> The percentage error which I found out =[(analytical value - finesse value)/analytical value]*100
Yes, I this does not give us 0.70%
(3.893408 - 3.8863685)/3.893408 *100 = 0.18%
But any way, go for the fitting.
Oopss !! I made a mistake while taking the values from my notes. Sorry.
The unfortunate discovery today was that the attenuator switches on the IMC WFS heads are actually assigned to individual segments, and they are active. That means that we have been running the WFS with an uneven gain setting. The attached PDFs show that the signals with the attenuators on and off all at the same time, while the WFS servo output was frozen. A more annoying feature is that when some of the attenuators are on, this does not lower the gain completely. I mean that the attenuated channels show some reduction of the gain, but that is not the level of reduction we see when all attenuators are turned on. This RF could come from some internal RF coupling or some similar effect.
Moreover, the demodulation phases are quite off for most of the segments.
So far, the WFS is running with this uneven attenuation. We take time to characterize the gain and retune the demod phases and input matrices.
Per this elog, we don't need any AIOut channels or Oplev channels. However, the latest wiring diagram I can find for the EX Acromag situation suggests that these channels are hooked up (physically). If this is true, there are 12 ADC channels that are occupied which we can use for other purposes. Question for Johannes: Is this true? If so, Kira has plenty of channels available for her Temperature control stuff..
As an aside, we found that the EPICS channel names for the TRX/TRY QPD gain stages are somewhat strangely named. Looking closely at the schematic (which has now been added to the 40m DCC tree, we can add out custom mods later), they do (somewhat) add up, but I think we should definitely rename them in a more systematic manner, and use an MEDM screen to indicate stuff like x4 or x20 or "Active" etc. BTW, the EX and EY QPDs have different settings. But at least the settings are changed synchronously for all four quadrants, unlike the WFS heads...
Unrelated: I had to key the c1iscaux and c1auxey crates.
I worked a bit on recovering the DRMI locking again tonight. I decided to shutter the AUX laser on the PSL table at least until I figured out the correct locking settings. As has become customary now, there was a cable in the AS beampath (leading from the AS55 DC monitor to nothing, through the enclosure side panel, it is visible in Attachment #3 in this elog) which I only found after 30mins of futility - please try and remove all un-necessary cables and leave the AS beampath in a usable state after working on the AS table! In the end, I got several short (~3mins) stretches in tonight, but never long enough to do the loop characterization I wanted to get in tonight, probably wrong gains in one or more of the loops. In the last 30 minutes, the IMC has been frequently losing lock, so I am quitting for now. The AUX laser remains shuttered.
Today I made the led (1050nm) circuit inside a box as given in my previous elog. Steve drilled a 1mm hole in the box as an aperture for led light.
Resistance (R) used = 665 .
We connected a power supply and IR has been detected using the card.
Later we changed the input voltage and measured the optical power using a powermeter.
Since the optical power values are very less, we may need to drill a larger hole.
Now the hole is approximately 7mm from led, therefore aperture angle is approximately 2*tan-1(0.5/7) = 8deg. From radiometric curve given in the datasheet of LED1050E, most of the power is within 20 deg. So a hole of size 2* tan(10) *7 = 2.5mm may be required.
I have also attached a photo of the led beam spot on the IR detection card.
With Koji's help, I got repeatable and reliable DRMI locking going again tonight - this is with the AS path optics for the spectroscopy measurement in place, although the AUX laser remained shuttered tonight. Results + spectra tomorrow, but here's what I did:
As I have found before, it is significantly easier to get the locking going post 11pm - the wall Seis BLRMS don't look that much quieter at midnight compared to 10pm, but this might be a scaling issue. I'll do a quantitative assessment next time... Also, Foton takes between 25-45 secs to save an updated filter (timed twice today).
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....
Measured loop TFs - PRCL is a big mystery. Used these to finalize loop gains.
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:
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.
The cavity scan data obtained from the Finesse simulation is attached here. Fig1 indicates the cavity scan data in the absence of induced misalignment. In that case only the fundemental mode is resonating. But when a misalignment is induced, higher order modes are also present as seen in Fig2. This is in the absence of surface figure error in the mirrors. Now I am trying to provide perturbations to the mirror surface in the form of zernike polynomials and get the scan data fom the simulation. These cavity scan data can be used to develop fitting models. Once we have a model, we can use it to analyse the data from the experimental cavity scan.
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.
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.
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:
[Attachment #3] - Tarball of data + script used to make Attachment #2.
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.
The unfortunate discovery today was that the attenuator switches on the IMC WFS heads are actually assigned to individual segments, and they are active. That means that we have been running the WFS with an uneven gain setting.
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 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:
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
├─sda1 8:1 0 446.9G 0 part /
├─sda2 8:2 0 1K 0 part
└─sda5 8:5 0 18.9G 0 part [SWAP]
sdb 8:16 0 2.7T 0 disk
└─sdb1 8:17 0 2T 0 part /home/cds
sr0 11:0 1 1024M 0 rom
sdc 8:32 0 1.8T 0 disk
└─sdc1 8:33 0 1.8T 0 part /media/40mBackup
sdd 8:48 0 1.8T 0 disk
└─sdd1 8:49 0 1.8T 0 part
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.
2018-06-06 07:00:01,086 INFO Updating backup image of /cvs/cds
2018-06-06 07:00:01,086 ERROR External drive not mounted!!!
2018-06-07 07:00:01,147 INFO Updating backup image of /cvs/cds
2018-06-07 07:00:01,147 ERROR External drive not mounted!!!
2018-06-08 07:00:01,244 INFO Updating backup image of /cvs/cds
2018-06-08 08:23:32,939 INFO Backup rsync job ran successfully, transferred 316870 files.
2018-06-09 07:00:01,465 INFO Updating backup image of /cvs/cds
2018-06-09 07:12:11,865 INFO Backup rsync job ran successfully, transferred 1926 files.
2018-06-10 07:00:01,842 INFO Updating backup image of /cvs/cds
2018-06-10 07:12:28,931 INFO Backup rsync job ran successfully, transferred 1656 files.
2018-06-11 07:00:01,294 INFO Updating backup image of /cvs/cds
2018-06-11 07:06:14,748 INFO Backup rsync job ran successfully, transferred 1664 files.
2018-06-12 07:00:02,081 INFO Updating backup image of /cvs/cds
2018-06-12 07:07:36,775 INFO Backup rsync job ran successfully, transferred 1870 files.
2018-06-13 07:00:02,194 INFO Updating backup image of /cvs/cds
2018-06-13 07:08:37,356 INFO Backup rsync job ran successfully, transferred 1818 files.
2018-06-14 07:00:01,753 INFO Updating backup image of /cvs/cds
2018-06-14 07:01:43,270 INFO Backup rsync job ran successfully, transferred 1744 files.
Local backup on chiara seems not working since Nov 19, 2017.
2017-11-18 07:00:01,504 INFO Updating backup image of /cvs/cds
2017-11-18 07:03:00,113 INFO Backup rsync job ran successfully, transferred 1954 files.
2017-11-19 07:00:02,564 INFO Updating backup image of /cvs/cds
2017-11-19 07:00:02,592 ERROR External drive not mounted!!!
We have 6 of these boards now in cabinet E7
I wired all 32 channels going to the AA board directly to the ADC as described in the previous log. However, instead of using the old AA board and bypassing the whole circuit, I just used a breakout board as is shown in the first attachment. I put the board back in the rack and reconnected all of the cables.
The seismic BLRMs appear to be working again. A PSD of the BS seismometers is shown in attachment 2. Tomorrow I'll look at how much the ADC alone is suppressing the common mode 60 Hz noise on each of the channels.
Steve: 5 of ADC DAC In Line Test Boards [ D060124 ] ordered. They should be here within 10 days.
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
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:
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.
Oplev sums of 240 days.
Since there have been various software/hardware activity going on (stack weighing, AUX laser PLL, computing timing errors etc etc), I decided to do a check on the state of the IFO.
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:
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:
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.
I will repeat the measurement tomorrow by eliminating some un-necessary patch fiber cables, and also calibrating out the cable delays.
We did the following today:
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.
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.
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
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)
> 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.
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
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:
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.
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.
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.
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.
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.
 - http://www.phys.ufl.edu/~bernard/papers/CQG20_S903.pdf
POP QPD checkout:
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:
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:
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.
Chris replaced some air condition filters and ordered some replacement filter today.
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:
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
Test 2: PRC Mode Scan
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.
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:
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...