequency. I don't think it's true free running noise, and I will try to fix it.

I completely forgot to mention that I fitted the modelled OLTF into the measured OLTF. I used the fitted OLTF for compensation.

Attachment 1: BSsus.PNG
Attachment 2: ITMXsus.PNG
Attachment 3: ITMY.PNG
Attachment 4: free_running.PNG
9128   Fri Sep 13 19:22:01 2013 MasayukiUpdateLSCMICH calbration

I made sure the yesterday's result was collect. I measured not only the error signal but also the feedback signal. And I compared those signals and measured the TF in order to confirm my servo filter model is not wrong.

The reason of dip at low frequency region is maybe the coherence of the ground motion. The ITMX and ITMY suspensions are put close. If ground motion has coherence, the mirrors move in common mode. That will suppress the free running noise. The attachment is the free running noise of Sep 13rd and Sep 12nd.

Attachment 1: noise.PNG
9131   Mon Sep 16 14:11:47 2013 ranaUpdateLSCMICH calbration

There doesn't seem to be any coherence among the different directions of ground motion (as expected from seismic theory), so I am suspicious of such a low MICH noise.

Attachment 1: Screen_Shot_2013-09-16_at_2.10.31_PM.png
Attachment 2: Screen_Shot_2013-09-16_at_2.18.47_PM.png
9134   Tue Sep 17 00:50:42 2013 MasayukiUpdateLSCMICH calbration

I found the bug in my calibration code, and I fixed it.

And I put the white Gaussian noise on the BS actuator, and calibrated to the differential length with my new code. We already know the efficiency of the actuator(elog#8242), so I could estimate how much I put the disturbance and compare the two values. The result is in attachment 1.  x_exc means the value of the disturbance.

You can see the PSD of the differential motion decrease factor of 3 by decreasing the disturbance by factor of 3 (except for the region from 1 Hz to 5 Hz), and the value at lower frequency than resonant frequency of the suspension is comparable to the value estimated with the actuator efficiency. Also there is no dip when I put the larger disturbance than free running noise.

Between 1 Hz and 5 Hz there seems to be a resonance of something (seismic stack?). And also on resonance of the suspension there seems to be some other noise source. One possibility is the active damping of each suspension.

Actually still there seems to be a dip between 0.1 Hz and 1 Hz. But if you consider about those effect, I think this result doesn't seems to be so strange. But according to the documentation of LIGO document-T000058, which I found the seismic motion in 40 m Lab is written in, the seismic motion at 0.1 Hz is 10^-7. I'm not sure about this factor of 10 difference. One possibility is the geophone doesn't have good sensitivity at low frequency. I'm still not sure this result is really collect.

Attachment 1: noise.PNG
6362   Tue Mar 6 01:35:03 2012 kiwamuUpdateLSCMICH characterization

[Keiko / Kiwamu]

Update on the MICH characterization:

• The OSAs weren't so great because the 11 MHz sidebands were covered by the carrier's tail
• It seemed that the frequency resolution depended on the mode matching. We will try improving the mode matching tomorrow.
• The noise budget looked very bad
• There were huge peaks at 1 Hz, 3 Hz, 16.5 Hz and 23 Hz. Something is crazy in the vertex suspensions.
• Keiko will post the calibrated noise budget.
• The MICH response at AS55Q was measured and we will calibrate it into watts / meter.

10803   Tue Dec 16 01:50:27 2014 rana, diegoFrogsLSCMICH filter is nuts

This is ridiculous.

How many RGs can I fit into one button???

9293   Fri Oct 25 20:11:08 2013 JenneUpdateLSCMICH gain in PRMI lowered by factor of 2

We were locking the PRMI, but it is very rumbly today.  I reduced the MICH servo gain from -0.8 to -0.4 , and things seem to be better.  Now my MICH UGF is about 60Hz.

9809   Mon Apr 14 19:02:09 2014 JenneUpdateLSCMICH gets noisy as CARM or DARM offset reduced

This afternoon, I was toying around with reducing either the CARM or DARM offsets (so, put in a CARM offset, leave DARM zero, lock the PRMI, then reduce CARM offset to zero.  Or, put in a DARM offset, leaving CARM offset zero, lock the PRMI, then reduce the DARM offset to zero).

When looking at the data, I see that the MICH error signal gets fuzzier when the arms get close to resonance. (Note here that because I forgot to zero the carm offset before finding the resonances, -3 is my zero point for this plot and the next.)

Here is a zoom of the last piece of this time series, but with both TRX and TRY plotted (along with POPDC, CARM_ERR and DARM_ERR), where you can see that I had a momentary power buildup of > 100 transmission counts, which is about 20% of our final expected power.

Here is a different time series, showing a reduction of the DARM offset, and you can see that as the offset approaches zero, the MICH error signal gets noticeably more fuzzy.  Somewhere near the 240 second mark, I lose PRMI lock.

9813   Tue Apr 15 09:32:19 2014 GabrieleUpdateLSCMICH gets noisy as CARM or DARM offset reduced

I guess this is normal. DARM has (almost) the same effect of MICH on the corner interferometer signals, just increased in amplitude by the arm cavity amplification. When the arm is out of resonance, DARM is almost completely depressed and it is not affecting MICH at all. On the other hand, when the cavities are exactly at resonance, DARM signal is amplified w.r.t. MICH by the cavity gain (2F/pi).

Since DARM is still controlled with ALS, it is probably noisy. The closer to resonance you move the cavities, the more ALS noise in DARM will affect MICH.

 Quote: When looking at the data, I see that the MICH error signal gets fuzzier when the arms get close to resonance. (Note here that because I forgot to zero the carm offset before finding the resonances, -3 is my zero point for this plot and the next.)

5413   Thu Sep 15 01:17:10 2011 KeikoUpdateLSCMICH locked and attempt to lock PRCL

Anamaria, Keiko

- We aligned MICH and were successfully locked MICH using AS55Q. The other mirrors were misaligned so that the other degrees of freedom didn't exist. AS55 was fed back to BS. The f2a filters on BS suspension were required to lock, because the pos feedback was unbalanced to angle degrees of freedom.

- We tried to lock PRCL next, however, because we aligned the MICH and the REFL beam paths were changed, REFL PDs didn't have the light anymore. The REFL paths were modified now, so we will try the PRCL locking next.

- We couldn't confirm REFL55 signals although we alined the REFL paths to REFL55 PD.

5414   Thu Sep 15 02:18:19 2011 AnamariaUpdateLSCMICH locked and attempt to lock PRCL

Kiwamu, Keiko, Anamaria

We were able to lock PRC using REFL11I after improving the MICH dark fringe a bit (moving BS) and rotating AS55 and REFL11 such that the signal was maximized in the phases we were using. The dark port is not so dark... but the lock is stable.

I had finished the whole REFL path alignment, but I didn't have a good input beam reference at the time, which is why we had to realign the PDs and the camera. We only had strength to realign 11 and 55. Otherwise, we just need to tweak and center beam on 33 and 165, figure out what's up with 55 and be done with the AP table mods. I hope.

 Quote: Anamaria, Keiko - We aligned MICH and were successfully locked MICH using AS55Q. The other mirrors were misaligned so that the other degrees of freedom didn't exist. AS55 was fed back to BS. The f2a filters on BS suspension were required to lock, because the pos feedback was unbalanced to angle degrees of freedom. - We tried to lock PRCL next, however, because we aligned the MICH and the REFL beam paths were changed, REFL PDs didn't have the light anymore. The REFL paths were modified now, so we will try the PRCL locking next. - We couldn't confirm REFL55 signals although we alined the REFL paths to REFL55 PD.

9082   Wed Aug 28 07:33:51 2013 manasaUpdateLSCMICH locking

I wanted to measure the OLTF of MICH.

What I did:
1. Ran LSC offsets script to zero all the offsets.

2. Restored the IFO configure settings for locking Michelson (locked on AS55Q).

3. MICH wouldn't lock on these settings.

4. The MICH servo was hitting its limits (10000 counts). I checked the filter module. After a little bit of looking into things, I disabled FM3 (0,0:5,5), FM4 (1:10) and FM7 (1:5). FM3 and FM7 were filter modules that were switched ON at the trigger. I set these to manual. Enabling any of the filters (FM3, FM4, FM7) caused MICH to lose lock.

5. MICH gain was changed from -20 to -30. MICH locked with ASDC suppressed to 0.01 counts. I looked at the power spectrum of C1:LSC-MICH_OUT on dtt. //edit: Manasa// The plot (uncalibrated) now shows MICH_OUT power spectrum with MICH PSL shutter closed, free-running MICH and loop-enabled MICH.

6. I then wanted to measure the OLTF of MICH using dtt. A channels were set to C1:LSC-MICH_IN1/C1:LSC-MICH_IN2 and excitation given through C1:LSC-MICH_EXC. But I have not been able to get any good coherence for the measurement as yet.

Attachment 1: MICH.pdf
16228   Tue Jun 29 17:42:06 2021 Anchal, Paco, GautamSummaryLSCMICH locking tutorial with Gautam

Today we went through LSC locking mechanics with Gautam and as a "Hello World" example, worked on locking michelson cavity.

### MICH settings changed:

• Gautam at some point added 9 dB attenuation filters in MICH filter module in LSC to match the 9 dB pre-amplifier before digitization.
• This required changing teh trigger thresholds, C1:LSC-MICH_TRIG_THRESH_ON and C1:LSC-MICH_TRIG_THRESH_OFF.
• We looked at C1:LSC-AS55_Q_ERR_DQ and C1:LSC-ASDC_OUT_DQ on ndscope.
• The zero crossings in AS55_Q correspond to ASDC going to zero. We found the threshold values of ASDC by finding the linear region in zero crossing of AS55_Q.
• We changed the thresold values to UP: -0.3mW and DOWN -0.05mW. The thresholds were also changed in C1LSC_FM_TRIG.
• We also set FM2,3,6 and 8 to be triggered on threshold.

We characterized the loop OLTF, found the UGF to be 90 Hz and measured the noise at error and control points.

gautam: one aim of this work was to demonstrate that the "Lock Michelson (dark)" script call from the IFOconfigure screen worked - it did, reliably, after the setting changes mentioned above.

15000   Wed Oct 30 11:53:41 2019 gautamUpdateLSCMICH loop shape tuning

I changed the shape of the low pass filter to reduce high frequency sensor noise injection into the MICH control signal. The loop stability isn't adversely affected (lost ~5 degrees of phase margin but still have ~50 degrees), while the control signal RMS is reduced by ~x10. This test was done with the PRMI locked on the carrier, need to confirm that this works with the arms controlled on ALS and PRMI lcoked on sideband.

Attachment 1: MICH_ELP.pdf
Attachment 2: MICH_ELP_TFs.pdf
1330   Fri Feb 20 19:31:16 2009 YoichiUpdateLSCMICH low gain problem
Last night, we found that MICH UGF was too low. Even after re-aligning the PDs, it was still too low.
Today, I compared the UGFs of MICH and PRC when in the DRMI configuration locked with the single demod. signals.
In this configuration, MICH signal comes from REFL33Q and the PRC signal comes from REFL33I (the same PD).
The PRC UGF was about 100Hz whereas MICH was only ~10Hz.
Since they uses the same PD, the low gain is not caused by the PD.
I checked conlog history and confirmed there is no change in the MICH->BS path in the last few days.
I also checked the svn history of chans directory for changes in filters. Nothing problematic found.

Then I noticed that the susvme computers were overloaded.
This time, I rebooted all the FE computers just in case.

Then the MICH gain was somewhat recovered (by a factor of 3 or so). Don't know why.

I adjusted the DD_handoff script to set the MICH gain to 0.7 before the bounce-roll filter is engaged.
6368   Tue Mar 6 23:37:31 2012 keikoUpdateSUSMICH noise budget - SUS check

Here are the OSEM spectrum of MICH suspensions (BS, IX, IY). Bounce and Roll modes are shown on 16 and 23 Hz. The filters for them has been checked.

keiko, kiwamu, Rana

Attachment 1: Mar6sus1
Attachment 2: Mar6sus2
Attachment 3: Mar6sus3
6376   Wed Mar 7 17:39:40 2012 keikoUpdateLSCMICH noise budget on 5 Mar

This is the calibrated MICH noise budget on Mar 5. There was a sharp peak at 1Hz and a blob on 3 Hz. The demod phase was adjusted for AS55Q.

Attachment 1: Mar5-MICHbudget.png
6380   Wed Mar 7 20:53:13 2012 keikoUpdateLSCMICH noise budget on 5 Mar

This is the MICH noise budget on 6th March. 1Hz peak got a bit better as the BS sus control gain was increased.

6385   Thu Mar 8 00:57:48 2012 keikoUpdateLSCMICH noise budget on Mar 5, Mar 6, and old

Here is the recent two noise budgets of MICH, with the old measurement by Jenne. The most latest Mar 6 data is quite close to the old data, even better around 20-30 Hz. Probably some scattering source was improved?

4822   Wed Jun 15 02:20:00 2011 JenneUpdateLockingMICH noise budget?

I would like to announce my confusion with regard to the MICH noise budget, in hopes that someone else has some inspiration

If you tilt your head sideways, you will notice that in this plot (totally uncalibrated, as yet), the BLACK trace, which is my white-light measurement of the AS55 shot noise is above the AS55Q noise when the Michelson is locked (true only at low frequency).  You will also notice that the same appears to be true for the Whitening Filter + Antialiasing Filter + ADC noise (GRAY trace).  Since Black, Gray, Pink and Green should all have the same calibration factor (a constant), calibrating the plot will not change this.  Brown and Blue are the MICH_OUT (aka MICH_CTRL) for dark and bright fringes, respectively.

I measure 58mV at the DC out of the AS55 PD when the Michelson is locked on the bright fringe.  This (assuming DC transimpedance of 50ohms) gives 1.16mA of DC photo current.

So.  What is going on here?  Am I totally confused??

In other news, assuming (which I'm not 100% confident about right now) that these traces are vaguely correct, the Michelson is limited by shot noise above ~20Hz.  This is...good?  We want to be shot noise limited.  Do we want to be limited at such a low frequency?

(Also, yes I can calibrate the plot to m/rtHz, but no, I won't tonight because something is funny with my calibration for the free running noise and I'll fix it tomorrow.)

4823   Wed Jun 15 12:16:37 2011 JamieUpdateLockingMICH noise budget?

 Quote If you tilt your head sideways, you will notice that in this plot (totally uncalibrated, as yet), the BLACK trace, which is my white-light measurement of the AS55 shot noise is above the AS55Q noise when the Michelson is locked (true only at low frequency).  You will also notice that the same appears to be true for the Whitening Filter + Antialiasing Filter + ADC noise (GRAY trace).  Since Black, Gray, Pink and Green should all have the same calibration factor (a constant), calibrating the plot will not change this.  Brown and Blue are the MICH_OUT (aka MICH_CTRL) for dark and bright fringes, respectively.

Hey, Jenne.  I think there are a couple of things.  First, you're missing a PD dark noise measurement, which would be useful to see.

But I think the main issue is that it sounds like all of your closed loop measurements are done with the in-loop PD.  This means that everything will be suppressed by the loop gain, which will make things look like they have a noise lower than the actual noise floor.

9478   Mon Dec 16 02:20:49 2013 DenUpdateLSCMICH rms is improved

When PRMI is locked on REFL 165 I&Q signals MICH rms is dominated by the 60 Hz line and harmonics. It comes from demodulation board.

To increase SNR ZFL-100 LN amplifier (+23.5dB) was installed in LSC analog rack. MICH 60 Hz and harmonics are improved as shown on the plot "mich_err"

I have also added a few resg at low frequencies. MICH rms is not 3*10-10. In Optickle I simulated power dependence in PRC and ARMs on MICH motion. Plot is attached.

I think we need to stabilize MICH even more, down to ~3*10-11 . We can think about increasing RF amplifier gain, modulation index and power on BB PD.

CARM offset reduction was a little better today due to improved MICH RMS. Power in arms increases up to 15 and than starts to oscillate up to 70 and then PRMI looses lock.

Tomorrow we need to discuss where to put RF amplifier. Current design has several drawbacks:

• DC power for the amplifier is wired from a custom (not rack based) +15V power supply that was already inside the lsc rack and used for other ZFL-100LN
• BNC cables are used because I could not find any long SMA cables
• we would like gain of ~40 dB instead of 23.5 dB
Attachment 1: MICH_ERR.pdf
Attachment 2: DC_power.pdf
Attachment 3: ARM_OFFSET.pdf
9767   Mon Mar 31 17:47:57 2014 ericqSummaryLSCMICH sensing oddities in REFL 3F

Last week, while I had the PRMI locked on REFL33, I did some poking around with mirror excitation to RFPD quadrature transfer functions. I got some indication of weird things with sensing MICH with the 3F REFL signals, but it should be explored more before taken as a real thing. I just figured I would show what I saw.

With that disclaimer out of the way, here's what I did:

• Locked PRMI on PRCL:REFL33_I and MICH:REFL33_Q, as detailed in my earlier ELOG
• Created PRCL and MICH excitations at two different frequencies, notched said frequencies out of the control filters
• Took transfer functions from mirror LSC output signals to 33 I, 33 Q, 165 I, 165 Q in DTT
• For each DOF, look at the measured transfer functions only at the excitation frequency. (Assuming good coherence, which was there)

The basic idea was, some PRCL motion (for instance), has a transfer function to both the I and Q quadratures at a given PD. As the PRCL excitation sine wave goes through one cycle, the REFL signals at the excitation frequency go through some coherent cycle. Thus, the excitation traces out some trajectory in the I vs. Q plane. I believe this is analogous to the typical "radar plot" that we make for sensing matrix elements.

However, the straight line that we normally plot in the radar plots assumes a certain phase relationship between the DOF-> I and DOF->Q transfer functions that results in a straight line. Here are the trajectories I actually measured, normalized by the excitation amplitudes.

The plotted traces are (x,y) = (H_prcl->I * prcl, H_prcl->Q * prcl) and  (x,y) = (H_mich->I * mich, H_mich->Q * mich) where H_prcl->I is the measured complex transfer function from prcl to REFL I, for instance, and prcl and mich are the excitation signals, normalized to unit amplitude.

PRCL looks like a nice straight line in both of these, and pretty well phased, but not only is MICH not very orthogonal to PRCL, there is quite a bit of ellipticity present, which means we can't fully decouple the two DOFs, even if they were nominally orthogonal.

I'm not sure what may cause this. To back up this measurement/interpretation, I tried to take measurements of these transfer functions across different excitation frequencies via swept sine DTT, but seismic activity kept me from staying locked long enough...

9768   Mon Mar 31 21:23:30 2014 GabrieleSummaryLSCMICH sensing oddities in REFL 3F

 I'm not sure what may cause this. To back up this measurement/interpretation, I tried to take measurements of these transfer functions across different excitation frequencies via swept sine DTT, but seismic activity kept me from staying locked long enough...

I guess that you get an ellipse when the transfer functions to I and Q have a different phase. One mechanism could be that when driving MICH we make some residual PRCL and this couples with a different transfer function to both I and Q. However, I would expect no phase lag in the PRMI configuration, since there is no enough optical delay in the system to give significant dephasing at few hundreds Hz. This effect might come from mechanical resonances.

It is worth measuring the optical transfer functions from both PRCL and MICH to REFL signals at all frequencies, to see if we have strange features in the TFs.

13395   Thu Oct 19 15:42:03 2017 jamieSummaryLSCMICH/PRCL reconstruction neural network running on c1lsc

Gabriele's PRCL/MICH reconstruction neural network is now running on c1lsc.  Summary:

• front-end model is called c1dnn, and is running as an experimental user-space process
• c1dnn is getting most of it's needed inputs from existing SHMEM IPC outputs from c1lsc
• none of the output signals from the network are being sent anywhere yet (grounded)
• c1dnn has not been integrated in any way, into the DAQ etc.  it is being run manually by hand, and will be completely shut down after this test

Simple MEDM screen I made to monitor the input/output signals:

The RTS process seems to run fine, but there is quite a bit of jitter in the CPU_METER, at the 50% level:

It's not running over the limit, but it is jumping around more than I think it should be.  Will look into that...

## cpuset for cpu isolation for user-space model

The c1dnn model is running on CPU6 on c1lsc.  CPU6 was isolated from the rest of the system using cpuset.  The "cset" utility was used to create a "system" CPU set that was assigned to CPU0, and the kernel was instructed to move all running processes to that set:

controls@c1lsc:~ 2$sudo cset set cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0,6 y 0 y 343 0 / controls@c1lsc:~ 0$ sudo cset set -c 0 -s system --cpu_exclusive
cset: --> created cpuset "system"
controls@c1lsc:~ 0$sudo cset set cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0,6 y 0 y 342 1 / system 0 y 0 n 0 0 /system controls@c1lsc:~ 0$ sudo cset proc --move -f root -t system -k
cset: moving all tasks from root to /system
cset: moving 292 userspace tasks to /system
cset: moving 0 kernel threads to: /system
cset: --> not moving 50 threads (not unbound, use --force)
[==================================================]%
cset: done
controls@c1lsc:~ 0$sudo cset set cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0,6 y 0 y 50 1 / system 0 y 0 n 292 0 /system controls@c1lsc:~ 0$ sudo cset proc --move -f root -t system -k --force
cset: moving all tasks from root to /system
cset: moving 50 kernel threads to: /system
[==================================================]%
cset: **> 29 tasks are not movable, impossible to move
cset: done
controls@c1lsc:~ 0$sudo cset set cset: Name CPUs-X MEMs-X Tasks Subs Path ------------ ---------- - ------- - ----- ---- ---------- root 0,6 y 0 y 29 1 / system 0 y 0 n 313 0 /system controls@c1lsc:~ 0$

I then created a set for the RTS process ("rts-c1dnn") on CPU6, and executed the c1dnn model in that set:

controls@c1lsc:~ 0$sudo cset set -c 6 -s rts-c1dnn --cpu_exclusive cset: --> created cpuset "rts-c1dnn" controls@c1lsc:~ 0$ sudo cset set
cset:
Name       CPUs-X    MEMs-X Tasks Subs Path
------------ ---------- - ------- - ----- ---- ----------
root        0,6 y       0 y    24    2 /
rts-c1dnn          6 y       0 n     0    0 /rts-c1dnn
system          0 y       0 n   340    0 /system
controls@c1lsc:~ 0\$ sudo cset proc -s rts-c1dnn --exec /opt/rtcds/caltech/c1/target/c1dnn/bin/c1dnn -- -m c1dnn
cset: --> last message, executed args into cpuset "/rts-c1dnn", new pid is: 27572
sysname = c1dnn
....

When done I just hit Ctrl-C.

I left the cpusets as they are, with all system processes in the "system" set.  This should not pose any problems since it's the identical configuration as would be if a normal kernel-level model was running in CPU6.

The c1dnn process and it's EPICS sequencer were shutdown after this test.

8816   Tue Jul 9 23:27:17 2013 KojiSummaryLSCMICH: ITMX/Y <=> PRM/BS

The MICH actuation with PRM/BS was investigated again.

(ITMX -1 / ITMY +1) is equivalent to (PRM -0.267 and BS +0.50).

- PRMIsb was locked with REFL33I&AS55Q.

- Using the locking module in the LSC model, actuate ITMX (-1) and ITMY (+1) at 580.1Hz. Note that the notch filters in the MICH/PRCL servos were on.

- Look at the peak in the AS55Q spectrum. Tune the BS element in the output matrix of the lock-in to minimize the peak height.
=> The peak was minimized at BS = -0.50.

- Look at the peak in the REFL33I spectrum. Tune the PRM element in the output matrix of the lock-in to minimize the peak height.
=> The peak was minimized at PRM = +0.267

- These measurement leads to the conclusion mentioned above.

8490   Thu Apr 25 04:10:09 2013 JenneUpdateLockingMICH_CTRL drifting away??

Koji is elogging separately of his exploration of different configurations.  The lock stretch that I'm looking at here uses the same parameters as Koji had for PRMI sb lock, using AS55Q for MICH and REFL33I for PRCL, with MICH gain of -0.8 and PRCL gain of 0.05 .

All of these plots are the same few second lock stretch, with different zooming.  Jamie's super-sweet getdata python script only accepts integers for the start time and duration parameters, so lots of this zooming happened by hand, but I tried to always keep the time axis aligned within each screenshot.  Sometimes the plot axis labels say differently, but they're lying to you.

Plot 1:  gps start time is 1050915916, duration = 6 seconds.  Overall view of the lock stretch.

Plot 2:  gps start time is 1050915921, duration = 1 second.  We're looking at the lockloss that happens at the left side of the plots.

Plot 3:  zoomed in (along the time-axis) version of plot 2, so much shorter time duration.  Some zooming on y-axes.

Plot 4:  zoomed in (along y-axes) version of plot 2.

It seems to me from these plots that maybe MICH CTRL is drifting away?  It seems like we lose the MICH lock, and that destroys the whole thing.

Koji made some comments to me earlier, regarding his work this evening, that the MICH signal quality is poor in general, and that we should calculate/think about changing our schnupp asymmetry.

11499   Wed Aug 12 16:39:46 2015 IgnacioUpdateIOOMISO WIener (T240-X and T240-Y) FF of MCL

Last night I performed some MISO FF on MCL using the T240-X and T240-Y as witnesses. Here are the results:

Filter:

T240-X

T240-Y

Training data + Predicted FIR and IIR subtraction:

Online subtraction results:

MCL
YARM

Subtraction performace:

Attachment 1: stsx.png
Attachment 2: stsy.png
Attachment 3: performance.png
Attachment 4: sub.png
Attachment 5: mcliir.png
Attachment 6: yarmiir.png
11547   Sun Aug 30 23:47:02 2015 IgnacioUpdateIOOMISO Wiener Filtering of MCL

I decided to give MISO Wiener filtering a try again. This time around I managed to get working filters. The overall performance of these MISO filters is much better than the SISO I constructed on elog:11541 .

The procedure I used to develope the SISO filters did not work well for the construction of these MISO filters. I found a way, even more systematic than what I had before to work around Vectfit's annoyances and get the filters in working condition. I'll explain it in another eLOG post.

Anyways, here are the MISO filters for MCL using the T240-X and T240-Y as witnesses:

Now the theoretical offline prediction:

The online subtractions for MCL, YARM and XARM. I show the SISO subtraction for reference.

And the subtraction performance:

11549   Mon Aug 31 09:36:05 2015 IgnacioUpdateIOOMISO Wiener Filtering of MCL

MISO Wiener filters for MCL kept the mode cleaner locked for a good 8+ hours.

15363   Tue Jun 2 14:05:24 2020 HangUpdateBHDMM telescope actuation range requirments

We computed the required actuation range for the telescope design in elog:15357. The result is summarized in the table below. Here we assume we misalign an IFO mirror by 1 urad, and then compute how many urad do we need to move the (AS1, AS4) or (LO1, LO2) mirrors to simultaneously correct for the two gouy phases.

 [urad/urad] ITMX ITMY ETMX ETMY BS PRM PR2 PR3 SR3 SRM AS1 1.9 2.1 -5.0 -5.5 0.5 0.5 -0.3 0.2 0.1 0.6 AS4 2.9 2.0 -8.8 -5.5 -5.9 -0.7 1.3 -0.7 -0.5 0.7 LO1 -4.0 -3.9 11.0 10.4 1.9 -0.4 -0.2 0.1 0.0 -1.1 LO2 -5.0 -3.7 15.1 10.4 8.7 0.8 1.9 1.1 0.7 -1.3

The most demanding ifo mirrors are the ETMs and the BS, for every 1 urad misalignment the telescope needs to move 10-15 urad to correct for that. However, it is unlikely for those mirrors to move more 100 nrad for a locked ifo with ASC engaged. Thus a few urad actuation should be sufficient. For the recycling mirrors, every 1 urad misalignment also requires ~ 1 urad actuation.

As a result, if we could afford 10 urad actuation range for each telescope suspension, then the gouy phase separations we have should be fine.

================================================================

Edits:

We looked at the oplev spectra from gps 1274418500 for 512 sec. This should be a period when the ifo was locked in the PRFPMI state according to elog:15348. We just focused on the yaw data for now. Please see the attached plots. The solid traces are for the ASD, and the dotted ones are the cumulative rms. The total rms for each mirror is also shown in the legend.

I am now confused... The ITMs looked somewhat reasonable in that at least the < 1 Hz motion was suppressed. The total rms is ~ 0.1 urad, which was what I would expect naively (~ x100 times worse than aLIGO).

There seems to be no low-freq suppression on the ETMs though... Is there no arm ASC at the moment???

Attachment 1: TM_OL_spec_1274418500_512.pdf
Attachment 2: CORNER_OL_spec_1274418500_512.pdf
15386   Tue Jun 9 14:55:43 2020 JonUpdateBHDMM telescope actuation range requirments

I don't think we ever discussed why the angular RMS of the ETMs is so much higher than the ITMs. Maybe that's a separate matter because, even assuming the worst case, the actuation range requirement is

which is still only order 1% of the pitch/yaw pointing range of the Small Optic Suspensions, according to P1600178 (sec. IV. A). Can we check this requirement off the list?

Quote:

We computed the required actuation range for the telescope design in elog:15357. The result is summarized in the table below. Here we assume we misalign an IFO mirror by 1 urad, and then compute how many urad do we need to move the (AS1, AS4) or (LO1, LO2) mirrors to simultaneously correct for the two gouy phases.

 [urad/urad] ITMX ITMY ETMX ETMY BS PRM PR2 PR3 SR3 SRM AS1 1.9 2.1 -5.0 -5.5 0.5 0.5 -0.3 0.2 0.1 0.6 AS4 2.9 2.0 -8.8 -5.5 -5.9 -0.7 1.3 -0.7 -0.5 0.7 LO1 -4.0 -3.9 11.0 10.4 1.9 -0.4 -0.2 0.1 0.0 -1.1 LO2 -5.0 -3.7 15.1 10.4 8.7 0.8 1.9 1.1 0.7 -1.3

The most demanding ifo mirrors are the ETMs and the BS, for every 1 urad misalignment the telescope needs to move 10-15 urad to correct for that. However, it is unlikely for those mirrors to move more 100 nrad for a locked ifo with ASC engaged. Thus a few urad actuation should be sufficient. For the recycling mirrors, every 1 urad misalignment also requires ~ 1 urad actuation.

As a result, if we could afford 10 urad actuation range for each telescope suspension, then the gouy phase separations we have should be fine.

================================================================

Edits:

We looked at the oplev spectra from gps 1274418500 for 512 sec. This should be a period when the ifo was locked in the PRFPMI state according to elog:15348. We just focused on the yaw data for now. Please see the attached plots. The solid traces are for the ASD, and the dotted ones are the cumulative rms. The total rms for each mirror is also shown in the legend.

I am now confused... The ITMs looked somewhat reasonable in that at least the < 1 Hz motion was suppressed. The total rms is ~ 0.1 urad, which was what I would expect naively (~ x100 times worse than aLIGO).

There seems to be no low-freq suppression on the ETMs though... Is there no arm ASC at the moment???

8084   Thu Feb 14 10:42:41 2013 JamieSummaryAlignmentMMT, curved TTs does not explain beam ellipticity at Faraday

After using alamode to calculate the round-trip mode of the beam at the Faraday exit after retro-reflection form the PRM, I'm not able to blame the MMT and TT curvature for the beam ellipticity.

I assume an input waist at the mode cleaner of [0.00159, 0.00151] (in [T, S]).  Propagating this through the MMT to PRM, then retro-reflecting back with flat TTs I get

w_t/w_s = 0.9955,  e = 0.0045

If I give the TTs a -600 m curvature, I get:

w_t/w_s = 1.0419,  e = 0.0402

That's just a 4% ellipticity, which is certainly less than we see.  I would have to crank up the TT curvature to -100m or so to see an ellipticity of 20%.  We're seeing something that looks bigger than 50% to me.

Below are beam size through MMT + PRM retro-reflection, TT RoC = -600m:

3578   Wed Sep 15 16:12:35 2010 koji, steveUpdateMOPAMOPA Controller is taken out of the PSL rack

We removed the Lightwave MOPA Controller, PA#102, NPRO206 power supply to make room for the IOO chassy at 1X1 (south) rack.

The umbilical cord was a real pain to take out. It is shading its plastic cover. The unused Minco was disconnected and removed.

The ref. cavity ion pump controller- power supply was temporarily taken out also.

Attachment 1: P1060843.JPG
663   Sun Jul 13 17:19:29 2008 ranaSummaryPSLMOPA SLOWM Calibration
John, Rana

We first unlocked the FSS and ramped the SLOW actuator. With the PMC locked we observed the PMC PZT voltage
as a function of SLOWM (SLOW loop actuator voltage). We believed this to be ~1-5 GHz / V. Since this is
not so precise we then ran a slow (2 min. period) triangle wave into the slow actuator and looked at the
ref cav transmission peaks to calibrate it.

Plot is attached>

We assume that the reference cavity length = 203.2 mm then the FSR = 737.7 MHz. So looking at the plot
and using our eye to measure the SLOWM calibration is 1054 +/- 30 MHz/V. This is probably dominated by
our eye method.

Note: we tried to get the length from T010159-00-R (Michele, Weinstein, Dugolini). In that doc,
the length used is 203.3 mm whereas its 203.2 mm in the PSL FDD (?). The calculation of the FSR is also
incorrect (looks like they used c = 299460900 instead of 299792458 m/s). We took the length from the PSL FDD
(T990025-00-D) but not the FSR, since they also did not find the right value of 'c'. I guess that the speed
of light just ain't what it used to be.
Attachment 1: SLOWDCcalibration.png
ELOG V3.1.3-