The spectrum was noise than usual due to the roughing pump. I already found out in the past that I can reduce the noise by tweaking the position of the pump. This time however I wasn't successful.
Here are the results:
% Freq Q Qlow (C.I. 95%) Qhi (C.I. 95%)
1111.5 6.0958e+06 6.0641e+06 6.1279e+06
2549.6 3.6416e+06 3.6305e+06 3.6528e+06
4441.7 2.6916e+06 2.6879e+06 2.6953e+06
4512.9 2.1090e+05 2.0993e+05 2.1188e+05
6777.5 1.1797e+06 1.1790e+06 1.1803e+06
6790.9 3.8621e+06 3.8540e+06 3.8701e+06
6858.4 1.2434e+06 1.2295e+06 1.2577e+06
9548.0 1.2177e+05 1.1878e+05 1.2491e+05
10234.6 3.9934e+05 3.9351e+05 4.0535e+05
10399.0 2.8135e+05 2.7455e+05 2.8849e+05
12744.2 1.3145e+06 1.3115e+06 1.3174e+06
14211.3 3.8414e+06 3.8136e+06 3.8696e+06
16123.3 2.0276e+06 2.0181e+06 2.0372e+06
16135.8 5.2811e+06 5.2770e+06 5.2852e+06
16370.0 1.4976e+06 1.4922e+06 1.5031e+06
18689.3 4.2954e+06 4.2738e+06 4.3172e+06
23632.0 2.2796e+06 2.2528e+06 2.3070e+06
24797.4 8.7545e+05 8.5819e+05 8.9341e+05
27214.5 1.2566e+06 1.2374e+06 1.2764e+06
28947.5 1.7367e+06 1.7130e+06 1.7611e+06
29144.0 3.2148e+06 3.1213e+06 3.3142e+06
And the measured Q values:
% Freq Q Qlow (C.I. 95%) Qhi (C.I. 95%)
1111.4 6.2206e+06 6.2061e+06 6.2351e+06
2549.6 4.1538e+06 4.1498e+06 4.1579e+06
2592.9 1.0952e+06 1.0887e+06 1.1017e+06
4441.7 2.8521e+06 2.8513e+06 2.8529e+06
4513.0 2.0592e+05 2.0455e+05 2.0730e+05
6777.5 1.1013e+06 1.1006e+06 1.1020e+06
6790.9 3.9913e+06 3.9879e+06 3.9947e+06
6858.2 1.3100e+06 1.3078e+06 1.3122e+06
9547.8 1.2492e+06 1.2469e+06 1.2514e+06
10234.7 3.4336e+06 3.4209e+06 3.4463e+06
10398.7 4.3217e+05 3.2860e+05 6.3104e+05
12744.2 4.5274e+05 4.5177e+05 4.5371e+05
14211.3 2.0254e+06 2.0081e+06 2.0430e+06
16123.0 2.1225e+06 2.1173e+06 2.1276e+06
16135.8 4.6547e+06 4.6529e+06 4.6564e+06
16370.3 1.4781e+06 1.4762e+06 1.4800e+06
18689.2 4.5978e+06 4.5891e+06 4.6064e+06
20299.5 4.1859e+05 4.1375e+05 4.2353e+05
20364.6 1.1099e+06 1.0630e+06 1.1612e+06
21418.2 4.5814e+06 4.5718e+06 4.5911e+06
23631.9 2.8907e+06 2.8700e+06 2.9116e+06
24797.4 1.1241e+06 1.1121e+06 1.1363e+06
27214.5 2.1015e+06 2.0752e+06 2.1285e+06
28947.3 2.1285e+06 2.1162e+06 2.1410e+06
29054.7 1.4873e+06 1.4631e+06 1.5124e+06
29143.8 4.1250e+06 4.1050e+06 4.1453e+06
29647.5 4.5456e+05 4.4215e+05 4.6768e+05
31135.4 7.5136e+05 7.3331e+05 7.7033e+05
32013.4 1.1846e+06 1.1565e+06 1.2140e+06
Koji, Rich, and I recently came up with a new QPD design which is better for general lab use than the aLIGO ones (which have a high-noise preamp copied from iLIGO).
This page has the mechanical drawing only, but perhaps Rich can tell us if he's ready to make the first version for you or not. I think you can get by with the old design, but this new one should be lower noise for low light levels.
M. D. Ediger, in PNAS (2014), pp. 11232–11233.
A. J. Leggett and D. C. Vural, arXiv cond-mat.dis-nn, arXiv:1310.3387 (2013).
L. Berthier and M. D. Ediger, arXiv cond-mat.mtrl-sci, 40 (2015). Phys. Today.
G. Parisi and F. Sciortino, Nature Materials 12, 94 (2013).
S. Singh, M. D. Ediger, and J. J. de Pablo, Nature Materials 12, 139 (2013).
I find sometimes that the probe configuration can give these distorted signals. For the Tektronix probes, its best to use a 500 MHz probe instead of the BNC clip leads. The probe also should be compensated by attaching to the gold fingers square wave generator on the scope front and adjusting the capacitor in the probe with a little screwdriver until the square wave becomes perfect.
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.
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.
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.
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.
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
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.
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.
Nothing has happened since Steve, the visiting highschool teacher, has left. Meanwhile, some parts of the multi-color BRDF setup were delivered. I assembled everything today and realigned the lasers. Everything is ready now for a three-color BRDF measurement (the previous Richter record was 2 colors). I will claim back my video capture device as soon as possible from my neighbors and then take new images.
To be used to automate the laser polishing.
We played around a bit with the cymac, in efforts to make things better.
As I see it, the main problems that persist are:
Low pressure gauge glitching again. Tried restarting the gauge a few times - no result. Vented the chamber.
15:50 restarted the rouging pump, then the tubbo - no result. Aborted the measurement
Mon May 13 18:37:37 2019
Entered CRIME lab to borrow 4x hair nets and face masks. Can you please advise on what I should order for clean lab equipment? There are more options on techmart than I anticipated. We're in the process of increasing the cleanliness of the SiQ experiment.
There is a buy list of approved clean room supplies posted here https://dcc.ligo.org/LIGO-E1300399. This list is used by designated people to keep clean rooms supplies stock at each site including LIGO labs in Downs, 40m and the CRIME lab. Not sure what lab you are working in and what regulations you have there. Typically we study the list of the approved supplies, figure out what budget can be used for supplies for a particular experiment. Depending on what your project is, you may be able to just take what you need from the existing LIGO stock (I believe there is one for Downs and one for Bridge and 40m) or work with Liz, Bob or Chub on ordering it for your via approved channels.
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.
Link to image1.JPG Link to image2.JPG
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 where is the difference in the field between the plus end and the minus end. Component wise, where d is a unit vector. This holds for y and z, the whole thing can also be written as . Since p=qd, we can write .
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 . This explicity explains the factor of two and is an interesting alternative explanation.
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