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ID Date Author Type Category Subject
10338   Wed Aug 6 12:44:52 2014 KojiUpdateASCPOP QPD signals

This is nice. Can we test this idea with POP22 + a razor blade?

Just to take transfer functions in PRMIsb between the PRM angle to POP QPD/POP22+razor blade
as well as the noise spectrum measurement are already useful.

We want to figure out the requirement for the 2f QPD.
(Transimpedance / Noise level / Beam size / etc)

Depending on the requirement we'll see if we need demodulation or just a power detector.

10398   Fri Aug 15 01:31:44 2014 JenneUpdateASCPOP QPD to ETMs model wiring complete

I have added a few things to the ASS model, and the ASC sub-block, so that we can send POP QPD information down to the ETMs for CARM angular control after we've reduced the CARM offset and gotten some carrier buildup.  I did not remove our ability to actuate on PRM, so that we can still play with it in PRMIsb cases.

The input matrix has been expanded so that it can send signals to new CARM_YAW and CARM_PIT filter banks.  The corresponding filter banks have been created.  The output matrix was also expanded to take in the 2 new servo outputs, and so it can send signals to both ETMs, pitch and yaw.  I did not include any triggering logic for this new CARM situation, since I assume we'll just turn it on and off with our scripts.  (We haven't really been using the triggering capability of the PRM ASC either lately, although it's all still there).  I added the inputs and outputs of the CARM servos to the list of acquired channels.

The ASC sub-block:

I also modified the top level of the ASS model.  This was just a simple addition of summing nodes for the ETMs, similar to what was already in place for the PRM, so that we can send both the ASS dither alignment signals and the ASC servo control signals to the optics.

The ASS top level:

I also quickly modified the ASC screen to expose all of the new options:

The ASS model was compiled, and restarted.  As usual, this temporarily removes the biases on the input pointing tip tilts, but the pointing seems to have come back without any trouble.

10454   Thu Sep 4 18:30:13 2014 GabrieleSummaryASCOptimal Gouy phase for POP QPD

Jenne asked me to simulate the signals on POP QPD when moving different mirrors, as a function of the Gouy phase where the QPD is placed.

I used the opportunity to create a MIST simulation file of the entire 40m interferometer, essentially based on my aLIGO configuration file. I used the recycling cavity lengths obtained from our survey, and other parameters from the wiki page. The configuration file is attached (fortymeters.mist).

Coming back to the main simulation, here is the result, both for the "regular" POP QPD and for a 22MHz demodulated one. The Gouy phase is measured starting from PR2. Cavity mirrors are easily decoupled from PRM in the "regular" QPD. As already demonstrated in a previous simulation, ETMs signals are very small in the 22 MHz QPD. Moreover, it is possible to zero the contribution from ITMs by choosing the right Gouy phase, at the price of a reduction of the PRM signal by a factor of 3-4. Simulation files are attached.

Attachment 2: fortymeters.mist
###########################################################################
# Configuration file for full dual recycled 40m interferometer
classname FortyMeters
################################################################ Parameters

# General parameters
const Pin 1             # input power

# Mirror parameters
const T_ITM 0.01384     # ITM transmission [from https://wiki-40m.ligo.caltech.edu/Core_Optics]

... 143 more lines ...
Attachment 3: fortymeters_pop_qpd.mist
###########################################################################
# Configuration file for full dual recycled 40m interferometer
classname FortyMetersPOP_QPD
################################################################ Parameters

# General parameters
const Pin 1             # input power

# Mirror parameters
const T_ITM 0.01384     # ITM transmission [from https://wiki-40m.ligo.caltech.edu/Core_Optics]

... 148 more lines ...
Attachment 4: pop_qpd.m
% compile and create simulation class
clear classes
MIST('fortymeters_pop_qpd.mist');
s = FortyMetersPOP_QPD(4);

% set angular motion of ITMs, ETMs and PRM
s.ETMX.setMotionShape('pitch');
s.ETMY.setMotionShape('pitch');
s.ITMX.setMotionShape('pitch');
s.ITMY.setMotionShape('pitch');

... 47 more lines ...
10503   Fri Sep 12 15:10:09 2014 JenneUpdateASCMICH ASS

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

ASS screen has been updated.

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

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

10662   Mon Nov 3 17:14:00 2014 ericqUpdateASCIMC to IFO angular motion

Something to note, as we have the IMC angular controls under consideration:

Jenne has the DRMI locked right now. I took a look at the coherence between the POP QPD and MC2 transmission QPDs. (Since she's using ASC, I also included those control signals. The coherences are about the same, unsurprisingly)

Based on the observed coherences, from about 1 to 6Hz, IMC motion is responsible for a fair amount of the DRMI angular motion. Also, PIT and YAW couple differently.

10663   Mon Nov 3 17:43:14 2014 KojiUpdateASCIMC to IFO angular motion

I wonder if this is the coherence caused by the beam itself, or caused by the same ground motion.
Jenne should be able to tell us...

10680   Thu Nov 6 12:53:09 2014 diegoUpdateASCX arm restored

[Diego, Koji]

X arm has been restored, after modifying the two parameters mentioned in http://nodus.ligo.caltech.edu:8080/40m/10676 (C1SUS_ITMX:  LSC/DAMP and LSC/BIAS); after that, a manual re-alignment of ETMX was necessary due to heavy PIT misalignment. I will check the ALS lock once work on the Y arm is done.

10745   Tue Dec 2 01:27:22 2014 diegoUpdateASCASS Scripts for arms

I updated the medm C1ASS page for the Arm scripts:

ON : same as before

FREEZE OUTPUTS: calls new FREEZE_DITHER.py script, which sets Common Gain and LO Amplitudes to 0, therefore freezing the current output values

START FROM FROZEN  OUTPUTS: calls new UNFREEZE_DITHER.py script, which sets Commong Gain and LO Amplitudes as in the DITHER_ASS_ON.py script, but no burt restore is performed

OFFLOAD OFFSETS: it's the old "SAVE OFFSETS", calls the WRITE_ASS_OFFSET.py script

OFF: same as before

StripTool: same as before

10752   Thu Dec 4 00:26:07 2014 JenneUpdateASCPOP yaw razor blade installed

We would like the option of feeding back the POP beam position fluctuations to the PRM to help stabilize the PRC since we don't have oplevs for PR2 and PR3.  However, we cannot just use the DC QPD because that beam spot will be dominated by carrier light as we start to get power recycling.

The solution that we are trying as of today is to look at yaw information of just the RF sidebands.  (Yaw is worse than pitch, although it would be nice to also control pitch).  I have placed a razor blade occluding about half of the POP beam in front of the POP PD (which serves POPDC, POP22 and POP110).  I also changed the ASS model so that I could use this signal to feed back to the PRM.  Loop has been measured, and in-loop spectra shows some improvement versus uncontrolled.

Optical table work:

The POP beam comes out of the vacuum system and is steered around a little bit, then about 50% goes to the DC QPD.  Of the remaining, some goes to the Thorlabs PD (10CF I think) and the rest goes to the POP camera.  For the bit that goes to the Thorlabs PD, there is a lens to get the beam to fit on the tiny diode.

There was very little space between the steering mirror that picks off the light for this PD, and the lens - not enough to put the razor blade in.  The beam after the lens is so small that it's much easier to occlude only half of the beam in the area before the lens.  (Since we don't know what gouy phase we're at, so we don't know where the ideal spot for the razor is, I claim that this is a reasonable place to start.)

I swapped out the old 50mm lens and put in a 35mm lens a little closer to the PD, which gave me just enough room to squeeze in the razor blade.  This change meant that I had to realign the beam onto the PD, and also that the demod phase angles for POP22 and POP110 needed to be checked.  To align the beam, before placing the razor blade, I got the beam close enough that I was seeing flashes in POPDC large enough to use for a PRMI carrier trigger.  The PRMI carrier was a little annoying to lock.  After some effort, I could only get it to hold for several seconds at a time.  Rather than going down a deep hole, I just used that to roughly set the POP22 demod phase (I -phase maximally negative when locked on carrier, Q-phase close to zero).  Then I was able to lock the PRMI sideband by drastically reducing the trigger threshold levels.  With the nice stable sideband-locked PRMI I was able to center the beam on the PD.

After that, I introduced the razor blade until both POPDC and POP22 power levels decreased by about half.

Now, the POP22 threshold levels are set to up=10, down=1 for both MICH and PRCL, DoF triggers and FM triggers.

ASS model work:

POP22 I and POP110 I were already going to the ASS model (where ASC lives) for the PRCL ASS dither readbacks.  So, I just had to include them in the ASC block, and increased the size of the ASC input matrix.  Now you can select either POP QPD pit, POP QPD yaw, POP221 or POP110I to go to either PRCL yaw, PRCL pit, CARM yaw or CARM pit.

Compiled, installed and restarted the ASS model.

Engaging the servo:

I took reference spectra of POP QPD yaw and POP 22, before any control was applied.  The shapes looked quite similar, but the overall level of POP22 was smaller by a factor of ~200.  I also took a reference spectra of the POP QPD in-loop signal using the old ASC loop situation.

Q looked at Foton for me, and said that with the boost on, the UGF needed to be around 9 or 10 Hz, which ended up meaning a servo gain of +2.5 (the old POP QPD yaw gain was -0.063).  We determined that we didn't know why there was a high-Q 50Hz notch in the servo, and why there is not a high frequency rolloff, so right now the servo only uses FM1 (0:2000), FM6 (boost at 1Hz and 3Hz) and FM7 (BLP40).

The in-loop residual isn't quite as good with POP22 as for the QPD, but it's not bad.

Here's the loop:

And here's the error spectra.  Pink solid and light blue solid are the reference traces without control.  Pink dashed is the QPD in-loop.  Red and blue solid are the QPD and POP22 when POP22 is used as the error signal.  You can definitely see that the boosts in FM6 have a region of low gain around 1.5Hz.  I'm not so sure why that wasn't a problem with the QPD, but we should consider making it a total 1-3Hz bandpass rather than a series of low-Q bumps.  Also, even though the POP22 UGF was set to 9 Hz, we're not seeing any suppression above about 4Hz, and in fact we're injecting a bit of noise between 4-20Hz, which needs to be fixed still.

10768   Tue Dec 9 03:34:52 2014 JenneUpdateASCPOP yaw razor tuning

With the re-do of the IFO alignment last week, I think that the beam was no longer about halfway on the POP22 razor blade.  To fix this, I locked the PRMI on sideband, removed the razor blade, and then put it back in such that it occluded about half of the light.

I'm not entirely sure why, but when I put the razor in, POP22 went from 104(ish) to 45(ish) but POPDC  went from 5200(ish) to 1600(ish).  [The 'ish'es are because the PRC wasn't angularly stabilized, so there was some motion changing the power levels that leaked out to the POP port].  The ETMs were misaligned, so this should not be a carrier vs. sideband effect, since they'll both share the cavity axis defined by the ITMs and the PRM.  It is possible, although I didn't check, that there is some oplev light scattered into the POP photodiode that is now blocked by the razor blade.  This light would only be at DC and not the 2f frequencies.  Since the signal levels for POP22 vs. POPDC didn't change with and without the table top on (and with and without room lights on), I don't think that it is an effect of ambient light getting into the diode.  To check if it is oplev light I should (a) just look, and (b) try to lock the PRMI without the ITMX oplev laser being on to see if there is a difference in the POPDC signal.

Anyhow, under the assumption that the POP22 signal level is correct, I tuned up the PRCL ASC a little bit.  These changes are now in the carm_cm_up script, and the carm_cm_down script resets things.  Before the PRC is locked, I have FM1 and FM7 (the basic servo shape and a 40Hz lowpass) on, the gain set to zero, and the input off.  After lock is acquired, the input is turned on, and the gain ramps from 0 -> 10 in 3 seconds.  Then FM2 and FM6 (boosts at 1 and 3Hz) are engaged.

In the plot below, the dark blue and red curves were taken when there was no angular control on the PRC.  Pink was taken last week with the old QPD yaw ASC on.  Light blue is today's version of the in-loop performance of the POP22 yaw ASC loop.  I didn't save the trace unfortunately, but the DC QPD saw out-of-loop improvement between about 0.8Hz - 4 Hz.

Also, has anything happened with the LSC rack in the last few weeks that might be causing lots of 60Hz noise? I saw these large lines last week, but I don't think I remember them from the past.

After I got the PRCL ASC working, I tried several iterations of locking.  ETMX is still being annoying, although the last hour or so have been okay.  CARM keeps getting rung up right around the transition to the sqrtInv error signal.  Since CARM and DARM are kind of entangled, it took me a few iterations to figure out that it was CARM that is ringing up, and not DARM.  I'm a little worried about the phase loss from the 1kHz lowpass that we turn on just before the transition to sqrtInv.  I want to keep the lowpass off until after we have transitioned DARM also over to DC transmission.  I tried once, but I lost lock before starting the CARM transition.  Anyhow, the ETM alignment issue is annoying.

Also, Jamie, Q, Diego and I were discussing last Friday, but none of us elogged, that we think there might be something wrong with one of the Martian network switches.  I'll start a separate thread about that right now, but it slows things down when you can't trust EPICS channels to be current, and I (without evidence) am a little worried that this might also affect the fast signals.

10789   Fri Dec 12 04:33:49 2014 JenneUpdateASCASS retuned

[Rana, Jenne]

We decided that tonight was the night for ASS tuning.

We started from choosing new frequencies, by looking at the transmission and the servo control signals spectra to find areas that weren't too full of peaks.  We chose to be above the OpLev UGF by at least a factor of ~2, so our lowest frequency is about 18Hz.  This way, even if the oplevs are retuned, or the gains are increased, the ASS should still function.

We set the peak heights for the lowest frequency of each arm to have good SNR, and then calculated what the amplitude of the higher frequencies ought to be, such that the mirrors are moving about the same amount in all directions.

We re-did the low pass filters, and eliminated the band pass filters in the demodulation part of the servo.  The band passes aren't strictly necessary, as long as you have adequate lowpassing, so we have turned them off, which gives us the freedom to change excitation frequencies at will.  We modified the lowpass filter so that we had more attenuation at 2Hz, since we spaced our excitation frequencies at least ~2.5 Hz apart.

The same lowpass filter is in every single demodulator filter bank (I's and Q's, for both length and transmission demodulation).  We are getting the gain hierarchy just by setting the servo gains appropriately.

We ran ezcaservos to set the demodulation phase of each lockin, to minimize the Q-phase signal.

We then tuned up the gains of the servos.  Rana did the Y arm, but for the X arm I tried to find the gains where the servos went unstable, and then reduced the gain by a factor of 2.  The Xarm is having trouble getting good alignment if you start with something less than about 0.7, so there is room for improvement.

Rana wrote a little shell script that will save the burt snapshot, if the gains need adjusting and they should be re-saved.

The scripts have been modified (just with the new oscillator amplitudes - everything else is in the burt snapshots), so you should be able to run the start from nothing and the start from frozen scripts for both arms.  However, please watch them just in case, to make sure they don't run away.

10807   Wed Dec 17 01:51:44 2014 rana, jenneUpdateASCASS retuned

Did a big reconfig to make the Y-arm work again since it was bad again.

1. Undid Koji's topology change. The A2L loops now feedback to the arm mirrors to adjust the cavity axis. The cavity transmission signals now feedback to the input beam.
2. The UGF of the Trans->Input beam servos is ~5-10x higher than the A2L servos.
3. The Trans loops have a ~10-15 s settling time.
4. The Input Matrix has been adjusted to fit with our intuition:The ETM tilt moves the beam equally on the ITM and ETM faces.
5. The Output Matrix has also been adjusted to do like this: we're using an intuitive matrix inverse rather than one based on measurement. It turns out to be a reasonable guess and we can tune this later.
6. Seems stable with many kinds of steps and misalignments. Seems not reliable if the arm power is less than ~0.5.
7. Reducing the dither amplitudes to make the power fluctuation less than 5% made it much more stable.

With the arm aligned and the A2L signals all zeroed, we centered the beam on QPDY (after freezing the ASS outputs). I saw the beam going to the QPD on an IR card, along with a host of green spots. Seems bad to have green beams hitting the QPD alogn with the IR, so we are asking Steve to buy a bunch of the broad, dielectric, bandpass filters from Thorlabs (FL1064-10), so that we can also be immune to the EXIT sign. I wonder if its legal to make a baffle to block it on the bottom side?

P.S. Why is the Transmon QPD software different from the OL stuff? We should take the Kissel OL package and put it in place of our old OL junk as well as the Transmons.

Attachment 1: ASSconfig_141217_0205.png
10811   Wed Dec 17 18:14:36 2014 ericqUpdateASCTransmon QPD -> ASC servos ready for comissioning

I have completed all of the model modifications and medm screen updates to allow for feedback from the transmon QPD pitch and yaw signals to the ITMs. Now, we can design and test actual loops...

The signals come from c1sc[x/y] to c1rfm via RFM, and then go to c1ass via dolphin.

Out of curiosity about the RFM+dolphin delay, I took a TF of an excitation at the end SUS model (C1:SUS-ETM[X/Y]_QPD_[PIT/YAW]_EXC) to the input FM in the ASC model (C1:ASC-ETM[X/Y]_QPD_[PIT/YAW]_IN1). All four signals exhibit the same delay of 122usec. I saved the dtt file in Templates/ASC/transmonQPDdelay.xml

This is less than a degree under 20Hz, so we don't have to worry about it.

10812   Wed Dec 17 19:04:12 2014 jenneUpdateASCASS retuned

I made the Xarm follow the new (old) topology of Length -> test masses, and Trans -> input pointing.

It takes a really long time to converge (2+ min), since the input pointing loops actuate on the BS, which has an optical lever, which is slow.  So, everything has to be super duper slow for the input pointing to be fast relative to the test mass motion.

Also, between last night and this afternoon, I moved the green ASX stuff from a long list of ezca commands to a burt file, so turning it on is much faster now.  Also, I chose new frequencies to avoid intermodulation issues, set the lockin demodulation phases, and tuned all 4 loops.  So, now the green ASX should work for all 4 mirrors, no hand tuning required.  While I was working on it, I also removed the band pass filters, and made the low pass filters the same as we are using for the IR ASS.  The servos converge in about 30 seconds.

10813   Wed Dec 17 19:31:55 2014 KojiUpdateASCASS retuned

I wonder what to do with the X arm.

The primary purpose of the ASS is to align the arm (=transmission), and the secondary purpose is to adjust the input pointing.

As the BS is the only steering actuator, we can't adjust two dof out of 8 dof.
In the old (my) topology, the spot position on ITMX was left unadjusted.

If my understanding of the latest configuration, the alignment of the cavity (=matching of the input axis with the cavity axis)
is deteriorated in order to move the cavity axis at the center of the two test masses. This is not what we want as this causes
deterioration of the power recycling gain.

10886   Mon Jan 12 18:11:25 2015 ericqUpdateASCTest Mass -> Transmon QPD TFs measured

We want to have some angular control of the arms during lock acquistion.

In single arm lock, Diego and I shook the TMs and measured how the QPDs responded. (I would've liked to do a swept sine in DTT, but the user envelope function still isnt' working!)

For now, we can close simple loops with QPD sensor and ITM actuator, but, as Rana pointed out to Diego and me today, this will drive some amount of the angular cavity degree of freedom that the QPD doesn't sense. So, ideally, we want to come up with the right combination of ITM and ETM motion that lies entirely within the DoF that the QPD senses.

I created a rudimentary loop for Yarm yaw, was able to get ~20Hz for the upper UGF, a few mHz for the lower, but it was starting to leak into the length error signal. Further tweaking will be neccesary...

Attachment 1: Jan12_singleArmSensing.pdf
Attachment 2: Jan12_singleArmSensing.xml.zip
10908   Thu Jan 15 18:57:41 2015 ericqUpdateASCTransmon QPD loops live

I've measured the sensing for each of the arms, by using our calibrated oplevs, in terms of QPD counts per micron. It is:

YARM ETMY: QPD PIT / OPLEV PIT =   22.0 count/urad       QPD YAW / OPLEV YAW =   17.1 count/urad ITMY: QPD PIT / OPLEV PIT =   -6.0 count/urad       QPD YAW / OPLEV YAW =    5.9 count/urad
XARM ETMX: QPD PIT / OPLEV PIT =   16.6 count/urad       QPD YAW / OPLEV YAW =   -9.3 count/urad ITMX: QPD PIT / OPLEV PIT =    4.0 count/urad       QPD YAW / OPLEV YAW =   -6.0 count/urad

In the absence of a lens, the QPD would be significantly more sensitive to cavity axis translation than tilt, and thus about equally sensitive to ITM and ETM angle. However, there are lenses on the end tables. I didn't go out and look at them, but found some elogs from Annalisa that mentioned 1m focal length lenses. Back-of-the-envelope calculations convince me that this can plausibly lead to the above sensitivity ratios.

I used these quantities to come up with an actuation matrix for the ASC loops, and measured the effective plant seen by the FM, fitted it to some poles( looks like zpk([],-2*pi*[1.47+3.67i,1.47-3.67i],160); ), and designed a control servo. Here is the designed loop:

The servo works on both arms, both DoFs. A DTT measurement agrees with the designed loop shape, up to a few degrees, which are probably due to the CDS delay. The RMS of the QPD error signals goes down by about 20dB, and are currently dominated by the bounce mode, so maybe we can try to sneak in some resonant gain...?

Once we confirm that they work when locking, we can write up and down lines into the locking scripts...

Attachment 1: loopDesign.pdf
10920   Mon Jan 19 18:27:16 2015 ericqUpdateASCQPD ASC saga continues.

# Herein, I will try to paint a more thorough picture of this whole QPD ASC mess.

## Motivation for QPD ASC loops:

• We would like to use the QPDs as a DC arm pointing reference during locking attempts, or over multiple days, if possible.
• It would be nice if the QPDs could complement the oplevs to reduce angular motion of the cavity.
• We must not make the single arm longnitudinal noise or RIN worse, because anything observable in the single arm case will be catastrophic at full sensitivity

## Actuation design:

As mentioned in a previous ELOG, in single arm lock, I measured the QPD response with respect to the calibrated oplev signals. They were:

YARM ETMY: QPD PIT / OPLEV PIT =   22.0 count/urad       QPD YAW / OPLEV YAW =   17.1 count/urad ITMY: QPD PIT / OPLEV PIT =   -6.0 count/urad       QPD YAW / OPLEV YAW =    5.9 count/urad
XARM ETMX: QPD PIT / OPLEV PIT = 16.6 count/urad       QPD YAW / OPLEV YAW = -9.3 count/urad ITMX: QPD PIT / OPLEV PIT =  4.0 count/urad       QPD YAW / OPLEV YAW = -6.0 count/urad

For reference, one microradian of either ITM or ETM motion produces about 60um of ETM beam spot displacement, compared to the spot size of ~5mm.

However, given the lenses on the end tables that are used for green mode matching, that the IR transmitted beam also passes through, the QPDs are not directly imaging the ETM spot position; if they were, they would have equal sensitivity to ITM and ETM motion due to our flat/curved arm geometry.

From this data, I calculated the actuation coefficients for each DoF as $A_{ETM} = \frac{d_{ETM}}{\sqrt {d_{ETM}^2 + d_{ITM}^2}}$, and similarly for the ITMs, where the d's come from the table above. However, it occurs to me that maybe this isn't the way to go... I'll mention this later.

## Loop design:

Up until now, at every turn, I had not properly been thinking about how the oplev loop plays into all of this. I went to the foton filters, and grabbed the loop and plant models for the ETMY oplev, and constructed the closed loop gain, 1/1+G, and the modified plant, P/1+G, which is what the ASC loop sees as its plant.

Here, the purple trace explains all of the features I was confused about earlier.

With this in hand, I set up to design a loop to satisfy our motivations.

• Bounce/roll mode notches to avoid exciting them
• 1/f UGF crossing at a few Hz, limited by the gain margin at ~10Hz, which is where the phase will hit 180, due to the notches
• 4th order Elliptic lowpass at 100, to avoid contaminating the longnitudinal signals
• 1/f^2 at low frequencies for DC gain

To do this, I inverted the oplev closed loop plant pole around 4Hz to smooth the whole thing out. Here's a comparison of the measured OLG with what I modelled.

There's a little bit of phase discrepency around 10Hz, but I think it looks about right overall.

## Evaluation:

So, here's the part that counts: How does this actually perform? I took spectra of the QPD error signals, the relevant OpLev signals as out of loop sensors, the PDH error signal and transmitted RIN while single arm locked, with this loop off, and on for all 4 DoFs simultaneously.

Verdict:

• In-loop signals get small, unsurprisingly.
• Cavity signals unchanged.
• ITM oplev signals are unchanged (and not plotted, to not clutter the plots (This isn't surprising since the loops mostly actuate on the ETMs).
• ETM oplev signals get smaller around the 3Hz peak, but are louder in other bands.

This is what makes me think I may need to revisit the actuation matrix. If I did it wrong, I am driving the "invisible" quadrant of the cavity angular DoFs, and this could be what is injecting noise into the oplevs.

## Conclusion:

In the end, I have a better understanding of what is going on, and I don't think we're quite there yet.

Attachment 1: oplevPlant.pdf
Attachment 2: loopDesignComparison.pdf
10921   Tue Jan 20 02:39:49 2015 ericqUpdateASCQPD ASC saga continues.

Although the QPD loops are less than ideal right now, I made changes to the ASC model to trigger the QPD loops on and off politely, depending on TRX and TRY. The settings are exposed on the ASC screen. However, I have not yet exposed the FM triggering that I also set up to make sure the integrator doesn't misbehave if the arm loses lock. We probably don't want to trigger them on at anything lower than arm powers of about 1.0.

I've tested the triggering by randomly turning LSC mode on and off, and making sure that the optics don't recieve much of a kick as the QPD loops engage a few seconds after the LSC boosts do, or when lock is lost. This works as long as there isn't much of a DC offset befire the loops are engaged. (Under 20 counts or so is fine)

As a side note, I was going to use the TRIG_SIG signals sent via the LSC model via SHMEM blocks for the ASC triggering, but oddly, the data streams that made it over were actually the MICH and SRCL TRIG_SIGs, instead of XARM and YARM as labelled. I double checked the simulink diagrams; everything seemed fine to me. In any case, ASS was already recieving TRX and TRY directly via RFM, so I just piped those over to the ASC block. This way is probably better anyways, because it directly references the arm powers, instead of the less obvious LSC triggering matrix.

10946   Tue Jan 27 21:33:39 2015 KojiUpdateASCASS retuned

I checked the situation of ASS. I wanted to know how much we are away from the maximum transmittion.

Conclusion:
ASS makes the X arm shifted from the maximum transmission. This causes the contrast degraded by ~3%.
We need to fix the Xarm ASS so that it can maximize the transmission and ignor the spot centering at ITMX.

Conditioning before the measurement:

- ASDC offset was removed
- X&Y arm was aligned by ASS

With ASS:

Average transmission: 0.86
Pmax = 1045 +/- 9 cnts
Pmin = 22 +/- 4 cnts

==> Contrast = (Pmax - Pmin)/(Pmax+Pmin) = 0.960+/-0.007

After manual alignment of the X arm (ignoring spot centering):

Average transmission: 0.88
Pmax = 1103 +/- 11 cnts
Pmin = 5 +/- 1 cnts

==> Contrast = (Pmax - Pmin)/(Pmax+Pmin) = 0.991+/-0.002

10952   Wed Jan 28 23:53:24 2015 KojiSummaryASCXarm ASS fix

X-Arm ASS was fixed.
ASS_DITHER_ON.snap was updated so that the new setting can be loaded from the ASS screen.

The input and output matrices and the servo gains were adjusted as found in the attached image.
The output matrix was adjusted by looking at the static response of the error signals when a DC offset
was applied to each actuator.

The servo was tested with misalignment of the ITM, ETM, and BS. In fact, the servo restored transmission
from 0.15 to 1.

The resulting contrast after ASSing was ~99% level. (I forgot to record the measurement but the dark fringe level of ASDC was 4~5count.)

Attachment 1: 12.png
10963   Mon Feb 2 12:24:27 2015 JenneUpdateASCPOP QPD centered

After aligning the PRC, I centered the POP QPD.

10974   Wed Feb 4 18:27:55 2015 KojiSummaryASCXarm ASS fix

Please remember that Xarm ASS needs FM6 (Bounce filters) to be ON in order to work properly.

10975   Wed Feb 4 19:21:37 2015 KojiUpdateASCArm ASS servos now have triggered gain with arm lock status

We had persistent frustration by occasional unlock during ASSing.
Today, I added triggers to the servo gains in order to elliminate this annoyance.

Each ASS servo gain slider is multiplied with the corresponding LSC Trigger EPICS channel (i.e. C1:LSC-iARM_TRIG_MON, where i=X or Y).
This has been done by ezcaread modules in RCG.

The model and screen have been commited to svn.

10997   Tue Feb 10 18:37:17 2015 ericqUpdateASCQPD ASC ready to go

I've remeasured the QPD ASC sensing coefficients, and figured out what I did weird with the actuation coefficients. I've rearranged the controller filters to be able to turn on the boost in a triggered way, and written Up/Down scripts that I've tested numerous times, and Jenne has used as well; they are exposed on the ASC screen.

All four loops (2 arms * pit,yaw), have their gains set for 8Hz UGF, and have 60 degrees of phase margin. The loop shape is the same as the previous ELOG post. Here is the current on/off performance. The PDH signals (not shown, but in attached xml) show no extra noise, and the low frequency RIN goes down a bit, whic is good. The oplevs error signals are a bit noisier, but I suppose that's unavoidable. The Y-arm performs a bit better than the X-arm.

The up/down scripts don't touch the filters' trigger settings at all, just handles switching the input and output and clearing history. FM1 contains the boost which is intended to have a longer trigger delay than the filters themselves.

Attachment 1: Feb10_loops_offOn.png
Attachment 2: Feb10_newLoops_offOn.xml.zip
11056   Fri Feb 20 19:09:48 2015 ericqUpdateASCQPD frontend code unified

I have changed all of the oplevs and transmon QPDs to use the common ISC QPD library block, which differs mainly in its divide by zero protection.

c1scx.mdl and c1scy.mdl were directly changed for the transmon QPDs. The oplevs were done by changing the sus_single_control.mdl library part, which is used for all of the SOSs.

Then, because of the underscore introduced (i.e. OLPIT becomes OL_PIT because there is an OL block), I went on a sed safari to find and replace the new channel names into:

• The filter ini files
• various MEDM screens
• The optic misaligning scripts (which currently live in medm/MISC/ifoalign, and need to get moved to scripts/)
• A recent BURT snapshot, to restore all of the switches and settings easily.
• scripts/activateDQ.py, which is responsible for renaming OL_PIT_IN1_DQ to OPLEV_PERROR, etc.

I've fixed everything that occured to me, and the usual ways I'm used to interacting with the oplevs all seem to work at this time, but it's entirely possible I've overlooked something.

One important note is: because we are now using an effectively immutable QPD library block, the oplev urad conversion has to take place in the DoF matrix. The EPICS records C1:SUS-[OPTIC]_OL_[DOF]_CALIB still exist, but do not multiply the fast signals. Rather, the OL_MTRX elements are multiples of the CALIB value. I thought about making a new QPD_CALIBRATED part or something, but then we're right back to using custom code, which is what we're trying to avoid.

All of the oplev DoFs are stable, I checked a few loop TFs like ETMY pitch and PRM yaw, and they looked normal.

11057   Mon Feb 23 08:06:59 2015 ranaUpdateASCQPD frontend code unified

Might have to also get the OL screens that go with this new code to see, but the calibrations don't go into the matrix, but rather into the OLPIT/OLYAW filter banks which follow the division, but before the servo filter banks.

11061   Tue Feb 24 18:54:26 2015 ericqUpdateASCSingle arm QPD ASC stability

I've lowered the UGFs for the transmission QPD servos to ~1-2Hz, and made it just an integrator. I left the arms locked with the QPD servos on for a few hours during the daytime today, and they succesfully prevented the Y arm from losing power from alignment drift for ~4 hours. Turning the servo off caused TRY to drop to ~0.6 or so.

The X arm was only held for 2 hours or so, because after some unlock/drift event the power was below the servo trigger threshold. However, after gently nudging ETMX to get the transmission above the threshold, the servo kicked in, and brought it right back to TRX=1.0

Unfortunately, daqd was dead for much of the day, so I don't have much data to show; the trend was inferred from the wall striptool.

It is not proven that there aren't further issues that prevent this from working with higher / more dynamic arm powers, but this is at least a point in favor of it working.

EDIT: Here's a screenshot of the wall StripTool. Brown is TRY, blue is TRX. The downturn at the very end is me deactivating the servos.

There is no scientific justifcation for the 0.9 threshold. Really, I should look at the noise/SNR again, now that there is some ND filtering on the QPDs.

Attachment 1: trend.png
11125   Mon Mar 9 18:10:59 2015 JenneUpdateASCOplev filters re-copied

Back on Feb 20th (elog 11056) Q replaced all of our oplev parts with the aLIGO version.

Unfortunately, after this it has seemed like there was something not quite right with the optical lever servos.

• When we would restore kicked optics, after the osem rms values come down the scripts try to engage the optical levers.  This would often kick and ring up the optics (I've seen this with ETMX and ETMY, and once or twice with the beam splitter)  Not good.
• Sometimes, if the optic wasn't kicked, it would oscillate.  I would see this in particular with ETMY, by seeing the green transmission at the PSL table oscillating.
• Q noticed that sometimes when the oplevs' outputs were turned off, the outputs were railed at the limiter values.

Since, when the models were changed which gave us an extra underscore in the oplev names, Q did a find-and-replace in the foton text files, I was worried that this might have broken things.  I'm not entirely sure how it would have broken them (I didn't see any difference in a diff), but I've heard enough horror stories about the delicacy of the foton text files.

Anyhow, I opened the last archived foton files from just before Q made the change, and copy-and-pasted the design strings from the old filter banks to the new ones.  Hopefully this fixes things.

11206   Tue Apr 7 04:21:45 2015 ericqUpdateASCAngular Control during Locking

[J, Q]

Alignment is making it tough for locks to last more than 10 minutes. Many (but not all) locklosses correlate with some optic drifting away, and taking all of the light with it. The other locklosses are the quick ones that seem to pop up out of nowhere; we haven't made any headway on these. We wanted to get to a state where we could just let the interferometer sit for some minutes, to explore the data, but got caught up with alignment and PRMI things.

We're finding that both ITMs experience some DC force when entering full PRFPMI lock. I will calculate the torque expected from radiation pressure + offset beam spot, especially for ITMX, where we choose the spot position to be uncontrolled by ASS.

I set up the QPD ASC servos to act in a common/differential way on the ETMs. The C1:ASC-XARM_[PIT/YAW] filter modules act on the common alignment, whereas the C1:ASC-YARM_[PIT/YAW] filter modules act on the differential alignment. This can soon be cleaned up with some model renaming to reduce confusion.

Using DC oplev values as a guide, we are hand tuning ITM alignment once the AO path is engaged and we see the DC drift occurring. Then, we set the QPD servo offsets and engage them.

In this manner, we were able to lock the interferometer at:

• Arm transmission 150 x single arm power
• POPDC indicated a recycling gain of ~5.5
• ASDC/POPDC indicated a contrast of 99.8%
• REFLDC indicated a visibility of 80%

We made the PRMI transition to 1f numerous times, but found that the sideband power fluctuations would get significantly worse after the transition.

We found that the gains that were previously used were too small by a factor of a few. There is a DC change visible in REFL165 before and after the transition (Also POP55, aka REFL55, is not DQ'd ). Really, it isn't certain that we've zero'd the offset in the CARM board either, so REFL55's zero crossing isn't necessarily more trustworthy that REFL165's. We can go back in the data and do some 2D histograming to see where in the error signal space the sideband power is maximized.

Jenne reports:

• The all RF transition succeeded 13/29 times.
• PRMI 1f transision succeeded 10/10 times.
11242   Fri Apr 24 01:16:30 2015 JenneUpdateASCBroken Xass?

I ran the "off" script for the Xarm ASS, followed by the "on" script, and now the Xarm ASS doesn't work.  Usually we just run the freeze/unfreeze, but I ran the off/on scripts one time.

Koji, if you have some time tomorrow, can you please look at it?  I am sorry to ask, but it would be very helpful if I could keep working on other things while the ASS is taken care of.

Steve, can you please find a cable that goes from the LSC rack to the IOO rack (1Y2 to 1X2), or lay a new one?  It must be one single long cable, without barrels sticking it together.  This will help me actuate on the Marconi using the LSC rack's DAC.

Thank you!!

11248   Sat Apr 25 03:32:45 2015 KojiUpdateASCBroken Xass?

I spent a day to fix the XARM ASS, but no real result. If the input of the 6th DOF servo is turned off, the other error signals are happy
to be squished to around their zeros. So this gives us some sort of alignment control. But obviously a particular combination of the
misalignment is left uncontrolled.

This 6th DOF uses BS to minimize the dither in ITMX yaw. I tired to use the other actuators but failed to have linear coupling between
the actuator and the sensor.

During the investigation, I compared TRX/TRY power spectra. TRX had a bump at 30Hz. Further investigation revealed that the POX/POY
had a big bump in the error signals. The POX/POY error signals between 10-100Hz were coherent. This means that this is coming from
the frequency noise stabilized with the MC. (Is this frequency noise level reasonable?)

The mysterious discovery was that the bump in the transmission exist only in TRX. How did the residual frequency noise cause
the intensity noise of the transmission? One way is the PDH offset.

Anyway, Rana pointed out that IMC WFS QPDs had large spot offsets. Rana went to the AS table and fixed the WFS spot centering.
This actually removed the bump in TRX although we still don't know the mechanism of this coupling.

The bump at 30Hz was removed. However, the ASS issue still remains.

11253   Sun Apr 26 01:10:18 2015 ranaUpdateASCunBroken Xass?

Today I tried some things, but basically, lowering the input gain by 10 made the thing stable. In the attached screenshotstrip, you can see what happens with the gain at 1. After a few cycles of oscillation, I turned the gain back to 0.1.

There still is an uncontrolled DoF, but I that's just the way it is since we only have one mirror (the BS) to steer into the x arm once the yarm pointing is fixed.

Along the way, I also changed the phase for POX, just in case that was an issue. I changed it from +86 to +101 deg. The attached spectra shows how that lowered the POX_Q noise.

I also changed the frequencies for ETM_P/Y dither from ~14/18 Hz to 11.31/14.13 Hz. This seemed to make no difference, but since the TR and PO signals were quieter there I left it like that.

This is probably OK for now and we can tune up the matrix by measuring some sensing matrix stuff again later.

Attachment 1: xasstune_150426.png
Attachment 2: xassnoise.pdf
11255   Sun Apr 26 15:05:35 2015 JenneUpdateASCunBroken Xass?

Thank you both.

I have updated the .snap file, so that it'll use these parameters, as Rana left them.  Also, so that the "unfreeze" script works without changes (since it wants to make the overall gain 1), I have changed the Xarm input matrix elements from 1 to 0.1, for all of them.  This should be equivalent to the overall gain being 0.1.

11269   Sun May 3 19:40:51 2015 ranaUpdateASCSunday maintenance: alignment, OL center, seismo, temp sensors

X arm was far out in yaw, so I reran the ASS for Y and then X. Ran OK; the offload from ASS outputs to SUS bias is still pretty violent - needs smoother ramping.

After this I recentered the ITMX OL- it was off by 50 microradians in pitch. Just like the BS/PRM OLs, this one has a few badly assembled & flimsly mounts. Steve, please prepare for replacing the ITMX OL mirror mounts with the proper base/post/Polaris combo. I think we need ~3 of them. Pit/yaw loop measurements attached.

Based on the PEM-SEIS summary page, it looked like GUR1 was oscillating (and thereby saturating and suppressing the Z channel). So I power cycled both Guralps by turning off the interface box for ~30 seconds and the powering back on. Still not fixed; looks like the oscillations at 110 and 520 Hz have moved but GUR2_X/Y are suppressed above 1 Hz, and GUR1_Z is suppressed below 1 Hz. We need Jenne or Zach to come and use the Gur Paddle on these things to make them OK.

From the SUS-WatchDog summary page, it looked like the PRM tripped during the little 3.8 EQ at 4AM, so I un-tripped it.

Caryn's temperature sensors look like they're still plugged in. Does anyone know where they're connected?

Attachment 1: itmx_ol_loops_150503.png
Attachment 2: Gur_150503.png
11296   Sun May 17 23:46:25 2015 ranaUpdateASCIOO / Arm trends

Looking at the summary page trends from today, you can see that the MC transmission is pretty flat after I zeroed the MCWFS offsets. In addition, the transmission from both arms is also flat, indicating that our previous observation of long term drift in the Y arm transmission probably had more to do with bad Y-arm initial alignment than unbalanced ETMY coil-magnets.

Much like checking the N2 pressure, amount of coffee beans, frames backups, etc. we should put MC WFS offset adjustment into our periodic checklist. Would be good to have a reminder system that pings us to check these items and wait for confirmation that we have done so.

11482   Thu Aug 6 04:36:41 2015 ericqUpdateASCReviving PRC angular feedforward

Tonight, I've taken a bunch of data where the PRC is carrier locked and the ITM oplevs have the DC coupling FM turned on, as we use during locking. This is to inform new feedforward filters to stabilize the PRC angular motion, by using Wiener filtering with the POP QPD as the target, and local seismometers/accelerometers as witnesses. So far I've looked at the 1800 seconds leading up to GPS time 1122885600, but there has been plenty of locked time tonight if I need to retrieve more.

I've also measured the PRM ASC output torque -> POP QPD spot motion with high (>0.95) coherence from 0.1Hz to 10Hz.

Prefiltering so far consists of a 4th order elliptic LP at 5 Hz, with the target subtraction band being the 1-3Hz range.

With offline FIR filtering, the RMS pitch motion is reduced by a factor of 3 just with the STS1_X data. IIR fitting remains to be done.

The PRC yaw motion, which is marginally noisier, is a little more tangled up across X and Y.

Plots / filters forthcoming pending more analysis.

11489   Tue Aug 11 02:26:46 2015 ericqUpdateASCPRC Angular FF Lives!

# PRC Angular FF is back in action!

Short and sweet of it:

• Took witness (T240 channels) and target (POP QPD) with DC coupled oplevs on. About 25 minutes of nice stationary data.
• Downsampled everything to 32Hz, since coherence suggests subtraction only really possible from 1-5Hz.
• Prefiltering done by detrending and ellip(3,3,40,5Hz)
• 4 second FIR impulse time was enough
• Filtered target by inverse actuator TF before sending to wiener code. The only difference between this and filtering the witnesses with the actuator TF directly is an effective RMS cost function, i.e. prefiltering.
• Spending time tweaking IIR fitting pays off. Divided out zpk(0, [p3, p3*],1), where p3 is some well fit stack/suspension resonance, so that vectfit fits remaining portion with equal numbers of poles and zeros, guaranteeing AC coupling and 1/f rolloff to prevent noise injection
• Quack->foton->OAF all worked fine
• ## All in all, seems to work well. POPDC RMS goes down by a factor of 2

• Code used lives in /users/ericq/2015-08-PRCFF and the NoiseCancellation github repo

## Subtraction prediction vs. reality (positive dB is good)

Attachment 1: fitExample.png
Attachment 2: FFspectra.png
Attachment 3: PITsub.png
Attachment 4: YAWsub.png
11562   Thu Sep 3 00:29:45 2015 ranaUpdateASCASS X not working

ran the ON script several times and it kept pulling it away from good alignment, even when TRX was > 0.9.

Also, for what reason was this model run at 16 kHz?? Makes no sense to me to have a low frequency servo system run so high. Only makes for more digital precision noise, more CPU time, etc. Of course, running it at 2k would mean having to think about all of the AA filtering needed to go up/down from 2k to 16k.

11721   Wed Oct 28 17:06:30 2015 ericqUpdateASCNew PRC Angular FF filters installed

I've installed new filters for the T240 -> PRM static online angular feedforward that were trained after some of the recent changes to the signal chain of the relevant signals (i.e. the counts->velocity calibration that Rana did for the seismometers, and fixing the improper dewhitening of the POP QPD channels used as the Wiener target.)

Quickly trying them out now shows about the same level of performance as the previous ones, but the real performance I care about is during after-hours locking-time, so I'll take more measurements tonight to be posted here.

11776   Tue Nov 17 20:40:08 2015 yutaroSummaryASCLoss maps of arm cavities

In preparation for the measurement of loss maps of arm cavities, I measured the relationship between:

the offset just after the demodulation of dithering loop (C1:ASS-YARM_ETM_PIT_L_DEMOD_I_OFFSET and C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET)

and

the angle of ETMY measured with oplev (C1:SUS-ETMY_OL_PIT_INMONC1:SUS-ETMY_OL_PIT_INMON and C1:SUS-ETMY_OL_PIT_INMONC1:SUS-ETMY_OL_PIT_INMON)

while the dithering script is running. With the angle of ETMY, we can calculate the beam spot on the ETMY assuming that the beam spot on the ITMY is not changed thanks to the dithering. What we have to do is to check the calbration of oplev with another way to measure the angle, to see if the results are reliable or not.

I will report the results later.

11779   Wed Nov 18 11:22:13 2015 yutaroUpdateASCLoss maps of arm cavities

I got linear relation between these. The results and method are below.

 Quote: In preparation for the measurement of loss maps of arm cavities, I measured the relationship between: the offset just after the demodulation of dithering loop (C1:ASS-YARM_ETM_PIT_L_DEMOD_I_OFFSET and C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET) and the angle of ETMY measured with oplev (C1:SUS-ETMY_OL_PIT_INMONC1:SUS-ETMY_OL_PIT_INMON and C1:SUS-ETMY_OL_PIT_INMONC1:SUS-ETMY_OL_PIT_INMON) while the dithering script is running. With the angle of ETMY, we can calculate the beam spot on the ETMY assuming that the beam spot on the ITMY is not changed thanks to the dithering. What we have to do is to check the calbration of oplev with another way to measure the angle, to see if the results are reliable or not. I will report the results later.

RESULTS

METHOD

I added offset (C1:ASS-YARM_ETM_PIT_L_DEMOD_I_OFFSET and C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET) to shift the beam spot on ETMY. For each data point, I measured the difference in angle of ETMY with oplev before and after adding offset. The precedure for each measurement I employed is following:

-- run dither

-- wait until error signals of dithering settle down

-- freeze dither

-- measure angle (10s avg)

-- wait until error signals of dithering settle down

-- freeze dither

-- measure angle (10s avg)

The reason why I measured the angle without offset for each measurement is that the angle which oplev shows changed with time (~several tens of minutes or something).

DISCUSSION

At the maximum values of offsets, the arm transmission power started to degrade, so the range where I can do this measurement is limited by these values as for now. However, we have to shift the beam spot more in order to make loss maps of sufficiently broad area on the mirror (the beam width (w) on ETM; w ~ 5 mm). Then, we have to find out how to shift the beam spot more.

Attachment 1: ETM_PIT_up.png
12175   Tue Jun 14 11:29:25 2016 JohannesSummaryASCYArm OpLev Calibration

In preparation for the armloss map I checked the calibration of the Y-Arm ITM and ETM OpLevs with the method originally described in https://nodus.ligo.caltech.edu:8081/40m/1247. I was getting a little confused about the math though, so I attached a document at the end of this post in which I work it out for myself and posteriority. Stepping through an introduced offset in the control filter for the corresponding degree of freedom, I recorded the change in transmitted power and the reading of the OpLev channel with the current calibration. One thing I noticed is that the calibration for ITM PIT is inverted with respect to the others. This can of course be compensated at any point in any readout/feedback chain, but it might be nice to establish some sort of convention where positive feedback to the mirror will increase the OpLev reading.

The calibration factors I get are within ~10% of the currently stored values. The table (still incomplete, need to relate to the current values) summarizes the results:

Mirror DoF Current Relative New
Y-Arm OpLev Calibration
ETM PIT   0.974 ± 0.029
YAW   1.077 ± 0.021
ITM PIT   -0.972 ± 0.020
YAW   0.920 ± 0.048

The individual graphs:

## ITM YAW

The math:

Attachment 1: CavityCoupling.pdf
12591   Wed Nov 2 12:05:00 2016 ericqUpdateASCQuick WFS thoughts

I poked around a bit thinking about what we need for a single AS WFS.

New things that we would need:

Things we have:

• Many Eurocard-style Whitening chassis, such as we use for all of the LSC PDs.
• Enough ADC (c1ioo has two ADCs, but doesn't even use 32 channels, so we can steal one, and throw it into c1lsc)

We'd have 12 new signals to acquire: 4 quadrants x DC, I, Q. In principle the DC part could go into a slow channel, but we have the ADC space to do it fast, and it'll be easier than mucking around with c1iscaux or whatever.

Open question: What to do about AA? A quick search didn't turn up any eurocard AA chassis like the ones we use for the LSC PDs. However, given the digital AA that happens from 64kHz->16kHz in the IOP, we've talked about disabling/bypassing the analog AA for the LSC signals. Maybe we can do the same for the QPD signals? Or, modify the post-demod audioband amplifer in the demod chassis to have some simple, not too agressive lowpass.

13985   Tue Jun 19 00:19:00 2018 gautamUpdateASCPOP status check

Motivation:

1. I want to use the QPD at POP, calibrate it into physical units, and quantify the amount of angular jitter in the PRC (which I claim is what limits DRMI stability atm).
2. I want to revive the PRC angular feedforward to try and mitigate this a bit. But is feedforward even the best approach? Can we use feedback using the POP QPD?

POP QPD checkout:

• The POP QPD sits on the ITMX optical table.
• It is interfaced to the CDS system via an OT301 and then a Pentek whitening stage (z:p = 15:150).
• The OT301 claims to have a switchable offset nulling capability - but despite my best efforts tonight, I couldn't use the knobs on the front to null the offset (even with the PRC locked on carrier and a strong POP beam on the QPD).
•
• So I moved the QPD with the PRC locked, to center the CDS readback of the spot position at (0,0).
• Next step is to calibrate the POP QPD readback into physical units.
• I'm thinking of using the EricG diode laser for this purpose.
• I can calibrate counts to mm of displacement on the QPD active area.
• After which I can use the estimated position to PR2 (from which POP is extracted) to convert this to angular motion.
• I guess I should check for coherence between the POP QPD signal and all angular sensors of PRM/BS/MC1/MC2/MC3 to try and confirm the hypothesis that the folding mirrors are dominating the angular noise of the cavity. Unfortunately we don't have readbacks of the angular positions of TT1 and TT2.
• I moved the POP camera a bit in YAW so that the POP spot is now better centered on the CCD monitor.
• I also wanted to check the centering on the other POP QPD (POP22/POP110/POPDC?) but I think the POPDC signal, used for triggering the PRCL LSC servo, is derived from that PD, so everytime I blocked it, the lock was lost. Need to think of another strategy.
• MC3 has been rather glitchy tonight.
• So I will wait for a quieter time when I can collect some data to train the WF for angular FF.
14205   Fri Sep 21 09:59:09 2018 yukiConfigurationASCY end table upgrade plan

[Yuki, Gautam]

Attachments #1 is the current setup of AUX Y Green locking and it has to be improved because:

• current efficiency of mode matching is about 50%
• current setup doesn't separate the degrees of freedom of TEM01 with PZT mirrors (the difference of gouy phase between PZT mirrors should be around 90 deg)
• we want to remotely control PZT mirrors for alignment
(Attachments #2 and #3)

One of the example for improvement is just adding a new lens (f=10cm) soon after the doubling crystal. That will make mode matching better (100%) and also make separation better (85 deg) (Attachments #4 and #5). I'm checking whether we have the lens and there is space to set it. And I will measure current power of transmitted main laser in order to confirm the improvement of alignment.

I am considering what component is needed.

Reference:

Attachment 1: Pic_CurrentSetup_AUXYgreen.jpeg
Attachment 2: ModeMatchingSolution_Current.pdf
Attachment 3: ModeMatchingSolution_Current_Magnified.pdf
Attachment 4: ModeMatchingSolution_Optimized.pdf
Attachment 5: ModeMatchingSolution_Optimized_Magnified.pdf
14211   Sun Sep 23 17:38:48 2018 yukiUpdateASCAlignment of AUX Y end green beam was recovered

[ Yuki, Koji, Gautam ]

An alignment of AUX Y end green beam was bad. With Koji and Gautam's advice, it was recovered on Friday. The maximum value of TRY was about 0.5.

14212   Sun Sep 23 19:32:23 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Gautam ]

The setup I designed before has abrupt gouy phase shift between two steering mirrors which makes alignment much sensitive. So I designed a new one (Attached #1, #2 and #3). It improves the slope of gouy phase and the difference between steering mirrors is about 100 deg. To install this, we need new lenses: f=100mm, f=200mm, f=-250mm which have 532nm coating. If this setup is OK, I will order them.

There may be a problem: One lens should be put soon after dichroic mirror, but there is little room for fix it. (Attached #4, It will be put where the pedestal is.)  Tomorrow we will check this problem again.

And another problem; one steering mirror on the corner of the box is not easy to access. (Attached #5) I have to design a new seup with considering this problem.

 Quote: One of the example for improvement is just adding a new lens (f=10cm) soon after the doubling crystal. That will make mode matching better (100%) and also make separation better (85 deg) (Attachments #4 and #5). I'm checking whether we have the lens and there is space to set it. And I will measure current power of transmitted main laser in order to confirm the improvement of alignment.

Attachment 1: Pic_NewSetup0923_AUXYgreen.jpeg
Attachment 2: ModeMatchingSolution_Result.pdf
Attachment 3: ModeMatchingSolution_Magnified_0923.jpg
Attachment 4: pic0923_1.jpg
Attachment 5: pic0923_2.jpg
14214   Mon Sep 24 11:09:05 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Steve ]

With Steve's help, we checked a new lens can be set soon after dichroic mirror.

 Quote: There may be a problem: One lens should be put soon after dichroic mirror, but there is little room for fix it. (Attached #4, It will be put where the pedestal is.)  Tomorrow we will check this problem again.
Attachment 1: pic0924_1.jpg
14216   Tue Sep 25 18:08:50 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Gautam ]

We want to remotely control steeing PZT mirrors so its driver is needed. We already have a PZT driver board (D980323-C) and the output voltage is expected to be verified to be in the range 0-100 V DC for input voltages in the range -10 to 10 V DC.
Then I checked to make sure ir perform as we expected. The input signal was supplied using voltage calibrator and the output was monitored using a multimeter.
But it didn't perform well. Some tuning of voltage bias seemed to be needed. I will calculate its transfer function by simulation and check the performance again tommorow. And I found one solder was off so it needs fixing.

Reference:
diagram --> elog 8932

Plan of Action:

• Check PZT driver performs as we expected
• Also check cable, high voltage, PZT mirrors, anti-imaging board
• Obtain calibration factor of PZT mirrors using QPD
• Measure some status value before changing setup (such as tranmitted power of green laser)
• Revise setup after a new lens arrives
• Align the setup and check mode-matching
• Measure status value again and confirm it improves
• (write programming code of making alignment control automatically)
ELOG V3.1.3-