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ID Date Author Type Category Subject
289   Wed Feb 1 16:58:10 2017 GabrieleGeneralCharacterizationExcitation tests

The excitation is working fine. However, there is a large cross coupling in the excitation between channels: so if I switch on only one of the ESD paths, I actually excite all other disks too.  It might be due to the common ground or to the fact that the cables run close to each other. This needs some investigation, but it's not a big issue for the moment being.

On the other hand, the optical levers are very well decoupled: each one sees a different set of modes. So there is no measurable cross coupling between the disks or the readout.

There seems to be something fishy with the Y picomotor of QPD3: it doesn't always move in the same direction for the same set of steps. Some investigations needed here too. Autocentering might fail, but it's still possible to center it manually.

Excitation at 4:56pm (quiet time before excitation 1170032165, quiet time after excitation 1170032234).

Another excitation at 8:30am (2017-02-02) (quiet time before excitation 1170088185, quiet time after excitation 1170088373)

422   Thu Aug 24 07:40:33 2017 GabrieleGeneralMeasurementsExcitations with new ESD

## 2017-08-23

• Excitations
• Quiet time before excitation: 1187577794
Quiet time after excitation: 1187577848

• Quiet time before excitation: 1187585078
Quiet time after excitation: 1187585133

• Quiet time before excitation: 1187592363
Quiet time after excitation: 1187592417

• Quiet time before excitation: 1187599647
Quiet time after excitation: 1187599701

• Quiet time before excitation: 1187606931
Quiet time after excitation: 1187606986

• Quiet time before excitation: 1187614217
Quiet time after excitation: 1187614271

424   Fri Aug 25 07:25:32 2017 GabrieleGeneralMeasurementsExcitations with new ESD

The results show very low Q values, so we suspected some issues. Yesterday we openend the chamber and moved the ESD up, as high as possible. New excitation followed:

• Quiet time before excitation: 1187676942
Quiet time after excitation: 1187676996

• Quiet time before excitation: 1187684226
Quiet time after excitation: 1187684280

• Quiet time before excitation: 1187691510
Quiet time after excitation: 1187691564

• Quiet time before excitation: 1187698794
Quiet time after excitation: 1187698848

Quote:

## 2017-08-23

• Excitations
• Quiet time before excitation: 1187577794
Quiet time after excitation: 1187577848

• Quiet time before excitation: 1187585078
Quiet time after excitation: 1187585133

• Quiet time before excitation: 1187592363
Quiet time after excitation: 1187592417

• Quiet time before excitation: 1187599647
Quiet time after excitation: 1187599701

• Quiet time before excitation: 1187606931
Quiet time after excitation: 1187606986

• Quiet time before excitation: 1187614217
Quiet time after excitation: 1187614271

425   Fri Aug 25 19:29:07 2017 GabrieleGeneralMeasurementsExcitations with new ESD

New set of excitations after raising the ESD:

• Quiet time before excitation: 1187676942
Quiet time after excitation: 1187676996
• Quiet time before excitation: 1187684226
Quiet time after excitation: 1187684280
• Quiet time before excitation: 1187691510
Quiet time after excitation: 1187691564
• Quiet time before excitation: 1187698794
Quiet time after excitation: 1187698848

Q values are now reasonable

Quote:

The results show very low Q values, so we suspected some issues. Yesterday we openend the chamber and moved the ESD up, as high as possible. New excitation followed:

• Quiet time before excitation: 1187676942
Quiet time after excitation: 1187676996

• Quiet time before excitation: 1187684226
Quiet time after excitation: 1187684280

• Quiet time before excitation: 1187691510
Quiet time after excitation: 1187691564

• Quiet time before excitation: 1187698794
Quiet time after excitation: 1187698848

Quote:

## 2017-08-23

• Excitations
• Quiet time before excitation: 1187577794
Quiet time after excitation: 1187577848

• Quiet time before excitation: 1187585078
Quiet time after excitation: 1187585133

• Quiet time before excitation: 1187592363
Quiet time after excitation: 1187592417

• Quiet time before excitation: 1187599647
Quiet time after excitation: 1187599701

• Quiet time before excitation: 1187606931
Quiet time after excitation: 1187606986

• Quiet time before excitation: 1187614217
Quiet time after excitation: 1187614271

105   Thu Sep 1 02:13:33 2016 GabrieleOpticsCharacterizationExpected frequencies for the 75 mm disks with flats

Here are the nominal parameters of the disk with flats

Parameter Value
Diameter (nominal) 75.0 mm
Thickness (nominal) 1.00 mm
Distance of flats from center of disk
(as measured by MO)
36.05 mm
Young's modulus (from G1601850) 72.3 GPa
Poisson's ratio (from G1601850) 0.164
Density 2202 kg/m^3

A COMSOL simulation gives the frequencies and mode shapes shown in the attached PDF file. Following the list of frequencies and a classification of the mode family (numer of radial nodes, number of azimuthal nodes in a half turn):

 Frequency [Hz] Radial Azimuthal 1089.7 0 2 1109.1 0 2 1661.1 1 0 2501.3 0 3 2542.3 0 3 3837.7 1 1 3909.8 1 1 4359.9 0 4 4421.2 0 4 6656 0 5 6665.3 1 2 6732.7 0 5 6780 1 2 7283.9 2 0 9381.5 0 6 9470.6 0 6 10054.1 1 3 10210.2 1 3 11244.2 2 1 11414.2 2 1 12528.4 0 7 12655.4 0 7 13970.1 1 4 14148.9 1 4 15854.8 2 2 15856.8 2 2 16101.1 0 8 16227.8 3 0 16853.9 3 0 18387.2 1 5 18562.6 1 5 19984.9 0 9 20045.8 0 9 21067.2 2 3 21358.1 2 3 22300.9 3 1 22848.8 3 1 23270.5 1 6 23419.4 1 6 24374.1 0 10 24425.2 0 10 26793.8 2 4 27083.9 2 4 28533.5 1 7 28637.8 1 7 28692 3 2 28998.5 4 0 29228.3 0 11 29271.9 0 11 29870.1 4 0 33040 2 5 33301.4 2 5 33949.1 0 12 33986.5 0 12
Attachment 1: allmodes_aggregated.pdf
213   Mon Nov 28 16:02:16 2016 GabrieleGeneralGeneralExpected frequencies for the MIT samples
 Disk 3 x 1"/0.1mm 4 x 1"/0.1mm 4 x 1"/0.125" 306 319 322 243 306 319 324 319 464 480 487 447 703 739 751 679 703 743 751 679 1082 1140 1163 1101 1082 1140 1163 1101 1225 1288 1306 1211 1225 1288 1314 1283 1869 1941 1985 1750 1869 1941 1985 1904 1883 2003 2011 1904 1883 2003 2032 2017 2034 2155 2203 2065 2633 2731 2783 2759 2633 2745 2783 2784 2843 2986 3029 2877 2843 3006 3029 2877 3176 3325 3394 3307 3176 3325 3394 3307 3515 3645 3694 3629 3515 3645 3694 3630 3953 4152 4197 3673 3953 4152 4216 4001 4491 4655 4695 4560 4491 4655 4717 4673 4514 4697 4719 4739 4514 4697 4828 5132 4660 4814 4896 5301 5205 5463 5538 5302 5205 5463 5538 5350 5628 5793 5854 5849 5628 5795 5854 5849 5970 6208 6290 6088
26   Wed Jun 29 16:44:17 2016 GabrieleGeneralConfigurationFirst disk eigenfrequency

The following table shows the lowest eigenfrequency (Hz) for different sizes of disks

Diameter \ Thickness [mm] 0.125 0.250 0.500 1.000
75 137 273 545 1090
100 77 154 307 613
150 34 68 136 272
200 19 38 77 153

107   Mon Sep 12 16:00:06 2016 GabrieleGeneralDaily ProgressFirst fully automated measurements of ring down

I finished the first version of the automation software to measure the ring down of the disk modes. I tested it with the new substrate that was installed yesterday. Here are some screenshots and a brief explanation of how it works.

It is based on a Python/Tk GUI, that can be launched on the workstation with the command ~/CRIME/crime.py

The main screen is similar to the following. Once a baseline spectrum is acquired, it is shown in the main panel:

The user should specify the folder and prefix of the result files, and other parameters related to the excitation. The when the "Excite and ring down..." button is pressed, here's what happens

1. If a baseline spectrum (before excitation) is not available, one is acquired with the specified parameters
2. A broadband white excitation is applied with the selected amplitude and duration

1. Another spectrum is taken. This is then whitened by dividing it with the baseline. This could be used directly to select the modes that have been excited. However, some parts of the noise floor are non stationary, so a second whitening is performed: the noise background is estimated by removing all lines, and it is then again divided out from the spectrum.
2. All lines above a SNR threshold are then selected and shown in the main window together with the whitened spectrum:

At this point the amplitude of the peaks are continuosly monitored (every second) and thei amplitude shown in a new window. The user can select a subset of the modes for the plotting.

There are some wandering peaks in the spectrum, so some of the peaks aren't actually modes that get excited. This is easily fixed in the post processing of the results.

All peak amplitudes are saved to files in real time, so if you stop the GUI you'll have some partial results.

49   Mon Jul 18 17:46:04 2016 GabrieleGeneralDaily ProgressFirst look at QPD signals

Here's the first spectrum of the QPD X and Y signals, acquired with the digital system. Roughing and turbo pumps are still on.

The noise floor seems quite non stationary. To be investigated.

93   Sat Aug 20 22:18:26 2016 GabrieleGeneralDaily ProgressFirst measured Qs

Using the first ring down of the day (GPS 1155754513 + 3600 seconds), I computed the amplitude of each of the modes already identified, using a short FFT spectrogram (each FFT is 1 second long, overlap of 0.5 s).

Then I used the same code I developed at LMA to fit the ring down, including the beat between the unresolved mode pairs. The fit is versy sensitive to the initial conditions, so I had to fine tune them for each of the 20 modes. Still, all fits were successful with 30 minutes of work.

Here are all the fits:

And in summary all the measured Qs, which turned out to be larger than what I was expecting, considering that the disk is not annealed.

The analysis code in MATLAB is attached.

Attachment 22: first_ringdown.m
%% Compare data right before and right after the excitation
gps0 = 1155754000;
gps1 = 1155754513;
dt = 180;

c = nds2.connection('cymac3.ligo.caltech.edu', 8088);
data0 = c.fetch(gps0, gps0+dt, {'X3:CR1-X_NORM_OUT_DQ', 'X3:CR1-Y_NORM_OUT_DQ', 'X3:CR1-ESD_OUT_DQ'});
data1 = c.fetch(gps1, gps1+dt, {'X3:CR1-X_NORM_OUT_DQ', 'X3:CR1-Y_NORM_OUT_DQ', 'X3:CR1-ESD_OUT_DQ'});

x0 = data0(1).getData();

... 606 more lines ...
53   Tue Jul 19 17:21:48 2016 GabrieleGeneralDaily ProgressFirst modes excited!

We can't generate any arbitary signal with the real time model, since awg is not working properly yet. For the moment being I added a uniform random number generator in the model (only option I found for noise) and send it into the ESD filter bank. In this way I can generate band-passed noise.

I plugged in the DAC output to the HV amplifier input, and I could send white noise to the electrostatic drive. Behold: I was able to excite quite a few modes. In the following trace blue is a reference and red is right after I sent white noise (3 V peak to peak) to the disk for a while (less than 1 minute). Excitation stopped at 4:56pm LT.

Using COMSOL and tuning the disk thickness at 1.018 mm I could hit the frequency of the first butterfly mode (1109 Hz) and get a reasobly good estimate of the other modes.

After about half a hour of ring down, most of the modes are gone but the two lowest are still going strong.

Note that the flattish background noise seems to be generated by some sort of glitches. I tried to swap the laser and the power supply, without change. More investigations are needed.

Note that the roughing pump was still on during the test.

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

92   Sat Aug 20 17:01:10 2016 GabrieleGeneralDaily ProgressFirst ring down measurements

Everything is working pretty well. This morning the pressure was about 1.2e-6 Torr. I connected the high voltage amplifier and I could drive the disk without problems.

I measured the beam shape and size at the QPD. We have about 50 uW, we see a TEM01-like mode due to the interference of the two disk surfaces (this is normal). The beam is about 3 mm in diameter. using this information and the estimated optical lever length of 1.2 m, I calbrated the QPD NORM signals in units of angular motion of the disk surface. The computation posted in CRIME_Lab/60 is actually wrong. I'll post the correct one later.

Injecting broadband white noise I could excite all the modes that are visible up to about 30kHz. I tuned the COMSOL model, by changing the thickess of the disk to 1.017 mm, to fit the frequency of the first few modes. Here are the modes I could measure:

Nominal frequency [Hz] Actual frequency [Hz]
1108 1109
2543 2543
4427 4424
6748 6739
6792 6781
9494 9475
10239 10216
12656 12623
14209 14168
16150 16107
16226 16173
18673 18606
20195 20116
21414 21338
23611 23510
24559 24708
27203 27084
29006 28859
29180 29053
29309 29151

Take a look at the attached PDF file for the shape of all the modes, including all that are not visible. We see all the modes we expect to be able to excite with the central suspension of the disk.

The roughing pump is making a lot of non stationary low frequency noise. I turned it off, and the pressure stayed constant at 1.2e-6 Torr over about 1.5 hours. Here's the difference in the QPD spectrum:

It turned out that I have enough excitation authority to knock the disk out of the right place. So I had to vent to recover the situation. I'll open the chamber tomorrow and see what happened.

Here's a first bird eye look at the ring downs. We see beating of the two almost denegerate modes in some cases. Fits will follow, using the procedure I used for the LMA measurements.

Attachment 1: modes.pdf
292   Mon Feb 6 14:09:07 2017 GabrieleGeneralMeasurementsFirst set of parallel measurements completed

The new laser is still acting up a bit, with a wandering line moving sometimes inside the band. Nevertheless, I could perform the first complete measurement of four samples in parallel.

Everything went as expected, there is no visible cross coupling between modes of different disks. The MATLAB code for the analysis is ready and working.

Here are the results:

Attachment 1: results_06-Feb-2017.png
267   Thu Jan 19 14:27:02 2017 AlenaGeneralVacuumFirst vacuum test new chamber

Turbo pump controller (new chamber) was configured. Need to reduce the frequency or setup a standby mode. First pump down: E-7 range reached within about an hour. See plot: blue - old crime chamber, pink - new crime chamber.

82   Sat Aug 13 14:05:02 2016 GabrieleGeneralDaily ProgressFirst work on the measurement user interface

Today I started programming part of the user interface that will be used to perform the measurements. Not much implemented so far, but you can get an idea of the look:

Buttons on the left sidebar will allow the user to perform some basic tasks. The main panel has a plot (which will show spectra or ring down measurements) and a log section.

Attachment 1: Screenshot-C.Ri.Me..png
87   Tue Aug 16 11:57:03 2016 GabrieleElectronicsConfigurationFixed cymac3 network and time issue

The cymac3 internal clock was off by about 10 seconds. When I tried to start the NTP service, I found out that the cymac3 couldn't reach any external server. It turned out that the gateway in /etc/network/interfaces was set to the wrong address. I fixed it and rebooted. Now NTP is working and the time is correct.

This fixed a small issue with diaggui, which always complained about a data receiving error when starting a measurement (although after the complian the measurement could continue)

364   Wed Jul 5 16:40:51 2017 ZachElectronicsModelingForce disparity-improvement

# 2017-07-05

• In order to improve my data I shrunk the region of the finer meshing slightly and made the mesh even smaller and then recalculated the force profiles. This time I tried sampling regions inside the disc rather than immediately at the surface. The attached graphs were sampled at the center of the disc. These two techniques vastly improved the data, now the profiles appear the same, but the magnitudes differ by a factor of 2 again. Previously this was due to an error in my calculation of the force, now I do not believe this to be the case. I will leave my work here for the purposes of my first report, it is an interesting result. I also restricted my data set to the finely meshed box which resolved the earlier data display issue.

363   Wed Jul 5 12:01:51 2017 ZachElectronicsModelingForce plots-Correct plots, force issue

# 2017-07-05

• I sorted out my mathematical lapse in logic and computed the correct force profiles in the perpendicular direction in both disks. The issue is that now the force profiles don't match up. The fact that there is a measured force distribution for the E^2 case outside the disk is only an artifact of the numerics because it is being calculated only from the electric field data which is defined outside the sample. It can be easily removed for final plots once the force distributions are matched by either redefining the cut plane or putting a data filter specifically on the E^2 plot. The jumps in the E^2 plot suggest that the meshing is still too large, I will try to fix this first, hopefully it will help resolve the difference.

368   Fri Jul 14 16:43:24 2017 ZachElectronicsModelingForce profile matlab script

# 2017-07-14

• I have completed a rough, but functioning script that calculates the modal force profiles. The force values are still coming out incorrect (on the order of 10^14) but the script can take in my model as a .m file and return an array with a force value per mode. I am attaching both the .m file and the matlab script
• I have done very little work with the numerical integration itself, based on the 2D numerical integration code I received I just appended a z component and left it at that so when I return from Livingston I will  fix that component
Attachment 1: forces.m
par.a = 75e-3/2;    % radius [m]
par.h = 1.004e-3;   % thickness [m]
par.E = 73.2e9;     % Young's modulus [Pa]
par.nu = 0.155;     % Poisson's ratio
par.rho = 2202;     % density [kg/m^3]

%Calculate fundamental modes of the disk
[freqs, modes, shapes, x, y] = disk_frequencies(par, 10000, 1, 'shapes', 0.5e-3);

%Now we extract the force profile from the COMSOL model

... 41 more lines ...
Attachment 2: faster.m
function out = model
%
% faster.m
%
% Model exported on Jul 14 2017, 14:47 by COMSOL 5.2.1.262.

import com.comsol.model.*
import com.comsol.model.util.*

model = ModelUtil.create('Model');

... 403 more lines ...
278   Thu Jan 26 17:06:59 2017 GabrieleGeneralDaily ProgressFour fold measurement system installation

Today I installed the four GeNS systems into the chamber, connected the ESD to the HV feedthrough and put the periscopes in place.

Note 1: the lens holders have been remachined to solve a dimension problem, by removing completely the two lips against which the lens was supposed to be sitting. To recover a reasonable centering of the lens, I added two small shims inside each holder. They are made out of wrapped aluminum foil.

Note 2: I added some small shims (again made of wrapped aluminum foil) below the base plate, to make it as close to horizontal as possible

Finally, I managed to align the optical level beam for the QPD1, using as usual a small container with water to get the horizontal reference.

Some pictures below.

Attachment 3: 2017-01-26_14.04.06.jpg
282   Mon Jan 30 15:16:54 2017 GabrieleGeneralDaily ProgressFour samples in chamber
• checked that the high voltage paths are working:
• the DAC signal is properly received and amplified by the Trek 2220 HV amplifier
• the HV switch box is working as expected: I can switch on and off each path individiually using the DAC signals
• installed four samples (refer to the optical drawing for the numbering)
• S1600472 in bay 1
• S1600478 in bay 2
• S1600473 in bay 3
• S1600480 in bay 4

• balanced all samples and centered all optical levers. There is a problem with the fifth connector in the ADC interface board (or maybe with one ADC channel). So one of the quadrants of QPD4 was not working. I moved the connector to number 6 and updated the model. Everything looks fine now.
• the power in the four QPD is quite diverse: this is not unexpected, since it depends on the interference of the reflection from the two surfaces of the disk

• installed the picomotor controllers on the bench, connected them to the net using the switch on the top of the clean room. For the moment being they are using DHCP.
• connected all picomotors to the controllers.
• Bottom controller, from left to right: QPD1x, QPD1y, QPD2x, QPD2y
• Top controller, from left to right: QPD3x, QPD3y, QPD4x, QPD4y
• tested the remote control and motion of all picomotors

356   Tue Jun 27 14:17:47 2017 ZachElectronicsModelingFurther plots and improving models

# 2017-06-27

• I built a new model of the ESD to determine whether or not the spikes in the electric field at the corners was affecting the results enough that it had to be accounted for in further models. To create the model, I created a 2D profile of the arm used in my original model and filleted the corners at a radius of .05 mm, since the electrode model is .1 mm thick, this made completely rounded edges. In creating this model I caught an earlier mistake in the original one, I only set one half of the surface of the electrodes to have a potential or to ground, the "bottom" was left with no charge. I fixed this mistake and then compared the two models at a potential of 1000 V. For speed of computation I ran both models with a finer mesh size and then calculated the electric field at approximately the middle of the ESD, 1mm above the fourth electrode arm. For the rounded electrodes the field had a value of 84024 V/m and for the rectangular electrodes the field had a value of 80728 V/m, which is less than a 4% difference in field magnitude. Furthermore, the field shapes appear nearly indistinguishable; I am confident from this test that I can proceed modelling the arms of the ESD as rectangles.
Attachment 1: E_field_corner.png
Attachment 2: E_field_round.png
476   Mon Mar 5 11:03:18 2018 Gabriele, AnthonyGeneralMeasurementsFused silica substrated for metallic glass tests

## 2018-03-05

• 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
873   Tue Jun 9 11:04:28 2020 GabrieleGeneralMeasurementsGaAs S1600805

## 2020-06-09

• 11:00 am in chamber
• GaAs in CR1
• S1600805 in CR2
• 11:04 am roughing pumps on
• 11:15 am turbo pump CR1-4 on
402   Thu Aug 10 10:47:54 2017 ZachElectronicsModelingGeometry Ratios

# 2017-08-10

• The attached plots compare the new and old geometries with .5 mm and 1 mm sample gaps. They are the same plot on linear and logarithmic axes respectively

Attachment 1: Optimization_plot_lin.pdf
Attachment 2: Optimization_plot_log.pdf
56   Thu Jul 21 12:10:14 2016 GabrieleGeneralDaily ProgressGlitch hunting

Yesterday I could clearly see the glitches as jumps in the time domain plot of X and Y signals, and trace them to somewhat harder to see jumps in the quadrant signals.

• I tried to catch them with an oscilloscope looking at the analog signals, but couldn't see any. However, for a brief period I had a persistent square wave oscillation in all transimpedance stages
• I hooked the single ended output of the whitening filter to an ADC, and I could see the jumps there too. So I can exclude it's a problem of the differential drivers

One suspect was an intermittend oscillation of the transimpendance amplifier, so I looked into the schematics (D1600196) to see what could be the optimal value of the compensating capacitor C7. Following some useful notes online I computed the optimal value of C7 to be close to 2pF (instead of 10pF). I used 30-35 pF as the QPD capacitance, and 10 MHz has the gain-bandwidth product of the opamp. I swapped all 10pF capacitors with 2pF. After this I can still see the glitches in the spectra, but I can't find them anymore in the time domain. So things seem to have improved, although I still have annoying glitches.

Rich suggested to test the stability of the transimpendance stage by driving the output with a square wave and looking for the signal ringing. Here's his note:

I tried this for both the TI stage and the whitening stage, using 1k and 1uF and a square wave at 10 kHz. Here are the results, which look reasonable to me (firts is the TI, ringing at about 0.5 MHz, second is the whitening, almost no ringing):

So now I'm quite confident that the electronics is working. In the first trace you can see some intermittend background noise, due to the ambient light leaking into the QPD.

More investigations will follow.

54   Tue Jul 19 20:19:38 2016 GabrieleElectronicsConfigurationGlitches are a digital artifact

The glitches I saw in the data happens roughly every second, even though not exactly on the second. They are suddend jumps on the signal values over one sample, so of clear digital origin

Attachment 1: glitches.png
57   Thu Jul 21 14:58:26 2016 GabrieleElectronicsGeneralGlitches are of digital origin

So here's the final proof that the glitches I see are digital:

• There is a positive jump (of random size) every second, every time 0.45s after the beginning of the second. There is a negative jump at a less constant time, but between 0.65s and 0.8s after the beginning of each second
• I moved my whole setup to the crackle lab. This included: HeNe laser with power supply, QPD with cable, interface board and power supply. I don't see any glitch there

I swapped the ADC board with a second one in the new cymac, but no change: glitches are still there.

61   Mon Jul 25 17:44:13 2016 GabrieleElectronicsCharacterizationHigh frequency noise budget

I measured the noise sources limiting the QPD sensitivity. Unfortunately, I had to do some MATLAB tricks to get rid of the glitches: basically I load the data directly from the raw frames (NDS access to data is not working yet) and remove all jumps in the signals that happen in one single sample and are larger than a manually tuned threshold. This is not perfect, but it's enough to give us a rough idea of the spectrum of the QPD signal. The following plot shows the QPD_X signal (in units of disk motion, radians) in a few situations:

• Blue: normal (laser on, room lights on)
• Orange: laser on, room lights off (including the vacuum gauge)
• Yellow: laser and room light off
• Purple: same as above, but I switched off the PC monitors too
• Green: QPD electronics off (this is the ADC noise)

The total power on the QPD is 30 uW, which correspond to a shot noise limited sensitivity of 4.3e-12 W/rHz. Considering that the signal is the quadrant asymmetry normalized by the total power, the shot noise limited sensitivity is sqrt(2) * SN / Power which once calibrated corresponds to 1.1e-10 rad/rHz.

The following plot shows that shot noise is the dominant source, followed closely by the electronics dark noise. The total agrees perfectly with the measured background noise above 2 kHz. Below that we have some leakage due to the large turbopump peak: this is due to FFT limitations but mostly to unsuppressed glitches.

From the QPD datasheet (Hamamatsu S5981) I learn that the noise equivalent power should be of the order of 2e-14 W/rHz at the sensitivity peak, so probably a factor of two or so worse at the HeNe frequency. It's still much lower than the measured dark noise.

This sensitivity is already pretty good, but we can improve it by increasing the power on the diode. Indeed, 30 uW corresponds to about 2.7 V after the transimpedance, so we could increase the power by a factor 4 and win a factor 2 in the shot noise to dark noise ratio. Probably not worth it, since it will give us only a 30% gain in high frequency noise.

62   Tue Jul 26 11:45:03 2016 GabrieleElectronicsCharacterizationHigh frequency noise budget

Just to confirm that my noise estimates make sense, here's a plot of the not-normalized QPD signal that gives the X motion (sum and difference of all four quadrants):

This is the signal after compensating for the whitening filter. If I remove this compensation, the following plot gives the noises in terms of the voltage directly in input to the ADC (or in output of the analog board):

So the total "dark" electronic noise is about 13 uV/rHz.

I did a roughly estimate of the sources of electronic noise:

• QPD dark current noise, from datasheet, at the peak sensitivity is equivalent to 2e-14 W/rHz, or 2 nV/rHz at the output of the TI stage
• First stage: Johnson-Nyquist noise of the TI resistor: 58 nV/rHz
• First stage: output voltage noise of the LT1124: 3 nV/rHz
• First stage: input curent noise of the LT1124, converted to the output: 60 nV/rHz

So the total noise at the outoput of the first stage is about 84 nV/rHz. The second stage adds a gain of 30 at high frequency, and negligible noise. So at the output of the whitening we have 2.5 uV/rHz. The DRV135 adds another gain of 2 and a neglegible output noise.

So the total electronic noise at the output of each quadrant is 5 uV/rHz. Since we are combining four of them, the total expected electronic noise is 10 uV/rHz, which is not too far from the measured value.

We are basically dominated equally by the Johnson-Nyquist noise of the TI resistor and by the input current noise of the LT1124. No gain to be obtained by changing the whitening.

 Quote: I measured the noise sources limiting the QPD sensitivity. Unfortunately, I had to do some MATLAB tricks to get rid of the glitches: basically I load the data directly from the raw frames (NDS access to data is not working yet) and remove all jumps in the signals that happen in one single sample and are larger than a manually tuned threshold. This is not perfect, but it's enough to give us a rough idea of the spectrum of the QPD signal. The following plot shows the QPD_X signal (in units of disk motion, radians) in a few situations: Blue: normal (laser on, room lights on) Orange: laser on, room lights off (including the vacuum gauge) Yellow: laser and room light off Purple: same as above, but I switched off the PC monitors too Green: QPD electronics off (this is the ADC noise) The total power on the QPD is 30 uW, which correspond to a shot noise limited sensitivity of 4.3e-12 W/rHz. Considering that the signal is the quadrant asymmetry normalized by the total power, the shot noise limited sensitivity is sqrt(2) * SN / Power which once calibrated corresponds to 1.1e-10 rad/rHz. The following plot shows that shot noise is the dominant source, followed closely by the electronics dark noise. The total agrees perfectly with the measured background noise above 2 kHz. Below that we have some leakage due to the large turbopump peak: this is due to FFT limitations but mostly to unsuppressed glitches. From the QPD datasheet (Hamamatsu S5981) I learn that the noise equivalent power should be of the order of 2e-14 W/rHz at the sensitivity peak, so probably a factor of two or so worse at the HeNe frequency. It's still much lower than the measured dark noise.  This sensitivity is already pretty good, but we can improve it by increasing the power on the diode. Indeed, 30 uW corresponds to about 2.7 V after the transimpedance, so we could increase the power by a factor 4 and win a factor 2 in the shot noise to dark noise ratio. Probably not worth it, since it will give us only a 30% gain in high frequency noise.

Attachment 1: noise_budget.png
226   Mon Dec 5 16:35:05 2016 GabrieleElectronicsGeneralHigh voltage relais

We want to be able to drive any combination of the four samples in the new setup, by using only one HV amplifier.

So I designed and built a remotely controlled relay box: one HV input and four HV outputs, controlled by four relais. The relais can be switched using a logic signal coming from DAC channels.

The system is finished, tested and working. Details in D1600456

276   Wed Jan 25 10:02:23 2017 GabrieleElectronicsDaily ProgressHigh voltage system in place

This morning I installed in the clean room the high voltage amplifier and the high voltage relays. Everything is cabled as planned. No way to test it yet, since there's nothing in the chamber!

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

Instructions on how to setup a workstation are available here:

https://nodus.ligo.caltech.edu:8081/Cryo_Lab/1135

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

PATH="/ligo/apps/ubuntu12/epics-3.14.12.3_long/extensions/bin/linux-x86_64:\$PATH"

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

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

148   Tue Oct 25 11:10:37 2016 GabrieleGeneralMeasurementsImage of S1600433

This is an image of the sample S1600433 under the microscope, courtesy of GariLynn:

The scale in the image is 20 microns per divison, 2 mm full scale

Attachment 1: IMG_3150.JPG
386   Tue Aug 1 16:10:42 2017 ZachElectronicsModelingImproved Gap Sweep

# 2017-08-01

• I completed an improved sweep of the gap between the ESD arms. I resolved some code issues, since it was passing the maximum value not the most extreme, smaller magnitude positive values were being included rather than the strongest force calculation.
• There are still three modes that show unique behavior relative to the others: 14, 19, and 25. Mode 14 is the (2,2), mode 19 is the (2,3) and mode 25 is (3,2).
• Plots of the mode shapes are included for reference. The black rectangle represents the region covered by the ESD.

286   Tue Jan 31 16:55:17 2017 GabrieleGeneralDaily ProgressImproved autocenter, excitation not working, wandering line

The autocenter script wasn't working in a very robust way (sometimes the socket connection to the controller failed, some times no motion was obtained after issuing a command). So I rewrote the interface to the Newport controller using the http server interface. The code is in picomotor8742_http.py. This version seems much more robust.

There is a large wandering line that spans all frequencies. Not sure what the origin is, but it will need some noise hunting. Here are spectrograms of all four QPD X signals. The line is visible in all of them, at the same frequency. So it's definitely something external coupling into the light or the QPD electronics. It's not visible in the sum of the QPD quadrants, but maybe just because it's buried in noise.

Finally, I tried to excite the disks, but I couldn't get any motion of the optical lever beams. To be investigated, there might simply be some cables disconnected.

Attachment 1: wandering_line.png
116   Tue Sep 20 15:34:00 2016 GabrieleOpticsDaily ProgressImproved optical lever layout

## Goal

Improve the optical setup, by increasing the response of the QPD to disk motion.

## The old configuration

In all my previous measurement the optical lever was as simple as possible: no lenses were used, and therefore the beam was free to expand over all its path. The estimated arm lever from the disk to the QPD was 1030 mm.

## QPD response to disk angular motion

The response of the QPD can be characterized with its optical gain in 1/rad, which is how much the normalized signal (difference / sum) changes for one radians of motion of the disk. This is the product of two parts:

1. the gain from angular motion of the disk to beam spot motion on the QPD. In the simple case of free propagation this is 2L, where L is the distance from the disk to the QPD, and the factor 2 is due to the fact that the beam deflection is the double of the disk angular motion. If there is a telescope in between the disk and the QPD, it is easy to compute the total ray transfer matrix:
$\begin{pmatrix} x_{QPD}\\ \theta_{QPD} \end{pmatrix}= \begin{bmatrix} A & B\\ C & D \end{bmatrix} \begin{pmatrix} 0\\ 2\theta_{disk} \end{pmatrix}$
Then the gain is simply the B element of the matrix.
2. the response of the QPD normalized signal to beam motion. This depends only on the beam spot radius w on the QPD. It can be computed by simple gaussian integration, and in the approximation of small beam motion, it is given by the following expression:
$g = \frac{2}{w}\sqrt{\frac{2}{\pi}}$

In the case of the old configuration, the beam spot size on the QPD was measured to be about 1.5 mm in radius, so the optical gain is of the order of 1900 /rad.

## Laser beam profiling

Since I wanted to improve the optical setup, I first needed to measure the beam coming out of the HeNe laser. I used the WinCam beam profile and a Newport rail to measure the beam X and Y sizes at different positions.

The measurements are not the best ever, but I can still get a fit for the evolution of the gaussian beam, as shown in the plot below. The beam waist is 254 um, located 340 mm behind the laser output (inside the laser tube).

## Design of the improved setup

I decided to try a brute force algorithmic optimization for the optical gain. I allow two lenses between the laser and the disk and two lenses between the disk and the QPD. I wrote a MATLAB script that picks the four lenses from a list of all those available (I have a Thorlabs LSB02-A lens kit). For each combination of lenses, MATLAB moves them around into pre-defined ranges, and try to find the maximum value of the QPD total optical gain, which is the product of the factor g above and of the B element of the ray tracing matrix.

It turned out that the best optical gains could almost always be obtained by making the beam huge on the disk (5-10 mm radius) and tiny on the QPD (tens of microns). This is not a good solution. So I decided that the beam on the disk must be smaller than 2mm in radius and the beam on the QPD must be larger than 200 microns. I enforced those limits into the optimization code by weighting the gain with a function which is one in the allowed range, and then quickly drops to zero when either of the beam sizes fall out of the allowed range.

The script ran for about half hour and gave me a lot of possible options. After some inspections, I decided to use the following one, which uses only one lens between laser and disk, and two between the disk and the QPD. Distances and focal lengths are shown below. Note that the first distance (laser to first lens) is from the laser beam waist to the lens, so the actual distance must take into account that the waist is estimated to be 340mm into the laser.

With this configuration the optical gain is computed to be 17000 /rad, or about 9 times larger than the original setup. The beam radius on the disk is 1 mm and on the QPD is 0.23 mm.

## Implementation

First of all I measured some distances:

• from the inner side of the viewport to the disk: 420 mm
• viewport thickness: 12 mm, which is about 18 mm optical length considering n~1.5
• so from the input to the chamber to the disk: 438 mm
• from the viewport to the upper external periscope mirror center: 110 mm
• distance between the periscope mirror centers: 275 mm

Using these distanced I build the designed optical setup. Some remarks on the procedure

• I first aligned the laser beam to be horizontal, then added the first lens and centered it by ensuring no beam shift far away from the lens
• I first aligned the periscope to get the beam roughly centered on the inner 45 degrees mirror, and then roughly centered on the black glass
• Then I put a small container with water inside the chamber, on top of the black glass. I aligned the inner mirror and the periscope so that the beam coming back from the horizontal water surface was perfectly overlapped with the input beam. I used an iris on the input beam path
• Then I removed the water container and installed a test disk. I moved the disk around until I got the same beam position in output. This tells me that the disk is horizontal
• Finally I moved the upper periscope mirror to separate horizontally the beam coming back, at the level of the table. The separation is large enough to allow me to pick up the outgoing beam with a mirror.

Here's a picture of the setup, with the optical path highlighted.

270   Fri Jan 20 17:20:20 2017 GabrieleOpticsDaily ProgressInput part of the optical lever setup installed and aligned

Today I installed and aligned part of the optical components for the optical lever of the new setup. For the moment being I installed only the input components, and aligned the beams into the vacuum chamber. Since I don't have any in-vacuum optics yet, there's nothing more that can be done now.

272   Mon Jan 23 16:29:52 2017 GabrieleOpticsDaily ProgressInput part of the optical lever setup installed and aligned

Today I cabled and installed the four QPD, in a temporary position. I also assembled four picomotor mounts that will be used for the auto-centering.

 Quote: Today I installed and aligned part of the optical components for the optical lever of the new setup. For the moment being I installed only the input components, and aligned the beams into the vacuum chamber. Since I don't have any in-vacuum optics yet, there's nothing more that can be done now.

421   Wed Aug 23 14:11:13 2017 Zach, GabrieleElectronicsMeasurementsInstalling ESD Prototype

# 2017-08-23

• Installed ESD Prototype design by taping it to the older design, we then lowered the mount until it was as close as we could reasonably get it. The new PCB lines up when the top of the new PCB is lined up with the last electrode on the old one. The new PCB was slightly too narrow, the mounting holes are very close to the edge of the PCB, this can easily be corrected in later models.
• Installed sample S1600541 into the single sample apparatus
• Roughing pump on at 12:32
• Turbo pump on at 2:28pm
Attachment 1: image1.JPG
Attachment 2: image2.JPG
58   Fri Jul 22 14:22:10 2016 GabrieleElectronicsConfigurationInvestigations on the signal jumps

[Rolf, Ben, Rich, Gabriele]

Rolf couldn't find any good explanation on the software side for the signals jumps. He investigated a bit the reason why IOP takes a long execution time, without success. It's still mysterious why it ran with low time for a while.

One effect of Rolf activity is that now the signal jumps happen at ~0.8 seconds (after the start of each second) instead that ~0.45. This is suspiciously pointing to a software issue...

Ben and I spent a few hours trying to better understand the origin of the glitches. Finally, we plugged in a function generator to the four ADC channels, and we could find the glitches again, at the expected time. So we could rule out completely that it's a problem of the QPD analog electronics.

Some more ivnestigations:

• swapped the SR DS345 with an Agilent 33210A for the timing signal. No change: jumps are still there
• rebooted and powered off the cymac many time, this never changed the glitches or the position in time
• swapped the ADC interface board (D1600196) with a new one similar to that of the crackle lab (D1500402): no change, jumps are still there
• switched off the roughin pump to reduce ambient acoustic noise. Not surprisingly, no change, still jumps
• according to the motherboad manual, PCIe slots 4 and 6 are PCI-EX16, while the other are PCI-EX8. I moved the ADC and DAC to those those slots. Guess what? No change, still jumps

On a bright side, Rolf recompiled the awgman software, and now excitation channels are working.

450   Thu Jan 11 15:40:28 2018 GabrieleGeneralMeasurementsLMA sample (post annealing)

## 2018-01-11

• 3:35pm in chamber CR1
• 3:36pm roughing pump on
• 3:46pm turbo pump on
• Excitations
• Quiet time before excitation: 1199760182
Quiet time after excitation: 1199760242
• Quiet time before excitation: 1199767472
Quiet time after excitation: 1199767532
• Quiet time before excitation: 1199774762
Quiet time after excitation: 1199774822
• Quiet time before excitation: 1199782052
Quiet time after excitation: 1199782112
• Quiet time before excitation: 1199789342
Quiet time after excitation: 1199789402
• Quiet time before excitation: 1199796632
Quiet time after excitation: 1199796692
• Quiet time before excitation: 1199803922
Quiet time after excitation: 1199803982
• More excitations
• Quiet time before excitation: 1200257200
Quiet time after excitation: 1200257260
• Quiet time before excitation: 1200264490
Quiet time after excitation: 1200264550
• Quiet time before excitation: 1200271780
Quiet time after excitation: 1200271840
• Quiet time before excitation: 1200279070
Quiet time after excitation: 1200279130
• Quiet time before excitation: 1200286360
Quiet time after excitation: 1200286421
• Quiet time before excitation: 1200293651
Quiet time after excitation: 1200293711
• Quiet time before excitation: 1200300941
Quiet time after excitation: 1200301001
• Quiet time before excitation: 1200308231
Quiet time after excitation: 1200308291
432   Thu Oct 5 14:28:35 2017 GabrieleGeneralMeasurementsLMA substrate

## 2017-10-05

• 2:17pm in chamber
• LMA substrate after cleaning in CR1
• 2:20pm roughing pump on
• 2:27pm turbo pump on
• Excitations:
• Quiet time before excitation: 1191288204
Quiet time after excitation: 1191288264

• Quiet time before excitation: 1191295494
Quiet time after excitation: 1191295554

• Quiet time before excitation: 1191302784
Quiet time after excitation: 1191302845

• Quiet time before excitation: 1191310075
Quiet time after excitation: 1191310135

• Quiet time before excitation: 1191317365
Quiet time after excitation: 1191317425

• Quiet time before excitation: 1191324656
Quiet time after excitation: 1191324716

358   Thu Jun 29 13:15:01 2017 Alastair, GabrieleGeneralGeneralLaser polishing

We laser polished S1600546, 547, 548, 549, 550 and 551

542   Fri Jun 22 10:53:06 2018 AlenaGeneralGeneralLaser failure

One of the HeNe lasers died (the one for measuring slots CR2 and CR4). It had no outgoing light when I came in this morning. I connected the laser to another identical power supply. The laser started going on and of and the power supply was making some sparkling noise. I swapped the laser with the test chamber (CR0). No re alignment was required for measurement slots CR1 and CR3. A very slight alignment was done for measuring slots CR2 and CR4 after the laser from the test chamber was installed. So temporary we do not have a setup to measure 2" samples easily. Attaching pictures of the broken laser`s label

Attachment 1: 20180622_112134.jpg
Attachment 2: 20180622_112138.jpg
220   Thu Dec 1 11:59:21 2016 Gabriele, AlastairGeneralGeneralLaser polishing

Today we laser polished S1600484, S1600485 and S1600486.

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.

208   Tue Nov 22 14:11:38 2016 GabrieleGeneralMeasurementsLaser polishing of bad disk improves Q, but they're still not very good

Laser polishing of a sample from the second batch (S1600487, bad Q as out of the box) improves the Q values, but they're still lower than what we got with a good sample (S1600439, first batch)

Attachment 1: polishing_Qs.png
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

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