40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Categoryup Subject
  2363   Wed Dec 31 15:59:59 1969 ShubhabrotoDailyProgress Little PMC Assembly
I collected the following things to assemble one unit of little PMC (attachment 1)
Item NameQuantity
Aluminium Spacer1
Curved Mirror1
Plane Mirror2
Piezoelectric Transducer (PZT) 1
O ring 2
Epoxy 30 CL 1

    1. Start by assembling the plane mirror to the clamp. First, put an O ring inside the clamp envelope(attachment 2) and then gently place the flat mirror on that(attachment 3). Rotate it 45 degrees and bolt this setup with the metal spacer using screws and Allen Key, Follow the same procedure for another plane mirror as well. The plane mirror is 99% reflecting on one side and transmitting on the other. The reflecting surface should be placed facing inside the clamp. An easy method to find the coating of the mirror is to hold it from the sides (never touch the middle part) and then checking if the bottom surface of the mirror is visible. If the bottom part is visible, then the side facing you transmits light and hence should be towards the outside. After this stage of assembly, it will look similar to attachment 4. Note: 3/8'' screw was used for this step.

    2. Next, proceed to assemble the endcap unit. The PZT should be glued centered on the endcap and the curved mirror should be glued centered on the PZT. As is it very difficult to align them properly, a jig can be used for gluing purpose. The external space has the same diameter of the PZT, the internal one has the same diameter of the curved mirror. The slots on the edges are used for the wires of the PZT. Epoxy 30 CL can be used for this purpose. A necessary support system can be assembled as per need.

I was assembling two units of the little PMC yesterday night. I followed step 1 of the procedure. It went uneventful. While assembling the 2nd unit, an unfortunate incident happened.
I was working on attaching the plane mirror between the spacer and the clamp(with O-ring). I bolted all the 3 bolts then observed a small crack in the mirror. To investigate further I opened the bolts. Then I observed that one of the bolts broke inside. The exact cause of the breaking of the bolt is not known. One possibility could be that it was a bit misaligned as it was the first bolt to be bolted and in the process got stuck to something. Not knowing what to do further, I wrapped up everything, kept all the things at their appropriate places, locked the lab and left.
Attachment 5 shows the broken screw on the left and a normal screw on the right. Attachment 6 shows a cracked mirror. Attachment 7 shows the broken screw fixed inside the spacer.

Today morning, Anchal and I went back to investigate the situation. It is quite unlucky to have a bolt broken from very near to the edge and getting it stuck in the spacer. Further investigation is required on how to take the broken screw out.
Attachment 1: Materials_Required.jpg
Attachment 2: O_ring.jpg
Attachment 3: Mirror_in_clamp.jpg
Attachment 4: Mirror_placed.jpg
Attachment 5: Bolt.jpg
Attachment 6: Cracked_Mirror.jpg
Attachment 7: Broken_Bolt_inside_spacer.jpg
  50   Fri May 2 22:00:17 2008 DmassComputing Daq Channels
I activated the channels C2:OMS-SUS_T3_ACT_OUT and C2:OMS-SUS_LEFT_IN1 in daqconfig, set both to acquire, and saved them to cvs/cds/caltech/chans/daq/C2OMS.ini

Real screens and naming conventions to follow.

[Edit: I do not know how to disable the auto smileys, so : O is seen as Yawn]
  51   Fri May 2 22:54:44 2008 DmassComputing Screens
I made a simulink model and put it here: /cvs/cds/advLigo/src/epics/simLink/atf.mdl

as instructed by the rolf wiki:

I then changed to the advLigo directory on oms, and "make atf" seemed to run successfully. Before finishing the process, I got the following error when dealing with c2atfepics:

[controls@oms c2atfepics]$ cat iocC2.log
dbLoadDatabase "dbd/a.dbd"
dbLoadDatabase "dbd/atf.dbd"
dbLoadDatabase "dbd/get_local_time.dbd"
dbLoadRecords "db/C2/local_time.db"
dbLoadRecords "db/C2/atf1.db"
Starting iocInit
### EPICS IOC CORE built on Aug 10 2005
### EPICS R3.14.7 $R3-14-7$ $2004/12/06 22:31:52$
iocInit: All initialization complete
seq &atf,("ifo=C2, site=caltech, sys=ATF, sysnum= 10")
SEQ Version 2.0.10: Wed Aug 10 23:41:07 2005
cas warning: Configured TCP port was unavailable.
cas warning: Using dynamically assigned TCP port 46391,
cas warning: but now two or more servers share the same UDP port.
cas warning: Depending on your IP kernel this server may not be
cas warning: reachable with UDP unicast (a host's IP in EPICS_CA_ADDR_LIST)
Couldn't open `/rtl_mem_atf' read/write
open("rtl_epics"): No such file or directory
  60   Fri Jul 11 16:20:21 2008 Stefan BallmerElectronics PMC
Since the digital system was in an ambigous state I locked the PMC using a SR560.
I did this so I can use the lab setup to test the newly modified Hanford ISS spare.
  154   Mon Jul 6 16:59:47 2009 Michelle Stephens, Connor MooneyLaser Power Output of 495 mW NPRO

We characterized the power output vs. drive current of the 495 mW NPRO laser for the gyro experiment. The current supply  goes up to 1.00 A. Here is our data:

C = [0.46 0.52 0.60 0.66 0.74 0.80 0.88 0.94 1.00];
Pd = [2 18 38 55 71 93 110 125 146];
Pu = [2 20 39 56 72 94 110 126 147];

C is drive current, Pd is lower limit on power output in mW, and Pu is upper limit.

We graphed the results and fit a line to it. The slope is 261.5 mW/A, and the intercept is -118.2 mW. The graph is attached.

directory is: \users\cmooney\Power495mW.m

Attachment 1: PowervCurrent495mW.pdf
  159   Wed Jul 8 10:36:44 2009 MichelleMisc Week 3 Update

We have mirrors! And clamps! And posts! In short, everything we need to actually put all the optics in their proper places. Thus, this week I have successfully placed the steering mirrors and the high reflectance mirrors into their mounts without touching/breaking any of them, and soon I'll be clamping them in their proper locations.

Connor and I  found out that Aidan's laser isn't behaving itself. The manufacturer specifies the waist as being in a different location than where we calculated it to be. We sent the beam through a half-wave plate and then a polarizing beam splitter and then measured the power along each axis, and the ratios are strange. We can't get the beam to be entirely transmitted along one axis by rotating the half-wave plate, like we should be able to if the beam is coming out linearly polarized. So the hypothesis is...it's not coming out linearly polarized. It may be elliptical. For the time being we're going to split the beam from the other NPRO and use it for both experiments, at least while the alignment is taking place. In the case of the gyro, we'll actually be feeding back to the laser and altering its frequency, so we'll definitely need separate lasers for each experiment at that time.

The 495 mW NPRO's SOP has finally been (mostly) approved and it first lased on Monday. This laser's power supply is a bit weird - the display for the power it thinks the laser is putting out doesn't match at all with what the powermeter actually says the laser is putting out. So we're not paying attention to the power display. The drive current goes up to 1.00 A, and at this maximum current, the laser is putting out ~150 mW. Apart from not being able to get a higher power than this, the laser is fairly well behaved - the power fluctuations as measured by the powermeter are small. The results of output power vs. drive currentmeasurements are on the eLog.

Connor and I also measured the electronics noise and intensity noise at various different powers, and then did a theoretical shot noise calculation for each of these. The setup and procedure are described in more detail in a recent eLog entry, which also includes graphs and the matlab code used to generate them.

Over the next week I'll be setting up the optics table for a simple PDH lock using a fabry-perot cavity, aligning the laser, and setting up the proper feedback using the DAQ. (Which I'll need to talk to Dmass about).

Oh, and we found out yesterday that Connor and I can't do any hazardous tasks in the lab without supervision, which includes aligning the lasers, even at low power. Aidan and Alastair will both be gone from tomorrow until next week Friday, so this poses a slight challenge. Hopefully Dmass will be around?

That's about it for now, I think.

  174   Wed Jul 15 14:40:44 2009 MichelleLaser NPRO ... fixed?

Alberto came over to have a look at the laser and discovered that the diode temperature was continuously increasing the longer the laser was kept on. The crystal temperature remained constant. He turned off the laser and shut the shutter, jiggled the cable connected to the laser a bit, and turned it back on. Lo! The temperature no longer increased...

So for the time being the laser seems to be fixed. If these problems start happening again, however, I may have to do some more rigorous troubleshooting/actually find out what's causing the problem.

  189   Wed Jul 22 09:43:53 2009 ConnorMisc Weekly Report #5

Most of this week has been spent aligning optics for the fiber stabilization experiment.  Part of the setup is shown here

The next step is to couple the beam into the fiber, single pass it and interferometrically beat it with the original signal so we can characterize the acquired phase noise.

Mode matching to various optical elements involves changing the beam parameter (i.e., beam width and radius of curvature) to fit specifications. We do this using lenses. Given the incoming beam parameter, the desired outgoing beam parameter, and lens focal lengths, we can find solutions (lens positions) to the problem.

  190   Wed Jul 22 11:09:45 2009 MichelleMisc Weekly Update 5

Over the course of the past week I've done a few things. When I began alignment I discovered that our laser was periodically shutting itself down. This was a very perplexing problem for about 2 days before Alberto came in with the diagnosis: the diode was overheating. We'll be sending that in to get it fixed, and we'll also put a heat sink on its casing. Hopefully that will be up and running by the time we really need it.

Right now, Aidan's laser is set up with a 50/50 beamsplitter, and then a half wave plate at each output of that. That way we can run the laser at full power, and each of us can independently adjust the power going into our respective experiments. This is working well while we're aligning things, but it clearly won't work long-term - we need to act directly on the laser's frequency to lock it to a cavity. This may not fare so well for fiber noise suppression.

We have our setup mostly aligned. The beam is going through some steering mirrors, through a lens, into the Faraday Isolator, through another set of steering mirros and a lens, and into the EOM. There is very little loss inside the isolator (putting in ~35 mW and getting out 33-34 mW), however I have not been able to get the power at the output of the EOM higher than ~ 24 mW. I don't think this is normal, but I will check that with people who know better than I do. I think it is probably the fault of poor alignment - the aperture is ~ 2mm and it's about 2 cm from the lens in the middle of the table, so it's hard to reach it or even view it properly to see what needs tweaking.

Over the next week I plan to finish the alignment and hopefully get a lock. I'll get a picture up once the rest of the setup is in place and aligned.


Oh, and I also helped clean the lab this week. It's pretty shiny, except for the heaps of garbage boxes now sitting in the hallway. We'll take care of that soon.

  197   Thu Jul 23 16:31:28 2009 MichelleLaser I've done some things in lab.


Today I aligned the laser beam through the EOM with something resembling a normal shape at the output. This was tricky. The powermeter isn't giving me very reasonable readouts, the aperture on the EOM is impossible to see with the IR viewer, the EOM is in the middle of the table where I can't really reach it, and it's very close to a focusing lens. The point being that I may have to tweak it a bit, but I really don't want to have to redo the alignment of that particular optic. So no earthquakes for a while.

A note on the power meter: It's been registering anywhere between -6 mW and 11 mW with no beam on it at all. I've been zeroing it before putting it in the beam before each use, but I don't know how much I trust it.

The beam shape coming out of the EOM  is still a bit funny - with one bright beam, and then a very faint ring, so it looks like a ring you would wear on your finger with a diamond on top. I am attributing this to the fact that the beam is slightly larger than the EOM's aperture; I have set it up so the center of the EOM coincides with the beam's waist. I'm also (according to the power meter) getting a high attenuation inside the EOM, but whether this is correct or normal I haven't yet figured out.

We need another mount for a beam splitter, this will go at the input to the cavity. We are also still in need of a quarter waveplate, and Aidan says he has a spare that he won't need to use for a few weeks. Also, CVI doesn't specify the damage threshold for the cavity mirrors for cw lasers, only for pulsed sources. Alastair has sent them an email requesting this information, and once we know that we can send the beam into the cavity at appropriate power levels.

  200   Fri Jul 24 19:00:37 2009 ranaLaser I've done some things in lab.
Make sure to use only ~5 mW to do all of the alignment.

Turn off the room lights if the power meter is not sitting well at zero.

Instead of the IR viewer, you can use a CCD camera to look at the input to the EOM and its output. You want to just center the beam in the EOM's apertures and then we will do the fine alignment by monitoring the RF AM.

Don't run the cavity with high power yet. Just 5 mW is easily high enough.
  236   Fri Aug 7 10:39:20 2009 MichelleLab Infrastructure Changing Lasers

We have to tweak the alignment of our PDH setup a bit, as well as change the cavity and profile the beam at different locations.

So we figure this is as good a time as any to stop using Aidan's laser and put in our one. We'll be working on that today, and we'll try to minimize the disruption this will cause to the fiber noise experiment.

  1889   Wed Dec 3 18:31:15 2014 KateLab Infrastructure First tilt-free seismometer entry

Stephanie Moon, Kate Dooley

We've started getting the lab in order and some parts assembled for putting together an early prototype of a tilt-free seismometer concept. We're using the optics table furthest from the door (i.e. not Zach's) and have cleaned up a good portion of it, putting things away in cabinets. Because we need a fair amount of height for the suspension cage, we disassembled half of the upper shelf that had been used for storing electronics. Last week we ordered Bosch-Rexroth struts for building the cage (invoice is attached). They arrived today and we now have them assembled per design with the exception of one additional bar that will go across the top:

Photo of frame 

Calum and Norna are letting us borrow 2 spools of phosphate-coated steel wire (and a pair of safety glasses). These are on the optics table. 

We also ordered a 10"x10"x1" piece of Aluminum from the machine shop on campus next to the 40m to be used as our first test mass. It is unfortunately so poorly machined!

Photo of Aluminum test mass



  1891   Tue Dec 16 21:36:07 2014 KateLaser Fiber coupler work

We started working on getting some stable light from the CTN experiment fiber-coupled into the ATF lab. It's not set up and working yet, but the fiber + coupler is fixed to the seismometer table and the output immediately dumped. Please take note that the laser hazard sign is more likely now to be on at times compared to the last couple months.

  2050   Wed Jun 22 13:42:38 2016 awadeMisc New silicon sample (8616P Tang) arrived: initial unbox and check

The new Si sample (8616P Tang) has arrived from Stanford. We will do scatter measurements at 1550 nm (and maybe 2 um). Its dimensions are 10x60x96 mm.

The two 10x96 mm surfaces have been high quality parallel polished (this was used for an absorption measurement) and one of the 60x96 mm surfaces is a moderate polish from which we will measure scatter. The sample is one half of a larger bar from which absorption measurements were made. The non-shiny side of the sample is labeled accordingly. Ashot Markosyan has sent us a bulk absorption uniformity scan across the sample, measuring the ppm/cm absorption stepping out from the center of the original bar. Attached is the absorption measured at 1550 nm, one side of our sample (labeled center) corresponds to position = 0 mm. Please note that for these 1550 nm measurements of absorption, the plotted alpha values need to be divided by a factor of 20. This is supposed to be their worst sample

A measurement of the sample at 2 um found absorption to be 2.5 ppm/cm.

I unboxed it from its shipping packaging to inspect the element. Some pictures are attached. It can be very hard to see some of the features as all I have is an old Kodak point and shot and Si is very shiny. I turned off the lights and used the Fiber coupled quartz lamp in the PSL flow cupboard to illuminate the sample a little better. Also attached are my hand sketched illustrations of the markings.  There is almost definitely a residue of a finger print on the inner edge (towards the 'middle') of the sample on one of the highly polished sides: you can just make this marking out in the photo, it is clear under room lights. 

The edges of the sample have been beveled but there is there are very small chips (<0.25 mm) out from most edges (couldn't get the camera to focus on these). Si is very brittle, so this is not something unexpected and won't affect scatter measurements.

There appear to be minor scratches on the large 60x96 mm surface (these are more obvious under the quartz lamp). There also might be some chemical splotch residue and dust around the edges. But I think a drag and wipe should remedy this. Otherwise I couldn't immediately identify any other potential defects. 


Highly polished front face (1 of 2)
Unpolished side
Above: moderately polished face


Unpolished back face.
See center bottom, mark
Some small chips on shaper edges
Under quartz spotlight #1
Under quartz spotlight #2
Under quartz spotlight #3


This might be a finger print ~17 mm in from edge (middle side)


Sketch scanned from log book with hard to see features
Attachment 1: image002.png
Attachment 2: LabbookSketchSiSampleFeatures.pdf
  2184   Fri Nov 10 20:23:48 2017 awadeComputing Reset top level router

I had to reset the top level router as something had hung. 

None of the computers in ATF/PSL lab were about to communicate out of their respective local routers.

  2186   Sun Dec 10 15:12:22 2017 awadeComputing Reset top level router

Couldn't see the outside internet this afternoon.  Restarted router again.



I had to reset the top level router as something had hung. 

None of the computers in ATF/PSL lab were about to communicate out of their respective local routers.


  2198   Sat May 5 06:08:35 2018 EricUpdate LabJack U3 New Setup

Changed the setup for LabJack testing so that we can better isolate problems with the DAC and ADC (if they exist). The previous setup consisted of passing two signals through the LabJack and comparing their outputs using the Rayleigh statistic. Since there are problems activating two DACs and two ADCs on the LabJack at once, we needed a different design that would only use one of these at a time. The new design (Figure 1) inputs a digital signal which is stored as a control signal to compare against. Next, the digital signal is passed through the DAC and comes out as an Analog signal through terminal DAC0. Since only the DAC or the ADC can run at one time, the DAC is then paused until the ADC converts the signal back to digital, at which point the ADC is paused and the DAC resumes functioning. Theoretically, this conversion should be happening at 100 Hz, and in practice, this number will be very close to 100 Hz. With this setup, problems occur after running the LabJack where either the DAC or the ADC stops passing through data. This doesn’t happen immediately but will happen seconds to minutes after the test begins. This seems to occur because the DAC and ADC are being turned on and off too quickly. However, if we run the DAC and ADC at too low of a rate then we lose resolution on the test wave and it becomes harder to run statistics on the data set. I believe I can get this setup to work by tuning the sampling frequency of the DAC and ADC so we're in a spot that allows the LabJack to both pass through data but also allows us to have a high enough resolution to run other tests on the data set.

I will attempt to get the first setup to work. However, if I can’t resolve the issues with the DAC or ADC not passing through data, we could also attempt a different setup that moves the Analog to Digital conversion out of the LabJack so that the DAC doesn’t need to be switched on and off (Figure 2). With this setup, we would need to purchase an ADC that can be soldered onto a Raspberry Pi (MCP3008).

Attachment 1: Figure1.JPG
Attachment 2: Figure2.JPG
  2202   Tue Jun 5 13:59:43 2018 EricSummary LabJack Summary

We used the setup specified in the previous eLog post. The design inputs a digital signal which is stored as a control signal to compare against. Next, the digital signal is passed through the DAC and comes out as an Analog signal through terminal DAC0. Since only the DAC or the ADC can run at one time, the DAC is then paused until the ADC converts the signal back to digital, at which point the ADC is paused and the DAC resumes functioning. Theoretically, this conversion should be happening at 100 Hz, and in practice, this number will be very close to 100 Hz. See Figure 1 for the setup diagram.

We passed two signals through the LabJack – 1 Hz sine wave and 10 Hz sine wave. These signals were converted to an analog signal through the DAC and then converted back to a digital signal using the ADC and the return signal was saved. We then ran Rayleigh statistic tests on this obtained data, which measured the continuous probability of a circular distribution for random variables. In GWpy, the Rayleigh statistic is a calculation of the coefficient of variation of the power spectral density (PSD) of a given set of data. It is used to measure the ‘Gaussianity’ of those data, where a value of 1 indicates Gaussian behaviour, less than 1 indicates coherent variations, and greater than 1 indicates incoherent variation. It is essentially a p-value for a frequency range where a Rayleigh value closer to zero means that we can reject the null hypothesis that the signal is not of the corresponding frequency. These methods were obtained from GWpy (https://gwpy.github.io/docs/stable/examples/spectrogram/rayleigh.html  and https://gwpy.github.io/docs/stable/examples/frequencyseries/rayleigh.html#gwpy-example-frequencyseries-rayleigh). This produced both Rayleigh spectrograms and Rayleigh spectrums. We also produced Rayleigh spectrograms and spectrums for the digital signal inputted into the LabJack to compare against the data read back from the LabJack. The attached 8 plots are these spectrograms and spectrums – 4 for each frequency containing 2 expected and 2 observed spectrograms and spectrums. We can see that the LabJack is mostly consistent with converting the data. We see clear signals in the observed plots that correspond to 1 Hz and 10 Hz. We can see in the spectrograms that the LabJack occasionally drops data, but very rarely – only around 3 times for sampling sessions of around an hour. The data drops no more than a few milliseconds each time (usually only one packet).

Attachment 1: Figure1.pdf
Attachment 2: 1hz_spectrograph_observed.pdf
Attachment 3: 1hz_spectrograph_expected.pdf
Attachment 4: 1hz_spectrogram_observed.png
Attachment 5: 1hz_spectrogram_expected.png
Attachment 6: 10hz_spectrograph_observed.pdf
Attachment 7: 10hz_spectrograph_expected.pdf
Attachment 8: 10hz_spectrogram_observed.png
Attachment 9: 10hz_spectrogram_expected.png
  2219   Sun Jul 22 20:12:23 2018 awadeDailyProgress Progress 7/22/18

Noise plot

I might be a good idea to plot your noise prediction on top of your data for comparison.  Also, aesthetically it could do with bigger fonts, voltage units closer to the order of magnitude of the data (i.e. nV/rtHz), add grid lines (with suitable alpha value) and reduce the margins of the x-axis scale from the edges of the plot area.  To reduce the gap on the x-axis I use ax.margins(x=0), where ax is the axis associated with the plotted data. The plot background is kind of weird, please only upload plots in vector graphics pdf format with transparent background (see rana's thoughts on the matter here PSL:1602).

You should also give some detail about the measurement itself.  What instrument you use (SR785), the fact that this was made using the A-B mode, AC or DC coupled, is it a stich of multiple spans, how much averaging etcetera.  You'll find that a lot of the settings are actually outputted by the python netgpibdata tools in the data file header.

Please zip/tar data and include in posts.

TF Plot

Transfer function plots should probably include both phase and amplitude information. Although all the information is encoded in the magnitude plot, phase is just +90 deg per 20 dB/dec of slope (in a loglog plot), it is better to present that data with on a second pane so readers can quickly see what is going on.

Craig makes really nice transfer function plots, see PSL:1871, maybe try to replicate that style.  Its a good idea to include a descriptive title and the date and time of the measurement.

Please zip/tar data and include in posts.


Have a feeling that these resistor values in the Sallen-Key are way too high.  Maybe this will leave you open conversion of current noise and bias current conversion into output voltage noise; at the very least, resistor values become sparse and values errors are big at this end of the resistor scale: you may want to check how this affects TF for different choices.  We have Wima caps that go up to 20 uF so maybe use that to bring the resistance down.

Photo diodes

Maybe do a deep search through the elog to see if Zach Korth mentioned the diodes used.  You can also email him.




Over the past few days, I have constructed two transimpedance amplifiers, whose circuits are displayed in the first attached figure. The main difference between this design and the previous one is the addition of 100 nF capacitors to the V+ and V- terminals of the op amp in the amplifier in order to provide a more stable DC input voltage. As Andrew mentioned, it may be advantageous to add some resistors into this circuit, and I will be looking into this soon.

In addition, we measured the noise and transfer function of one of these amplifiers using spectrum analyzers. These devices measure output voltages for input voltages over a range of frequencies in order to calculate these quantities. The noise and transfer function plots resulting from these measurements are shown in the next two attached figures.

The noise plot agrees fairly well with the calculations from LISO, which predicted a noise floor of ~10-8 V Hz-0.5. The transfer function displays a roll off, but it is not exactly what we had expected or calculated from LISO. We believe this discrepancy to be due to the capacitance of the solderless breadboard, which generally takes values of a few pF. Hence, this circuit soldered to a protoboard (with less parasitic capacitance) ought to show better behavior. 

After this, I soldered the two TIA circuits to protoboards. I plan to conduct more tests on these to ensure that they behave well. 

Lastly, in regards to the specs of the photodiodes that we will use, I have not yet been able to find information about them from the serial number listed on their rim. I plan to take a closer look at the photodiodes this afternoon and see if I can find these specifications. 


  2222   Fri Jul 27 12:26:58 2018 John MartynDailyProgress Progress 7/25/18

I don't think this 50 Ohm resistor is a good idea. For the noise, you should plot the LISO noise and data in units of the 'input-referred' current noise, rather than voltage noise. Also include a photo of the as-built circuit.

  2246   Wed Aug 22 14:13:18 2018 RahulLab Infrastructure Cryo-vacuum chamber layout

Attached file shows the layout of the new cryo-vacuum chamber (on optical bench), jib crane, cryocooler and pumping station in the QIL lab.

Attachment 1: cryo_vacuum_schematic.jpg
  2256   Mon Oct 22 09:46:10 2018 RahulLab Infrastructure Cryo vacuum chamber setup

The optical bench at the QIL has been re-arranged to accommodate the new cryo vacuum chamber. Today the vacuum chamber (collar fabricated by Nor Cal) will be moved inside the lab, on the optical bench. We have also received the cryocooler from SHI, which will be unboxed and moved inside the lab - to be kept on a separate table. The pumping station (along with the vacuum gauges) has arrived and is currently sitting in the lab. I have filled up the roughing pump with oil and attached a T section (covered up blank flange) to the flange of the tourbopump for a quick start up test. I used a small hose for the exhaust. However, I am in the process of getting a longer hose (12 feet) for a more permanent setup. 

Lab crane has also arrived, which has been assembled (I will attach a pic later on) in the lab.

Attachment 1: lab.jpeg
Attachment 2: Guages_and_controller.jpg
Attachment 3: Crane.jpg
Attachment 4: pumping_station.jpg
  2258   Tue Oct 30 10:17:44 2018 RahulUpdate SHI Cryocooler

We have received the SHI cryocooler CH-104 (figure attached), which has been moved to the QIL. I have inspected all the components after unboxing it. Cold head test report supplied by SHI is attached below.

The cryocooler comes with a HC-4A Zephyr air cooled helium compressor. This compressor is a single stage, air cooled and designed to deliver high pressure helium gas to the cryocooler.

There are 2 helium supply/return (although both the hose says supply, which I am not sure why, hence will check it out) hose along with a kit to install it. This is currently charged with helium pressure of 280 psi, however, once it is installed then the helium pressure has to be adjusted (I am currently reading the manual to assemble the system).

The cryoocoler cold head will be finally placed on a bench which we have bought. I plan to use a breadboard to clamp it down. The compressor will be placed a few feet (based on hose length) away from it. Typically the compressors are noisy, hence later on we can get longer hose to keep the compressors further away.

The vacuum chamber (collar) will be moved in the lab and on the optical bench this Thursday (although this was supposed to be moved in last week, however due inadequate communication by the Caltech moving service this couldn't happen).

The top and bottom flange covers for the vacuum chamber (fabricated by Kurt Lesker) has been shipped on 24 Oct and we should be receiving it this week.

Attachment 1: cryocooler.jpg
Attachment 2: compressor.jpg
Attachment 3: supply_hose.jpg
Attachment 4: Cold_test_report_SHI.jpg
  2259   Fri Nov 2 08:59:26 2018 RahulUpdate Vacuum chamber

We have our shiny new vacuum chamber (fabricated by Nor-Cal), now sitting on the optical bench.

Attachment 1: IMG_0005.jpg
Attachment 2: IMG_0008.jpg
Attachment 3: IMG_0007.jpg
  2260   Fri Nov 9 14:57:54 2018 RahulUpdate Cryo-vacuum chamber

SHI Cryocooler – Vacuum chamber assembly

The attached picture shows a schematic of the assembly/connection of SHI cryocooler to the vacuum chamber. The cryocooler has warm flange mounting holes. Using a mating flange – hose/bellows will be connected to the cryocooler. The mating flange will have a port for roughing pump and vacuum gauge connection. The hose/bellows will be connected to the flange reducer which will be bolted to the CF (4-5/8 size) flange of the cryostat.

I will upload a CAD model of the mating hose and will also look for an appropriate size hose and flange reducer.

Attachment 1: Picture1.jpg
  2265   Thu Nov 29 16:52:50 2018 RahulSummary Cryo-vacuum chamber

I would like to give a brief update on the ongoing effort for the assembly of the cry-vacuum chamber at the QIL. Gabriele has been kind enough to spare some time to help me with safe crane operation, considering the chamber and plates are 70 kg each.

At first, I prepared an aluminum spacer (made out of bosch extrusion) which is 90 mm in height. The idea is to lift the bottom plate (which has 16 through holes and counterbore for bolting purpose) such that the bolts can be easily inserted from the bottom. The spacer is strong enough to take the load of the entire assembly (i.e. around 200 kg, bottom and top plate + collar). The assembly will be resting on this spacer, even during the in-situ baking procedure. After baking and pump down testing is complete, the spacer will be removed and the vacuum chamber will be resting flat on the optical bench.

Next, with the help of a crane we tried lifting the collar using eye bolts and nylon slings, however the suspension point was way too high giving us no room for the crane to lift. This required shortening the length of the nylon sling. Firstly, I got shorter length eye bolts (2.5 inch against 4 inch) and secondly I used carabiners to tie up the sling. Using this set up we were able to lift the collar successfully.

The collar has groove for single dovetail O-ring (pictured attached) at the top and bottom surface.

The specifications for the viton O-ring was provided by Nor-Cal. I bought the viton O-ring (2-474V, 24.94’’ ID) from Kurt Lesker, the dimensions of which is given below,

O-RING,FKM,24.940"ID X .275" W(ACT),25"ID X 1/4"W (NOM),ISO 630

The challenge is to keep the O-ring held in the groove at the bottom of the collar (against gravity) during it’s mating with bottom plate. However, the O-ring always falls off. At this point I am not inserting the O-ring completely inside the groove (and I will come to this point next) and just slightly pushing it in. I want the O-ring to move in naturally from the pressure created by the plate and collar. I contacted Zach since he has faced similar issues with his tank (Chris gave me this information) and he used vacuum grease to keep the O-ring sticking on to the groove. However, outgassing from the grease could be a point of concern.

Next, I tried to insert the O-ring completely inside the grove, strangely in this case I find it to be longer by at least an inch. The inner diameter of the groove is 25 inches.

I contacted Nor-Cal to cross-check the size they have recommended. They realized that they have made a mistake with the size and have agreed to ship one size smaller O-ring (i.e. 2-473 having an ID of 23.94) which should give a stretch of 4%. I will use this once we receive it.

I found a Youtube video of the O-ring installation in a half or full dovetail groove. Given below is the link, since this is different from the usual method, hence important. The advantage of using dovetail groove is that the O-ring will stay inside during the assembly without falling off.  




I asked Nor-Cal about in-situ baking to reduce outgassing and they recommended that with viton O-ring seals 200C is max and 150C or lower is safe. I will go with 100 C. Steve doesn’t agree and doesn’t like the idea of baking it during pump down. As per him, once a turbo pump was destroyed (I guess at 40m) after some parts of the O-ring got damaged and got sucked inside. However, I think keeping things at 100 C should be safe as other folks at the cryolab have done the same, successfully.







Attachment 1: bottom_plate_on_spacer.jpg
Attachment 2: Crane_dovetail.jpg
  2266   Thu Nov 29 17:00:37 2018 RahulMisc Nor-Cal: leak rate of the chamber (collar)

Nor-Cal indicated leak rate of the collar is 9.8*10^-10 std. cc/ss (Std.cc/sec= One cubic centimeter of gas flow per second at 14.7 psi of pressure and a temperature of 77 F.). I have uplaoded their spec. sheet (which I hope is their measured data) for future reference. The surface finish is Electropolish.

Put it on a wiki page and put the link here. Thanks! (Koji)

I apologise for my mistake, given below is the wiki link for the outgassing rate data supplied by Nor-Cal for our chamber.


  2301   Fri Mar 8 17:05:52 2019 AnjaliUpdate Frequency stabilization of 2 micron source


The schematic of the homodyne configuration is shown below.

Following is the component list

Item Quantity Availability Part number Remarks
Laser diode 1 Yes EP 2004-0-DM-B06-FA  
Isolator 1 Yes    
Coupler(50/50) 5 Yes TW2000R5A2A Fiber type : SM2000
Delay fiber   Yes SM2000 Need to check the exact length of the fiber
Photodetector 4 Yes DET10D  
SR560 3 Yes    


Attachment 1: Homodyne_setup_2micron.png
  2403   Thu Aug 15 15:45:30 2019 DuoLab Infrastructure Floor plan around the big cryostat

Chris and I went to the lab and made some plans about how to use the space around the optics table. Attached a drawing of it. A couple notes about the drawing:

1. Green: underneath. The rough pump is under the table. The connection to the coldhead goes on the floor.

2. Rack: electronics rack.

3. Yellow cabinet: the cabinet that has chemicals in it.

4. Turbo/Rough: pumps.

Attachment 1: autodraw_8_15_2019.png
  2405   Sun Aug 18 14:16:59 2019 DuoSummary Measuring the dark current of PD

Koji set up an experiment measuring the dark current of the photodiodes. A bias voltage is given and the current is converted to voltage via a TIA, where it is measured. Also note that in order to provide a high quality bias voltage, we LP the output of the device with a second order sallen key filter cutoff at 1Hz. 

Attachment 1: exp.pdf
Attachment 2: IMG_2921.png
  2414   Tue Sep 3 16:47:08 2019 DuoLab Infrastructure QIL lab floor plan

We plan to set up the big cryostat in the QIL lab. We make a plan on how to use the space in this area.

We have these items related to this experiment: the chamber, the compressor, the pump and the crane. The crane is used to lift the lid of the chamber when we open it. 

The chamber sits on the table, its diameter is about 2'4''. We put it at the corner of the table, giving us more accessible space around it.

The compressor is used to cool the system. It is connected to the chamber via the coldhead so we will need a small table to hold the coldhead at the output of the chamber.

The pump has two parts: rough pump and turbo pump. Rough pump has more noise so we put it under the table. The turbo pump is connected to the chamber and we need a stand for that too.

The current plan for the crane is that we want to screw the crane onto the floor. We do not have space for a big crane base.


Attachment 1: qilfloor.pdf
  2415   Wed Sep 4 22:14:12 2019 ranaLab Infrastructure QIL lab floor plan

what about attaching a crane to the ceiling on one of the supporting beams?


  2426   Thu Sep 26 18:05:31 2019 DuoLab Infrastructure Cryo cooler and pump test run

[Chris, Duo]
We tested the cryo cooler and the turbo pump this afternoon. We ran the cryo cooler for two hours. The equalization pressure is 275psi(the pressure before we turn it on) and operating pressure (pressure after running for two hours) is 295psi(attachment 1). The operating pressure is lower than expected; the manual indicates the pressure is expected to be 300-320psi.

We cycled the turbo pump. It appears to be functioning properly.

Attachment 1: IMG_0990.jpg
  2433   Thu Oct 17 14:12:10 2019 DuoLab Infrastructure IOGEAR GWU637 failure

The spectrum analyzer SR785 uses a Ethernet-Wifi converter GWU637 from IOGEAR to connect to the WIFI in the lab. Today I am trying to download experiment data from SR785 as always but somehow it cannot find the device anymore. After struggling for a while, I restart the GWU637 device (unplug and plug the power cable) and then I can download data again.

I think it needs to be restarted after running for a couple weeks.

  Draft   Mon Nov 18 17:17:29 2019 DuoSummary Restart model in QIL lab

Here are the commands.

ssh fb4
sudo /sbin/rmmod c4tst c4iop && cd /opt/rtcds/caltech/c4/target/c4iop/scripts/

./startupC4rt && cd ../../c4tst/scripts/ && ./startupC4rt && systemctl start rts-awgtpman@c4iop.service && systemctl start rts-awgtpman@c4tst.service && systemctl restart daqd@standiop.service

  2551   Mon Apr 5 18:50:54 2021 RadhikaSummary Current PD testing schematic

I'm attaching my rough first draft of the QIL photodiode testing schematic. Please provide comments for fixes/improvement!

Attachment 1: QIL_PD_testing.jpg
Attachment 2: QIL_PD_testing.graffle
  2715   Mon Jan 31 15:40:21 2022 StephenDailyProgress 31 Jan Fastest Radiative Cooling run started

As discussed during the 21 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling (again, see QIL/2706) through the following configuration choices:

  • move heater to test mass
  • add thermal grease to inner shield - coldplate interface (clamped joint)

Actions completed 27, 28, and 31 Jan 2022

  • Vent.
  • Remove Test Mass in frame.
    • For simplicity, we snipped the RTD lead (we didn't want to have to redo the cryovarnish joint).
      • Of course, the joint failed during the repairs so we had to redo the workpiece RTD cryovarnish joint anyway!
  • Use cryovarnish to affix heater.
    • Removed aquadag in area of joint using IPA-soaked Alpha wipe and scrubbing motion.
    • First, varnished cigarette paper anchor pad, then added heater.
    • We allowed the cryovarnish to cure overnight between the 27th and 28th, then allowed the joint to hang in its vertical orientation over the weekend to confirm its integrity.
  • Use conventional pin-socket arrangement to add junction to heater leads and workpiece RTD leads.
    • Confirm all RTD leads are functional, and repair crimp joints and Kapton tape insulation where needed.
  • Clean up aquadag flakes on coldplate.
  • Remove inner shield, add Apiezon M thermal grease, and bolt down again.
  • Touch up position of mylar shield on cold linkage, aluminum foil aperture covers.
    • All apertures are covered except:
      • Inner Shield: cold linkage (not an issue - partially occluded by copper bar, mylar tube extends into cold head view and mylar mitten)
      • Outer Shield: electrical port, cold linkage (aperture has been extended to have additional area underneath the original circular aperture)
  • Insert Test Mass in frame. Dog clamp down frame.
  • Pump down, cool down.
    • Pump down started at ~15:15.
    • Cool down started at 15:44.

Model updates required to reflect new configuration:

  • estimate conductive leak from 24 AWG heater leads to test mass
  • model conductance of cryovarnish joint between heater and test mass - does cigarette paper make a difference?
  • model greased joint of inner shield - cold plate interface
    • confirm clamp load is adequate for effective greased joint, at room temp and cold temp!
  2716   Fri Feb 4 14:00:19 2022 RadhikaDailyProgress 31 Jan Fastest Radiative Cooling run started

Attached are best fits for cooldown runs on 01/14 and 01/31. The setup for both cooldowns can be found in the previous ELOGs. We noticed that the outer shield did not cool as significantly on 01/31 than on 01/14, hinting that there might have been more thermal contact between the outer shield and cold plate / copper bar. 

The model considers the resistances of the following conductive elements (and uses these resistances as fit parameters):

   1.) Joint between cold head and copper bar
   2.) Bulk of copper bar
   3.) Joint between copper bar and flexible strap
   4.) Bulk of flexible strap
   5.) Joint between flexible strap and cold plate

These additions helped the model more closely resemble our recorded data, with a few exceptions:

   - At early cooldown times, the model seems to be underestimating the heat load on the inner shield and outer shield.

   - The best fit was performed on the inner shield and outer shield data (to fine tune elements of the cold linkage), so the test mass fit is not optimized. (This will be performed next to refine emissivity predictions.)

To identify bottlenecks in the cold linkage, I used the 01/31 model and tweaked the resistances to see which would provide the largest gains in cooldown. The results from such tweaks are below:

   - Halfing the resistance of the greased joints (1, 3, 5) made negligible change to the cooldown. 
   - Halfing the resistance of the bulk of the copper bar made significant improvement to cooldown (Attachment 3).
   - Halfing the resistance of the bulk of the flexible strap made some improvement to cooldown (Attachment 4).

From these observations, it seems like the greased joints are thermally efficient, and the bulk area of the copper bar appears to be the largest bottleneck. 


Attachment 1: Cooldown_0114_analyzed.pdf
Attachment 2: Cooldown_0131_analyzed.pdf
Attachment 3: Cooldown_0131_copperbar_halfR.pdf
Attachment 4: Cooldown_0131_flexstrap_halfR.pdf
  2718   Mon Feb 7 16:06:36 2022 StephenDailyProgress 31 Jan Fastest Radiative Cooling run, ended 07 Jan

[Radhika, Stephen]

The heater was turned on at 3:13pm on Friday 2/4.

We specified a set temperature of 123K. However, the CTC100 PI control included a 1 W lower limit on the input to the heater, so there was a steady load of 1 W applied to the Silicon Workpiece over the weekend.

At 16:01 the cryocooler was turned off to start the warmup.

The CTC100 PI control was configured with a setpoint of 250 K on the Workpiece RTD, to aid in the warmup, and an allowable power range from 0 W to 22 W.

  2749   Tue Apr 5 16:47:46 2022 RadhikaDailyProgress Rerun of cooldown with indium gaskets in copper bar joints

[Radhika, Stephen]

On Thursday 3/31 we opened up with a goal to diagnose and fix the heater connection (previously reporting an error). Upon opening, we realized the steel wires suspending the test mass had snapped, and the test mass was sitting on the cold plate [Attachments 1, 2]. The mirror had fallen off one face of the test mass, and the heater had also debonded from the other face [Attachments 3, 4]. Our suspicion was that the wires somehow got sliced by the metal zip tie whose function was to mechanically secure the heater in place. Since it did not serve this function anyway and caused more harm, we decided to ditch the zip tie moving forward. 

Procedure (3/31-4/1):

  • Removed suspension frame and fallen test mass from chamber
  • Addressed debonded heater
    • Cleaned up varnish from where the heater had been previously bonded [Attachments 5, 6]
    • Re-varnished heater to the test mass face
      • We did not rebond the mirror to the opposite face, since it doesn't currently serve a purpose
  • Addressed snapped suspension
    • Removed old steel wires
    • Cut 2 new wires, adjusted to desired length, and tightened them in place
  • Re-inserted the test mass into suspension, and placed the whole system back into the chamber [Attachments 7-9] 
  • Tested the heater output before closing up

The vacuum pump was started ~4:15pm on 4/1, followed by the cryocooler at 5pm. 

On 4/5, I realized the CTC100 log did not contain any data from the weekend cooldown. I expected it would record the data locally even if the workstations were powered off, but this turned out not to be the case. I turned off the cryocooler at 11:45am, with the heater set to 295K. We will redo the cooldown once the chamber gets close to RT.

During the above investigation, I realized the CTC100 channel values were stale - the values are not being updated and all the channels are showing ~255K. None of the RTDs on the CTC100 front panel were are reporting this temperature, so something is getting in the way of proper telnet connection. The warmup waiting period will give me time to diagnose and debug the issue.

Attachment 1: IMG_3252.jpeg
Attachment 2: IMG_3253.jpeg
Attachment 3: IMG_3255.jpeg
Attachment 4: IMG_3259.jpeg
Attachment 5: IMG_3262.jpeg
Attachment 6: IMG_3263.jpeg
Attachment 7: IMG_3269.jpeg
Attachment 8: IMG_3270.jpeg
Attachment 9: IMG_3271.jpeg
  2750   Wed Apr 6 10:31:55 2022 ranaDailyProgress Rerun of cooldown with indium gaskets in copper bar joints

I think this is a nice debugging find. Its not very robust to use the workstations as 24/7 script machines (as we have found out over the years).

Best is to install a conda env on the main framebuilder machine, and run the perpetual scripts there in a tmux session.

Once its all sehup, update the ATF Wiki with a description of haw its done. Workstations crash when users do stuff, so its better if the data gettin script can run as a system service (e.g. systemctl, etc)

  2066   Thu Sep 29 08:21:07 2016 AidanLaser2micronLasersTwo micron fiber set-up (dry run)
I set up most of the two micron fiber optics as described in T1600146. I discovered that (a) our 90:10 splitters were accidentally ordered with 
FC/PC connectors, not FC/APC connectors [but Iíve already spoken to Thorlabs to arrange a swap] and (b) we definitely need fiber trays to 
handle spools of extra fiber.

Other than that, the basic layout looks good.
Attachment 1: PastedGraphic-1.pdf
Attachment 2: IMG_7260.JPG
Attachment 3: IMG_7259.JPG
  2114   Sat May 27 13:53:15 2017 awade, AidanMisc2micronLasersExamining response of InGaAs CCD camera's at 2 um

Andrew, Aidan

Previously (see ATF:2094) we examined the response of regular InGaAs PDs to 2 µm light to get an idea of the kind of QE we could get with these detector material types. Eventually it would be nice to image scatter in Si at 2 µm but the response of the detectors is expected to be low.  Single element detectors such as regular (non-extended) InGaAs PDs have a QE of 1 part in 10^5, not great. 

We did a quick test pointing the output of of the 2 µm setup, 500 µW, directly onto the CCD of two different InGaAs cameras that I have been trialing: the Hamamatsu C12741-03 (a 10C cooled CMOS InGaAs detector) and a Pembroke WiDy SWIR 640U-A (uncooled InGaAs CCD).  Images are attached of the dark field response (room lights off) and for both cameras with fiber pointed directly at the CCDs.  There were no collimating lenses or imaging optics in front of the sensor. This is really just a qualitative measurement as its hard to calibrate the power distributed across the sensor for such a basic measurement.

Its tough to calibrate the exact response from these initial tests, but it appears that with sufficient light there is enough for diagnostic beam viewing and maybe profiling, providing enough power can be supplied. We can see 2 µm light on these detectors.

The dark noise of the uncooled detectors seems to be on the order of 1200 counts per pixel per millisecond for 1 ms frames.  Above 2 ms the WiDy camera appears to make a step switch to a different internal gain/ADC setting that is then 7500 counts per pixel which remains relatively constant up to the max 200 ms shutter time.  ~1 mW of power produces about 3000 counts at 1550 nm for 1 ms exposure.  I'm still analyzing the linearity test snaps I took this week for the two cameras but we would expect a SNR of 3 for the uncooled camera at that power level at 1550 nm.  The 2000 nm response will be much worse.

Attachment 1: Hamamatsu_2um_DN_1.tif
Attachment 2: Hamamatsu_2um_DN_2.tif
Attachment 3: Hamamatsu_2um_DN_3.tif
Attachment 4: WiDy_2um_500uW_1.tif
Attachment 5: WiDy_2um_500uW_2.tif
Attachment 6: WiDy_2um_500uW_3.tif
Attachment 7: WiDy_2um_500uW_4.tif
Attachment 8: WiDy_2um_500uW_5.tif
Attachment 9: WiDy_2um_500uW_13-43-44.tif
Attachment 10: WiDy_2um_500uW_13-44-23.tif
Attachment 11: WiDy_2um_500uW_13-45-26.tif
Attachment 12: WiDy_2um_500uW_13-45-29.tif
Attachment 13: WiDy_2um_DN_13-45-1.tif
  2207   Fri Jun 29 09:18:32 2018 Vinny W.DailyProgress2micronLasersPower Loss in Fiber Optic Cable

One of the factors we're taking into account when figuring out the optimal fiber cable length to use in the 2um laser characterization project is the power loss present as a function of such length. Andrew and I worked through some figures and came up with the following plots, sampling a few values of the attenuation coefficient alpha. The process was relatively straightfoward, we introduced some loss, e^{-\alpha L}, into a signal. Thus, at one of the outputs of the MZ, the signal we receive would be:

e^{-2\alpha L_1}+e^{-2\alpha L_2}+2e^{-\alpha (L_1+L_2)}\cos (2\pi \Delta Lf/c)


Next, since we ideally want our signal to be locked at mid-fringe, we take the derivative of the function with respect to frequency and observe the maxima. 

In order to best visualize the points at which the slope is of highest sensitivity, we take the derivative once more and observe the zero points.

Through ThorLabs data on the SM2000 fiber optic cable ( https://www.thorlabs.com/drawings/d7a7404567d69154-FBD8C6B1-0D0E-7F1A-14D2F3A96ED2FF2E/SM2000-SpecSheet.pdf ), we came to a good approximation that our attenuation coefficient is approximately 8.63*10^-3 dB/m. The orange line in the above graph is a close approximation to this value, but the sensitivity slope for the approximation we obtained is shown in the following graph:

When considering power loss in the fiber optic cable, the optimal fiber cable length is roughly 116.8 meters. If we are willing to sacrifice roughly 10% of the calculated sensitivity*, then we can drop the cable length to approximately 72 meters. 


*This was done by subtracting 10% of the maximum value of the derivative of the output power w.r.t frequency (using the actual attenuation coefficient from ThorLabs). Maximum was 8.776*10^-8 W/Hz , 90% of max = 7.893*10^-8, which falls around 72 meters.


**First elog, critiques are very much welcome!

Attachment 2: dp_df.png
Attachment 3: dpdf_dl.png
Attachment 6: dpdf_dl_actual.png
  2208   Fri Jun 29 17:33:44 2018 ranaDailyProgress2micronLasersPower Loss in Fiber Optic Cable

In order to pick a length, we'll have to go beyond this optimization and consider cost and acoustic sensitivity.

Also, we have to start by making a guess at the frequency noise PSD of this laser, and also what sensitivity we want the MZ to have, as well as the PD electronics noise.

Please upload a noise budget plot in units of Hz/rHz showing a bunch of these noises as well as the frequency noise sensing requirement. Every 2 meters of fibers means 1 less pizza, so we'd like to take the length down from 100 meters to roughly 10 meters.

  2211   Wed Jul 11 16:30:40 2018 Vinny W.Summary2micronLasersAcoustic and Thermal Sensitivity

I found some relevant work done on the discussion of acoustic and thermal sensitivity within a optic fiber. For reference, it's important to have an idea of the geometrics of the fiber. The core, cladding, and coating are 11 +/- 1 um , 125 +/- 1 um, and 245 +/- 10um in diameter, respectively. Though the cladding is pure silica, the coating is Ge-doped. ( http://www.thorlabs.com/drawings/65f0b20de1051938-7503B425-91B4-7335-B52672A2FD1F6447/SM2000-SpecSheet.pdf ). Additionally, the fiber's sensitivity to some pressure depends on its characteristic elastic coefficients ( Young's Modulus, E, and Poisson's Ratio, \sigma) and Pockels coefficients, P_{12} and P_{44} [1]. The elastic coefficients for fused silica can be found online but are also referenced below. 

Acoustic Sensitivity:
To have an idea of the approximate sensitivity we could expect, we can consider some preform silica cylinder that is undergoing a uniform pressure. Many of the references I found measured that pressure from variations of the relative phase change between two interferometer arms- one static and the other undergoing a pressure difference relative to it. The optical phase retardation per unit of pressure (in dyne/cm^2) can be expressed as:

\frac{\Delta\phi}{\phi} = \frac{(1-2\sigma)}{E}[\frac{n^2}{2}(3P_{12}+2P_{44})-1]

This comes out to be approximately  -1.23*10^{-14}${dyn}/{cm^2}$ .

Obviously there's more to the picture than just that. We need to consider the differences in refractives indices and and elastic coefficients between the different materials present in our optic fiber, as well as account for the radial and axial displacements in the "cylinder" caused by some pressure. The approach in reference [2] consideres a two layer cylinder, and assumes that the center is of homogenous material much like the example above. We can place the optic fiber in a cylindrical coordinate system as shown below:

(Insert crudely made cylinder coordinate system here)

Following reference [2], we'll assume that the axial stress at the very ends of the fiber is zero. ( \sigma _{22} = 0 at z = \pm L, where 2L is the full length of the fiber). This is referred to as the radial model, a form of boundary condition. Since axial symmetry is also assumed, the stresses and strains will be functions of r and z. For a single material solid cylinder, the solutions for the differential equations for the axial/radial displacements are expressed as products the trigonometric and modified Bessel functions. When we consider a multilayered cylinder, the general solution will be the the series expansion of those products, and their coefficients are determined by the boundary conditions.

It was shown both experimentally and theoretically that a 2D model of the above scenario (i.e. a plane strain ) gives nearly identical results as the 3D model, and involves much less calculation power. The reference goes in-depth at how the following equation was is derived, but to keep this concise, the average induced fractional phase change can be expressed as:

\frac{\Delta \phi}{\phi}= e_z-\frac{1}{2}n^2[2e_r(p_{11}-p_{44})+e_z(p_{11}-2p_{44})]

where e_z,e_r are the axial and radial strain, respectively. When the strains are a function of position along the axis of the fiber, we would need to average of its length:

\frac{\Delta \phi}{\phi} = \frac{1}{2L}[\int_{-L}^{+L}e_zdz-\frac{n^2}{2}[2(p_{11}-p_{44})\int_{-L}^{+L}e_rdz+(p_{11}-2p_{44}\int_{-L}^{+L}e_zdz)]]


[Work in progress. -Vinny (7/19/18)]

  2213   Thu Jul 19 11:50:11 2018 Vinny W.DailyProgress2micronLasersThe case of the DET10D Photodiode, featuring TIA

Down in the machine shop we've been developing and modifying a transimpedance amplifier to be used in conjuction with the photodiode in the 2micron experiment, schematic and noise analysis(with PD shot noise as horizontal line!) are shown below. With a dual 9V battery supply, we ran the output through our signal analyzer but quickly noticed the signal's unstable nature- a consequence of the lack of phase margin between the open loop gain and feedback factor. To address this issue and improve the circuit's stability, we simply added a phase compensator(i.e. a capacitor) in parallel with the gain resistor. Its capacitance can be calculated through a straightforward relationship between,

1. the intercept frequency, f_i ,  of the open loop gain curve and the reciprocal of the feedback factor.

2. The pole corner frequency, f_F.

3.  The unity-gain bandwidth, f_{GBWP}.

The intercept frequency can be expressed as,

f_i = \frac{1}{2\pi R_FC_F}

Where R_f and C_f are the values of gain resistor and phase compensator capacitance respectivel. Additionally, it follow that the pole corner frequency is,

f_F = \frac{1}{2\pi R_F(C_F+C_i)}

Where C_i is the capacitance of the PD's junction capacitor in parallel with the input capacitance of the op-amp. They are brought together by the following expression:

f_i = \sqrt{f_f*f_{GBWP}}

Solving for the phase compensator capacitance, we reach,

C_F = \frac{1}{4\pi R_Ff_{GBWP}}(1+\sqrt{1+8\pi C_if_{GBWP}})

Inputting the values of our circuit's components, we reach a capaticance of 200pF. Fortunately, the TIA proved to be more stable after this modification. Finally, we implemented our TIA circuit into our PD in the 2micron experiment and achieved better readings, which I'll be sure to elaborate more upon tomorrow.

Attachment 1: TIAcircuit.JPG
Attachment 2: TIAnoiseanalysis.JPG
  2214   Sat Jul 21 01:45:00 2018 Vinny W.DailyProgress2micronLasersThe Gentle Sway of the EP2004

We ran some more measurements of our laser's output and noticed a certain ampltiude swaying of our signal (a video of this will be commented below tomorrow) caused most likely by power fluctuations(any advice to fix this would be super appreciated!). Combined with the fringes that cycle along with the swaying, it made the task of locking the signal to mid-fringe for analysis very difficult. We checked the integrity of the optic fibers in the experiment and didn't notice much issue besides a few mottled tips which were cleaned. We noticed the experiment was most sensitive at the actual MZ interferometer segment, so we made a few changes to increase the radius of curvature of the optic fiber loops. (Picture below). This made a slight difference, but the sway is still there.

This all proved to be a good opportunity to start setting up the encasement for the project. We rounded up a structure that was in the lab, along with some insulated wall-plates. It hasn't been fully built yet, but the casing fortunately fits around the work-space of the experiment. (casing dimensions: 117.5x25.5x60.5 cm. LxHxW)

I did a little bit of characterization for the laser diode's power output as a function of applied current. A plot of that is also shown below. Tomorrow Andrew and I are going to work on settling the question of the noise budget, as well as start building some thermal sensors (AD590) to be used within, outside, and around the encasing of experiment. Using this will allow us to get a sense of the environment temperature differences and adjust our experiment accordingly. Finally, we're on a way to developing a circuit for our thermocoolers to be used within the casing that Aidan built.



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  2215   Sat Jul 21 13:32:07 2018 awadeDailyProgress2micronLasersThe Gentle Sway of the EP2004

Can you please reupload the plot as a pdf (i.e. vecor graphics) and also make a .tar or .zip of the data and script to plot it.  This will help future people using the laser who may want to replot or use the data for something else.  

Unless the dataset is enormous its a good idea to bundle/compress it and attach it to posts.



We ran some more measurements of our laser's output and noticed a certain ampltiude swaying of our signal (a video of this will be commented below tomorrow) caused most likely by power fluctuations(any advice to fix this would be super appreciated!). Combined with the fringes that cycle along with the swaying, it made the task of locking the signal to mid-fringe for analysis very difficult. We checked the integrity of the optic fibers in the experiment and didn't notice much issue besides a few mottled tips which were cleaned. We noticed the experiment was most sensitive at the actual MZ interferometer segment, so we made a few changes to increase the radius of curvature of the optic fiber loops. (Picture below). This made a slight difference, but the sway is still there.

This all proved to be a good opportunity to start setting up the encasement for the project. We rounded up a structure that was in the lab, along with some insulated wall-plates. It hasn't been fully built yet, but the casing fortunately fits around the work-space of the experiment. (casing dimensions: 117.5x25.5x60.5 cm. LxHxW)

I did a little bit of characterization for the laser diode's power output as a function of applied current. A plot of that is also shown below. Tomorrow Andrew and I are going to work on settling the question of the noise budget, as well as start building some thermal sensors (AD590) to be used within, outside, and around the encasing of experiment. Using this will allow us to get a sense of the environment temperature differences and adjust our experiment accordingly. Finally, we're on a way to developing a circuit for our thermocoolers to be used within the casing that Aidan built.




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