In normal conditions the RMS of the QPD signals is dominated by the 58 Hz line generated by the roughing pump. Also, when the modes are excited, they exhibit large sidebands at +- 58 Hz that are an annoyance for the analysis.
I improved a bit the level of the 58 Hz in the QPD signals by putting the roughing pump on top of a "Very Useful Box":
Despite the fact that this advanced vibration isolation is already a little bit effective, it might be good to try to build some better suspension and maybe add an acoustic isolation around the pump.
The 12 following substrates have been measured and are ready for the first coating experiment in Montreal:
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
This afternoon I completed the assembly of the electronics boards to interface the ADC and DAC. The ADC is interfaced with a new custom board, which accepts up to eight QPD inputs, the syncronization signal, and it's connected to the ADC:
For the DAC I used one spare board from the Crackle experiment. However, that board had a wrong pinout for the DAC side connector, so I had to implemented again the same hack I did for the crackling noise experiment.
All boards are connected to the ADC and DACs, and to the syncronization signal generated with a SR DS345. No boxes for the moment being, I'll figure out a better organization of the boards in the future if needed. I still haven't tested if the real time system is able to communicate properly with the new interfaces.
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:
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.
Installed the ADC and DAC boards into a proper box. Also, swapped the temporary DAC board (with cale hack) with the final one. Schematics and PCB are in the DCC: D1600196 and D1600301
The box is sitting on top of the cymac computer, on the back, since I don't have any long cable to connect the ADC.
I added to the model CR0 an additional bias path for the ESD driver:
Some funny RGC idiosyncrasy: if you have a filter bank named "SUM", you can't add a summation block: if you do you get a name conflict at compilation time. That's why I used a matrix
Updated the MEDM screen accordingly
A quick test shows that working with a bias does not improve the ability to excite the modes. The DAC saturates at +-32k, which corresponds to +-10V out of the ADC, matched to the input range of the HV amplifier. The largest excitation of high frequency modes is obtained by using white noise, no bias, and maximum amplitude.
Here's a ongoing summary of the substrate aging tests.
Mark Optics with polished edges and CO2 polished, stored in the CR0 vacuum chamber.
Mark Optics with polished edges, stored in standard wafer container in the dessicator cabinet
Mark Optics with polished edges, stored in standard wafer container in vacuum sealed envelope with dessicant
Mark Optics with polished edges and CO2 polished, stored in standard wafer container in the dessicator cabinet
Annealing run (447-448) on 3" wafers - Crime 10/27/2016 https://dcc.ligo.org/T1600485-v1
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
Started annealing of blank disks: S1600541 S1600542 S1600545 S1600546 S1600551 S1600552 S1600554 S1600555
900C for 9 hours, starting at 10:30am
Annealing run (449-453) on 3" wafers - Crime 11/01/2016 https://dcc.ligo.org/T1600507
Started annealing of S1600577 S1600580 S1600582 S1600585 at 5pm
ramp up to 600C at 100C/h
hold at 600C for 10 h
ramp down at 100C/h
Started annealing of S1600579 S1600581 S1600583 S1600586 at 5:00pm
At 11:35am, started annealing of ten fused silica wafers (50.8mm / 0.1 mm) [S1800611 S1800612 S1800613 S1800614 S1800615 S1800616 S1800617 S1800618 S1800619 S1800620]
Started annealing of S1600579 S1600581 S1600583 S1600586 at 3:25pm
Samples S1600519 S1600522 S1600565 S1600566 S1600567 S1600568 S1600569
Started annealing of S1600579 S1600581 S1600583 S1600586 at 7:00pm 03/30
Started annealing run Annealing run (489-490) on 3" wafers - Crime 01/18/2017 https://dcc.ligo.org/T1700027 using new hardware
Started Annealing run (491-496) on 3" wafers - Crime 01/20/2017 https://dcc.ligo.org/LIGO-T1700036 Will be done by Monday
Started an annealing run https://dcc.ligo.org/LIGO-T1700271
Will be ready by Friday morning
Started annealing run https://dcc.ligo.org/T1700293
Will be ready by June 28th afternoon
Yesterday I cloned the cymac2 disk and installed it into the cymac3.
Jamie tweaked a few things (I can't really give more details) and now cymac3 is up an running with the same software as cymac2.
I compiled and installed the CR1 model, to readout the QPD. No more jumps in the signals!
To be able to access testpoints and have AWG working I had to follow the hack explained here: Cryo_Lab/781
I tested the following features:
The plot below shows the spectrum of the QPD. For the moment being I'm just sending a straight HeNe beam into the QPD, since the test setup with the disk is no more available. Units are arbitrary
Not so sure anymore...
I was suspecting dust crossing the beam, so I build a very rough enclosure, that should help with dust. I don't think I saw any change in the glitches.
So one might conclude that the glictches are produced by the analog QPD electronics. However, I plugged in a scope and I couldn't see any in the analog signal. But I checked only before the DRV135 stages. I'll need some sort of breakout board to test the output of the DRV135.
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
I modified the autocenter script. Now while the picomotor is moving, the variable X3:CR1-AUTOCENTER takes the value 1, otherwise it is 0.
I wrote an autocenter script for the four QPD in the new setup (autocenter14.py) and renamed the script for the old chamber (autocenter0.py).
Tested and working properly, with network connection to the picomotor controllers. Be aware that if the picomotor controllers are switched off, their IP address might change.
Removed the peak meter lock from the model, since it's not used
Added and EPICS binary bit to control the autocenter, added corresponding buttons to the MEDM screen.
Now the GUI stops the autocentering when acquiring the reference spectrum.
The auto_excite.py also stops the autocentering 35 seconds before the excitation and until 35 second after the excitation, to provide for two reference quiet periods.
Excitation started at 20:15:30LT, 20 seconds long. The excitation is band-limited (10 Hz) centered around each of the predicted mode frequencies. Amplitude inversely proportional to the mode frequency. The system was quiet before the excitation for many minutes.
For reference, here's the code used for the excitation:
from noise import *
from numpy import *
x = loadtxt('predicted_modes.txt')
bands = map(lambda x: [x-5,x+5], x)
ampl = x/x
xx = multi_band_noise(bands, ampl, T=20, fs=65536)
n = AWGNoiseStream(1e-2*xx, channel='X3:CR1-ESD_EXC', rate=65536)
I measured the beam profile of the new Thorlabs HeNe (21.8 mW measured). The beam waist is 355 microns, very close to the laser output port.
Using those numbers and the optical gain optimization algorithm, I tweaked the optical lever design. The simplest solution uses two lenses right after the laser to focus the beam down to about 300 microns on the QPD. The arm lever length is about 1.6 m, corresponding to an optical gain of about 18000/rad. I updated the DCC drawing in D1600213
Yesterday we assembled the lase polishing system. The Co2 laser power can be controlled using a waveplate, so we can turn on the laser at maximum power and let it stabilize, before actually turning up the power sent to the disk.
The beam is focused with a 10" focal length lens, and sent to the disk edge, poiting slightly upward to avoid hitting any other part of the disk.
The disk is moved with a combination of a linear and rotation stage, controlled with a MATLAB script. We tuned the translation and rotation speed so that the edge always moves at about 0.5 mm/s. Some refinement of the movimentation procedure will follow.
We tried the setup with one of the damaged samples, and the results are quite good.
More work this afternoon
We improved the control software of the laser polishing system: now the rotation speed is large when the laser is missing the disk because of the flats.
We used S1600479 as a test. This substrate was marked as damaged and had a clear chip. It went thoruhg two different polishing runs
The second run was probably too slow, and we can see some kind of traces left on the main surface close to the edges
We then laser polished a good subtrate (S1600439) which was already measured before (137) and after annealing (144), with good Q values. This is a substrate from the first batch we received from Mark Optics. The polishing was done at ~ 18W and 0.5 mm/s.
Some pictures below:
The four surviving University Wafers 76.2mm/0.5mm wafers have been CO2 polished. They are identified by numbers from 1 to 4 on the container. Number 4 was used for tests, so it might not be as good as the other three. During number3 polishing, the CO2 laser tripped, so I restarted the process from the beginning.
Polished S1600619 S1600620 S1600621 S1600622
The plot below shows that the Q values of S1600439 improved a lot after the CO2 laser polishing. About 15 modes have Q above 10e6. The first mode at 1kHz has a Q of 37e6, the highest ever measured so far!
Here's a comparison of the Q values of this sample before annealing, after annealing and after CO2 polishing.