40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Category Subject
13920   Wed Jun 6 14:36:15 2018 gautamUpdateLSCTRX clipping

For some time now, I've been puzzled by the unreliability of the ASS_X dither alignment servo. Leaving the servo on, TRX often begins to decay to a lower value, and even after freezing the dither at the maximum TRX values, I can manually align the mirrors to increase TRX. We have suspected some kind of clipping in the TRX path that is responsible for this behaviour. Today I decided to investigate this a bit further. To have the arm locked and to inspect the beam, we have to change the locking trigger - TRX is what is normally used, but I misaligned the Y arm completely, and used AS110 as a trigger instead. There is some strangeness in the triggering topology, but this deserves a separate elog.

Once the arm was locked (and relocks using the AS110 trigger in the event of an unlock), I was able to trace the beampath on the EX table with an IR card. The TRX beam is rather large and weak, so it is hard to see, but as best as I can tell, the only real danger of clipping (or perhaps the beam is already clipped) is on the final steering mirror before the beam hits the (Thorlabs) PD. Steve/Pooja are working on getting a photo of this, and will upload it here shortly. Options to mitigate this:

1. Use the harmonic separator to steer the beam lower, and center it on the 1" steering mirror. However, this could possibly lead to clipping on some of the upstream lenses.
2. Raise the height of the 1" steering mirror by 0.25". However, this would require a custom 3/4" dia post height or some shims, which I am not sure is in line with our optomechanic mounting practises.
3. Use a 2" mirror instead of a 1" mirror.

The EX QPD has stopped working since the Acromag install. If it were working, we wouldn't have to rely on the alternate triggering with AS110 and instead just use the QPD as TRX, while we debug the Thorlabs PD path.

13921   Wed Jun 6 14:50:25 2018 gautamUpdateGeneralLSC triggering

I though that the "C1LSC_TRIG_MTRX" MEDM screen completely controls the triggring of LSC signals. But today while trying to trigger the X-arm locking servo on AS110 instead of TRX, I found some strange behaviour. Summary of important points:

1. Even though the servo was supposed to be triggered on AS110, the act of me blocking the beam on the EX table destroyed the lock. I verified the correlation between me blocking the beam and the lock being destroyed by repeating the blocking at least 10 times at different locations along the beam path (to make sure I wasn't accidentally clipping the Oplev beam for example).
2. Investigating further, I found that me turning off the TRX signal digitally also deterministically led to the X arm lock being lost. To be clear, the TRX DC element in the trigger matrix was 0.
3. Confirmed that TRX wasn't involved in any way in the locking servo (I was checking for normalization of the PDH error signal by the DC transmission value, but this is not done). To do this, I locked the arm, and then turned all elements corresponding to TRX in the PowNorm matrix to 0. Then I disabled the locking servo and re-enabled it, and the lock was readily re-acquired readily.

All very strange, not sure what's going on here. The simulink model diagram also didn't give me any clues. Need's further investigation.

Attachment 1: LSC_TRIG.png
13922   Wed Jun 6 15:12:29 2018 KiraUpdatePEMparts from lab

Got this 1U box from the Y arm that we could potentially use (attachment 1). It doesn't have handles on the front but I guess we could attach them if necessary. Attachment 2 is a switch that could be used instead of a light up switch, but now we need to add LEDs on the front panel that indicate that the switch is functional. Attachment 3 is a terminal block that we can use to attach the 16 gage wire to since it is thick and attaching it directly to the board would be difficult. If this is alright to use then I'll change up my designs for the front panel and PCB to accomodate these parts.

Attachment 1: IMG_20180606_141149.jpg
Attachment 2: IMG_20180606_141851.jpg
Attachment 3: IMG_20180606_141912.jpg
13924   Thu Jun 7 10:26:36 2018 keerthanaUpdatePSLobserving the resonance signal corresponding to the injected frequency.

(Johannes, Koji, Keerthana)

The PLL loop ensures that the frequency difference between the PSL laser and the AUX laser is equal to the frequency we provide to the Local Oscillator (LO) with the help of a Marconi. Only a small pick off part of both the AUX and PSL lasers are going to the PLL loop. The other part of both the lasers are going to the interferometer. Before entering into the optical fibre, the AUX laser passes through an AOM which changes its frequency by an amount of 80MHz. When the PLL is locked, the frequency coming out of the PLL will be equal to the frequency set up in the Marconi (fm). When it passes through AOM, the frequency becomes fdiff = fm ±80 MHz. If this frequency beam and the PSL laser beam is aligned properly, and if this frequency is equal to the product of an integer and the free spectral range of the cavity, this will resonate in the cavity.  Then we expect to get a peak in the ETM transmission spectrum corresponding to the frequency we injected through the optical Fibre.

Through out the experiment we need to make sure that the PSL is locked. Thus, the signal detected by the photo detector when only PSL is resonating inside the cavity, act as a DC signal. Then we give a narrow scan to the Marconi. When fdiff = N*FSRy this condition is satisfied, we will observe a peak in the output. Here FSRy  is the free spectral range of the cavity which is approximately equal to 3.893 MHz.

Yesterday afternoon, Johannes, Koji and myself tried to observe this peak. We aligned the cavity by observing the output signal from the AS100 photo detector. We made the alignment in such a way that the intensity output getting from this photo detector is maximum. We used a Spectrum analyser to see the output. After that we connected a photo detector to collect the YEND transmission signal from the ETM mirror. We used a lens to focus this directly to the photodetector. Then we connected this photodetector to the spectrum analyser, which was located near the AS table. We took a large cable to meet this purpose. But still the cable was not lengthy enough, so we joined it with another cable and finally connected it with the spectrum analyser. Then we gave a scan to the Marconi from 51 MHZ to 55 MHz. We repeated this experiment with a scan of 55 MHz to 59 MHz also. We repeated this a few times, but we were not able to see the peak.

We assume that this can be because of some issue with the alignment or it can be because of some issue with the photo detector we used. We would like to repeat this experiment and get the signal properly.

I am attaching a flow chart of the setup and also a picture of the mirrors and photo detector we inserted in the Y-End table.

Attachment 1: photodetector_alignment.jpg
Attachment 2: design1.PNG
13925   Thu Jun 7 12:20:53 2018 gautamUpdateCDSslow machine bootfest

FSS slow wasn't running so PSL PZT voltage was swinging around a lot. Reason was that was c1psl unresponsive. I keyed the crate, now it's okay. Now ITMX is stuck - Johannes just told be about an un-elogged c1susaux reboot. Seems that ITMX got stuck at ~4:30pm yesterday PT. After some shaking, the optic was loosened. Please follow the procedure in future and if you do a reboot, please elog it and verify that the optic didn't get stuck.

Attachment 1: ITMX_stuck.png
13926   Thu Jun 7 14:35:26 2018 keerthanaUpdateelogTable- useful for doing the scanning.

I think this table will help us to fix the scanning range of the Marconi frequency. This will also help in predicting the position of the resonance peak corresponding to the injected frequency.

fdiff = fm ±80 MHz ;                     fdiff = N*FSRy ;              FSRy = 3.893 MHz.

 N = Integer number fdiff =injected fm = Marconi frequency 1 3.893 76.107 2 7.786 72.214 3 11.679 68.321 4 15.572 64.428 5 19.465 60.535 6 23.34 56.66 7 27.251 52.749 8 31.144 48.856 9 35.037 44.963 10 38.93 41.07 11 42.79 37.21 12 46.716 33.284 13 50.609 29.391
13927   Thu Jun 7 16:15:03 2018 gautamUpdateLSCTRX clipping

I opted for the quickest fix - I raised the height of the offending steering mirror using a 0.25" shim. In the long term, we can get a taller post machined. After raising the mirror height, I then checked the DC centering of the spot on the DC PD using a scope.

Looking at the performance of the X arm ASS, I no longer see the strange oscillatory behaviour I described in my previous post . Moreover, the TRX level was ~1 before be raising the steering mirror - but it is now ~1.2. So we were certainly losing some power.

13928   Thu Jun 7 20:19:53 2018 poojaUpdate

Just to inform, I'm working in optimus to develop python code to train the neural network since it requires a lot of memory.

13929   Thu Jun 7 20:21:15 2018 KojiUpdateComputer Scripts / Programs/cvs/cds Backup in danger

Local backup on chiara seems not working since Nov 19, 2017.
/opt/rtcds/caltech/c1/scripts/backup/localbackup.log

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!!!

13930   Thu Jun 7 22:36:09 2018 not keerthanaUpdatePSLobserving the resonance signal corresponding to the injected frequency.

I worked a bit on the PSL table today

13931   Fri Jun 8 00:36:54 2018 gautamUpdatePSLobserving the resonance signal corresponding to the injected frequency.

It isn't clear to me in the drawing where the Agilent is during this measurement. Over 40m of cabling, the loss of signal can be a few dB, and considering we don't have a whole lot of signal in the first place, it may be better to send the stronger RF signal (i.e. Marconi pickoff) over the long cable rather than the weak beat signal from the Transmission photodiode.

13932   Fri Jun 8 01:08:22 2018 johannesUpdatePSLFirst light of AUX at YEND

Among the things that we hadn't taken care of yesterday before beginning to look for transmission signals were the polarization of the AUX beam on the AS table and optimizing the PLL feedback. The AUX beam is s-polarized on the PSL table (choice due to availablility of mirrors), and I added a half waveplate in front of the fiber to match it's axes. I placed another half-waveplate at the fiber output and send the reflection port of a PBS cube onto a PDA1CS photodetector. By alternatingly turning the waveplates I minimized the reflected light, giving strongly p-polarized light on the AS table for best results when interfering with the IFO beam. I wiggled the fiber and found no strong dependency of the output polarization on fiber bending. Attachment 2 shows the current layout.

The beat signal between AUX and PSL table is at -20dBm, and I adjusted the PLL gain and PI-corner to get reliable locking behavior. I think it's a good idea to keep the AUX beam on the AS table blocked while it's not in use, and only unblock it when it is phaselocked to avoid a rogue beam with no fixed phase relation to the PSL in the IFO.I blocked the beam after completing this work today.

I used the signal chain that Keerthana, Koji, and I set up yesterday to look for mode flashed of the AUX light in the YARM using the RF beat with the PSL carrier in transmission. To align the AUX beam to the arm the following steps were performed:

1. Using a spectrum analyzer to look at the RF power at the target frequency between frequency-shifted AUX beam and PSL carrier on AS110, align the beam using the mirror pair closest to the fiber coupler for maximum signal.
2. Initiate a sweep of the PLL LO frequency sourced by the Marconi using GPIB scripts over about 1 FSR. A strong peak was visible at ~31.76 MHz offset frequency
3. Tune and hold LO frequency (in this case at 48.2526 MHz) such that AUX beam resonates in the arm. Optimize alignment by maximizing RF signal on PD in transmission.

This was followed by a sweep over two full FSRs. Attachment #1 shows the trace recorded by the AG4395 using the max data hold setting during the sweep. Essentially the beat between AUX and PSL carrier traced out the arm's transmission curve. At minimum transmission there was still a ~82dB beat on the transmission PD visible.

The YEND QPD is currently blocked and sees no light.

Attachment 1: AG4395A_07-06-2018_205019.pdf
Attachment 2: PSL_AUX_SETUP.pdf
Attachment 3: AS_AUX_SETUP.pdf
13933   Fri Jun 8 01:58:56 2018 gautamUpdateLSCDRMI locking attempt again

Given the various changes to the IFO config since last Thursday when I was last able to lock the DRMI, I wanted to try once again tonight. However, I had no success. By my judgement, the alignment is fine as judged by looking at mode flashes on the cameras. However, despite following the usual alignment procedures, I did not get a single lock in tonight.

Perhaps we can use a flip mount on the BS that combines the PSL and AUX beams on the AS table, so we have the option of recovering the usual IFO config when we so desire - while Jon needs the SRC locked for his measurement, it would be nice to not have to figure out the correct demod phases etc each time there is a change in the optical setup of the AUX beam.

13934   Fri Jun 8 14:40:55 2018 c1lscUpdateCDSi am dead
Attachment 1: 31.png
13935   Fri Jun 8 20:15:08 2018 gautamUpdateCDSReboot script

Unfortunately, this has happened (and seems like it will happen) enough times that I set up a script for rebooting the machine in a controlled way, hopefully it will negate the need to repeatedly go into the VEA and hard-reboot the machines. Script lives at /opt/rtcds/caltech/c1/scripts/cds/rebootC1LSC.sh. SVN committed. It worked well for me today. All applicable CDS indicator lights are now green again. Be aware that c1oaf will probably need to be restarted manually in order to make the DC light green. Also, this script won't help you if you try to unload a model on c1lsc and the FE crashes. It relies on c1lsc being ssh-able. The basic logic is:

1. Ask for confirmation.
2. Shutdown all vertex optic watchdogs, PSL shutter.
3. ssh into c1sus and c1ioo, shutdown all models on these machines, soft reboot them.
4. ssh into c1lsc, soft reboot the machine. No attempt is made to unload the models.
5. Wait 2 minutes for all machines to come back online.
6. Restart models on all 3 vertex FEs (IOPs first, then rest).
7. Prompt user for confirmation to re-enable watchdog status and open PSL shutter.
Attachment 1: 31.png
13936   Sun Jun 10 03:46:38 2018 KojiUpdateIOOWFS HEAD SW confusion

I was checking on the slow machine channels and found something I could not understand.

On the IOO WFS HEAD screen, there are two sets of 4 switches (magenta rectangles in Attachment 1) labeled 2/4/8/16dB.
But as far as I could confirm with the WFS demod (D980233) and WFS head (D980012) drawings, they are the gain (attenuation) switches for the individual segments.
Their epics variable names are "C1:IOO-WFS1_SEG1_ATTEN", "C1:IOO-WFS1_SEG2_ATTEN", etc...

I confirmed the switches are alive (effective), and they are not all ON or OFF. I wonder what is the real situation there...

Attachment 1: C1IOO_WFS_HEADS.png
13937   Sun Jun 10 15:04:33 2018 poojaUpdateCamerasDeveloping neural network

Aim: To develop a neural network in order to correlate the intensity fluctuations in the scattered light to the angular motion of the test mass. A block diagram of the technique employed is given in Attachment 1.

I have used Keras to implement supervised learning using neural network (NN). Initially I had developed a python code that converts a video (59 sec) of scattered light, after an excitation (sine wave of frequency 0.2 Hz) is applied to ETMX pitch, to image frames (of size 480*720)  and stores the 2D pixel values of 1791 images frames captured into an hdf5 file. This array of shape (1791,36500) is given as an input to the neural network. I have tried to implement regular NN only, not convolution or recurrent NN. I have used sequential model in Keras to do this. I have tried with various number of dense layers and varied the number of nodes in each layer. I got test accuracy of approximately 7% using the following network. There are two dense layers, first one with 750 nodes with a dropout of 0.1 ( 10% of the nodes not used) and second one with 500 nodes. To add nonlinearity to the network, both the layers are given an activation function of tanh. The output layer has 1 node and expects an output of shape (1791,1). This model has been compiled with a loss function of categorical crossentropy, optimizer = RMSprop. We have used these since they have been mostly used in the image analysis examples. Then the model is trained against the dataset of mirror motion. This has been obtained by sampling the cosine wave fit to the mirror motion so that the shapes of the input and output of NN are consistent. I have used a batch size ( number of samples per gradient update) = 32 and epochs (number of times entire dataset passes through NN) = 20. However, using this we got an accuracy of only 7.6%.

I think that the above technique gives overfitting since dense layers use all the nodes during training apart from giving a dropout. Also, the beam spot moves in the video. So it may be necessary to use convolution NN to extract the information.

The video file can be accesses from this link https://drive.google.com/file/d/1VbXcPTfC9GH2ttZNWM7Lg0RqD7qiCZuA/view.

Gabriele told us that he had used the beam spot motion to train the neural network. Also he informed that GPUs are necessary for this. So we have to figure out a better way to train the network.

gautam noon 11Jun: This link explains why the straight-up fully connected NN architecture is ill-suited for the kind of application we have in mind. Discussing with Gabriele, he informed us that training on a GPU machine with 1000 images took a few hours. I'm not sure what the CPU/GPU scaling is for this application, but given that he trained for 10000 epochs, and we see that training for 20 epochs on Optimus already takes ~30minutes, seems like a futile exercise to keep trying on CPU machines.

Attachment 1: nn_block_diag_2.pdf
13938   Mon Jun 11 11:45:13 2018 keerthana UpdateelogComparison of the analytical and finesse values of TMS and FSR.
 Quantity Analytical Value Finesse Value Percentage Error Free Spectral range (FSR) 3.893408 MHz 3.8863685 MHz 0.180 % Transverse Mode Spacing (TMS) 1.195503 MHz 1.1762885 MHz 1.607 %

The values obtained from both analytical and finesse solution is given in the above table along with the corresponding percentage errors.finesse1.pdf

The parameters used for this calculation are listed below.

 Parameter Value length of the cavity (L) 38.5 m Wavelength of the laser beam ($\lambda$) 1064 nm Radius of curvature of ITM (R1) $\infty$ Radius of curvature of ETM (R2) 58 m

The cavity scan data obtained from Finesse is also attached here.

Attachment 1: finesse1.pdf
13939   Mon Jun 11 13:55:33 2018 keerthanaUpdateGeneralProject Updates

As of now, I have made the codes needed to sweep the marconi frequency for taking the cavity scan data, the photo diode at the y-end is conected to the spectrum analyser already and I also have the finesse simulation of the Ideal Fabry-perot cavity. By seeing my last elog entry, Gautam suggested me that I need to take a different approach for estimating the FSR and TMS value from the Finesse graph. That is, by using least square fit models. Now I am trying to do that and get a better estimate of the error values. Based on my understanding I am dividing this project into various tasks.

1. Getting a better estimate of the error value by using least square fits. Also plotting a graph of frequency Vs mode number and finding the value of Free Spectral Range from its slop.

2. Inserting zernike polynomials to the Finesse simulation and with the help of least square fit, plotting the graph of frequency Vs mode number. Understanding the shifts from the Ideal graph we obtained from step 1. Using this data, plotting the phase map corresponding to this.

3. Repeating step 2 by taking different zernike polynomials and creating a data base which will be useful for the analysis of the real data. This will also prepare me to do the fitting models easily.

4. Collecting data from the IFO and applying these fitting models to it. Finding the set of zernike polynomials which are similar to the actual fugure error of the mirror. Plotting the Phase map corresponding to those zernike polynomials.

If you feel that there is some mistake in the steps, please correct me. It will be really helpful!

13940   Mon Jun 11 17:18:39 2018 poojaUpdateCamerasCCD calibration

Aim: To calibrate CCD of GigE using LED1050E.

The following table shows some of the specifications for LED1050E as given in Thorlabs datasheet.

 Specifications Typical maximum ratings DC forward current (mA) 100 Forward voltage (V) @ 20mA (VF) 1.25 1.55 Forward optical power (mW) 1.6 Total optical power (mW) 2.5 Power dissipation (mW) 130

The circuit diagram is given in Attachment 1.

Considering a power supply voltage Vcc = 15V, current I = 20mA & forward voltage of led VF = 1.25V, resistance in the circuit is calculated as,

R = (Vcc - VF)/I = 687.5$\ohm$$\ohms$$\Omega$

Attachment 2 gives a plot of resistance (R) vs input voltage (Vcc) when a current of 20mA flows through the circuit. I hope I can proceed with this setup soon.

Attachment 1: led_circuit.pdf
Attachment 2: R_vs_V.pdf
13941   Mon Jun 11 18:10:51 2018 Koji UpdateelogComparison of the analytical and finesse values of TMS and FSR.

Hmm? What is the definition of the percentage error? I don't obtain these numbers from the given values.
And how was the finesse value obtained from the simulation result? Then what is the frequency resolution used in Finesse simulation?

13942   Mon Jun 11 18:49:06 2018 gautamUpdateCDSc1lsc dead again

Why is this happening so frequently now? Last few lines of error log:

[  575.099793] c1oaf: DAQ EPICS: Int = 199  Flt = 706 Filters = 9878 Total = 10783 Fast = 113
[  575.099793] c1oaf: DAQ EPICS: Number of Filter Module Xfers = 11 last = 98
[  575.099793] c1oaf: crc length epics = 43132
[  575.099793] c1oaf:  xfer sizes = 128 788 100988 100988
[240629.686307] c1daf: ADC TIMEOUT 0 43039 31 43103
[240629.686307] c1cal: ADC TIMEOUT 0 43039 31 43103
[240629.686307] c1ass: ADC TIMEOUT 0 43039 31 43103
[240629.686307] c1oaf: ADC TIMEOUT 0 43039 31 43103
[240629.686307] c1lsc: ADC TIMEOUT 0 43039 31 43103
[240630.684493] c1x04: timeout 0 1000000
[240631.684938] c1x04: timeout 1 1000000
[240631.684938] c1x04: exiting from fe_code()

I fixed it by running the reboot script.

Attachment 1: 36.png
13943   Mon Jun 11 19:16:49 2018 keerthanaUpdateelogComparison of the analytical and finesse values of TMS and FSR.

The percentage error which I found out =[(analytical value - finesse value)/analytical value]*100

But inorder to find the finesse value, I just used curser to get the central frequency of each peak and by substracting one from the other I found TMS and FSR.

The resolution was 6500 Hz. Thus, it seems that this method is not actually reliable. I am trying to find the central frequency of each mode with the help of lorentzian fits. I am attaching a fit which I did today. I have plotted its residual graph also.

I am uploading 4 python scripts to the github.

1. Analytical Solution

2. Finesse model- cavity scan

3. Finesse model- fitting

4. Finesse model- residual

 Quote: Hmm? What is the definition of the percentage error? I don't obtain these numbers from the given values. And how was the finesse value obtained from the simulation result? Then what is the frequency resolution used in Finesse simulation?

fitting_1.pdf

Attachment 1: fitting_1.pdf
13944   Mon Jun 11 22:05:03 2018 KojiUpdateelogComparison of the analytical and finesse values of TMS and FSR.

> 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.

13945   Mon Jun 11 22:18:18 2018 keerthanaUpdateelogComparison of the analytical and finesse values of TMS and FSR.

Oopss !! I made a mistake while taking the values from my notes. Sorry.

 Quote: > 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.

13946   Mon Jun 11 22:46:24 2018 KojiUpdateIOOWFS HEAD SW confusion

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.

Attachment 1: 180611_IMC_WFS1.pdf
Attachment 2: 180611_IMC_WFS2.pdf
13947   Mon Jun 11 23:22:53 2018 gautamUpdateCDSEX wiring confusion

[Koji, gautam]

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.

13948   Tue Jun 12 03:22:25 2018 gautamUpdateLSCAUX laser shuttered

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.

13951   Tue Jun 12 19:27:25 2018 poojaUpdateCamerasCCD calibration

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 $\Omega$.

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.

 Input voltage (Vcc in V) Optical power 0 (dark reading) 60 nW 15 68 $\mu$W 18 82.5 $\mu$W 20 92 $\mu$W

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.

Attachment 1: IMG_20180612_163831.jpg
13952   Wed Jun 13 01:02:40 2018 gautamUpdateLSCReliable and repeatable 1f DRMI locking

[koji, gautam]

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:

• Initial alignment procedure was as usual - use arms+ASS to align ITMs, and then PRMI carrier+ASS to align PRM and BS.
• Found the appropriate gains and demod phases.
• Measured loop TFs - PRCL is a big mystery. Used these to finalize loop gains.
• Ran some sensing lines.
• Whitened DRMI PDs for a calibrated "low-noise" spectrum (although the coils were not de-whitened).

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).

13953   Wed Jun 13 11:17:40 2018 gautamUpdateLSCPRCL loop shape anomaly

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....

 Quote: Measured loop TFs - PRCL is a big mystery. Used these to finalize loop gains.
Attachment 1: PRCL_12Jun2018_WeirdShape.pdf
13954   Wed Jun 13 11:59:03 2018 keerthanaUpdateelogcommand line enabled code for frequency scanning

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.

13955   Wed Jun 13 12:21:09 2018 gautamUpdateALSPDFR laser checkout

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.

13956   Wed Jun 13 18:08:36 2018 keerthanaUpdate Finesse code for cavity scan

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.

 Quote: 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.
Attachment 1: finesse1.pdf
Attachment 2: finesse2.pdf
13957   Wed Jun 13 22:07:31 2018 gautamUpdateALSBeatMouth PDFR measurement

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.
Attachment 1: IMG_7056.JPG
Attachment 2: BeatMouthPDFR.pdf
Attachment 3: BeatMouth_PDFRdata.tgz
13958   Wed Jun 13 23:23:44 2018 johannesUpdateCDSEX wiring confusion

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:

 TYPE Total Available now Available after ADC 24 2 14 DAC 16 8 12 BIO sinking 16 7 7 BIO sourcing 8 8 8

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

Attachment 1: c1auxex_channels.pdf
Attachment 2: XEND_slow_wiring.pdf
13959   Thu Jun 14 00:40:42 2018 gautamUpdateLSCPRCL loop shape anomaly

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

Quote:
 Quote: Measured loop TFs - PRCL is a big mystery. Used these to finalize loop gains.

13960   Thu Jun 14 00:46:09 2018 ranaUpdateIOOWFS HEAD SW confusion

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.

 Quote: 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.

13961   Thu Jun 14 10:41:00 2018 gautamUpdateCDSEX wiring confusion

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.

Quote:

 TYPE Total Available now Available after ADC 24 2 14

13962   Thu Jun 14 13:29:51 2018 gautamUpdateGeneralPSL shutter closed, all optics misaligned

[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.

13963   Thu Jun 14 15:21:58 2018 gautamUpdateComputer Scripts / Programs/cvs/cds Backup in danger

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

controls@chiara|~> lsblk 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.
 Quote: Local backup on chiara seems not working since Nov 19, 2017. /opt/rtcds/caltech/c1/scripts/backup/localbackup.log 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!!!

13964   Thu Jun 14 15:24:32 2018 SteveUpdatePEM ADC DAC In Line Test Boards are in

We have 6 of these boards now in cabinet E7

 Quote: 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.

Attachment 1: ADC_DAC_in_(1).JPG
13965   Thu Jun 14 15:31:18 2018 johannesUpdateCDSEX wiring confusion

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.

Attachment 1: XEND_slow_wiring.pdf
Attachment 2: c1auxex_channels.pdf
13966   Thu Jun 14 18:09:24 2018 gautamUpdateLSCReliable and repeatable 1f DRMI locking

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

Attachment 1: DRMI1f_June14.pdf
13967   Thu Jun 14 19:30:12 2018 gautamUpdateGeneralIFO alignment restored

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

13968   Thu Jun 14 22:45:05 2018 johannesUpdateGeneralAUX beam SRC alignment

[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.
13969   Fri Jun 15 00:53:21 2018 gautamUpdateLSCCalibrated MICH spectrum

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.

 Quote: 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.
Attachment 1: C1NB_disp_40m_MICH_NB_2018-06-14.pdf
13971   Fri Jun 15 09:14:42 2018 SteveUpdateGeneralOplev sums

Oplev sums of 240 days.

 Quote: 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. c1susaux, c1aux and c1iscaux crates were keyed as they were un-telnet-able. Single arm locking worked fine, TT alignment was tweaked (as these had drifted due to the ADC failure in c1lsc) to maximize Y arm transmission using the dither servos. Arms weren't staying locked for extended periods of time. I particularly suspected ITMX, as I saw what I judged to be excess motion on the Oplev. @Steve - ITMX and BS HeNes look like they are in need of replacement judging by the RIN (although the trend data doesn't show any precipitous drop in power). If we are replacing the BS/PRM Oplev HeNe, might be a good time to plan the inejction path a bit better on that table. RIN in Attachment #1 has been normalized by the mean value of the OL sum channel. There is now a script to make this kind of plot from NDS in the scripts directory (as I found it confusing to apply different calibrations to individual traces in DTT).

Attachment 1: opSums.png
13972   Fri Jun 15 09:51:55 2018 poojaUpdateCamerasDeveloping neural network

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.

Attachment 1: nn_1.pdf
Attachment 2: nn_2.pdf
13973   Fri Jun 15 14:22:05 2018 gautamUpdateALSBeatMouth PDFR measurement

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.

 Quote: 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.
Attachment 1: BeatMouthPDFR.pdf
Attachment 2: BeatMouth_PDFRdata.tgz
ELOG V3.1.3-