I completed the translation of the .db files for the EPICS database records from the VME notation to the Acromag/Modbus/Asyn notation. The channels are now organized into 5 database files, located in /cvs/cds/caltech/target/c1iscaux3/, for convenience:
For reasons unknown to me, the database files in the other Acromag system target directories (e.g. c1susaux, c1auxex) all had 755 level access permission - maybe this is required for systemctl to handle the EPICS serving? Anyways, I upgraded the permission level of the above 5 files using chmod.
There are almost certainly typos / other errors, and I may have missed copying over some soft/calibrated channels, but I hope that this way of grouping by subsystem will make the debugging less painful. Once Chub connects up the power lines to the Acromags, I will run the soft tests. For this purpose, I've also made a C1_ISC-AUX.cmd file and a C1_ISC-AUX.env file in the above target directory, and also made the modbusIOC.service file in /etc/systemd/system on the supermicro.
Along with the plan in ELOG 14744, the ISC PD interface and the whitening filter board have been modificed. The ISC PD I/Fs were restored to the crate and the cables were connected. The whitening filteres are still on the electronics bench for some more tests before being returned to the crate.
The updated schematics were uploaded as https://dcc.ligo.org/D1900318 and https://dcc.ligo.org/D1900319
- Modification of the ISC PD interface: Jumpers between DIN96 P1 and P2. Replace all AD797s with OP27. In fact only I/F #1 (the left most) had total 12 AD797 but the other units already had OP27s.
- Modification of the whitening filter: Jumpers between DIN96 P1 and P2.
Koji pointed out an important subtlety pertaining to the "LATCH ENABLE" signal line on the CM board. The purpose of this line is to smoothly facilitate the transition of a change in the "multi-bit-binary-outputs", a.k.a. "mbbo", that are controlled by MEDM gain sliders, to the analog electronics on the CM board. Why is this necessary? Imagine changing the gain from 7dB (=0111 in mbbo representation) to 8dB (=1000 in mbbo representation). In order to realize this change, all 4 bits have to change their state. But this almost certainly doesn't happen synchronously, because our EPICS interface isn't synchronous. So at some intermediate times, the mbbo representation could be 0100 (=4dB), or 1111 (=15dB), or many other possible values, which are all significantly different from either the initial value or the desired final state. This is clearly undesirable.
In order to protect against this kind of error, a Latched output part, 74ALS573, is used to buffer the physical digital logic levels from the switches in the analog gain stages. So in the default state, the "LATCH ENABLE" signal line is held "LOW". When a change happens in the EPICS value corresponding to a gain slider, the "LATCH ENABLE" state is quickly toggled to "HIGH", so as to enable the appropriate analog gain stages to be switched, and then again to "LOW", at which point the latch holds its output state. This logic is currently implemented by a piece of code called "latch.o", which is the compiled version of "latch.st", which may be found in /cvs/cds/caltech/target/c1iool0 where it presumably was written for the IMC servo board, but not in /cvs/cds/caltech/target/c1iool0 , which is where the CM board database files reside. The only elog reference I can find pertaining to this particular piece of code is from Alan, and doesn't say anything about the actual logic.
For the new c1iscaux, we need to implement this logic somehow. After discussion between Koji and me, we feel that a piece of python code is sufficient. This would continuously run in the background on the supermicro server machine. The channel hierarchy for each gain channes is as follows (I've taken the example of C1:LSC-CM_REFL1_GAIN):
So the logic will be that it continuously scans the EPICS channel C1:LSC-CM_REFL1_GAIN for a change in set value. When a change is detected, it has to update the C1:LSC-CM_REFL1_SET channel. In the next EPICS refresh cycle, this would result in the mbbo bits, C1:LSC-CM_REFL1_BITS , all changing to the appropriate values. After these changes have happened, we need to toggle the LATCH ENABLE in order to allow the changes to propagate to the analog gain stage switches. Need to think about what's the best way to do this.
I've taken the MC2 analog camera down and put another GigE (unit 151) in its place. This is just temporary and I'll put the analog camera back once I finish the MC2 loss map calibration. I'm using a 25mm focal length camera lens with it and it gives a view of MC2 similar to the analog camera one. But I don't think it is completely focused yet (pictures attached).
...more to follow
gautam - Attachment #3 is my (sad) attempt at finding some point scatterers - Kruthi is going to play around with photUtils to figure out the average size of some point scatterers.
Kruthi noticed that she could not login to rossa from giada.
I checked /etc/resolv.conf and it was
so obviously it is useless to refer localhost (i.e. giada) as a nameserver.
I copied our usual resolv.conf to giada as following:
Giada's ssh known_host had unupdated entry for rossa, so I had to clean it up, but after that we can connect to rossa from giada just by "ssh rossa".
[Kruthi, Gautam, Rana]
Gautam installed Atom text editor on Pianosa yesterday.
MC spot position measurement scripts (these can be found in /scripts/ASS/MC directory):
I worked on preparing for the c1iscaux upgrade a bit today.
All the required additional parts should be here by the end of the week - I'd like to aim for Wednesday 7/24 for the installation in 1Y3 and in-situ testing. While talking to Rana, I realized that we should also factor in the c1aux slow channels into this acromag crate - there is no need for a separate machine to handle the shutters and illuminators. But let's not worry about that for now, those channels can simply be added later.
Yutaro talked about the BIO bug in KAGRA elog. http://klog.icrr.u-tokyo.ac.jp/osl/?r=9536
I think I made the similar change for the 40m model somewhere (don't remember), but be aware of the presense of this bug.
There were several small/medium earthquakes in Ridgecrest and one medium one in Blackhawk CA at about 2000 UTC (i.e. ~ 2 hours ago), one of which caused BS, ITMY, and ETM watchdogs to trip. I restored the damping just now.
In addition to c1psl needing a reboot, megatron was un-ssh-able (although it was responding to ping). Clue was that the NPRO PZT control voltage was drifting a lot on the StripTool trace. Koji hard-rebooted the machine. Now IMC is locked, and FSS slow servo is also running.
Mode cleaner was not locked today. Koji came in and concluded that PSL had died. So we keyed it. Then we ran my unstick.py code. Mode cleaner is locked now.
Today, Gautam keyed the C1PSL crate and we got to test my unstick.py code. It seems to be working fine. Remarks:
Following this, we tested my PMC autolocker code. The code ran for about a minute before achieveing lock. Remarks:
I've set up network with a CNN encoder (front end) feeding into a single LSTM cell followed by the output layer (see attachment #1). The network requires significantly more memory than the previous ones. It takes around 30s for one epoch of training. Attached are the predicted yaw motion and the fft of the same. The FFT looks rather curious. I still haven't done any tuning and these are only the preliminary results.
Rana also suggested I try LSTMs today. I'll maybe code it up tomorrow. What I have in mind- A conv layer encoder, flatten, followed by an LSTM layer (why not plain RNNs? well LSTMs handle vanishing gradients, so why the hassle).
Well, what about the previous conv nets?
What I did:
What I observed:
What I think is going wrong:
What I will try now:
I made some rough measurements, using the setup I had used for CCD calibration, to get an idea of how good of a Lambertian scatterer the white paper is. Following are the values I got:
Note: All the measurements are just rough ones and are prone to larger errors than estimated.
I also measured the transmittance of the white paper sample being used (it consists of 2 white papers wrapped together). It was around 0.002
On Friday, Koji helped me find various components required for the scatterometer setup. Like he suggested, I'll first set it up on the SP table and try it out with an usual mirror. Later on, once I know it's working, I'll move the setup to the flow bench near the south arm and measure the BRDF of a spare end test mass.
On Friday, I took images for different power outputs of LED. I calculated the calibration factor as explained in my previous elog (plots attached).
Power incident on photodiode (W)
To estimate the uncertainity, I assumed an error of at most 20mV (due to stray lights or difference in orientation of GigE and photodiode) for the photodiode reading. Using the uncertainity in slope from the linear fit, I expect an uncertainity of maximum 4%. Note: I haven't accounted for the error in the responsivity value of the photodiode.
Johannes had reported CF as 0.0858E-15 W-sec/counts for 12 bit images, with measured a laser source. This value and the one I got are off by a factor of 25. Difference in the pixel formats and effect of coherence of the light used might be the possible reasons.
Optical chopper borrowed from CryoLab to 40m
All suspension watchdogs were tripped ~90mins ago. I restored the damping. IMC is locked.
ITMX was stuck. I set it free. But notice that the UL Sensor RMS is higher than the other 4? I thought ITMY UL was problematic, but maybe ITMX has also failed, or maybe it's coincidence? Something for IFOtest to figure out I guess. I don't think there is a cable switch between ITMX/ITMY as when I move the ITMX actuators, the ITMX sensors respond and I can also see the optic moving on the camera.
Took me a while to figure out what's going on because we don't have the seis BLRMS - i moved the usual projector striptool traces to the TV screen for better diagnostic ability.
Update 16 July 1515: Even though the RMS is computed from the slow readback channels, for diagnosis, I looked at the spectra of the fast PD monitoring channels (i.e. *_SENSOR_*) for ITMX - looks like the increased UL RMS is coming from enhanced BR-mode coupling and not of any issues with the whitening switching (which seems to work as advertised, see Attachment #3, where the LL traces are meant to be representative of LL, LR, SD and UR channels).
I looked at the PSL/IOO racks to check for which boards, if any, require an additional P2 interface, so that we can try and design a generic one for the IMC/CM boards and whatever else may require it. While searching the elog, I saw that Koji and Johannes had already done this, see Koji's elog in this thread. Some remarks:
Conclusion: Only the IMC Servo and CM boards need their P2 connectors connected to Acromag.It would be helpful to remove the TTFSS Interface board and figure out what exactly the pin-mapping for the backplane connectors are, but I didn't do this today because there is a "High Voltage" line going to the Interface Board and I'm not actually sure of the signal chain for the FSS servo.
Arnaud has taken 1 TT suspension from the 40m clean lab to Downs for modal testing. Estimated time of return is tomorrow evening.
I heard a popping sound in the control room; the projector lightbulb has blown out.
it will connect to a 15 pin breakout board in the Acromag chassis
It's nice and compact, and the cost of new 15-pin DSUB cables shouldn't be a factor here. What does the 15p cable connect to?
I looked into the design of the P2 interface board. The main difficulty here is geometric - we have to somehow accommodate sufficient number of D-sub connectors in the tight space between the two P-type connectors.
I think the least painful option is to stick with Johannes' design for the P1 connector. For the CM board, the P2 connector only uses 6 pairs of conductors for signals. So we can use a D-15 connector instead of 2 D-37 connectors. Then we can change the PCB shape such that the P1 connector can be accommodated (see Attachment #1). The other alternative would be to have 2 P-type connectors and 3 D-subs on the same PCB, but then we have to be extra careful about the relative positioning of the P-type connectors (otherwise they wont fit onto the Eurocrate). So I opted to still have two separate PCBs.
I took a first pass at the design, the files may be found here. I just auto-routed the connections, this is just an electrical feedthrough so I don't think we need to be too concerned about the PCB trace routing? If this looks okay, we should send out the piece for fab ASAP.
I will work on putting together the EPICS server machine (SuperMicro) this afternoon.
2. D040180 / D1500308 Common Mode Board
CM servo board itself doesn't need any modification. The CM board uses P1 and P2. So we need to manufacture a special connector for CM Board P2. (cf The adapter board for P1 T1800260). See also D1700058.
I trained a bunch (around 25 or so - to tune hyperparameters) of networks today. They were all CNNs. They all produced garbage. I also looked at lstm networks with CNN encoders (see this very useful link) and gave some thought to what kind of architecture we want to use and how to go about programming it (in Keras, will use tensorflow if I feel like I need more control). I will code it up tomorrow after some thought and discussion. I am not sure if abandoning CNNs is the right thing to do or if I should continue probing this with more architectures and tuning attempts. Any thoughts?
Right now, after speaking to Stuart (ldas_admin) I've decided on coding up the LSTM thing and then running that on one machine while probing the CNN thing on another.
Update on 10 July, 2019: I'm attaching all the results of training here in case anyone is interested in the future.
I received access today. After some incredible hassle, I was able to set up my repository and code on the remote system. Following this, Gautam wrote to Gabriele to ask him about which GPUs to use and if there was a previously set up environment I could directly use. Gabriele suggested that I use pcdev2 / pcdev3 / pcdev11 as they have good gpus. He also said that I could use source ~gabriele.vajente/virtualenv/bin/activate to use a virtualenv with tensorflow, numpy etc. preinstalled. However, I could not get that working, Therefore I created my own virtual environment with the necessary tensorflow, keras, scipy, numpy etc. libraries and suitable versions. On ssh-ing into the cluster, it can be activated using source /home/millind.vaddiraju/beamtrack/bin/activate. How do I know everything works? Well, I trained a network on it! With the new data. Attached (see attachment #1) is the prediction data for completely new test data. Yeah, its not great, but I got to observe the time it takes for the network to train for 50 epochs-
Therefore, I will carry out all training only on this machine from now.
Note to self:
Steps to repeat what you did are:
I attempted to train a bunch of networks on the new data to test if the code was alright but realised quickly that, training on my local machine is not feasilble at all as training for 10 epochs took roughly 6 minutes. Therefore, I have placed a request for access to the cluster and am waiting for a reply. I will now set up a bunch of experiments to tune hyperparameters for this data and see what the results are.
We noticed that the PRM watchdog was tripping frequently. This is a period of enhanced seismic activity. The reason PRM in particular trips often is because the SIDE OSEM has 5x increased transimpedance. We implemented a workaround by modifying the watchdog tripping condition to scale the SD channel RMS by a factor of 0.2 (relative to the UL and LL channels). We restarted the modbus process on c1susaux and tested that the new logic works. Here is the relevant snippet of code:
# PRM Side is special, see elog 14745
field(DESC,"Tests whether RMS too high")
field(INPA,"C1:SUS-PRM_ULPD_VAR NPP NMS")
field(INPB,"C1:SUS-PRM_PD_MAX_VAR NPP NMS")
field(INPC,"C1:SUS-PRM_LLPD_VAR NPP NMS")
field(INPD,"C1:SUS-PRM_SDPD_VAR NPP NMS")
The db file has a note about this as well so that future debuggers aren't mystified by a factor of 0.2.
The list of the iscaux channels and pin assignments were posted to google drive.
The spreadsheet can be viewable by the link sent to the 40m ML. It was shared with foteee@gmail for full access.
Necessary electronics modification
1. D990694 whitening filter modification (4 modules)
This module shares the fast and slow channels on the top DIN96pin (P1) connector. Also, the whitening selector (done by an analog signal per channel) is assigned over 17pin of the P1 connector, resulting in the necessity of the second DSUB cable. By migrating the fast channels, we can swap the cable from the P1 to P2. Also, the whitening selectors are concentrated on the first Dsub. (See Attachment1 P1)
3. D990543A1 LSC Photodiode Interface
PD I/F board has the DC mon channels spread over the 16pin limit. P1 21A can be connected to 6A so that we can accommdate it in the first Dsub.
Also the board uses AD797s. This is not necessary. We can replace them to OP27s. I actually don't know what is happening to those bias control, temp mon, enable, and status. These features should be disables at the I/F and the PDs. (See Attachment2 P1)
In fact the projector is still working. The lamp timer showed ~8200hrs. I just reset the timer, but not sure it was the cause of the shutdown. I also set the fan mode to be "High Altitude" to help cooling.
Arnaud and I moved one of the two spare TT suspensions from the south clean cabinet to the bake lab clean room. The main purpose was to inspect the contents of the packaging. According to the label, this suspension was cleaned to Class A standards, so we tried to be clean while handling it (frocks, gloves, masks etc). We found that the foil wrapping contained one suspension cage, with what looked like all the parts in a semi-assembled state. There were no OSEMs or electronics together with the suspension cage. Pictures were taken and uploaded to gPhoto. Arnaud is going to plan his tests, so in the meantime, this unit has been stored in Cabinet #6 in the bake lab cleanroom.
There was no green light even though the EX NPRO was on. I checked the doubling oven temperature controller and found that its power cable was loose on the rear. I reconnected it, and now there is green light again.
Last documented replacement in Nov 2018, so ~7 months, which I believe is par for the course. I am disconnecting its power supply cable.
The Y-arm ASS was tuned to be in a workable state. Basically, I followed Koji's recipe.
The SNR of the dither lines in the TRY and YARM control signals were checked - Attachment #1. The dither frequencies are marked with vertical dashed lines (can't figure out how to add 4 cursors in DTT so there's two in each row for a total of 4). A couple of days ago, when I was doing some preliminary checks, I found that the oscillator at 24.91 Hz caused a broadband increase in the TRY noise between DC and ~100 Hz. But today I saw no evidence of such behaviour. So I decided against changing the frequency.
The linearity of the demodulated error signals around the quadratic maxima of the TRY level was checked. I did not, however, investigate in detail the frequency-dependent offset Koji has reported in his elog.
After this work, the TRY level is at 0.95. This is commensurate with the MC trans level being lower by ~7% relative to July 2018. Furthermore, the ASS servo is able to return to TRY~0.95 with a time-constant of ~5 seconds in response to misalignment of the cavity optics. After I investigate the X-arm ASS, I will reset the normalization for TRX and TRY.
Update 645pm: In the spirit of general IFO recovery, I re-centered the ITM and ETM oplev spots, and also the IR beam on the IPPOS QPD to mark the new input pointing alignment (the spot is slightly lower on the AS camera than what I remember). I then tweaked the XARM transmission to maximize it, and re-set the TransMon normalization. I edited the normalization script to comment out the normalizing of the TransMon QPD gains as the QPDs are in some kind of indeterminate state now. Attachment #2 shows the current status, you can also see the normalization being reset. LSC mode disabled for overnight.
Once the XARM ASS is also checked out, I propose moving back to locking the DRMI / PRFPMI configs.
After this activity, the DC bias voltage required on ETMX to restore good X arm cavity alignment has changed by ~1.3 V. Assuming a full actuation range of 30 mrad for +/- 10 V, this implies that the pitch alignment of the stack has changed by ~2 mrad? Or maybe the suspension wires shifted in the standoff grooves by a small amount? This is ~x10 larger than the typical change imparted while working on the table, e.g. during a vent.
Main point is that this kind of range requirement should probably be factored in when thinking about the high-voltage coil driver actuation.
We unstuck ETMX by shaking the stack. Most effective was to apply large periodic human sized force to the north STACIS mounts.
you have to use a BS with a larger wedge angle (5 arcmin ~ 1 mrad) so that the beams don't overlap on the camera
After the two earthquakes, I collected some data by dithering the optic and recording the QPD readings. Today, I set up scripts to process the data and then train networks on this data. I have pushed all the code to github. I attempted to train a bunch of networks on the new data to test if the code was alright but realised quickly that, training on my local machine is not feasilble at all as training for 10 epochs took roughly 6 minutes. Therefore, I have placed a request for access to the cluster and am waiting for a reply. I will now set up a bunch of experiments to tune hyperparameters for this data and see what the results are.
Trainng networks with memory
I set up a network to handle input volumes (stacks of frames) instead of individual frames. It still uses 2D convolution and not 3D convolution. I am currently training on the new data. However, I was curious to see if it would provide any improved performance over the results I put up in the previous elog. After a bit of hyperparameter tuning, I did get some decent results which I have attached below. However, this is for Pooja's old data which makes them, ah, not so relevant. Also, this testing isn't truly representative because the test data isn't entirely new to the network. I am going to train this network on the new data now with the following objectives (in the following steps):
I hope this looks alright? Rana also suggested I try LSTMs today. I'll maybe code it up tomorrow. What I have in mind- A conv layer encoder, flatten, followed by an LSTM layer (why not plain RNNs? well LSTMs handle vanishing gradients, so why the hassle).
The quoted elog has figures which indicate that the network did not learn (train or generalize) on the used data. This is a scary thing as (in my experience) it indicates that something is fundamentally wrong with either the data or model and learning will not happen despite how hyperparameters are tuned. To check this, I ran the training experiment for nearly 25 hyperparameter settings (results here)with the old data and was able to successfully overfit the data. Why is this progress? Well, we know that we are on the right track and the task is to reduce overfitting. Whether, that will happen through more hyperparameter tuning, data collection or augmentation remains to be seen. See attachments for more details.
Why is the fit so perfect at the start and bad later? Well, that's because the first 90% of the test data is the training data I overfit to and the latter the validation data that the network has not generalized well to.
I came across a paper (see reference) where they have used DAOPHOT, an astronomical software tool developed by NOAO, to study the point scatterers in LIGO test masses using images of varying exposure times. I'm going through the paper now. I think using this we can analyze the MC2 images and make some interesting observations.
Reference: L.Glover et al., Optical scattering measurements and implications on thermal noise in Gravitational Wave detectors test-mass coatings Physics Letters A. 382. (2018)
The beam splitter (BS1-1064-33-2037-45S) that is currently being used has an antireflection coating on the second surface and a wedge of less than 5 arcmin; yet it leads to ghosting as shown in the figure attached (courtesy: Thorlabs). I'm also attaching its spec sheet I dug up on internet for future reference.
I came across pellicle beamsplitters, that are primarily used to eliminate ghost images. Pellicle beamsplitters have a few microns thick nitrocellulose layer and superimpose the secondary reflection on the first one. Thus the ghost image is eliminated.
Should we go ahead and order them? (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=898
I modified the autolocker code I wrote to read from a .yaml configuration file instead of commandline arguements (that option still exists if one wishes to override what the .yaml file contains). I have pushed the code to github. I started reading about MCMC and will put up details of the remaining part of the work ASAP.
P.P.S. He also said that it would not do to have command line arguments as the main source from which parameters are procured and that .yml files ought to be used instead. I will make that change asap.
At first, we noticed that the face OSEMs showed nearly zero variation.
We tried unsticking it through the usual ways of putting large excitations through AWG into the pit/yaw/side DOFs. This produced only ~0.2 microns of motion as seen by the OSEMs.
After the stack shake, we used the IFO ALIGN sliders to get the oplev beam back on the QPD.
The ETMX sensor trends observed before and after the earthquake are attached.
** plots deleted; SOMEONE, tried to take raster images and turn them into PDF as if this would somehow satisfy our vetor graphics requirement. Boo. lpots must be actual vector graphics PDF
In fact, ETMX was not stuck until the M7.1 EQ today. After that it got stuck, but during the after shocks, all the OSEMs occasionally showed full swing of the light levels. So I believe the magnets are OK.
- ITM unstuck now
- IMC briefly locked at TEM00
A series of aftershocks came. I could unstick ITMX by turning on the damping during one of the aftershocks.
Between the aftershocks, MC1~3 were aligned to the previous dof values. This allowed the IMC flashing. Once I got the lock of a low order TEM mode, it was easy to recover the alignment to have a weak TEM00.
Now at least temporarily the full alignment of the IMC was recovered.
Koji came to the lab to align the IMC/IFO, but found the mirrors are dancing around. Kruthi told me that there was M7.1 EQ at Ridgecrest. Looks like there are aftershocks of this EQ going on. So we need to wait for an hour to start the alignment work.
ITMX and ETMX are stuck.
And finally, a network is trained!
Result summary (TLDR :-P) : No memory was used. Model trained. Results were garbage. Will tune hyperparameters now. Code pushed to github.
More details of the experiment:
What I saw
What I think is going wrong-
Well, what now?
I got to speak to Gabriele about the project today and he suggested that if I am using Rana's memory based approach, then I had better be careful to ensure that the network does not falsely learn to predict a sinusoid at all points in time and that if I use the frame wise approach I try to somehow incorporate the fact that certain magnitudes and frequencies of motion are simply not physically possible. Something that Rana and Gautam emphasized as well.
So Cal Earthquake. All suspension watchdogs tripped.
Tried to recover the OSEM damping.
=> The watchdogs for all suspensions except for ITMX were restored. ITMX seems to be stuck. No further action by me for now.
There was a magnitude 6.6 earthquake just a few minutes ago. I am attaching photographs of the monitor feeds for reference here. Is there a standard protocol to be followed in this situation? I'm looking through the wiki now.
Further, the IMC seems to be misaligned and is not locking! As Koji has let me know, I really hope this is not too serious and can be fixed easily.
Tried collecting data today. Was unable to keep the camera_server code running for any length of time as it threw segfaults. Will take a shot again tomorrow.
The GigE is focused now (judged by eye) and I have closed the lid. I'm attaching a picture of the MC2 beam spot, captured using GigE at an exposure time of 400µs.
What was the solution to resolving the flaky video streaming during the alignment process????
-> I think, the issue was with either the poor wireless network conection or the GigE-PoE ethernet cable.
Turns out, focusing the GigE is actually a bit tricky. With pylon, everytime I change the exposure or the focus, I'm running into the error I had mentioned earlier in one of my elogs; so I tried using the python scripts to interact with the GigE. But whenever I try to change the focal plane distance by rotating the lens coupler, the ethernet cable connection becomes loose and the camera server needs to be relaunched every now and then. Also, everytime we want to change the distance between the lenses, the telescope needs to be dismantled and refocused again. I'll try to come up with a better telescope design for this.
Yesterday, I had focused the GigE using a low exposure time and small aperture of iris, to make sure that we are actually seeing a sharp image of the beam spot. I'm attaching a picture of the beam spot I had clicked while focusing it, unfortunately, I forgot to take a picture after I had focused it completely. I'm also attaching a picture of the final setup for future reference.
Yesterday night, Rana asked me to lock the MC2. I figured that the PSL shutter was closed; I just opened it and was able to see the beam spot on the analog camera screen.
A question was raised as to how much passive filtering we benefit from if we pick off the local oscillator beam for BHD from the PRC. I did some simplified modeling of this. For the expected range of arm cavity round trip losses (20-50 ppm), I think that the 40m CARM pole will be between 75-85 Hz. The corresponding recycling gain will be 40-50, with the current PRM. I assumed 1000 ppm loss inside the PRC. The net result is that, assuming the single pole coupled cavity response, we will get ~8-9 dB of filtering at ~200 Hz of the intensity noise of the input laser field to the interferometer if we pick the LO beam off from the PRC (e.g. PR2 transmission), instead of picking it off before.
The next questions are: (i) can we do a sufficiently good job of achieving the required RIN stability on the LO field for BHD without relying on the passive filtering action of the PRC? and (ii) is the benefit of the PRC filtering ruined in the process of routing the LO field from wherever the pickoff happens to the BHD setup?
The latest in my fling with the PMC. Though PMC trans is back to nominal levels (~0.713 V), we'd still like to understand the PMC noise.
Last time, I took some spectra with the RF probe (Agilent 41800A). I had already measured the PDH error signal by sweeping the PZT at ~1 Hz. The notebook I used for analysis has been updated in /users/aaron/analysis/PDH_calibrate.ipynb. The analysis was the following:
There are a few problems remaining:
In preparation for the ASS debugging, I decided to check out the beam path on the EY table. In order to be able to do this, I had to setup the POY locking to trigger on AS110 instead of TRY (as is usual for this kind of debugging). Then I could poke an IR card in the beam path without destroying the lock.
There are two irides in the beam path immediately between the vacuum window and the harmonic separator that splits off the IR and green beams. I found that the beam was in fact getting clipped on both of them. It was also somewhat off center on a 2" beamsplitter that sends half of the light to the QPD (currently decommissioned). The purpose of these irides are (I think) to eliminate some ghost reflections of the green beam and also the Oplev beam. I opened up the irides until I felt that there wasn't any more clipping of the IR beam, but the appropriate ghost beams were still getting caught.
I also re-aligned the beam onto the TRY Thorlabs PD so as to better center it on the active area. In summary, the result of this work was that the TRY level went from ~0.6 to ~0.93. There may still be some scope for optimizing this - I tried running the Y-arm ASS scripts, and already, the loops don't run away any more. I'll do the systematic analysis of the servo anyways. But given that the IMC Trans lev el used to be ~15,500 counts and is now ~14,500 counts, I think ~7% drop in TRY level is in line with what we "expect" (assuming the pre-power-degradation TRY level was 1.000).
Note that these irides were installed (I think) by Yuki, and so cannot explain the ASS anomalies of July 2018 (i.e. it does not exonerate in-vacuum clipping of the beam, as Koji had already verified that the in-air path was clean back then).