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ID Date Author Type Category Subjectdown
  5070   Sat Jul 30 10:03:32 2011 JennyUpdateComputer Scripts / ProgramsMode matching

I ended up having to switch to a different mode-matching solution, because I was unable to find the f = 572.7 mm lens. See my next elog entry (5069).

  2452   Sat Dec 26 19:22:13 2009 KojiSummaryGeneralMode coupling of two astigmatic beams

In this note, amplitude and power couplings of two astigmatic (0,0)-th order gaussian modes are calculated.

Attachment 1: mode_coupling.pdf
mode_coupling.pdf mode_coupling.pdf
  5949   Fri Nov 18 15:45:11 2011 MirkoUpdateIOOMode cleaner noise projection

[Rana, Den, Mirko]

Updated the MC noise projection to include the longitudinal motion of the MC mirrors.

WholeMCNoiseProjection.png

=> Lots of OSEM - local dampling noise!

Consistent with static wiener filter showing only benefits in the 1 - 4Hz region.

Attachment 2: WholeMCNoiseProjection.fig
  5952   Fri Nov 18 19:57:19 2011 MirkoUpdateIOOMode cleaner noise projection

 

Some more info on this:
 

f > 1 Hz:

At these frequencies the pendulum should be quieter than the stacks. By quite a bit actually since there is the stack resonance at a couple Hz. 'Glueing' them together via the local control is not wise. We put an elliptic LP ( 2.5Hz, 4th order 6dB) into the C1:SUS-MC?_SUSPOS pathes and MC-F got better above 1Hz

MC_ELP.png

Added an extra LP @ 10 Hz afterwards. Doesn't make a visible difference.

f < 1 Hz:

Now here is more stuff to consider.

1. The OSEMs glue the MC mirrors to the stacks
2. The pendulum TF should be 1
3. It shouldn't matter if the OSEMs do or do not act on the mirror at these frequencies, assuming they don't add extra noise.
4. Page http://nodus.ligo.caltech.edu:8080/40m/5547 seems to indicate OSEM sensor noise is so low it can be neglected.

Reduced OSEM gain below 1Hz:

If we reduce the gain in the OSEMs by adding additional HP filters ( cheby2, HP 0.3Hz, 6dB 4th order ) the happens:

1. MC length gets a bit more noisy at low frequencies - should be looked into some more
2. Coherence between the GUR1 seismometer and MC length goes up between 1E-2 and 1E-1 Hz:

( Ref is with low OSEM gain )

WithAndWithoutHPs.pdf

Possible explanation:

The stacks might be more correlatedly moving together than the pendulums. This would be not so nice for OAF test, but really fine for actually using the MC.
Todo: Measure the OSEM to seismometer coherences with high and low OSEM gains.

For reference the seismometer coherence with one another:
SeismCoh.pdf

 

 

  5953   Fri Nov 18 23:44:33 2011 ranaUpdateIOOMode cleaner noise projection

Could use some more detail on how this measurement was done. It looks like you used the SUSPOS signal with the mirror moving, however, this is not what we want. Of course, the SUSPOS with the mirror moving will always show the mirror motion because the OSEMs are motion sensors.

Instead, what we want is to project how the actual OSEM noise in the presence of no signal shows up as MC length. For that we should use the old traces of the OSEM noise with no magnets and then inject that spectrum of noise into the SUSPOS filter bank with all the loops running. We can then use this TF to estimate the projection of OSEM noise into the MC length.

As far as improving the damping filter, the 2.5 LP is not so hot since it doesn't help at low frequencies. Instead, one can compute the optimal filter for the SUSPOS feedback given the correct cost function. To first order this turns out to be the usual velocity damping filter but with a resonant gain at the pendulum resonance. This allows us to maintain the same gain at the pendulum mode but ~3x lower gain at other frequencies.

In the past, we had some issues with this due to finite cross-coupling with the angular loops. It would be interesting to see if we can use the optimal damping feedback now that the SUS DOFs have been diagonalized with the new procedure.

  5957   Sat Nov 19 01:26:16 2011 DenUpdateIOOMode cleaner noise projection

Quote:

Instead, what we want is to project how the actual OSEM noise in the presence of no signal shows up as MC length. For that we should use the old traces of the OSEM noise with no magnets and then inject that spectrum of noise into the SUSPOS filter bank with all the loops running. We can then use this TF to estimate the projection of OSEM noise into the MC length.

That's right. The easier problem arises if we consider one of  MC mirrors. The coherence between OSEM sensors and GUR1_X in free moving regime is equal to 0.9 at frequencies 0.1 - 1 Hz. But with local dumping coherence is 0.6. We have

Mirror -> Sensor -> Satellite Module -> Whitening -> ADC -> Computer -> DAC -> Dewhitening -> Satellite Module -> Actuator -> Mirror

Somewhere we produce noise that kills part of coherence. We can use this method with the injection of spectrum of noise into the SUSPOS filter bank only for one mirror and see how the coherence between OSEM sensor and GUR1_X will change. If the change is small, we deal with something else. It the coherence will change from 0.6 to ~0.4, than we have big OSEM noise.

It might be also the problem that the amplitude of COIL_OUT signal is ~25. If it is in counts we may have noise from DAC. 

  5960   Sat Nov 19 12:57:55 2011 MirkoUpdateIOOMode cleaner noise projection

Quote:

Could use some more detail on how this measurement was done. It looks like you used the SUSPOS signal with the mirror moving, however, this is not what we want. Of course, the SUSPOS with the mirror moving will always show the mirror motion because the OSEMs are motion sensors.

Instead, what we want is to project how the actual OSEM noise in the presence of no signal shows up as MC length. For that we should use the old traces of the OSEM noise with no magnets and then inject that spectrum of noise into the SUSPOS filter bank with all the loops running. We can then use this TF to estimate the projection of OSEM noise into the MC length.

As far as improving the damping filter, the 2.5 LP is not so hot since it doesn't help at low frequencies. Instead, one can compute the optimal filter for the SUSPOS feedback given the correct cost function. To first order this turns out to be the usual velocity damping filter but with a resonant gain at the pendulum resonance. This allows us to maintain the same gain at the pendulum mode but ~3x lower gain at other frequencies.

In the past, we had some issues with this due to finite cross-coupling with the angular loops. It would be interesting to see if we can use the optimal damping feedback now that the SUS DOFs have been diagonalized with the new procedure.

 The measurement was done with the MC in lock and the OSEMS active.

1. I injected noise into MC1-3 SUSPOS_EXC at a level that domiated the SUSPOS output.
2. Then I calculated the coupling coefficients of the SUSPOS outputs to MC_F during the time the noise is injected.
3. Without noise injection I projected the SUSPOS outputs to MC_F by multiplying the coupling coefficients with the SUSPOS outputs.

All on 11-11-18. White noise inj. from 0.1Hz to 20Hz. Duration 4mins each.

DOF      Amplitude(counts)     Time(UTC)
MC1      200                           22:08
MC2      25                             22:25
MC3      25                             22:50

Some thoughts on this, bare with me:

As you say this does not show the dark / bright noise of the OSEMs. It shows the influence of the OSEMS output onto MC_F in normal operation of the MC. I would have expected that to be very low everywhere except at the pendulum resonance. Reason for that not to be true could either be the OSEMs having considerable gain off of the resonance, or noise intrinsic to the OSEMs knocking the mirrors around. Since we know the OSEM signal to MC_F TF we only need to compare the OSEM signal to OSEM noise to see the noise contribution to MC_F. We know from http://nodus.ligo.caltech.edu:8080/40m/5547 that the OSEM sensor bright noise is considerably below the OSEM signal above 0.1Hz in actual operation. We checked that the MC OSEM signals are above the noise in the reference above 0.1Hz by a factor 3-10.

We actually measured the cost function with the noise projection (valid to 10Hz). It's just the coupling coefficient, right?

CouplingMClengthsToMCF.pdf

 

Attachment 2: NpModeCleaner.pdf
NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf NpModeCleaner.pdf
  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.
  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.
  3088   Fri Jun 18 21:45:39 2010 kiwamuUpdateIOOMode Profile after Mode Matching Telescope (Round 2)

           [Joe, Kiwamu]

The better mode overlap of 99.3% was achieved by moving MMT2 by ~5 cm 

In the past measurement (elog entry #3077) we already succeeded in getting 99.0% mode overlap.

But according to the calculation there still was a room to improve it by moving MMT2 by 10 cm.

Today we moved MMT2 by ~5 cm which is a reasonable amount we could move because of the narrow space in the chamber.

Eventually it successfully got the better mode overlap.

So we eventually finished mode matching of the new IOOs 


(details)

     Actually moving of MMT2 was done by flipping the mount without moving the pedestal post as Koji suggested. 

At the same time we also flipped the mirror itself (MMT2) so that the curved surface is correctly facing toward the incident beam.

By this trick, we could move the position of MMT2 without losing precious available space for the other optics in the OMC chamber.

     The attached plot shows the result of the mode measurement after the MMT.

During the fitting I neglected the data at x=27 m and 37 m because the beam at those points were almost clipped by the aperture of the beam scan.

- - Here are the fitting results

w0_v             = 2.81183       +/- 7.793e-03  mm  (0.2772%)

w0_h             = 2.9089        +/- 1.998e-02  mm  (0.687%)

z_v             = 5.35487        +/- 0.2244     m   (4.19%)

z_h             = 1.95931        +/- 0.4151     m   (21.18%)

All the distances are calibrated from the position of MMT2 i.e. the position of MMT2 is set to be zero.

        In order to confirm our results, by using the parameters listed above I performed the same calculation of mode overlaps as that posted on the last entry (see here)

The result is shown in Attachement 2. There is an optimum point at x=62mm.

This value is consistent with what we did because we moved MMT2 by ~5 cm instead of 10 cm. 

 

Attachment 1: MMT20100618_edit.png
MMT20100618_edit.png
Attachment 2: newIOO_overlap_edit.png
newIOO_overlap_edit.png
  3089   Fri Jun 18 22:12:29 2010 AlbertoUpdateIOOMode Profile after Mode Matching Telescope (Round 2)

GJ

  3077   Tue Jun 15 16:28:32 2010 kiwamuUpdateIOOMode Profile after Mode Matching Telescope

We obtained a good mode match overlap of 99.0% for the new IOO.

And if we move the position of MMT2 by another 10 cm away from MMT1, we will have 99.6% overlap. 

Yesterday Jenne and I put MMT2 on the OMC table. MMT2 was carefully put by measuring the distance between MMT1 and MMT2.

The position looked almost the same as that drawn on the CAD design.

After putting it we measured the profile after the MMT.

 

The attached figure shows the computed mode overlap according to the fitting result while changing the position of MMT2 in a program code.

The x-axis is the position of MMT2, the current position is set to be zero. The y-axis is the mode match overlap.

Right now the overlap is 99.0% successfully, but this is not an optimum point because the maximum overlap can be achieved at x=100 mm in the plot.

It means we can have 99.6% by moving the position of MMT2 by another 10 cm. This corresponds to an expansion of the MMT length.

If this expansion is difficult due to the narrow available space in the chamber, maybe staying of MMT2 at the current position is fine.

Attachment 1: newIOO_overlap_edit.png
newIOO_overlap_edit.png
  3078   Tue Jun 15 19:24:25 2010 ranaUpdateIOOMode Profile after Mode Matching Telescope

Quote:

We obtained a good mode match overlap of 99.0% for the new IOO.

And if we move the position of MMT2 by another 10 cm away from MMT1, we will have 99.6% overlap.

 That's hot stuff.

  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
MCtf.pdf
  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.

WhatThenNow
pole frequency3.789kHz3.765kHz
loss per optic99ppm91ppm
finesse14601470
trans86.7%87.7%
Attachment 1: mctf.pdf
mctf.pdf
  4303   Tue Feb 15 17:48:22 2011 JenneUpdateIOOMode Cleaner resonating again

[Valera, Jenne]

After Steve and Valera switched out the PMC, the Mode Cleaner resonance needed to be brought back.  We spent some time playing with the 2 steering mirrors directly after the PMC, to get the beam through the EOM, and to achieve flashing in the MC.  Valera then adjusted those 2 steering mirrors to minimize MC_REFL_DC.  I did a little bit more, and it's kind of close now, but we're only at ~half normal transmitted power.  Since the 2 steering mirrors after the PMC are so close together, the beam alignment is pretty sensitive to even small touches.  So it's probably time to move on to using the last zigzag steering mirrors on the PSL table, since they're farther apart. 

I have to head out for a little while, but I'll be back in a few hours. Kiwamu said he might continue the alignment into the MC, if he needs the IFO.  Also, we should measure the power before and after the EOM, just to confirm that we're getting through it optimally.  The beam looks good after the EOM, and the MC is resonating, so it should be fine, but it can't hurt to check.

  9303   Mon Oct 28 14:12:48 2013 manasaUpdateIOOMode Cleaner relocked

Quote:

 The MC had been unlocked for the last 4 hours and was crying out to me so I gave it some attention. Its happier now.

From the trend (AtM #1), I saw that the MC2 suspension has moved by ~10 microradians. Since the MC cavity divergence angle is lambda/(pi*w0) ~ 200 microradians, this isn't so much, but enough to cause it to lock on bad modes sometimes. Attackmint too shows that there's not much in monotonic drift over the last 40 nights.

I moved back MC2 to its old alignment with these commands:

ezcaservo -r C1:SUS-MC2_SUSPIT_INMON -s -1017 -g 0.0009 C1:SUS-MC2_PIT_COMM -t 300

ezcaservo -r C1:SUS-MC2_SUSYAW_INMON -s 490 -g 0.0009 C1:SUS-MC2_YAW_COMM -t 332

Then I went out to the table and aligned the beam into MC using the last two steering mirrors good enough so that the WFS coming on doesn't make the visibility any better. In this nominal state, I unlocked the MC and then aligned the reflected beam onto the center of the LSC PD as well as the WFS. The beam on the first WFS is a little small - next time someone wants to improve our Gouy phase telescope, we might try to make it bigger there. On the LSC PD, the beam was off-center by a few hundred microns.

Masayuki was running LAN cables near the MC2 chamber. This caused the MC2 suspension to move and unlocked the MC. I looked at the long term (2 days) and short term (2 hours) trend of the MC suspensions. I restored the old alignment as described above using ezcaservo.

C1:SUS-MC2_SUSPIT_INMON was restored to 1020 and C1:SUS-MC2_SUSYAW_INMON was restored to 490.

Attachment: Dataviewer trend (2 hours)

Attachment 1: Screenshot-Untitled_Window-3.png
Screenshot-Untitled_Window-3.png
  9315   Wed Oct 30 01:53:52 2013 JenneUpdateIOOMode Cleaner relocked

The MC (mostly MC2) decided a few minutes ago to move, so I put the SUSPIT and SUSYAW numbers back where they were, and the tweaked up the alignment from there to get a low MC REFL DC number.  Now the MC is staying locked again, after 20 minutes of not.

  1913   Sat Aug 15 22:50:18 2009 ClaraUpdateLockingMode Cleaner is out of lock again

It was fine when I came in earlier today, but I just got back from dinner, and it's not good. I looked in dataviewer, and it seems to have been sliding out for the past couple of hours... Here is a picture:

MC_trans.png

I swear I am not responsible this time... all I've been doing is working in the control room.

  1914   Sun Aug 16 04:33:11 2009 ClaraUpdateLockingMode Cleaner is out of lock again

Quote:

It was fine when I came in earlier today, but I just got back from dinner, and it's not good. I looked in dataviewer, and it seems to have been sliding out for the past couple of hours... Here is a picture:

MC_trans.png

I swear I am not responsible this time... all I've been doing is working in the control room.

 Mode cleaner bounced back on its own about 2 hours ago.

  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.
  1312   Mon Feb 16 20:47:48 2009 ranaConfigurationIOOMode Cleaner WFS Loop Gain change
I found the MCWFS gain slider down at 0.012. In this state the UGFs are probably around 10-30 mHz
and so there is no reduction of seismic noise. It is mainly a DC alignment tool in this state.

We often have reduced the loop gain thusly, to prevent the dreaded "MCWFS eating CM loop gain" disease.
That disease is where there are CM loop instabilities at ~5-30 Hz because of loop cross-couplings
who's exact nature has never been understood (TBI).

Today, I implemented a 4th order, 7 Hz low pass (RLP7) into the loops and turned up the gain by a factor
of 30 to 0.3. In this state, the damping time constants seem to be ~0.5-2 seconds as shown in the first
PDF. I didn't have enough patience to do the interminable swept sine measurements down to 0.1 Hz.

The second PDF shows the Bode plot of the RLP7 filter compared to the pre-existing but unused ELP10.

The third PDF shows my estimate of the OLG TF. This is made by just putting a "Pendulum" filter into the
MCWFS bank and then plotting all the filters together using FOTON. The BLUE curve shows the old TF but
with the new high gain and the RED curve shows the new TF with the new gain.

With this new filter, I bet that we can get away with the higher WFS gain, but if there's any problem during the
handoff, the gain should be reverted to the low value.


In the 4th PDF file, I plot the spectra of 4 of MC2's control signals so that you can see what is bigger than what.
ASCPIT is the one that has the feedback from the WFS's in it. These are all just in units of counts and so to compare
them in some sort of displacement units you have to take into account the pitch moment of inertia, the mirror mass,
and the mis-centering of the beam from the center of rotation of MC2...
Attachment 1: pmc-pzt-cal.pdf
pmc-pzt-cal.pdf
Attachment 2: a.pdf
a.pdf
Attachment 3: olg.pdf
olg.pdf
Attachment 4: mc2.pdf
mc2.pdf
  3357   Wed Aug 4 11:10:28 2010 nancyUpdateIOOMode Cleaner WFS

Yesterday, I started twiddling with the Mode Cleaner at about 2 pm.

So the seismic data should be all good before that.

I was using it till about 3.30 am, and then left for the night with locking it and swithcing on back the WFS control

Today morning, I have started twiddling with it again, at about 10.30 am.

 

About my work with the mode cleaner :

 

I am primarily exciting the mirrors in pitch and yaw, and trying to measure the response of the WFS and the MC2 OPLEV wrt the excitation.

This thus involves switching off the WFS control while measurement.

After two more of those measurements today, I will get to finding new values for the Output Matrix of the WFS for controlling MC1 & 3, and also, try giving in control to MC2 alignment using OPLEV signals.

 

  3358   Wed Aug 4 12:49:42 2010 nancyUpdateIOOMode Cleaner WFS

Quote:

Yesterday, I started twiddling with the Mode Cleaner at about 2 pm.

So the seismic data should be all good before that.

I was using it till about 3.30 am, and then left for the night with locking it and swithcing on back the WFS control

Today morning, I have started twiddling with it again, at about 10.30 am.

 

About my work with the mode cleaner :

 

I am primarily exciting the mirrors in pitch and yaw, and trying to measure the response of the WFS and the MC2 OPLEV wrt the excitation.

This thus involves switching off the WFS control while measurement.

After two more of those measurements today, I will get to finding new values for the Output Matrix of the WFS for controlling MC1 & 3, and also, try giving in control to MC2 alignment using OPLEV signals.

 

 TFs after the measurement -

 In the order - MC1 , MC2 , MC3 -pitch and yaw.

These plots let us know about how do the wavefront sensor signals actually respond to the mis-alignments in the mirrors.

For legibility, legend has been includded in only one plot in each pdf., its typically the same for all  3 plots.

the actual xml files for this measurement are in the directory /cvs/cds/caltech/users/nancy/Align_Matrix/highpower/spot_center

It was made sure before each measurement that the MC is best aligned, the WFS are turned off, and the spots on all 3 QPDs are centered.

 

Attachment 1: pit.pdf
pit.pdf
Attachment 2: yaw.pdf
yaw.pdf
Attachment 3: pit.pdf
pit.pdf
Attachment 4: yaw.pdf
yaw.pdf
Attachment 5: pit.pdf
pit.pdf
Attachment 6: yaw.pdf
yaw.pdf
  3365   Thu Aug 5 01:29:39 2010 nancyUpdateIOOMode Cleaner WFS

 

I calculated the MC1&3 Vs WFS1&2 Output Matrix today from the above measurements with koji's help.

the matrix can be generated from the m file at /cvs/cds/caltech/users/nancy/Align_Matrix/matrix.m

these values were put in, and the direction of control is sort of confirmed. I tried twiddling with the gains in the loop to get a 4*4 stable control, but could not succeed.

the mode cleaner is back locked now, and WFS matrix as well as gains are reverted to the old values.  (1.30 am)

 

The output Matrices are

Pitch

0.724
0.197
0
0
-1.448
-0.758

Yaw

0.919
0.139
0
0
-0.0106
-0.1245

 

  3366   Thu Aug 5 11:48:52 2010 nancyUpdateIOOMode Cleaner WFS

Quote:

 

I calculated the MC1&3 Vs WFS1&2 Output Matrix today from the above measurements with koji's help.

the matrix can be generated from the m file at /cvs/cds/caltech/users/nancy/Align_Matrix/matrix.m

these values were put in, and the direction of control is sort of confirmed. I tried twiddling with the gains in the loop to get a 4*4 stable control, but could not succeed.

the mode cleaner is back locked now, and WFS matrix as well as gains are reverted to the old values.  (1.30 am)

 

The output Matrices are

Pitch

0.724
0.197
0
0
-1.448
-0.758

Yaw

0.919
0.139
0
0
-0.0106
-0.1245

 

 I realised today morning that there was a flaw in my calculations for the yaw matrix.

Correcting the values, and also making teh tables more readable.

I will test these values once our computers are back to working condition.


PITCH
WFS1
WFS2
MC1
0.724
0.1964
MC2
0
0
MC3
-1.4436
-0.756


YAW
WFS1
WFS2
MC1
0.0710
0.1074
MC2
0
0
MC3
0.0082
-0.962

 

 

  3367   Thu Aug 5 13:05:53 2010 KojiUpdateIOOMode Cleaner WFS

Upon Nancy's request, I checked the status of the suspensions.

I found that the power strip of the 1Y4 rack was turned off.
Since it has a over current breaker, I don't know whether it happened by someone or over current.

Anyway, I restarted the sus computers, and now the suspensions are damping as usual.
The MC has been aligned, the auto locker is also working.


Incidentally, I found that the WFS servos are not working. Actually since the last night
It repeated losing lock and unlock.

Probably some values of the matrix or the gain is wrong.
I left the WFS as it is because Nancy will put new values this afternoon.
I will ask her to confirm that the old values work at the end of her work.

  3372   Fri Aug 6 10:44:55 2010 nancy, kojiUpdateIOOMode Cleaner WFS

Quote:

Upon Nancy's request, I checked the status of the suspensions.

I found that the power strip of the 1Y4 rack was turned off.
Since it has a over current breaker, I don't know whether it happened by someone or over current.

Anyway, I restarted the sus computers, and now the suspensions are damping as usual.
The MC has been aligned, the auto locker is also working.


Incidentally, I found that the WFS servos are not working. Actually since the last night
It repeated losing lock and unlock.

Probably some values of the matrix or the gain is wrong.
I left the WFS as it is because Nancy will put new values this afternoon.
I will ask her to confirm that the old values work at the end of her work.

 Yesterday , I put in the Output Matrix, and changed the gain sliders for the 4 WFS loops.

It worked and was keeping the lock for the MC.

I then tested whether the MC1 and 3 were following any change in MC2 alignment. It was indeed workinng,

Next we stepped to putting in the gains for the MC2 oplev servo.

the signs are decided on the basis of convergence, and the magnitude is kept very low, to have a very slow control for MC2.

This complete 6 * 6 model does work, and was able to keep the transmission held.

I also tried poking each mirror in pitcg and yaw, and the cavity comes back to high resonance after some time.

This time is indeed large if the poking is made for MC2, and the transmission comes back to normal after big oscillations.

I tried to measure the Open loop TFs for all these loops yesterday, but somehow could not find a correct excitation.

I will do it today.

Plan ahead :

1.  Center the spot on MC2 and the QPD

2. Optimize the gains by looking at response to noise.

3. Measure Power Spectrum Density of each error signal.

 

  3374   Fri Aug 6 12:33:10 2010 KojiUpdateIOOMode Cleaner WFS

 Yesterday , I put in the Output Matrix, and changed the gain sliders for the 4 WFS loops.

From how much to how much have you chnged the gain?

Next we stepped to putting in the gains for the MC2 oplev servo.

I like to put the credit to Aidan for teaching Nancy how to use FOTON.

 

This complete 6 * 6 model does work, and was able to keep the transmission held.

This should be in this size:

This complete 6 * 6 model does work,
and was able to keep the transmission held.
Y
eeeeah
!

 

  3386   Mon Aug 9 12:46:24 2010 NancyUpdateIOOMode Cleaner WFS


 Yesterday , I put in the Output Matrix, and changed the gain sliders for the 4 WFS loops.

From how much to how much have you chnged the gain?

I changed the gains from all 4 0.01 to o.27, 0.23, 0.32 and 0.11 and the main alignment gain to be 0.8

 

 

Next we stepped to putting in the gains for the MC2 oplev servo.

I like to put the credit to Aidan for teaching Nancy how to use FOTON.

 Yes, I am sorry for not mentioning this.

Thanks Aidan

 

 

  1895   Thu Aug 13 00:11:43 2009 JenneUpdateIOOMode Cleaner Unlock

So that I can collect a bit of free-swinging Mode Cleaner data, I started a script to wait 14400 seconds (4 hours), then unlock the mode cleaner.  It should unlock the MC around 4am.  As soon as someone gets in in the morning, you can relock it.  I should have plenty of data by then.

  9296   Sat Oct 26 21:46:33 2013 RANAUpdateIOOMode Cleaner Tune-UP

 The MC had been unlocked for the last 4 hours and was crying out to me so I gave it some attention. Its happier now.

From the trend (AtM #1), I saw that the MC2 suspension has moved by ~10 microradians. Since the MC cavity divergence angle is lambda/(pi*w0) ~ 200 microradians, this isn't so much, but enough to cause it to lock on bad modes sometimes. Attackmint too shows that there's not much in monotonic drift over the last 40 nights.

I moved back MC2 to its old alignment with these commands:

ezcaservo -r C1:SUS-MC2_SUSPIT_INMON -s -1017 -g 0.0009 C1:SUS-MC2_PIT_COMM -t 300

ezcaservo -r C1:SUS-MC2_SUSYAW_INMON -s 490 -g 0.0009 C1:SUS-MC2_YAW_COMM -t 332

Then I went out to the table and aligned the beam into MC using the last two steering mirrors good enough so that the WFS coming on doesn't make the visibility any better. In this nominal state, I unlocked the MC and then aligned the reflected beam onto the center of the LSC PD as well as the WFS. The beam on the first WFS is a little small - next time someone wants to improve our Gouy phase telescope, we might try to make it bigger there. On the LSC PD, the beam was off-center by a few hundred microns.

Attachment 1: MCtrend.pdf
MCtrend.pdf
Attachment 2: MC40days.png
MC40days.png
  9306   Mon Oct 28 21:33:55 2013 RANAUpdateIOOMode Cleaner Tune-UP

 

8 day minute trend of some of the IMC alignment signals.

That step ~2 days ago in the WFS2 yaw control signal shows that I didn't do such a good job on yaw.

Nic is going to come over some time and give us a new Gouy telescope that let's us have bigger beams on the WFS. At LLO, Hartmut demonstrated recently how bigger beams can reduce offsets somehow...mechanism TBD.

Also, we must angle the WFS and figure out how to dump the reflections at the same time that we rework the table for the telescope.

Steve, can you please put 2 mounted  razor dumps near the WFS for this purpose??    

            Tuesday: Razor dumps are waiting for you.

 

Attachment 1: Untitled.png
Untitled.png
  9323   Thu Oct 31 20:05:48 2013 RANAUpdateIOOMode Cleaner Tune-UP

Quote:

Steve, can you please put 2 mounted  razor dumps near the WFS for this purpose??    

            Tuesday: Razor dumps are waiting for you.

 I couldn't find any dumps near the WFS. Koji looked. I looked twice. Maybe they are spooky and absorbing all of the light?

The MC alignment was bad and the WFS were making it drift. Koji aligned the beam into the PMC. I then restored the MC suspensions to where they were 8 days ago (back when the transmission and reflection were good). With the WFS OFF, this gave us a MC trans ~ 16000. With WFS ON it goes to 17500 which is about as good as its been over the last 80 days.

I centered the beam on the WFS with the MC unlocked and also centered the beam on the whole WFS path (it was near clipping between WFS 1 & 2). Also for some reason that beamsplitter which steers the beam onto WFS1 is a R=33% (!? why is this not a R=50% ??).

Steve, please swap this out to a BS1-1064-50-1025-45S if we have one sitting around. If not, we want to add this to the CVI purchase list, but not buy until we get a bigger list together.

I also centered this newly aligned beam into the IMC onto the PSL QPDs. We should now use these as a pointing reference for the beam into the IMC.

While doing this I noticed that the beam was almost clipping on the Uniblitz shutter used to block the PSL beam. That shutter is mounted too short and was also not centered horizontally. I removed it for now so that Steve can find a more adjustable mount for it and put it back into play. The beam going into the IMC is BIG, so you have to very careful when centering the shutter. Might be that we cannot leave it at 45 deg and still get a big enough aperture.

Note #3 for Steve: please also replace the mount for last steering mirror into the IMC with a Polanski or a Superman, that black Ultima is no good. Also the dogs must be steel - no aluminum dogs for our sensitive places.

Attachment 1: drifty.png
drifty.png
  1194   Fri Dec 19 11:18:52 2008 AlbertoConfigurationGeneralMode Cleaner Temperature Monitor
I reduced from 10 to 5 the gain of the SR560 that Caryn has set up after the lock-in amplifier nest to the PSL rack because the overload LED was flashing.
  1429   Wed Mar 25 20:41:43 2009 JenneUpdateIOOMode Cleaner Servo Board Transfer Functions (to be updated)

When all things fail (netgpibdata.py is giving me weird data.  When I plot the data it has saved from the 4395A, it's some wierd other universe's version of my transfer function.  I don't really know what's up.  I'm pretty sure I'm getting the 'correct' data, since each TF looks vaguely like it should, but with some crazy humps.  I'll talk to Yoichi in the morning about it maybe.) (also, we're low on emergeny floppy discs), you can always take a picture of the Agilent 4395's screen, as shown below.

* Mode cleaner and PMC are both relocked after my shenanigans, and I'll try again in the morning (I assume locking is going on tonight) to get real TF's with real data, as opposed to the photo method.

Note to self:  post the data of the TFs in the elog along with the plots, for posterity.

 

These TFs are of the Mode Cleaner servo board, exciting IN1 (or the 3.7MHz notch pomona box which is connected to IN1), and measuring at the SERVO out of the board.

One with the box, one without the box, and one of just the box for good measure.

Attachment 1: MCwithBoxsmall.JPG
MCwithBoxsmall.JPG
Attachment 2: MCnoBoxsmall.JPG
MCnoBoxsmall.JPG
Attachment 3: PomonaBoxforMCsmall.JPG
PomonaBoxforMCsmall.JPG
  1430   Thu Mar 26 00:45:24 2009 JenneUpdateIOOMode Cleaner Servo Board Transfer Functions (to be updated)

Quote:

netgpibdata.py is giving me weird data.  When I plot the data it has saved from the 4395A, it's some wierd other universe's version of my transfer function.  I don't really know what's up. 

 Yoichi, in all his infinite wisdom, reminded me that the netgpibdata script saves the data as the REAL and IMAGINARY parts, not the Mag and Phase.  Brilliant.   Using that nugget of information, here are the TFs that I measured earlier:

The last attachment is the .dat and .par files which contain the data and measurement parameters for the 3 TFs in the plots.

Attachment 1: MCwithandwithoutfilter25Mar2009.png
MCwithandwithoutfilter25Mar2009.png
Attachment 2: PomonaBoxMCfilter25Mar2009.png
PomonaBoxMCfilter25Mar2009.png
Attachment 3: MCServoData25Mar2009.tar.gz
  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
mode-track.pdf
Attachment 2: trends.pdf
trends.pdf
Attachment 3: mcmodetrack.zip
  1192   Thu Dec 18 12:52:00 2008 AlbertoConfigurationSUSMode Cleaner Cavity Alignment
This morning I found the MC locked to the 10 mode. When I locked it on the 00 mode, it was unstable and eventually it always got locked to the wrong mode.

I looked at the Drift Mon MEDM screen, which shows a reference record for position, pitch and yaw of each mirror, and I found that the MC optics were in a different status. Moving the sliders of the mirrors' actuators, I brought them back to the reference position. Then the lock got engaged and it was stable, although the MC reflection from the photodiode, with the wave front sensors (WFS) off, was about 2V. That's higher than the 0.5V the it could get when we aligned the cavity and the input periscope last time.

With the WFS on, the reflection dropped to 0.3V and, so far, the the cavity has been stably locked.
  1193   Thu Dec 18 19:15:54 2008 Alberto, YoichiConfigurationSUSMode Cleaner Cavity Alignment

Quote:
This morning I found the MC locked to the 10 mode. When I locked it on the 00 mode, it was unstable and eventually it always got locked to the wrong mode.

I looked at the Drift Mon MEDM screen, which shows a reference record for position, pitch and yaw of each mirror, and I found that the MC optics were in a different status. Moving the sliders of the mirrors' actuators, I brought them back to the reference position. Then the lock got engaged and it was stable, although the MC reflection from the photodiode, with the wave front sensors (WFS) off, was about 2V. That's higher than the 0.5V the it could get when we aligned the cavity and the input periscope last time.

With the WFS on, the reflection dropped to 0.3V and, so far, the the cavity has been stably locked.


This evening the mode cleaner was again locking on a higher mode so we tweaked the mirrors' actuators by their sliders on the MEDM screen until we improved the reflection to 0.3V.

Then we went inside and, on the AS table, we centered the beam on the wave front sensors.

Now the mode cleaner is locked, the reflection is less than 0.3V and the transmission about 3V, tha is it is in ideal conditions. We'll see if it holds.
  1896   Thu Aug 13 02:17:56 2009 JenneUpdateIOOMode Cleaner Alignment

When Rob and I were getting started on locking for the evening, Mode Cleaner lost lock a few times, but every time it lost lock, it took forever to reaquire, and was pretty insistent on locking in the TEM10 mode.  I proposed that the alignment might be sketchy.  I've been fiddling with the MC alignment sliders for the last hour and a half or so, but I think I'm not 100% in tune with the 3 mirror parameter space.  The mode cleaner now locks, but I'm not in love with its' alignment.  The WFS are definitely catywhompus.  Before doing hardware things like recentering the WFS, I'm going to wait until tomorrow to consult with an alignment expert.

In case this is helpful for tomorrow, before I touched any of the sliders:

Optic, Pitch, Yaw

MC1, 3.1459, -0.7200

MC3, -0.8168, -3.0700

MC2, 3.6360, -1.0576

 

Now that mode cleaner locks, although not in a great alignment:

MC1, 3.1089, -0.7320

MC3, -0.7508, -3.0770

MC2, 3.6610, -1.0786

 

If I knew how to kill my script to unlock the mode cleaner, I would.  But I sourced it, and Rob didn't know earlier this evening how to kill something which is started with 'source' since it doesn't seem to get a process number like when you './'  to run a script. So the Mode Cleaner will probably be unlocked in the morning, and it may be persnickity to get it relocked, especially if the tree people are doing tree things with giant trucks again in the morning.

  3387   Mon Aug 9 13:32:02 2010 nancyUpdateIOOMode Cleaner ASC

 E-log entry for Friday - will attach more plots to this entry on wednesday after i am back   to the 40.

 
Started working at some 1030 hrs and recording the Open Loop Tfs for all 6 loops.
The control was not so good, and I lost the lock quite a number of times while measureing
WFS  did not converge when the spot was aligned to the center. But there was convergence to a non-center point. So if  the control system was switched on near those points, it was converging to that point.
 
Autolocker : switches WFS control on directly, whereas the best way is to gradually increase the gain to 1. Also, the autolocker code now needs to be changed to incoporate the switing off the MC2 oplev in down and switch it on in the up script.
 
After Koji locked the Reference Cavity in the evening, I resumed measurements for the Open Loop TFs.
 
Measurement of the Open Loop Transfer Functions :
 
 
noise waveform was generated using arbitrary wf generator and injected into each loop.
An LPF was applied to have max co-relation at minimum disturabnce. (thanks to Rana)
The Transfer functions, Co-relations and Power Spectra were then measured using the DTT.
 
 
Power Spectrum of the IN1, IN2 and EXC shows clearly the suppression of the noise, and OLTF shows the phase margins.
 
- Courtesy Rana again for suggesting the idea of plotting power spectra of all signals in the same graph.
 
Later in the night , Koji worked with me and we reflected upon all TFs and changed gains whereevr required according to the phase margin considerations from the Open Loop TFs.
We used the same output matrix given in the previous e-log.   
 
 
Final gains -
 
Alignment Gain in the WFS Master - 1.000
 
Loop Gain
WFS1 P 0.27
WFS1 Y 0.7
WFS2 P 0.15
WFS2 Y 0.110
MC 2OPLEV P -0.1
MC2 OPLEV Y -0.1
 
 
this measurement invloved locking the MC to the correct position, with the spot centered at both the WFS and the QPD. invloved some cheating (offsets) after we tried centering w/o offsets.
demod signal was also centered while alignment.
credits to Koji for getting the correct lock position and also staying with me till late night in the lab
 
Important Points to be noted
 
1. All loops' histories have to be cleared while swtiching them on.
2. turn the loop output before the loop input so that there is no remnant history in the loop.
2. Alignment gain was gradually increased to 1. and tehn the oplevs turned on.
 
 
Later measured teh PSD of  6 error signals under 3 conditions -
 
New Control ON
 
New Control OFF
 
Old Control ON
 
 
Also measured the time series for the MC_trans and MC_refl for the 3 conditions.
 
 
 Status MC_Trans  MC_REF 

  

New Control ON  trans_on.pdf refl_on.pdf   
New Control OFF trans_off.pdf  refl_off.pdf  
Old Control ON trans_old.pdf refl_old.pdf  
 
 
 
 
 
 
 
  

 

Attachment 5: refl_off.pdf
refl_off.pdf
  3388   Mon Aug 9 15:54:43 2010 KojiUpdateIOOMode Cleaner ASC

The WFS and QPD servos were working. That was great.
Everything was fine except for the time series plots.

I could not get what story you are telling with the time series.
(e.g. your's are good or bad or anything)

  3389   Mon Aug 9 21:50:50 2010 nancyUpdateIOOMode Cleaner ASC

Quote:

The WFS and QPD servos were working. That was great.
Everything was fine except for the time series plots.

I could not get what story you are telling with the time series.
(e.g. your's are good or bad or anything)

 Well, the data is kind of not enough to be analysed in time domain,

But by far from what I analyse, I think that the new control is not worse than the old one.

I donot also find any better results, except for this one being theoritically stronger.

  14497   Tue Mar 26 18:35:06 2019 JonUpdateUpgradeModbus IOC is running on c1susaux2

Thanks to new info from Johannes, I was able to finish setting up the modbus IOC on c1susaux2. It turns out the 17 Acromags draw ~1.9 A, which is way more than I had expected. Hence the reason I had suspected a short. Adding a second DC supply in parallel solves the problem. There is no issue with the wiring.

With the Acromags powered on, I carried out the following:

  • Confirmed c1susaux2 can communicate with each Acromag at its assigned IP address
  • Modified the EPICS .cmd file to point to the local modbus installation (not the remote executable on /cvs/cds)
  • Debugged several IOC initialization errors. All were caused by minor typos in the database files.
  • Scripted the modbus IOC to launch as a systemd service (will add implementation details to the documentation page)

The modbusIOC is now running as a peristent system service, which is automatically launched on boot and relaunched after a crash. I'm able to access a random selection of channels using caget.

What's left now is to finish the Acromag-to-feedthrough wiring, then test/calibrate each channel.

  10666   Tue Nov 4 14:46:00 2014 manasaUpdateGreen LockingMissing beatnotes

Summary: Cannot find beatnotes between the arms and PSL.

I wanted to measure the ALS out of loop noise before putting stuff on the PSL table for frequency offset locking.

But I was not able to find the beat notes between the arms and PSL green. All I could find while scanning through the end laser temperatures is the beatnote between the X and Y green.

EricQ says that he spent some time yesterday and could not find the beatnotes as well.

Debugging and still could not find:

1. Checked the FSS slow actuator. This was close to zero ~0.003

2. Checked the green alignment on the PSL table. Everything seems fine.

3. Checked the actual PSL laser temperature. It was 31.28deg and not very far from when it was last set at 31.33deg elog.

4. Also checked the end laser temperatures. Both the lasers are ~40deg (where I could see the beatnote between the arms). Based on the plot here and  here , we are very much in the regime where there should be a beatnote between the PSL and the arms.

  10796   Sat Dec 13 14:26:36 2014 ericqUpdateLSCMismatched gains on ETMY Transmon QPD

Yesterday, we were seeing anomalously high low frequency RIN in the y-arm (rms of 4% or so). I swung by the lab briefly to check this out. Turns out, despite TRY of 1.0, there was reasonable misalignment. ASS with the excitation lowered by a factor of two, and overall gain at 0.5 or so aligned things to TRY=1.2, and the RIN is back down to ~0.5% I reset the Thorlabs FM to make the power = 1.0

I then went to center the transmitted beam on the transmon QPD. Looking at the quadrant counts as I moved the beam around, things looked odd, and I poked around a little... 

I strongly suspect that we have significantly mismatched gains for the different quadrants on the ETMY QPD. 

Reasoning: With the y-arm POY locked, I used a lens to focus down the TRY beam, to illuminate the quadrants individually. Quadrants 2 and 3 would go up to 3 counts, while 1 and 4 would go up to 0.3 and 0.6, respectively. (These counts are in some arbitrary units that were set by setting the sum to 1.0 when pitch and yaw claimed to be centered, but mismatched gains makes that meaningless.)

I haven't looked more deeply into where the mismatch is occurring. The four individual whitening gain sliders did affect the signals, so the sliders don't seem sticky, however I didn't check the actual change in gains. Will the latest round of whitening board modifications help this?

Hopefully, once this is resolved, the DC transmission signals will be much more reliable when locking...

  5646   Mon Oct 10 18:53:04 2011 KatrinUpdateGreen LockingMirrors whose angle of incidence is not 45

The angle of incidence of light is for some mirrors on the YARM end table different from 45° even though the mirrors are coated for 45°.

The mirrors below are useful if there are plans to replace these mirrors by properly coated ones.

 

Mirror
Angle of incidence (degree)
1st 1" mirror right after laser* 10
2nd 1" mirror right after laser 35
1st 2" steering mirror to vacuum system 15
2nd 2" steering mirror to vacuum system 28

 

* This is the new mirror as decribed on http://nodus.ligo.caltech.edu:8080/40m/5623

 

  2987   Wed May 26 00:50:16 2010 JenneUpdateIOOMirrors moved in prep for round 2 of MC mode measuring

[Jenne, Kevin, Kiwamu]

We moved some optics in preparation for measuring the MC mode after the first MMT curved optic, RoC -5m. 

Kevin and I found the box of DLC (sp?) mounts with the 2" Y1-45P optics in the clean tupperware boxes.  We removed one of the Y1-45P's, and replaced it with the MMT1 -5m optic, which was baked several weeks ago.  We left the Y1-45P on the cleanroom table next to where the MMT optics are.  We placed this MMT mirror in the place it belongs, according to Koji's table layout of the BS table. 

We drag wiped one of the other Y1-45P's that was in the box since it was dirty, and then placed the optic on the IOO table, on the edge closest to the BS table, with the HR side facing the BS table, so that the beam reflected off the curved mirror is reflected back in the direction of the BS table.  This was aligned so the beam hits the same PZT mirror we were using last time, to get the beam out of the BS chamber door.  We left a razor dump on the edge of the BS table, by the door, which will need to be removed before actual measurements can take place. 

Rana pointed out that the anticipated mode calculation should be modified to include the index of refraction of the crystals in the Faraday, and the polarizers in the Faraday.  This may affect where we should put MMT1, and so this should be completed before round 2 measurements are taken, so that we can move MMT1.

Also, the optics are in place now, and the beam is going out the BS chamber door, but we have not yet measured distances (design distances quoted on the MMT wiki page), and confirmed that everything is in the right place.  So there is a bit more work required before beginning to measure round 2.

 

Note:  While I was poking around on the BS table, I had to move several optics so that we could fit MMT1 in the correct place.  When preparing to move these optics, I found 2 or 3 that were totally unclamped. This seems really bad, especially for tall skinny things which can fall over if we have an earthquake.  Even if something is in place temporarily, please clamp it down.

  2991   Wed May 26 14:28:01 2010 KojiUpdateIOOMirrors moved in prep for round 2 of MC mode measuring

That's true. But I thought that you measured the mode after those optics and the effect of them is already included.

So:

  • We need to model the transmissive optics in order to understand the measured mode which is different from the MC mode slightly.
  • We just can calculate the modes based on the measurement in order to figure out the realistic positions of the MMT1 and MMT2.

Quote:

Rana pointed out that the anticipated mode calculation should be modified to include the index of refraction of the crystals in the Faraday, and the polarizers in the Faraday.  This may affect where we should put MMT1, and so this should be completed before round 2 measurements are taken, so that we can move MMT1.

 

ELOG V3.1.3-