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ID Date Author Type Categoryup Subject
  3045   Thu Jun 3 14:13:20 2010 JenneUpdateIOOmode measurement of new input optics

Quote:

I checked the measured data of the mode profile which was taken on the last Tuesday.

For the vertical profile,

the plot shows a good agreement between the expected radius which is computed from the past measurement, and that measured on the last Tuesday.

However for the horizontal profile,

it looks like being overestimated. This disagreement may come from the interference imposed on the Gaussian spot as we've been worried. 

So we should solve this issue before restarting this mode matching work.

 - The next step we should do are;

checking the effect of MMT1 on the shape of the beam spot by using spare MMT1

 

NOTE:

The expected curve in the attached figure were computed by using the fitted parameter listed on the entry 2984 .

In the calculation the MMT1 is placed at 1911mm away from MC3 as we measured.

And the focal length of MMT1 is set to be f=-2500mm.

 When / if you use the other MMT1 mirror, make sure to take note whether or not it says "SPARE" on it in pencil.  I don't remember if it's the other MMT1, or if it's one of the MMT2's that says this.  The mirror was baked, so it's okay to use in the vacuum, however it's the one which was dropped on the floor (just prior to baking), so any discrepancies measured using that optic may not be useful.  I don't know how strong the CVI coatings are to scratches resulting in being dropped from a ~1m height.  Bob and I didn't see any obvious big scratches that day, but that doesn't necessarily give it a clean bill of health. 

The optic labeled "SPARE" should NOT be used as the final one in the IFO.

  3046   Thu Jun 3 14:40:28 2010 Alberto, KiwamuUpdateIOOmode measurement of new input optics

Quote:

inside_vac_2.png

 

For the record, we wanted to check whether the fringes on the beam spot were caused by SM2 (see diagram above). We tried two different mirrors for SM2,

The first was one of the flat, 45 degree ones that were already on the BS table. The last, which is the one currently in place, was inside the plastic box with the clean optics that Jenne left us .

The fringes were present in both cases.

  3049   Fri Jun 4 11:32:51 2010 Alberto, kiwamuUpdateIOOMC MMT1 Mirror Tests
[Alberto, Kiwamu]
Last Wednesday, we measured the beam profile after the MC mode matching telescope n.1 (MMT1). We found that the reflected beam had an irregular profile when observed with the beam scan. Fringes also appeared on an IR card.
We thought that such effect could be due to interference of the main reflected beam with the beam reflected by the back surface of the mirror.
 
To test the hypothesis we checked the transmitted and the reflected beams of a spare optic identical to MMT1. (This was the same optic that got dropped during the cleaning/baking process.)
 
We tested it on the PSL table, using a 200mW beam coming from the new 2W Innolight  laser. To maximize the separation between the two beams, we tested MMT1 at 45 degrees. The setup we used is shown here:
 
MCMMT1spareOpticsTestSetup.png
 
We looked at the beam reflected by MMT1 about 5 meters from the mirror. At that distance the beam spot had a size of about 1-2cm. it didn't look perfectly round, but it showed no fringes, as it had happened with original MMT1 inside the MC chamber.
At the transmission, the second ghost beam due to the back surface reflection (see picture above) was very week. In order to be able to see it on an IR card, we had to increase the laser pumping current from 1A to about 1.5A.
 
We are now thinking of a way to measure the relative power between the two. The problem is that they run very close to each other and it's not easy to resolve them with a power meter or a photodiode.
  3054   Tue Jun 8 00:38:22 2010 Koji, KiwamuUpdateIOOimproved Gaussian beam in new IOO

The shape of the beam spot in the new input optics got much much better 

As Alberto and Kiwamu found on the last week, the beam spot after MMT1 had not been good. So far we postponed the mode measurement due to this bad beam profile.

Today after we did several things in the vacuum chamber, the beam spot became really a good Gaussian spot. See the attachment below.

There were two problems which had caused the bad profile:

(1)  a steering mirror after MMT1 with the incident angle of non 45 deg

(2) clipping at the Faraday.

 

Also MCT_QPD and MCT_CCD were recovered from misalignment  

Tomorrow we are going to restart the mode matching. 

 


(what we did)

* We started from checking the shape of the beam going out from the BS chamber. There still were some stripes which looked like an interference on the spot. 

* We found a steering mirror after MMT1 had the incident angle of non 45 deg. In fact the mirror had a large transmission. After we made the angle roughly 45 deg, the stripes disappeared.

However the spot still didn't look a good Gaussian, it looked slightly having a bump on the horizontal profile.

* Prior to moving of some optics in the vacuum, we ran the A2L_MC scripts in order to check the beam axis. And it was okay.

* To recover the MCT, we steered one of the vacuum mirrors which was located after the pick off mirror.  And after aligning some optics on the AP table, finally we got MCT recovered.

 * We rearranged MC_refl mirrors according to the new optical layout that Koji has made. At the same time the mirrors for IFO_refl was also rearranged coarsely.

 * We leveled the optical table of the MC chamber by moving some weights. Then we locked the MC again and aligned it. We again confirmed that the beam axis was still fine by running the A2L scripts.

 * We found the beam going through Faraday was off-centered by ~5mm toward the west. So we moved it so that the beam propagates on the center of it. 

 * Then looking at the beam profile after MMT1, we found that the profile became really nicer. It showed a beautiful Gaussian. 

In the attachment below, the top panel represents the horizontal profile and the bottom one represents the vertical profile.

The blue curves overlaid on the plot are fitted Gaussian profile, showing beautiful agreements with the measured profile.

Attachment 1: 2010-6-7_2.png
2010-6-7_2.png
  3068   Fri Jun 11 14:31:04 2010 kiwamuUpdateIOOmode matching of new IOO

We decided not to care about the mode after MMT1.

So far Koji, Alberto and I have measured the beam profile after MMT1,

but we are going to stop this measurement and go ahead to the next step i.e. putting MMT2

There are two reasons why we don't care about the profile after MMT1:

     (1) it is difficult to fit the measured data

     (2) The position of MMT1 is not critical for the mode matching to the IFO.

The details are below.

 


(1) difficulty in fitting the data

The precision of each measured point looked good enough, but the fitting result varies every measurement.

The below shows the data and their fitted curves. 

 profile_MMT.png

In the label, "h" and "v" stand for "horizontal" and "vertical" respectively.

The solid curves represent the fitting results, varying by each measurement.

In order to increase the reliability of the fitting, we had to take some more data at further distance.

But we couldn't do it, because the beam radius already becomes 3 mm even at 2 m away from MMT1 and at this point it starts to be clipped on the aperture of the beam scan.

Thus it is difficult to increase the reliability of the fitting. 

Once if we put MMT2 the beam should have a long Rayleigh range, it means we can measure the profile at further distance, and the fitting must be more reliable.

 


(2) positioning of MMTs

Actually the position of MMT1 is not so critical for the mode matching. 

The most important point is the separation distance of MMT1 and MMT2.

As written in Jenne's document, if we slide the positions of MMT1 and MMT2 while keeping their appropriate separation distance, the mode match overlap still stays above 99%

This is because the beam coming from MC3 is almost collimated (ZR~8m), so the position of MMTs doesn't so matter. 

To confirm it for the real case, I also computed the mode overlap while sliding the position of MMTs by using real data. The below is the computed result.

dist_MMO.png

It is computed by using the measured profile after MC3 (see the past entry).

The overlap still stay above 99% when the distance from MC to MMT is between 1300 and 3000mm.

This result suggests to us putting MMT1 as we like.  

  3076   Mon Jun 14 22:16:08 2010 JenneUpdateIOOMode scan after Mode Matching Telescope

[Jenne, Kiwamu]

We measured the mode after the Mode Matching Telescope. 

 

---- fitted parameters ----

       w0_h =  2.85 +/- 0.0115 mm

       w0_v =  2.835 +/- 0.00600 mm

       z0_h = 5.4 +/- 0.447  m

       z0_v  = 6.9 +/- 0.305  m

Attachment 1: after_MMT.png
after_MMT.png
  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.

  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

  3117   Thu Jun 24 18:47:26 2010 FrankDAQIOOVME crate rebooted

we had to reboot the IOO VME crate right before lunch as the DAQ wasn't working correct meaning showing no real signals anymore, only strange noise. The framebuilder and everything else was working fine at that time.

  • The channel used for the phase noise measurement stopped showing any useful signal right after midnight, so all the other IOO-MC signals.
  • The data taken with those channels showed something like a 140 counts or so of steady offset with something which looked like the last bit fluctuating.
  • Whatever signal we connected to the input it didn't change at all, floating/shorted input, sine wave etc.
  • the other channels for the MC which we checked showed the same strange behaviour

As the other channels showed the same effect we decided to reboot the crate and everything was fine afterwards.

  3151   Wed Jun 30 23:03:46 2010 ranaConfigurationIOOPower into MC restored to max

Kiwamu, Nancy, and I restored the power into the MC today:

  1. Changed the 2" dia. mirror ahead of the MC REFL RFPD back to the old R=10% mirror.
  2. Since the MC axis has changed, we had to redo the alignment of the optics in that area. Nearly all optics had to move by 1-2 cm.
  3. 2 of the main mounts there had the wrong handedness (e.g. the U100-A-LH instead of RH). We rotated them to some level of reasonableness.
  4. Tuned the penultimate waveplate on the PSL (ahead of the PBS) to maximize the transmission to the MC and to minimize the power in the PBS reject beam.
  5. MC_REFL DC  =1.8 V.
  6. Beams aligned on WFS.
  7. MC mirrors alignment tweaked to maximize transmission. IN the morning we will check the whole A2L centering again. If its OK, fine. Otherwise, we'll restore the bias values and align the PSL beam to the MC via the persicope.
  8. waveplates and PBS in the PSL were NOT removed.
  9. MC TRANS camera and QPD have to be recentered after we are happy with the MC axis.
  10. MC REFL camera has to be restored.
  11. WFS measurements will commence after the SURF reports are submitted.

We found many dis-assembled Allen Key sets. Do not do this! Return tools to their proper places or else you are just wasting everyone's time!

 

  3173   Wed Jul 7 22:52:38 2010 rana, nancyConfigurationIOObad length control offset for the MC

Rana found out that a connection was bad in the shown place, due to which the MEDM screen was showing bad offset for length control.

Basically, the offset slider value would not go into the system because of that bad connection, and was locking the mode cleaner at the wrong location.

Attachment 1: P7070251.jpg
P7070251.jpg
Attachment 2: Screenshot.png
Screenshot.png
  3174   Wed Jul 7 22:58:08 2010 nancyUpdateIOOMC alignment values.

Nancy and Koji:

This is what I and Koji measured after aligning the MC in the afternoon.

MC_Trans 4.595 (avg)

MC_Refl 0.203 (avg)

MC2_trans :

power = 1.34mW

13.5% width : x=6747.8 +- 20.7 um  , y = 6699.4+- 20.7 um

 

  3175   Wed Jul 7 23:11:08 2010 KojiUpdateIOOMC alignment values.

Hmm. I expect that you will put more details of the work tomorrow.
i.e. motivation, method, result (the previous entry is only this),
and some discussiona with how to do next.

Quote:

Nancy and Koji:

This is what I and Koji measured after aligning the MC in the afternoon.

MC_Trans 4.595 (avg)

MC_Refl 0.203 (avg)

MC2_trans :

power = 1.34mW

13.5% width : x=6747.8 +- 20.7 um  , y = 6699.4+- 20.7 um

 

 

  3182   Thu Jul 8 19:43:16 2010 nancyUpdateIOOWFS calculations

The WFS error signals were recorded in the order

WFS1_PIT

WFS1_YAW

WFS2_PIT

WFS2_YAW

these measurements are made in the linear region, that is the MC is nearly perfectly aligned.

This is  the average and std. dev.of 5 measurements taken of the same signals over 10 secs each. The std. dev are under 10%. And hence, I will be using 10 secs for measurements for the WFS signals after perturbations to the mirrors.

avg =

829.4408
-517.1884
297.4168
-944.7892


std_dev =

9.0506
22.9317
15.4580
8.9827

I perturbed the Pitch and Yaw of the Three mirrors (in order MC1,2,3), using ezcastep and calculated the coefficients that relate these perturbations to the WFS error signals.

The perturbation made is of -0.01 in each dof , and after measuring the WFS error for it, the system is reverted back to the previous point before making the other perturbation.

I was able to calculate the coefficients since I have assumed a linear relationship..

Following are the coefficients calculated using 10 secs measurements

coef_mat =

   1.0e+05 *

                            MC1_P   MC1_Y  MC2_P   MC2_Y    MC3_P   MC3_Y  constant
WFS1_PIT        -0.1262    0.3677   -0.4539   -0.6297   -0.1889   -0.1356   0.013664
WFS1_YAW     -0.0112   -0.7415   -0.1844    2.4509   -0.0023   -0.3531  -0.016199
WFS2_PIT         0.1251    0.4824   -0.2028   -0.6188    0.0099   -0.1490   0.006890
WFS2_YAW      0.0120   -0.7957   -0.1793    0.9962   -0.0493    0.2672 -0.013695

Also, I measured the same thing for 100s, and to my surprize, even the signs of coeficients are different.

coef_mat =


   1.0e+05 *

                           MC1_P   MC1_Y  MC2_P   MC2_Y    MC3_P   MC3_Y   constant
WFS1_PIT       -0.1981    0.3065   -0.6084   -0.9349   -0.4002   -0.3538   0.009796
WFS1_YAW     0.0607   -0.6977    0.0592    2.8753    0.3507    0.0373   -0.008194
WFS2_PIT        0.0690    0.4769   -0.2859   -0.7821   -0.1115   -0.2953  0.004150
WFS2_YAW     0.0580   -0.8153   -0.0937    1.1424    0.0650    0.4203  -0.010629

The reason I can understand is that the measurements were not made at the same time, and hence conditions might have changed.

A thing to note in all these coefficients is that they relate the error signals to the 'perturbation' around a certain point (given below). That point is assumed to lie in the linear region.

MC1_PIT      2.6129
MC1_YAW   -5.1781
MC2_PIT       3.6383
MC2_YAW    -1.2872
MC3_PIT      -1.9393
MC3_YAW    -7.518

 

  3183   Thu Jul 8 20:32:22 2010 nancyUpdateIOOMC alignment values.

I and Koji were trying to lock the mode cleaner for measuring the beam power at MC2 end. That is when we obtained the trans and refl values.

The beam characteristics at the MC2 were measured so that we could now use a dummy beam of similar power to test and characterize the QPD we are about to install at the MC2 end. This QPD wil provide two more signals in pitch and yaw, and hence complete 6 signals for 6 rotatioanl dof of the cavity. (4 are coming from WFS).

Once the QPD is characterised, it can be used to see the spot position at MC2. This is related to the mirror angles.

The width measurements were done using a beam scan. the beam scan was properly adjusted so that the maxima of the intensity of the sopt was at its center.

We also fitted gaussian curve to the beam profile, and it was a substantially good fit.

 

The whole idea is that I am trying  to look how the Wavefront sensors respond to the perturbations in the mirror angles. Once this is known, we should be able to control the mirror-movements.

the starting point would be to do just the DC measurements (which I did today). For proper analysis, AC measurements are obviously required.(will be done later).

The matrices so calculated can be inverted, and if found enough singular, the method can be used to control.

The first shot is to see teh dependency of teh error signals only on MC1 and MC3, and see if that is kind of enough to control these two mirrors.

If this works, the QPD signals could be used to control MC2 movements.

Quote:

Hmm. I expect that you will put more details of the work tomorrow.
i.e. motivation, method, result (the previous entry is only this),
and some discussiona with how to do next.

Quote:

Nancy and Koji:

This is what I and Koji measured after aligning the MC in the afternoon.

MC_Trans 4.595 (avg)

MC_Refl 0.203 (avg)

MC2_trans :

power = 1.34mW

13.5% width : x=6747.8 +- 20.7 um  , y = 6699.4+- 20.7 um

 

 

 

  3184   Thu Jul 8 21:44:43 2010 nancyUpdateIOOWFS calculations

 

I just found the singular values and the condition number of the 4*4 matrix relating the WFS error signals and the MC1 and MC2 movements.

the condition number is ~12.5. I think its small enough to continue with the scheme. (if the measurements and all are reliable).

 

  3208   Tue Jul 13 17:36:42 2010 nancyUpdateIOOWavefront Sensing Matrix Control

For yesterday - July 12th.

Yesterday, I tried understanding the MEDM and the Dataviewer screens for the WFS.

I then also decided to play around with the sensing matrix put into the WFS control system and see what happens.

I changed the sensing matrix to completely random values, and for some of the very bad values, it even lost lock :P (i wanted that to happen)

Then I put in some values near to what it already had, and saw things again.

I also put in the matrix values that I had obtained from my DC calculations, which after Rana's explanation, I understand was silly.

Later I put back the original values, but the MC lock didnot come back to what it was earlier. Probably my changing the values took it out of the linear region. THE MATRIX NOW HAS ITS OLD VALUES.

I was observing the POwer Spectrum of teh WFS signals after changing the matrix values, but it turned out to  be a flop, because  I had not removed the mean while measuring them.  I will do that again today, if we obtain the lock again (we suddenly lost MC lock badly some 20 minutes ago).

  3209   Tue Jul 13 19:26:47 2010 ranaUpdateIOOMC still broken

After whatever Joe/Alberto did this afternoon, the MC was not locking. Koji and I removed several of the cables in the side of the rack where they

were apparently working (I say apparently because there's no elog).

MC is now locking but the autolocker did not work at first - op340m was unable to access any channels from c1iool0. After several minutes, it mysteriously

started working - the startup.cmd yields errors seen on the terminal. I attach the screen dump/.

Attachment 1: a.txt.gz
  3231   Thu Jul 15 19:13:03 2010 ranaUpdateIOOMC_F check

Sometimes I like to plot the spectrum of MC_F. Its a good diagnosis of whether something is wrong.

The red trace is noisier than the blue reference. What is the cause of this?

Attachment 1: a.png
a.png
  3236   Fri Jul 16 15:39:27 2010 nancyUpdateIOOWavefront Sensors- switched off

I tuned the gain of WFS to 0 last night at about 3am.

I turned it back on now.

  3242   Sun Jul 18 20:50:03 2010 ranaConfigurationIOOMC TRANS optics changed

To make the beam on the MC trans camera bigger, I removed the lens + ND filter that was in that path.

The camera was getting the transmission through a BS1-33 (33% reflector). The reflection went to the TRANS QPD. I changed

the R=33% into an HR mirror (Y1-45P) so now the camera has a nice beam. The QPD was now saturating so I put a ND06 into that path

so now the TRANS_SUM is ~4.5-5 V when the MC is aligned.

The MC was also misaligned and failing to lock all weekend (why??) so I aligned the MC mirrors to get it to acquire again. Since we want to

collect MC seismic data, please make sure the MC is locked and running after finishing with your various MC or PSL work (this means YOU).

  3244   Mon Jul 19 14:14:03 2010 nancy, kojiUpdateIOOQPD Response Transfer Function

Friday night myself and Koji measured the Transfer function of the QPD circuit at MC2 side using a chopper . Following was our procedure :

 

We connected some wires at the input and output of the filter circuit to one of the segment of teh QPD. - seg 1.

A laser light was shined on to the QPD, it was pulsed using a chopper. The frequency of rotation of the chopper was varied.

These wires were then fed to the spectum analyser , and a transfer funstion was observed, It was nearly a low pass filter

The chopper frequency was then made variable by giving the chopper a signal from the spectrum analyser. This signal just swiped a large range of the rpm of the chopper.

Now the input signal looked like a sine wave of varying frequency. the transfer function looked like a perfect LPF, with a small SNR.

Attaching the plot of the TF in the next e-log (this one is on windows and can't access /cvs/cds)

 

  3245   Mon Jul 19 14:16:01 2010 nancy, kojiUpdateIOOQPD Response Transfer Function

Quote:

Friday night myself and Koji measured the Transfer function of the QPD circuit at MC2 side using a chopper . Following was our procedure :

 

We connected some wires at the input and output of teh filter circuit to one of the segment of teh QPD. - seg 2.

A laser light was shined on to  the QPD, it was pulsed using a chopper. The frequency of rotation of teh chopper was varied.

These wires were then fed to the spectum analyser , and a transfer funstion was observed, It was nearly a low pass filter

The chopper frequency was then made variable by giving the chopper a signal from teh spectrum analyser. This signal just swiped a large range of the rpm of the chopper.

Now the input signal looked like a sine wave of varying frequency. the transfer functino looked like a perfect LPF, with a small SNR.

Attaching the plot of the TF in the next e-log (this one is on windows and cant access /cvs/cds)

 

 QPDTF2.png

  3253   Tue Jul 20 18:29:43 2010 nancyUpdateIOOQPD installed behind the MC2

 

Yesterday I installed teh QPD on the table behind MC2, and observed teh signal on it.

The MC_leak is directed to it by a steering mirror.

I used the A2L_MC2 script to minimise  teh pitch and yaw gains, and estimated teh spot position on teh MC2 using that.

This spot position was aligned to the center of teh QPD.

In the night while before taking measurements, I decided to turn off the Wavefront Sensor Servos, but just after that, the MC alignment went very bad, and I could not align it in the next 2 hours.

For some reason, the MC was really mad the whole day yesterday, and was getting misaligned again and again, even when the WFS feedback was on.

 

The table also had another IR laser in it, which I and Koji switched off.

 

I will continue measuring once we pump down again.

For now, I am analysing teh QPD circuit Transfer Function.

  3264   Thu Jul 22 03:08:27 2010 KojiUpdateIOOVent and MC lock

Summary

- The vacuum chambers have been vented.

- The north heavy door of the BS chamber has been opened by Genie (not by the crane).
It was replaced by the light door. The door is currently closed.

- The MC has been locked with 20mW incident and aligned. MC REFL was left unchanged but lock was able to be achieved.

- The optics before MCT CCD and MCT QPD have been adjusted for the low power operation.


Details

- The first HWP for the variable optical attanuator (HWP/PBS/HWP pair) was set to be 86deg from the maximum transmission at 126deg.
The incident power of 19mW has been measured.

- The PSL mechanical shutter has been manually opened. Two other beam blocks has been removed.

- I found the MC was totaly misaligned with no resonance.- I tried to align it based on the previous OSEM values but in vain.

How to align the MC mirrors from the scratch

- MC1 has been aligned so as to maximize REFL PD and DC signal of WFS QPDs.

- MC3 has been aligned by looking at the scattered light on the MC2 frames. The spot is centered on the MC2 approximately.

- MC2 has been aligned so that any resonance is seen in MC_F.

Modification of the MCT optics

- The ND filter before the MCT was removed.

- The Y1-45S mirror before the MCT CCD, which is also used to steer the beam to the MCT QPD path, was replaced to BS1-50-45P.
The reason I used 45P is to obtain higher reflectivity. Because S has higher reflectivity than P in the each layer, I expected to have higher reflectivity for S than 50%.

- The MC REFL path has not been untouched.

Modification of the servo

- The lock was attempted after alignment of the mirrors.  Here how to lock the MC is described below.

1. Run script/MC/mcloopson

2. Open the MC Servo screen in MEDM

3. Change the input gain from 6dB to 22dB.
Change offset from 0.78 to -0.464 (such that the length output has no offset).
Change VCO Gain from 3dB to 21dB

Change MC Length path Gain from 0.3 to 1.6

  3350   Mon Aug 2 21:52:57 2010 KojiUpdateIOOMC is running at the full power

[Nancy and Koji]

We restored the full power operation of the MC.

Restoration of the suspensions

  1. Found the suspension watch dogs are left turned off.
  2. Found c1susvme1/2 were not running.
  3. Launched the realtime processes on c1susvme1/2 and c1iscey
  4. Restored the watch dogs. The suspensions looked fine.

Preparations for the high power

  1. Put an ND2.0 before the MCT CCD. Confirmed the ND reflection is damped.
    MCT QPD is not necessary to be touched.

The high power operation of the MC / post lock adjustment

  1. Locked the MC under the autolocker being disabled.
  2. Adjusted the aperture on the MC2 face camera
  3. Adjusted the spot positions on the WFS QPDs
  4. Reverted the scripts to the high power ones
    (mcup / mcdown / autolockMCmain40m)
  5. Logged in to op340m and restarted autolockMCmain40m

The autolocker seems working correctly.

  3352   Tue Aug 3 03:15:06 2010 nancyUpdateIOOMC back to locked mode

I turned the WFS gain to 0.02 back, and the MC is locked, the data for the seismic motion might be meaningful nowforth.

  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.

 

  3373   Fri Aug 6 12:22:04 2010 JenneUpdateIOOMC data taking over the weekend

Nancy has the Mode Cleaner for her work for the night, and is going to leave the MC happy, locked, autolocker on, WFS enabled, the works, and write down in the elog the time that she's finished. After that, I'm taking MC/seismic data all weekend long.  During the weekend, if at all possible, please don't go into the IFO room, especially near the Mode Cleaner.  If you do need to go into the IFO room, please elog the time you went in, and the time you left so I can correlate it with my dataThis is actually important, so please stick a quick elog entry in if you even think about opening the doors to the IFO room. It is much appreciated. 

  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
!

 

  3375   Fri Aug 6 12:44:29 2010 KojiUpdateIOOMC data taking over the weekend

Question:

Do you like to keep the WFS turned on?

This may change the transfer functions between the ground motion to the angle time by time,
and thus change the TF between the GND and the MCL.

Quote:

Nancy has the Mode Cleaner for her work for the night, and is going to leave the MC happy, locked, autolocker on, WFS enabled, the works, and write down in the elog the time that she's finished. After that, I'm taking MC/seismic data all weekend long.  During the weekend, if at all possible, please don't go into the IFO room, especially near the Mode Cleaner.  If you do need to go into the IFO room, please elog the time you went in, and the time you left so I can correlate it with my dataThis is actually important, so please stick a quick elog entry in if you even think about opening the doors to the IFO room. It is much appreciated. 

 

  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

 

 

  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.

  3713   Thu Oct 14 01:09:17 2010 yutaUpdateIOOtried to lock MC but failed

(Rana, Koji, Kiwamu, Suresh, Yuta)

 We attempted to lock the MC and finally got flashes of the MC, but no luck. 

Tomorrow we are going to check every components one by one to make sure if everything is okay or not.


Background:
 MC suspensions are well damped now.
 We need MC locked for the alignment of the in-vac optics.

Issues:

  These are the issues which we are going to fix.
1. DC alignment of the MC2 suspension doesn't seem to be working correctly. (see here)

  We should check the satellite box and the cable connection.

  The coils look like woking fine because we can kick MC2 by using each of the coils.


2. Incomplete modematching.

The spot size of the reflected light from MC1 looked like bigger. 

3. beam axis of the injection light to MC1

  3725   Thu Oct 14 23:33:45 2010 SureshUpdateIOO2W NPRO laser output power versus temperature

Steve measured an apparent power drop in the 2W NPRO output from 2.1W to 1.6W(elog entry no 3698) at 2.1A of diode current in the laser (elog entry:  2822).  It was later noticed that the laser temperature was set to about 45 degC while the initial calibration was done at 25 deg C.  

It was felt that the recent power drop may have something to do with the increase in the operating temperature of the laser from 25 to 45 deg C.  Therefore the laser was returned to 25 deg C and the power output was remeasured and found to be 2.1W as it was at the begining(elog entry:3709)

It was also noticed that returning the laser to 25 deg. C resulted in a loss of efficiency in coupling to the PMC.  We suspected that this might be due to multimode operating conditions in the laser at particular operating temperatures.  In order to see if this is indeed the case the laser power output was observed as a function of temperature.  We do notice a characteristic saw-tooth shape which might indicate multimode operation between 39 and 43 deg C.  It is best to verify this by observing the power fluctuations in the transmitted beam of the stabilised reference cavity.

 

tempscan.png

 

The measurement was made by attenuating the roughly 2W laser beam by a stack of two Neutral Density filfers and then measuring the transmitted light with the PDA36A photodetector.  This was because both the power meters used in the past were found to have linear drifts in excess of 30% and fluctuations at the 10% level. 

 

 

Attachment 2: Scan2010.zip
  3726   Fri Oct 15 00:15:52 2010 KojiUpdateIOO2W NPRO laser output power versus temperature

From the plot, you observed the reduction of the output power only by 1% between 25deg to 45deg.
This does not agree with the reduction from 2.1W to 1.6W.
Is there any cause of this discrepancy?

Quote:

 

tempscan.png

 

The measurement was made by attenuating the roughly 2W laser beam by a stack of two Neutral Density filfers and then measuring the transmitted light with the PDA36A photodetector.  This was because both the power meters used in the past were found to have linear drifts in excess of 30% and fluctuations at the 10% level. 

 

  3730   Fri Oct 15 21:25:23 2010 SureshUpdateIOO2W NPRO laser output power drop question

  The power meter used in the measurements of elog entries 2822, 3698 and 3709 was the Ophir PD300-3W.  This power head has several damaged patches  and a slight movement of the laser spot changes the reading considerably.  To verify I checked the power out with another power meter (the Vector S310) and found that there is no significant variation of the power output with the temperature of the laser.  And the power at 2.1A of diode current is 2W with 10% fluctuation arising from slight repositioning of the laser head.  There are regions of the Ophir PD300 which show the laser power to be about 1.9W.

  3779   Mon Oct 25 23:10:06 2010 KojiUpdateIOOMC is now flashing

[Suresh / Koji]

The MC mirrors are aligned. Now the flashing of the resonances are visible on the MC2 CCD

although the modematching seemed pretty poor.


- The incident power was adjusted to be ~20mW by rotating HWP after the laser source.
The power before the window of the chamber was ~450mW. Where are those missing 1.5W?

- We checked the spot on the last two steering mirrors and the incident beam on MC1.
The beam was too much off from the center of the 1st steering mirror. It was also hitting 1cm north of the MC1.
We adjusted the steering mirrors such that the incident and reflected beams are symmetrically visible at the MC1 tower.

- The MC mirrors are aligned. We first tried to use only MC2 and MC3. And then we used MC1 too as the spot on the MC2 was too high.

- We saw some TEM00 flashes but with many other modes flashing. We checked the beam diameter on the PSL table and on the MC REFL.
The latter one looked twice large as the former one. We concluded the beam is diverging.

- We closed the tank and decided to work on the mode matching tomorrow.

  3791   Wed Oct 27 02:26:15 2010 kiwamuUpdateIOOMC locked

(Rana, Koji, Suresh, Yuta, Thanh, Kiwamu)

 MC was locked successfully !

 Instead of feeding back the signal to the MC length we just injected it to the NPRO pzt with a high voltage (HV) amplifier.

So now we can move on to an in-vac work which needs the main beam to align the stuff.

 


(mode matching to MC)

Suresh and Thanh (a visitor from ANU) improved the mode matching to the MC. 

As written in the entry #3779  the beam after the mode matching lenses were diverging.

It is supposed to converge from 1.7mm radius at the last lens to 1.6 mm radius at the middle point of MC1 and MC2.

They slided the last lens toward the MC to make it more collimated and roughly measured the beam size using a sensor card.

As a fine tuning, they looked at some higher order modes showing up in the MC2 camera, and tried reducing the higher order modes by slightly sliding the last lens.

(assuming the lens position doesn't so much change the alignment)

During the work we removed a steering mirror for green locking because it was on the way of the lens slider.

 

- - measured optics' distances - - 

25.5 cm  from 1st lens to the front surface of the EOM

5.5 cm  length of the EOM

24.5 cm from the front surface of the EOM to the 2nd lens (concave)

15.5 cm  from the 2nd lens to the 1st steering mirror in the zig-zag path

20.5 cm  from the steering mirror to the last lens

 

(preparation for locking) 

Rana, Yuta and Koji prepared an old instant amplifier which can produce +/-13V output instead of usual SR560s.

We added an offset (~5V) on the signal to make it within 0-10V which is the input range of the HV amplifier.

If we take SR560, it's probably not sufficiently wide range because they can handle handle only about +/-4V.

 

We strung a cable from Marconi via the RF stabilizer to the wideband EOM in order to drive the EOM at 24.5MHz.

SInce the EOM doesn't have 50 Ohm input impedance we had to put a 50 Ohm load just before the EOM in order to drive it efficiently.

From a medm screen we set the driving RF amplitude slider (C1:IOO_MCRF_AMPADJ) to 0.0, which provides the maximum RF power on it.

 

(locking mode cleaner)

At first we unlocked the PMC to see an offset in the error signal without any lights on the MC_REFL PD.

Then we adjusted the offset to zero on the MC servo screen.

At the beginning of the locking the PMC was not stable for some reasons during the MC was locked.

But after increasing the laser power to the MC twice bigger, it looks like the PMC and the MC are quite stable.

 

 

  3805   Thu Oct 28 03:39:58 2010 yutaUpdateIOOgot very stable MC locking

(Rana, Suresh, Jenne, Kiwamu, Kevin, Yuta)

Summary:
  Last night we locked MC by feeding back the signal to NPRO PZT.
  But it was not so stable.
  We wanted more gain to lower the seismic motion, but we don't need high gain in high frequency part(>~1kHz) because it may cause something bad(NRPO PZT oscilatting, PMC not able to catch up with the NPRO frequency change, etc).
  So, we put DC gain boost today.
  It successfully made MC locking stable!

What we did:
1. Lowered the main laser temperature from 32.2° C to 31.8° C.
  When we increased the laser temperature, PMC transmission get lower.  32.2° C was on the cliff, so we put it to plateau region.

2. Lowered the gain of PMC servo (2dB instead of 8dB last night), because PMC was oscillating.
  We got 5.3V OMC transmission.

3. Made 3Hz pole, 30Hz zero filter and put in NPRO PZT servo loop.
  0dB at DC, -20dB at high frequency (see Kevin's elog #3802)

4. Put more gain to NPRO PZT servo loop to compensate -20dB at high frequency.
  In a word, we put DC gain boost.
  Attachment #1 is the MEDM screen screenshot for MC servo.

5. Aligned the beam into QPD at MC2 trans.
  We put lens in front of the QPD.
  Now, we can see the actual motion of the beam, and resonance peaks(Attachment #2; not locked at the highest).
    (We added 30Hz LPF after each 4 quadrant inputs to reduce noise)

Plan:
 - optimize MC suspension alignments
 - activate OL DAQ channels
 - reduce RFAM
 - install tri-mod box
 - QPD signal at MC2 should be more high(currently, ~7counts which equals to ~4mV)
 - change temperature of X-end laser to get green beat

Attachment 1: C1IOO_MC_SERVO20101028.png
C1IOO_MC_SERVO20101028.png
Attachment 2: MCrocks!.png
MCrocks!.png
  3806   Thu Oct 28 04:23:38 2010 ranaUpdateIOOA2L prep

To get the angle to length signal before the c1ioo processor gets going, we need a length signal. We can use either the error signal or the control signal.

I recommend using the control signal since its not puny. The 4-pin LEMO inputs to the OSEM ADC that Suresh has wired are differential so we can, in principle, use either the BNC output of the SERVO plug or the 2-pin LEMO output.

The analog whitening on the OSEM Whitening board should be engaged via the SUS MEDM screen so that we get a good SNR at the A2L dither frequencies.

If the ADC saturates, then we should use a pomona box RC low pass to cut everything off above 100 Hz.

Also, a comment about Yuta's elog: we estimated that the seismic motion was ~1e-7 - 1e-6 meters. The MC linewidth ought to be ~lambda/(2*Finesse) ~ 1e-9.

So, the MC servo as it was was not giving us enough gain (1/f above 50 Hz; UGF ~5-10 kHz) to get the error signal to stay in the linear PDH region. Kevin's filter gave us ~10x more gain at the seismic frequencies (1-3 Hz) of concern.

ELOG V3.1.3-