- The new REFL165 PD was installed on the AP table
- The REFL165I/Q signals are now showing sensible and robust PRCL/MICH signals
- PRMIsb was locked only with these REFL165 signals
- Installation of the REFL165 PD
We prepared the REFL165 PD for the 4" optical height. The actual issue was the power supply for the PD.
We soldered wires between the PD and the RF PD interface break-out board. Then the PD interface
cable for the old REFL165 (iLIGO style) was connected.
At the REFL port, most of the light is rejected by the first beam splitter (R=90%?). We attenuated the beam by a factor of 10
using an ND filter. The new PD showed the DC output of ~10V. This corresponds to the photocurrent of 5mA.
(cf. the shot-noise intercept current is ~1mA)
The output of the REFL165 PD was checked with the RF spectrum analyzer. It was a bit surprising but we had a forest of
RF signals betwen 11MHz and 178MHz. We tried to use a high-pass filter with fc=100MHz (SPH-100) but still the rejection
was not enough. We ended up with using SPH-150 (fc=150MHz).
- Whitening / Demodulation phase
Then we connected the RF output to the SMA cable to the LSC rack. We immediately saw the nice signals from REFL165I/Q
channels, namely sensible structure of pendulum resonances (1/3/16Hz peaks) and floor level.
The whitening level was changed from 21dB to 45dB (max). The DC offsets in the I/Q channels (of the order of 2000~4000)
were removed by the ./LSC/LSCoffset script.
Firstly we locked the PRMI with the usual signals (REFL33I and AS55Q).
The demodulation phase was roughtly tuned (1deg precision) such that the Q phase signal is minimized,
assuming most of the signal is coming from PRCL. Our choise is 74deg.
In this configuration, PRCL shows same quality of signal as our prefered PRCL (i.e. REFL33I) in the amplitude and the sign.
We switched to the REFL165 signal by handing off at the input matrix. The input matrix element for REFL165_I was gradually
increasded up to 0.8 while the element for REFL33I was gradually reduced to 0. We did the same for REFL165_Q with the element of 0.2.
Now we tried locking with REFL165I/Q from the beginning. Once the alignment is adjusted, the lock was immediately obtained
only with REFL165I/Q. Today we did not adjusted the ASC stuff (OPLEVs and PRM ASC) so the lock was not long (<1min). Particularly
ITMX poiting kept drifting and it made the lock difficult. We should check the oplev setup carefully.
- LSC summary
Signal source: REFL165I (74deg) / Whitening gain 45dB
Normalization sqrt(POP110I x 0.1) / Trigger POP110I 100up 3down
Servo: input matrix 0.80 -> PRCL Servo FM3/4/5 Always ON G=+2.50
Actuator: output matrix 1.00 -> PRM
Signal source: REFL165Q (74deg) / Whitening gain 45dB
Normalization sqrt(POP110I x 10.0) / Trigger POP110I 100up 3down
Servo: input matrix 0.20 -> MICH Servo FM4/5 Always On G=-40
Actuator output matrix -1.00 -> ITMX / +1.00 -> ITMY
- Refine the PRM asc servo (AC coupled)
- Align oplevs
- ITMX oplev is drifting quickly (~1min time scale)
Since Q has found that REFL165 will be better for holding the PRMI while we reduce the CARM offset, I had a look at locking PRMI sideband locking with both 3f PDs.
I checked the REFL165 demod phase, and changed it from -142.5 deg to -138.5 deg. to minimize the Q signal while driving PRM length.
I found that keeping the MICH and PRCL loop gains the same, and using matrix elements +0.1 for both I and Q for REFL165, rather than +1 for both I and Q for REFL 33.
MICH gain is +0.8, PRCL gain is -0.02. FMs 4,5 on for both, FM 2 triggered for MICH, FMs 2,3,6 triggered for PRCL.
I then locked the PRMI on sideband with REFL 33 and then REFL 165, and measured the other one as an out of loop sensor of the motion. I find that REFL33 and 165 are both comparable, and so we shouldn't have any trouble using REFL165 for locking.
[Rana, Gabriele, Jenne]
We have now locked the PRMI using REFL55 I&Q for more than one minute!!!!!
This isn't really the most useful plot as is, but it was created using:
/opt/rtcds/caltech/c1/scripts/general/getdata C1:LSC-POP22_I_ERR_DQ C1:LSC-REFL55_I_ERR_DQ C1:LSC-REFL55_Q_ERR_DQ C1:LSC-MICH_IN1_DQ C1:LSC-MICH_OUT_DQ C1:LSC-PRCL_IN1_DQ C1:LSC-PRCL_OUT_DQ -d 80 -s 1049013520 -c
This is just one of several long lock stretches. If I can get the TRIG_MON channels to be saved, we can automatically (versus my by-hand search) find lock stretches and make this kind of plot. Although we want them saved in some raw format so we can zoom in on selected axes, I think. This might require some python-fu from Jamie, or learning of python-fu for Jenne.
The secret sauce:
* The big key was changing REFL55's phase. It was -4 when we looked at the I&Q signals, and minimized the PRCL information in the Q-phase. We were able to get short lock stretches with this. During these stretches, Rana changed the REFL55 phase until the lock sounded (audibly) quieter. The final phase we settled on was +26. As we changed the phase, the lock stretches got longer and longer.
* We also tweaked up the POP22 phase. It was close from our previous efforts of looking at non-locked time series, but we perfected it by minimizing the signal in the Q-phase during lock stretches. We also found that it drifted (according to this method) by ~5 degrees over ~half an hour (I don't remember the exact time between our phase tunings).
* POP22's low pass filters (both options, ELP10 and ELP50) must be OFF for any lock to be acquired. Turning on either filter prevents locking.
* Normalization helped a lot. Without normalization we weren't really able to catch any locks, certainly not of any significant length. (0.004, using POP22I, for both MICH and PRCL).
** Normalization: use POP22I for both MICH and PRCL, value = 0.004
** Input matrix: MICH with REFL55Q, value = 0.01; PRCL with REFL55I, value = 0.01 (we used the small number in the matrix so our servo gains weren't too tiny).
** POP22 lowpass filters OFF
** Analog whitening OFF for REFL55, POP22.
** Analog gain for REFL55 I&Q = 27 dB
** Analog gain for POP22 I&Q = 15 dB
** Output matrix: MICH with -1 to ITMX, +1 to ITMY. PRCL with +1 to PRM.
** Servo gains: PRCL = 0.75; MICH anywhere between -3 and -20. Best in the -8 to -15 range.
** Vio2 filters in ITMX, ITMY, PRM (all actuated-on mirrors) were OFF. (Still need to lower the Q on these so they don't ring).
** PRCL and MICH triggering on POP22I. The trigger-off was always 20, but the trigger-on changed throughout the night from ~170 to ~50. I think 130 was a trigger value for at least some of the long-time locks.
** Low frequency seismic was small (i.e. no anomalous 0.1 Hz - 1 Hz noise) during successful lock times. (Not to say it must be low, but it was low when we were able to lock for long stretches).
Things we had looked at and thought about throughout the evening:
* Oplev calibration. See elog 8391 and 8393. Optimized BS and PRM to reduce yaw angular motion.
* Actuators all functioning as expected. We checked transfer functions of MICH_OUT/MICH_IN1 for locking with different optics, to ensure that at high frequency the response was 1/f^2. Also, we locked MICH with (a) both ITMs, (b) BS, (c) ITMX and (d) ITMY. We locked the PR-ITMY half-cav with (a) PRM and (b) ITMY. We locked the PR-ITMX half-cav with (a) PRM and (b) ITMX. Thus, we conclude that all of the PRMI-related optics are functioning as expected.
* Realigned REFL55 beam onto PD. It was clipping a bit, so the DC power wasn't steady (when ITMs were misaligned, PRM aligned). After alignment, the DC power as seen on a 'scope was much smoother.
* Turning off the limiters for the MICH and PRCL control signals allowed us to hear a high-pitched whine. From looking at the time series, it's predominantly in MICH_OUT. Rana speculates that perhaps the normalization is causing the UGF to wander temporarily to an unstable place. For a time there was a high-Q peak between 500 and 600Hz, but reducing the gain (of MICH?) eliminated that. Then we heard several times, irrespective of gain setting, the ~400Hz broad peak (I say broad because I was able to see it on DTT looking at the error and control signals, and it spanned +/-100Hz).
Things to investigate:
* Is there a good reason that we should switch to triggering on POP110, rather than the current POP22? From Gabriele, Jamie and my Finesee/Mist modelling last week, without the arms, the 11MHz and 55MHz resonate at different PRC lengths. If this difference is very small, then we are fine, but if the difference is large, it could be causing trouble - we're trying to catch the lock at the linear part of the 55MHz signal, but if that does not coincide with the linear part of the 11MHz signal, we're doing the wrong thing.
* For the POP normalization, should we be using the amplitude or the power ( POP22 or sqrt(POP22) )? Why? Look at this with a modelling sweep and/or analytically.
* Look at different noise sources, potentially sensing noise, coil actuator noise,..... We should check these out, and make sure we're not limited by anything obvious.
* Make a "restore" medm screen, rather than restore script. IFO Configure restore script can pull in values from the screen (EPICS values). One screen per configuration.
* Get TRIG_MON signals saved, write script to search for triggered lock times (between given gps times), then plot interesting signals for just before lock, during lock, and until just after a lockloss.
Koji is working on PRMI locking, and while he was doing that I glanced at the oplevs' spectra for the ITMs and PRM.
I found that when the PRMI was locked (for only 1 second or so max lock time) on the 55MHz sideband, and the error signals show a big peak around 400Hz (definitely audible in the control room), the only OpLev that I see a similar peak in is ITMX pitch.
In the plot below, I have grabbed a time when the PRMI was flashing as the black reference traces, and then a time when the PRMI was locked as the active traces. You can see that there is a similar peak in both REFL55I and ITMX_OL_PIT when the cavity is locked.
I tried to reproduce the locking situation described in this entry tonight.
The momentary lock was regularly seen but there was no stable lock.
I wonder why the actuators are always saturated. The feedback signals have the dominant component at ~400Hz.
It would also be nice if the servos have some immunity to gain fluctuation.
I didn't check how the situation of the AP table is. I'll look into some details tomorrow.
- Disabled MCL path in mcdown/mcupscript.
Nominal gain in mcdown/mcup was -50 and -100 respectively.
- Confirmed the stable lock was just because of the quiet seismic of the Friday night.
- Improvement of the PRM ASC servo
RG3.2 (3.2Hz Q=2 Height 30dB)
RG3.2 (3.2Hz Q=10 Height 30dB) + zero[f, 1, .5] pole[f, 2, 3] zero[f, 4.5, .5] pole[f, 3.5, 3]
Filter shape comparison is found in the second plot attached.
The resulting spectra (freerun vs controlled) is found in the first plot.
Nominal PRM ASC gain is +70
- Openloop TF measurement
OLTF PRCL 250Hz 30deg / MICH 200Hz 45deg
- REFL55/REFL33 phase adjustment (in lock)
REFL55 phase fine tune (95.25deg) (x1,x0.3)
REFL33 phase (-13.0deg) (x1, x2)
We wanted to try the PRC length measurement,but we ended up spending all the afternoon to lock the PRMI on sidebands. Here are some results
- Locked PRMI with REFL165 I/Q
- Aligned the POP beam on the QPD. We found that the vertical motion of the beam appeared in the yaw signal, and horizontal motion in the pitch signal.
This was fixed by swapping the cables to the ADC. Later it turned out that this was caused by the calibration setup for the QPD.
We requested Jenne to fix the QPD on the table with the current orientation.
- Re-implemented the AC-coupled ASC servo. The filters were just copied from the previous PRM ASC servo (in the SUS ASC filter).
The same filter was installed to the pitch and yaw filter modules for now. The gains were adjusted to have some stable lock stretches.
The power spectra of C1:ASC-PRCL_YAW_IN1 and C1:ASC-PRCL_PIT_IN1 were attached.
The reference curves are the ones with the servo on. The other two are the free-running stability of the QPD output.
- Modified the up and down scripts for the PRM ASC for the new setup.
It first turns on the inputs of the filters and then turn on FM2/3.
It assumes that the outputs are engaged all time.
Here are some details about the PRMI locking done last night.
REFL11 has been installed on the AP table. The RF signal from the RFPD is sent by a heliax cable which has been called ASDD133.
Before the beam goes into the RFPD a HWP and PBS are installed such that we can adjust the amount of light entering to the photo diode.
One thing I didn't like was that I had to introduce a big amount of the light into the PD to get a reasonably big RF signal.
I was trying to look for an RF signal by looking at a spectrum analyzer, then I realized that the RF signal at 11 MHz was quite tiny when the DC_MON was less than 1.5 V.
After I increased the amount of the light up to 1.9 V in DC_MON, which sounds already too much, I then got able to see the 11 MHz signal on the analyzer.
Note that I decreased the amount of the light down to 0.5 V after I finished locking the PRMI.
We should make sure what is going on with the 11 MHz modulation.
First I started locking the MIchelson with AS55. The demodulation phase was already somewhat optimized to the I-signal port.
So I decided not to touch the demodulation phase matrix because it may take some times.
After I eliminated electrical offsets in the digital side, I was easily able to lock the Michelson. The control sign was plus.
Then I started playing with the PRC control too. The demodulation phase in REFL11 looked nearly 45 deg although I didn't carefully measure it.
I made a 45 deg rotational matrix to maximize the I-port signal and tried to lock the PRC. Then immediately I was able to lock PRC as well as MICH.
GAIN_MICH = 100
GAIN_PRC = 100
Also GAIN_PRC = -100 gave a carrier resonant lock.
The control filters are the same in MICH and PRC. I used my favorite filters as usual.
FM1 = 1000 : 10
FM6 = 0.1 : 1
FM7 = 1 : 50
Somehow I frequently failed to engage the boost filters (i.e. FM6 and FM7) it looks offsets in the control path kicks either BS or PRM.
The PRMI has been successfully locked
Details will be posted in the morning.
Also changing the sign of the PRC control gave me the lock of the carrier resonant condition.
The screenshot above is the time series of the error signals when I was locking the PRMI in the sideband resonant condition (i.e. carrier is non-resonant).
Note that I used REFL11 for the PRC control and AS55 for the MICH control as planed.
Details will be posted in the morning.
Today we will try to lock the PRMI.
I was trying to measure the sensing matrix in the PRMI configuration, but basically gave up.
It is mainly because the lock of PRMI wasn't so stable and it didn't stay locked for more than a minute.
It looked like an angular motion fluctuated a lot around 1- 3 Hz. The beam spot on the AS camera moved a lot during the lock.
I have to figure out who is the bad suspension and why.
All the suspensions are bad until you fix them. But, ... there is a script which can be used to diagnose them today:
Today we will try to lock the PRMI. Here is a plan for it.
(to be done in the daytime)
- setup REFL11 RFPD
- setup AS55 RFPD
- install a demod board for 55 MHz
- install a 3-way RF combiner on EOM.
- prepare 55 MHz RF source (Marconi or RF source box ?)
- adjustment of each demodulation phase
- activation of PRM oplev
- AS55_Q ==> BS
- REFL11_I ==> PRM
Since we've got the PRMI locked we now should be able to do more qualitative measurements.
Here is a task list that we will measure/develop in the PRMI condition.
- Optical gain measurements
- Characterization of control loops
- MICH and PRC calibrations
- Noise budget
- Development of automatic noise budget scripts
- Arm loss measurement
- Shnupp asymmetry measurement
- AS55 RFPD
With a help from Jamie the AS55 RFPD was installed.
- 55 MHz demodulation board
The AS55 demod board was installed on 1Y2.
- 3-way combiner
ZFSC-3-13 has been installed. All the RF cables from the source side were connected to the combiner.
- installation of the REFL11 RFPD
- DAQ check for AS55 and REFL11
PRMI alignment procedure for carrier locking has been kept the same except that a couple of issues that have persisted are now taken care of.
We were able to keep PRMI locked for over a minute (POPDC measures 2200) .
1. Trigger levels to MICH and PRCL for PRMI locking have been changed
Whenever we enabled LSC controls to lock PRMI, ITMY moves haphazard if PRM is not aligned. This is because of the low trigger levels of POPDC which keeps MICH triggered all the time while we align PRM. Increasing POPDC trigger (Upper level : 1000 and Lower level:20) for both MICH and PRCL solved this problem and resulted in a more stable ITMY. Also this has stabilized locking greatly if the alignment is fair enough.
2. C1:SUS-ITMY_LSC_GAIN reset
Quoting Yuta's elog " I found C1:SUS-ITMY_LSC_GAIN is somehow set to be 2.895 recently. I think this should be 1.0. Maybe this is why we had actuation imbalance in ITMs(elog #8212)."
This has been reset to 1.0 and it has not affected PRMI locking.
1. Filter module (FM1) on PRCL and MICH show significant delay while enabling and disabling.
2. I tried to fix PMC alignment (PMC trans was 0.76). I was not able to get PMC trans more than 0.79.
PMC has been this way since yesterday.
3. MICH is still bright when locked (ASDC_OUT reads 0.08 for dark and 2.0 for bright). We suspect it is because of the AS55_I error offset that persists even after running LSCoffsets script.
4. PRMI shows some dither at 3Hz when locked.
- What about normalizing POPDC to indicate the carrier recycling gain?
- When you align the PMC, confirm FSS SLOW DC is around zero. Some region of the slow thermal actuation makes the laser source emit at multiple frequencies. In the case, the cavity visibility get worse.
- Do you guys think we can determine if the TT is longitudinally quiet enough? Is there any comparison between the simple Michelson and the PRC motion in m/rtHz?
I swapped the name of two demodulation boards (AS55 and REFL55).
Now the REFL11 and AS55 demodulation boards are ready to go for the PRMI locking.
The physical labels, which are on the front surface of the boards, are also corrected to avoid a confusion.
Here is the latest RF status.
The files are on https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/.
I had a quick look at PRM optical lever.
The He-Ne beam is still successfully coming out from the chamber and I could guide it to the QPD by using steering mirrors.
But the beam size looks too big for the QPD. We should slide the lens which is standing before the injection to get a moderately smaller beam size at the QPD.
[Jenne, Gabriele, Jamie]
We have looked at Koji's old Finesse code, and determined that the PRMI sensing matrix that he calculated was for the sideband-resonant case. Thus, this is the sensing matrix we are interested in for locking. Gabriele has confirmed this using independently written code with his software, Mist.
Pics or it didn't happen:
The sensing matrix is:
Numerical values are on the wiki: https://wiki-40m.ligo.caltech.edu/IFO_Modeling/SensingMatrix
For any of the REFL PDs (1*f1, 1*f2, 3*f1, 3*f2), the PRCL signal is a factor of ~100 larger than the MICH signal. Rana assures us that, with some clever triggering, we should be able to lock the PRMI.
This means that we will not be venting in the next few days to flip the SRC folding mirror. We will work on PRMI lock (probably first with 1*f, but then quickly moving on to 3*f), and as soon as Annalisa and Manasa have the new ETMY table ready for us, we will then do PRFPMI. (We can also play with the Xarm green until Yarm green is back).
[Jenne, Rana, Diego]
After deciding that the Yend QPD situation was not significant enough to prevent us from locking tonight, we got started. However, the PRMI would not acquire lock with the arms held off resonance.
This started some PRMI investigations.
With no arms, we can lock the PRMI with both REFL55 I&Q or REFL165 I&Q. We checked the demod phase for both Refl 55 and 165. REFL55 did not need changing, but REFL165 was off significantly (which probably contributed to the difficulty in using it to acquire lock). I didn't write down what REFL165 was, but it is now -3 degrees. To set the phase (this is also how Rana checked the 55 phase), I put in an oscillation using the sensing matrix oscillators. For both REFL165I and 165Q, I set the sensing matrix demod phases such that all of the signal was in the I phase (so I_I and Q_I, and basically zero in I_Q and Q_Q). Then, I set the main PD demod phase so that the REFL165Q phase (the Q_I phase) was about zero.
Here are the recipes for PRMI-only, REFL55 and REFL165:
Both cases, actuation was PRCL = 1*PRM and MICH = (0.5*BS - 0.2625*PRM). Trigger thresholds for DoFs and FMs were always POP22I, 10 up and 0.5 down.
REFL55, demod phase = 31deg.
MICH = 2*R55Q, gain = 2.4, trig FMs 2, 6, 8.
PRCL = 12*R55I, gain = -0.022, trig FMs 2,6,9.
REFL165, demod phase = -3deg.
MICH = -1*R165Q, gain = 2.4, trig FMs 2,6,8.
PRCL = 2.2*R165I, gain = -0.022, trig FMs 2,6,9.
These recipes assume Rana's new resonant gain filter for MICH's FM6, with only 2 resonant gains at 16 and 24 Hz instead of a whole mess of them: elog 10803. Also, we have turned down the waiting time between the MICH loop locking, and the filters coming on. It used to be a 5 second delay, but now is 2 sec. We have been using various delays for the PRCL filters, between 0.2s and 0.7s, with no particular preference in the end.
We compared the PRCL loop with both PDs, and note that the REFL 165 error signal has slightly more phase lag, although we do not yet know why. This means that if we only have a marginally stable PRCL loop for REFL55, we will not be stable with REFL165. Also, both loops have a non-1/f shape at a few hundred Hz. This bump is still there even if all filters except the acquisition ones (FM4,5 for both MICH and PRCL) are turned off, and all of the violin filters are turned off. I will try to model this to see where it comes from.
To Do list:
Go back to the QPDY situation during the daytime, to see if tapping various parts of the board makes the noise worse. Since it goes up to such high frequencies, it might not be just acoustic. Also, it's got to be in something common like the power or something, since we see the same spectra in all 4 quadrants.
The ASS needs to be re-tuned.
Rana was talking about perhaps opening up the ETMX chamber and wiggling the optic around in the wire. Apparently it's not too unusual for the wire to get a bit twisted underneath, which creates a set of places that the optic likes to go to.
Diego is going to give us some spectra of the MC error point at various levels of pockel's cell drive. Is it always the same frequencies that are popping up, or is it random?
I found out that the Spectrum Analyzer gives bogus data... Since now is locking time, tomorrow I'll go and figure out what is not working
However, the PRMI would not acquire lock with the arms held off resonance.
This is entirely my fault.
Last week, while doing some stuff with PRY, I put this filter in SUS_PRM_LSC, to stop some saturations from high frequency sensing noise
After the discussion at today's meeting, it struck me that I might have left it on. Turns out I did.
20 degree phase lag at 200Hz can explain the instability, some non-flat shape at few hundreds of Hz explains the non 1/f shape.
Sorry about all that...
EricQ's crazy people filter has been deleted. I'm trying to lock right now, to see if all is well in the world.
The first thing I looked at tonight was locking the PRMI on REFL 165.
I locked the PRMI (no arms), and checked the REFL 165 demod phase. I also found the input matrix configuration that allowed me to acquire PRMI lock directly on REFL165. After locking the arms on ALS, I tried to lock the PRMI with REFL 165 and failed. So, I rechecked the demod phase and the relative transfer functions between REFL 165 and REFL 33. The end of the story is that, even with the re-tuned demod phase for CARM offset of a few nanometers, I cannot acquire PRMI lock on REFL 165, nor can I transition from REFL 33 to REFL 165. We need to revisit this tomorrow.
For the PRMI-only case, I ended up using 0.1's in the input matrix, and I added an FM 1 to the MICH filter bank that is a flat gain of 2.2, and then I had it trigger along with FM2.
I turned this FM1 off (and no triggering) while trying to transition from REFL33 to REFL165 in the PRFPMI case, but that didn't help. I think that maybe I need to remeasure my transfer functions or something, because I could put values into the REFL165 columns of the input matrix while REFL33 was still 1's, but I couldn't remove (even if done slowly) the REFL33 matrix elements without losing lock of the PRMI. So, we need to get the input matrix elements correct.
I also recorded some time series for a quick RAM investigation that I will work on tomorrow.
I left the PRM aligned, but significantly misaligned both ITMs to get data at the REFL port of the RAM that we see. I also aligned the PRMI (no arms) and let it flash so that I can see the pk-pk size of our PDH signals. I need to remember to calibrate these from counts to meters.
Raw data is in /users/jenne/RAM/ .
I have not tried any new DARM signals, since PRMI wasn't working with 3f2.
We should get to that as soon as we fix the PRMI-3f2 situation.
Tonight PRMI was locked on REFL55 I&Q for PRCL and MICH with POP110I as a trigger and power normalizer.
I could see power fluctuations and beam motion on the POP camera very much the same as for carrier. The difference is that carrier stays for hours while sidebands for a few minutes.
I&Q analog gains were set to 15 dB. Relative phase was set to 25 degrees by looking at I and Q components when the cavity goes through the resonance. Q should be 0.
Phase rotation was measured by exciting PRM at 20 Hz and minimizing this line at REFL55_Q. I stopped at 33 degrees.
I compared power fluctuations of PRCL when it was locked on carrier (POP_DC) and on sidebands (POP110_I).
Time series of POP110_I during one of the locks
[Rana, Gabriele, Jenne, Jamie, Lisa, Rana]
We have tuned the oplev servos for PRM, BS, ITMX, ITMY. For each, we measured the servo transfer function. Most had a UGF ~ 3Hz. For those, we increased the gain by a factor of 2, and engaged the 3.3Hz resonant gains. The other case, such as PRM yaw, the gain was already okay, we just needed to engage the resonant gain. We also checked the new phase margin, and for some of them switched the elliptic lowpass to 50Hz rather than 30 or 35.
Before and afters:
We need to, as a last check, look at the spectra before and after to ensure that no modes (like bounce or roll) are newly excited.
We have achieved PRMI locks of the order ~5 seconds! Here is an example lock:
This was actuating MICH on the ITMs (+1 for ITMY, -1 for ITMX in the output matrix), and PRCL on PRM (+1).
PRCL gain was +1, MICH gain was -10.
PRCL signal was normalized with POP22I with a matrix value of 0.003 . (No normalization of MICH).
Both PRCL and MICH were triggered on POP22I with high thresh of 200, low of 50. MICH and PRCL FM2 (integrators) were triggered on POP22I with thresh of 400 and low thresh of 50. FMs 4 and 5 were on for both MICH and PRCL always.
We zoomed in on the MICH_OUT signal, and the instability looks like it is around 300 Hz. We aren't sure what this is. I think this is a similar frequency to an oscillation that Yuta saw, but I'll have to check the old elogs.
PRM and BS SUS_LSC_POS filter banks both have notches between 1280-1290Hz. The ITMs do not have this "Vio2" filter.
This is one of the first locks with the new triggering of both the INPUT and OUTPUT of the control filter banks. I modified the lsc model before lunch.
To do: Where is this 300Hz coming from, and what can we do about it? Why are we losing lock? It's not due to the oscillation - maybe too much afternoon seismic? Steve says he went next door and the rock monster / river is on medium/high.
[Gabriele, Rana, Jenne, Jamie, Lisa, Zach]
We tweaked some things after dinner, and our locks got longer (~10sec) and more frequent!
What happened / notes:
* Increased analog gain from 15dB to 27dB for REFL55 I&Q.
* No analog whitening during lock acquisition. (Need trigger + wait so whitening comes on after ~1sec...but this is not our limitation right now).
* Limit MICH and PRCL control to 5000, so that we don't kick optics too much, which makes them take too long to settle.
* ITMX and ITMY Vio2 filters turned off (PRM still has it on) in the SUS-optic_LSC module.
* MICH and PRCL DoFs triggering on POP22I, with levels 200 & 50. FMs 4&5 always on.
* MICH and PRCL FM2 triggering on POP22I with levels 400 & 50.
* MICH gain = -0.200
* PRCL gain = +0.150
* MICH and PRCL normalization using POP22I, with matrix values 0.00160 . This value is ~1/600, where 600 was the peak value of POP22I_ERR.
* REFL 55 phase set back to -15, to minimize PRCL signal in I phase.
* Checked signs for ITMX and ITMY in output matrix for MICH. Lock MICH using only ITMX or ITMY, find sign to hold on the dark fringe for each. +1 for ITMY, -1 for ITMX was correct.
* Tweaked up the oplev servos. See separate elog 8362. May need more tweaking, such as increasing the UGF, engaging 1Hz resonant gain.
* May need better coil actuator balancing on suspensions at 1Hz.
* Found a weird thing in DTT, which went away after closing and reopening, when looking at time series. Sometimes we would see a square wave-like jump in the signals, all signals at the same time, with a frequency of 16.6Hz. This was not present in other data retreival programs, like Jamie's getdata python script.
* We are not sure right now why we are falling out of lock. We need to investigate more signals, to try to figure out what our current problem is.
* Reduced the amount of misalignment with the "misalign" script, to reduce hysteresis.
To Do / ideas:
* Calibrate oplev signals - see if one optic is moving more than others.
* Calibrate ERR and CTRL - look at CTRL in meters, see if cavities are moving around like crazy.
* Calibrate POP22 using something like an AM laser modulation trick into units of PRCL SB gain. Compare with expectation - are we locked optimally, or do we have more power that we can be getting out?
* Try feeding back PRCL CTRL to MC2, to make the laser to follow the power recycling cavity, in hopes of reducing angular motion. Rana tried this quickly with a 1 in the output matrix, but this kicked the MC out of lock - need to try smaller values.
A key step was turning off the whitening filters. With the previous setting (G = 15 dB, white on), the error signals (post anti-whitening) had amplitudes of ~500 counts. This means that they can go as high as (150/15)^2 * 500 = 50000 counts on the ADC.
The purpose of the whitening filter is to match the noise / range of the signal to the ADC. What we would like to do is use the minimum gain so as to make the RFPD electronics noise + shot noise be ~equal to the ADC noise. i.e.
sqrt(V_PD^2 + v_shot^2) * G_white = V_ADC
The RFPD noise is ~3 nV before the internal preamp. The MAX4107 has a gain of 10. There is a factor of 1/2 from the voltage division of the RFPD's 50 Ohm series resistor and the input impedance of the mixer. There is also a power splitter between the PD output and the mixer which gives us a 3 dB loss. The mixer has a conversion loss of ~5-6 dB depending upon the LO level.
V_PD = 3e-9 * (10 * 1/2 * 1/sqrt(2) * 1/2) = 5e-9 V/rHz (this is already bad; the signal coming out of the mixer needs to be amplified by x10 before going out to the whitening board).
In any case, its clear that we need something like 60 dB of gain for the PD noise to match the ADC noise. This is why increasing the whitening gain improves the error signal's SNR, reduces the hash driving the optics, and improves the locking. We should run with 45 dB gain and the switch on whitening after the lock.
Even better would be to modify the LT1128 input stage of the card to have the single stage of fixed whitening as we did for iLIGO. Then we can have triple whitening in lock.
After all the work at the LSC rack over the last couple of days, I re-locked the PRMI (ETMs misaligned), and measured the sensing matrix once again. The PRMI was locked using 1f error signals, with AS55_Q as the MICH sensor and REFL11_I as the PRCL sensor. As shown in Attachment #1, the situation has not changed, there is still no separation between the DoFs in the REFL signals. I will measure the MC lock point offset using the error point dither technique today to see if there is something there.
Just so we have some numbers, I did a by-hand analysis of the PRMI sensing matrix numbers I posted here in the elog the other day. This analysis is ignoring the error bar data.
For each sensor (PD_I or PD_Q), I do loop compensation, since these measurements were taken fairly close to the UGFs of the loops, and notches were not in use at the drive frequency. To do the loop compensation, I multiply the complex value (lockin_I + i*lockin_Q) by (1-G), where G is the (complex) open loop gain of the degree of freedom I'm shaking.
When I'm shaking a single degree of freedom (ex. shaking the PRM to get PRCL information), for each PD_I or PD_Q, we get 2 numbers, the lockin_I and lockin_Q values. I check the phase between the lockin_I and lockin_Q values, since that phase (after loop compensation) should be either 0 or 180, and if it is not, something is wrong.
Of the 16 sensors I measure (where PD_I and PD_Q count as 2 sensors), 11 sensors had phases more than 20 degrees away from either 0 or 180. This is not good, and indicates that something is wrong with my measurement. I suspect that I may not be driving hard enough - I was using an amplitude 4x smaller than the previous value. Next time the PRMI is locked, I will turn on the drive oscillation, and ensure that I can see the line in all of the PD signals.
The results of my quickie analysis script:
Bad REFL11_I_MICH phase! Phase is -82.0185 degrees!
Bad REFL11_Q_MICH phase! Phase is -35.9697 degrees!
Bad REFL33_I_MICH phase! Phase is -134.952 degrees!
Bad REFL55_I_MICH phase! Phase is -79.7997 degrees!
Bad AS55_I_PRCL phase! Phase is -142.6016 degrees!
Bad AS55_Q_PRCL phase! Phase is 90.6194 degrees!
Bad REFL11_I_PRCL phase! Phase is 52.471 degrees!
Bad REFL11_Q_PRCL phase! Phase is 52.2324 degrees!
Bad REFL33_I_PRCL phase! Phase is 52.909 degrees!
Bad REFL33_Q_PRCL phase! Phase is 25.14 degrees!
Bad REFL55_I_PRCL phase! Phase is 52.8113 degrees!
Sensing Matrix, calculated even though most of the measurement data isn't any good:
AS55: MICH = 0.13502, -1.6122deg. PRCL = 0.14993, -2.245deg
REFL11: MICH = 29.6373, -2.6365deg. PRCL = 7376.3206, -2.9098deg
REFL33: MICH = 0.35649, -2.9633deg. PRCL = 69.5133, -3.1302deg
REFL55: MICH = 0.62084, -2.0261deg. PRCL = 75.0214, 3.1176deg
For now forget about the demodulation phase and assume all of the ports are independent.
I want to know the numbers in the following format.
PRCL MICH (unit: cnt/m)
REFL11I: x.xxxEx x.xxxEx
REFL11Q: x.xxxEx x.xxxEx
REFL33I: x.xxxEx x.xxxEx
REFL33Q: x.xxxEx x.xxxEx
REFL55I: x.xxxEx x.xxxEx
REFL55Q: x.xxxEx x.xxxEx
REFL165I: N/A N/A
REFL165Q: N/A N/A
AS55I: x.xxxEx x.xxxEx
AS55Q: x.xxxEx x.xxxEx
PRCL MICH (unit: cnt/m)
REFL11I: x.xxxEx x.xxxEx
REFL11Q: x.xxxEx x.xxxEx
REFL33I: x.xxxEx x.xxxEx
REFL33Q: x.xxxEx x.xxxEx
REFL55I: x.xxxEx x.xxxEx
REFL55Q: x.xxxEx x.xxxEx
REFL165I: N/A N/A
REFL165Q: N/A N/A
AS55I: x.xxxEx x.xxxEx
AS55Q: x.xxxEx x.xxxEx
If you really want to resolve the TF phase difference between the I and Q demod-signals,
you need to look at the transfer functions between the excitation and these ports.
We can't understand what is happening only from the single point measurement.
The PRMI sensing matrix, as measured last Thursday, in a more readable format:
EDIT: DON'T Look at this yet! I forgot to calibrate it! Please hold.....
AS55_I 1.228E-01 5.476E-03
AS55_Q 1.547E-01 1.345E-01
REFL11_I 9.946E+03 8.106E+01
REFL11_Q 2.346E+03 2.707E+01
REFL33_I 9.639E+01 8.717E-01
REFL33_Q 9.707E-01 6.626E-02
REFL55_I 1.040E+02 8.464E-01
REFL55_Q 2.018E+00 5.803E-01
Okay, Calibrated, but forgot to include loop compensation (since notches didn't exist yet):
Sensing Matrix, units = cts/meter
AS55_I 5.024E+08 9.418E+07
AS55_Q 6.328E+08 2.313E+09
REFL11_I 4.068E+13 1.394E+12
REFL11_Q 9.594E+12 4.656E+11
REFL33_I 3.942E+11 1.499E+10
REFL33_Q 3.970E+09 1.140E+09
REFL55_I 4.253E+11 1.456E+10
REFL55_Q 8.252E+09 9.981E+09
I locked the PRMI and remeasured the sensing matrix, this time at 580Hz. The excellent news here is that the matrix looks quite similar to the one measured the other day, recorded in elog 8632. Yay! I'm not sure why the REFL11 MICH error is so much larger this time around.
Raw data: .../scripts/LSC/SensMatData/sensematPRM_2013-05-23.202312.dat
Sensing Matrix, units = cts/meter, phase in degrees
PRCL Mag PRCL Phase MICH Mag MICH Phase
AS55 5.485E+08 162.424 2.679E+09 25.608
REFL11 1.126E+13 -122.832 1.618E+11 85.296
REFL33 2.658E+11 -87.973 8.910E+09 79.226
REFL55 3.012E+11 -99.534 1.210E+10 12.486
Can you clarify the definition of the phase "0deg" of your plot?
Is "I" the definition of "0deg"? Or does the demod phase of "0deg" define "0deg"?
I want to know if the demod phase of REFL55 is correctly adjusted or not.
With the decent level of the separation, we should be able to keep the decent lock of PRMI with REFL55.
"0 degrees" is 0 degrees of demod phase. I have now added the PD demod phases to the plot:
It's hard to believe but is AS55Q really almost insensitive to MICH?
Well, anyway, now it is the time to use the automatic demod phase (and input matrix) adjustment.
Okay, I think I am finished with the sensing matrix scripts!
I had the syntax for atan2() wrong, so I was calculating the demod phase wrong. Do not trust the phase in any previous elogs!!
Also, the theta=0 axis of the plots are for 0 degree demod phase, but our PDs are not at 0 deg. The measured sensing matrix phase is relative to the current demod phase, not 0 (unless the demod phase for that PD is currently 0degrees). So, now I take that into account. I add the current PD demod phase to the measured sensing matrix phase, so that the plot is actually true.
For interested parties, I have made all of the sensing matrix scripts, and the data folder a subdirectory of the /scripts/LSC folder, since it was starting to get crowded in there. I have moved the 2 data sets that have been collected (21May, 23May) into the new place.
* Save the amplitude and modulation frequency and the current demod phases in the data file. Right now the ampl and mod freqs are included in the title of the data file, but there is no record of what the demod phase was at the time. I need to fix this.
So, really, really, the Sensing Matrix:
Sensing Matrix, units = counts/meter, phase in degrees
PRCL Mag PRCL Phase MICH Mag MICH Phase
AS55 5.485E+08 -43.424 2.679E+09 93.392
REFL11 1.126E+13 -7.168 1.618E+11 135.296
REFL33 2.658E+11 164.973 8.910E+09 -2.226
REFL55 3.012E+11 -75.216 1.210E+10 172.764
Just so we have it, here is the re-analysis with the correct plot and phases for the May 21st data, taken near the violin mode:
Sensing Matrix, units = counts/meter, phase in degrees
PRCL Mag PRCL Phase MICH Mag MICH Phase
AS55 9.048E+11 -22.880 2.927E+12 107.071
REFL11 2.954E+16 -21.628 3.670E+14 123.857
REFL33 2.757E+14 -192.608 9.186E+12 -4.037
REFL55 2.868E+14 -82.690 1.186E+13 170.097
Even though this data was taken near the violin mode (oops!), it is fairly consistent with the stuff taken a few days later at 580Hz (elog 8644).
Neither of these is at all similar to what Kiwamu had measured a year ago (elog 6283), but we have changed many, many things since then. He also includes an Optickle simulation, which is fairly similar to the Koji simulation in the wiki, but neither his measurements nor mine are particularly close to the simulated version. I should think about why this is.
Also, I have fixed up the measurement scripts so that they record all of the relevant current settings / information: Current actuator calibration, current PD demod phases, drive amplitude and drive frequency. The "Analyze Saved Data" script has been updated to read all of this info from the files. If you want to plot / look at any old data, open up SensMatAnalyzeSavedData in /scripts/LSC/SensingMatrix/ and put in the relevant filename that you want (which should be saved in /scripts/LSC/SensingMatrix/SensMatData/)
- We want to add POX11/POY11 in the collection. They may indicates some abnormal asymmetry between two arms (for PRMI).
- We also want to PRCL/MICH after the input matrix. This will be useful when we want to adjust the input matrix to give the optimul
demod phase for the two signals from a single port.
I am also wondering if I understand / am using the demod phase from the screen correctly. This plot is indicating that MICH is entirely in I, and not at all in Q.
Currently, I take the demod phase, and plot that as the "I" line, then plot the "Q" line 90 degrees away from the I line. Maybe it should be the other way around?
Re: the auto-demod phase, I was starting to wonder about that. For each sensor, can I declare what degree of freedom I want in which quadrature to take priority (ex. MICH goes to REFL55 Q), and set the demod phase to the value that makes that true?
We succeeded in locking PRMI in sideband and carrier.
Measured power recycling gain was ~60 power recycling gain was 4 (edited by YM on Feb 27; see elog #6947), but we have many things we cannot explain.
Here you are, Jamie.
PRMI sideband locked
PRMI carrier locked
I centered POP camera and put attenuator to take these snapshots.
Compare with previous ones.
Aug 17, 2012 elog #7213
Jun 28, 2012 elog #6886
Mar 15, 2012 elog #6421
== MI only ==
MICH: AS55_Q_ERR, AS55_PHASE_R = -12 deg, MICH_GAIN = -7, feedback to BS
== PRMI sideband ==
MICH: AS55_Q_ERR, AS55_PHASE_R = 24.5 deg, MICH_GAIN = -0.05 (acquisition) -> -5 (UGF ~100 Hz), feedback to BS
PRCL: REFL33_I_ERR, REFL33_PHASE_R = -22.65 deg, PRCL_GAIN = 4 (UGF ~120 Hz), feedback to PRM
== PRMI carrier ==
MICH: AS55_Q_ERR, AS55_PHASE_R = 24.5 deg, MICH_GAIN = -0.08 (couldn't measure UGF), feedback to BS
PRCL: REFL33_I_ERR, REFL33_PHASE_R = -22.65 deg, PRCL_GAIN = -0.3 (couldn't measure UGF), feedback to PRM
Power recycling gain:
POPDC was 32 when PRM is misaligned, 25 when PRMI sideband locked, ~2000 when PRMI carrier locked.
This means, power recycling gain is ~60 power recycling gain is ~4 (=POPlocked/POPmis*T_PRM=2000/30*0.06). Expected power recycling gain for PRMI is ~45, when there's no loss (see elog #6947).
I reduced POPDC PD gain so that it doesn't saturate.
- We optimized AS55_PHASE_R to -12 deg by looking at MI signal. But somehow, -12 deg didn't work for PRMI.
- Somehow, REFL11_I didn't work to lock PRCL.
- REFL11_Q didn't work to lock MI. SNR not enough?
- We saw POPDC flashing up to ~15000. What is this?
- Carrier lock was not stable, we couldn't hold for more than ~30 sec. It looks like PRM moves too much when PRMI is locked.
- Input pointing is drifting a lot in pitch. I had to re-align TT2/TT1 to the arms every ~1 hour to get good MI alignment. When I tweak TT2/TT1, both TRY and TRX gets better. I think this shows that input pointing is drifting, not the arms.
- redo PRM/BS coil balancing
- optimize REFL33 rotation phase
- stabilize carrier lock somehow
- measure PRC g-factor
I have 12 tick marks for times I got all the way to 1f for all 4 degrees of freedom in the PRFPMI. The CARM / DARM transitions now succeed more than they fail, which is nice.
At Q's suggestion, I am turning off all the violin filters in the MC2 path during the CARM transition. This also means that I don't need any of the notches that Den and I put into the CARM_A and CARM_B filter banks last week, which were right at the edges of the violin notches. Anyhow, this seems to make the transition much more likely to succeed. I don't ever use the CM_SLOW FM10 "crossover helper" that Q had to use last night. The violin filters are turned back on after the CARM transition is complete. We don't ever need those other notches.
I checked the REFL165 vs. REFL55 transfer functions for PRCL and MICH, and they are mostly flat. REFL55 seems like it'll give us extra phase for some reason.
I tried setting offsets for PRMI, but they seem to be strongly dependent on arm alignment. I ended up being pretty confused, and since all the REFL signals are pretty close to zero (when CARM/DARM on RF, PRMI on 3f), I have given up on that avenue for tonight.
I think many of my locklosses tonight (lost from the all 1f state) have been fast things, faster than the ADCs can handle. On the lockloss plots that I've looked at, the FSS PC drive is railed at 10V about 200msec before I lose lock. So, something (presumably in the fast CARM path) is making the MC/FSS loop unhappy. I have plugged in the Agilent to the Out2 of the CM board, so that it looks at REFL11. Unfortunately, this is after the input gain slider, so we don't see much until we're locked, but that seems fine. A video camera is pointed at the screen, so that I get real time spectra. It's hard to watch the TV at the same time as everything else, so I haven't witnessed the moment of lockloss in the fast spectrum yet. Be careful when walking down the Yarm. The tripod is partly in the walkway.
Q, I took a few TFs of the total CARM loop, although none of them are particularly good below a few kHz. I can't push hard enough to get coherence, without blowing the lock. TF data is in /users/jenne/PRFPMI/CM_TFs/CM_TFs_2Apr2015/ .
I was worried for a while that, after I transition PRMI to 1f, I hear lots of low frequency rumbling. However, watching the spectra (relative to references taken with CARM and DARM on RF, but PRMI on 3f), the low frequency error and control signals are staying the same for all 4 DoFs, but the high frequency for PRCL and MICH goes down significantly, so it's probably just that the low frequency stuff sounds more obvious, since it's not drowning in high frequency fuzz.
I got the PRMI transitioned from REFL165 over to REFL55 two times tonight. Also, I had 2 long-ish locks, one 9 minutes, and one 6 minutes. All the other locks were short - less than a minute or two.
I've done some shuffling around of the point in the CARM transition when the anti-boosts (1:20 filters) come on in the CARM A filter bank. I've moved the turn-on of these filters a several gain steps earlier, but I'm not sure that they're in the best place yet. Fiddling with the turn-on of the anti-boosts makes the big CARM oscillations last for longer or shorter - if they last too long, they blow the lock, so we don't want them to get too big.
The PRMI angular feedforward has helped a lot tonight, I think. I've added a line to the up script to enable the output of the OAF after the PRMI is locked, and the down script turns it off again. It's not so great when the PRM isn't aligned, since it's designed to work when the oplev is on, so it should be off unless the PRM is aligned. I tried to get a comparison of off vs. on PRC powers with the arms resonating, but I can't hold the lock for long enough when the OAF is not on to get even one average on my 0.01Hz bandwidth spectrum.
I've turned the arm ASC on a few times, but not every lock. Around 12:34am, I set the offsets when CARM and DARM were on RF signals, and I had hand-aligned the ETMs to minimize the power at the AS port. But, this wasn't a good spot for the next lock - the AS port was much darker with the ASC off for that lock. It would be nice to think about trying some dither alignment, and then maybe resetting the setpoints every lock. I'm using Q's original loop shapes, but as he left them yesterday, only actuating on the ETMs (with Yarm Yaw gain 0.7 rather than 0.9).
The CARM crossover might need more tuning. There's some gain peaking around 400 Hz that goes mostly away if I turn the digital CARM gain down by 2dB. (I'm not using any filters in the CM_SLOW filter bank).
I think that the CARM/DARM transition is more likely to be successful if the FSS slow DC is greater than 0.55ish. So far this is pretty anecdotal, but I think I have more success when it's higher. We should pay attention, and see if our trouble locking later in the nights correlates with smaller FSS slow DC values.
I got the PRMI over to 1f two times, at 1:54am and at 2:25am. I did not re-phase "POP"55 (which is the REFL55 signal), but I did check the values for the input matrix. I needed MICH = 0.01*POP55Q and PRCL = 0.008*POP55I. The first time I lost lock because I turned down the CARM digital gain too much. The second time I forgot to turn down the PRCL gain (I was *actually* using 0.01*POP55I for the PRCL input matrix, but needed to lower the gain from -0.08 to -0.07, which is about the same as just using 0.008 in the input matrix). Anyhow, I think PRCL loop oscillations were the cause of the second lockloss.
Here's a strip chart of my first lock of the night, which was the 9 minute lock. Up until about -6 minutes, I was hand-aligning (including the dip around -7.5 minutes, where I was figuring out which direction to move the ETMs). Around -3.5 minutes there is a significant dip down, that corrected itself. By the time I realized that the power had gone down, and was trying to figure out why, it came back. Maybe the same thing happened at the end of the lock, but it kept getting worse? Self, re-look at this time (around 11:50pm) to find out why the power dips.
My tummy feelings (without any data) make me think that this could be something with ITMX, like Q saw earlier today. Or, maybe ETMX, like we've seen for ages. Anyhow, my tummy feeling says this is an optic pointing problem. I certainly think this might be the same thing we see at the end of many locks, the power going low suddenly. So, it might give a big clue to our locklosses. Maybe.
RXA: I've changed the above text into pink Comic Sans to lend it the appropriate level of gravitas, given its scientific justification.
[Gabriele's work, I'm just spectating]
Annalisa is working on finding the PSL/AUX laser beatnote, so the PSL temp is changing, but Gabriele is still able to lock. Here are some videos:
Lots of work, no solid conclusions yet. In-vac, we aligned MICH and the PRM. Out of vac, we got beam on AS and REFL paths. We can lock MICH, but we're not as happy with PRCL.
To get the beam centered on TT2 in yaw, Koji helped us out and moved TT1 with the sliders a little bit. Then to get the beam centered on PRM and PR2, Koji moved the TT2 sliders a little bit.
Yuta and I then moved PR2 forward a few mm, to keep the optical path length of the PRC approximately (within ~1mm, hopefully) the same as always. After my PR2 optic swapping earlier, the pitch alignment was no longer good. I loosened the screws holding the wire clamp to the optic holder, and tapped it back and forth until the alignment was good. Of course, the screw-tightening / pitch-checking is a stochastic process, but eventually we got it. A small amount of yaw adjustment by twisting the PR2 TT was also done, but not much was needed.
Beam was a little off in pitch at ITMY, so Yuta poked the top of PR3, and that one single poke was perfect, and the beam was very nicely centered on the ITMY target. Beam was getting through BS target just fine. We checked at ITMX, and the beam looked pretty centered, although we didn't put in a target. We didn't do anything to BS while we were in-vac, since it was already good.
We aligned the ITMs so that their beams were retroreflecting back to the BS. After this, we saw nice MICH fringes.
We aligned the PRM so that its beam was retroreflecting.
We checked that we were getting REFL and AS beams out of the vacuum, which we were (a small amount of adjustment was done to AS path steering mirrors).
AS table alignment:
We did a bit of tweaking of the REFL path, and lots of small stuff to the AS path.
The AS beam was coming out of vac at a slightly different place in yaw, so we moved the first out of vac AS steering mirror so the beam hit the center, rather than ~1/3 of the way to the edge. We then aligned the beam through the lens, to the camera, and to AS55. Most significantly, we removed the BS that was just before AS55. This was sending beam to a dump, but it is in place to send beam over to AS110, once we get back to real locking. We measured ~30 microwatts of power going to the AS55 PD, while MICH fringes were fringing.
The REFL path didn't need much, although we had never been going through the center of the HWP and PBS that are used to reduce the power before going to the PDs, so we translated them a millimeter or two.
We see signal on dataviewer for all of the channels that we're interested in....AS55 I&Q, ASDC, REFL11 I&Q, REFLDC (which comes from REFL55).
Locking MICH was very easy, after we rotated the phase of AS55 to get all the good MICH signal in the Q phase. Part of the criteria for this was that the AS55_Q_ERR signal should cross zero when ASDC went to 0. This was done very coarsely, so we need to do it properly, but it was enough to get us locked. We changed the phase from 24.5 to 90 deg.
PRCL has been more of a challenge, although we're still working on it.
On the back face of the Faraday, we see the michelson fringes, but they are not getting through the Faraday's aperture. This implies that we have a poorly aligned michelson, in that the interference between the returning beams from the ITMs is happening at a different place than the original beam splitting. Yuta is working on getting a better MICH right now. EDIT, 10 minutes later.... This seems to be fixed, and the MICH fringes enter the back aperture of the FI, but there is still the PRM refl problem (next paragraph).
Also, when we get the most bright REFL beam, we see that there is some very obvious clipping in the back of the Faraday aperture, and this is matched by a clipped-looking REFL beam on the AS table. We must understand what we have done wrong, such that when the beam is actually going through the Faraday, we see a much dimmer beam. It's possible that there is some clipping happening at that time with the in-vac REFL path....we need to check this. It's not a clipping problem on the AS table - I checked, and the beams are still reasonably well centered on all of the mirrors.
We think that the MICH / REFL beam problems may be that the input pointing is close, but not perfect. We have not confirmed today that the beam is centered on ETMY. We should do this as part of our final alignment procedure before putting on doors.
Plans for tomorrow:
Get POP aligned, especially the camera, so we can see what our intracavity mode really looks like in the PRC. This is probably (in part, at least) due to our having moved PR2 around, so the transmitted beams aren't in exactly the same place.
We think that it's more useful in the short term to check out the PRC, and since the clipping problem with the REFL beam is likely an imperfect input pointing, we want to use the other measured G&H mirror, and do another half-PRC test, with the test mirror in front of the BS. This requires much less perfection in the input pointing, so it should be very quick to set up.
Confirm that PRM oplev is still aligned (turn laser back on first).
Plans for next week:
Perfect the input pointing, by checking the beam position at ETMY. Recheck all corner alignment.
Try again locking PRMI in air. First, confirm ITM and BS oplevs are all aligned.
I feel it's too hasty to use the PRMI.
I support the idea of the half-PRC test, to make an apple-to-apple comparison.
Make haste slowly.
I completely agree with Koji. We definitely should have locked the half PRC first. We were all set up for that. Why go through all this work to align MICH when we haven't confirmed with the half PRC that the flipping is helping us? The first rule of debugging is to only make one change at a time. We have measurements from the half PRC, so we could have made a direct comparison with those to see how things have changed. If we jump the gun we're going to end up wasting more time when we have to back-track.
Also, we never talked about moving PR2 to adjust optical path length, although I can understand why we would think that should be done. My calculations were all done assuming the free-space separation between PRM/PR2 and PR2/PR3 were unchanged. It's possible changing the position is better, but again, it's more work and it changes multiple things at one. I can redo my calculations for this new scenario, but we need to update our drawings with this new configuration. Please note precisely where PR2 has moved to.
We should have just flipped PR2 and that's it. Then we could have run the exact same measurements we had previously. Only then, once we understood this new simple cavity, should we have done further adjustments.
Half-PRC at this time already have two changes from the previous half-PRC; PR2 replaced/flipped and different TM before BS.
PRMI has only one change from the previous PRMI; PR2 replaced/flipped.
This is why I wanted to try PRMI first. But we now recognized that MI alignment (including REFL and AS alignment) is tough without using the arms, I agree that we should try half-PRC first.
I don't exactly know what the situation in the Jamie's calculation, but to make the optical path length the same before and after flipping, PR2 holder have to move about n*t, where n is the substrate refractive index and t is the thickness of the mirror, towards PRM/PR3.
The first rule of debugging is to only make one change at a time.
Also, we never talked about moving PR2 to adjust optical path length,