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ID Date Authorup Type Category Subject
  11392   Tue Jul 7 17:22:16 2015 JessicaSummary Time Delay in ALS Cables

I measured the transfer functions in the delay line cables, and then calculated the time delay from that.

The first cable had a time delay of 1272 ns and the second had a time delay of 1264 ns. 

Below are the plots I created to calculate this. There does seem to be a pattern in the residual plots however, which was not expected. 

The R-Square parameter was very close to 1 for both fits, indicating that the fit was good. 

  11395   Wed Jul 8 17:46:20 2015 JessicaSummaryGeneralUpdated Time Delay Plots

I re-measured the transfer function for Cable B, because the residuals in my previous post for cable B indicated a bad fit. 

I also realized I had made a mistake in calculating the time delay, and calculated more reasonable time delays today. 

Cable A had a delay of 202.43 +- 0.01 ns.

Cable B had a delay of 202.44 +- 0.01 ns. 

  11416   Wed Jul 15 17:05:06 2015 JessicaUpdateGeneralBandpass Pre-Filter created

I applied a bandpass filter to the accelerometer huddle data as a pre-filter. The passband was from 5 Hz to 20 Hz. I found that applying this pre-filter did very little when comparing the PSD after pre-filtering to the PSD with no pre-filtering. There was some improvement though, just not a significant amount. For some reason, it also seemed as though the second accelerometer improved the most from pre-filtering the data, while the first and third remained closer to the unfiltered noise. Also, I have not yet figured out a consistent method for choosing passband ripple and stopband attentuation, both of which determine how good the filter is. 

My next step in pre-filtering will be determining a good method for choosing passband ripple and stopband attenuation, along with implementing other pre-filtering methods to combine with the bandpass filter. 

  11421   Thu Jul 16 16:33:56 2015 JessicaUpdateGeneralAdded Bode Plots of Bandpass Filter

I updated the bandpass filter I was using, finding that having different stopband attenuations before and after the passband better emphasized the area from 3 Hz to 20 Hz. I chose a low passband ripple but high stopband attenuation to do this. My passband ripple was 2 dB, the first stopband was 25 dB, and the second stopband attenuation was 40 dB. As can be seen in the filter Magnitude plot, this resulted in a fairly smooth passband and a fairly step dropoff to the stopband, which will better emphasize the region I am trying to isolate. My goal was to emphasize the 3-20 Hz region 10-30 times more than the outside regions. I think I accomplished this by looking at the Bode plot, but I may have chosen the second stopband attenuation to be slightly too high for this. 

  11440   Thu Jul 23 20:54:42 2015 JessicaUpdateGeneralALS Delay Line Box

The front panels for the ALS delay line box came in last week. Some of the holes for the screws were slightly misaligned, so I filed those and everything is now put together. I just need to test both front panels to determine if the SMAs should be isolated or not.


Koji had also suggested making the holes in the front and back panel conical recesses so that flat head screws could be used and would counteract the anodization of the panel and avoid the SMAs being isolated. I think if we did that then conductivity would be ensured throughout the panel and also through the rest of the box. I also think one way we could test this before drilling conical recesses would be to test both front panels now, as one has isolated SMAs and one has conductive SMAs. If the anodization of the panel isolated the SMA regardless, we could potentially figure this out by testing both panels. But, would it also be that it is possible that the isolation of the SMA itself does not matter and so this test would tell us nothing? Is there a better way to test if the SMAs are being isolated or not? Or would this be more time consuming than just drilling conical recesses as a preventative measure?

  11441   Thu Jul 23 20:57:15 2015 JessicaSummaryGeneralApplying Pre-filter to data before IIR Wiener Filtering

I updated my bandpass filter and have included the bode plot below in Figure 1. It is a fourth order elliptic bandpass filter with a passband ripple of 1dB and a stopband attenuation of 30 dB. It emphasizes the area between 3 and 40 Hz.

Below, I applied this filter to the huddle test data. The results from this were only slightly better in the targeted region than when no pre-filter was applied. 

When I pre-filtered the mode cleaner data and then used an IIR wiener filter, I found that the results did not differ much from the data that was not pre-filtered. I'm not sure yet if I'm targeting the right region of this data with my bandpass filter, and will be looking more into choosing a better region. Also, I am only using certain regions of ff when calculating the transfer function, and need to optimize that region also. I uploaded the code I used to make these plots to github.

  11456   Tue Jul 28 20:42:50 2015 JessicaSummaryGeneralNew Seismometer Data Coherence

I was looking at the new seismometer data and plotted the coherence between the different arms of C1:PEM_GUR1 and C1:PEM_GUR2. There was not much coherence in the X arms, Y arms, or Z arms of each seismometer, but there were within the x and y arms of the seismometer.

I think the area we should focus on with filtering is lower ranges, between 0.01 and 0.1, because that it where coherence is most clearly high. It is higher in high frequencies but also incredibly noisy, meaning it probably wouldn't be good to try to filter there. 

  11458   Wed Jul 29 11:15:21 2015 JessicaSummaryLSCPSDs of Arms with seismometer subtraction

Ignacio and I downloaded data from the STS, GUR1, and GUR2 seismometers and from the mode cleaner and the x and y arms. The PSDs along the arms have the most noise at frequencies greater than 1 Hz, so we should focus on filtering in that area. The noise levels start dropping at around 30 Hz, but are still much higher than is seen at frequencies below 1 Hz. However, because the spectra is so low at frequencies below that, Wiener filtering alone injected a significant amount of noise into those frequencies and did not do much to reduce the noise at higher frequencies. Pre-filtering will be required, and I have started implementing a pre-filter, but with no improvements yet. So far, I have tried making a bandpass filter, but a highpass filter may be ideal in this case because so much of the noise is above 1 Hz. 

  11471   Thu Jul 30 18:58:36 2015 JessicaUpdateGeneralALS Delay Line Box Front Panel Testing

I tested both of the front panels (conductive and isolated SMAs) with the ALS Delay Line Box by driving extremely close frequencies through the cables. By doing this, we would expect that a spike would show up in the PSD if there was crosstalk between the cables. 

In the plots below, for the conductive panel, the frequencies used were

               X Arm:  22.329 MHz                        Y Arm: 22.3291 MHz        

For the isolated panel, the frequencies were

              X Arm: 22.294 MHz                         Y Arm: 22.2943 MHz    

This gives a difference of 100 Hz for the conductive panel and 300 Hz for the isolated panel. Focusing on these areas of the PSD, it can be seen that in the Y Arm cable there is a very clear spike within 30 Hz of these differences when frequencies are being driven through both cables as opposed to the signal being in only the Y Arm. In the X Arms, the noise in general is higher when both cables are on, but there is no distinct spike at the expected frequencies. This indicates that some sort of crosstalk is probably happening due to the strong spikes in the Y Arm cables.          


  11477   Mon Aug 3 18:19:09 2015 JessicaUpdateGeneralAnodization of front panels accounted for

Previously, I had gotten the same results for the conductive and the isolated front panels. Today, I sanded off the anodized part on the back of the conductive front panel. I checked afterwards with a mulitmeter to ensure that it was indeed conductive through all the SMA connectors. 

I drove a frequency of 29.359 Hz through the X Arm cable and 29.3592 Hz through the Y Arm cable, giving a difference of 200 Hz. Previously, there would only be a spike in the Y Arm at the difference, while the X Arm did not change if the Y arm was on or off. Now that the panel is fully conductive, a spike can also be seen in the X arm, indicating that crosstalk may possibly be happening with this panel, now that the spike corresponds to both the X arm and Y arm. These results are only after one set of data. Tomorrow I'll take two more sets of data with this panel and do a more in depth comparison of these results to what had been previously seen.  

  11484   Thu Aug 6 11:45:01 2015 JessicaUpdateGeneralALS Delay Line front panel testing

Koji had suggested that I sync up the two function generators to ensure that they have the same base frequency and so that crosstalk will actually appear at the expected frequency. After syncing up the two function generators, I drove the following frequencies through each cable:

Conductive SMAs:

     X: 29.537 MHz           Y: 29.5372 MHz

Isolated SMAs:

     X: 29.545 MHz           Y: 29.5452 MHz

Each time, the difference between the frequencies was 200 Hz, so if there was crosstalk, a spike should appear in the PSDs at 200 Hz when frequencies are being driven through both cables simulataneously, but not when just one is on. We very clearly see a spike at 200 Hz in both the X arm and the Y arm with the conductive SMAs, indicating crosstalk. For the front panel with isolated SMAs, we see a spike at 200 Hz when both frequencies are on, but it is much less pronounced than with the conductive SMAs. It seems as though there will be crosstalk using either panel, just less with the isolated SMAs. 

  11491   Tue Aug 11 10:13:32 2015 JessicaUpdateGeneralConductive SMAs seem to work best

After testing both the Conductive and Isolated front panels on the ALS delay line box using the actual beatbox and comparing this to the previous setup, I found that the conductive SMAs improved crosstalk the most. Also, as the old cables were 30m and the new ones are 50m, Eric gave me a conversion factor to apply to the new cables to normalize the comparison.

I used an amplitude of 1.41 Vpp and drove the following frequencies through each cable:
      X: 30.019 MHz          Y: 30.019203 MHz

which gave a difference of 203 Hz. 

In the first figure, it can be seen that, for the old setup with the 30m cables, in both cables there is a spike at 203 Hz with an amplitude of above 4 m/s^2/sqrt(Hz). When the 50m cables were measured in the box with the conductive front panel, the amplitude drops at 203 Hz by a factor of around 3. I also compared the isolated front panel with the old setup, and found that the isolated front panel worse by a factor of just over 2 than the old setup. Therefore, I think that using the conductive front panel for the ALS Delay Line box will reduce noise and crosstalk between the cables the most. 

  11495   Tue Aug 11 18:43:42 2015 JessicaUpdateIOOMCL Online Subtraction

Today I finished fitting the transfer function to a vectfit model for seismometers T240_X and T240_Y, and then used these to filter noise online from the mode cleaner. 

The Bode plot for T240_X is in figure 1, and T240_Y is in figure 2. I made sure to weight the edges of the fit so that no DC coupling or excessive injection of high frequency noise occurs at the edges of the fit.

I used C1:IOO-MC_L_DQ as the first channel I filtered, with C1:IOO-MC_L_DQ(RMS) for RMS data. I took reference data first, without my filter on. I then turned the filter on and took data from the same channel again. The filtered data, plotted in red, subtracted from the reference and did not inject noise anywhere in the mode cleaner. 

I also looked at C1:LSC-YARM_OUT_DQ and C1:LSC-YARM_OUT_DQ(RMS) for its RMS to see if noise was being injected into the Y-Arm when my filter was implemented. I took reference data here also, shown in blue, and compared it to data taken with the filter on. My filter, in pink, subtracted from the Y-Arm and injected no noise in the region up to 10 Hz, and only minimal noise at frequencies ~80 Hz. Frequencies this high are noisy and difficult to filter anyways, so the noise injection was minimal in the Y-Arm. 

  11502   Thu Aug 13 12:06:39 2015 Jessica SummaryIOOBetter predicted subtraction did not work as well Online

Yesterday I adjusted the preweighting of my IIR fit to the transfer function of MC2, and also managed to reduce the number of poles and zeros from 8 to 6, giving a smoother rolloff. The bode plots are pictured here:

The predicted IIR subtraction was very close to the predicted FIR subtraction, so I thought these coefficients would lead to a better online filter.

However, the actual subtraction of the MCL was not as good and noise was injected into the Y arm.

The final comparison of the subtraction factors between the online and offline data showed that the preweighting, while it improved the offline subtraction, needs more work to improve the online subtraction also.

  6372   Wed Mar 7 13:30:17 2012 JimUpdatePEMadded TPs and JIMS channels to PEM front-end model

[Jim Ryan]

The PEM model has been modified now to include a block called 'JIMS' for the JIMS(Joint Information Management System) channel processing. Additionally I added test points inside the BLRMS blocks that are there. These test points are connected to the output of the sqrt function for each band. I needed this for debugging purposes and it was something Jenny had requested.

The outputs are taken out of the RMS block and muxed, then demuxed just outside the JIMS block. I was unable to get the model to work properly with the muxed channel traveling up or down levels for this. Inside the JIMS block the information goes into blocks for the corresponding seismometer channel.

For each seismometer channel the five bands are processed by comparing to a threshold value to give a boolean with 1 being good (BLRMS below threshold) and 0 being bad (BLRMS above threshold). The boolean streams are then split into a persistent stream and a non-persistent stream. The persistent stream is processed by a new library block that I created (called persist) which holds the value at 0 for a number of time steps equal to an EPICS variable setting from the time the boolean first drops to zero. The persist allows excursions shorter than the timestep of a downsampled timeseries to be seen reliably.

The EPICS variables for the thresholds are of the form (in order of increasing frequency):




The EPICS variables for the persist step size are of the form:




I have set all of the persist values to 2048 (1 sec.) for now. The threshold values are currently 200,140,300,485,340 for the GUR1X bands and 170,105,185,440,430 for the GUR1Y bands.

The values were set using ezcawrite. There is no MEDM screen for this yet.

PEM model was restarted at approx. 11:30 Mar. 7 2012 PST.


  6397   Fri Mar 9 20:44:24 2012 Jim LoughUpdateCDSDAQ restart with new ini file

DAQ reload/restart was performed at about 1315 PST today. The previous ini file was backed up as c1pem20120309.ini in the /chans/daq/working_backups/ directory.

I set the following to record:

The two JIMS channels at 2048:
[C1:PEM-JIMS_CH1_DQ] Persistent version of JIMS channel. When bit drops to zero indicating something bad (BLRMS threshold exceeded) happens the bit stays at zero  for >= the value of the persist EPICS variable.
[C1:PEM-JIMS_CH2_DQ] Non-persistent version of JIMS channel.

And all of the BLRMS channels at 256:
Names are of the form:

On monday I intend to look at the weekend seismic data to establish thresholds on the JIMS channels.

256 was the lowest rate possible according to the RCG manual. The JIMS channels are recorded at 2048 because I couldn't figure out how to disable the decimation filter. I will look into this further.

  12140   Mon May 30 18:19:50 2016 JohannesUpdateCDSASS medm screen update

I noticed that the TRY button in the ASS main screen was linking to LSC_TRX instead of LSC_TRY. Gautam fixed it.

  12175   Tue Jun 14 11:29:25 2016 JohannesSummaryASCYArm OpLev Calibration

In preparation for the armloss map I checked the calibration of the Y-Arm ITM and ETM OpLevs with the method originally described in https://nodus.ligo.caltech.edu:8081/40m/1247. I was getting a little confused about the math though, so I attached a document at the end of this post in which I work it out for myself and posteriority. Stepping through an introduced offset in the control filter for the corresponding degree of freedom, I recorded the change in transmitted power and the reading of the OpLev channel with the current calibration. One thing I noticed is that the calibration for ITM PIT is inverted with respect to the others. This can of course be compensated at any point in any readout/feedback chain, but it might be nice to establish some sort of convention where positive feedback to the mirror will increase the OpLev reading.

The calibration factors I get are within ~10% of the currently stored values. The table (still incomplete, need to relate to the current values) summarizes the results:

Mirror DoF Current Relative New
Y-Arm OpLev Calibration
ETM PIT   0.974 ± 0.029  
  YAW   1.077 ± 0.021  
ITM PIT   -0.972 ± 0.020  
  YAW   0.920 ± 0.048  

The individual graphs:






The math:



  12176   Tue Jun 14 11:52:08 2016 JohannesUpdateGeneralEPICS Installation | SURF 2016

We generally want to keep the configuration of the 40m close to that of the LIGO sites, which is why we chose BusWorks, and it is also being established as a standard in other labs on campus. Of course any suitable DAQ system can do the job, but to stay relevant we generally try to avoid patchwork solutions when possible. Did you follow Aidan's instructions to the book? I haven't set up a system myself, yet, so I cannot say how difficult this is. If it just won't work with the Raspberry Pi, you could still try using a traditional computer.

Alternatively, following Jamie's suggestions, I'm currently looking into using python for the modbus communications (there seem to be at least a few python packages that can do this), which would reportedly make the interfacing and integration a lot easier. I'll let you know when I make any progress on this.


About acquiring data: Initially I couldn't start with proper Acromag setup as the Raspberry pi had a faulty SD card slot. Then Gautam gave me a working pi on which I tried to install EPICS. I spent quite a time today but couldn't setup acromag over ethernet.  But, it would be great if we have a USB DAQ card. I have found a good one here http://www.mccdaq.com/PDFs/specs/USB-200-Series-data.pdf It costs around 106$ including shipping (It comes with some free softwares for acquiring data) . Also, I know an another python based 12bit DAQ card (with an inbuilt constant current source) which is made by IUAC, Delhi and more information can be found here http://www.iuac.res.in/~elab/expeyes/Documents/eyesj-progman.pdf  It costs around 60$ including shipping.

About temperature sensing: The RTD which I found on Omega's list is having a temperature resolution of 0.1 deg C. I have also asked them for the one with good resolution. Also according to their reply, they have not performed any noise characteristics study for those RTDs.



  12188   Thu Jun 16 11:25:00 2016 JohannesUpdateLSCY-Arm round-trip loss measurement with ALS

Using the ALS green beat and armlength feedback I mapped an IR resonance of the Y-Arm by stepping through a ramp of offset values.

First I optimized the IR alignment with the dither scripts while LSC kept the arm on resonance, and then transitioned the length control to ALS. The beat frequency I obtained between the Y-arm green and the PSL was about 25 MHz. Then I applied a controlled ramp signal (stepping through small offset increments applied to LSC-ALSY_OFFSET, while logging the readback from channels LSC-TRY_OUT16 and ALS-Y_FC_SERVO_INMON with an averaging time of 1s.

The plots show the acquired data with fits to  T(x)=\frac{T_0}{1+\frac{(x-x_0)^2}{\mathrm{HWHM}^2}}+\mathrm{offset} and f(x)=mx+b, respectively.


The fits, weighted with inverse rms uncertainty of the data points as reported by the cds system, returned HWHM = 0.6663 ± 0.0013 [offset units] and m = -0.007666 ± 0.000023 [MHz/offset unit], which gives a combined FWHM = 10,215 ± 36 Hz. The error is based purely on the fit and does not reflect uncertainties in the calibration of the phase tracker.

This yields a finesse of 388.4 ± 1.4, corresponding to a total loss (including transmissivities) of 16178 ± 58 ppm. These uncertainties include the reported accuracies of FSR and phase tracker calibration from elog 9804 and elog 11761.

The resulting loss is a little lower than that of elog 11712, which was done before the phase tracker re-calibration. Need to check for consistency.

  12192   Thu Jun 16 18:08:57 2016 JohannesUpdatePSLBefore the AOM installation

There was only one razor blade beam dump labeled for atmospheric use left, but that's all we need. Steve is working on restocking. I placed the modified AOM mount on the PSL table near its intended location (near the AOM where it doesn't block any beams).

Things to keep in mind:

  • The laser power needs to be turned down for the installation of the AOM. Current laser settings are: Crystal Temperature: 29.41 C, Diode Current: 2.1 A.
  • The AOM driver must not be left unterminated when turned on (which it currently is and will be).
  • The HEPA filters are currently running at ~50%. While the PSL enclosure is open for the work we'll set them to 100% and lower them after a job well done.

The setup:

The AOM has a deflection angle of about 20 mrad, which requires about 10cm of path for a separation of 2mm of the two beams. I need to survey closer and confirm, but I hope I can fit the beam dump in before the PMC (this of course also depends on the spot size). Alternatively, the PMC hopefully isn't resonant for anything remotely relevant at 80MHz offset, in which case we can also place the beam dump in its reflection path.

So this is the plan:

  • Determine coupling efficiency into PMC for reference
  • Turn down laser power
  • No signal on AOM driver modulation input
  • Mount AOM, place in beam path, and align
  • Correct alignment into PMC?
  • Secondary beam detectable? Adjust modulation input and laser power until detectable.
  • Find a place for beam dump
  • Confirm that primary beam is not clipping with PMC
  • Turn up laser power
  • Determine coupling efficiency with restored power to compare

Any thoughts? Based on the AOMs resting place I assumed that it is supposed to be installed before the PMC, but I'm actually not entirely sure where it was sitting before.

  12196   Fri Jun 17 22:36:11 2016 JohannesUpdatePSLAOM installation

Subham and I have placed the AOM back into the setup right in front of the PMC.

Steps undertaken:

  1. The HEPA filters were turned off for some reason. They were turned back on, running at 100% while the enclosure was open.
  2. Before the installation, after initial realignment, the PMC TRANSPD read out 748 mV.
  3. The laser injection current was dialed down to 0.8 A (just above the threshold, judging by PMC cameras.
  4. AOM was attached to the new mount while staying connected to its driver. Put in place, a clamp prevents the cable from moving anywhere near the main beam.
  5. Aligned AOM to beam, centering the beam (by eye) on front and back apertures.
  6. We then applied an offset to the AOM driver input, eventually increasing it to 0.5 V. A secondary beam became clearly visible below the primary beam.
  7. In order to place the razor blade dump (stemming from a box, labeled "cleaned for atm use") before the PMC, where the beam separation was about 3 mm, to make sure we can hit the edged area, we had to place the dump at an angle, facing up.
  8. Keeping the 0.5V offset on the driver input, with the lights off, we increased the laser diode current in steps of ~200 mA to its original value of 2.1A, while checking for any IR light scattered from the beam dump. Not a trace.
  9. At original current setting, we realigned the beam into the PMC, and obtained 743 mV on the TRANSPD in the locked state.
  10. Closed off PSL table, dialed HEPAs down to 50%



  12270   Thu Jul 7 17:12:50 2016 JohannesUpdateGeneralVent progress

I performed a visual inspection of ITMY in its natural habitat today. I did not get any great pictures from the HR side because it's located very towards the edge of the table towards the arm. Before that I checked the levelness of the table. East-west direction was fine, north-south was slightly off but still within the marks for 'level'.

The AR side had several speckles, a few of them located somewhat near the geometrical center of ITMY. The top of the barrel was worse of, as expected. The HR side was a little better, but there were a few pieces of dust? near near the center. Sample pictures are attached, I uploaded all the good ones to Picasa.

Clamps that mark the position of ITMY were already in place. I did not move the optic just yet, and we will have to move a cable block out of the way to bring ITMY near the opening for us to work on it. We will markt the position of that to preserve the weight distribution. Then we can probably take some better before/after pictures. Tomorrow I will be looking at ETMY.

  12291   Tue Jul 12 09:35:51 2016 JohannesUpdateGeneralSlippery substance mystery

I've noticed the spot that Rich means before, too. I think you only notice this when you're wearing the shoe covers, not sneakers or crocs. I didn't see any 'substance', it seems more like the floor finish (wax?) seems to be more slippery in that area than others.


I found a note on Steve's desk that R. Abbott left yesterday afternoon about an unidentified slippery substance being present on the floor by cabinet S12, along the X arm. (Steve is away this week)

Just now, I found no trace of the substance in the vicinity of that cabinent (which is one of the cabinets for clean objects). Maybe the janitor cleaned it already?


  12295   Tue Jul 12 23:51:16 2016 JohannesUpdateGeneralVent progress - ETMY inspection

On Monday I inspected ETMY, and found nothing really remarkable. There was only little dust on the HR side, and nothing visible in the center. The AR side has some visible dust, nothing too crazy, but some of it near the center.

  12296   Wed Jul 13 00:01:38 2016 JohannesUpdateGeneralITMX dust

We ran out of illuminator juice, and short-term charging couldn't restore enough battery life to continue the work. We should be able to get some better pictures tomorrow.


Looked at ITMX. Johannes and I both saw a fairly large speck of dust near the center of the HR side. We tried to take some photos but couldn't get any with good focus


  12297   Wed Jul 13 00:38:25 2016 JohannesUpdateGeneralVent progress - ETMY attempted repositioning

[Lydia, Johannes]

We attempted to move the ETMY suspension near the access port in preparation for the cleaning process. The plan was to move in the face restraints first to the point of almost making contact, then the ones underneath so the optic is sitting on them, followed by the top one facing down, and then bringing in the stops on the faces.

While moving in the stoppers I noticed that the far lower stopper on the HR side was barely touching the face of the optic in its resting position and was basically pushing it sideways when moved forward. It was just on the edge, so I tried to compensate minimally by moving the underneath stops a little further on the near side, trying to let it 'slide' over a little so the screw would have better contact. I must have been too generous with the adjustment, because while proceeding I noticed at some point that the stick magnets on one side of the optic were not attached anymore but laying inside the OSEMs. The side magnet was also missing, it is now sitting on the suspension jig base plate. The dumbbells all seem intact, but we'll test them before we reglue the magnets to the optic. This is extremely unfortunate, but hopefully won't take too long to fix. At the very least, as Koji put it, the cleaning will be easier with the optic out of the suspension. Still, what a bummer.

  12310   Tue Jul 19 13:21:42 2016 JohannesUpdateGeneralVent progress - ETMY attempted repositioning

[Lydia, Johannes]

We moved ITMY from its original position to a place near the access point. We took the OSEMs off first, and noticed that the short flat head screw driver was still a little too long to properly reach the set screws for the lower OSEMs. We were able to gradually loosen them, though and thus remove the lower OSEMs as well. We had to move a cable tower out of the way, but used clamps to mark its position. After making sure the optic is held by its earthquake stops, we moved it to its cleaning location. All magnets are still attached.

  12456   Wed Aug 31 18:07:43 2016 JohannesUpdateSUSITMY free swinging

[Lydia, Gautam, Koji, Johannes]

Summary of things done today:

  • Rebalanced ITMY table
    • After waiting until today to see if the table would relax into a level position, engaged the earthquake stops for SRM and moved the large counterweight by ~4 inches. The table is now level to within ~0.1 mrad in direction of the access port
    • Since the relaxing seems to take some time, we will open ITMX and ETMX chamber tomorrow and level the tables with additional weights, so the springs can get used to 'levelness' again
  • Cleaned ITMY, SRM and SR2 optics
    • Koji drag-wiped all three optics and cleaned the table in general where accessible. He was able to remove the sliver discussed in elog https://nodus.ligo.caltech.edu:8081/40m/12455
    • We measured the particle count in the chamber and found it to be 4000 for 0.3 microns and 660 for 0.5 microns.
  • We pulled out stops on ETMY ITMY and roughly centered the OSEMs half-way, using photos of the previous OSEM rotation as a reference point for their orientation. We foudn that the green beam is hitting ITMY almost centered and that the reflection doesn't seem to steer off too much, but were not yet able to see any returned light on the ETMY cameras.

Unless we get lucky and get the green light to flash in the cavity by playing with the mirror alignment, we will open the ETMY chamber tomorrow. On one hand we can look for the reflected green light in the chamber, or alternatively the IR beam transmitted by ITMY. This way we can obtain estimates for the OSEM biasing and perform the final centering of the OSEMs. We will then also address the bounce mode minimization in ITMY and check if the previous orientations still hold.

  12464   Thu Sep 1 19:18:14 2016 JohannesUpdateSUSITMX and ETMX preemptive table leveling

I balanced the ITMX and ETMX tables into level position today, for which I had to move quite a few of the on-table weights. I'm recording their original positions for future use here.


This table was only off in 'pitch', I moved the middle weight to a new location as shown in the pictures. I added secondf disk weight on top of the one I moved, this one has to come out again when we install ETMX.

ETMX chamber original configuration
Reference for original position
Moved weight here


I moved some weights around as shown in the image, but didn't have to add any. We simply have to move them back to their original location when the time comes.

ITMX chamber original configuration
Reference for square blocks: the lower one is a double stack
Reference for disk weights: These two are stacked.


While in the chambers, I also took some pictures of the ETMX window and PR2, motivated by the dirty state of SR2. We might want to consider cleaning both, specifically PR2 is relatively easily accessible and can be cleaned when we open the ITMX chamber to remove its FC and move it back into position.


  12465   Thu Sep 1 19:59:22 2016 JohannesUpdateSUSIR mode flashes in Y arm

[Gautam, Lydia, Johannes]

  • After placing the irises on the ETMY and ITMY cages we found that the green beam pointing was off in YAW and corrected it to hit the center of ITMY
  • The green beam was well centered on ETMY to begin with, so we used it as a reference for the alignment of ITMY, sending it back through the ETMY iris
  • We used the green transmission to tune the pitch and yaw of ETMY
  • Using TT1 and TT2 we steered the beam IR through both irises and were hoping to see mode flashes in the IR arm transmission, which we did

The next step is the tip tilt fine alignment of the IR into the arm, using TRY, from which we removed the ND filter for the time being.

  12482   Mon Sep 12 17:15:22 2016 JohannesUpdateGeneralPRM SRM alignment

[Gautam, Steve, Johannes]

We put on the remaining heavy doors on the chambers (ITMY, ITMX,ETMX, in this order) this morning. On the ITMY and ETMX tables we placed old OpLev steering mirrors that are clean and baked as witness plates such that may one day provide some insight into dust accumulation on optics.

With the heavy doors on we confirmed that we were still able to lock both IFO arms and used the dither scripts to optimize the alignment. Following that we centered all OpLevs and aligned the X and Y green beams.

ITMY table witness plate
ETMX table witness plate


  12493   Wed Sep 14 19:41:23 2016 JohannesUpdateGeneralPSL back to high power

Today's summary:

  • Replaced mirror in MC REFL path with R=10% BS and aligned beam on PD while still at low power
  • Replaced HR mirror in Transmon path at EY table with 50/50 BS. Alignment onto QPD not yet confirmed because we need IR from the YARM for it.
  • Put ND filters back on Transmon QPDs at both X and Y ends. For now I put all the filters on, for a combined OD of 1.6 at both ends (1.0 + 0.6 at YEND and 1.0 + 0.4 + 0.2 at XEND).
  • Put ND filter back on Transmon CCD on EY table.
  • Reverted MC autolocker to nominal, high power version.
  • Raised PSL output power back to nominal level by turning the waveplate. At the PSL shutter I measured a power of 1.03W. It occured to me too late that I realigned the PMC only afterwards and increased its transmission by a few percent, so I'll have to re-measure the actual PSL power.
  • MC is locked with its transmission back up to ~15,400 counts. The autolocker is not very good at obtaining the lock, as it seems to try to turn the VCO gain up too far and loses lock. The script probably needs a revision.
  • The YARM was pretty badly aligned. We used the green light to visually center the beam on the test masses AND had to go exploring with the TTs to see IR flashes in the first place. We got the YARM to lock to IR and were able to run the dither alignment. The maximum transmission we saw was on the order of 0.85. However, something strange is happening with the LSC control of the armlength. When the lock is engaged it drives PIT and YAW, which manifests itself in the OpLev signal and variable transmitted power on the TRY PDs. Osamu helped us diagnose this and was able to reduce the effect by tuning the POS gains to the individual ETMY OSEMS. The problem persisted even after using the new matrix diagonalization coefficients, we'll have to investigate this further and also take a look at the filters in the feedback path.
  • ITMX is still stuck and way out of alignment, so we couldn't even start with the green light in the XARM.
  12524   Thu Sep 29 20:21:29 2016 JohannesUpdateGeneralYARM loss measurement

[Gautam, Johannes]

I scripted a series of YARM DC reflectivity measurements last night alternating between locked state and unlocked state (with ETMY misaligned) for measuring the after-vent armloss. The general procedure is based on elog 11810, but I'll also give a brief summary here.

  • To measure the locked reflectivity the dither script is executed with a stop condition that depends on the rms values of its error signals.
  • The dithering is stopped, and while the arm is locked the reflected power is recorded from both POX/POY DC and ASDC, as well as the mode cleaner transmission for normalization.
  • The arm locking is switched off, and ETMY moved to is 'misaligned' position. This gets rid off unwanted mode flashes.
  • In the unlocked state the same quantities are recorded.
  • Rinse and repeat for a set number of times (for this run I set it to 100 and left the interferometer alone).

I did this back in June (but strangely never posted what I found, shame on me). What I found back then was a YARM loss of 237 ppm +/- 41 ppm and an XARM loss of 501 ppm +/- 105 ppm

Last night's data indicates a YARM loss of 143 ppm +/- 24 ppm after cleaning with first contact. yeslaugh

THIS IS STILL ASSUMING THAT THE MODE-MATCHING HASN'T CHANGED. We had however moved ETMY closer to ITMY during the vent by 19mm. Gautam and I had some trouble setting up the ALS to confirm the mode-matching, but we're in the process of recovering the XARM IR beat.

  12528   Mon Oct 3 21:24:02 2016 JohannesUpdateGeneralXARM loss measurement

[gautam, johannes]

I started a script on Friday night to collect some data for a reflection armloss measurement of the XARM. Unfortunately there seemed to have been a hickup in some data transfer and some errors were produced, so we couldn't really trust the numbers.

Instead, we took a series of manual measurements today and made sure the interferometer is well behaved during the averaging process. I wrote up the math behind the measurement in the attached pdf.

The numbers we used for the calculations are the following:

While we average about 50 ppm +/-15 ppm for the XARM loss with a handful of samples, in a few instances the calculations actually yielded negative numbers, so there's a flaw in the way I'm collecting the data. There seems to be a ~3% drift in the signal level on the PO port on the order of minutes that does not show in the modecleaner transmission. The signals are somewhat small so we're closing the shutter over night to see if it could be an offset and will investigate further tomorrow. I went back and checked my data for the YARM, but that doesn't seem to be affected by it.

  12531   Tue Oct 4 22:18:24 2016 JohannesUpdateGeneralX/YARM loss measurement

[gautam, johannes]

We let the PSL shutter closed overnight and observed the POXDC, POYDC and ASDC offsets. While POY has small fluctuations compared to the signal level, POX is worse off, and the drifts we observed live in the DC reading are in the same ballpark as the offset fluctuations. The POXDC level also unexpectedly increased suddenly without the PSL shutter being opened, which we can't explain. The data we took using POXDC cannot be trusted.

Even the ASDC occasionally shows some fluctuations, which is concerning because the change in value rivals the difference between locked and misaligned state. It turns out that the green shutters were left open, but that should not really affect the detectors in question.

We obtained loss numbers by measuring the arm reflections on the ASDC port instead. LSCoffsets was run before the data-taking run. For each arm we misaligned the respective other ITM to the point that moving it no longer had an impact on the ASDC reading. By taking a few quick data points we conclude the following numbers:

XARM: 247 ppm +/- 12 ppm
YARM: 285 ppm +/- 13 ppm

This is not in good agreement with the POYDC value. The script is currently running for the YARM for better statistics, which will take a couple hours.

ITMX is misaligned for the purpose of this measurement, with the original values saved.

GV edit 5Oct2016: Forgot to mention here that Johannes marked the spot positions on the ITMs and ETMs (as viewed on the QUAD in the control room) with a sharpie to reflect the current "well aligned" state.

  12581   Wed Oct 26 16:06:01 2016 JohannesUpdateGeneralAutolocker maintenance

[Gautam, Johannes]

The autolocker was acting up today, Gautam traced it to EPICS channels ( namely C1:IOO-MC_LOCK_ENABLE and C1:IOO-MC_AUTOLOCK_BEAT ) served by c1iool0 not being responsive and keyed the crate. This restored it nominal operation.

  12604   Mon Nov 7 19:49:44 2016 JohannesUpdateCDSacromag chassis hooked up to PSL

[Lydia, Johannes]

We're waiting on the last couple electrical components to arrive that are needed to complete the acromag chassis, but it is essentially operational. Right now it is connected to the PSL Mephisto's diagnostics port, for which only a single XT1221 A/D unit is needed. We assigned the IP address to it. For the time being I'm running a tmux session on megatron (named "acromag") that grabs and broadcasts the epics channels, with Lydia's original channel definitions. Since the chassis is 4U tall, there's not really any place in the rack for it, so we might want to move it to the X-end before we start shuffling rack components around. Once we finalize its location we can proceed with adding the channels to the frames.

For the eventual gradual replacement of the slow machines, we need to put some thought into the connectors we want in the chassis. If we want to replicate the VME crate connectors we probably need to make our own PCB boards for them, as there don't seem to be panel-mount screw terminal blocks readily available for DIN 41612 connectors. Furthermore, if we want to add whitening/AA filters, the chassis may actually be large enough to accomodate them, and arranging things on the inside is quite flexible. There are a few things to be considered when moving forward, for example how many XT units we can practically fit in the chassis (space availability, heat generation, and power requirements) and thus how many channels/connectors we can support with each.

Steve: 1X3 has plenty of room

  12614   Mon Nov 14 19:15:57 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

Looking back at elog 12528, the uncertainty in the armloss number from the individual quantities in the equation for \mathcal{L} can be written as:

\delta\mathcal{L}^2=\left(\frac{T_1(1-\frac{P_L}{P_M}-2T_1)}{4\gamma}\right)^2\left(\frac{\delta T_1}{T_1}\right)^2+T_2^2\left(\frac{\delta T_2}{T_2}\right)^2+\left(\frac{T_1(1-\frac{P_L}{P_M}-T_1)}{4\gamma}\right)^2\left(\frac{\delta\gamma}{\gamma}\right )^2+\left(\frac{T_1}{4\gamma}\right )^2\left[\left(\frac{\delta P_L}{P_L}\right )^2+\left(\frac{P_L}{P_M} \right )^2\left(\frac{\delta P_M}{P_M}\right )^2\right ]

Making some generous assumption about the individual uncertainties and filling in typical values we get in our measurements, results in the following uncertainty budget:

\delta\mathcal{L}^2\approx\left(12\,\mathrm{ppm}\right)^2\left(\frac{\delta T_1/T_1}{5\%}\right)^2+(0.7\,\mathrm{ppm})^2\left(\frac{\delta T_2/T_2}{5\%}\right)^2+\left(2\,\mathrm{ppm}\right)^2\left(\frac{\delta\gamma/\gamma}{1\%}\right )^2+\left(140\,\mathrm{ppm}\right )^2\left(\frac{\delta P/P}{2.5\%}\right )^2

In my recent round of measurements I had a 2.5% uncertainty in the ASDC reading, which completely dominates the armloss assessment.

The most recent numbers are 57 ppm for the YARM and 21 ppm for the XARM, but both with an uncertainty of near 150 ppm, so while these numbers fit well with Gautam's estimate of the average armloss via PRG, it's not really a confirmation.

I set the whitening gain in ASDC to 24 dB and ran LSC offsets, and now I'm getting a relative uncertainty in measured reflected power of .22%, which would be sufficient for ~25ppm accuracy according to the above formula. I'm going to start a series of measurements tonight when I leave, should be done in ~2 hours (10 pm) the latest.

If anybody wants to do some night work: I misaligned ITMY by a lot to get its reflection off ASDC. Approximate values are saved as a restore point. Also the whitening gain on ASDC will have to be rolled back (was at 0dB) and LSC offsets adjusted.

  12617   Tue Nov 15 20:26:35 2016 JohannesUpdateCamerasBasler GigE-Camera on Optimus (+Mafalda dead)

I powered up the existing ace100gm GigE cam with the PoE injector and tried to interface with it as described in elog 4163. After a few initial problems with IP assignment and interfacing I connected it to one of the gigabit hubs and installed the most recent pre-compiled software suite on /opt/pylon5 on optimus, after which I was able to find it with the configuration software. I named it "c1gige_bas100-1" and gave it the static IP address

Afterwards the image acquisition worked without problems.

It may be a good idea to leave the gigecam interfacing up to a dedicated machine. I was thinking I could use Mafalda for this, and also for developing the code for framegrabbing and imager settings, but found that it was dead, burnt at the stake so to say. I guess it wasn't running anything critical, since it wasn't even connected to the network and smelled like burnt electronics. I'll get a replacement desktop for it.

  12618   Tue Nov 15 20:35:19 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I had a mistake in my script that reported the wrong error after averaging several datapoints, and because I hadn't looked at the individual numbers I didn't catch it so far. Thanks to Gautam it is no more.

The updated numbers are (with fresh, more trustworthy data):

XARM: 21 +/ 35 ppm
YARM: 69 +/- 45 ppm

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.

  12624   Thu Nov 17 21:54:11 2016 JohannesUpdateGeneralAchievable armloss measurement accuracy

I don't like AS110 or AS55. Neither of them are designed for DC and so the DC readout chain is hokey. How about use an actual transimpedance PD with a 100-1000 Ohm resistor and a 3 mm diode? This would eliminate the alignment sensitivity and the drifts due to electronics and room lights.

This looks much better. I'm planning to take more data with the AS110 PD rather than AS55 when I get the chance, increase the averaging time, and also sigma filter the datapoints. That should get us to a good spot and cut down the uncertainty even further.


  12625   Fri Nov 18 00:25:08 2016 JohannesOmnistructure40m upgradingAcromag Chassis Development

I had Rich show me his approach to a chassis for the Acromag modules. The document tree for his design can be found on the DCC. Note that he's using the high densitymodel ES series, which is available as a bare board variant with pluggable screw terminals:

He can fit up to 4 of these in a 2U chassis and has outsourced the wiring from front panel Dsubs to the board connectors to an external company. At the 40m (and in West Bridge) we currently only have the rail mounted XT series

At first glance the specs are very similar. Both A/D and D/A flavors have 16-bit precision in both cases. The high density ES series with Rich's layout can achieve 128 A/D per 2U, 64 D/A per 2U, or 384 DIO per 2U. Into a 4U chassis of the type we have currently we can fit ~32 XT modules (assuming two rows), which results in very similar numbers, except for the DAC, of which we could fit more.

XT1221-000 (8 diff. channel 16-bit ADC)                          $495.00      $61.88/ch
XT1541-000 (8 channel 16-bit DAC and 4 discrete I/O )    $525.00      $65.63/ch
XT1120-000 (16 channel DIO)                                         $320.00     $20.00/ch

ES2162-0010 (32 diff. channel 16-bit ADC)                     $2050.00    $64.06/ch
ES2172-0010 (16 channel 16-bit DAC)                           $1400.00    $87.50/ch
ES2113-0010 (96 channel DIO)                                      $1100.00    $11.46/ch

It's cheaper to stick with the current XT models, but they need the bulkier 4U chassis. The good news is that actually all these models have 16 bit precision, which wasn't clear to me before. Lydia and I will work out what connectors we want on the boxes, and how many modules/channels we need where. Rich also got me in touch with Keith Thorne, who handles the analog I/O Acromag at LLO, and I will ask him for advice. From his documents on the DCC it seems that he is using yet another series: EN. The 968EN-4008 for example is a rail-mounted ADC with pluggable connections, but looses quite clearly in price per channel.

For a generic multipurpose DAQ interface box the ES series is the best approach in my opinion, because it offers a more compact design. We could for example fit 1 ADC, 2 DAC, 1 DIO in a 2U chassis for 32/32/96 channels. The combined price tag for this scenario would be ~$6k.



  12632   Mon Nov 21 19:54:13 2016 JohannesUpdateCDSacromag chassis hooked up to PSL

[Lydia, Johannes]

We connected and powered up the Acromag chassis today. It lives in 1X4 and is powered by the Sorensen +20V power supply in 1X5 via the fuse rail on the side of 1X4. For this we had to branch off the 20V path to the dewhitening and anti-image filter crate of the c1:susaux driven SOS optics. After confirming that none of the daughter modules in the crate draw from the 20V line, we added a wire leading to a new fuse we added for this unit and ran a power cable from there.

The diagnostic connector of the PSL laser is now connected to the unit and a tmux session was created on megatron that interfaces with the chassis and broadcasts the EPICS channels. We need to watch out in the coming days for epics freezes/outages, as in the past these seemed to occur around the same times we were toying with the Acromags.


We set up the chassis in 1X7 today. Steve is ordering a longer 25 pin cable to reach. Until then the PSL diagnostic channels will not be usable.


  12634   Tue Nov 22 13:55:32 2016 JohannesOmnistructure40m upgradingAcromag Chassis

Current Acromag chassis status:

I found out that Acromag offers DIN rail mounting kits for the open boards, so we can actually fit both XT series and ES/EN series in the same boxes, depending on the signal needs. The primary design driver will be the ES footprint, but if we find we don't need that many channels in some of the units, it's interchangable. For the wiring to the front panel - for which we will have a standard front panel express design, but may order modified ones for the custom needs of the 40m, I will contract the same company that Rich used for the wiring in his DIO box (Panel mount connectors terminating in loose wires/pre-routed plugs for Acromag units). We will either run a single DIN rail along the length of the chassis, or have two in parallel across.

Lydia and I took close looks at the breakout arrangements on the rack sides, and determined that because of the many cross-connects between non-DAQ ports it is not possible to redo and debug this in a reasonable amount of time without essentially shutting down the interferometer. So instead, we will connect the chassis directly to the slots that were previously leading to the slow machines. They come in two different flavors: The ADC modules have 64 pins, while the DIO and DAC ones have 50. There are a couple things we can do:

  • For ADC: Put favorite 64+ pin connector on front panel. I would advocate for the 68 pin VHDIC (SCSI-5). This standard ist widely used, has a sturdy connector, and usually off-the-shelf cables have twisted pair leads.
  • For DAC+DIO: Either use favorite 50 pin connector (there are 50-pin DSUB connectors, and also 50-pin IDC connectors with backshell), or also send the signals through VHDIC connectors, tolerating a few unused lanes. I would prefer the second option, after all it all goes to some 64 pin VME-crate backplane connector in the end, so if we ever get rid of the rack-side breakouts the wiring will much more uniform.
  • For good measure, we will add a few (16 maybe) BNC connectors to the front panel.
  • A standardized front panel could have a variety of different connectors by default: DSUBs, BNCs, etc., to be used when needed with some initial default wiring.
  • Note that THEORETICALLY we could even connect all backplane EUROCARD ports to the Acromag chassis and do the cross-connect wiring entirely inside, although that would make the inside extremely messy.

Based on Rich's design I will get started on a parts list and wiring diagrams to send out to the cable company.

  12651   Wed Nov 30 14:54:01 2016 JohannesUpdateCDSSlow machine replacement

I was talking with Larry yesterday, and he suggested the rack-mounted supermicro machines SYS-5017A-EP (~$400) or SYS-5018A-FTN4 (~$600) that he uses for moving data around in LIGO. They have 2 gigabit ethernet ports and can thus function as modbus gateways, conveniently placed in the rack close to the slow DAQ/DIO chassis and running some local ubuntu or other distro (I think Aidan uses CentOS in the PSL lab). These only have atom processors, which would be sufficient for the slow machine replacement, but there are many more powerful models with sometimes subtle differences. If we motion towards a more complete GigECam coverage in the lab it could be better to kill two birds with one stone and get something a little faster that can do the video capture/processing, since these machines will be distributed more or less strategically around the lab. Just a thought, as I have currently no clear idea what resources are required for this or how much we're throwing at this GigECam upgrade.



I've attached a schematic for how we will connect the Acromag mosules to the slow channel I/O curently going to c1auxex. The following changes are made:

  • We are getting rid of the slow readbacks from the Anti-Image and Oplev boards, as Rana says they are unnnecessary.
  • The whitening switching for the QPD is currently done by a Contec "fast" binary I/O module, but can be managed by acromag instead. This alllows CAB_1Y9_34 to  be fed directly into the Acromag box since all of its connections can now be managed slow. 
  • There's no need to change the PD whitening scheme around (since the signals never get huge), so we can set those to always be on and then lose those Contec channels. This means all of the necessary pins on CAB_1Y9_10 can go to Acromag. 
  • All the other backplane cables go the the fast machines only. 



  12704   Thu Jan 12 02:45:53 2017 JohannesUpdateGeneralNext armloss steps

As stated in elog 12618, using an oscilloscope to average the reflected powers and thus circumventing all filtering yielded much better results than before:

XARM: 21 +/- 35 ppm
YARM: 69 +/- 45 ppm

We can probably decrease the measurement uncertainty further by using a larger photodiode that is more suited for DC measurements. It will be placed in the AS pathtemporarily. If we get below 10 ppm systematic errors will begin to matter. To get those under control I will have to re-determine the visibility in the arm cavities and the modulation indices. The numbers to match from an estimate via the power recycing gain are <= 50 ppm arm average from elog 12586. Once the measurement scheme is up and running, we can proceed to generate ETM lossmaps. ITM will still be tricky but let's see what we can do.

Following Yutaro's approach, we can move the beams on the optcs in a deterministic way by several mm on the ETMs. Moving the beam is achieved by introducing offsets into the ASS auto alignment. As an example, the Yaw dither for ETMY is shown:

Each of the 8 test mass rotational degrees of freedom is driven by a particular frequency, and 2 signals are digitally demodulated in the real-time system: The arm transmission ("T") and the LSC arm length feedback signal to the ETM (L). The T signal feeds back to the input pointing, aka Tip Tilts and BS. This maximizes the transmission for a given test mass orientation. The L feedback controls the beam position on the mirrors in the arms. It minimizes the coupling of the dither to the length feedback, which is achieved when the beam goes through the axis of the rotational motion. This is where we introduce the offset:

The signal C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET (for this example) moves the locking point of the dither-to-length coupling and thus moves the beam around on the ETM. This is true for the PIT and YAW of all test masses except ITMX. In the current configuration the TTs optimize the alignment into the YARM, and for the X we only have the BS, which is why the beam spot on ITMX cannot be independently controlled as-is. We could, however, for the sake of this measurement, temporarily temporarily give TT authority to the XARM feedback to control the ITMX beam position. I imagine something like dither-aligning with ASS the normal way, and then run a customized script in which the XARM is treated as the YARM, feecback to the BS is cut, and the YAW signals are inverted due to the reflection on BS.

Knowing the angle of the offset gives us a way to calculate the beam spot displacement with the cavity geometry. For best results I want to make sure our OpLev calibration is still good (laser power decay, although last time this was done was only about a year ago), which would be analogous to elog 11831.

As for ITM beam position, this scheme only works partially, because it would require the beam to steer further off its axis than in the ETM case. This is problematic because of the spacing between tip tilts and ITMs. I summarize:

  1. Place larger DCPD in AS path
  2. Confirm mode-matching and mod-indices
  3. Assess loss in center with zero offsets
  4. Uncertainty low enough? If not get better.
  5. Calibrate OpLevs
  6. Introduce calibrated offsets in dither alignment
  7. Wander beam on test masses, recording arm losses
  8. ???
  9. Profit
  12710   Fri Jan 13 08:54:32 2017 JohannesUpdateGeneralDC PD installed

I installed a DC PD (Thorlabs PDA 520) in the beam path to AS55. I placed a 2" 90/10 BS on a flip mount that picks of enough light for the PD to spit out ~8V when the port is bright. Single arm continuous signal will be ~2V. While most of the light still continues towards AS55, the displacement from the BS moves the beam off AS55, so I used the flip mount in case anyone needs to use AS55. The current configuration is UP.

When we're done with loss investigations the flip mount should be removed from the bench.

I hooked the PD up to an ethernet-enabled scope and started scripting the loss map measurement (scope can receive commands via http so we can automate the data acquisition). The scope that was present at the bench and had been used for the MC ringdown measurements had a 'scrambled' screen that I couldn't fix so I had to retrieve another scope ("scope1"). I'll try to find out what's wrong with it but we may have to send it in for repair.


  12781   Tue Jan 31 22:15:02 2017 JohannesUpdateCDSvme crate backplane adapter boards

I made a crude sketch for how Lydia and I envision the connector situation on the back of the vme crates to be solved. Essentially the side panels of each crate extend about 2" (52 mm) beyond the edge of the DIN connectors. This is plenty of space for a simple PCB board. The connector of choice is D-Sub. We can split the 64 used pins into 2x 37 D-Sub OR (2x25 pin + 1x15pin). The former has fewer cables, but a few excess unused leads. A quick google search showed me that it is much cheaper to get twisted pair cables for 15 and 25 pin D-Subs. From what I remember, the used pins on the DIN connectors are concentrated on the low numbers end and the high numbers end, so might not need the 'middle' connector in many cases if we decide to break it up into three. I have to check this with Lydia though.

The D-Sub connectors would be panel mounted, for which we need a narrow panel piece with dsub cutouts. We can run horizontal struts across the vme crate from side panel to side panel. This way the force upon cable (dis)connection is mostly on the panel which is attached to the struts which are attached to the crate. This will also prevent gravitational sag or cable strain from pulling on the DIN connection, and we can use twisted pair cables with backshell, screws, and strain reliefs.

I was lookng into getting started with the PCB when Altium complained that the license is expired and to renew it. This is a relatively simple board layout so some free software out there is probably enough.

  12810   Tue Feb 7 19:14:59 2017 JohannesUpdateCDSvme crate backplane adapter board layout

After fighting with Altium for what seems like an eternity I have finished putting my vision of the vme crate backplane adapter board into an electronic format. It is dimensioned to fill the back space of the crate exactly. The connectors are panel mount and the PCB attaches to the connectors with screws, such that the whole thing will be mechanically much more stable than the current configuration. A mounting bracket will attach to horizontal struts that need to be installed in the crates, mechanical drawings to follow.

ELOG V3.1.3-