I took a look at the TRX/TRY RIN reported in the single arm POX/POY lock, and compared the performance of the two available PDs at each of the two ends. Attachment #1 shows the results. Some remarks:
Some ideas Koji suggested:
For the second idea, it is convenient to be able to control the arms in the XARM/YARM basis as opposed to the CARM/DARM basis as we usually do when going through the locking sequence. After some fiddling, I am able to reliably execute this transition, and achieve a state where the FP arm cavities are resonant for the IR with the ALS beat note frequency being the error signal being used. Some important differences:
TL;DR: Got the x-arm aux laser locked again and took more data - my fit on my transfer functions need improvement and my new method for finding coherence doesn't work so I went back to the first way! See attached file for an example of data runs with poor fits. First one has the questionable coherence data, second one has more logical coherence. (ignore the dashed lines.)
We were able to lock the Y-arm using Megatron and the RCG generated code, with nothing connected to c1iscey.
All relevant cables were disconnected from c1iscey and plugged into the approriate I/O ports, including the digital output. Turns out the logic for the digital output is opposite what I expected and added XOR bitwise operators in the tst.mdl model just before it went out to DO board. Once that was added, the Y arm locked within 10 seconds or so. (Compared to the previous 30 minutes trying to figure out why it wouldn't lock).
[Jenne, Rana, EricQ]
We tried a few times to engage the AO path while holding CARM on sqrtTrans and DARM on ALS, but failed every time. Since we cannot stably hold lock at arm powers of 1, even though we were able to do so early last week, we think that we have a problem (obviously). One noticeable thing is that while held with ALS, the Xarm transmission fluctuates almost full power.
As we were seeing late last week, the Xarm IR transmission while held with ALS was fluctuating wildly, whether we were locked on individual arms or on CARM/DARM.
Tonight we took some out of loop spectra, with different HEPA settings, to see how that affected things. It looks like HEPA at the nominal ~20% is okay, but anything higher than that starts to affect the Xarm beatnote sensing, while it mostly leaves the Yarm beatnote sensing okay. Perhaps this is something that isn't tightened enough in the Xarm path, or something on a skinny floppy mount that needs to be more secure.
I am still a little confused though, why we don't see large power fluctuations in *both* arms while using ALS to control CARM/DARM. Why are we not seeing this Xarm noise being fed back into the Yarm, through either the ETM via DARM, or common stuff via CARM actuating on MC2.
Note that the change at high frequency is because I switched from using non-DQ channels to DQ channels, so that's not anything to pay attention to. The noise reduction we see is below about 20Hz.
Rana pointed out that our POPDC level was very small. We don't have screens for them, but the DC PDs have the same analog whitening as the RF PD signals do. I changed C1:LSC-POPDC_WhiteGain.VAL from 0 to 11. Now our POPDC while locked on sidebands is about 8,000 counts.
We also swapped the cables between the SR785 and the CM board around. Now channel 2 of the 785 goes to TP2A, channel 1 goes to TP2B, and the source goes to EXCB. This is so that we can break the AO loop with the disable switch just after the slow/fast split, and look at the transfer function before we close the loop.
No major progress today.
I fixed a bug in my lockloss script that was asking it to start gathering data just after the lockloss, rather than some seconds beforehand. Ooops. Anyhow, with this handy-dandy plotting, I still don't know why we are losing lock when we have PRMI on REFL33, CARM on sqrtInvTrans, and DARM on AS55. I don't see any oscillations, just the arm power drops off, and a moment later the POP power drops.
For example, here is one of the best states we got to tonight. Data for this is in ..../scripts/LSC/LocklossData/1094369700 . You can re-create the plot by going to ..../scripts/LSC/LocklossData/ and doing ./PlotLockloss.py 1094369700 . We had set the triggers for the trans PD/QPD such that we were using the QPD transmission signals the whole time (above trans of 0.2). We saw that the noise at high frequency during low transmission powers for sqrtInvTrans as an error signal was higher using the QPDs than with the Thorlabs PDs, but that both cases are below the noise for ALS. The arm powers were pretty steady above 3 for the last bit of this lock stretch. I lost lock while trying to transition DARM over to AS55Q. CARM was on sqrtInvTrans(QPDs), PRMI on REFL33 I&Q as usual.
./PlotLockloss.py 1094369700 .
Other things from this evening:
* When I was starting, I saw that when I locked the PRMI, the PRM was oscillating in pitch. Oscillation only happened when PRM pitch oplev was on. I'm not sure what could have changed to make the oplev loop unstable, but the gain was 7.0, and now I have left it at 5.0.
* I recentered the PRM and ITMY oplevs.
* Plugged in the Yend PDH error monitor and pzt output monitors, since I forgot them last week. Hopefully this will allow the Yend SLOW servo to work, and keep us away from the limits of the PZT range.
Some small things I did tonight which did little to nothing to help:
My main concern with tonights situation was the huge low frequency fluctuations of TRY while CARM/DARM locked on ALS. We saw this being very smooth very recently, but when one arm is fluctuating by multiple line widths, it isn't surprising that locks aren't stable. I want to know why the out of loop stability is so unpredictable.
Kiwamu and Koji
The target is to realize DRMI or PRMI + one arm with ALS.
The focus of the night is to achive stable lock of the PRMI (SB resonant) with 3f signals.
Particularly, REFL165 is back now, we are aiming to see if any of the 165 signals is useful.
We made a comparison between REFL33Q/REFL165Q/AS55Q to find any good source of MICH.
However, none of them showed a reasonable shape of the spectra. They don't have reasonable coherence between them.
Nonetheless, we have tried to lock the IFO with those REFL signals. But any of them were useful to keep the PRMI (SB resonant).
The only kind of stable signal for MICH was AS55Q as we could keep the PRMI locked.
- Adjutsed the IMC WFS operating point. The IMC refl is 0.42-0.43.
- The arms are aligned with ASS
- The X arm green was aligned with ASX. PZT offsets slides were adjusted to offload the servo outputs.
- I tried the locking once and the transition was successfull. I even tried the 3f-1f transition but the lock was lost. I wasn't sure what was the real cause.
I need to go now. I leave the IFO at the state that it is waiting for the arms locked with IR for the full locking trial.
This is as far as I got last night. The first step is to see how reliable the settings determined last night are, today. I don't understand how changing the output matrix element can have brought about such a significant change in the MICH/PRCL separation in all the RF photodiodes.
Last night I worked on the several locking configurations:
General preparations / AS table inspection
- The AS beam looked clipped. I went to the AP table and confirmed this is a clipping in the chamber.
This may be fixed by the invacuum PZTs.
Modulation frequency tuning
RFPD Mon of the MC demodulator was check with the RF analyzer. Minimized the 25.8MHz (=55.3-29.5MHz) peak by changing the marconi freq.
This changed the modulation freq from 11.066147MHz to 11.066134MHz. This corresponds to the change of the MC round-trip length from
27.090952m to 27.090984m (32um longer).
- I wonder why I could not see good Michelson signal at REFL ports.
- I roughly aligned the Michelson. On the AP table, the RF analyzer was connected to the REFL11 RF output.
By using "MAX HOLD" function of the analyzer, I determined that the maximum output of the 11.07MHz peak
- I went to the demodboard rack. I injected -61dBm from DS345 into the RFEL11 demodboard. This produced
clean sinusoidal wave with the amplitude of 4 count. The whitening gain was 0dB.
- The output from the PD cable was -64.0dBm. So there is ~2.5dB loss in the cable. Despite this noise, the demodulation
system should be sufficiently low noise. i.e. the issue is optical
- The Michelson was locked with AS55Q. And the REFL11 error signals were checked.Fringe like feature was there.
This suggested the scattering from the misaligned PRM. The PRM was further misaligned. Then some reasonable
(yet still noisy) Michelson signal appeared. (Usual misaligned PRM is not at the right place)
Q. How much scattering noise (spurious cavity between PRM and the input optics) do we have when the PRM is aligned?
Q. Where should we put the glass beam dumps in the input optics?
Q. Can we prepare "safe" misaligned place for the PRM with the beam dump?
- The Michelson was locked with REFL11Q. From the transfer function measurement, the gain difference between AS55Q (whitening gain 24dB)
and REFL11Q was 32dB. The whitening gain was 0dB. In fact I could not lock the Michelson with the whitening gain 33dB (saturation???)
The element in the Input matrix was 1, The gain of the servo was +100. BS was actuated.
Coupled cavity tests
- At least REFL11 is producing reasonable signals. So what about the other REFL ports? The Michelson signals in the other frequencies
were invisible. So I decided to use three-mirror coupled cavity with the loss PRC.
- Aligned X arm, Misaligned ETMX, ITMY. Aligned PRM.
- Locked the PRM-ITMX cavity with REFL11 and REFL33.
- Aligned ETMX. If I use REFL11I for the PRC locking, I could not lock the coupled cavity. But I could with REFL33I.
This is somewhat familiar to me as this is the usual feature of the 3f signal.
- The coupled cavity could be locked "forever". To realize this I needed to tweak the normalization factor from 1.0 to 1.6.
Q. How does the coupled cavity change the response of the cavity? Can we compensate it by something?
Q. Measure open loop transfer functions to check if there is any issue in the servo shapes.
- Transmission during the lock is 3.2 while the nominal TRX with PRM misaligned was 0.93.
This corresponds to power recycling gain of 0.17.
- X arm:
- Source: POX11I, phase 79.5 deg, whitening gain 36dB
- Input matrix: POX11I->1.0->XARM, Normalization TRX*1.60
- XARM servo gain +0.8, actuation ETMX
- XARM trigger 0.25 up, 0.05 down. XARM Filter trigger untouched.
- PRC: (sideband locking)
- Source: REFL33I, phase -34.05 deg, whitening gain 30dB
- Input matrix: REFL33I->1.0->PRCL, Normalization None
- PRCL servo gain +4.0, actuation PRM
- PRCL trigger None
- Same test for the Y arm. At the moment ETMY did not have the OPLEV.
Same level of transmission (~3.3)
- Y arm:
- Source: POY11I, phase -61.00 deg, whitening gain 36dB
- Input matrix: POY11I->1.0->YARM, Normalization TRX*2.1
- YARM servo gain +0.25, actuation ETMX
- YARM trigger 0.25 up, 0.05 down. YARM Filter trigger untouched.
- PRC: (sideband locking)
- same as above
Sideband PRMI attempt
- Now I got some kind of confidence on the REFL33 signal.
- So I tried to get any stable setup for sb PRMI, then to find any reasonable MICH signals anywhere else than AS55Q.
- With REFL33I(PRCL) & AS55Q(MICH), I got maximum ~10sec lock. It regularly locked. It was enough long to check
the spectrum on DTT. But it was not enough long to find anything about the MICH signals at the REFL ports.
- I tried REFL33Q for MICH. The lock was even shorter but could lock for 1~2 sec.
Q. What is the cause of the lock loss? I did not see too much angluar fluctuation. The actuation was also quiet (below 10000).
- PRCL: (sideband locking)
- Same as above except for
- the PRCL servo gain +0.05, No limitter at the servo output.
- Trigger POP22I (low pass filtered by LP10) 20 up, 3 down
- AS55Q -24.125 24dB -> x1.0 -> MICH -0.7, No limitter -> ITMX/Y differential
- REFL33Q -34.05dB -> x2.0 -> MICH same as above
- For both case, trigger POP22I (low pass filtered by LP10) 20 up, 3 down
At this point Jenne came back from dinner. Explained what I did and handed over the IFO.
When I talked with Den via phone, he recommended to use the trigger and normalization with POP110I.
So I decided to try this approach. Also I investigated how the REFL33 signals are useful.
I could find the state where the PRMI(sb) locks regularly, although the lock is ~1min at most.
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain 0.2~0.12 FM3, 4, 5, 6 always on, no triggered FMs
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain -20 FM4, 5 always on, no triggered FM
-> ITMX (-1.0) and ITMY (+1.0)
I needed to tune the phase very precisely to reach this state. Also the alignment of the michelson and PRM
was very crtiical to acquire the lock.
Later in the same night I was plagued by PRM alignment drift. It seems that the PRM alignment is bistable or
slightly drifting in pitch. I had to align PRM continuously. When the PRMI is locked, the alignment fluctuation
was mainly in yaw. This was as people commented before.
Not much luck locking tonight; we made the RF transition to CARM numerous times, but it never lasted more than a minute or so. We were able to take a couple of loop and spectrum measurements as we transistioned.
Here are some spectra showing the noise evolution of CARM_IN1 and DARM_IN1 as we start to transition CARM to RF. We did not manage to grab spectra while CARM was RF only; we can go back in the DQ to find some data.
As we transition, our phase bubble is shrinking, which may explain our poor stability. On the following plot, I actually mistyped the legend. The cyan trace is ALL RF. I'm not sure why we have a 1/f^2 shape from 100->200Hz.
We adjusted the pole compensation frequency by looking at REFL11/ALS during a CARM swept sine measurement, the -3db/-45degree point looked more like 80Hz. Strangely, the compensated REFL11 signal appears to lag the ALS signal around the UGF. Maybe this is a loop effect?
In terms of practical improvements, I've written a script that reliably transitions from POX/POY IR lock to ALS CARM/DARM lock already on resonance. This is saving us a bunch of time. I've svn'd the new ALS script and the new carm_cm_up that uses it.
We looked into the odd oplev behavior as well. We had earlier seen what looked like railed values on the FM output medm screen (which seemed unexpected for an AC coupled loop), but dataviewer showed it was actually ringing/railing at some 10+Hz as the oplev beam fell off the QPD. The ringing continues even after the quadrant values stop crossing zero, so I think it may be the filters themselves misbehaving. Why there is new behavior here is still beyond me.
We lost a fair bit of time to a fussy mode cleaner tonight; there was a good 45 minute stretch where it refused to lock for more than a minute or so, the PC drive angriliy never falling below 5. The thing I changed when it started working was using the fast C1:IOO-MC_F channel instead of the slow C1:IOO-MC_FAST_MON as a readback for the FSS input offset; oddly there is a DC difference between the two. This has resulted in a FSS offset of ~4.2, whereas it was previously ~1.8. After this change, the PC drive fell to ~1.0 levels, and the IMC has been mostly ok.
Given our problems stabilizing the RF lock, we attempted to give the FOOL path a shot, since we now had a better idea of the neccesary REFL11 gain. In short, no luck. Every attempt to use some RF signal just disturbed the lock further. We didn't really pursue it too much after a couple of attempts showed little promise.
We were working on getting back into the locking groove tonight.
The POP2F and REFL3F demod angles needed some tuning to lock the PRC reliably. The green alignments were mostly fine, the X end PZT ASS works reasonably well. Suspensions, especially the ITMs, seemed to be drifting a fair deal; today was fairly hot out, I guess.
We only got to the point of attempting the SqrtInv handoff once (which failed because I forgot to check the filter bank offsets). This was because the Mode Cleaner refused to stay locked longer than ~5-10 minutes at a time. We adjusted the MC and FSS servo offsets by the usual means, but this didn't make a difference.
We discussed and decided that the time is right to roll up our sleeves and dig into the MC loop, and try to figure out why these intermittent times of unreliability keep cropping up. We will check out the servo board, and see if we can find the missing phase than Evan observed, as well as characterize the FSS/PZT crossover, and investigate what kind of conditions we may create that cause the PC to saturate.
I am still unable to achieve arm powers greater than TRX/TRY ~10 while keeping the PRMI locked. A couple of times, I was able to get TRY ~50, but TRX stayed at ~10, or even dropped a little, suggestive of a DARM offset? On the positive side, the ALS system seems to work pretty reliably, and I can keep the arms controlled by ALS for several tens of minutes.
More tomorrow, but I tried the following tonight:
In preparation for attempting some DRMI locking, I did the following:
Not related to this work, but I turned the Agilent NA off since we aren't using it immediately.
In preparation for some locking work tonight, I did the following at the POP in air table with the PRMI locked on carrier:
Tonight we want to measure the LSC matrix for PRMI and compare the simulation posted last night (#5495).
First. we locked MICH and PRCL, and measured the OLT to see how good the locking is. The following rough swept sine plots are the OLTs for MICH and PRCL. The gain setting was -10 and 0.5 for MICH and PRCL, respectively. Integrators were off. Looking at the measured plots, MICH has about 300 Hz UGF, when the gain is -20, and PRCL has about 300 HZ UGF, too, when the gain is 0.8.
As these lokings seemed good, so we tried the LSC matrix code written by Anamaria. However it is not working well at this point. When the script add excitations to the exc channels, they kick the optics too much and the lockings are too much disturbed...
Also, we have been trying to lock PRC with the SB resonant, it doesn't work. Looking at the simulated REFL11I (PRCL) signal (you can see it in #5495 too), the CR and SB resonances have the opposite signs... But minus gain never works for PRCL. It only excites the mirror rather than locking.
Both loops basically have no phase margins. i.e. unstable. How can you lock PRMI with these servos?
The following rough swept sine plots are the OLTs for MICH and PRCL. The gain setting was -10 and 0.5 for MICH and PRCL, respectively. Integrators were off. Looking at the measured plots, MICH has about 300 Hz UGF, when the gain is -20, and PRCL has about 300 HZ UGF, too, when the gain is 0.8.
The scripts I wrote can be found in /users/anamaria/scripts/sensemat/
]There are two of them:
- one that sets all the switches, gains, frequencies, etc, then cycles through the various RFPDs I and Q into the LOCKIN signal, so as to see the sensing matrix.
- the second one is a matlab script that takes the crappy file tdsavg outputs and makes it into a cute mag/phase matrix.
They're quite primitive at this point, I've forgotten a lot of tcsh... may improve later. But could be useful later to someone else at least.
I don't think it's particularly the fault of the script that we can't measure the sensing matrix. We can slam on the excitation by hand, and it holds for a little while. I set a wait time for lock to adjust, and most times it just oscillates a bit for a few seconds. Also, the script turns on the excitation and it's done, the rest is just measurement, then turns it off at the end. So during the script, there's not much to deal with, except keeping the lowpass filters quiet when switching the signal to demod; but that doesn't go anywhere, so it definitely doesn't disturb the ifo. Turns out pressing the RSET clear history button needs a 2 to make it happen.
I think I might prefer to set the excitation to run, and then do the old retrieve-data-later-nds-matlab thing. I do not trust these measurements without coherence and a bit of variance study, given instabilities.
Point is... Even on carrier, the PRC lock is not stable by any means. Can barely turn on low freq boosts, every other lock. Until we fix the lock stability issue, there's not much to measure I guess.
Unfortunately, I don't know how to make that happen. Before we leave on Friday we could do a few sanity checks such as measuring the noise of the RFPDs vs ADC+whitening, which I may have said I would do; and perhaps setting up a couple OSAs, one on REFL, one on AS, to make sure we know what the sidebands are doing. Both of which Rana suggested at some point.
(There used to be a quote here from Keiko here but I got mad when it reformated my entire log to be one cluster- hence the look)
Hardware issues that need addressing:
The DQ channels of the ETM coils were active tonight, so I'll make the coil driver actuation budget over the next couple of days.
Some locking efforts tonight; many locklosses due to PRC angular motion. Furthest progress was arm powers of 15, and I've stared at the corresponding lockloss plot, with little insight into what went wrong. (BTW, lastlock.sh seems to catch the lock loss reliably in the window)
CARM and DARM loops were measured not long before this lock loss, and had nominal UGFs (~120Hz, ~20deg PM). However, there was a reasonably clear 01 mode shape at the AS camera, which I did nothing to correct. Here's a spectrum from *just* before the lockloss, recovered via nds. Nothing stands out to me, other than a possible loss of DARM optical gain. (I believe the references are the error signal spectra taken in ALS arms held away + PRMI on 3F configuration)
The shape in the DARM OLTF that we had previously observed and hypothesized as possible DARM optical spring was not ever observed tonight. I didn't induce a DARM offset to try and look for it either, though.
Looking into some of the times when I was measuring OLTFs, the AS55 signals do show coherence with the live DARM error signal at the excitation frequencies, but little to no coherence under 30Hz, which probably means we weren't close enough to swap DARM error signals yet. This arm power regime is where the AS55 sign flip has been modeled to be...
A fair amount of time was spent in pre-locking prep, including:
There seems to be stronger-than-expected coupling between CARM and the 3f sensors.
Full analysis tomorrow, but I collected sensing matrix measurements with lines driven in PRCL,MICH and CARM at a couple of CARM offsets. I also wanted to calibrate the CARM offset to physical units so I ran some scans of the CARM offset and collected the data so I can use the arm cavity FSR to calibrate CARM. Koji suggested using REFL165_I for PRCL and REFL165_Q for MICH control - this would allow us to see if the problem was with the 1f sideband only. While the lock could be established, we still couldn't push the arm powers above 10 without breaking the PRMI lock. While changing the CARM offset, we saw a significant shift in the DC offset level of the out-of-loop REFL33_I signal. Need to think about what this means...
The CARM-->RF transition remains out of reach. No systematic diagnosis scheme comes to mind.
TBC. Mercifully at least the shaker stayed still tonight.
I managed to partially stabilize the arm citculating powers - they stay in a region in which the REFL 11 signal is hopefully approximately linear and so I can now measure some loop TFs and tweak the transition appropriately.
The main change I made tonight was to look at the REFL11 signal as I swept the ALS CARM offset through 0. I found that the maximum arm powers coincided with a non-zero REFL11 signal value (i.e. a small CARM offset was required at the input to the CARM_B filter bank). Not so long ago, I had measured the PM/AM ratio for 11 MHz to be ~10^5 - so it's not entirely clear to me where this offset is coming from. Then, I was able to turn on the integrator (z:p = 20:0) in the CARM_B filter bank while maintaining high POP_DC. At this point, I ramped up the IN2 gain on the IMC servo board (= AO path), and was able to further stabilize the power.
Attachment #1 shows this sequence from earlier in the evening. Note that in this state, both ALS and IR control of CARM is in effect. The circulating power is fluctuating wildly - partly this is probably the noisy ALS control path, but there is also the issue of the (lack of) angular control - although looking at the transmon QPDs and the POP QPD signals, they seem pretty stable.
The next step will be to try and turn off the ALS control path. Eventually, I hope to transition DARM control to AS55 as well. But at this point, I can at least begin to make sense of some of the time series signals, and get some insight into how to improve the lock.
No systematic diagnosis scheme comes to mind.
No real progress tonight - I made it a bunch of times to the point where CARM was RF only, but I never got to run a measurement to determine what the DARM_B loop gain should be to make the control fully RF.
Today the locking was not as easy as that was last Friday.
So I tried something new. Today Rana talked about the ASDC locking with POPDC normalization.
This technique was tried. (This is somewhat similar to DC readout.)
Signal source: REFL33I / Normalization POP110I x 0.04 / Trigger POP110I 20up 3down, otherwise untouched from Friday locking
Servo: input matrix 1.00 -> PRCL Servo FM3/4/5/6 Always ON G=+0.06
Actuator: output matrix 1.00 -> PRM
Signal source: ASDC Offset -109.5 (nominal of the day -49.5) / Normalization POPDC x 1.00 / Trigger POP110I 20up 3down
Servo: input matrix 1.00 -> MICH Servo FM5 Always On G=+10000
ActuaroL output matrix -1.00 -> ITMX / +1.00 -> ITMY
- POP110I was ~120 during the lock (cf 170 on Friday). So there is some small leakage from the dark port.
- Lock was easier when FM4 of the MICH loop was turned off.
- During the lock horizontal motion of the intracavity mode was visible as usual.
I tried using the POX_I error signal for the DC CARM_B path today a couple of times. Got to a point where the AO path could be engaged and the arm powers stabilized somewhat, but I couldn't turn the CARM_A path off without blowing the lock. Now the IMC has entered a temperemental state, so I'm abandoning efforts for tonight, but things to try tomorrow are:
I have some data from a couple of days ago when the PRFPMI was locked as usual (CARM_B on REFL for both DC and AO paths), and the sensing lines were on, so I can measure the relative strength of the sensing lines in POX/REFL and get an estimate of what the correct digital gain should be.
The motivation here is to see if the sensing matrix looks any different with a modified locking scheme.
The usual technique is that keeping the IFO locked with the old set of the signals and the relative gain/TF between the conventional and new signals are measured in-lock so that you can calibrate the new gain/demod-phase setting.