I gave up tonight's locking activity because the MC can't stay locked.

It seems that somehow the seismic noise became louder from about 1:00 AM.

I walked around the outside of the 40-m building to see what's going on, but no one was jumping or partying.

I am leaving the MC autolocker disabled so that the laser won't be driven crazy and the WFS won't kick the MC suspensions.

The attachment is a 3-hour trend of the seismometer outputs and the MC trans.

 Something has started shaking last night.  Everybody is claiming to be innocent next door.

I turned off the 40m AC at 11:06

The shaking has stopped at 9:32am  The AC was turned back on at 11:30am  We still do not have any explanation

[ Koji / Kiwamu ]

The frequent unlock of the MC are most likely unrelated to ground motion.

Although the reason why MC became unstable is still unclear.

There are two facts which suggest that the ground motion and the MC unlock are unrelated :

(1) It turned out that the seismometer signals (C1:PEM-SEIS-STS_AAA ) have a big cross talk with the MC locking signals.

    For example, when we intentionally unlocked the MC, the seismometer simultaneously showed a step-shaped signals, which looked quite similar to what we have observed.

    I guess there could be some kind of electrical cross talk happening between some MC locking signals and the seismometer channels.

    So we should not trust the signals from the STS seismometers. This needs a further investigation.

(2) We looked at the OSEM and oplev signals of some other suspended optics, and didn't find any corresponding fluctuations.

    The suspensions we checked are ETMX, ETMY, ITMX and MC1.

     None of them showed an obvious sign of the active ground motions in the past 24 hours or so.

The MC became crazy again.

It seems that there were corresponding steps in the OSEM signals. Look at the one-day trend posted below.

[Koji / Kiwamu]

 The MC is now back to normal. The beam pointing to the interferometer is good.

There were two different issues :

• A mechanical mount was in the MC WFS path.
• There were some loose connections in the SUS rack

Slid have we the position of the mechanical mount. Nicely the WFS beam go through now.

And also I pushed all the connectors associated with the MC SUS OSEMs in the SUS rack.

After pushing the connectors, the MC1 OSEM readouts dramatically changed, which actually more confused us.

As shown in the 3 hours trend below, the OSEM readouts have changed a lot (shown in the middle of the plot with arrows). Some bumps after the steps correspond to our alignment efforts.

When I came to the 40m this afternoon, the MC was unlocked. Here is the trend of MC_F for last 2 hours

C1:PSL-PMC_PMCTRANSPD = 0.800

Should I just disable the auto locker or try to realign it?

[ Den / Kiwamu]

 We have realigned the MC suspensions so that the WFS servos are smoothly engaged.

Now it seems working fine. The beam pointing to the interferometer also looks okay.

The WFSs control kept failing to engage the servos because of large misalignments in the MC suspensions.

When the TEM00 was locked, the transmitted light was only about 1200 counts and the reflected light was about 2.8 counts.

We tweaked MC1, MC2 and MC3.

PZT1, the one with Koji's custom mid-HV driver (#5447), is getting degraded.

The movable range in the pitch direction became narrower than what it used to be (maybe a factor of 3 estimated by looking at the beam spots).

I think we should raise the priority level of the active TTs for the next vent.

I have been having a feeling that the PZT1 response is getting smaller since the end of the last year, but now I am confident

because I could see the difference between the movable ranges of Yaw and Pitch, and they used to have approximately the same amount of the movable ranges.

Right now this is not a serious issue as the beam pointing determined by the MC alignment is so good that the Pitch range doesn't rail.

I won't be surprised if it becomes completely immovable in 3 month.

PZT1 started railing in the pitch direction and because of this TRY doesn't go more than 0.7. I will leave it as it is for tonight.

Tomorrow I will shift the alignment of the MC to make the PZT1 happier.

I have slightly shifted the MC beam pointing to relax the PZT1 PITCH. As a result the TRY value went to 0.97 in a first lock trial.

However another issue arose:

   The polarity for controlling the PZT1 PITCH seems to have flipped for some reason.

Since it is still sort of controllable, I am leaving it as it is.

If I remember correctly, sliding the PZT1 pitch value to the positive side brought the beam spot upward in the AS CCD. But now it moves in the opposite way.

Also the ASS feedback looks tending to push the PZT1 pitch to the wrong direction.

I am not 100 % sure if the polarity really flipped, but this is my current conclusion.

(MC pointing)

1. Locked the Y arm and aligned ITMY and ETMY with the ASS servos such that the beam spot on each test mass is well centered on the test mass.
   • With this process the eigen axis of the Y arm cavity is well prepared.
2. Checked the beam positions of the prompt reflection light and cavity leakage field in the AS CCD.
   • It looked the incident beam needed to go upward in the CCD view.
3. Offloaded the MC WFS feedback values to the MC suspension DC biases in a manual way.
4. Disabled the MC WFS servos. The MC transmitted light didn't become worse, which means the suspensions were well aligned to the input beam
5. Changed the DC bias in the MC2 PITCH, to bring the beam spot upward. I changed the DC bias by ~ 0.1 or in the EPICS counts.
6. Aligned the zig-zag steering mirrors on the PSL table to match the incident beam to the new MC eigen beam axis.
   • The transmitted DC light and reflected DC values went back to 27000 counts and 0.58 counts respectively without the WFS servos.
7. Re-engaged the WFS servos.

I disabled the feedback to the PZT1 PITCH in the Y arm dithering scripts so that it won't push the beam away from the good point.

Currently one has to do a manual alignment only for the PZT PITCH but the rest of DOFs are still able to be automatically aligned with the script.

As the PZT1 has not been functional, I have been aligning the Y arm to the input beam instead of aligning the beam to the Y arm.

It turned out that this procedure leads to two extra works everytime after alignments of the Y arm:

1. The Y green beam must be always aligned to the Y arm
   • The amount of the misalignment was found to be relatively big compared with how it used to be.
2. The PSL beat note setup must be always realigned because the Y green path is determined by the orientation of the Y arm.
   • In the past I didn't often realign the beat note path, but currently it needs to be pay more attentions.

Sad ..

The MC alignment servo wasn't great in the last 1 hour or so as it kept disturbing the MC lock. It was found to be due to some offsets in the MC trans QPD signals.

I put some values to cancel the offsets and then the lock became stable.

This is a first aid. So we need to take a closer look at the QPD signals and also probably the spot position on the QPD.

The symptom was that every time the alignment servo was engaged, at the beginning the amount of the transmitted light went to 27000 counts, which is good.

However, then the amount of the transmitted light slowly decreased in a time scale of ~ 20 sec or so, ending up with destruction of the MC lock.

According to the time scale I suspected that the servos using the trans QPD signals were doing something bad because their control width had been designed to be slow and slower than the rest of the servo loops.

I switched off the servos, called C1:IOO-TRANS_PIT and C1:IOO-TRANS_YAW and found the MC stayed locked stably with 27000 counts of the transmitted light.

Leaving the trans QPD servos off, I zeroed the offsets and then switched them on. It worked.

The values below are the current offset that I put.

                C1:IOO-MC2_TRANS_PIT_OFFSET = -0.115203
                C1:IOO-MC2_TRANS_YAW_OFFSET = -0.0323576
 

Today is janitor day. It still does not explain why the 2W Innolight tripped off about an hour ago. All back to normal.

.......................................................I asked Keven later, he admitted hitting the emergency shut off next to the chemical storage cabinet.

[Suresh / Kiwamu]

Currently the REFL beam is bypassed by additional mirrors and blocked by a razor blade dump.

Therefore the signals associated with the REFL ports (e.g. REFL11, REFLDC and etc.) are unavailable.

Just be aware of it.

[Kiwamu, Suresh]

   Today we attempted to measure the beam profile of the REFL beam under two conditions:

              (a) with PRM aligned and ITMs misaligned 

              (b) with PRM misaligned and ITMs aligned

The raw data is shown below.  In each of the above conditions we measured in both the vertical (v) and horizontal (h) directions.   The measurements in the vertical direction were better than the ones in the horizontal direction because the optics had a horizontal oscillation which gave larger errors in measurement.

Looking at the general trend of these lines it is clear that modes are not matched since the beam reflected by the PRM has a different divergence than that reflected from ITMs.  The beam is also astigmatic as the vertical and horizontal directions have different divergences.

I could find beam parameters only for the Blue line above (Profile in the vertical direction while PRM was aligned).   The fit is quite sensitive to the data points close to the waist, so we need to make better (lower St.Dev.) measurements near the AP table closer to the beam waist.  The intensity with only one ITM aligned is too low and also contributes to the errors.   The beam size is close to 6mm in the horizontal direction, this coupled with yaw oscillations give large errors in this measurement.

Here is the only reliable fit that could be obtained, which is for the prompt reflection from the PRM in the vertical direction

The fit function I used is  Beam Dia = Waist { Sqrt [ 1+  ((z + z0)/zr)^2). The fit parameters we get for this data are

z0 = 7.7 m 

Waist = 2.4 mm

zr = 6.9 m

Will make another attempt later today...

I have estimated how the mode profile of the PRM reflection should be, as shown in the plot blow.

A conclusion here is :

   we should be able to constrain the PRM curvature situation if measurements are precise and accurate enough with a level of less than ~ 100 um

In the calculation two cases are considered :

      (1) PRM has the correct curvature of  +122 m. This is shown as solid curves in the plot.

      (2) PRM has a wrong curvature of - 122 m (mirror is flipped) This is shown as dashed curves in the plot. 

Note:

 I have omitted the effect from the PRM thickness. Therefore PRM is dealt as just a curved reflector with RoC of +/- 122 m in the calculation.

[Suresh / Kiwamu]

 We did the 2nd round of the PRM reflection mode scan on Friday.

It seems that the PRM curvature maybe correct if we look at the vertical mode, however but the horizontal mode doesn't seem to agree with any of the expected lines.

In order to increase the reliability of the measurement, we need to confirm the beam profile of the incident beam by looking at the IP-POS beam.

Right now Suresh and Keiko are mode-scanning the IP-POS beam.

The plot below shows both the expected beam profiles (see the detail in #6444) and the actual data. 

(Discussion)

• Clipping at some optics. (Since the beam shape looked very Gaussian, the amount of the clipping could be very slight ?)
• Astigmatism at some optics. (Possibly in the telescope ?)

(Some distances)

(Some notes)

We did the following things prior to the measurement.

• Put a boost filter in the PRM_OLYAW to suppress the beam jitter below 1 Hz.
• Checked the MC WFS servo loop although it looked healthy.

For those who are interested in the actual data, I attache the actual data in zip file together with a python plot code.

The distance was set such that the 1st steering mirror (the one at the very left in the previous cartoon diagram #6445 ) in the REFL path is positioned at zero.

- - - Fitting results (chi-square fitting done by gnuplot):

All values are in unit of meter

# PRM (v) (Last tree points are excluded as the beam were clipped at the aperture of the beam scan)


w0          = 0.0015114        +/- 2.192e-05    (1.451%)
z0           = -4.46073         +/- 0.05605      (1.256%)

# PRM (h)

w0           = 0.00212796       +/- 1.287e-05    (0.6049%)
z0           = -2.53079         +/- 0.1688       (6.668%)

# ITM (v) (Last two points are excluded as the beam were clipped at the aperture of the beam scan)

w0           = 0.00190696       +/- 4.964e-05    (2.603%)
z0           = -8.09908         +/- 0.1525       (1.882%)

# ITM (h)

w0           = 0.0032539        +/- 4.602e-05    (1.414%)
z0           = -1.89484         +/- 1.524        (80.42%)

[Keiko, Suresh]

   Keiko and I measured the IPPOS beam profile.  The fit parameters  are :

The data files are attached. 

If we assume the nominal wavelength of the IR light to be 1064nm and constrain the Rayleigh length to be zr = (pi w0^2)/lambda we obtain the following fit parameters: (these are compared with the beam profile measurements of June/18/2010 available in the wiki )

* I updated the waist waist location coz because I missed-out the distance in air from the vacuum port to the optic on the IPPOS table.

Keiko, Rana, Suresh

Related to the beam profile of IPPOS today, we tried to measure the beam size at the ETMY point in order to estimate the input beam mode. We measured the beam size hitting at the suspension frame by a camera image, with two situations to see two "z" for beam profile.

(1) Input beam is slightly misaligned and the injected beam hits the end mirror frame. Assuming z=0 at the input mirror, this should be z=40m.

(2) Input beam hits the centre of the end mirror, and ITMY is slightly misaligned and the beam hits the end mirror frame after the one-round trip. Assuming z=0 at the ITM, this position should be z=120m.

The injected beam at the end point and the one round trip ligt at the end point should be the same size, if the input mode matches to the cavity mode. You can see if your injected light is good for the cavity or not. We compared and assumed the above two beam sizes by looking at the photo of the beam spot.

(1)  (2) 

 Assuming the zoom factor difference by the part below the beam (shown with allow in the photos. Arbitrary unit.), the beam in (2) is smaller than expected (roughly 40%?).

However this is a very rough estimation of the beam sizes! It is difficult to assume the beam size shown on the photos! It looks smaller only because the power of (2) is smaller than of (1). I don't think we can say anything from this rough estimation. One may be able to estimate better with CCD camera instead of this normal camera. 

The dump and some temporary mirrors were removed and now the REFL beam is available again.

I locked PRMI with REFL signals, it locked as usual.

I'd like to know what we expect for these numbers.  I've added to Kiwamu's drawing some more distances, so I can calculate the expected beam size at the IPPOS port.

I changed the ETMY CCD camera angle so that we can see the suspension frame in order to repeat the same thing as yesterday. The ETMY camera is not looking at the beam or mirror right now.

The mode looks quite terrible in the plot, but in reality it is an illusion of the plot.

The actual TEM00 content in this beam is ~99.7%

mode_coupling.pdf

Based on the above document, you can calculate power coupling between two elliptic gaussian modes.

Give the parameters of one beam as

zRy1 = pi*(2.77e-3)^2 / 1064e-9
z1y = 3.37
zRx1 = pi*(2.47e-3)^2 / 1064e-9
z1x = 4.15

Then, assume a round beam for the other.

zRx2 = zRy2 = zR
z2x = z2y = z0

Then run the optimizer to find the maximum for the quantity |C|^2

|C|^2 max: 0.9967
zR = 20.19
z0 = 3.804

I'm meditating over the mode matching from the mode cleaner to the ITMs, and I had another thought:

Have we changed the pointing of the MC significantly enough that we are no longer on the center of the MMT mirrors?  To be this significant, we would probably also have had to scoot the Faraday a bit too, since it's skinny like a straw.  It looks like our measurements of the input beam have been the following:

MC waist, 21 May 2010

After MMT2, 18 June 2010 (a few days before this, we flipped the MMT2 mount to 'perfect' the mode matching up to 99.3%, so I don't think the MMT has moved since then.)

After MMT2, 26 March 2012

There's a big o' ~2 year gap between our measurements, and we've been in and out of the vacuum a few times since then.  I'll flip through the elog, but does anyone have any memory of us moving the Faraday after June 2010?  When was the last time we made sure that we were at least close to the center of the MMT mirrors? 

It is quite likely that we touched the Faraday in Nov 2010.

In this entry http://nodus.ligo.caltech.edu:8080/40m/3874 I wrote that I removed the MCT optics in the chamber.
This is the pickoff between the IMC and the Faraday. This causes the beam shift. Therefore, the Faraday had
to be moved.

There were intensive in-chamber activities from Nov to Dec 2010. I am sure that almost everytime we went into
the chamber, we checked the spot position on the MMT mirrors as well as the TT and PZT mirrors.

Does the miscentering of the spots on the MMT mirrors cause the mode matching significantly changed?

This is wrong!  See following elog for corrected plot (and explanation)

I'm not done meditating on what's going on, but here's what I've got right now:

This is a beam profile, using the distances from the combined Kiwamu / Jenne sketch earlier today. 

0 meters along the horizontal axis is meters from the Mode Cleaner waist. (Yes, I was bad and forgot to label it.  Get over it.)

The pink and green dots to the left of the plot are the MC fitted waist measurements that we made in May 2010.

The pink and green dots in the ~center of the plot are the fitted waist measurements that Suresh and Keiko took yesterday, of the IPPOS path, so after the MMT.

The black dot is where we would like our non-astigmatic beam to be.  This is the calculated waist size of the cavity mode, using the new ~37.76m distance, after we moved the ETMs to their current positions.  The black dot indicates 3.036 mm at the ITM (averaged between the BS-ITMX and BS-ITMY distances).

The moral of the story that I'm getting from this plot:  something funny is going on.

The distances Kiwamu quoted on the sketch are very close to the ones that I used for designing and checking the MMT in the first place, which were based off of measurements using rulers etc to measure distances.  Steve said he looked at photos today, and agreed that Kiwamu's numbers looked reasonable also.

Something that we haven't done lately is measure the position of each optic from every other optic, along the beam path.  I propose we come up with a clever way to put a target on top of / next to mirrors, and then a way to hold the laser distance measure-er at an optic, so that we can go thorough systematically and measure the actual path that our beam is seeing.  Maybe this is too much work, and not worth it, but it would make me happier.  In my head, these 'fixtures' are just small pieces of cleaned aluminum, one that can sit on a mirror mount, and one which we can use to align the laser ruler to approximately the front of an optic.  Nothing fancy.

 Yup, something funny was going on.  Nic's MM code that I used, "a la mode", calls for the focal length of the optics, whereas the code that I wrote and used for ages called for the radius of curvature.  f = R/2.  Fixing that factor of 2 I get something more like:

This is obviously much better, in that the beam profile goes through (within some error) both of the measured sets of points - the MC waist measured in May 2010, and after the MMT measured yesterday.

So, what does it all mean?  That I'm not sure of yet.

 From the mode measurement I and Suresh have done yesterday, I calculated what beam size we expect at ETM ((1) upper Fig.1)  and at ETM after one bounce ((2) lower Fig.1).

Fig.1 (Yarm)

In case of (1), we expect approximately w=6300 um (radius), and w=4800 um for one-bounce spot (2) from the measured mode, see Fig.2.

Fig.2

This roughly agree with what we observed on CCD camera. See, pic1 for (1) and pic2 for (2). The spot at the ETMY (1) is larger than the one-bounced spot (2). From the monitor it is difficult to assume the radius ratio. The observed spot of (2) is a bit smaller than the prediction. It could happnen when (A) the ETMY (as a lens) is slightly back of the ideal position (= the distance between the ITM and ETM is longer than 40m) (B) the real waist is farer than ITM position toward MC (I assumed roughly 5 m from Jenne's plot, but could be longer than that).

pic1 (left): beam spot hitting on the suspension frame. pic 2 (right): the one-bounced beam spot hitting on the suspension frame.

 In an attempt to estimate the errors on the fit parameters I upgraded my Mathematica code to use the function 'NonlinearModelFit', which allows us to define weights and also reports the errors on the fit parameters.   The plots have been upgraded to show the error bars and residuals.

The parameters determined are given below and compared to the earlier measurements of 06/18/2010

Vertical Profile:

Horizontal Profile:

There is a significant change in the beam waist location (as compared to previous report) because I corrected a mistake in the sign convention that I was using in measuring the distances to the waist from the zero-reference.
 

As I was a little dissatisfied with the inaccuracy in the distance numbers in Kiwamu's sketch, I went back to the 18 Dec 2010 table layout drawing for more accurate numbers.  These are now included in this round of plots.

Also, I include astigmatism due to the incident angles on MMT1 (~3.5 deg) and MMT2 (~1 deg).

First plot, IPPOS path, using the recent (fixed) measurements from Suresh to fix the beam width.  Note that the old 2010 measurements of the MC waist are consistent with this measurement.

Second plot, Main IFO path all the way to the ITM (average) position, using the 2010 MC waist measurements to fix the beam width.

Third plot, Main IFO path all the way to the ITM position, but with PRM flipped (negative RoC), using the 2010 MC measurement to fix beam width.

With the PRM correctly oriented (2nd plot), I get beam waists of (x = 2.529 mm, y = 2.646 mm), which corresponds to a mode matching to the arm cavity of (eta = 97.43%, PRM correct).

With the PRM flipped (3rd plot), I get beam waists of (x = 3.176 mm, y = 3.3 mm), which corresponds to a mode matching to the arm cavity of (eta = 99.55%, PRM flipped).

First plot:

Second plot (this is how the MMT was designed to be, before the ETMs were moved, which made the ideal waist larger):

Third plot:

For both the 2nd and 3rd plot, we can't look at the post-MMT waist measurements, since that distance on the plots is after the PRM, which is a curved optic.  So the fact that the post-MMT measurements match the correct-PRM plot better than the flipped-PRM plot can't be taken to be meaningful.

Moral of the story:  I'm not sure how to interpret any of this to tell us if the PRM is flipped or not, since the measurements are all of the beam profile before the beam sees the PRM.  We'd have to measure the profile after the PRM somehow in order to get that information.  We have okay but not great mode matching to the arm if the PRM is correct, but I don't know that we readjusted the MMT after we moved the ETMs.  I don't remember recalculating any optimal telescope lengths after the arm length change.  If we need better mode matching, I can do that calculation, although given how much space we don't have, it would be hard in practice to move the MMT mirrors by much at all.

More calculations....

Game Plan:  Using MC waist measured beam as the starting point of beam propagation, move MMT mirrors around until the beam profile fits with the IPPOS measurements from Monday.

Plot 1:  Allow MMT mirrors to move as much as they want to.  Note that the Y-beam goes through the IPPOS measured point. (This implies we put the MMT in the wrong place by ~half a meter.  Unlikely)

Plot 2: Using MMT locations from plot 1, what does the beam look like at the ITMs? 

Plot 3:  Allow MMT mirrors to move as much as 2cm.  Note that the Y-beam doesn't quite go through IPPOS measured point.

Plot 4: Using MMT locations from plot 3, what does the beam look like at the ITMs?

For all of the above, I was optimizing the propagation of the Y-beam profile.  Since the X-beam profile measurement is so different, if I want to optimize to X and let the MMT mirrors move as much as they want, MMT1 ends up inside the MC.  Unlikely.  So I'm just looking at Y for now, and maybe Suresh or someone needs to rethink the error bars on their measurements or just remeasure.

Plot 1:

Plot 2:

Plot 3:

Plot 4:

I fitzed by hand with the numbers for the incident angles on MMT1 and MMT2, and then let the code optimize the position of MMT1 and MMT2.

Here I have set the incident angle for MMT1 = 25deg, and MMT2 = 12deg (should be 3.5deg, 1deg by design).  The length of the telescope doesn't want to change by more than 7mm, but the position of the telescope wants to change by 1.3meters.  Is it possible that the distances on the Monday IPPOS measurements aren't actually correct?

Suresh noted that I never wrote down the waist positions of the beam propagated through the MMT (based on where we think it is from ruler-based measurements).  This uses the MC waist measured beam as the starting point, and just propagates through the MMT, out to the IPPOS port.

Yq:

  Properties:
                    q: 2.2488 +23.8777i
               lambda: 1.0640e-06
            waistSize: 0.0028  (at z = 13.2676 meters)
               waistZ: 2.2488    (relative to z = 13.2676 meters)
      divergenceAngle: 1.1910e-04
    radiusOfCurvature: 255.7849
            beamWidth: 0.0029
        rayleighRange: 23.8777

So, to sum up, the vertical beam waist is 2.8438 mm at 11.0188 meters from the MC waist.

Xq:

  Properties:
                    q: 5.1953 +24.7342i
               lambda: 1.0640e-06
            waistSize: 0.0029   (at z = 13.2676 meters)
               waistZ: 5.1953    (relative to z = 13.2676 meters)
      divergenceAngle: 1.1702e-04
    radiusOfCurvature: 122.9525
            beamWidth: 0.0030
        rayleighRange: 24.7342

So, to sum up, the horizontal beam waist is 2.8943 mm at 8.0723 meters from the MC waist.

In pictorial form,

I am trying to track down possible errors in our measurements. 

So as a first step I am recomputing the IPPOS waist location with respect to the MC waist, using the same optical layout diagram as the one used by Jenne in her calculations.  Pic of Jenne's lab notebook showing location of optics is attached.  

 Let us compare it with the old measurement of the IPPOS beam from June/18/2010.

Note that there is a discrepancy of about 3.2 m in the waist location for the vertical profile and about 3.5 m for the horizontal profile between these two measurements. 

Let us compare these measurements with what is expected from calculations.  Jenne uses the known parameters of MC waist and the locations of the MMT optics to compute the parameters for the IPPOS beam:

 As the 2010 measurements are reported wrt to MMT2 and calculations are wrt MCwaist, I have used the distance between the MCwaist to MMT2 = 3.910 m to shift the reference from MMT2 to MC waist. Refer to the attached diagram from Jenne's notes for this MMT2 <--> MC waist distance.

There is a discrepancy of 1.5 meters between the calculations and recently measured waist location.  The discrepancy with the 18Jun2010 measurement is much larger, about 3 meters in both v and h.

Are such variations to be expected between two successive measurements?  I looked at another case where we have two measurements of a beam to see what to expect.

I looked at the REFL (Reflection from PRM) case, where we repeated a measurement, to see how much variation could happen in w0 and zr, between repeated measurements. This was a particularly bad case as our first attempt had problems due to OL servo loop oscillations in the PRM suspension damping.  We fixed that later and measurement 2 has smaller residuals. And I think we are doing okay in IPPOS case as seen by the reduced scatter of the residuals.

 These are the fits from the REFL beam measurement 1

 I have also recomputed the fits to the data from REFL beam measurement 2.  They match the earlier fits reported by kiwamu in his elog 6446

Note that between these two measurements the beam waist location has shifted by 0.5 m for the vertical and about 1.3 m for the horizontal cases.  So variations of 1.5 m in the waist locations are possible if we are not careful.  But this is a particularly extreme example, I think we are doing better now and the measurement is unlikely to change significantly if we repeat it.

Some notes:

Fits for IPPOS and both REFL measurements 1 and 2 are attached. 

The zero reference for the z axis of the IPPOS beam plot is at a distance of 6.719 m from MC waist for a beam propagating towards the IPPOS QPD.

The zero reference for the z axis of the REFL beam plots is at a distance of 5.741 m from the MMT2 in the direction of a beam reflected by PRM and propagating towards the REFL port.

I think we can try to damp 1 Hz resonance more. In September it was not seen because of the digital noise. After we've figured it out, 1 Hz resonance began to be more clear (blue line).

Now applying oaf we reduce the effect of the stack and the 1 Hz resonance is even more clear:

...Mostly just recollections at this point.

I re-looked at the mode matching's sensitivity to misplaced optics.  Here is the plot that the original MMT code from 2010 spits out:

What this plot is telling us is that we should lose no more than 0.1% of mode matching "goodness" if we messed up the curved optic's positions by up to 2 cm.  If we can't place optics to within 2 cm, we might as well go back to optics kindergarten, because that's pretty lame.

UPDATE: Here is a histogram using the new code, which definitely includes the non-unity index of refraction for the transmissive optics and the Faraday.  The only optics which are permitted to move are the 2 curved optics, and they are allowed a stdev of 20mm.  Again, we shouldn't be doing worse than ~99% mode matching, even if we're 2cm off from the MMT positions that we measured with a ruler.  This histogram only has 300 iterations, since it takes quite a while (~0.5sec) to calculate each iteration.  Note this is mode overlap using the measured MC waist, propagated through optics, compared to the ideal arm mode.  This is completely ignoring the IPPOS measurements so far.

UPDATE 2: Allowed 5 degrees of incident angle motion for both curved optics, which changes the astigmatism of the beam downstream.  Still, no big change from ~99% mode matching efficiency.  Again, this doesn't include any information from the IPPOS measurements.  3000 iterations this time around, since I didn't need my computer.  Curved optics still allowed to move back and forth by 2cm. 

More meditations and conclusions to follow...  currently running hist code to allow tilt of optics, to account for astigmatism changes also. 

Suresh and I are going to do some beam measurements tomorrow with the beamscanner, and then we will do a few measurements with the razor blade technique, to confirm that we're doing things okey dokey.

Another histogram.  This one allows the MMT mirror positions to move, the MMT incident angle for both curved optics to change, and the MC waist size and position to change.  The error quoted for the MC waist size measurement from 2010

was +\- 0.01mm, and the MC waist position was +\- 28mm.  

This histogram is showing that we're pretty sensitive to the MC waist measurement, which is used to define the beam.  We can be up to ~2% off in our ideal mode matching to the arms if we're using the incorrect initial beam for the telescope design.

[Suresh, Jenne]

  The input beam is most probably being clipped at the Faraday Isolator.  

Evidence: 

a)  The beam scan of the IPPOS beam showed a nongaussian beam in the horizontal direction.  This was visible in the beam scan since it overlays a gaussian-fit over the data.

b)  I was able to remove this departure from gaussian profile by introducing an offset of 5 into the C1:IOO-WFS2_YAW_OFFSET.  

c)   We made a few measurements of the beam diameter as a function of distance at an offset of 7.  At a distance of beyond 3 m the deviation from gaussian profile was once again apparent. 

d)  We increased the offset to 14 to remove this deviation. 

e)  When we measured the beam diameter again with this new offset the horizontal diameter and vertical diameters dropped by 2.sigma.  Indicating there the beam was clipped till then.

f)   We increased the offset to 16 and the beam diameter did not change further (within 1.sigma). Implying no more clipping, hopefully. 

And then the earthquake stopped us from proceeding further. 

We plan to investigate this further to be sure..  Data attached.

Subsidiary effects to keep track of:

1) Introducing an offset into the WFS loops decreases the coupling from PSL into MC. 

2) If the beam is being clipped at the Faraday Isolator then the REFL beam would also show lesser clipping with WFS offsets.

I tried to determine an optimal WFS2YAW offset to be used so that we may avoid clipping.

Initially, I just measured the beam diameter as a function of offset.  If the beam diameter would become independent of offset if it is not clipped.  However a systematic effect became apparent when I shifted the beam on the detector to a slightly different location.  So I repeated the measurements while recentering the beam to the same location everytime  (centered at -1650+/- 50 for both H and V directions).

I have attached plots of the scans for both cases, with recentering and without.    I have not been able to figure out what is going on since the beam diameter does not become independent of the offset.  While the beam profile becomes more gaussian beyond offsets of about 7 or so, the beam diameter does not seem to follow a clear pattern.  The measurements are repeatable (within one sigma) so the experimental errors are smaller than 1 sigma.

The photographs below show the improvement of Horizontal beam profile with WFS2Yaw offset.  These seem to indicate a good gaussian beam for offsets beyond 7 or so.  At offsets more than 12 the MC unlocks.

Offset = -2	Offset = 0	Offset = 2	Offset = 8

This seems to indicate that the beam diameter does not vary for WFS2Yaw offset > 8	But if we recenter the beam for each measurement this effect seems to vanish

 Will continue tomorrow.   Jenne wants to do some IFO locking now.

[Jamie, Suresh]

Yesterday Den and Koji reported that the WFS loops were causing the MC to become unlocked.  They had aligned the PMC.   The input beam into the MC seems to be well aligned.  MCREFL DC close to minimum it gets while MC is locked (~0.45 V).

I checked and saw that the WFS heads and the MC2_TRANS_QPD had picked up DC offsets.  To reset them I turned off the MC_autolocker and closed the PSL shutter.

The ADC offsets were set using this script /cvs/cds/rtcds/caltech/c1/scripts/MC/WFS/WFS_QPD_offsets.  (Jamie fixed the paths to ezcaservo to get this script to work)

The WFS sensor head offsets were manually set to adjust the Q and I signals from the sensor head to zero.  (This operation is supposed to be done by a script which is available, but I will check it out before I direct people to it).

Then we noticed that the ASC outputs were turned off.  (Presumably Koji turned them off yesterday, when the MC was repeatedly unlocking due to the WFS loops).

We turned on the ASC outputs and the MC stayed locked with reasonable outputs on the WFS output channels.  (+/-100)

However, engaging the WFS servo increases the MCREFL DC signal to 0.7 V from the 0.45 V value when the servo is not engaged.  This could be because of DC offsets in the WFS servo filters.   I will adjust these offsets to maintain good MC transmission when the WFS servo is engaged.

I tried to figure out where additional (to seismic) noise enters to MC_F, so the coherence below 1 Hz is low (~0.2-0.5). I've examined noise in the path

PD -> DEMOD -> MC BOARD -> FSS -> PZT Controller -> LASER

• I terminated ADC and measured its noise
• connected MC BOARD OUT to ADC, terminated INPUT1 of the MC BOARD and measured noise
• connected DEMOD Q OUT to MC BOARD INPUT1, terminated PD INPUT on the DEMODULATOR and measured noise
• connected PD to DEMOD, blocked the beam incident to the PD and measured noise

 MC BOARD noise shows up only below 0.1 Hz and at 10 Hz where the whitening filter starts to work. SNR is ~2 at 4 Hz, so we might want to slightly improve whitening filter. But other then that path PD->DEMOD->MC BOARD is not responsible for additional noises below 1 Hz.

Next I connected SR785 to the laser and measured the closed loop feedback signal while MC was locked.

Coherence between MC BOARD OUT1 and feedback signal is high enough to assume that FSS and PZT controller are also not responsible for additional noise.

From the other hand MC2 SUSPOS measured by OSEMS shows good coherence with GUR1_X

That means that MC2 is indeed driven by seismic motion. In order to figure out if this is the case for MC1 and MC3, I rotated GUR2 by 45 degrees. When it will calm down, I'll measure coherence between OSEMs and seismic motion.

I've measured coherence between seismometer signals and OSEMS of MC 1,2,3

GUR1 was rotated on the angle pi / 4 relative to x arm to match suspos axis of MC1 and MC3. Coherence between MC2 and GUR2_X is high, between MC3 and GUR1_X is ~0.2 but is compensated by GUR1_Y, between MC1 and GUR1_Y below 1Hz is ~0.5 and is not compensated by GUR1_X.

Then I measured coherence between GUR1_Y and MC3 OSEMS in 3 regimes :

• FEEDBACK OFF, WFS OFF
• FEEDBACK ON, WFS OFF
• FEEDBACK ON, WFS ON

Once WFS are ON, signal becomes noisy, FEEDBACK is OK. Then I measured coherence between MC_F and GUR2_X with WFS ON and OFF

Coherence between MC_F and GUR2_X is less when WFS are ON in the range 0.2 - 1 Hz and 4 - 10 Hz. Moreover PSD of MC_F seems to be higher at 10 - 100 Hz. But this may be caused by other reasons.

Then I measured the coherence between IN and OUT signals in WFS_SERVO

One filter bank adds noise to WFS signals and because of that we loose coherence between MC_F and seismic motion.

 This effect is due to C1:IOO-WFS1_PIT_LIMIT=2000. When I turned if off, coherence between C1:IOO-WFS_PIT input and output signals restored

The other thing is that WFS actuate on the angular motion, but this couples to the position motion. We need to diagonalize the actuator.

OK. Then we should make this number bigger such that the coherence is still completely maintained.
Is this set in the auto locker? Or manually set?

LIMIT is set manually, auto locker does not change it. I've put C1:IOO-WFS1_PIT_LIMIT=4000, it seems to be fine for now.

No leaving the OAF running until you're sure (sure-sure, not kind of sure, not pretty sure, but I've enabled guardians to make sure nothing bad can happen, and I've been sitting here watching it for 24+ hours and it is fine) that it works okay.

OAF (both adaptive and static paths) were left enabled, which was kicking MC2 a lot.  Not quite enough that the watchdog tripped, but close.  The LSCPOS output for MC2 was in the 10's or 100's of thousands of counts.  Not okay.

This brings up the point though, which I hadn't actively thought through before, that we need an OAF watchdog.  An OAF ogre?  But a benevolent ogre.  If the OAF gets out of control, it's output should be shut off.  Eventually we can make it more sophisticated, so that it resets the adaptive filter, and lets things start over, or something. 

But until we have a reliable OAF ogre, no leaving the adaptive path enabled if you're not sitting in the control room.  The static path should be fine, since it can't get out of control on it's own.

Especially no leaving things like this enabled without a "I'm leaving this enabled, I'll be back in a few hours to check on it" elog!