Attachment #1 shows the measured PRCL loop shape. The blue line is meant to be the "expected" loop shape. While the measured loop shape tracks the expectation down to ~100 Hz, I cannot explain the shape below it. I am also not sure what to make of the fact that there is high coherence down to 10 Hz fron IN2 to IN1, but no coherence between EXC/IN2. I confirmed that the low-frequency boost filters were ON during the measurement. I don't understand how a pendulum TF + the digital filters we used can account for the shape below 100Hz.

gautam 11pm: After discussing with Koji, I conclude that the low frequency loop shape is consistent with the excitation amplitude being insufficient below 100 Hz. Coherence is good between In1/In2 because they are the same signal effectively - what we need is coherence between In1 and EXC, which isn't plotted. It is still strange that Coherence between In2/EXC is ZERO....

I have modified the code for frequency scanning and have made it completely command line enabled. The code is written in python. It is saved in the name "frequency_scanning_argparse.py". I have uploaded it to the Mode-Spectroscopy Github repository.

Inorder to use this code there are two ways.

1. We can mention the ' frequency' on which marconi need to work. Then it will change the marconi frequency to that perticular value.

eg: Type in the terminal as follows for changing the marconi frequency to 59 Mhz.

python frequency_scanning_argparse.py 59e6

2. Inorder to give a scan to the marconi frequency, provide the 'start frequency', 'end frequency' and the 'number of points' in between. This will be more conveniant when we want to run the scan in different ranges.

eg: Type in the terminal as follows for a start frequency of 59 Mhz, end frequency of 62MHz and number of points in between equal to 1000.

python frequency_scanning_argparse.py 59e6 62e6 1000

In both cases the code will show you the frequency of the marconi before we run this code and it will change the marconi frequency to the desired frequency.

I want to use the Fiber Coupled laser from the PDFR system to characterize the response of the fiber coupled PDs we use in the BeatMouth. The documentation is pretty good: for a first test, I did the following in this order:

• Removed the input fiber to the 1x16 splitter located in the rack near the OMC chamber.
• Connected aforementioned fiber to a collimator.
• Aligned the output of the collimator onto a razor beam dump.
• Turned on the laser controller - it came on with a TEC temperature of 22.5 C and I_diode 0 mA, and the "output shorted" LED was ON (red).
• Turned up the diode current to 80 mA, since the "threshold current" is stated as 75 mA in the manual. In fact, I could see a beam using an IR card at 30 mA already.
• At 80mA, I measured 3.5 mW of output power using the Ophir.

Seems like stuff is working as expected. I don't know what the correct setpoint for the TEC is, but once that is figured out, the 1x16 splitter should give me 250 uW from each output for 4mW input. This is well below any damage threshold of the Menlo PDs. Then the plan is to modulate the intensity of the diode laser using the Agilent, and measure the optoelectronic response of the PD in the usual way. I don't know if we have a Fiber coupled Reference Photodiode we can use in the way we use the NF1611 in the Jenne laser setup. If not, the main systematic measurement error will come from the power measurement using a Fiber Power Meter.

The unit mentioned in the x-axis was wrong. So I have remade the graphs. The point where frequency equals to zero is actually the frequency corresponding to the laser, which is in the range of 10¹⁴ Hz and it caliberated as zero.

finesse1.pdffinesse2.pdf

Summary:

Neither of the Menlo FPD310 fiber coupled PDs in the beat mouth have an optoelectronic response (V/W) as advertised. This possibly indicates a damaged RF amplification stage inside the PD.

Motivation:

I have never been able to make the numbers work out for the amount of DC light I put on these PDs, and how much RF beat power I get out. Today, I decided to measure the PD response directly.

Details:

In the end, I decided that slightly modifying the Jenner laser setup was the way to go, instead of futzing around with the PDFR laser. These PDs have a switchable gain setting - for this measurement, both were set to the lower gain such that the expected optoelectronic response is 409 V/W.

[Attachment #1] - Sketch of the experimental setup. 

[Attachment #2] - Measured TF responses, the RF modulation was -20dBm for all curves. I varied the diode laser DC current a little to ensure I recovered identical transfer functions. Assumptions used in making these plots:

1. NF1611 and FPD310 have equal amounts of power incident on them.
2. The NF1611 transimpedance is 700V/A.

[Attachment #3] - Tarball of data + script used to make Attachment #2.

Conclusions:

• The FPD310 does not have a DC monitor port. 
  • So the dominant uncertainty in these plots is that I don't know how much power was incident on the PD under test.
  • The NF1611 DC power level could be measured though, and seemed to scale with DC pump current linearly (I had only 3 datapoints though so this doesn't mean much).
• Neither PD has transimpedance gain as per the specs.
  • The X PD shows levels ~x10 lower than expected.
  • The Y PD shows levels ~x3 lower than expected.
• I will repeat the measurement tomorrow by eliminating some un-necessary patch fiber cables, and also calibrating out the cable delays.
  • The setup shown in Attachment #1 was used because I didn't want to open up the BeatMouth.
  • But I can pipe the port of the BS not going to the FPD310 directly to the collimator, and that should reduce the systematic uncertainty w.r.t. power distribution between FPD310 and NF1611.

It's true.

I went through the wiring of the c1auxex crate today to disentangle the pin assignments. The full detail can be found in attachment #1, #2 has less detail but is more eye candy. The red flagged channels are now marked for removal at the next opportunity. This will free up DAQ channels as follows:

This should be enough for temperature sensing, NPRO diagnostics, and even eventual remote PDH control with new servo boxes.

don't use IN_1/IN_2: recall pizza meeting from a few weeks back: use IN1/EXC + Al-Gebra

its painful, but you and I should probably take these out, bypass the switches and use them with fixed gain; the 'Reed Relay' attenuators are not a good part for this app.

The historical problem is that they tend to self oscillate with full gain because they had 2 MAX4106 in series which couple to each other in the bad way --- need to remove one of them and set the gain of the other one to 10.

Do we really have 2 free ADC channels at EX now? I was under the impression we had ZERO free, which is why we wanted to put a new ADC unit in. I think in the wiring diagram, the Vacuum gauge monitor channel, Seis Can Temp Sensor monitor, and Seis Can Heater channels are missing. It would also be good to have, in the wiring diagram, a mapping of which signals go to which I/O ports (Dsub, front panel BNC etc) on the 4U(?) box housing all the Acromags, this would be helpful in future debugging sessions.

[jon, gautam]

Jon is doing some characterization of the AUX laser setup for which he wanted only the prompt retroreflection from the SRM on the AS table, so the PSL shutter is closed, and both ITMs and ETMs are misaligned. The prompt reflection from the SRM was getting clipped on something in vacuum - the ingoing beam looked pretty clean, but the reflection was totally clipped, as I think Johannes aligned the input beam with the SRM misaligned. So the input steering of the AUX laser beam into the vacuum, and also the steering onto AS110, were touched... Also, there were all manner of stray, undumped beams from the fiber on the AS table Jon will post photos.

Before we began this work, we found that c1susaux was dead so we rebooted it.

I think this is because /cvs/cds is getting too big. lsblk reveals:

I believe one of sdc or sdd is connected via SATA while the other is an external USB drive. Maybe we have to get bigger backup disks, but this may be a huge pain to setup as it will involve taking chiara down. Actually, now that I check the backup log, seems like backup is executing successfully - not sure if this is due to my unelogged mounting of sdc (using sudo mount /dev/sdc1 /media/40mBackup) last week, or if this is some LDAS backup. But in any case, seems undesirable that sdb1 is larger than sdc1 or sdd1.

We have 6 of these boards now in cabinet E7

Bad wording, sorry. Should have been channels in excess of ETMX controls. I'll add the others to the list as well.

Updated channel list and wiring diagram attached. Labels are 'F' for 'Front' and 'R' for - you guessed it - 'Rear', the number identifies the slot panel the breakout is attached to.

I finally analyzed the sensing measurement I ran on Tuesday evening. Sensing responses for the DRMI DOFs seems consistent with what I measured in October 2017, although the relative phasing of the DoFs in the sensing PDs has changed significantly. For what it's worth, my Finesse simulation is here. 

All optics have been re-aligned. Jon/Johannes will elog about the work today.

[Jon, Gautam, Johannes]

Jon spent some time trying to align the AUX beam to the SRC today, I got to the game kind of late so maybe others can add more detail.

The AUX beam that is reflected by the SRM looks terribly misshapen - it is quite elongated in vertical direction. Unfortunately I didn't snap a picture of it - anybody? It seemed at first as if this could be clipping - but after confirming the alignment of the AUX beam with the PSL output beam with aligned SRM, a slow dither of the SRM just moved the ugly pattern on the AS camera with no change to its shape - so clipping is unlikely. I'm now thinking that this is just the output beam of the fiber coupler after propagating ~15 meters to the SRM and back - even though this aspheric lens triplet coupler is supposed to be super-duper. I found that if I loosen the fiber slightly and pull it back just a bit at least the spot on the AS camera becomes nice and round - so maybe the fiber just doesn't sit well in this collimator? Not sure why that would be. I checked the fiber tip with the microscope, and while there was some gunk present, the central region and the core were clear (still cleaned using the fiber cleaning kit, which got rid of the debris). Either way, before switching to a different collimator I think we should give the Guoy phase measurement a shot - after all there was plenty of RF signal present on both AS110 and the PDA10CF placed at the YEND.

Looking for rogue beams on the AS table, I started placing some beam dumps. There was one particularly strong source of stray beams - a lens that was labeled with KPX094AR.33_F100. It became apparent after alignment efforts to the IFO had moved the AUX beam signifcantly off-center on this lens. According to the label it should have an AR coating for 1064nm, however judging by the amount of reflected light, it was certainly NOT AR-coated for 1064nm. I replaced it with a bi-convex f=100mm lens with confirmed AR-behavior.

The AUX laser is currently shuttered.

Per our Wednesday meeting, some items to work on are

• Align the zero-order AUX beam into a second collimator on the PSL table, so we can switch the fiber output and look for RF signals at the offset-phaselock frequency without the additional frequency shift from the AOM. This will simpligy the mode spectroscopy scheme significantly
• Abandon the R10/T90 beamsplitters in favor of R90/T10 beamsplitters. We'll swap the large mirror in front of the AS camera with an R90/T10 BS, and follow it up with a second R90/T10 BS that sends the AUX beam to the IFO. This way we'll have identical power levels on AS110 and AS55, and still 90% of the current AUX light going into the IFO, but without strong secondary beams from R10/T90 optics.

Using the numbers from the sensing measurement, I calibrated the measured in-loop MICH spectrum from Tuesday night into free-running displacement noise. For convenience, I used the noise-budgeting utilities to make this plot, but I omitted all the technical noise curves as the coupling has probably changed and I did not measure these. The overall noise seems ~x3  higher everywhere from the best I had last year, but this is hardly surprising as I haven't optimized anything for low noise recently. To summarize:

• DRMI was locked using 1f error signals.
• MICH was controlled using AS55_Q.
• Main difference is that we have a little less (supposedly 10%) light on the AS55 PD now because of the AUX laser injection setup. But the AUX laser was shuttered.
• 1f LSC PDs (REFL11, REFL55 and AS55) had ADC whitening filters engaged in while this data was taken.
• ITM and BS coils were not de-whitened.

I will do a more thorough careful characterization and add in the technical noises in the coming days. The dominant uncertainty in the sensing matrix measurement, and hence this free-running noise spectrum, is that I haven't calibrated the actuators in a while.

The cabeling was cleaned up a little bit yesterday morning. The upper back side is still massy.

Oplev sums of 240 days.

Aim : To develop a neural network on simulated data.

I developed a python code that generates a 64*64 image of a white Gaussian beam spot at the centre of black background. I gave a sine wave of frequency 0.2Hz that moves the spot vertically (i.e. in pitch). Then I simulated this video at 10 frames/sec for 10 seconds. Then I saved this data into an hdf5 file, reshaped it to a 1D array and gave as input to a neural network. Out of the 100 image frames, 75 were taken as training dataset and 25 as test data. I varied several hyperparameters like learning rate of the optimizer, number of layers, nodes, activation function etc. Finally, I was successful in reducing the mean squared error with the following network model:

• Sequential model of 2 fully connected layers with 256 nodes each and a dropout of 0.1
• loss function = mean squared error, optimizer = RMSprop (learning rate = 0.00001) and activation function that adds nonlinearity = relu
• batch size = 32 and number of epochs = 1000

I have attached the plot of the output of neural network (NN) as well as sine signal applied to simulate the video and their residula error in Attachment 1. The plot of variation in mean squared error (in log scale) as number of epochs increases is given in Attachment 2.

I think this network worked easily since there is no noise in the input. Gautam suggested to try the working of this network on simulated data with a noisy background.

I did the measurement with the BeatMouth open today. Main changes:

• Directly pipe the RF output of the Menlo PDs to the Agilent, bypassing the 20dB coupler inside the BeatMouth.
• Directly pipe the unused port of the Fiber Beamsplitter used to send light to the Menlo PD to an in-air collimator, which then sends the beam to the NF1611 reference detector.

So neglecting asymmetry in the branching ratio of the fiber beamsplitter, the asymmetry between the test PD optical path and the reference PD optical path is a single fiber mating sleeve in the former vs a collimator in the latter. In order to recover the expected number of 409 V/W for the Menlo PDs, we have to argue that the optical loss in the test PD path (fiber mating sleeve) are ~3x higher than in the NF1611 path (free space coupler). But at least the X and Y PDs show identical responses now. The error I made in the previously attached plot was that I was using the 20dB coupled output for the X PD measurement .

Revised conclusion: The measured optoelectronic response of the Menlo PDs at 10s of MHz, of ~130 V/W, is completely consistent with the numbers I reported in this elog. So rogue polarization is no longer the culprit for the discrepancy between expected and measured RF beatnote power, it was just that the expectation, based on Menlo PD specs, were not accurate.#2 of the linked elog seems to be the most likely, although "broken" should actually be "not matching spec".

While killing time b/w measurements, I looked on the ITMY optical table and found that the NF1611 I mentioned in this elog still exists. It is fiber coupled. Could be a better substitute as a Reference PD for this particular measurement.

[Jon, Gautam, Johannes]

We did the following today:

1. Dither align arms such that ITMs were reliable arm references.
2. Configure the IFO such that ITMX single bounce was the only visible beam reaching the AS port from the symmetric side - ITMY, both ETMs, PRM and SRM were misaligned.
3. Do coarse alignment on the AS table using the usual near field / far field overlap technique, with "near" and "far" dictated by arm reach on the AS table. In this way, the ingoing AUX beam and the PSL single bounce from ITMX were collimated on the AS table.
4. Lock the AUX / PSL PLL. We expected a beatnote on AS110 at eithe (80-50)=30 MHz or (80+50)=130 MHz. 80 MHz is the AOM driver frequency, while 50 MHz is the PLL offset. (Marconi was actually set to 60 MHz, prolly Keerthana forgot to reset it after some remote experimentation).
5. Beat was found at 30 MHz. 
6. Input steering of AUX beam into the IFO was tweaked to maximize the beat. Johannes claims he saw -35 dBm on AS110 last week. But Jon reported a best effort of ~-60 dBm today. Not sure how to square that circle.
7. Once we were confident that the input of the AUX and PSL beams were well aligned, we decided to do a scan. PRC was chosen as PRMI can be locked but I don't yet know the correct settings for SRMI locking, and DRMI seemed too ambitious for daytime.
   • PRMI was locked on carrier.
   • Jon can comment more here, but the measurement with AM sidebands does not rely on any beatnote on the AS110 PD, it is just looking for coupling of the AM sideband into the IFO from the AS port at resonant frequencies of the PRC.
   • For a coarse sweep, we swept from 1-60 MHz, 801 points, and the IF bandwidth was set at 30 kHz on the AG4395.
   • Transfer function being measured was the ratio of AM signal detected at AS110 PD, to RF drive applied to the AOM driver.
   • We were expecting to see dips separated by the PRC FSR (~25 MHz, since the PRC RT length is ~12.5m), when the AM sideband becomes resonant in the PRC.
   • But we saw nothing. Need to think about if this is an SNR problem, or if we are overlooking something more fundamental in the measurement setup.

This measurement seems like a fine candidate to trial the idea of looking for the FSRs (and in general, cavity resonances) of the PRC in the phase of the measured TFs, rather than the amplitude.

The PRC FSR is, of course, very close to twice of our f1 moudlation frequency (11MHz x 2 = 22MHz) .

I still don't understand what response the measurement is looking for. I understood the idea of using the subcarrier as a stablized carrier to the PRC with a certain freq offset from the main carrier. I suppose what was swept was the AOM modulation frequency (i.e. modulation frequency of the AM applied to the subcarrier). If that is the case, the subcarrier seemed fixed at an arbitorary frequency (i.e. 50MHz) away from the carrier. If one of the AM sidebands hits the PRC resonance (i.e. 22, 44, 66MHz away from the main carrier), you still have the other sideband reflected back to the AS. Then the RF signal at the AS is still dominated by this reflected sideband. I feel that the phase modulation is rather suitable for this purpose.

If you are talking about ~MHz AM modulation by the AOM and scanning the PLL frequency from 1MHz to 60MHz, the story is different. And this should involve demodulation of the AS signal at the AM modulation frequency. But I still don't understand why we don't use phase modulation, which gives us the PDH type signal at the reflection (i.e. AS) port...

Here's a Finesse modeling of what we're expecting to observe with this test. It uses Gautam's base model of the 40m IFO with appropriate modifications for the needed configuration.

The idea is to lock the IFO in the SRMI configuration, with the phase-locked AUX beam injected from the AS port. The AUX beam is imprinted with AM sidebands and slightly misaligned relative to the SRC so as to transfer power into HOM1. The RF network analyzer provides the drive signal for the AOM, and its frequency is swept to coherently measure the transfer function [reflected AUX beam / drive]. The reflected AUX beam is sensed by the AS110 PDA10CF.

It is also possible to drive PM sidebands as Koji suggests, but the squeezer group has encouraged using AM for practical advantages. The SNR with AM is a bit higher (less power lost into harmonics at large modulation index), there is a broadband AOM already available aligned to the SQZ beam at LLO, and there is also concern that driving strong PM could interfere with the SQZ control loops.

Expected SRMI Response

Attachment #1 shows the expected response to swept-AM in SRMI. Resolving just the FSR and the first-order mode splitting is sufficient to extract the SRC Gouy phase.

Expected DRMI Response

Since the 40m has not been opearted in SRMI since ~2016 (last done by Eric Q.), Gautam believes it may take some time to relock this configuration. However, the modeling indicates that we can likely obtain sufficient sensitivity in DRMI, which would allow us to proceed faster. Attachment #2 shows the expected response to swept-AM in DRMI. The PRC leakage signal turns out to be significantly smaller than the SRC reflection (a factor of ~30 in amplitude), so that the signal still retains its characteristic shape to a very good approximation. The tradeoff is a 10x reduction in SNR due to increased PSL shot noise reaching AS110.

Based on this, we should proceed with DRMI scans instead of PRMI next week.

I have connected a 4TB disk to chiara via a USB-SATA adapter. This disk has been recognized as /dev/sde. A GUID Partition Table (GPT), not MBR was made with gdisk to make a partition with the size beyond 2TB.
I tried to use "dd" to copy /home/cds (/dev/sdb1) to /dev/sde1, but failed. The copy was done (taking ~12h) and the partition was not recognized as a complete filesystem.

So I decided to use rsync instead.

sudo mkfs -t ext4 /dev/sde1
sudo mkdir /media/usb4g
sudo mount -t ext4 -o rw /dev/sde1 /media/usb4g
sudo rsync -a --progress /home/cds/ /media/usb4g

Progress
14:33 Copied     33G/1831G
14:38 Copied     36G/1831G
17:02 Copied   365G/1831G (~2.2GB/min)
01:18 Copied 1449G/1831G (~2.2GB/min)
04:36 Completed
> sent 1907955222607 bytes  received 126124609 bytes  37010956.31 bytes/sec
> total size is 1907271994803  speedup is 1.00

I'm running a comsol job on optimus in a tmux session named cryocavs. Should be done in less than 24 hours, judging by past durations.

Since I am finishing my job at the lab, I have stored all my electronics in a box (attachment 1) and placed it under the table in the control room where some other electronics are stored. The box contains the heater circuit box, two temperature sensor boards, one temperature sensor, a short power cable and +/- 15V supply cables. In the lab I left the wires for the current setup and tied them down to the wall so that they aren't in the way (attachment 2). I left the can as is and the other temperature sensor is still attached to the inside of the can. I have labeled the wires going from the sensor as 'in' and 'out'. I've also left the wires for the heater there as well (attachment 3). I turned off the PID control and deactivated the tmux session on megatron.

Thanks to Rana and the LIGO team for giving me the opportunity to work at the 40m on this project with the seismometer.

The initial local backup with rsync was done. Now the new 4TB disk is (supposed to be) automatically mounted at boot as /media/40mBackup so that we can run the daily backup on this disk. (<- This was confirmed by "sudomount -a")

controls@chiara|~> sudo blkid
...
/dev/sde1: UUID="92dc7073-bf4d-4c58-8052-63129ff5755b" TYPE="ext4"

controls@chiara|~> cat /etc/fstab
...
UUID=92dc7073-bf4d-4c58-8052-63129ff5755b   /media/40mBackup    ext4    defaults    0   0

Here I've used UUID rather than the device name "/dev/sde1" because the device name can get altered depending on the order of the usb connection.

This new disk is just a bare HDD drive sitting on the top of the chassis. We eventually want to accommodate this disk in the chassis so that we can recover the function only with the modification of /etc/fstab.  We need to wait for a next chance to have chiara down. In fact, when we can isolate chiara, we want to use this disk as the main disk and install another 4TB disk as a backup.

Yesterday, I moved the following optics:

1. Lens in front of AS110 PD.
2. BS splitting light between AS110 and AS55.

After moving these components around a bit, I locked them down once I was happy that the beam was pretty well centered on both of them, and also on AS110 and AS55 (measured using O'scope with single bounce from one ITM, other optics misaligned).

The beam was close to clipping on the lens mentioned in #1, probably because this wasn't checked when the 90-10 BS was installed for the AUX laser. Furthermore, I believe we are losing more than 10% of the light due to this BS. The ASDC (which is derived from AS55 PD) level is down at ~110cts as the Michelson is fringing, while it used to be ~200 cts. I will update with a power measurement shortly. But I think we should move ahead with the plan to combine the beam into the IFO's AS mode as discussed at the meeting last week.

Unrelated to this work, but c1psl and c1iscaux were keyed. 

ASDC has something weird going on with it - my main goal yesterday was to calibrate the actuators of ITMX, ITMY and BS using the Michelson. But with the Michelson locked on a dark fringe, the ASDC level changed by up to 50 counts seemingly randomly (bright fringe was ~1000 cts, I had upped the whitening gain to +21dB), even though the CCD remained clearly dark throughout. Not sure if the problem is in the readout electronics or in the PD itself.

Is the 10% specified for P-Pol or for UNP? I contacted CVI about beamsplitters, since their website doesn't list a BS1-1064-90-... option on the website. They say a R=90% beamsplitter would be a custom job. The closest stock item they got is BS1-1064-95-2025-45UNP specified at R=95% for UNPolarized beams. They were kind enough to sent me the measured transmission curves for a recent lot of these, which is attached was uploaded to the wiki [Elog Police K: NO PROPRIETARY DOCUMENTS ON THE ELOG, which is public. Put it on our wiki and put the link here]. The figure is not labeled, but according to the contact Red is S-Pol and Blue is P-Pol, which means that this one actually has R=~90% for P, pretty much what we want. We'll need to buy two of these to make the swap in the setup.

Back to your original point: There's only a BS1-1064-10-2025-45UNP on the website, so unless we got these as custom items, the R for P-Pol is probably NOT actually 10%, just somewhere between 0% and 20%

Of course, many (but no all) of the optics were custom-ordered back in ~2000.

Summary:

The actuator (pendulum) gains for the Beam Splitter and the two ITMs were measured to be:

BS: 9.54 +/- 0.05 nm/ct [100 ohm series resistor in coil driver board]

ITMX: 2.44 +/- 0.01 nm/ct [400 ohm series resistor in coil driver board]

ITMY: 2.44 +/- 0.02 nm/ct [400 ohm series resistor in coil driver board]

Counts here refers to DAC counts at the output of the coil filter banks (as opposed to counts at the LSC servo output). The dominant (systematic) uncertainty (which isn't quoted here) in this measurement is the determination of the peak-to-peak swing of the dark port sensor, AS55_Q. I estimate this error to be ~1ct/33cts = 3%. These values are surprisingly consistent with one another once we take into account the series resistance.

Details:

The last time this was done, we used ASDC to do the measurement. But I don't know what signal conditioning ASDC undergoes (in PD or in readout electronics). In any case, in my early trials yesterday, ASDC was behaving unpredictably. So I decided to do redo the measurement.

[Attachment #1]- Flowchart describing the calibration procedure.

[Attachment #2] - AS55_Q output while the Michelson was freeswinging. I had first aligned the ITMs using ASS. The peak-to-peak value of this corresponds to . So we know AS55_Q in terms of cts/m of MICH displacement.

[Attachment #3] - Magnitudes of transfer function from moving one of the MICH optics, to the now calibrated AS55_Q. Fits are to a shape , with  being the fitted parameter. Coherence during the measurement is also plotted.

• Note that the excitation is applied to the channels C1:SUS-<optic>_LSC_EXC, for <optic> in [BS, ITMX, ITMY]. But since my de-whitening board re-work to remove the analog x3 gain, there is a digital x3 gain in the coil driver filter banks. So while the calibration numbers given above are accurate, be aware that when using them for sensing matrix measurements etc, you have to multiply these by x3.
• Furthermore, moving the BS by results in a Michelson length change of , and this has been factored into the above number.

Next Steps:

1. Now that I have a calibration I trust more, re-analyze my DRMI sensing matrix data. Actually the sensing response numbers aren't significantly different from what I have been assuming. It's just that in terms of counts applied at the LSC input of a suspension, there is a digital x3 gain that has to be explicitly factored in.
2. Calibrate POX and POY by locking the arms and driving the now calibrated ITMs by a known number of counts.
3. Calibrate the ETMs, and MC1/MC2/MC3 by looking at calibrated POX/POY.
4. Lock DRMI, and calibrate SRM and PRM.

Reference:

[1] - http://www.phys.ufl.edu/~bernard/papers/CQG20_S903.pdf

Motivation:

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

POP QPD checkout:

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

Aim: To measure the optical power from led using a powermeter.

Yesterday Gautam drilled a larger hole of diameter 5mm in the box as an aperture for led (aperture angle is approximately 2*tan^-1(2.5/7) = 39 deg). I repeated the measurements that I had done before (https://nodus.ligo.caltech.edu:8081/40m/13951). The measurents of optical power measured using a powermeter and the corresponding input voltages are listed below.

So we are able to receive optical power close to the value (1.6mW) given in Thorlabs datasheet for LED1050E (https://www.thorlabs.com/drawings/e6da1d5608eefd5c-035CFFE5-C317-209E-7686CA23F717638B/LED1050E-SpecSheet.pdf). I hope we can proceed to BRDF measurements for CCD calibration.

Steve: did you center the LED ?

Not much progress today with the AUX cavity scans. I've determined there still are some alignment issues.

At the start of today a large AUX/PSL beat note was visible on the AS110 sensor, at a similar power as where we left off last night (-60 dBm). Proceeding from there, I attempted to reproduce Johannes' measurement of the cavity transmission resonances. I misaligned the X-arm, locked the Y-arm cavity, and scanned the AUX RF offset approximately 8 MHz in 2 kHz steps. This should have swept through two FSRs, but nothing was visible.

Further inspection revealed that none of the PSL light was making it back to through the AUX fiber to the PSL table. I take this to mean that the beam seen earlier on AS110 was the ITMY reflection, and that the AUX injection axis was no longer reaching ETMY. I also found that the AUX beam size just after the 90/10 beasmsplitter looks anomolously large. Maybe a lens was recently changed? In any case, the mode-matching looks like it is going to need to be readjusted.

Per discussion today eve, barring objections, I will do the following tomorrow morning:

1. Remove ETMX coil driver board from 1X9
   • Change series resistances on the fast path to 2x4k in parallel. One will be snipped off once we are happy we can still lock.
   • Remove AD797s, potentiometers.
   • Thick film-->thin film for important components.
2. Remove ETMX de-whitening board from 1X9
   • Remove x3 analog gain.
   • Thick film-->thin film for important components.

We did swap a lens as discussed in elog 13968, but they both had f=100mm specified, the difference being one was AR-coated for 1064 and bi-convex, while the other one was plano-convex and had a different coating. The reason for the large beam spot was something else: The fiber wasn't sitting in the coupler properly. When reconnecting the fiber after taking it out make sure to align the key on the fiber end with the notch in the coupler before tightening. After discovering this the following was done:

• Fixed fiber mounting situation
• Tested AUX alignment into fiber on PSL table, was still good
• The AUX polarization was aligned to the wrong fiber axis. I fixed this. The coupler on the PSL table has it's noth oriented vertically since we're using s-polarized light. The AS-table coupler is rotated by 90 degrees, such that the notch points to the side. This way we technically don't need any halfwaveplates for rotation. However, there are still current HWPs installed.
• Locked both arms and ran dither alignment until satisfactory
• Misaligned ITMX and ETMX, and further set the ITMX pitch offset to 0.0
• Started overlapping the expectedly misaligned beams by eye. For this I turned the power of the deflected beam down to 50mV bias voltage, which gives the PSL and AUX lasers similar card-brightness on the shared path
• Misaligned SRM more because there was still the strong prompt reflection coming out the AS port.
• Restored phaselock between AUX and PSL, with beat at 30MHz between 1st-order diffracted in fiber and PSL
• Immediately saw STRONG 30MHz RF signal on AG4395. Disappeared when blocking AUX, and optimized alignment brought the signal up to -10dBm, as shown in attachment #1
• Checked YEND PDA10CF and saw a -80dBm RF signal at 30 MHz (#2), compatible with earlier observations.

Before leaving I restored the XARM alignment. SRM remains misaligned, LSC off. Alignment shouldn't change drastically over night, so I suggest when picking this work up tomorrow to directly look for the beats after phaselocking AUX and PSL

You should wipe off the table cover before you take it off next time.

It is important to turn up the PSL encloure HEPA Variac voltage if you are working in there. It takes less than 10 minutes to reach lab condition.

Lab air count normal. It is not logged. I have a notebook of particle count on the SP table next to the Met One counter.

Yes.

I finished the re-soldering work today, and have measured the coil driver noise pre-Mods and post-Mods. Analysis tomorrow. I am holding off on re-installing the board tonight as it is likely we will have to tune all the loops to make them work with the reduced range. So ETMX will remain de-commissioned until tomorrow.

I decided to take a quick look at the data. Changes made to the ETMX coil driver board:

1. Fast path series resistances: 400 ohm ---> 2.25 kOhm (= 2x 4.5 kohm in parallel). Measured (with DMM) resistance in all 5 paths varied by less than 3 ohms (~0.2%).
2. All thick film resistors in signal (fast and bias) paths changed to thin film.
3. AD797 ---> Op27 for monitor output.
4. Above-mentioned mon output (30Hz HPF-ed) routed to FP LEMO mon via 100ohm for diagnostic purposes.
5. 4x Trim-pots in analog path removed. 

I also took the chance to check the integrity of the LM6321 ICs. In the past, a large DC offset on the output pin of these has been indicative of a faulty IC. But I checked all the ICs with a DMM, and saw no anomalies.

Measurement condition was that (i) the Fast input was terminated to ground via 50ohm, (ii) the Bias input was shorted to ground. SR785 was used with G=100 Busby preamp (in which Steve installed new batteries today, for someone had left it on for who knows how long) for making the measurement. The voltage measurement was made at the D-Sub connector on the front panel which would be connected to the Sat. Box, with the coil driver not connected to anything downstream.

Summary of results:

[Attachment #1] - Noise measurement out to 800 Hz. The noise only seems to agree with the LISO model above 300 Hz. Not sure if the low-frequency excess is real or a measurement artefact. Tomorrow, I plan to make an LPF pomona box to filter out the HF pickup and see if the low-frequency characteristics change at all. Need to think about what this corner freq. needs to be. In any case, such a device is probably required to do measurements inside the VEA.

[Attachment #2] - Noise measurement for full SR785 span. The 19.5 kHz harmonics are visible. I have a theory about the origin of these, need to do a couple of more tests to confirm and will make a separate log.

[Attachment #3] - zip of LISO file used for modeling coil driver. I don't have the ASCII art in this, so need to double check to make sure I haven't connected some wrong nodes, but I think it's correct.

Measurements seem to be consistent with LISO model predictions.

*Note: Curves labelled "LISO model ..." are really quad sum of liso pred + busby box noise.

My main finding tonight is: With the increased series resistance (400 ohm ---> 2.25 kohm), LISO modeling tells me that even though the series resistance (Johnson noise) used to dominate the voltage noise at the output to the OSEM, the voltage noise of the LT1125 in the bias path now dominates. Since we are planning to re-design the entire bias path anyways, I am not too worried about this for the moment.

I will upload more details + photos + data + schematic + LISO model breakdown tomorrow to a DCC page. 

gautam noon 21 June 2018: I was looking at the wrong LISO breakdown curves. So the input stage Op27 voltage noise used to dominate. Now the Bias path LT1125 voltage noise dominates. None of the conclusions are affected... I've uploaded the corrected plots and LISO file here now. 

[Jon, Keerthana, Sandrina]

Yesterday we carried out preliminary proof-of-concept measurements using the new AS-port-injected AUX laser to resolve cavity mode resonances.

At the time we started, I found the beat note levels consistent with what Johannes had reported the night before post-realignment. Hence we did not change the AUX alignment.

Test 1: YARM Mode Scan

• IFO locked in YARM configuration on carrier.
• Confirmed the presence of a -80 dBm beat note on the temporary YEND broadband PD (i.e., at the cavity transmission).
• Slowly canned the RF offset of the AUX laser from 50 MHz (nominal) to 60 MHz in 10 kHz steps.
• Attachment 1 shows the measured scan in "max hold" mode. The bottom panel is the transmission spectrum and the top panel is the reflection, with the AUX/PSL carrier-carrier beat note visible to the far left. In addition to the FSR, it looks to me like the scan resolves at least two HOMs.

Test 2: PRC Mode Scan

• IFO locked in PRMI configuration on carrier.
• Moved the temporary 150 MHz PDA10CF from the YEND to an unused pickoff of the REFL33 beam (i.e., the PRC transmission of the AUX beam). There was an existing 50-50 beamsplitter just before REFL33 whose reflected beam was directed onto a beam dump. The PD is now placed in that location. The modification to the AS table is shown in Attachment 2.
• We made a similar slow scan of the AUX RF offset over ~35 MHz in 10 kHz steps.
• We resolve the 22 MHz FSR, but it is apparent that an incoherent "max-hold" analyzer measurement is inadequate. The problem is that in max-hold mode, because the 11 MHz-spaced PSL sidebands also beat with the AUX subcarrier, we measure a messy superposition of the PSLcarrier-AUXcarrier beat AND all of the PSLsideband-AUXcarrier beats. The next step is to use the AOM to make a coherent measurement at only the frequency of PSL/AUX carrier-carrier beat.

The SURFs have the data from last night's scans and will be separately posting plots of these measurements. We'll continue today with mode scans using AM sidebands rather than the AUX RF offset.

(Jon, Keerthana, Sandrine)

We tried to align the AUX and PSL laser yesterday. We collected the data from the spectrum analyser for the Y-ARM reflection and also for the Y-ARM transmission from the ETM mirror. I am attaching the plots here.

Here’s a quick summary of the Tip-Tilt Design updates (all files are in the dropbox in [TipTiltSus>TT_New]) that I have been working on with Koji and Steve's help.

1. Plate on top to hold mirror in place:

The plate is 0.5 mm thick. I did a rough FEA with 10 N force on the point of pressure on it, and it bent easily.

2. Weighted screw rod at the bottom for tilting the mirror-holder:

I did a very simplified free body analysis to calculate the required length of the rod to achieve a +/- 15 mRad tilt, and got around 1.5 inches.

3. Set-screws on both side of wire clamp to adjust its horizontal position:

• Front view (showing set screws on either side of the clamp to push it into the desired position, and the clamp in the middle with screws on top and bottom to fix its position):

• Exploded view showing protrusion in clamp that sits in the mirror holder inset:

• Exploded view showing inset in the mirror holder to slide protrusion in:

Comments:

1. Used the same screw size in most places to reduce complexity.

2. The mirror holder I have worked on is a little different from the actual piece I have on my table. Which one do you prefer (Koji)?

> 2. Weighted screw rod at the bottom for tilting the mirror-holder:

Too long. The design of the holder should be check with the entire assembly.
We should be able to make it compact if we heavier weights.
How are these weights fixed on the shaft?
Also can we have options for smaller weights for the case we don't need such a range?
Note the mass of the weights.

> 3. Set-screws on both side of wire clamp to adjust its horizontal position:

How much is the range of the clamp motion limited by the slot for the side screws and the slot for the protrusion? Are they matched?
Can you show us the design of the slot made on the mirror holder?

>>

Where is the center of mass (CoM) for the entire mirror holder assy and how much is the height gap between the CoM and the wire release points. Can you do this with 3/8" and 1/2" fused silica mirrors?

[steve, gautam]

I took this opportunity of EX downtime to change the supply voltage for the AA unit (4-pin LEMO front panel) in 1X9 from +/-5V to +/-15V. Inside the AA board are INA134 and DRV135 ICs, which are rated to work at +/-18V. In the previous state, the inputs would saturate if driven with a 2.5Vpp sine wave from a DS345 func. gen. After the change, I was able to drive the full range of the DS345 (10Vpp), and there was no saturation seen. This AA chassis is only used for the OSEM signals and also some ALS signals. Shadow sensor levels and spectra are consistent before and after the change. The main motivation was to not saturate the Green PDH Reflection signal in the digital readout. The steps we took were:

1. Confirm (by disconnecting the power cable at the back of the AA box) that the power supplied was indeed +/- 5 V.
2. Remove DIN fuse blocks from DIN rail for the relevant blocks.
3. Identify a +15 V, -15 V and GND spot to plug the wires in. 
4. Effect the swap.
5. Re-insert fuses, checked supply voltage at connector end of the cable was now +/- 15 V as expected.
6. Re-connect power cable to AA box.

Initial tests look promising. Local damping works and I even locked the X arm using POX, although I did it in a fake way by simply inserting a x5.625 (=2.25 kohm / 400 ohm) gain in the coil driver filter banks. I will now tune the individual loop gains to account for the reduced actuation range.

Now I have changed the loop gains for local damping loops, Oplev loops, and POX locking loop to account for the reduced actuation range. The dither alignment servo (X arm ASS) has not been re-commissioned yet...

pianosa has been upgraded to SL7. I've made a controls user account, added it to sudoers, did the network config, and mounted /cvs/cds using /etc/fstab. Other capabilities are being slowly added, but it may be a while before this workstation has all the kinks ironed out. For now, I'm going to follow the instructions on this wiki to try and get the usual LSC stuff working.

We (Rana and I) are re-assembling the temperature controls on the seismometer to attempt PID control and then improve it using reinforcement learning.

We tried to re-assemble the connections for the heater and in-loop temperature sensor on the can that covers the seismometer.

We fixed (soldered) two of the connections from the heater circuit to the heater, but did not manage to get the PID working as one of the wires attached to the MOSFET had come off. Re-soldering the wire would be attempted tomorrow.

Equipment for undertaking all this is still left at the X-end of the interferometer and will be cleared soon.

Two out of the four over-head fluorescent lights in the X end of the interferometer were flickering today.