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ID Date Author Type Category Subjectup
  497   Tue Mar 27 16:36:49 2018 GabrieleOpticsConfigurationOptical levers re-aligned for 50mm substrates
  51   Mon Jul 18 18:05:46 2016 GabrieleOpticsDaily ProgressOptical setup

Small modifications to the optical setup:

  • added a 1m focal lenght lens (AR coated for 1064nm...) right before the beam enters the viewport, to reduce the beam spot size on the QPD
  • added a 0.3 ND right after the laser, to avoid saturation of the QPD (about 75 microwatts total on the QPD)

  401   Wed Aug 9 17:07:57 2017 ZacharyElectronicsModelingOptimization Summary

2017-08-09

  • From the data I have gathered from a variety of MATLAB sweeps, I think that the optimal geometry I can produce has the parameters in the attached image. Neither the original or optimized drawing is to scale. The gap between the arms of the electrodes should be 1.25 mm, the arm width 0.55 mm, the arm length 16 mm, and the offset of the arms 3.5 mm.

  • It is also optimal to place the ESD as close to the sample disk as can reasonably be achieved, at around 0.5 mm away. Since the force on the disk scales exponentially with the distance from the ESD, decreasing that gap is the most substantial way to impact the excitation. Decreasing the gap from 1 mm to .5 mm increases the excitation of the modes by approximately a factor of 8.

  • From my simulations, the shift in geometry alone still has a useful impact on the excitation. Modes 1 and 3 are the only two modes that are less excited by the new geometry, mode 1 is 10% weaker  and mode 5 is 5% weaker. Modes 5 and 6 are nearly unaffected by the shift, mode 5 is 2% stronger and mode 6 is 5% stronger.  Modes 7, 18 and 19 are outliers, 7 is excited by a factor of 7, 18 by a factor of 4 and 19 by a factor of 17. The rest of the modes are improved by between a factor of 1.5 and 3. For mode numbers, shapes, and frequencies a plot is included.

Attachment 1: resonantmodes.pdf
resonantmodes.pdf
  416   Thu Aug 17 23:34:51 2017 ZachElectronicsModelingOptimized ESD Drawing

2017-08-17

  • 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
OptimizedESD.pdf
  389   Wed Aug 2 15:40:00 2017 ZachElectronicsModelingParameter diagram

I am posting a diagram of the geometric parameters that I swept. The only one not included is the vertical space between the ESD and sample that sweeps perpendicularly out of the image

 

  375   Mon Jul 24 09:13:45 2017 ZachElectronicsModelingParametric Sweep

2017-07-24

  • I wrote a MATLAB script that is capable of sweeping parameters, the code is attached. The next step is to create nested loops so that I can sweep multiple parameters in a single run. I also should add a function in the script to eliminate the modes that cannot be measured by the experimental setup.
  • My first sweep was for the gap between electrodes and swept from 1 to 2 mm. In the plot the gap grows from steps 1 to 6 and the only obvious effect in the plot is a decrease in force from the highest mode. Intuitively it makes sense that a wider gap would decrease the force because the electric field is diminished by spreading out the electrodes.
  • I would like to add a parameter for the overlap of the electrodes, but this would require substantial redesigning of the COMSOL model due to the multilevel dependency on parameters. 

Attachment 2: forcesweep.m
fpro = zeros(6, 27);
no = 1;
for count = 1:.2:2
    gap = strcat(num2str(count), ' [mm]')
    model = fst2(gap);
    forces;
    fpro(no, :)= product(:);
    no = no + 1;
end
  381   Wed Jul 26 21:22:50 2017 ZachElectronicsModelingParametric Sweep Results

2017-07-26

  • I resolved the major bugs in the parametric sweep scripts and ran low resolution sweeps of the gap between the ESD and sample (Gap Sweep) and the spacing between the ESD arms (ESD Arm Gap Sweep).
  • The arm gap sweep largely behaved in a reasonable way with a maximum excitation at a 1.25 mm gap. However modes 14, 19, and 25 did not follow the general trends and had sharp drops and increases compared to the other modes.
  • The sample gap sweep had less intuitive behavior, all of the modes followed the same general double peak trend that drops to zero when the gap is 1.5 mm. I cannot explain exactly why it is behaving that way, I will run a higher resolution sweep and examine the geometry in greater detail.

 

  378   Tue Jul 25 13:38:30 2017 ZachElectronicsModelingParametric Sweep of ESD gap

2017-07-25

  • I completed a short sweep of the gap between the drive and the sample, between .5 and 1 mm in .1 mm increments. It appears that a 1 mm distance is the ideal distance by approximately a factor of two. I will next sweep larger distances and see how the force profile behaves at greater distances.

  189   Tue Nov 15 10:35:11 2016 GabrieleMechanicsDaily ProgressParts for laser polishing setup are here

The parts all fit as expected. They're mounted on the stages.

  70   Fri Jul 29 14:08:31 2016 GabrieleGeneralDaily ProgressPeak tracking code for real time model

Summary

I wrote a C function to reconstruct the amlplitude and frequency of a line. It can be added as a block into a real time monitor. The idea is to use it to track in real time the frequency and amplitude of the disk modes, during the ring down. I did some tests and finally managed to get the function to compile and run on the cymac2 (the crackling lab cymac).

The following plot shows a simulation, since I can't run the code on the new cymac and I don't have the disk installed anymore. The top panel gives the amplitude of a decaying line, and the bottom panel the frequency offset from a reference local oscillator (more below). The nominal values are an initial amplitude of 1, frequency of 1109.375 Hz to be compared to a 1109.0 local oscillator. The fitted decay time is 10.005 seconds, to be comapred with 10 seconds nominal. There is some additive gaussian noise, that causes the ring down to be unmesurable after about 70 seconds of data.

This code will be used for real time estimation of the disk modes, once theot frequency has been roughly estimated with FFTs. The estimation of the frequency work remarkably well. In the first 20 seconds the mean value is 0.3747 Hz, with a standard deviation of 1.5 mHz. When the SNR gets worse (between t=30s and t=50s) the mean value is 0.3745 with a standard deviation of 20 mHz. 

Because of the way it's built (see below) the code is sensitive to DC offsets, so the input signal must be high-passed.  

Details on the implementation

The code is based on demodulation of the input signal with a reference local oscillator thta must have a frequency as close as possible to the line we want to track.  The inputs to the block are: the signal to be monitored, sine of the local oscillator, cosine of the local oscillator. The outputs are: amplitude squared of the peak, frequency offset in Hz from the local oscillator.

Here's the math. Let's assume that the signal is

x(t)=A \sin (2\pi f t + \phi)

and the local oscillator has a frequency f0:

s(t)= \sin (2\pi f_0 t) \qquad c(t)= \cos (2\pi f_0 t)

The code multiply the signal by the two local oscillators and average the result over 65kHz / 8 Hz samples. Therefore we get two output streams at 8 Hz which are

\left< x(t) s(t) \right> = -\frac{A}{2} \sin\left[2\pi(f-f_0)t + \phi \right]

\left< x(t) c(t) \right> = \frac{A}{2} \sin\left[2\pi(f-f_0)t + \phi \right]

Then the sum of the two squared 8 Hz streams give an estimate of the amplitude squared. The code computes this every second

\hat A = 4 \left[ \left<x(t) s(t)\right>^2+\left<x(t) c(t)\right>^2\right]

while the arctangent of the ratio gives a phase that varies linearly with time.

\arctan \frac{\left< x(t) c(t)\right>}{\left< x(t) s(t)\right>} = \phi + 2\pi(f-f_0)t

For each of the 8Hz samples the code computes the arctangent (using a home-brewed function based on a lookup table, since we can't import math.h in the RCG). It unwraps it, and then every second fit a line to the unwrapped arctangent, to estimate the frequency offset with respect to the local oscillator.

The C function has some parameters hard coded: the main sampling frequency (65536 Hz), the number of points per second to use for the frequency estimation (8 Hz), the fact that the output is computed every second. The first two parameters can be changed, the third one cannot for the moment being.

Attachment 2: Screen_Shot_2016-07-29_at_2.02.24_PM.png
Screen_Shot_2016-07-29_at_2.02.24_PM.png
  275   Tue Jan 24 11:45:55 2017 GabrieleElectronicsConfigurationPicomotor drivers
  • Changed the library Picomotor8752.py to add a third axis 'r' that will allow moving the in-vacuum retaining ring. The controller remains connected to the workstation through a serial cable
  • Tested a new NewFocus 8741 controller with USB and ethernet. The USB driver works only on Windows, so I tested it by running a Windows virtual machine. I used this trick to get the IP address of the controller. Then I wrote another library Picomotor8742.py that uses TCP/IP sockets to communicate with the driver via ethernet. Tested and working. Each driver can control up to four axis, so the user can choose which QPD centering mirror to move (1/2 or 3/4) and which axis (x or y)
  85   Sun Aug 14 18:26:19 2016 GabrieleGeneralGeneralPlans for the automatic mode search

Here's how I imagine the mode search to proceed:

  1. the user select the list of nominal frequencies and the frequency range for the search
  2. the automation creates an excitation which is a sum of band-limited white noise, centered around each of the modes, with the desired bandwidth. The excitation is normalized to match a reasonable fraction of the DAC range
  3. the excitation is injected for a given amount of time and each band is searched for the mode. In each band, if a mode is found, the frequency is estimated together with the maximum SNR obtained and the results are saved
  4. if some modes are not found, the automation will try to improve the noise, by scaling all band amplitudes in such a way to have the same resulting SNR for the modes. In this way we should get more dynamical range and could increase the excitation for the modes that were not found
  5. if some modes are still unidentified, then the user will be asked to choose between a few options:
    1. skip the mode
    2. try to excite it with an excitation focused on that band only
    3. increase the bandwidth for the search
    4. maintain the same bandwidth but move the band to adjacent frequencies
  6. At the end all identified modes will be stored in memory and saved to a file defined by the user
  353   Fri Jun 23 12:02:12 2017 ZachElectronicsModelingPlots

2017-06-23

  • I created plots of the E field and potential from my rough model of the ESD. This model has 1mm electrode arm widths and spacings, the length of each arm is 16 mm, and the resulting total size is 38mm x 20 mm x 0.1 mm. One comb has ten arms while the other has nine to match the actual ESD currently in use in the lab. 
  • I set the ten arm comb to a potential of 100 V and the other to ground. I then used physics controlled mesh with an extremely fine element size to computer the simulations. With mesh sizes larger than extra fine, there was clearly non-physical error in the electric field and potential graphs that appeared as inexplicable field lines, spikes, and coarseness in the plots. 
  • To create readable plots of the potential I created a Cut Plane in the center of the ESD perpendicular to both the arms and the plane of the device. The plots are attached with a milimeter length scale. I created a filled contour plot of the potential that is very clean, I tried a couple of different options for the electric field because it is harder to represent well. I created a contour plot for the norm of the electric field as well as superimposing a streamline plot of the field lines over that. Everything behaves generally as expected though I do suspect the spikes in electric field at the edges of each electrode are due to the fact that they are sharp corners and not smooth edges.

 

 

Attachment 1: Potential.png
Potential.png
Attachment 2: E_w_Lines.png
E_w_Lines.png
Attachment 3: Mesh.png
Mesh.png
  71   Mon Aug 1 16:56:57 2016 GabrieleElectronicsDaily ProgressPopulated four new QPD boards

Today I populated four more QPD boards. All components are installed, except for the QPD themselves.

  157   Fri Nov 4 08:13:25 2016 GabrieleElectronicsGeneralPower outage?

This morning I found the cymac and the workstation rebooted, so I suspected a power cut in the last days. However, the function generator and the power supply for the QPD were off. So somebody must have turned them off.

Please write those actions in the elog!

  399   Wed Aug 9 12:10:47 2017 ZachElectronicsModelingPreliminary improvement from ESD optimization

2017-08-09

  • I created a plot of the ratio of the force in the optimized design to the force in the original design. The improvement factor is huge, some modes are excited by more than a factor of 100. I took the same ratio keeping the gap between the ESD and the sample constant and it decreased the excitation by almost a factor of 10. Keeping that gap constant, the geometric modifications to the ESD give an improvement factor ranging from almost 2 to almost 4 for most of the modes. Modes 10 and 25 are outliers but in the original geometry they are barely excited at all, so this could easily be a numerical artifact where those modes were excited at a minimum in the original geometry.

Attachment 1: Ratio.jpg
Ratio.jpg
  63   Wed Jul 27 08:59:12 2016 GabrieleElectronicsGeneralPressure now in torr

The old channel X3:CR1-PRESSURE_LOGTORR does not exist anymore. The new channel is now directly in torr and it is called X3:CR1-PRESSURE_TORR.

I had to write a C function to compute the 10^x operation, since it is not included in the RCG routines. Also it's not possible to include library functions, so I had to write an ad-hoc function, which first compute the integer part of the exponent, and then approximate the fractional part with linear interpolation and a look-up table. Code is in /opt/rtcds/userapps/release/models/pow10.c

  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

Quote:

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.

 

  84   Sun Aug 14 18:13:52 2016 GabrieleElectronicsDaily ProgressProgress on the user interface

Some progress on writing the user interface:

Now the user can open a file that defines the nominal mode frequencies (from COMSOL simulations) and select which modes to search for:

The plan is that the automation will then inject band limited noise around each nominal frequency, to excite the mode, and then find the exact frequency. The user can set some additional parameters like

  • the duration of the excitation (I plan to use this as a maximum: if the mode rings up with large enough SNR after a shorter time, the injection will stop earlier)
  • the amplitude of the excitation (units to be determined)
  • the bandwitdh, otr in other words how many Hz the noise will be spread around the nominla frequency to search for the mode.
  • the minimum SNR to detect a peak (here the automation will get a spectrum before any excitation, to be used as the baseline to whiten all further spectra)
  117   Tue Sep 20 16:12:09 2016 GabrieleGeneralGeneralPump down

As a test, I installed MO1 (the disk with the burn mark, used for the first edge laser polishing test) and started pumping down. Roughing pump on at 3:05pm, turbo pump on at 3:16pm.

  45   Sat Jul 16 14:15:44 2016 GabrieleFacilityDaily ProgressPump down started

Following Alena's procedure, at about 1:30pm LT I started the chamber pump down. At 14:15pm LT the pressure was still 240 mTorr

At 6:20pm the pressure was about 70 mTorr, so I started the turbo pump.

  46   Mon Jul 18 13:39:45 2016 GabrieleFacilityDaily ProgressPump down started

Today at 1:40pm pressure is 8.5e-7 Torr

Quote:

Following Alena's procedure, at about 1:30pm LT I started the chamber pump down. At 14:15pm LT the pressure was still 240 mTorr

At 6:20pm the pressure was about 70 mTorr, so I started the turbo pump.

 

  111   Thu Sep 15 08:13:20 2016 GabrieleGeneralGeneralPump had no effect on ring down measurements

The plot below shows three measurements of the Q of the same disk: during the first two the roughing pump was on, while during the third it was off. No significant difference is visible in the Q values.

  115   Fri Sep 16 14:06:43 2016 GabrieleGeneralGeneralPump had no effect on ring down measurements

Same plot as below, but this time with estimated 95% confidence intervals for the Q values, as obtained from the fit only.

Quote:

The plot below shows three measurements of the Q of the same disk: during the first two the roughing pump was on, while during the third it was off. No significant difference is visible in the Q values.

 

 

  65   Wed Jul 27 11:27:11 2016 GabrieleFacilityGeneralPumps stopped and venting

11:25am LT: closed valve between roughing and turbo pumps, switched off both pumps. Turbo pump is slowing down

After lunch I opened the chamber and removed everything from the inside.

The chamber around the vacuum gauge is really dirty now, see picture:

In addition, the electrostatic driver shows some signs of "burn" even though it was still working quite well. Unfortunately, whatever happened contaminated our sample:

  343   Mon May 15 13:19:12 2017 GabrieleGeneralMeasurementsQ measured again after four weeks in vacuum

I measured again two of the substrates that have been sitting in the pumped-down vacuum chamber for about four weeks. The pressure now is below 1e-7 Torr. There is no significant difference between the two sets of measured Q values.

  318   Fri Feb 24 13:21:03 2017 GabrieleGeneralMeasurementsQ of substrates with polished edges

Below the measured Q values of the six Suprasil 313 substrates, with polished edges, after annealing at 900 degrees C for 9 hours.

They are all consistently at a level of 100e6 at 1 KHz and showing a similar frequency dependency going down to a about 30e6 at 20-30 kHz. The only exception is S1600522 which has clearly lower Q values at all frequencies.

Below a comparison of the substrate loss angles compared wiht Steve Penn's model:

Attachment 7: losses_model.png
losses_model.png
  127   Mon Sep 26 15:59:09 2016 GabrieleOpticsDaily ProgressQPD auto centering

We have a few motorized mounts (with New Focus picomotors) and one controller (an old New Focus 8753, six axis total) that I connected with a makeshift null modem cable to the laboratory workstation (better cabling and power supply coming soon).

I wrote a couple of python scripts that can be used to continuosly read out the QPD values and move the picomotors if needed. It's wortking quite well, so we should be able to use it in the future to keep the QPD centered during the measurement. 

The scripts are in the ~/CRIME directory. Launch the function center() in the autocenter.py script.

  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.

  301   Thu Feb 9 11:35:27 2017 GabrieleOpticsConfigurationQPD calibration

This morning I measured the beam profiles at the QPD positions. As expected, the beams are not gaussian there, since we are seeing the interference of the reflections from the two faces of the disks. Nevertheless, the measured sizes are

  Beam radius [microns]
QPD1 302
QPD2 338
QPD3 270
QPD4 401

Here are the images of the beams:

The arm lever lengths (distance from the disk surface to the QPD) can be estimated from the optical drawing:

  Distance disk to QPD [mm]
QPD1 1540
QPD2 1813
QPD3 1587
QPD4 1652

The optical gain (normalized QPD signal over disk surface angle) is given by

g = \frac{4 L}{w} \sqrt{\frac{2}{\pi}}

  Gain 1/rad
QPD1 16300
QPD2 17100
QPD3 18800
QPD4 13150

The uncertaint in those numbers is quite large, both from the beam size and from the arm lever. Anyhow, I'm using the average to have a rough calibration of the QPD signals in terms of disk surface angular motion. The value I plugged in into the X_NORM filter banks is 16300 /rad. Therefore now the signals *NORM_OUT_DQ are calibrated in radians (deflection of the disk surface).

Finally, I also measured the profiles of the beams going into the chamber, somewhere before the 2" folding mirror. They have nice gaussian shapes

Attachment 1: qpd1.bmp
Attachment 9: IN3.png
IN3.png
  44   Fri Jul 15 17:56:50 2016 GabrieleGeneralDaily ProgressQPD connected to digital system

I connected the QPD to the ADC interface with a temporary cable running on the floor.

I could get signals. I still have a problem with the digital system: I can't access test points with dataviewer, but I get them with DTT. This will have to be fixed.

 

  24   Fri Jun 24 17:03:47 2016 GabrieleElectronicsDaily ProgressQPD electronics

Between yesterday and today I populated one QPD board (based on D1600196), and started testing it. The transimpedance stages seems to work fine (they show about 5-6 V in ambient light). However the whitening stages show a large ~100 kHz oscillation. While trying to fix it I probably burnt one of the output drivers.

I'll continue the investigations and debugging on Monday.

  25   Tue Jun 28 10:17:28 2016 GabrieleElectronicsDaily ProgressQPD electronics

Transimpendance and whitening are working properly. I can't get useful signal out of the differential stages yet. I replaced the channel 1 DRV134 that was burnt (very hot when powered on). But the new one got hot too after powring on, so there might be something else wrong there. I'm also wondering if it's ok to use an oscilloscope to look at the differential stage output. The scope will ground one of the two outputs: according to the DRV134 datasheet this should be ok, but I'll check better later on.

Quote:

Between yesterday and today I populated one QPD board (based on D1600196), and started testing it. The transimpedance stages seems to work fine (they show about 5-6 V in ambient light). However the whitening stages show a large ~100 kHz oscillation. While trying to fix it I probably burnt one of the output drivers.

 

  27   Thu Jun 30 16:18:28 2016 GabrieleElectronicsDaily ProgressQPD electronics is working

Today I gave up trying to fix the first board I populated, and built a second one. The good news is that it's working as expected.

With 27.5 uW incident on each quadrant, I measure about 4.5 V, which is in line with the transimpedance of 200k, a responsivity of about 0.4 A/W and ad additional gain of two coming from the differential driver.

I also measured the noise with a SR785 (it wasn't connected to a GPIB interface and I couldn't find any, so all I have are the following numbers and the attached screenshots). 

Frequency [kHz] Noise [uV/rHz] Equivalent beam motion [m/rHz]
1 1.3 5.7e-14
5 2.2 9.6e-14
10 3.3 14e-14
30 2.4 10e-14
60 1.2 5.2e-14

At low frequency we are dominated by 60 Hz harmonics (probably coming from the laser). At high frequency there are some large peaks of unknown origin. I can't acquire digitally the signals to compute the difference, so I don't know if the noise we see is, for example, laser intensity noise. As soon as the cymac is up and running, I'll run some more tests.

 

  29   Fri Jul 1 15:12:12 2016 GabrieleElectronicsDaily ProgressQPD electronics noise

 

I turned out that all the noise I was seeing in the QPD spectrum was due to ambient light. I covered the QPD with a box and switched off all the light. As shown in the following plot the noise is lower.

Considering that in the final setup we'll have a beam spot radius of 0.5mm, the sensitivity to beam motion on the QPD will be 23e6 V/m. The following plot shows the resulting beam motion sensitivity, if limited by electroninc noise:

It's at a level of 6e-15 m/rHz at all frequencies above 120 Hz.

  47   Mon Jul 18 13:42:46 2016 GabrieleElectronicsCharacterizationQPD signal convention

The QPD quadrants are wired accoridng to the following convention

  77   Thu Aug 11 08:45:19 2016 GabrieleGeneralGeneralQPD signals with dielectric filter

I installed a dielectric laser line filter (Thorlabs FLH05633-5, center wavelength 633 nm, FWHM 5 nm) in front of the QPD. In this way we are no more affected by the room light. In the plot below blue is without filter, red with filter. A lot of peaks at high frequency are eliminated by the filter.

The plot below shows the QPD signal quadrant signals in a few different configurations: blue with the room light on and laser off, red with the room light off and laser off, green with the laser on. With the filter installed, when the laser is on we are dominated by its intensity noise, which shows a lot of peaks at high frequency. Those peaks are not completely eliminated by the difference of the quadrants.

  79   Thu Aug 11 10:59:39 2016 GabrieleElectronicsConfigurationQuadrant calibration

I cross checked the calibration of the sum channel with a  power meter. Now all quadnant signals X3:Q?_OUT and the sum signal X3:CR1-SUM_OUT are correctly calibrated in microwatts.

  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.

   

  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.

  517   Thu Apr 12 10:33:06 2018 GabrieleGeneralVacuumRead-out of vacuum gauges

I failed to interface in a reliable way the datalogger with Linux. So i hooked up the four analog outputs of the vacuum gauge controller to the fast ADC. The voltages are read and saved to disk at a reduced rate (16 Hz, throught the epics channels):

X3:CR0-VACUUM_VAC1_OUTMON
X3:CR0-VACUUM_VAC2_OUTMON
X3:CR0-VACUUM_VAC3_OUTMON
X3:CR0-VACUUM_VAC4_OUTMON

A python script running on the workstation (~/pycrime/automation_scripts/vacuum.py) reads the voltage every second and update four epics channels:

X3:CR0-VACUUM_CG0 = convection gauge of test chamber (high pressure gauge)
X3:CR0-VACUUM_IGM0 = ionization gauge of test chamber (low pressure gauge)
X3:CR0-VACUUM_CG1 = convection gauge of main chamber (high pressure gauge)
X3:CR0-VACUUM_IGM1 = ionization gauge of main chamber (low pressure gauge)

See below for an example during pump down (the test chamber is at a too high pressure for the IGM to work, so it returns a bogus number).

Here's an example of venting and pumping down

  78   Thu Aug 11 09:10:01 2016 GabrieleElectronicsConfigurationReal time model

Compiled and installed an updated real time model. It acquires the four QPD segments, compute sum and differences, and normalize. I also added three experimental peak tracking components, that will be used to track in real time the amplitude and frequency of the disk modes.

I also created a summary medm screen that can be used to control all the QPD readout. It can be opened from any terminal with the command 'cr1'. I haven't added the peak tracking parts yet.

The X_NORM_OUT and Y_NORM_OUT signals are high passed at 500 Hz, to get rid of low frequency stuff that can affect the peak tracking.

 

  254   Wed Jan 4 14:28:03 2017 GabrieleElectronicsConfigurationReal time models for new measurement system
  • changed the name of the test chamber real time model from CR1 to CR0. Updated all MEDM screens and scripts (autocenter.py, auto_excite.py, crime.py)
  • created new real time models CR1, CR2, CR3, CR4 to be used for the new chamber system. Created MEDM screens and updated all EPICS values
     
  479   Thu Mar 8 09:40:10 2018 GabrieleOpticsConfigurationRealigned all optical levers to horizontal reference
  658   Fri Apr 12 09:36:54 2019 GabrieleOpticsConfigurationRealignment

I realigned the entire CR1-4 setup

  • ensured that beam out of the chamber are at 6" height everywhere. Moved some iris to center them
  • ensured that the beam hits the 45 degrees in-vacuum mirrors at a height of 3.78" = 96 mm
  • checked that all incoming beams are roughly centered on the 45 degrees in-vacuum mirrors. Move some of them in-vacuum mirror posts
  • realigned the input steering mirros horizontally and the in-vacuum mirros so that the beams reflected from a water-level are not clippe anywhere
  • realigned the horizontal reference to the center of all QPDs
  196   Thu Nov 17 12:08:28 2016 GabrieleGeneralGeneralRemote control of air filters and roughing pump

I installed a network controlled power strip. The two air filters and the roughing pump are connected to this power strip and can be controlled remotely.

I added new buttons to the main MEDM screen to control them remotely.

  298   Thu Feb 9 08:35:24 2017 GabrieleElectronicsConfigurationRemoved ESD bias path to model CR0

Removed, since iit was not useful to improve the actuation authority.

Quote:

I added to the model CR0 an additional bias path for the ESD driver:

 

  143   Fri Oct 21 15:27:15 2016 GabrieleElectronicsConfigurationRemoved low pass filter in SUM

I removed the low pass filter in the QPD SUM signal, used for normalization. This reduced a lot the bump at ~20kHz due to laser intensity noise.

I also switched off the 500 Hz high pass filters in the X_NORM and Y_NORM signals.

  366   Thu Jul 6 12:48:54 2017 ZachElectronicsModelingResolving the factor of two

2017-07-06

I resolved the factor of two from Griffiths' discussion of dipoles in non-uniform electric fields. The force on a dipole in a non-uniform field is \textbf{F}=\textbf{F}_+ + \textbf{F}_-=q(\Delta \textbf{E}) where \Delta \textbf{E} is the difference in the field between the plus end and the minus end. Component wise, \Delta E_x = (\nabla E_x) \cdot \textbf{d} where d is a unit vector. This holds for y and z, the whole thing can also be written as \Delta \textbf{E} = (\textbf{d} \cdot \nabla) \textbf{E}. Since p=qd, we can write \textbf{F} = (\textbf{p} \cdot \nabla) \textbf{E}

Jackson derives it differently by deriving the electrostatic energy of a dielectric from the energy of a collection of charges in free space. He then derives the change in energy of a dielectric placed in a fixed source electric field to derive that the energy density w is given by w = -\frac{1}{2} \textbf{P} \cdot \textbf{E}_0. This explicity explains the factor of two and is an interesting alternative explanation.

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