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ID Date Author Type Category Subject
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
459   Tue Feb 13 16:28:49 2018 GabrieleOpticsConfigurationSetup resigned for 75mm disks
479   Thu Mar 8 09:40:10 2018 GabrieleOpticsConfigurationRealigned all optical levers to horizontal reference
497   Tue Mar 27 16:36:49 2018 GabrieleOpticsConfigurationOptical levers re-aligned for 50mm substrates
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
413   Wed Aug 16 14:35:05 2017 GabrieleGeneralComputersWorkstation is down

While I was working, the network connection went down. I tried to reboot the workstation, but I won't boot anymore.

• First issue: firmware of network card disappeared. I managed to download it on a USB stick and install it back
• Second issue: mismatch of NVIDIA graphic card drivers and kernel. Can't start X

Working on it...

418   Fri Aug 18 14:05:36 2017 GabrieleGeneralComputersWorkstation is now up

Reinstalled Debian 8, all packages and CDS software.

Everything seems to be working fine now.

 Quote: While I was working, the network connection went down. I tried to reboot the workstation, but I won't boot anymore. First issue: firmware of network card disappeared. I managed to download it on a USB stick and install it back Second issue: mismatch of NVIDIA graphic card drivers and kernel. Can't start X Working on it...

1   Wed Jul 11 23:01:01 2012 janoschOpticsCharacterizationstarting the multi-color scatter experiment

Steve Maloney, a visiting highschool teacher, and I have started to set up a new scattering experiment in the Richter lab. The idea is to take images of large-angle scattered light using different lasers. We have one 633nm laser, and 532nm and 405nm laser pointers. The goal is to uniformly illuminate the same disk of about 1cm diameter on a silver-coated mirror with all three colors. We use a silver-coated mirror to make sure that the light is reflected from the same layer so that all colors are scattered from the same abberations.

The image shows one of the laser pointers and the HeNe laser. The first step is to widen the beam with a f=5cm broadband, AR coated lens (Newport PAC15AR.15). The diverging beam is then aligned through an iris to give it the right size on the mirror. In this way, illumination is almost uniform on the mirror surface.

The mirror is mounted over the rotation axis of a unipolar stepper motor. For the moment we only took images from fixed direction (initially with a commercial digital camera, later with a monochromatic Sony XT-ST50 CCD camera. The problem with the commercial camera was that you cannot completely control what the camera is doing. Also it would have been very difficult to calibrate the image once you start comparing scattering with different colors. A f=7.5cm lens is used to image the illuminated disk on the CCD chip to make maximal use of its resolution. The CCD signal is read out on a Windows machine with an EasyCap video capture device connected to a USB port. Standard software can then be used to take images or record videos. For some reason the capture device reduces the image size to 640x480 pixels (a little less than the size of the CCD chip).

Eventually the camera and lens will be mounted on a metal arm whose orientation is controlled by the stepper motor. The stepper motor was part of the Silicon Motor Reference Design (Silicon Laboratories). It comes with all kinds of cables and a motor control board. Software is provided to upload compiled C code to the board, but for our purposes it is easiest to use primitive communication methods between the PC and the board. We are working with HyperTerminal that used to be part of Windows installations, but now it has to be downloaded from the web. This program can send simple commands through TCP/IP and COM ports. These commands allow us to position the motor and define its rotation speed. Since our PC does not have a serial port, we purchased a Belkin USB Serial Adapter. You will have to search the web to find suitable drivers for Windows 7 x64. Luckily, Magic Control Technology has similar products and the driver for their U232-P9 USB/serial adapter also works for the Belkin product.

So our goal for the remaining weeks is to take many images from various angles and to set up the experiment in a way that we can VNC into our lab PC and control everything from the Red Door Cafe.

2   Fri Jul 13 10:34:35 2012 janoschOpticsCharacterizationcamera image

We were confused a bit about how the camera image changes when you move the arm that holds the camera and lens around the mirror. It seems that scattering centers move in ways that cannot be explained by a misaligned rotation axis. So we wanted to make sure that the mirror surface is actually imaged as we intended to. We generated a white grid with 0.7cm spacing and black background on a monitor. The image that we saw is exactly how we expected it to be. So the image mystery has other reasons.

3   Fri Jul 13 20:53:35 2012 janoschOpticsCharacterizationtwo images

The following two pictures were taken from the same angle with green (left) and red (right) incident laser at an angle of 15deg from the incident beam (reflected to about -5deg). Some scattering centers are collocated. The green laser power is about 5 times as high as the red laser power, but this factor does not seem to calibrate the image well (the green image becomes too dark dividing all pixel values by 5). So there seems to be a significant difference in the divergence of the two lasers. We will have to use a photodiode to get the calibration factor. These images were taken after cleaning the mirror. Before cleaning, there was way too much scattering and the images were mostly saturated.

4   Tue Jul 17 18:32:11 2012 janoschOpticsCharacterizationpurple images

We have the new 405nm laser pointer.  The image to the left shows the scattered light from the red laser, the image to the right scattered light from the purple laser. Both images were taken 30deg with respect to the normal of the mirror surface. Also, we got a new gallon of Methanol. After cleaning the mirror multiple times, the scattered light became significantly weaker. So the purple images look very different from red and green. It could be that the lens that we use to image the mirror surface is the problem since it is specified for the wavelength range 1000nm-1550nm. Could it also be the CCD camera? Anyway, to be sure I will order another broadband lens.

5   Wed Jul 18 18:43:34 2012 janoschOpticsCharacterizationgone with the wind

Here a little purple video. It starts with scattering angle around 15deg and stops at about 80deg.
There are some clear point defects visible especially at small angles.
I will not start to think about some other interesting details of this video before I got the new lens.

Ed: The AVI did not run on Mac. I posted it on youtube. Koji

6   Fri Jul 20 18:35:42 2012 janoschOpticsCharacterizationpurple improvements and first uncalibrated BSDF curves

Today we improved alignment of the lens-camera arm. We discovered earlier that this alignment affects the amount of "snowfall" on the scattering images. Looking at the latest 405nm video (see attachment), one can still see snowfall, but it is considerably weaker now and the true scatter image is clearly visible. We took a set of scatter images at certain scattering angles and produced BSDF curves. The shape of these curves has partially to do with the snowfall contribution, but one also has to keep in mind that the mirror quality is much worse than what has been used in the Fullerton measurement. We still need to calibrate these curves. The calibration factor is different for the two images so that you cannot even compare them at the moment except for their shape.

Today we also got the new broadband lens for the camera arm. First measurements show that image quality is better. Playing a bit around with distances between object mirror, lens and image plane, we also found that image quality becomes better when the lens and camera get closer to the mirror (which is only an issue for the 405nm measurement since 633nm and 532nm look very good anyway). So we are thinking to change the camera arm setup to make it much shorter.

7   Tue Jul 24 10:59:59 2012 janoschOpticsCharacterizationsum of purple and red

We played around with Matlab today. The first step was to convert light wavelengths into RGB colors. In this way we can combine images taken at different colors. The picture shows the purple and red images (stored in gray scale) in heat colormap. Then the sum of these two images is calculated in their natural RGB colors.

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.

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

The QPD quadrants are wired accoridng to the following convention

60   Mon Jul 25 15:35:31 2016 GabrieleOpticsCharacterizationCalibration of the QPD in physical units

### The equations below are wrong. Please refer to https://nodus.ligo.caltech.edu:8081/CRIME_Lab/116 for the correct results

I measured the properties of the beam on the QPD. The total power is 31 uW. The beam shape is not gaussian, since we are seeing the interference of the reflection from the two surfaces:

The X and Y diameters are 1400 and 1300 microns, so I take the average of the two as an estimate of the beam size: 1300 +- 100 um. I also estimated the lever arm length to be 1.03 +- 0.02 m.

This allows me to esitmate the response of the normalized QPD signal to a tilt of the disk surface:

$\frac{s}{P_0}=\frac{4}{\pi w^2} \cdot 2L \cdot \theta_{disk}$

Plugging in the numbers gives a gain of (1900 +- 300) /rad for the normalized signals. I implemented those numbers in the filter banks: now X_NORM and Y_NORM have units of radians, and measure the disk surface angular motion. I also calibrated the SUM channel in microwatts, using the nominal responsivity of 0.45 A/W and the transimpedance of 200k (gain 11.1 uW/V)

Here's teh calibrated spectrum: note that the background noise is much larger than the real one because of the signal jumps.

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.

73   Tue Aug 2 16:00:32 2016 GabrieleElectronicsCharacterizationMore on the signal jumps

So I’m sending a 1.123 Hz sinusoid into the ADC, and generating 3.123 Hz sines and cosines in the model. Frequencies are reasonably incommensurable with one second.

The plots below shows all three signals. In the top panels, I just separate the two segments in each second: the “normal” segment in blue, and the “jumped” segment in orange.
In the bottom panels, I took the jumped segments (orange) and shifted them “in the future” by exactly one second. The signals are perfect!

I think we could explain this if the order of the samples in each second is scrambled, like we have a circular buffer but we point to the wrong starting point…

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
207   Tue Nov 22 08:21:35 2016 GabrieleElectronicsCharacterizationADC saturation

Last night measurements didn't work well: even without exciting the modes, the ADC was saturating because of the low frequency signal, particularly a 58 Hz peak:

When the modes were rang up, thing got clearly even worse:

## Modification of whitening filter

So I modified the whitening filter, changing C6 from 2.2u to 220nF. The old and new whitening filters are shown below. We have the same amount of whitening at high frequency, but less amplification of the junk at ~50-100 Hz

With this modification, there's no more saturation, even when the modes are excited.

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)

263   Wed Jan 18 14:29:16 2017 AlenaGeneralAnnealingAnnealing run (489-490) on 3" wafers - Crime 01/18/2017

Started annealing run Annealing run (489-490) on 3" wafers - Crime 01/18/2017 https://dcc.ligo.org/T1700027 using new hardware

269   Fri Jan 20 16:00:36 2017 AlenaGeneralAnnealingAnnealing run (491-496) on 3" wafers - Crime 01/20/2017

Started Annealing run (491-496) on 3" wafers - Crime 01/20/2017 https://dcc.ligo.org/LIGO-T1700036 Will be done by Monday

350   Wed Jun 21 17:04:20 2017 AlenaGeneralAnnealingAnnealing run (541-542) on 3" wafers - Crime 06/25/2017

Started an annealing run https://dcc.ligo.org/LIGO-T1700271

Will be ready by Friday morning

355   Tue Jun 27 09:20:16 2017 AlenaGeneralAnnealingAnnealing run (546-551) on 3" wafers - Crime 06/27/2017

Started annealing run https://dcc.ligo.org/T1700293

Will be ready by June 28th afternoon

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

155   Tue Nov 1 15:34:49 2016 Alena, CalumGeneral Annealing run

Annealing run (449-453) on 3" wafers - Crime 11/01/2016 https://dcc.ligo.org/T1600507

430   Thu Sep 14 15:59:10 2017 GabrieleFacility All wrapped up for Saturday plumbing work

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