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  Coating Ring-down Measurement Lab elog, Page 2 of 18  Not logged in ELOG logo
ID Date Authordown Type Category Subject
  412   Wed Aug 16 11:36:13 2017 ZachElectronicsModelingMiddle ESD


  • I created a model with a drive offset in the middle. It improved one of the modes by a factor of 14 or so, but overall, it diminished the vast majority of the modes by as much as a factor of 100. 

Attachment 2: overlay23.jpg
  414   Wed Aug 16 16:05:09 2017 ZachElectronicsModelingTwo ESD First test


  • I created a model with two ESD's, essentially a combination of my previous two attempts with one ESD on the edge and one closer to the center of the disk. This test was quite successful compared to previous trials, the improvement seems to be on an average of a factor of 10. No modes are weakened by this design. I am going to run a sweep adjusting the central ESD and see what placement is best.
  • Attached is an overlay of the force profile and all of the modes. Note that this image is very large, and is useful as a digital reference or very large print only.

  415   Thu Aug 17 14:19:04 2017 ZachElectronicsModelingTwo ESD Optimization


  • I ran a sweep of the position of the middle ESD to determine the optimal arrangement. From the original geometry I offset the central ESD between -2 mm and 11 mm. From the plots below I conclude that the optimal geometry is the one that is shifted 2 mm to the right of the original design. 
  • The first plot is the sweep data as a ratio to the data of the current geometry for all modes. The second plot is the root mean square of the eight high frequency modes that change the most over the course of the sweep, those are modes 9, 11, 13, 14, and 17-20. The frequencies of those modes in order are 9.5kHz, 11 kHz, 14 kHz, 16 kHz, 19 kHz, 20 kHz, 21 kHz, and 23 kHz. There is a very apparent peak at 2 mm which is the driving force behind my conclusion that it is the optimal design. The next two plots are the 2mm shifted design and the original design as ratios to the original geometry. The 2mm shifted geometry is much more consistent than the original design, there is a very noticeable minimum in the original design (improvement by a factor of 2) for the 23 kHz mode that is resolved in the shifted design to a factor of 9.
  • The final plot are ratios of the two designs relative to each other. I found this plot useful to convince myself that the 2 mm shifted design was better than the original, particularly in the region above 1.5 kHz.

Attachment 1: Two.jpg
Attachment 2: Two.jpg
Attachment 3: RMS.jpg
Attachment 4: 2mm_shifted.jpg
Attachment 5: Sweep_Ratio.jpg
Attachment 6: Dynamic_Modes.jpg
Attachment 7: Sweep_Ratio.jpg
Attachment 8: Comparing.jpg
Attachment 9: 0mm_shifted.jpg
Attachment 10: Comparing.jpg
Attachment 11: 0mm_shifted.jpg
Attachment 13: 2.Dynamic_Modes.jpg
  416   Thu Aug 17 23:34:51 2017 ZachElectronicsModelingOptimized ESD Drawing


  • I made a drawing of the Optimal ESD design. The bottom combs (right hand in the rotated image) are set to ground and the 5 arm comb is set to a positive voltage and the 2 arm comb is set to a negative voltage. 

Attachment 1: OptimizedESD.pdf
  417   Fri Aug 18 10:50:53 2017 ZachElectronicsModelingESD's with positive voltage


  • With both electrodes driven at a positive voltage, the results are still an improvement over the original design, but by smaller factors, particularly in 3 of the higher frequency modes at around 2 and 3 kHz. With another parametric sweep I may be able to find a better design. The opposite voltage was useful because it could couple force in opposite directions to adjacent anti-nodes with opposing signs. An adjusted configuration could probably be found to interact with anti nodes with the same signs. An alternative option would be to leave the radial position of the more central ESD constant but rotate it relative to the sample by some amount, though this would also require an additional parametric sweep as well as a much larger ESD. 

  419   Fri Aug 18 14:15:47 2017 ZachElectronicsModelingSame Voltage ESD Sweep


  • I ran a sweep of the central position in the two ESD setup with both set at the same voltage. There were two designs that maximized excitation by different metrics, the design with a 3 mm shift from the original design maximized excitation overall, but the 20 kHz mode was worse by a bout a factor of 5. The design with a -2 mm shift maximized the high frequency modes, particularly the modes most affected by the shift.
  • MATLAB crashed shortly after the sweep so I will have to recreate the RMS plots of the dynamic modes later.


Attachment 1: two_positive_ratio_sweep.pdf
Attachment 2: -2mm_two_positive.jpg
  826   Tue Jan 14 10:10:25 2020 Seth LinkerGeneralMeasurementsS2000089, S2000090, S2000091, S2000092


  • 10:10 am in chamber
    • S2000089 in CR1
    • S2000090 in CR2
    • S2000091 in CR3
    • S2000092 in CR4
  • 10:16 am roughing pump on
  • 10:26 am turbo pump on
  828   Fri Jan 17 09:16:45 2020 Seth LinkerGeneralMeasurementsS2000093, S2000094


  • 9:16 am in chamber
    • S2000093 in CR1
    • S2000094 in CR2
  • 9:17 am roughing pump on
  • 9:26 am turbo pump on
  521   Fri Apr 20 16:50:41 2018 Liyuan Zhang, Gabriele VajenteGeneralMeasurementsS1600577 S1600580 S1600582 S1600585


  • 3:10pm in chamber
    • S1600577 in CR1
    • S1600580 in CR2
    • S1600582 in CR3
    • S1600585 in CR4
  • 3:30pm roughing pump on
  • 4:00pm turbo pump on
  • 4:30pm It was found IGM gauge didn't start and pressure stopped at 1.8e-3. Gabriel vented chamber and re-pumped it.
  • 4:50pm roughing pump on
  • 17:05pm turbo pump on
  • 17:10 pm pressure 1.7e-3, IGM display " starting"
  • We start measurement.
  522   Mon Apr 23 08:28:19 2018 Liyuan Zhang, Gabriele VajenteGeneralMeasurementsS1600577 S1600580 S1600582 S1600585

There was no problem with either the gauges nor the pressure. The IGM took a long time to go on, but finally all pressures looked good. The measurement is also good



  • 3:10pm in chamber
    • S1600577 in CR1
    • S1600580 in CR2
    • S1600582 in CR3
    • S1600585 in CR4
  • 3:30pm roughing pump on
  • 4:00pm turbo pump on
  • 4:30pm It was found IGM gauge didn't start and pressure stopped at 1.8e-3. Gabriel vented chamber and re-pumped it.
  • 4:50pm roughing pump on
  • 17:05pm turbo pump on
  • 17:10 pm pressure 1.7e-3, IGM display " starting"
  • We start measurement.


  510   Tue Apr 3 16:12:15 2018 Liyuan Zhang, Gabriele GeneralMeasurementsS1600541, S1600542, S1600545, S1600546


  • 4:12pm in chamber
    • S1600541 in CR1
    • S1600542 in CR2
    • S1600545 in CR3
    • S1600546 in CR4
  • 3:30pm roughing pump on
  • 4:00pm turbo pump on
  349   Tue Jun 20 16:01:27 2017 Gabriele, Zach, AlastairGeneralMeasurementsS1600541 S1600542 (laser polished)


  • The two substrates were laser polished (CO2 power ~ 23 W)
  • 3:50pm installed in chamber
    • S1600541 in CR1
    • S1600542 in CR3
  • 3:52pm roughing pump on
  • 4:00pm turbo pump on
  • Excitations
    • Quiet time before excitation: 1182045787
      Excitation broadband: 1182045822
      Quiet time after excitation: 1182045887

    • Quiet time before excitation: 1182056717
      Excitation broadband: 1182056752
      Quiet time after excitation: 1182056817

    • Quiet time before excitation: 1182067648
      Excitation broadband: 1182067683
      Quiet time after excitation: 1182067748

    • Quiet time before excitation: 1182078578
      Excitation broadband: 1182078613
      Quiet time after excitation: 1182078678

    • Quiet time before excitation: 1182089509
      Excitation broadband: 1182089544
      Quiet time after excitation: 1182089609



  • 1:56pm, valve closed, pumps off


  405   Thu Aug 10 13:36:08 2017 Gabriele, ZachMechanicsConfigurationESD moved closer to disk in CR0

We first measured the distance of the ESD from the disk in the test chamber (CR0). We had to remove the retaining ring to have reliable measurements

  • distance between top of the ESD and mounting plate: 12.30 mm
  • distance between top of the disk and mounting plate: 10.53 mm
  • ESD thickness: 0.55 mm

So initially the distance between disk and ESD is 1.22 mm

We re-aligned the optical setup to a horizontal reference, and moved down the ESD as much as we could. It's not completely clear if the ESD is touching the disk. We'll see after pump down. The new distance from the top of the ESD to the mounting plate is about 11.80 mm, so we should have moved the ESD 0.5mm closer to the disk.

Pump down started at ~1:30pm


  • Old configuration, 1.2mm distance ESD-disk:
    • GPS before exc. 1186417492 
    • GPS after exc. 1186417546
  • New configuration, 0.7mm distance ESD-disk
    • GPS before exc. 
    • GPS after exc.
  384   Mon Jul 31 13:21:37 2017 Gabriele, RosalieGeneralMeasurementsS1600520 S1600521 S1600523 S1600524


  • 1:20pm in chamber
    • S1600520 in CR1
    • S1600521 in CR2
    • S1600523 in CR3
    • S1600524 in CR4
  • 1:21pm roughinp pump on
  • 1:30pm turbo pump on
  • Excitations:
    • Quiet time before excitation: 1185582780
      Excitation broadband: 1185582815
      Quiet time after excitation: 1185582840

    • Quiet time before excitation: 1185584070
      Excitation broadband: 1185584105
      Quiet time after excitation: 1185584130

    • Quiet time before excitation: 1185585360
      Excitation broadband: 1185585395
      Quiet time after excitation: 1185585420

    • Quiet time before excitation: 1185586650
      Excitation broadband: 1185586685
      Quiet time after excitation: 1185586710

    • Quiet time before excitation: 1185587940
      Excitation broadband: 1185587975
      Quiet time after excitation: 1185588000

    • Quiet time before excitation: 1185589230
      Excitation broadband: 1185589265
      Quiet time after excitation: 1185589290

    • Quiet time before excitation: 1185590520
      Excitation broadband: 1185590555
      Quiet time after excitation: 1185590581

    • Quiet time before excitation: 1185591811
      Excitation broadband: 1185591846
      Quiet time after excitation: 1185591871


  • 9:55am, valve closed, venting, pumps off
  385   Tue Aug 1 10:19:39 2017 Gabriele, RosalieGeneralMeasurementsS1600519, S1600522


  • 10:05am, in chamber
    • S1600519 in CR1
    • S1600522 in CR2
  • 10:11am, roughing pump on
  • 10:19am, turbo pump on
  • Excitations
    • Quiet time before excitation: 1185649996
      Excitation broadband: 1185650031
      Quiet time after excitation: 1185650056

    • Quiet time before excitation: 1185651286
      Excitation broadband: 1185651321
      Quiet time after excitation: 1185651346

    • Quiet time before excitation: 1185652576
      Excitation broadband: 1185652611
      Quiet time after excitation: 1185652636

    • Quiet time before excitation: 1185653866
      Excitation broadband: 1185653901
      Quiet time after excitation: 1185653926

    • Quiet time before excitation: 1185655156
      Excitation broadband: 1185655191
      Quiet time after excitation: 1185655216

    • Quiet time before excitation: 1185656446
      Excitation broadband: 1185656481
      Quiet time after excitation: 1185656506

    • Quiet time before excitation: 1185657737
      Excitation broadband: 1185657772
      Quiet time after excitation: 1185657797

    • Quiet time before excitation: 1185659027
      Excitation broadband: 1185659062
      Quiet time after excitation: 1185659087


  • 11:25am valve closed, venting, pumps off
  387   Wed Aug 2 11:45:27 2017 Gabriele, RosalieGeneralMeasurementsS1600553, S1600554, S1600555, S1600556


  • 11:33am in chamber
    • S1600553 in CR1
    • S1600554 in CR2
    • S1600555 in CR3
    • S1600556 in CR4
  • 11:35am roughing pump on
  • 11:45am turbo pump on
  • Excitations:
    • Quiet time before excitation: 1185760223
      Excitation broadband: 1185760258
      Quiet time after excitation: 1185760283

    • Quiet time before excitation: 1185767513
      Excitation broadband: 1185767548
      Quiet time after excitation: 1185767573

    • Quiet time before excitation: 1185774804
      Excitation broadband: 1185774839
      Quiet time after excitation: 1185774864

    • Quiet time before excitation: 1185782094
      Excitation broadband: 1185782129
      Quiet time after excitation: 1185782154

    • Quiet time before excitation: 1185789384
      Excitation broadband: 1185789419
      Quiet time after excitation: 1185789444

    • Quiet time before excitation: 1185796675
      Excitation broadband: 1185796710
      Quiet time after excitation: 1185796735


  • 11:00am valve closed, pumps stopped, venting
  390   Thu Aug 3 11:55:18 2017 Gabriele, RosalieGeneralMeasurementsS1600520 S1600521 S1600523 S1600524


  • 11:43am in chamber
    • S1600520 in CR1
    • S1600521 in CR2
    • S1600523 in CR3
    • S1600524 in CR4
  • 11:46am roughing pump on
  • 11:55am turbo pump on
  • Excitations:
    • Quiet time before excitation: 1185835692
      Excitation broadband: 1185835727
      Quiet time after excitation: 1185835752

    • Quiet time before excitation: 1185837582
      Excitation broadband: 1185837617
      Quiet time after excitation: 1185837642

    • Quiet time before excitation: 1185839472
      Excitation broadband: 1185839507
      Quiet time after excitation: 1185839532

    • Quiet time before excitation: 1185841362
      Excitation broadband: 1185841397
      Quiet time after excitation: 1185841422

    • Quiet time before excitation: 1185843252
      Excitation broadband: 1185843287
      Quiet time after excitation: 1185843312

    • Quiet time before excitation: 1185845143
      Excitation broadband: 1185845178
      Quiet time after excitation: 1185845203

    • Quiet time before excitation: 1185847033
      Excitation broadband: 1185847068
      Quiet time after excitation: 1185847093

    • Quiet time before excitation: 1185848923
      Excitation broadband: 1185848958
      Quiet time after excitation: 1185848983


  • 2:00pm valve closed, pumps off, venting
  391   Fri Aug 4 14:15:16 2017 Gabriele, RosalieGeneralMeasurementsS1600535, S1600536, S1600537, S1600538


  • 2:04pm in chamber
    • S1600535 in CR1
    • S1600536 in CR2
    • S1600537 in CR3
    • S1600538 in CR4
  • 2:06pm roughing pump on
  • 2:15pm turbo pump on
  • Excitations:
    • Quiet time before excitation: 1185930952
      Excitation broadband: 1185930987
      Quiet time after excitation: 1185931013

    • Quiet time before excitation: 1185932843
      Excitation broadband: 1185932878
      Quiet time after excitation: 1185932903

    • Quiet time before excitation: 1185934733
      Excitation broadband: 1185934768
      Quiet time after excitation: 1185934793

    • Quiet time before excitation: 1185936623
      Excitation broadband: 1185936658
      Quiet time after excitation: 1185936683

    • Quiet time before excitation: 1185938513
      Excitation broadband: 1185938548
      Quiet time after excitation: 1185938573

    • Quiet time before excitation: 1185940403
      Excitation broadband: 1185940438
      Quiet time after excitation: 1185940463

    • Quiet time before excitation: 1185942293
      Excitation broadband: 1185942328
      Quiet time after excitation: 1185942353

    • Quiet time before excitation: 1185944183
      Excitation broadband: 1185944218
      Quiet time after excitation: 1185944243



  • 1:23pm valve closed, pumps stopped, venting


  297   Wed Feb 8 17:06:11 2017 Gabriele, LarryElectronicsConfigurationPrivate network

This morning Larry set up a network switch to create a local network for the power strip and the two Newport picomotor controllers. The laboratory workstation serves as gateway between the networks.

I still have to configure the power strip and the picomotor controllers to use the new static IP address.

  299   Thu Feb 9 09:10:17 2017 Gabriele, LarryElectronicsConfigurationPrivate network

I reconfigured the powerstrip and the two Newport controllers to use static IP address in the new 10.10.10.X network, using the workstation as gateway. All scripts updated and working


This morning Larry set up a network switch to create a local network for the power strip and the two Newport picomotor controllers. The laboratory workstation serves as gateway between the networks.

I still have to configure the power strip and the picomotor controllers to use the new static IP address.


  456   Tue Jan 30 15:56:36 2018 Gabriele, CraigElectronicsConfigurationTemporary data acqusition for PSL lab beat note and accelerometers

We set up the model x3tst to acquire at 65kHz four signals coming from the PSL lab:

  • X3:TST-BEAT_OUT_DQ: beat note
  • X3:TST-ACC_X_OUT_DQ: accelerometer X
  • X3:TST-ACC_Y_OUT_DQ: accelerometer Y
  • X3:TST-ACC_Z_OUT_DQ: accelerometer Z
  241   Mon Dec 12 16:34:15 2016 Gabriele, Brittany, AaronGeneralMeasurementsS1600480


  • 4:32pm, in chamber, balanced
  • 4:33pm, roughing pump on
  • 4:46pm, turbo pump on


  • Excitation:
    • Quiet time before excitation: 1165689679
      Excitation brodband (3 kV, 60s)
      Quiet time after excitation: 1165689920
  453   Thu Jan 25 15:33:51 2018 Gabriele, BenGeneralAnnealingAnnealing of 50mm disks

Annealing of 8 fused silica substrates (50mm/0.5mm) started at 3:30pm, January 25th 2018. Standard program: 9 hours ramp up to 900 C, 9 hours hold, 9 hours ramp down

  476   Mon Mar 5 11:03:18 2018 Gabriele, AnthonyGeneralMeasurementsFused silica substrated for metallic glass tests


  • 10:45am in chamber:
    • AK_01 in CR1
    • AK_02 in CR2
    • AK_03 in CR3
    • AK_04 in CR4
  • 10:55am roughing pump on
  • 11:05am turbo pump on
  88   Wed Aug 17 16:41:05 2016 Gabriele, AlenaCleanDaily ProgressClean room construction progress

The clean room frame is built and secured to the floor and wall. Panels are being installed on the ceiling and back. Also, the optical table has been leveled.

  89   Thu Aug 18 18:15:18 2016 Gabriele, AlenaCleanDaily ProgressClean room construction progress

Ceiling, back and side panels are installed. The air filters have been cabled and connected to the power supply.

  285   Tue Jan 31 16:50:55 2017 Gabriele, AlenaGeneralVacuumFirst pump-down with setup

This afternoon we started the pump-down with all the system installed into the chamber. Unfortunately the IGM vacuum gauge isn't working, so we can't be sure what the pressure is. To be fixed

  101   Mon Aug 22 16:59:13 2016 Gabriele, AlastairOpticsDaily ProgressLaser polishing of the disk edges

We set up a test facility for laser polishing the disk edges, using the CO2 laser in the TCS laboratory. We focused the beam with a 10" focal length lens, and installed the disk on a "rotation stage" that we motorized with a hand drill. We used a HeNe optical lever and a small container with water to define the horizontal plane and adjusted the disk as well as we could.

We first tested the procedure on the MO02 disk, which is the one already scared with the electrostatic drive burn mark. This disk is now definitely in bad shape. However, we felt confident in our procedure, so we took out the MO03 disk that was into the measurement system and proceeded to laser polish the edges. Things went quite smothly. Unfortunately we added some small damages to the disk surface in a couple of spots where the CO2 laser went out of alignment and melted the fused silica support of the disk. The edge however looks quite good now.

Q measurement is on-going at the timw of writing

  192   Wed Nov 16 09:43:25 2016 Gabriele, AlastairGeneralDaily ProgressCO2 laser polishing setup

Yesterday we assembled the lase polishing system. The Co2 laser power can be controlled using a waveplate, so we can turn on the laser at maximum power and let it stabilize, before actually turning up the power sent to the disk.

The beam is focused with a 10" focal length lens, and sent to the disk edge, poiting slightly upward to avoid hitting any other part of the disk.

The disk is moved with a combination of a linear and rotation stage, controlled with a MATLAB script. We tuned the translation and rotation speed so that the edge always moves at about 0.5 mm/s. Some refinement of the movimentation procedure will follow.

We tried the setup with one of the damaged samples, and the results are quite good.

More work this afternoon

Attachment 2: 2016-11-15_16.35.14.jpg
  198   Thu Nov 17 17:59:44 2016 Gabriele, AlastairGeneralGeneralCO2 laser polishing tests

We improved the control software of the laser polishing system: now the rotation speed is large when the laser is missing the disk because of the flats.

We used S1600479 as a test. This substrate was marked as damaged and had a clear chip. It went thoruhg two different polishing runs

  • CO2 power ~19.5 W, speed 0.5 mm/s
  • CO2 power ~18.5 W, speed 0.25 mm/s

The second run was probably too slow, and we can see some kind of traces left on the main surface close to the edges

We then laser polished a good subtrate (S1600439) which was already measured before (137) and after annealing (144), with good Q values. This is a substrate from the first batch we received from Mark Optics. The polishing was done at ~ 18W and 0.5 mm/s.

Some pictures below:

  205   Mon Nov 21 16:21:12 2016 Gabriele, AlastairGeneralGeneralLaser polishing of S1600487

The sample has been laser polished this afternoon, 0.5mm/s, average power 23 W.

We moved the lens that focuses the beam about one inch toward the sample, to make the beam slightly larger.

  220   Thu Dec 1 11:59:21 2016 Gabriele, AlastairGeneralGeneralLaser polishing

Today we laser polished S1600484, S1600485 and S1600486.

  445   Mon Dec 11 08:49:08 2017 Gabriele, Aaron, Brittany, SethGeneralMeasurements50mm / 0.5mm substrate from University Wafers
  • Installed in the test chamber CR0
  • Excitations:
    • Quiet time before excitation: 1196822477
      Excitation broadband: 1196822509
      Quiet time after excitation: 1196822532
    • Quiet time before excitation: 1196826162
      Excitation broadband: 1196826194
      Quiet time after excitation: 1196826216
    • Quiet time before excitation: 1196829846
      Excitation broadband: 1196829879
      Quiet time after excitation: 1196829901
    • Quiet time before excitation: 1196833531
      Excitation broadband: 1196833563
      Quiet time after excitation: 1196833585
    • Quiet time before excitation: 1196837215
      Excitation broadband: 1196837248
      Quiet time after excitation: 1196837270
    • Quiet time before excitation: 1196840900
      Excitation broadband: 1196840933
      Quiet time after excitation: 1196840955
    • Quiet time before excitation: 1196844585
      Excitation broadband: 1196844617
      Quiet time after excitation: 1196844639
    • Quiet time before excitation: 1196848269
      Excitation broadband: 1196848301
      Quiet time after excitation: 1196848323


  480   Thu Mar 8 11:27:01 2018 Gabriele Alena Eric LiyuanGeneralMeasurementsS1600620 S1600621 S1600623 S1600624


  • 11:00am in chamber
    • S1600620 in CR1
    • S1600621 in CR2
    • S1600623 in CR3
    • S1600624 in CR4
  • 11:10am roughing pump on
  • 11:20am turbo pump on
  485   Tue Mar 13 17:20:09 2018 Gabriele Alena GeneralMeasurementsS1600609 S1600611 S1600612 S1600613


  • 5:15pm in chamber
    • S1600609 in CR1
    • S1600611 in CR2
    • S1600612 in CR3
    • S1600613 in CR4
  • 5:20pm roughing pump on
  • 5:34pm turbo pump on
  30   Thu Jul 7 16:40:22 2016 Gabriele ElectronicsDaily ProgressQPD boxes

To mitigate the issue of ambient light pulluting the QPD signal, I mounted the prototype into a custum built box. This helps a lot. My plan is to add a short piece of black pipe in the front, to further shield from incident light.

The new box also provides a clean way to mount the QPD.

  9   Mon May 2 11:46:45 2016 GabrieleFacilityDaily ProgressTable and vacuum chambers in the lab

Elogs for the new Coatin RIng-down MEasurement lab had to start somewhere, so here is a couple of pictures of the optical table with shorter legs and of one of the two vacuum chambers that have been moved in.

  10   Tue May 3 11:57:47 2016 GabrieleFacilityDaily ProgressTable and vacuum chambers in the lab

We discovered a couple of days ago that the table was sitting on three legs only and the fourth one was dangling. I managed to adjust the height of the fourth leg using the large screw on the leg support. Now the table is properly supported by all four legs.


Elogs for the new Coatin RIng-down MEasurement lab had to start somewhere, so here is a couple of pictures of the optical table with shorter legs and of one of the two vacuum chambers that have been moved in.


  11   Fri May 6 14:20:43 2016 GabrieleElectronicsDesignDesign of optical lever electronics

For the optical levers we are going to use the same QPD that are used in aLIGO optical levers (see T1600085 and D1100290): Hamamatsu S5981

Based on the aLIGO design, I put together a design fof the QPD boards, see the first attached PDF file. Some comments:

  • I'm using a quad opamp to implement the transimpendance and a doubel stage of whitening for the readout of each quadrant. I haven't decided yet which is the right whitening
  • The bias to the QPD is just coming from the +15V with a capacitor to ground, as in the aLIGO setup. However, I allowed the possibility of supplying a lower noise bias if needed, by removing R0 and connecting an external circuit
  • There is no sum or difference computation, each quadrant is sent directly to the ADC with a differential driver (DRV135)
  • Each board hosts one QPD, and it is interfaced with a 14 pin header (we're going to use twisted cables for the signals)

The stable power supply will be provided by an additional board, which will also interface 8 QPD boards to the ADC connector, see the second attached PDF. The ADC signal grounds can be connected directly to the power supply ground, left floating, or connected with a RC filter, depending on what we find to be the best solution.

Total cost estimated for PCB manufacturing and components, including the QPDs is less than 3k$, for a total of 12 boards (we need 8, plus some spares)

Attachment 1: qpd.PDF
qpd.PDF qpd.PDF
Attachment 2: Breakout.PDF
Breakout.PDF Breakout.PDF
  13   Tue May 10 13:32:17 2016 GabrieleElectronicsDesignDesign of optical lever electronics

After a very useful discussion with Rich this morning, I think the circuit based on aLIGO optical levers design should be good for our applications.

It uses a LT1125 as input stage, which has

  • (maximum) current noise of 1e-12 A/rHz @ 100 Hz and 0.4e-12 A/rHz @ 1 kHz
  • (maximum) voltage noise of 4e-9 V/rHz @ >100 Hz

We expect to send about 5 mW into the disk, getting back a 4% reflection, which would correspond to 200 uW on the QPD. Let's say we lose half of this power in reflections through viewports and such, so we have a total of 100 uW on the QPD, or 25 uW on each quadrant. From the QPD datasheet the repsonse is about 0.4 A/W, so we have a photocurrent of 10 uA. The corresponding shot noise limit is about 1.8e-12 A/rHz.

Using a transimpendace of 200k, the noise at the output of the transimpendance is

  • shot noise = 3.6e-7 V/rHz
  • voltage noise = 4e-9 V/rHz
  • current noise = 2e-7 V/rHz @ 100 Hz, 0.8e-7 V/rHz @ 1 kHz

So in the worst case the current noise will be about half of the shot noise. This seems good enough.


Koji, Rich, and I recently came up with a new QPD design which is better for general lab use than the aLIGO ones (which have a high-noise preamp copied from iLIGO). 


This page has the mechanical drawing only, but perhaps Rich can tell us if he's ready to make the first version for you or not. I think you can get by with the old design, but this new one should be lower noise for low light levels.


  14   Thu May 19 11:33:44 2016 GabrieleElectronicsDesignOptical lever electronics design

The circuit design sent out for fabrication is available in the DCC: D1600196

  15   Thu May 19 11:36:04 2016 GabrieleMechanicsDesignA first design of the disk assembly

Here are some screenshots of the disk assembly and a look at how four of them will sit into the vacuum chamber. The Solidworks models are available here: D1600197

Attachment 3: Screen_Shot_2016-05-18_at_3.41.25_PM.png
  16   Fri May 20 15:18:58 2016 GabrieleOpticsDesignOptical levers layout

Attached a first layout of the optical lever systems. The beam spot radius on the QPD is about 0.8 mm, and the lever arm length is of the orer of 1.4-1.5 m for all four beams.


Attachment 1: crime_v1.pdf
  17   Sun May 22 23:40:45 2016 GabrieleOpticsDesignOptical levers layout

An improved design is attached. I modified the input telescope to avoid using shor focal length lenses, to make it less critical, and to reduce the beam spot radius at the QPD to 0.5 mm.


Attached a first layout of the optical lever systems. The beam spot radius on the QPD is about 0.8 mm, and the lever arm length is of the orer of 1.4-1.5 m for all four beams.



Attachment 1: crime_v1.pdf
  18   Thu May 26 02:51:27 2016 GabrieleElectronicsDesignESD design

A preliminary design of the ESD board is available on the DCC: D1600214

  19   Fri May 27 02:09:37 2016 GabrieleMechanicsCharacterizationLowest usable mode of fused silica disks

I did some FEA simulation of fused silica disks, to identify the lowest usable eigenmode. By usable I mean a mode that has zero elastic energy stored in the center. 

Diameter Thickness Frequency
75 mm 1 mm 2500 Hz
100 mm 0.4 mm 564 Hz
200 mm 0.4 mm 141 Hz
75 mm 0.12 mm 293 Hz

In the attached figures, the dfisk deformation is shown exaggerated, and the color map shows the elastic energy density. All results are obtained with COMSOL/MATLAB, the disk are constrained at a point corresponding to the center of the lower surface. No gravity.

Attachment 1: disk_75mm_0.12mm.png
Attachment 2: disk_75mm_1mm.png
Attachment 3: disk_100mm_0.4mm.png
Attachment 4: disk_200mm_0.4mm.png
  20   Mon Jun 6 13:35:36 2016 GabrieleElectronicsGeneralComponents

The PCBs for the QPD circuit and ADC interface are here and look ok. All electronics components are also here (except for the ADC connector which should be ordered separately from Mouser, after confirming that the ADC we're going to use have the same cable as the one we use in the Crackling Noise experiment). The QPD will be shipped on 06/17.

  21   Tue Jun 7 14:07:55 2016 GabrieleFacilityGeneralRack and workstation

I moved the unused rack from the Crackling Noise lab to the C.Ri.Me lab. It will be used for the new cymac. I also started putting the new workstation together, but I'm missing some adaptors for the monitors.

  22   Fri Jun 10 13:44:06 2016 GabrieleElectronicsConfigurationHow to setup a workstation

Instructions on how to setup a workstation are available here:


I'll copy them here and integrate once I got the C.Ri.Me. workstation up and running


** libmotif4 >> libxm4 : sudo apt-get install libxm4

** all .sh files in etc must be modified to point to the correct version of the downloaded software

** add the following line to the end of the ligoapps-userv-end.sh file to get medm and striptool working


** to fix diaggui problem, create a symbolic link in /usr/lib/x86_64-linux-gnu/

sudo ln -s libtiff.so.5 libtiff.so.4

  23   Thu Jun 16 00:47:42 2016 GabrieleOpticsDaily ProgressQuality factor measurement of a Mark Optics disk at LMA

[Massimo Granata (LMA), Quentin Cassar (LMA), Gabriele] 

This week I'm visiting LMA to learn how their Gentle Nodal Suspension system works and to measure the quality factors (Q) of one of Mark Optics disks. First of all we annealed the disk for 9 hours at 900 degrees (plus 9 hours warm up and 9 hours cool down).

Then we installed the disk into the measurement system and started by searching for all the resonances.

My COMSOL simulation proved to be good enough to give us the frequencies, especiallty after a small fine tuning of the disk thickness (within specs). We identifies a total of 32 modes of different families, and measured the ring down of all of them. Since our disk has no flats, each mode is actually a doublet with very small frequency separation. The analysis software has a bandwith of 1 Hz to find the peak amplitude, so it can't resolve the two modes. When both are excited to a significant amplitude by the electrostatic actuator, we see a clear beat in the ring-down. I had to write a new fitting code to take this into account. More details will follow in a DCC document. However, here I can say that the fit works remarkably well for all modes. 

A couple of examples:


Here is a summary plot of the quality factor and loss angle for all modes. We measured Q as high as 10e6, in line with other LMA samples (2") we tested in these days. In conclusion, the Mark Optics disks, as they are, are good enough for our coating tests.


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