Cleaned the chamber in the washing machine at 40m and started 48 baking at 120 C
Disk excited at 12:01pm. Exited the room at 12:03pm.
Opened the chamber at about 2:30pm, got the disk out for edge polishing, installed it back at 3:30pm, pumping down at 3:40pm.
Stopped the roughing pump at 4:44:00pm (+60 seconds clean data, GPS 1155944657). Switched on the HV amplifier, excitation at 4:47:30pm. Recentered QPD, clean data from 4:48:30pm (GPS 1155944927)
After a first look at the data, it seems that something went wrong. I restearted the roughing pump and will pump overnight. I found the QPD miscentered, so I centered it again.
Excited again at about 5:46:35pm. Clean data from 1155948460
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:
Links to the two videos:
This morning I installed temporarily a second QPD to monitor the input beam. The goal was to understand where the vibrations at frequencies below 2kHz couple from. As shown in the photo, the second QPD was close to the first one.
The signals in the two QPDs were quite different, and the coherence between them wasn't great. So I concluded that the main coupling path is not through input beam of QPD vibration, but more likely real motion of the disk.
I removed the additional QPD and restored the setup to its nominal configuration. The readout infrastructure is still in the model.
We set up the model x3tst to acquire at 65kHz four signals coming from the PSL lab:
Elogs for the new Coatin RIng-down MEasurement lab had to start somewhere, so here is a couple of pictures of the optical table with shorter legs and of one of the two vacuum chambers that have been moved in.
We discovered a couple of days ago that the table was sitting on three legs only and the fourth one was dangling. I managed to adjust the height of the fourth leg using the large screw on the leg support. Now the table is properly supported by all four legs.
Here's a trend of the QPD signals when the IGM was turned on:
Turning it off does not bring the disk back.
Since I had recurrent problems with the picomotors used for QPD3, I swapped them with another Newport motorized mirror that was previously used in the Crackle1 experiment. This is the same model used for the other three QPD centering. Everything looks to be working fine now.
I also realigned all optical levers and swapped out an iris with a smaller one, to avoid beam clipping. All beam paths look clear now.
The JDSU HeNe laser 1103P that I was using is dead. I swapped it with a JDSU 1125P borrowed from the 40m.
I suspended the roughing pump with four springs. The reduction of the 58 Hz peak is similar to what I got when the pump was sitting on a box. So most of the coupling is due to acousting noise.
Four fused silica substrates from University Wafers, 76.2mm diameter / 0.5 mm thickness installed in chamber
Installed two new 2TB disks into the cymac3. Also, the main disk has a 1TB partition with the operating system, so I created a new 1TB partition. I created a logic volume that spans the three partitions, for a total of about 5TB. This partition is mounted in /mnt/data and linked to the /frames folder. Frames are written to this new logic volume.
The plot below shows the best loss angle we expect foer our samples, based on Steve Penn's model of surface and volume losses (Phys. Lett. A 352, 3). That paper contains data only for Suprasil 2 and Suprasil 312, so it might be a bit wrong for our Corning 7980. The two experimental data sets are for samples that have been laser polished.
I checked that the QPD electronics works as expected, and that I can acquire the signals using the ADCs. A new model (x3cr1) is up and running. It acquires the four quadrants, convert them from counts to volts, and compensate for the analog whitening filter. The four quadrant signals are X3:CR1-Q1_OUT, X3:CR1-Q2_OUT, X3:CR1-Q3_OUT, X3:CR1-Q4_OUT.
A matrix is used to compute the X and Y signals, defined as X = (Q1+Q4-Q2-Q3) and Y = (Q2+Q4-Q1-Q3). The SUM signal is also computed as SUM = (Q1+Q2+Q3+Q4).
Finally, the X and Y signals are normalized with the sum to produce X3:CR1-X_NORM_OUT and X3:CR2-Y_NORM_OUT.
A filter bank (ESD) is connected to the DAC channel #0 to produce the excitation that will be sent to the high voltage amplifier. I checked that the DAC is working properly (adding offsets). The input to the ESD filter bank is in volts.
The normalized X and Y signals, the sum of all four quadrants and the output of the ESD driver filter bank are saved to frames. The model runs at 65kHz.
The real time system seems to be working properly, except for the excitations: we can't activate any excitation using awggui or diaggui
Eric rebuilt the workstation from scratch installing Debian 8.5. All CDS software seem to be working. We setup a ssh-key for ssh'ing into cymac3 and configured the automatic mount of the remote /opt/rtcds.
We initially received 20 disks (75 mm diameter, 1 mm thickness) from Mark Optics. Here's their status as of today
All the other disks have been sent back to Mark Optics to grind out flats.
I did two set of measurements with the new coated samples from Montreal. I reshuffled the position in the two measurements. In both cases, the measurement being performed in bay 4 was bad, in the sense that it was very hard to see excited modes. Since the two measurements were carried out with two different disks, it's clear it is a problem with that setup.
SOLVED: there was a connection problem for the DAC output signal controlling the switch
REALLY SOLVED: it was not a cabling issue. The power supply for the switching box had the current limiter on: when all four switches are closed, the box drain about 270mA, which is more than the limit of 250mA. Therefore the power supply voltage dropped and only three switches were actually closed. I switched the power supply to 500mA range and maxed the current limit. Now all four switches are working properly
Today I wrote some auxiliary functions that will be useful for the measurement system:
The SkyHook has been put in place and bolted down to the floor.
I finished populating the new four QPD boards, and fixed the first one I populated weeks ago. I tested all five new boards: the output of the transimpendance respond correctly to the ambient light; the output of the whitening also respond correctly and has increased high frequency noise; the differential driver stages are all functional and balanced.
In summary, we have six QPD circuits ready: serial 02 is installed into the box and it has been used for the previous tests. Serial number 01, 03, 04, 05, 06 are not yet into a box, but fully functional. Boxes are ready.
For testing purposed, I also built another ADC interface board: it's complete with the exception of the connector that goes to the ADC.
I made a COMSOL simulation of our wafer (75 mm with flats, 1 mm thick) with a 1 micron thick coating (Tantala), and computed the dilution factor (E_coating / E_total). The result is shown in the plot below:
The dilution factor is slighly mode dependent, around a value of 5.7e-3.
The Q we measured on the latest two annealed wafers are in the range of 5e6 - 10e6 for the good modes, meaning that the total loss angle (subtrate, surface and edge combined) is 1e-7 - 2e-7.
Assuming an undoped tantala coating with loss angle of 4e-4 (http://authors.library.caltech.edu/55765/2/1501.06371.pdf), the disk loss angle after coating will be 2.2e-6, a factor 5 to 10 higher than our uncoated and annealed wafers.
So we can use the wafers as they are for our measurements.
Silicon wafer from WRS materials, diameter 3", thickness 356-406 microns.
Quiet time before excitation: 1165359305
Excitation (broad band) at 1165359337 (60 s)
Quiet time after excitation: 1165359399
% Freq Q Q (C.I. 95%) Q (C.I. 95%)
2043.9 6.5333e+03 6.5061e+03 6.5607e+03
2307.9 1.6958e+04 1.6895e+04 1.7022e+04
3671.0 2.7458e+04 2.7324e+04 2.7595e+04
4909.0 4.1605e+04 4.1322e+04 4.1892e+04
5268.1 2.5236e+04 2.5186e+04 2.5286e+04
6079.0 2.6835e+04 2.6311e+04 2.7382e+04
7317.4 5.1946e+04 5.1799e+04 5.2095e+04
7391.0 1.3702e+04 1.3441e+04 1.3973e+04
8586.6 5.3491e+04 5.2271e+04 5.4769e+04
8719.9 5.4501e+04 5.3904e+04 5.5111e+04
9600.4 6.6514e+04 6.6390e+04 6.6639e+04
9622.1 3.0667e+04 3.0505e+04 3.0830e+04
10507.0 8.1040e+04 8.0965e+04 8.1115e+04
11053.9 6.0651e+04 5.9853e+04 6.1471e+04
11397.5 5.2873e+04 5.2242e+04 5.3520e+04
11950.0 3.2045e+04 3.1514e+04 3.2593e+04
12083.0 8.8181e+04 8.7571e+04 8.8800e+04
12330.6 4.9761e+04 4.8997e+04 5.0549e+04
13799.0 4.8752e+04 4.7609e+04 4.9951e+04
14911.9 8.7301e+04 8.6550e+04 8.8066e+04
15849.6 3.7500e+04 3.6882e+04 3.8139e+04
17381.4 7.5930e+04 7.4582e+04 7.7328e+04
17585.0 9.7947e+04 9.6811e+04 9.9110e+04
17597.0 2.8465e+04 2.7318e+04 2.9712e+04
18310.4 9.0019e+04 8.9175e+04 9.0879e+04
18542.1 6.8287e+04 6.7506e+04 6.9088e+04
18547.5 1.4131e+05 1.4017e+05 1.4248e+05
18774.9 1.0588e+05 1.0490e+05 1.0687e+05
19066.6 8.0216e+04 7.8924e+04 8.1551e+04
20253.5 9.6914e+04 9.4540e+04 9.9411e+04
20463.0 1.0020e+05 9.9323e+04 1.0109e+05
21188.2 1.1931e+05 1.1851e+05 1.2012e+05
21828.5 1.4420e+05 1.4290e+05 1.4552e+05
21837.5 1.5768e+05 1.5639e+05 1.5899e+05
22976.0 5.6472e+04 5.6229e+04 5.6717e+04
23356.5 1.2871e+05 1.2729e+05 1.3017e+05
23398.5 1.4698e+05 1.4422e+05 1.4984e+05
23455.0 1.1209e+05 1.0950e+05 1.1479e+05
23457.7 1.0716e+05 1.0509e+05 1.0932e+05
23496.0 1.4477e+05 1.4295e+05 1.4665e+05
23703.5 1.5954e+05 1.5695e+05 1.6222e+05
23993.0 1.3344e+05 1.3183e+05 1.3510e+05
24758.2 1.4752e+05 1.4655e+05 1.4850e+05
24952.6 1.3025e+05 1.2972e+05 1.3077e+05
25139.0 3.3941e+04 3.3575e+04 3.4316e+04
25298.5 1.0825e+05 1.0603e+05 1.1056e+05
25387.1 1.3101e+05 1.3055e+05 1.3148e+05
25391.7 1.2021e+05 1.2011e+05 1.2032e+05
26752.9 1.0624e+05 1.0595e+05 1.0653e+05
26762.0 1.8838e+05 1.8490e+05 1.9200e+05
26838.0 6.9555e+04 6.7066e+04 7.2237e+04
27147.7 1.0675e+05 1.0571e+05 1.0780e+05
27698.0 8.3204e+04 8.1975e+04 8.4471e+04
28101.4 1.7792e+05 1.7748e+05 1.7836e+05
28109.4 8.9486e+04 8.8527e+04 9.0466e+04
28480.6 1.1985e+05 1.1934e+05 1.2037e+05
28972.0 4.5087e+04 4.3490e+04 4.6806e+04
28979.3 1.3823e+05 1.3750e+05 1.3897e+05
29044.6 1.7261e+05 1.7177e+05 1.7347e+05
29166.4 1.7820e+05 1.7785e+05 1.7855e+05
29222.0 1.8986e+05 1.8640e+05 1.9345e+05
29451.0 3.4557e+04 3.3927e+04 3.5211e+04
30284.4 1.9755e+05 1.9701e+05 1.9810e+05
30691.3 9.7139e+04 9.6728e+04 9.7553e+04
31228.6 1.2060e+05 1.2028e+05 1.2092e+05
32159.5 2.0041e+05 1.9800e+05 2.0288e+05
32226.8 7.3880e+04 7.3119e+04 7.4658e+04
32366.0 2.0220e+05 2.0185e+05 2.0255e+05
S1600525 has been coated in Fort Collins with 480nm of pure tantala. I used the emasured loss angles (after deposition, before annealing) to estimate the shear and bulk loss angles.
First, my COMSOL simulation shows that even if I don’t include the drum-like modes, I still have a significant scatter of shear/bulk energy ratio. The top panel shows indeed the ratio shear/bulk for all the modes I can measure, and the variation is quite large. So, contrary to my expectation, there is some room for fitting here. The bottom panel just shows the usual dilution factors.
To quantify which of the fit below is the most significant, I did a Bayesian analysis (thanks Rory for the help!).
In brief, I compute the Bayes factors for each of the models considered below. As always in any Bayesian analysis, I had to assume some prior distribution for the fit parameters. I used uniform distributions, between 0 and 20e-4 for the loss angles, and between -100e-6 and 100e-6 for the slope. I checked that the intervals I choose for the priors have only a small influence on the results.
The model that has the highest probability is the one that considers different bulk and shear frequency depent loss angles. The others have the following relative probabilities
One loss angle constant: 1/13e+13
One loss angle linear in frequency: 1/5.5
Bulk/shear angles constant: 1/48784
Bulk/shear angles linear in frequency: 1/1
So the constant loss angle models are excluded with large significance. The single frequency dependent loss angle is less probable that the bulk/shear frequency dependent model, but only by a factor of 5.5. According to the literature, this is considered a substantial evidence in favor of frequency dependent bulk/shear loss angles.
I repeated the analysis for bulk and shear losses described in an early elog entry, with the same coating, but after annealing at 500C for 9 hours.
The COMSOL model is the same as before, so the dilution factors are the same, except that this time I could measure a few more modes at high frequency:
As in the previous analysis, I fitted four different models:
1) one single loss angle for both bulk and shear, constant in frequency
2) one single loss angle for both bulk and shear, linear in frequency
3) separate bulk and shear loss angles, constant
4) separate bulk and shear loss angles, linear in frequency
The data strongly favor the last model: two loss angles for shear and bulk, linearly dependent on frequency (Bayes factor -22.7 for the second best model, which is the frequency dependent single loss angle).
The results are below.
I realigned all optical levers to measure the 50mm disks. In brief, I moved the input 2" mirrors, the in-vacuum 2" mirrors and the PZT mirrors so that the beam hits the 50mm sample and gets back into the QPD. Re-aligned everything to the horizontal reference using water.
Just for fun, I installed the disk thas has been etched in the center with "1234". I figured out that the ESD PCB was probably too close to the disk, so I moved it a bit up.
Pump down started at about 2:38pm LT.
Cleaning and baking (200 C air foe SS and 120 for Al) parts for the new vacuum chamber
% Freq First Q of pair Second Q of pair
1117.4 2.3392e+07 2.3392e+07
2555.9 1.8650e+07 1.8650e+07
4441.1 1.3003e+07 1.3003e+07
6759.2 1.6003e+07 1.5656e+07
6781.8 1.4795e+07 1.4795e+07
9499.2 5.6765e+06 5.6765e+06
10219.5 1.3148e+07 2.7060e+06
10222.3 1.3909e+07 4.2609e+04
11444.0 2.0756e+06 6.5364e+05
12649.4 1.0264e+07 8.7228e+06
12650.7 8.6808e+06 8.6808e+06
14176.3 1.0290e+07 1.0290e+07
14177.5 1.0185e+07 1.0185e+07
16113.7 1.0856e+07 9.7535e+06
16202.5 8.6733e+06 5.0176e+06
18619.0 1.3113e+07 1.3113e+07
18622.1 1.4864e+07 1.4864e+07
20149.0 1.4047e+06 1.4047e+06
21348.8 6.9944e+06 6.9944e+06
21353.3 8.0679e+06 3.1734e+05
23529.5 1.3076e+07 1.3076e+07
24482.3 9.6841e+06 9.6841e+06
24669.1 4.8629e+06 4.8629e+06
24670.5 6.3609e+06 6.3609e+06
25499.2 5.2216e+06 5.2216e+06
25828.0 3.3780e+06 3.3780e+06
27101.0 1.4934e+07 1.4934e+07
27103.5 1.4956e+07 1.4956e+07
28883.5 1.2076e+07 1.2076e+07
29068.6 1.1494e+07 1.1494e+07
29072.0 9.7555e+06 9.7555e+06
29190.0 5.9610e+06 5.9610e+06
29193.2 7.9280e+06 7.9280e+06
29502.2 7.8254e+06 7.8254e+06
30867.0 6.3681e+06 6.3681e+06
31267.0 1.6836e+06 1.4541e+05
32194.4 5.3275e+06 5.3275e+06
32200.0 5.9215e+06 2.6587e+06
The following plot compares the Q measured on this sample yesterday here at Caltech with the GeNS system, with the measurement perfomed by Raymond Robie in Glasgow.
- blue dots: measurements on the flame polished sample here at Caltech
- orange crosses and yellow triangles: Raymond’s measurements on the flame polished sample at in Glasgow (after annealing)
- purple crosses: typical Q values measured on disk samples (not annealed nor flame polished) here at Caltech
Flame polishing of the edges did not change significantly the Q we measure with the GeNS system. However, the GeNS system rovide systematically higher Q values for basically all measurable modes.
prefix = '2016_10_20'; % name of the folder where result will be saved
gps0 = 1161034552; % GPS time of clean data before excitation
gps1 = 1161034619; % GPS time right after excitation
dt = 30; % how much data to be used to search peaks
minsnr = 6; % minimum peak SNR
minfr = 1000; % minimum peak frequency
Dt = 3600; % total amount of time for the ringdown measurement