I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit.
In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands.
The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.
This implies a IMC round trip length of 27.090800m +- 2um.
Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency.
Last night I measured the modulation depth of the MC incident beam.
The beam is taken from one of the PO beam at the wedge plate before the IMC.
After removing the knife edge to dump this beam, the beam is sent to the west side
of the PSL table and put into the OSA cavity.
[The beam dump was returned after the measurement.]
I had some confusion and after all I use the OSA labeled as AS OSA rather than the one on the PSL table.
[The AS OSA was returned to the AP table.]
The transmission was detected by PDA255 and filtered by ITHACO 1201 preamp with G=10, no HPF, 30kHz LPF.
It was confirmed that the peak amplitudes are not reduced by the LPF filter. The resulting time series
was recorded by an oscilloscope.
Three measurements have been taken. The 11MHz peaks are offset by the carrier peak. They appropriately
removed. The ratio of the sideband and carrier peaks is converted to the modulation depth using the following formula.
P_sb / P_ca = [J1(m)/J0(m)]^2
The modulation depth for the 11MHz: 0.190 +/- 0.003
The modulation depth for the 55MHz: 0.2564 +/- 0.0003
The three scans showed very similar numbers. That's why the statistical error is such small.
I don't think the systematic error is not such good.
This number is much different form the previous meaurement by Mirko.
http://nodus.ligo.caltech.edu:8080/40m/5519 m=0.14 (11MHz) & 0.17 (55MHz)
but the measured voltages and the modulatio depths are inconsistent.
http://nodus.ligo.caltech.edu:8080/40m/5462 m=0.17 (11MHz) & 0.19 (55MHz)
Probably the modulation depths should be checked by the IMC again.
However, it is certain that the 55MHz modulation exists, and even larger than the 11MHz one.
The next is to confirm that the modulation frequency is matched with the IMC FSR.
It is to make sure that the modulation is transmitted to the main IFO without attenuation.
I measured the modulation depth at 11 MHz andf 55 MHz using an optical beat + PLL setup. Both numbers are ~0.2 rad, which is consistent with previous numbers. More careful analysis forthcoming, but I think this supports my claim that the optical gain for the PDH locking loops should not have decreased.
I decided to analyze the data I took in December more carefully to see if there are any clues about the weird LSC sensing.
Attachment #1 shows the measurement setup.
Attachment #2 shows the measured spectrum with the PSL and EX laser frequency offset locked via PLL.
Fitting the measured sideband powers (up to n=7, taking the average of the measured upper and lower sideband powers to compute a least squares fit if both are measured, else just that of the one sideband measured) agains those expected from a model, I get the following best fit parameters:
To be explicit, the residual at each datapoint was calculated as
The numbers compare favourably with what Koji reported I think - the modulation depths are slightly increased, consistent with the RF power out of the RF box being slightly increased after I removed various attenuators etc. Note the large uncertainty on the relative phase between the two modulations - I think this is because there are relatively few sidebands (one example is n=3) which has a functional dependence that informs on phi - most of the others do not directly give us any information about this parameter (since we are just measuring powers, not the actual phase of the electric field).
Attachment #3 shows a plot of the measured modulation profile, along with the expected heights plugging the best fit parameters into the model. The size of the datapoint markers is illustrative only - the dependence on the model parameters is complicated and the full covariance would need to be taken into account to put error bars on those markers, which I didn't do.
Attachment #4 shows a time domain measurement of the relative phasing between the 11 MHz and 55 MHz signals at the EOM drive outputs on the RF source box. I fit a model there and get a value for the relative phase that is totally inconsistent from what I get with this fit.
Last night I worked at the PSL table for the modulation depth measurement for an aLIGO EOM. Let me know if the IFO behavior is unusual.
What I did was:
aLIGO EOM test: Setup
The new matching circuit was tested.
f_nominal f_actual response required mod. drivng power
[MHz] [MHz] [mrad/V] [rad] needed [dBm]
9.1 9.1 55 0.22 => 22
118.3 118.2 16 0.01 => 6
45.5 45.4 45 0.28 => 25
24.1 N/A 2.1 0.014 => 27
- 9.1MHz and 118.3MHz: They are just fine.
- 24.1MHz: Definitely better (>x3) than the previous trial to combine 118MHz & 24MHz.
We got about the same modulation with the 50Ohm terminated bare crystal (for the port1).
So, this is sort of the best we can do for the 24.1MHz with the current approach.
The driving power of 27dBm is required at 24.1MHz
- About the 45MHz
- The driving power of 27dBm is required at 24.1MHz
- The maximum driving power with the AM stabilized driver is 23dBm, nominally to say.
- I wonder how we can reduce resistance (and capacitance) of the 45MHz further...?
- I also wonder if the IFO can be locked with reduced modulation (0.28 rad->0.2 rad)
- Can the driver max power be boosted a bit? (i.e. adding an attenuator in the RF power detection path)
The 3IFO EOM was formerly tuned as the H2 EOM, so the resonant frequencies are different from the nominal aLIGO ones.
PORT1: 8.628MHz / 101 +/- 6 mrad_pk/V_pk
PORT2: 24.082MHz / 41.2 +/- 0.7 mrad_pk/V_pk
PORT3: 43.332MHz / 62.2 +/- 4 mrad_pk/V_pk
9MHz modulation is about x2.4 better than the one installed at LHO.
24MHz modulation is about x14 better. (This is OK as the new 24MHz is not configured to be resonant.)
45MHz modulation is about x1.4 better.
Caution: Because of this work and my negligence, the RF output of the main Marconi for the IFO modulation is probably off. The amplifier (freq gen. box) was turned on. Therefore, we need to turn the Marconi on for the IFO locking.
I worked on my EOM m easurement using the beat setup. As there was the aux injection electronics, I performed my measurement having tried not to disturb the aux setup. The aux Marconi, the splitted PD output, and an open channel of the oscilloscope were used for my purpose. I have brought the RF spectrum analyzer from the control room. I think I have restored all the electronics back as before. I have re-aligned the beat setup after the EOM removed. Note that the aux NPRO, which had been on, was turned off to save the remaining life of the laser diode.
The marconi RF output was turned on and thus the RF generator condition was restored to the nominal state on Friday 11th.
I used the Beat Mouth to make a quick measurement of the PMC and EX modulation depths. They are, respectively, 60mrad and 90mrad. See Attachments #1 and #2 for spectra from the beat photodiode outputs, monitored using the Agilent analyzer, 16 averages, IF bandwidth set to resolve peaks offset from the main beat frequency peak by 33.5MHz for the PMC and by ~230kHz for the EX green PDH.
For this work, I had to re-align the IFO so as to lock the arms to IR. c1susaux was unresponsive and had to be power-cycled. As mentioned in the earlier elog, to avoid saturating the Fiber Coupled beat PDs, I placed a ND=0.5 filter in the fiber collimator path, such that the coupled power was ~1mW, which is well inside the safe regime.
For the EX modulation depth, I could have gotten multiple estimates of the modulation depth using the higher order products that are visible in the spectrum, but I didn't.
EDITED by YM on 22:11 June 27, 2022 to correct for a factor of two in the modulation index
Since we have measured optical gain in MICH to be an order of magnitude less compared with Yehonathan's FINESSE model (40m/16923), we measured the power at AS55 RF PD, and measured the modulation depths using Yarm cavity scan.
We found that 50/50 beam splitter which splits AS55 path into RF PD and RF QPD was not included in the FINESSE model. Measured modulation index were as follows:
TEM00 peak height: 0.6226 +/- 0.0237
RF11 peak height: 0.0067 +/- 0.0007
RF55 peak height: 0.0081 +/- 0.0014
RF11 modulation index: 0.208 +/- 0.012
RF55 modulation index: 0.229 +/- 0.020
RF11 modulation index: 0.104 +/- 0.006
RF55 modulation index: 0.114 +/- 0.010
Here, modulation depth m is defined in E=E_0*exp(i*(w*t+m*sin(w_m*t))), and m m/2 equals to square of the intensity ratio between sidebands and TEM00.
Power measurement at AS55 RF PD:
- ITMY and ITMX single bounce reflection was measured to be 50-60 uW at the front of AS55 RFPD.
- In the FINESSE model, it was expected to be ~110 uW with 0.8 W input to PRM (0.8 W * 5%(PRM) * 50%(BS) * 50%(BS) * 10%(SRM) * 10%(AS2) gives 100 uW)
- In AP table, AS55 beam was split into two paths with 50/50 beam splitter, one for AS55 RF PD and one for AS WFS and AS110. This will be included in the FINESSE model.
Modulation depth measurement using Yarm cavity scan:
- Aligned Yarm using ASS, and unlocked Yarm to get the 2sec scan data of C1:LSC-TRY_OUT_DQ, C1:LSC-POY11_I_ERR_DQ, C1:LSC-AS55_I_ERR_DQ.
- TRY data was used to get TEM00 peak heights
- POY11/AS55 data was used to find RF11/RF55 sideband peaks, and height was measured at TRY (see attached).
- If we define m to be E=E_0*exp(i*(w*t+m*sin(w_m*t))), the amplitude of TEM00 I_00 is proportional to J_0(m) and the amplitude of upper/lower sideband I_f1 is proportional to J_1(m), where J_n(m) is the bessel function of the first kind.
- m can be calculated using 2*sqrt(I_f1 / I_00).
- Results were shown above. Error is calculated from the standard deviation of multiple measurements with multiple peaks,
- The code for doing this lives in https://git.ligo.org/40m/measurements/-/blob/main/LSC/YARM/modulationIndex.ipynb
- Power at AS55 account for the factor of 2, In the FINESSE model, modulation index of 0.3 was used (could be m=0.3/2 or m=0.3; needs check). These combined can explain a factor of 3 at least (or 6).
- Gautam's measurement in Jan 2021 (40m/15769) gives almost double modulation index, but I'm not sure what is the definition Gautam used. It agrees with Gautam's measurement in Jan 2021.
The main IFO modulation frequency was adjusted to match with the FSR of the IMC.
The new frequency is 11.066128 MHz. This corresponds to the IMC round-trip length of 27.0910 m
This has been done by looking at the peak at 25.845MHz (5* fmod - 29.5MHz) in the MC REFL PD mon.
We found Mon7 in control room dead today afternoon. It's front power on green light is not lighting up. All other monitors are working as normal.
This monitor was used for looking at IMC camera analog feed. It is one of the most important monitors for us, so we should replace it with a different monitor.
Yehonathan and Paco disconnected the monitor and brought it down. We put it under the back table if anyone wants to fix it. Paco has ordered a BNC to VGA/HDMI converter to put in any normal monitor up there. It will happen this Wednesday. Meanwhile, I have changed the MON4 assignment from POP to Quad2 to be used for IMC.
We replaced the Mon 7 with an LCD monitor from back bench. It is fed the analog signal from BNC converted into VGS with a converter box that Paco bought. We can replace this monitor with another monitor if it is required on the back bench. For now, we definitely need a monitor to show IMC camera's up there.
Nothing like a good ol' Bootfest to get back into the swing of things after vacation....
It was a regular bootfest, keying crates and running everyone's startup.cmd . There wasn't any RFM funny business which we had been dealing with a lot earlier in December (maybe Kiwamu took care of that part of things last night).
After finishing the bootfest, I tried to re-enable the watchdogs. I noticed that the optics weren't damping at all (not that any of them were swinging crazily, they just weren't damped like regular). This was traced to the OSEM sensor inputs and outputs being disabled on all of the suspensions' screens. I suspect that no burt-restoring happened after c1dcuepics was powercycled yesterday.
All of the optics are now happy as clams.
The moral of the story here is that none of the suspensions are overwhelmingly awesome, but most of them will be fine if we leave them as-is.
pit yaw pos side butt
UL 0.438 1.019 1.050 -0.059 0.717
UR 0.828 -0.981 1.128 -0.215 -0.956
LR -1.172 -1.201 0.950 -0.275 1.241
LL -1.562 0.799 0.872 -0.120 -1.087
SD -0.579 -0.847 2.539 1.000 -0.170
pit yaw pos side butt
UL 1.157 0.185 1.188 -0.109 0.922
UR 0.020 -1.815 0.745 -0.051 -0.970
LR -1.980 -0.090 0.812 -0.024 1.158
LL -0.843 1.910 1.255 -0.082 -0.949
SD -0.958 1.080 1.859 1.000 0.325
pit yaw pos side butt
UL 0.338 0.476 1.609 0.316 1.046
UR 0.274 -1.524 1.796 -0.069 -1.180
LR -1.726 -1.565 0.391 -0.100 0.938
LL -1.662 0.435 0.204 0.286 -0.836
SD 0.996 -2.629 -0.999 1.000 -0.111
pit yaw pos side butt
UL 1.123 0.456 1.812 0.231 0.936
UR -0.198 -1.489 0.492 -0.096 -1.098
LR -2.000 0.055 0.188 -0.052 0.764
LL -0.679 2.000 1.508 0.275 -1.201
SD 0.180 -0.591 3.355 1.000 0.200
pit yaw pos side butt
UL 1.575 0.697 0.230 0.294 1.045
UR 0.163 -1.303 1.829 -0.133 -0.958
LR -1.837 -0.308 1.770 -0.171 0.944
LL -0.425 1.692 0.171 0.257 -1.053
SD 0.769 0.345 -3.380 1.000 0.058
pit yaw pos side butt
UL 0.597 1.553 2.000 -0.469 1.229
UR 1.304 -0.447 0.383 -0.043 -0.734
LR -0.696 -1.048 -0.277 0.109 0.687
LL -1.403 0.952 1.340 -0.317 -1.350
SD 0.518 -1.125 -1.161 1.000 0.394
pit yaw pos side butt
UL 0.831 1.039 1.153 -0.140 1.065
UR 1.071 -0.961 1.104 -0.057 -1.061
LR -0.929 -0.946 0.847 -0.035 0.837
LL -1.169 1.054 0.896 -0.118 -1.037
SD 0.193 -0.033 1.797 1.000 0.045
"They (shellfish) shall be an abomination to you; you shall not eat their flesh, but you shall regard their carcasses as an abomination." (Leviticus 11:11)
I've pushed an MCMC simulation to the A+ BHD repo (filename MCMC_TFs.ipynb). The idea is to show how random offsets around ideal IFO change the noise couplings of different DOFs to readout.
At each step of the simulation:
1. Random offsets for the different DOFs are generated from a normal distribution. The RMSs are taken from experimental data and some guesses and can be changed later. The laser frequency is tuned to match the CARM offset.
These are the current RMS detunings I use:
2. A transfer function is computed for the noisy DOFs.
3. Projected noise is calculated.
These are the noise level for the DOFs:
The attachments show the projected noise levels for the noisy DOFs. Each curve is a different instance of random offsets. The ideal case - "zero offsets" is also shown.
OMC Comm and OMC diff refer to the common and differential length change of the OMCs.
that's great. I think we would like to figure out how to present this so that its clear what the distribution of TFs is. Maybe we can plot the most likely curve as well as a shaded region indicating the 5% and 95% values?
and then we add the loops
I fixed some stuff in the MCMC simulation:
1. Results are now plotted as shades from minimum to maximum. I tried making the shade the STD around a mean but it doesn't look good on a log scale when the STD is bigger than the mean.
2. Added comparison with aLigo. The OMCL diff and comm motions in A+ are both compared to the single OMCL DOF of aLigo.
3. I fixed a serious error in the code that produced incorrect results.
4. Imbalances in the IFO such as differential arm loss are generated randomly at the beginning and stay fixed for the rest of the simulation instead of being treated as an offset.
5. The simulation now runs with maxtem=2. That is, TEM modes up to 2nd order are considered.
The results are attached.
I re-plotted the MCMC results as semi-transparent lines so that probable lines stick out.
This also reveals what is behind the extreme sparsity in the aLIGO simulation results (In the previous post).
There seem to be some bi-stability/phase transition/whatever in the aLIGO simulation. The aLIGO transfer functions are very sensitive to one or more of the DOFs. Not sure which yet.
Turns out what was causing the instability in the aLIGO plots were the lock commands which I forgot to remove before running the simulation. Removing these also made the simulation much faster.
Other than that I improved other stuff in the simulations:
Still need to do:
Feel free to add to the todo list.
Pushed another update to MCMC simulation. This includes:
The DOFs<->RFPD associations I use are:
However, one thing that bothers me is that for some reason ~ 15 out of 160 aLigo simulations are discarded while none for A+. It can also be seen that the A+ simulations are more spread-out which might be related.
The new simulation results are attached.
I found this H1 alog entry by Izumi confirming that the calibrated channels CAL-CS_* need the same dewhitening filter.
This encouraged me to download the PRCL and MICH data and using Jon's example notebook. I incorporated these noise spectra into the MCMC simulation. The most recent results are attached.
I am still missing:
Also, now the MCMC repeats a simulation if it doesn't pass the RF PDs test so the number of valid simulations stays the same. I'm still not sure about why the A+ simulations are much more robust to these tests than aLigo simulations.
I have rebuilt the MCMC simulation in an OOP fashion and incorporated Lance/Pytickle functionality into it. The usage of the MCMC now is much less messy, hopefully.
I made an example that calculates the closed-loop noise-coupling from SRCL sensing and displacement to DARM in A+. I used the control filters that Kevin defined in his controls example.
The resulting noise budget is in attachment 1. The code is in the 40m/bhd git.
I also investigated why aLIGO simulations behave so different than the A+ simulation (See few previous elogs in this thread). That is why aLIGO results are much less variable, and the simulations in aLIGO barely pass the validity checks, while A+ simulations almost always pass.
The way I check for the validity of a kat model is by scanning all the DOFs and checking that the corresponding sensing RFPDs demodulated signals cross zero. Attachment 2 shows these scanning for 3 such RFPDS for 3 cases:
A+ model with maxtem = 2
ALigo model with maxtem = 2
ALigo model with maxtem = 'off'
It seems like the scanning curves for A+ and ALigo with no HOMs are well behaved and look like normal PDH signals, while the ALigo with maxtem = 2 curves look funky. I believe that the aLIGO+HOMS curves indicate that the IFO is not really in a good locking point. All the IFO lockings were done by using the locking methods straight out of the PyKat package.
Cool. Can you give us Bode plots of the open loop gain for each of the 5 length control loops?
I spent a few hours monkeying around with the control filters. They are totally made up and also it's my first time trying to design control filters.
The OLTFs of the different length controls are shown in attachment 1.
The open-loop couplings of the DOFS to DARM are shown in attachment 2.
Note that in Lance/Pytickle the convention is that CLTFs are 1/(1 - G). Where G is the OLTF.
I dived into the alog to make the OLTFs in the MC_controls example more realistic. I was mainly inspired by these entries:
and Evan's and Dennis's Theses.
Attachment 1 shows the new OLTFs. I tried to make them go like 1/f around the UGF and fall as quickly as possible at higher frequencies. I didn't do more advanced stability checks.
I also noticed that imbalances and detunings in the MC simulation can change the plants significantly. Especially DARM, CARM, and sometimes PRCL. I added the option to fix some OLTFs throughout the simulation. At every iteration, the simulation computes the required control filter to fix the selected OLTFs such that it will match the OLTFs in the undetuned and balanced IFO.
Link to OMC_Lab ELOG 308
We received 10x 16bit ADC adapter boards from Todd. S2100687~S2100696
The number of soldered resistors seems to be less than that on the schematics. They are related to duotone, so check if it's OK upon use.
Work done today:
Testing of functionality:
Much testing remains to be done, but I defer further testing till Monday - the main functionality to be verified in the short run is the whitening gain stepping. The strain-relief of cables and general cleanup will be undertaken by Chub. Current state of affairs is in Attachment #3, leaves much to be desired in terms of cleanliness.
I will also setup the autoburt for the new machine on Monday. We will also need to add some channels to C0EDCU.ini if we want to trend them over some years (e.g. RF signal powers for monitoring ERA-5 health).
* c1lsc FE was rebooted using the usual script, and everything seems to be healthy in CDS-land again, see Attachment #4.
Similar to what Jenne did the other night, I kept the PRFPMI arm DoFs locked on ALS, in hopes to check out the RF error signals.
I was able to stably sit at nominally zero offset in both CARM and DARM, tens of minutes at a time, and the PRMI could reacquire without a fuss. Arm powers would rest between 10 and 20, intermittently exhibiting the "buzzing" behavior that Jenne mentioned when passing through resonance. 100pm CARM offset means arm powers of around 10, so since our ALS RMS is on this order, this seems ok. I saw TRX get as high as 212 counts, which is just about the same that I've simulated as the maximum power in our IFO.
To get this stable, I turned off all boosts on MICH and PRCL except PRCL FM6, and added matrix elements of 0.25 for TRX and TRY in the trigger line for the PRMI DoFs. The logic for this is that if the arm powers are higher than 1, power recycling is happening, so we want to keep things above the trigger down value of 0.5, even if POP22 momentarily drops.
I also played around a bit with DARM offsets. We know from experience that the ALS IR resonance finding is not super precise, and thus zero in the CARM FM is not zero CARM offset when on ALS. The same obviously holds for DARM, so I moved the DARM offset around, and could see the relative strengths of flashes change between the arms as expected.
I've written down some GPS times that I'm going to go back and look at, to try to back out some information about our error signals.
Lastly, there may be something undesirable happening with the TRX QPD; during some buzzing, the signal would fluctuate into negative values and did not resemble the TRY signal as it nominally would. Perhaps the whitening filters are acting up...
Attachment #1: Result of AM sweeps with EX laser crystal at nominal operating temperature ~ 31.75 C.
Attachment #2: Tarball of data for Attachment #1.
Attachment #3: Result of AM sweeps with EX laser crystal at higher operating temperature ~ 40.95 C.
Attachment #4: Tarball of data for Attachment #2.
More BHD SUS screens added to sitemap (Attachment 1)
I spent most of today fighting various CDS errors.
Let's see how stable this configuration is. Onto some locking now...
Stability was short-lived it seems. When I came in this morning, all models on c1lsc were dead already, and now c1sus is also dead (Attachment #1). Moreover, MC1 shadow sensors failed for a brief period again this afternoon (Attachment #2). I'm going to wait for some CDS experts to take a look at this since any fix I effect seems to be short-lived. For the MC1 shadow sensors, I wonder if the Trillium box (and associated Sorensen) failure somehow damaged the MC1 shadow sensor/coil driver electronics.
I've left the c1lsc frontend shutdown for now, to see if c1sus and c1ioo can survive without any problems overnight. In parallel, we are going to try and debug the MC1 OSEM Sensor problem - the idea will be to disable the bias voltage to the OSEM LEDs, and see if the readback channels still go below zero, this would be a clear indication that the problem is in the readback transimpedance stage and not the LED. Per the schematic, this can be done by simply disconnecting the two D-sub connectors going to the vacuum flange (this is the configuration in which we usually use the sat box tester kit for example). Attachment #1 shows the current setup at the PD readout board end. The dark DC count (i.e. with the OSEM LEDs off) is ~150 cts, while the nominal level is ~1000 cts, so perhaps this is already indicative of something being broken but let's observe overnight.
Overnight, all models on c1sus and c1ioo seem to have had no stability issues, supporting the hypothesis that timing issues stem from c1lsc. Moreover, the MC1 shadow sensor readouts showed no negative values over a ~12hour period. I think we should just observe this for another day, in any case I don't think there is any urgent IFO related activity scheduled.
I am starting the c1x04 model (IOP) on c1lsc to see how it behaves overnight.
Well, there was apparently an immediate reaction - all the models on c1sus and c1ioo reported an ADC timeout and crashed. I'm going to reboot them and still have c1x04 IOP running, to see what happens.
[97544.431561] c1pem: ADC TIMEOUT 3 8703 63 8767
[97544.431574] c1mcs: ADC TIMEOUT 1 8703 63 8767
[97544.431576] c1sus: ADC TIMEOUT 1 8703 63 8767
[97544.454746] c1rfm: ADC TIMEOUT 0 9033 9 8841
2 more earthquakes in Chile: a M6.4 and a M7.8.
We got them about 15 minutes ago (according to the BLRMS on the wall), but when I go tin, the MC was already locked, and engaging the LSC immediately got me PRMI lock (since that's the alignment state that the IFO was left in).
Some more measurements of the PZT resonances (now zoomed in!) I'm adjusting parameters on our model to try and fit to it by hand a bit, definitely still needs improvements but not bad for a 2-pole 2-zero fit for now. I don't have a way to get coherence data from the moku yet but I've got a variety of measurements and will hopefully use the standard deviation to try and find a good error prediction...
Prep for this work:
I was trying to get some pics of the optics as a zeroth-level reference for the pre-vent loss with the single arms locked, but since our SL7 upgrade, the sensoray won't work anymore . I'll try fixing this during the daytime.
In the end I decided to access the available spare DAC channels via the C1ASS model - for this purpose, I added a namespace block "TEST" in the C1ASS simulink model, which is a SISO block. Inside is just a single CDS filter module. My idea is to use the EXC of this filter module to inject excitations for measuring various couplings. Rather than have a simple testpoint, we also have the option of adding in some filter shapes in the filter module which could possibly allow a more direct read-off of some coupling TF. Recompiling the model went smooth - there was a crash earlier in the day which required me to hard-reboot c1lsc (and also restart all models on c1sus and c1ioo but no reboots necessary for those machines).
Note that to get the newly added channels to show up in the channel lists in DTT/AWGGUI etc, you need to ssh into fb1 and restart the daqd processes via sudo systemctl restart daqd_*. If I remember right, it used to be enough to do telnet fb 8088 followed by shutdown. This is no longer sufficient.
It took me a while to get the DRMI locking going again. The model restarts earlier in the evening had changed a bunch of EPICS channel settings (and out config scripts don't catch all of these settings). In particular, I forgot to re-enable the x3 digital gain for the ITMs, BS and SRM (necessitated by removing an analog x3 gain on the de-whitening boards). I was hesitant to spend time re-adjusting all damping / oplev loop gains because if we change the series resistor on the coil driver board, we will have to do this again. I also didn't want this arbitrary FM to be enabled in the SDF safe.snap. But maybe it's worth doing it anyways - if nothing it'll be good practise.
Once I hunted down all the setting diffs and tweaked alignment, the DRMI locks were pretty robust.
I had hoped to make some of these TF measurements tonight. But I realized I needed to look up a bunch of stuff in manuals/datasheets, and think about these measurements a little. I wasn't sure if the DW/AI board could drive a signal over 40m of BNC cabling so I added an SR560 (DC coupled, gain=1, low noise mode, 50ohm output used) to buffer the output. The Marconi's external modulation input is high impedance (100k) but for the AOM driver we want 50ohm. For the Marconi, the external input accepts 1Vrms max, while for the AOM driver, we want to drive a signal between 0V and 1V at most.
The general measurement setup is schematically shown in Fig 1. Questions to address:
Am I missing something?
We want to know that we can lock the interferometer with the ALS beat note being generated by beating IR pickoffs (rather than the vertex green transmission). The hope is also to make the ALS system good enough that we can transition the CARM offset directly to 0 after the DRMI is locked with arms held off resonance.
Attachment #1: Shows the layout. The realized MM is ~36 %. c.f. the 85% predicted by a la mode. It is difficult to optimize much more given the tight layout, and the fact that these fast lenses require the beam to be well centered on them. They are reasonably well aligned, but I don't want to futz around with the pointing into the doubling crystal. Consequently, I don't have much control over the pointing.
Attachment #2: Shows pictures of the fiber tips at both ends before/after cleaning. The tips are now much cleaner.
The BeatMouth NF1611 DC monitor reports ~580 mV with only the EY light incident on it. This corresponds to ~60 uW of light making it to the photodiode, which is only 25% of what we send in. This is commensurate with the BS loss + mating sleeve losses.
To find the beat between PSL and EY beams, I had to change the temperature control MEDM slider for the EY laser to -8355 cts (it was 225 cts). Need to check where this lies in the mode-hop scan by actually looking at the X-tal temperature on the front panel of the EY NPRO controller - we want to be at ~39.3 C on the EY X-tal, given the PSL X-tal temp of ~30.61 C. Just checked it, front panel reports 39.2C, so I think we're good.
EY enclosure was closed up and ETMY Oplev was re-enabled after my work. Some cleanup/stray beam dumping remains to be done, I will enlist Chub's help on Monday.
As shown in the Attachments, it seems like IMC DAC and coil driver noise is the dominant noise source above 30Hz. If we assume the region around the bounce peak is real motion of the stack (to be confirmed with accelerometer data soon), this NB is starting to add up. Much checking to be done, and I'd also like to get a cleaner measurement of coil driver and DAC noise for all 3 optics, as there seems to be a factor of ~5 disagreement between the MC3 coil driver noise measurement and my previous foray into this subject. The measurement needs to be refined a little, but I think the conclusion holds.
Since I sunk some time into it already, the motivation behind this work is just to try and make the IMC noise budget add up. It is not directly related to lowering the IR ALS noise, but if it is true that we are dominated by coil driver noise, we may want to consider modifying the MC coil driver electronics along with the ITM and ETMs.