2020-03-27

• 3:31pm in chamber
  • S1600789 in CR1
  • S1600791 in CR2
• 3:32pm roughing pump on
• 3:40pm turbo pump on

2020-03-31

• 1:00 pm in chamber
  • S1600784in CR1
  • S1600785 in CR2
  • S1600789 in CR3
  • S1600791 in CR4
• 1:05 pm roughing pump on
• 1:14 pm turbo pump on

2020-03-31

• 7:05pm in chamber
  • S1600775 in CR1
  • S1600788 in CR2
• 7:09pm roughing pump on
• 7:18pm turbo pump on

2020-04-02

• 2:05 pm in chamber
  • S1600784 in CR1
  • S1600785 in CR2
  • S1600789 in CR3
  • S1600791 in CR4
• 2:07 pm roughing pump on
• 2:17 pm turbo pump on

2020-04-03

• 10:24am in chamber
  • S1600775 in CR1
  • S1600788 in CR2
• 10:25am roughing pump on
• 10:35am turbo pump on

2020-04-07

• 10:05 am in chamber
  • S1600775 in CR1
  • S1600784 in CR2
  • S1600788 in CR3
  • S1600791 in CR4
• 10:06 am roughing pump on
• 10:16 am turbo pump on

2020-04-07

• 3:50pm in chamber
  • S1600785 in CR1
  • S1600789 in CR2
• 3:53pm roughing pump on
• 4:03pm turbo pump on

2020-04-09

• 1:46 pm in chamber
  • S1600775 in CR1
  • S1600784 in CR2
  • S1600788 in CR3
  • S1600791 in CR4
• 1:47 pm roughing pump on
• 1:57 pm turbo pump on

2020-04-10

• 10:17am in chamber
  • S1600785 in CR1
  • S1600789 in CR2
• 10:20am roughing pump on
• 10:30am turbo pump on

2020-04-14

• 12:18 pm in chamber
  • S1600775 in CR1
  • S1600784 in CR2
  • S1600788 in CR3
  • S1600791 in CR4
• 12:19 pm roughing pump on
• 12:29 pm turbo pump on

2020-04-14

• 6:35pm in chamber
  • S1600785 in CR1
  • S1600789 in CR2
• 6:40pm roughing pump on
• 6:48pm turbo pump on

2020-04-16

• 2:21 pm in chamber
  • S1600775 in CR1
  • S1600784 in CR2
  • S1600788 in CR3
  • S1600791 in CR4
• 2:22 pm roughing pump on
• 2:30 pm turbo pump on

2020-04-17

• 10:17am in chamber
  • S1600785 in CR1
  • S1600789 in CR2
• 10:20am roughing pump on
• 10:28am turbo pump on

2020-04-23

• 2:00pm in chamber
  • S1600776 in CR1
• 2:02pm roughing pump on
• 2:12pm turbo pump on

2020-04-24

• 10:51 am in chamber
  • S1600801 in CR1
  • S1600802 in CR2
  • S1600803 in CR3
  • S1600804 in CR4
• 10:52 am roughing pump on
• 11:00 am turbo pump on

2020-04-24

• 10:25 am in chamber
  • S1600805 in CR1
  • S1600806 in CR2
  • S1600807 in CR3
  • S1600808 in CR4
• 10:28 am roughing pump on
• 10:38 am turbo pump on

2020-05-28

• 11:40 am in chamber
  • S1600801 in CR1
  • S1600802 in CR2
  • S1600803 in CR3
  • S1600805 in CR4
  • S1600806 in CR0
• 11:43 am roughing pumps on
• 11:53 am turbo pump CR1-4 on
•  turbo pump CR0 on not on yet

2020-05-28

• 10:00 am in chamber
  • S1600806 in CR1
• 10:05 am roughing pumps on
• 10:15 am turbo pump CR1-4 on

2020-06-02

• 10:15 am in chamber
  • S1600801 in CR1
  • S1600802 in CR2
• 10:20 am roughing pumps on
• 10:30 am turbo pump CR1-4 on

2020-06-05

• 6:50 pm in chamber
  • S1600803 in CR1
  • GaAs in CR2
• 6:55 pm roughing pumps on
• 7:05 pm turbo pump CR1-4 on

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

2020-06-15

• 7:32 pm in chamber
  • S1600803 in CR1
  • GaAs in CR2
• 7:36 pm roughing pumps on
• 7:46 pm turbo pump CR1-4 on

2020-06-16

• 3:42 pm in chamber
  • S1600805 in CR1
• 3:45 pm roughing pumps on
• 3:55 pm turbo pump CR1-4 on

2020-06-18

• 5:45 pm in chamber
  • S1600806 in CR1
• 5:50 pm roughing pumps on
• 6:00 pm turbo pump CR1-4 on

2020-06-23

• 4:20 pm in chamber
  • S1600806 in CR1
• 4:21 pm roughing pumps on
• 4:31 pm turbo pump CR1-4 on

2020-06-24

• 2:26 pm in chamber
  • S1600805 in CR1
  • S1600806 in CR1
• 2:27 pm roughing pumps on
• 2:37 pm turbo pump CR1-4 on

2020-06-25

• 8:47 am in chamber
  • S1600803 in CR1
  • S1600805 in CR2
  • S1600806 in CR3
• 8:49 am roughing pumps on
• 9:00 am turbo pump CR1-4 on

2020-07-01

• 1:42 pm in chamber
  • S1600803 in CR1
• 1:43 pm roughing pumps on
• 1:53 pm turbo pump CR1-4 on

2020-07-02

• 2:41 pm in chamber
  • S1600794 in CR1
  • S1600795 in CR2
  • S1600796 in CR3
  • S1600797 in CR4
• 2:42 pm roughing pump on
• 2:52 pm turbo pump on

2020-07-02

• 3:39 pm in chamber
  • S1600809 in CR1
  • S1600810 in CR2
  • S1600811 in CR3
  • S1600812 in CR4
• 3:40 pm roughing pump on
• 3:50 pm turbo pump on

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

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. 

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.

Yesterday we received the prototype of the disk suspension and retain system. Everything looks good. I checked that the disk fits in the holder, and all dimensions are good. The coil holders are out for winding, so I couldn't test the movimentation yet.

In brief, it doesn't work. The magnets and coils are strong enough to push up the ring with a sample inside, but the friction with the three alignment pins is too large and random, so when the current to the coils is increased slowly, the ring doesn't move up smoothly (see first attached video). On the other hand, if the current is switched on abruptly, the ring shoot to the top and stays there. However, if a disk is placed on the support, it is ejected out (see second video). When the current is cut (smoothly or abruptly) the ring doesn't alway comes back to the bottom, but sometimes it stays stuck inclinded.

On the positive side, we probably don't need such a complicated system:

1. in all the pump down I've done so far (ten or more), the disk never moved
2. the ring is very useful, even when used manually, to find the initial centering of the disk: if we machine three small aluminum wedges that can be put under the ring to keep it raised (or three set screws), it can be used to place down the sample in a roughly centered position, that has always been good enough to get the beam almost back into the QPD.

Links to the two videos:
Video1 Video2

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

Since my experiment with coil and magnets didn't work out very well, here's a new concept for the motion of the four retaining rings (all together) using a translation stage and a picomotor. This follows the same idea put forward by Steve Penn. The translation stage is a Newport 9066-COM-V and the picomotor (which we already have) is a Newport 8301-V. Both stage and picomotor are vacuum compatible (rated at 1e-6 Torr) and tested down to 1e-8 Torr by Steve.

Here's the jig integrated in the full system:

All parts for the motion of the retaining rings have been received and are ok. We're going to clean and bake them. 

This afternoon I installed the picomotor and the translation stage that will be used to move the retaining rings up and down. No partciular problem: I only had to add some small aluminum foil shims between the ear of some rings and the square plate, to make the rings as horizontal as possible.

I tested the motion: with 300000 steps it's possible to move the rings all the way from the parked (down) position, to the up position. I also checked that when the rings are up, I can place four substarates and they fall properly into the alignment groove. Since the maximum speed of the picomotor is 2000 steps/s, it takes 150 seconds to move up and down the ring. 

Finally, positive steps means that the rings are moving up, negative that they're moving down.

I raeligned the optical levers to the position I obtained by centering the samples with the rings. I haven't tested the repeatability yet.

The ring motion up and down was not very smooth, again due to friction on the centering pins.

So, after centering the rings using the pins and securing the rings to the translation stage, I removed all pins.

Now the motion up and down is very smooth.

I still have to fine tune the amount of steps that are needed to go up and down.

However, initial tests don't show a good repeatability of the positioning. My main suspect is that the vibration caused by the picomotor cause the disks to slip on the silicon lens. Indeed, when the disks are sitting on the rings, one can clearly hear them "rattle".

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

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

So initially the distance between disk and ESD is 1.22 mm

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

Pump down started at ~1:30pm

Excitations

• Old configuration, 1.2mm distance ESD-disk:
  • GPS before exc. 1186417492 
  • GPS after exc. 1186417546
• New configuration, 0.7mm distance ESD-disk
  • GPS before exc. 
  • GPS after exc.

The plots below compare the SNR and peak amplitude of all excited modes, in the new and old configuration. The new confgiuration is worse than the old one. This is unexpected, since the distance between ESD and disk is smaller.

However, yesterday we found out that setting the ESD so close to the disk is very tricky, and we might have some touching.

Additionally, the measured Q values of all modes are signfiicantly lower (by factors of >3), so it seems there is some additional friction. The mode frequencies are still compatible with the expected values, so it's unlikely that the ESD is touching the disk. One possible explanation for the worse Q can be residual gas damping in the area between the ESD and the disk: basically the gas moelcules that are left in the enclosed region between disk and ESD can create a viscous damping, which gets larger when the distance gets smaller [PhysRevLett.103.140601, arxiv:0907.5375]. I'll try to do some computations later today.

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.

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