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ID Date Author Typeup Category Subject
  1761   Tue Oct 17 14:56:53 2017 GabrieleComputingCrackleCoil current monitors

Changed CURRMON_Z1 gain from 1 to 0.854

  1820   Fri Aug 30 14:45:42 2019 ranaComputingDAQDownload data with pyNDS

I'm attaching a script to download data from the LIGO sites with python.

I recommend using it in your anaconda3 ENV:

conda install -c conda-forge nds2-client python-nds2-client

and then before running the script you have to initialize your Kerberos token:

kinit miley.cyrus@LIGO.ORG

then you run the script:

python getData.py --ifo=L1 --fs=1024

as usual, run with the -O or -OO flags to silence the debug messages.

  1848   Wed Mar 11 12:46:20 2020 ranaComputingNoise BudgetNoisemon at L1

you have to overlay the estimated displacemnt noise with the existing L1 noise bud or else we cant tell what the importance of the result is

  1849   Sat Apr 18 16:21:32 2020 DuoComputingNoise BudgetNoisemon:DAC noise analysis from L1 and H1

There we go. Based on the noisemon data at L1 and H1, I calculated the DAC noises at those sites, using roughly the same approach as described in 1847.

I used the coherence between the master channel and the noisemon channel to calculate the total noise going into the coils.

Then I converted the ADC noise and noisemon noise to DAC volts and subtracted them from the total noise. I compared the result of the subtraction, which should be DAC noise, at least in the passband (20-100Hz), with the G1401399 model and made a noise budget, shown in attachment 1. We can see that, as designed, the DAC noise is sufficiently amplified so that it dominates over the noisemon noise or the ADC noise in the passband.

Next, I projected the DAC noise to strain noise and summed them up for all the four channels in all the four stations.

Finally, I compared this with the interferometer noise spectrum based on data in L1:OAF-CAL_DARM_DQ and H1:CAL-DELTAL_EXTERNAL_DQ. I calibrated these data with calibration files here. The results are shown in attachment 3. All the data and scripts are included in attachment 4, where analysis.py is the script that does the job. Based on the plots, it seems DAC noise could be potentially a limiting factor for the interferomter sensitivity.

The coil driver states for L1 is LP off, ACQ off (state 1). For H1 is LP on, ACQ off. The LISO files calculating the current transfer functions and the voltage transfer functions are attached in attachment 4. 

I used a resolution of 1mHz in the diaggui measurement. The data files are too large so I can not upload them here. I am figuring out what to do.

Note: I fell into a few traps during the calculation. Many of them was about data and transfer functions. I have been more careful about what data is used in these calculations. For example, the noisemon data downloaded from the sites when MASTER was off still has DAC noise in it. I thought it was ADC noise + noisemon noise before and used it for subtraction. Another example, the transfer function measured at the sites has all the noise in it. We do not see the noises in the passband but ADC noise dominates at high frequencies. If you use this transfer function to figure out how much noisemon noise contributes, you result will be tampered by the noises, like ADC noises at high frequency. Last example, if you use the noisemon noise data measured in the digital system in our lab, you should be aware that, although it does not have DAC noise (I disconnected DAC when measuring the noises), it also has ADC noise. Therefore, it would be better to use data from SR785 or LISO simulations (which has been shown to agree with each other). I drew a diagram in attachment 2 to help thinking about what data or transfer functions should be used. 

Quote:

you have to overlay the estimated displacemnt noise with the existing L1 noise bud or else we cant tell what the importance of the result is

 

  20   Fri Oct 26 21:48:40 2007 waldmanConfigurationOMCFiber to 056
I set up a 700 mW NPRO in Rana's lab and launched it onto a 50m fiber. I got a few mW onto the fiber, enough to see with a card before disabling the laser. The fiber now runs along the hallway and terminates in rm 056. Its taped down everywhere someone might trip on it, but don't go out of your way to trip on it or pull on it because you are curious. Tomorrow I will co-run a BNC cable and attenuate the NPRO output so it can only send a few mW and so be laser safe. Then we can try to develop a procedure to align the beam to a suspended OMC and lock our suspended cavity goodness.

Notes to self: items needed from the 40m
  • ND10 and ND20 neutral density filter
  • EOM and mount set for 4 inch beam height
  • Post for fiber launch to get to 4 inch
  • Mode matching lens at 4in
  • 3x steering mirror at 4in
  • RF photodiode at 4in
  • Post for camera to 4in
  • Light sheild for camera
  • Long BNC cable
Some of these exist at 056 already
  21   Sat Oct 27 19:00:44 2007 waldmanConfigurationOMCHanging, locked OMC with REFL extracted.
I got the OMC locked to the fiber output today. It was much more difficult than I expected and I spent about 30 minutes or so flailing before stopping to think. The basic problem is that the initial alignment is a search in 4-dimensional space and there is naturally only one signal, the reflected DC level, to guide the alignment. I tried to eyeball the alignment using the IR card and "centering" the beams on mirrors, but I couldn't get close enough to get any light through. I also tried to put a camera on the high reflector transmission, but with 1.5 mW incident on the cavity, there is only 1.5 microwatts leaking through in the best case scenario, and much, much less during alignment.

I resolved the problem by placing a high reflector on a 3.5 inch tall fixed mount and picking off the OMC transmitted beam before it reaches the DC diodes. I took the pickoff beam to a camera. The alignment still sucked because even though the beam cleanly transmitted the output coupler, it wasn't anywhere close to getting through the OTAS. To resolve this problem, I visually looked through the back of M2 at M1 and used the IR card to align the beam to the centers of each mirror. That was close enough to get me fringes and align the camera. With the camera aligned, the rest was very easy.

I restored the PDH setup we know and love from the construction days and locked the laser to the OMC with no difficulty. The laser is in Rana's lab so I send the +/- 10V control signal from the SR560 down a cable to 058E where it goes into the Battery+resistor box, the Throlabs HV amplifier, and finally the FAST channel of the NPRO. BTW, a simple experiment sows that about 35 +/- 3 V are required to get an FSR out of the NPRO, hence the Thorlabs HV. The EOM, mixer, splitter, etc is on the edge of the table.

With this specific OMC alignment, ie. the particular sitting on EQ stops, it looks like all of the ghost beams have a good chance of coming clear. I can fit a 2 inch optic in a fixed mount in between the end of the breadboard and the leg of the support structure. A picture might or might not be included someday. One of the ghost beams craters directly into the EQ stop vertical member. The other ghost barely misses M2 on its way down the length of the board. In its current configuration, the many REFL beam misses the leg by about 1.5 inches.
  26   Mon Oct 29 12:20:15 2007 waldmanConfigurationOMCChanged OMS filters
I changed the OMS configuration so that some of the OMC-SUS LED channels go to a breakout box so that we can input the PDH error signal. After lunch, we will try to lock the cavity with a PDH error signal and digital filters. Then its on to dither locked stuff. Note that this LED business will have to be changed back some day. For now, it should be extremely visible because there are dangling cables and a hack job interface lying around.
  27   Mon Oct 29 23:10:05 2007 waldmanConfigurationOMCLost in DAQspace
[Pinkesh, Sam]

In setting up a Digital based control of the hanging OMC, we naively connect the Anti-Imaging filter output to an Anti-Aliasing input. This led to no end of hell. For one thing, we found the 10 kHz 3rd order butterworth at 10 kHz, where it should be based on the install hardware. One wonders in passing whether we want a 10 kHz butter instead of a 15 kHz something else, but I leave that for a later discussion. Much more bothersome is a linear phase shift between output and input that looks like ~180 microseconds. It screams "What the hell am I!?" and none of us could scream back at it with an answer. I believe this will require the Wilson House Ghost Busters to fully remedy on the morrow.
  30   Tue Oct 30 13:58:07 2007 ajwConfigurationIOOMC Ringdowns
Here's a quick fit-by-eye to the latter part of the data from tek00000.xls.

The prediction (blue) is eqn 41 of
http://www.ligo.caltech.edu/docs/P/P000017-A.pdf

T1 = T2 = 0.002. Loss1 = Loss2 = 150 ppm.
MC3 assumed perfectly reflecting.
Velocity = 320 um/s (assumed constant), 2 usec into the ringdown.

OK, there's one little fudge factor in the prediction:
I multiplied D by 2.
  73   Tue Nov 6 23:45:38 2007 tobinConfigurationComputerstektronix scripts!
I cooked up a little script to fetch the data from the networked Tektronix scope. Example usage:

linux2:scripts>tektronix/tek-dump scope0 ch1 foo.csv

"scope0" is the hostname of the scope, "ch1" is the channel you want to dump, and "foo.csv" is the file you want to dump it to. The script is written in Python since Python's libhttp gave me less trouble than Perl's HTTP::Lite.
  166   Thu Jan 6 01:03:24 2011 ZachDailyProgressCreakPZT installed/tested

  I rigged up a way to use the small ThorLabs PZTs we took from the 40m yesterday. After an hour or so of going back and forth from the ATF to the SUS lab with random optical hardware to find something suitable, I finally found a solution using one of the fancy translation stages we have for the eventual gyro modematching. Here's a shot of the whole assembly:

 
2011-01-05_17.21.29.jpg
 
That was just to find a way to mount to the magnetic base we are using; I still needed a way to actually hold the PZT and connect it to the mirror on the shim "blade". We knew we wanted to have something give-y like rubber between the PZT and the blade itself to suppress high-frequency noise in the actuator, so I found a piece of rubber grommet to do the trick. The grommet had a hole in it, of course, so I wrapped it in a piece of shrinkwrap so that I could glue it along the flatter surface to the PZT. On the other end, I needed something firm attached to the PZT with which to hold it (gripping the PZT itself might damage it and in any case would reduce the range of motion). I chose to use a polyester film capacitor---with the leads trimmed---and glued it to the other side. Here is a closeup:
 
2011-01-05_16.30.40.jpg
 
This thing is supposed to put out 4.5 um with 150 V applied, so I figured I could get a decent signal using a drive on the order of 5-10 V (since we are using 633-nm light, this is on the order of a fringe). I installed a PDA100A at the AS port of the interferometer and realigned the beams from both arms to overlap. The manufacturer warns never to reverse the polarity of the PZT leads, so I applied a ~6 Vpp drive with an offset of +5V. I could clearly see an output coherent with the drive on the scope over a wide range of frequencies. I decided to plug it into the Agilent and look at the spectrum. Here is an example of one with a 3-Hz drive signal. There is a lot of upconversion because the mirror is swinging through a couple of fringes. I was able to change the overtone structure by adjusting the drive amplitude and offset (so that it stayed roughly linear).
 
3Hz_spect.png
For the heck of it, I thought I might try and measure a transfer function from the PZT to the PD signal. It can be seen below. Even with maximum integration, the ambient noise is very high at the moment, and turning up the drive doesn't help since the thing quickly loses linearity, but to the naked eye the TF looks roughly like what one would expect from a driven pendulum with a resonance somewhere around 100-200 Hz. Rana and I noticed that the simple system with the shim clamped to the base and the mirror glued to its top had a fairly high Q, but the thing is now damped by the rubber contact, so the resonance is not very evident in the TF.
 
PZT-AS_TF.png
From these very simple trials, I would guess that these PZTs will work quite nicely once we can close the loop and operate at the dark fringe. I have unfastened the second unit from the mirror on which we found them, and I will try and put a new wire on the ground lead tomorrow so that we can test it.
  167   Thu Jan 6 21:58:12 2011 ZachDailyProgressCreakSecond mirror/PZT installed, rough CMRR measured

 After yesterday's success with the PZT we scavenged from the Drever cabinets, I decided to repair the second one and make a duplicate mirror assembly. It isn't quite as pretty as the last one since I had to solder it (so I won't show a closeup), but all in all it came out pretty well. I used the other shim that matched the one we used for the first mirror, and glued the fully-silvered mirror that bore the PZTs to the top of it. (I later found out that Rana put the new shim stock on my desk, but we will use the stuff that's in place now until we get some kinks worked out. In any case, we have yet to use any nice 5101 mirrors.) I also installed a beam dump to block the second ghost beam from hitting the PD. Here is a shot of the second mirror assembly and another of the full setup:

2011-01-06_18.52.51.jpg 2011-01-06_18.52.33.jpg

I brought some SR560s in to set up the control loop, but it was difficult to bias the PZTs enough (so that the polarity never reversed) and still have enough range on the SR560 output; we need a voltage amp to really get going with these guys. In the meantime, I thought it would be somewhat useful to characterize the relative strengths of the PZTs by driving them both and maximizing the CMRR. I drove them at 2 Hz with the Tektronix FG, using an offset of +5Vand I determined that the best amplitude ratio was about 3:5. Below is the voltage spectrum of the PD output while driving one and both mirrors, respectively, showing a CMRR of about 36. I am certain that we can do better, but it is difficult to tweak it in view of the excess noise at the moment with the loop open.

CMR.png

 

 

  168   Fri Jan 7 20:14:39 2011 ZachDailyProgressCreakREFL installed

This morning I installed the polarizing optics for the REFL isolation. I thought I would need another QWP to linearize the output beam of the HeNe, but the JDSU supposedly has a 500:1 linear polarization ratio out of the box, so all I had to do was turn the head to the right orientation. Below is a raytrace of the setup. 

mich_diag.png

I hooked up the PDs to the scope to see if things were working correctly, and though the DC levels are off (i.e. the contrast is not great due to the rather hodgepodge setup), the AC response looks correct. Here is a screenshot. Here, both of the mirrors were being driven common-mode at 2-Hz with the 3:5 ratio I figured out yesterday. You can still see some 2-Hz harmonics here (particularly ~8 Hz), but the majority of the signal is just the ambient noise.

TEK00000.PNG

EDIT: I just realized that, interestingly enough, the dominant low-frequency signal here is probably not exactly 8 Hz, but slightly above; if you look at the previous entry, when both mirrors are driven at 2 Hz, the strongest peak is at a bit above 8 Hz, where there is no peak in the single-mirror case (though there is one at 8 Hz existing as a 2-Hz overtone there). I am not sure what this is from.

 

  184   Wed Mar 9 18:32:45 2011 JanDailyProgressNoise BudgetLimits to NN subtraction

I wanted to push the limits and see when NN subtraction performance starts to break by changing the number of seismometers and the size of the array. For aLIGO, 10 seismometers in a doubly-wound spiral around the test mass with outer radius 8m is definitely ok. Only if I simulate a seismic field that is stronger by a factor 20 than the 90 percentile curve observed at LHO does it start to get problematic. The subtraction residuals in this case look like

Residuals_Spirals.jpg

The 20 seismometer spiral is still good, but the 10 seismometer spiral does not work anymore. It gets even worse when you consider arrays with circular shape (and one seismometer at the center near the test mass):

Residuals_Circles.jpg

This result is in agreement with previous results that circular arrays have trouble in general to subtract NN from locally generated seismic waves or seismic transients (wavelets).

I should emphasize that the basic assumption is that I know what the minimum seismic wavelength is. Currently I associate the minimum wavelength with a Rayleigh overtone, but scattering could make a difference. It is possible that there are scattered waves with significantly smaller wavelength.

  185   Thu Mar 10 14:59:54 2011 JanDailyProgressSeismometryThoughts about how to optimize feed-forward for NN

If the plan is to use feed-forward cancellation instead of noise templates, then the way to optimize the array design is to understand where gravity perturbations are generated. The following plot shows a typical gravity-perturbation field as seen by the test mass. It is a snapshot at a specific moment in time. The gravity-perturbation force is projected onto the line along the arm (Y=0). Green means no gravity perturbation along the arm generated at this point.

Snap_41.jpg

The plot shows that the gravity perturbations along the direction of the arm seen by the test mass are generated very close to the test mass (most of it within a radius of 10m), and that it is generated "behind" and "in front of" the mirror. This follows directly from projecting onto the arm direction. As we already know, for feed-forward, we can completely neglect the existence of seismic waves and focus on actual gravity perturbations. In short, for feed-forward, you would place the seismometers inside the blue-red region and don't worry about any locations in the green. The distance between seismometers should be equal to or less than the distance between red and blue extrema. So even though I haven't simulated feed-forward cancellation yet, I already know how to make it work. Obviously, if subtraction goals are more ambitious than what we need for aLIGO, then feed-forward cancellation of NN would completely fail generating more problems than solving problems. Unless someone wants to deploy hundreds to a few thousand seismometers around each test mass.

  187   Fri Apr 15 18:42:40 2011 tara, MingyuanDailyProgressCreakStart crackling (again)

Ming Yuan, tara

We setup the basic Michelson interferometer with one arm which can driven by a PZT and another one whose position is adjustable. 

The laser we got didn't work at the beginning. We found that the power supplier was not functional. Tara borrowed another power supplier for the laser.

The basic Michelson interferometer was setup. One of the mirror attached on copper plate was replaced by a regular mirror with position adjustable. One of the PZT is needed to be fixed.

We observed Dark Fringe by adjusting position of the regular mirror.

We got the signal from a basic Michelson setup with one of the arm being driven by a PZT.

 This is the signal from the oscilloscope.

First, we check the signal when there is no voltage applied to the PZT, the signal is plotted in green.

Then, we drove only one of the mirror by PZT. The voltage is 6Vpkpk, with 7V offset. 

 The signal is plotted in blue when the mirror was driven. We can see strong signal on the scope.


PD.png

 

 

 
  188   Tue Apr 19 19:41:51 2011 taraDailyProgressCreakStart crackling (again)

 mingyuan, tara

            We setup the Michelson interferometer with two identical x and y arms. We drove both mirrors at 2 Hz and observed signal at 10 Hz using a lockin amplifier. We saw no significant difference whether the mirror were dirven or not.

           (The pzt for the second mirror is fixed. The wire is soldered back to its electrode.)

             We setup the Michelson interferometer, now with similar setups on two arms. The end mirrors on both arms are attached on metal shims. The shims touch the PZTs which are driven by 2Hz, 6Vpkpk sinusoidal signal with 7 V offset.

             We use a voltage divider(we planned to make one, but we found a nice one in EE lab lying on the floor, so we borrowed it) to adjust the voltage on one of the PZTs to make sure that both mirrors are driven by the same distance. We adjusted the divider to minimize the signal at 2Hz.

vdivide.png

              fig 1: With a voltage divider, we can adjust the voltage on the PZT so that both mirrors are pushed by the same distance and the 2Hz common mode is minimized. On the plot, Y axis shows the signal output from the lock in amplifier at 2Hz. The higher value means the stronger signal at 2Hz. X axis is time scale. The setup was 5mV sensitivity range, filter in 300 ms, phase -152.3 degree.

 The signal output from the lock in amp has not been calibrated to length yet. We just want to see the qualitative result.

 

                 Once we made sure that we minimized the common mode, we tried to measure the possible up converted noise at 10Hz. (We used the internal oscillator in the lockin amplifier for reference signal at 10 Hz.)

               First, we did not drive the mirror, so that we could see the signal at 10 Hz due to background. Then, we drove the mirror at 2 Hz, and observed any possible up-converted noise at 10Hz

              There is nothing conclusive yet. The 2Hz signal that drives the PZTs are plotted here for comparison. From a quick glance, there is no obvious correlation between the noise and the driving signal.

10Hz.png

fig2:  Signal from the lock in amp at 10Hz. Setup: sensitivity at 500 uV, in filter 300 ms.

 

Why are we doing this:

We want to measure any possible up-converted noise when the material under stress is driven at low frequency. For example, the system is driven at 2Hz, there might be broadband noise occurs due to the motion. If there is, we can try driving the system with different amplitude to see if the noise changes or not.

  189   Tue Apr 26 17:06:37 2011 Mingyuan, TaraDailyProgressCreakstart crackling

 

 

We are trying to chopping the signal today.

   The low noise amplifier can be used as bandpass filters for 10-100 HZ.

   We are trying to figure out the signal squaring. The mixers in the lab only work for high frequency (> 500 KHZ).

   Frank recommends us to use AD734 4-Quadrant multiplier. 

   We checked the electronics lab in Downs and 40 m and couldn't find it. We plan to order some AD734.

 

 
  190   Thu Apr 28 21:55:25 2011 taraDailyProgressCreakstart crackling

 

 I ordered 5 of AD734 and thinking about how to make a circuit for squaring the signal.

 

    The "chopping" signal readout technique requires that we square the signals.  Basically we need to (as rana suggested):

(1) square the signal from PD, (after 10-100Hz bandpass) to convert it to power, and band pass it again.

(2) square the driving signal (might be varied from 0.1- 1Hz.) This is illustrated in the diagram as doubling the frequency ("2 x freq" box.)  The driving signal for PZT is offset. So the signal is  V drive = A + B xsin (2pi fdrive t) with A > B. This ensures that the voltage on one end of the PZT is always higher than another end. We might need to high pass this signal first, to get a signal with only 2 fdrive frequency after we square it.      

(3) multiply signal from (1) and (2) to demodulate the signal.

 

Basically, 3 multipliers are needed.

The first one is for (1), so the input frequency is ~ 10 -100Hz, and the output is 20-200 Hz.

The second multiplier is for (2), the signal is ~ 0.1 - 1 Hz, but this one might have large DC term after we square it.

The third one is for (3), this one has to multiply 2 low f signals together which is quite similar to (2), so the design can be the same.

 

I'll consult Frank and/or Koji again before finalize the multiplier circuit.

 chopping.pdf

 

  191   Fri Apr 29 18:39:37 2011 taraDailyProgressCreakstart crackling

In the mean time, we might try this mixer to multiply the signal. I'll order one.

  192   Fri Apr 29 21:23:15 2011 taraDailyProgressCreakstart crackling

koji, mingyuan, tara: We designed the circuit for multiplying/ squaring signals with AD734. 

    The details for each signal are discussed here. 

    The "general multiplying circuit" box in the diagram shows how each AD734 will be powered/ fed input signal.

     For the signal from the PD, we need to bandpass(10-100Hz) it first. We plan to use a SR560. To split the signal to x and y input, we will use a T connector. Then square the signal and band pass it again at 0.1 - 100Hz bandwidth.

     For the signal from the function generator which drives the PZT. We will high pass it, by either SR560 or a high pass circuit. We might need a buffer here if the output impedance of the function generator is not high. Split the signal with a T again, and square it.

    After both signals are squared, we multiply them together. Send one to X1 input, another signal goes to Y1 input. Then we FFT the output signal from W.

 

  194   Mon May 9 11:25:05 2011 Mingyuan, taraDailyProgressCreakShim/mirrors replaced

  We switched the current metal shim with the thicker Aluminium shim. Now both mirrors are also the same. We tested and showed that the shim is not too hard to be pushed by pzt.

First, the thicker Al shims have bigger bending stiffness and more difficult to bend under the surrounding perturbation. Therefore, the signal we got has less noise from the surrounding perturbation.

By using the PZT we have, we can still drive the shim well. With the driving, we observed intensity oscillates from ~50 mV to ~200 mV. 

We also observed a low frequency (~80 mHz) oscillation of the signal. I didn't find the source of this oscillation. The sensitivity of response to driving is lower while the intensity is near the minimum and Maximum and higher while intensity is at the middle.

 

pdout.png

 
  195   Mon May 9 12:06:10 2011 tara, mingyuanDailyProgressCreakQ measurement for test blades

We measured the weight needed for pulling the blades down, and measured Q, f0 of the blades. For Rom blade, the weight is 1.279 kg, f0 = 2.27 Hz, Q = 300. For Rem blade, the weight is 2.005kg, f0 = 2.35Hz, Q = 475.  The test blades are named Romulus(Rom) and Remus(Rem).

     Why do we do this:

    The maraging blades are designed to be flat when they are in used, so we need to know how much weight do we need to pull them down to their operating level. The weight will determine the size of the load mass we want in the drawing as well. We plan to mount mirror mount on the load mass, so we can align the mirror for the interferometer's end mirror.  Plus, resonance frequencies and Qs of the blades and seismic noise will be used to estimated the noise budget of the setup.

    The weight was applied to the blade until the blade horizontally leveled. Then the total weight was recorded.  After that, we used shadow sensing technique to determine their resonance frequencies and Q factors.

The results are summarized here:

Blade     load mass       f0               Q

Rom         1.279 kg       2.27 Hz     300

Rem         2.005           2.35 Hz      475

.Photo_74.jpg

fig1: determining the weight. The blade mounted on the table appears flat with the right weight.

 

rom.png

fig2: Q measurement from Rom

REM.png

fig3: Q measurement from Rem

  198   Tue May 10 18:29:44 2011 Mingyuan, TaraDailyProgressCreakSolid work drawing

We measured the tip tilt angle of the blade while the main part of blades was bent flat.  REM: ~9 degree; ROM: ~ 7 degree. This angle should be able to cancel by mirror holder.

One block of Al was designed to mount mirror holder with the blades. The SolidWork drawing is attached below.

Two screws (2-56, A2, 3/16) will be used to mount the block onto blades through the two holes in the head of blades.

One screw (8-32) will be used to mount the mirror holder onto the block. The mirror hold is light, the block should be able to hold it firmly.

The other drawings will be uploaded by Tara

  199   Wed May 11 22:17:35 2011 taraDailyProgressCreakstart crackling

 I tested the mixer, the demodulated signal from input at 10 - 100 Hz might be too small and too distorted to get reliable data.

 

  As we want to square/demodulate  signal in 10 - 100 Hz BW. a low frequency mixer might be a good tool. I asked Alastair to buy this mixer for me, and it arrived today.

  The lowest acceptable frequency in the design is 500 Hz, but I don't know how well it works at 10 - 100 Hz so I tested it.

   

   ==Setup and result==

   I used  SR785 to generate sine wave, then split it with a T and connected the output to LO and RF of the mixer. 

   I tested that the mixer works fine at the designed frequency.  The plot below shows the result from  1kHz signal input.

1khz.png

Next, I changed the frequency to 10 Hz, 50Hz, and 100Hz.

  The demodulated signal is then observed in frequency domain (left column of the plot) and in time domain ( right column of the plot)

I think the peaks at driving frequencies (10Hz, 50Hz, 100Hz and their harmonics) appear because of the offset of the sine input signal.

f_t_response.png

 

The results for low frequency  seem to be too distorted. We will test the AD734 chips tomorrow. I got the package this afternoon.

  201   Thu May 12 23:18:27 2011 ryan, taraDailyProgressCreakstart crackling

 We tested AD734 on the diagnostic bread board, the result is good.

     We want to square/multiply signals between 10 to 100 Hz, so we use AD734 chip to do the work. The circuit is connected as described here

We try to square the signal. the test signals are sine waves at 10 Hz, 50Hz. The output are nice sine waves, but the gain is high (72dB). The chip rails as the input exceeds 0.5 Vpkpk. We will have to check the signal from the PD in the setup to see if it is higher than 0.5 Vpkpk or not. If so we can change the gain of the chip. Otherwise we can go ahead and use it.

 ad734.png

The spectrum of the output, for 10Hz input, there's a peak at 20Hz output. For 50Hz input, there's a peak at 100Hz. The response is flat between this bandwidth.

 

  202   Fri May 13 00:06:32 2011 MingyuanDailyProgressCreak 

 

The low frequency oscillation we mentioned in the previous Log could originate from the creep of the rubber between PZT and the Shim. Because the initial stress caused the creep of the rubber, the Shim relaxed slowly and changed the optical path and caused the low frequency oscillation. This mechanism can explain the phase change between the driving and the signal. Rana recommended to use a spring to replace the rubber. To calculate the spring constant of the spring: Spring constant of the Shim, ks = 3EI/L^3; Amplitude of displacement of PZT ~ A; Amplitude of displacement of the Shim ~ B; the spring constant of the spring ~ k;

k = ks*B/(A-B)

From current dimension, ks ~ 10000 N/m. If we don't want to drive PZT too hard, assume A = 2B; k = ks = 10000 N/m.

  204   Fri May 13 12:24:47 2011 tara, ryanDailyProgressCreakAD734 multiplier info

Some useful things to remember for the AD734:

The transfer function when wired as a multiplying circuit is: W = ((X1-X2)*(Y1-Y2) / 10V) + Z2
For this to be true the Z1 pin should be wired to the output W, to provide feedback, which isn't shown explicitly on Tara's general multiplying circuit diagram. Also for testing the chip inputs were wired as differential, not with one leg grounded as shown on the GMC diagram.

The 10 V comes from the default division voltage when the denominator control inputs (U0, U1, U2) are grounded. If you want some added offset to the output you can send it to the Z2 pin.

The input impedance is listed as 50k for all X, Y, and Z pins.


We measured the noise with 0V X/Y inputs, it was around 1 mV/rtHz at 10 Hz, as you can see in Tara's earlier post, slightly improving at higher frequency.
The input noise is listed as 1 uV/rtHz from 100 Hz to 1 MHz. The amplifier gain is listed as 72 dB which is ~ 4000x, and we were at the default denominator of 10V so this corresponds to a noise of 1e-3 * 10 / 4000 = 2.5 uV/rtHz at the input, seems reasonable compared to spec sheet. The signal to be squared in the creak setup (the output of the Michelson) will have to be bandpassed first, probably by an SR560, so gain can be applied there to get in over the multiplier noise floor.

As Tara noted the output does rail for signal amplitudes well below the listed maximum input, so we need a better understanding of how to control the gain.

  205   Tue May 17 19:24:58 2011 mingyuan, taraDailyProgressCracklestart crackling

We brought the setup back. The interferometer is working and more stable. We will try extracting signal next.

    From this entry, we noticed the 180 degree phase shift in the signal when one arm was driven. The signal from PD followed the driving signal before drifted up and phase shifted by 180 with respect to the driving signal. We believed that this was the effect from the drift of the arm length. Suppose that we operate the IFO at the fringe's maximum slope. The drift in arm length will move the operating point on the fringe, and we might end up on the other side of the fringe which will show up in the 180 degree phase shift of the signal.

    The mirror was pushed by a piece of soft rubber which was glued to a pzt. Another end of the pzt was glued to a piece of plastic. This plastic piece was clamped on a translational stage. We thought that the soft rubber, the plastic and the translational stage caused the drift of the arm length.

So we tried to improved this by

  • replacing the rubber and plastic with two pieces of magnets. One was glued on the back of the mirror, another one was glued to the pzt. This did not work, the combination of the force, and the shim stiffness, had to be matched so the mirror position can be adjusted without letting the magnets touch each other. So we tried
  • replacing the rubber and plastic with stainless steel nuts, one nut is for clamping, another one is for pushing the mirror.
  • IMG_1580.JPG

we haven't got rid of the stage because we still need it for position adjustment purpose. We will use dc voltage offset on pzt to adjust the position later once we can add dc signal to the driving voltage.  Currently, we use a single function generator to drive both pzt simultaneously.

 

     With new pushing scheme, the drift becomes much less than before. The signal is in phase for more than a minute or two which should be enough for chopping technique later. The picture below shows the signal from driving voltage @ 2Hz(blue), and readout from PD at maximum slope (yellow).

IMG_1579.JPG

     Once we made sure that the signal was quite stable, (that is, the operating point stays at the maximum slope most of the time), we measured the background noise. This is a readout from PD and maximum slope on the fringe without driving voltage applied on the pzt. Then we measured the signal when one arm was driven at 2 Hz. Finally, we drove two arms at 2Hz and adjust the voltage on the pzt so that the 2Hz common mode cancelled out.

compare.png

 The plot shows the noise of the setup: 1) the background 2) when one arm was driven at 2 Hz. 3) Both arms are driven, with common mode at 2Hz minimized.

 We will try squaring the signal next. The read out from PD is ~ 200 mV. This value will determine if we need a divider for the signal or not.

  206   Thu May 19 21:31:28 2011 Mingyuan, TaraDailyProgressCreakstart crackling

 

We used a big box to cover the optical loop. The interferometer is more stable now.

We build other two AD734 chip circuits for signal square and multiplier.

We already tested that we could square the driving signal and PD signal.

The square of the PD signal has a big offset from the AD 734 circuit. We need figure out how to take the offset out.

  207   Fri May 20 23:19:36 2011 Mingyuan, TaraDailyProgressCracklestart crackling

We tried read out the signal from chopping technique.We could not see anything yet.

The signal when both IFO arms were driven were similar to the signal when there was no driving.

 

   After we made the necessary electronics for chopping technique, we tested if we could see the signal or not.

    ==setup==

    We used a 4 mW HeNe laser as a source with a simple Michelson interferometer setup. We tried to operate at the maximum slope of the fringe. Each mirror was attached to a metal shim which could be pushed by a PZT behind it, see here . We drove the mirror with the same distance so that the common mode was canceled and only incoherent noise from crackle in each blade could be detected.

 crackle_chopping.pdf

    The diagram omits the IFO part and the blades. The output beam from the IFO was incident on the PD. We operated at the maximum slope of the fringe. The driving voltage Vdrive was send to the PZTs pushing blades (with mirrors attached on them) at the end of both arms.

    The 1/2 and 1/10 dividers are used to reduce the signal down below 0.5 V. This number comes from the square testing. When the input signal to be squared is larger than 0.6, the output starts to rail. So we use 0.5V to be the upper limit for now.

 

   ==result==

    chopping.png

       The PSD of the signal output when two arms are driven are similar to the background signal (arms are not driven). It might be that the gain setting are not optimized, the setup is too noisy, or problems from offset from the AD734 chip. We will figure that out next. We will also make a sturdy box for multiplying chip. Currently we just use temporary test board to operate the chips for the read out.

  208   Tue May 24 19:47:16 2011 Mingyuan, TaraDailyProgressCracklestart crackling

 1) We removed the squaring circuit from the test board and built it on a board. The box for the circuit was prepared.

 2) We replaced the crappy beam splitter with a Thorlabs 20mm cube 400-700 nm beamsplitter. The beam power is evenly divided and has no multiple reflections. We measured the noise psd at the AS port.

 

      1) The circuit for squaring, multiplying signals was temporarily built on a plug-and-play test board which was neither sturdy nor compact. So We used a breadboard available in the EE lab to build the circuit.

The cartoon schematic is shown below.

circuit.jpg

      A) The signal from PD at AS port is band passed before squared (not shown here), then band passed again before.

      B) The driving voltage for PZT will be high pass to get rid of DC component (not shown here), then divided. We want a divider here because we might need to drive the pzts with higher voltage. The second divider might be unnecessary, but we have it just in case.

     C) Then we multiply  A and B and get the signal out for FFT.

     Currently, the chips have offset added to the output, ~ from -1 to -2 V. We tried adding the offset in Z2 let as suggested in the datasheet, but it killed the signal ??!!!. So we are planning to high pass signals that we care only their AC parts. Currently, we are not sure if we care about DC part of the V drive or not. We have to think about it.

    

     2) The beam splitter used in the original setup is not really for a beam splitter for Michelson IFO. It is not 50/50, and there are multiple reflections from the surfaces.

Thus, we ordered a cube beam splitter suitable the job and replaced it. It is mounted on a beam splitter mounted directly mounted on a 2" post, so we expect it to be more stable.

IMG_1582.JPG

 

 

We measured the noise from AS port when the armed was not driven vs driven at 1 Hz. The result is shown below.

The calibration from V to differential arm length (Lx - Ly) is approximated from

dx ~ dV x  lambda/ 4 / (Vmax - Vmin)

At the maximum slope of the fringe, as we tap the table, the voltage will fluctuate between Vmax (from constructive interference)and Vmin (destructive interference.)  On the fringe, the differential arm length between maximum to minimum V output is lambda/4 (so the accumulated distance from round trip is lambda/2, a condition for changing from maximum Vout to minimum Vout). We can approximate the slope to be (Vmax - Vmin)/ (lambda/4).

Vmax - Vmin ~ 500 mV, lambda = 660 nm. so

dx = dV x 3x 10^ -7

 

vas.png

The result is 5 - 6 orders of magnitude above the shot noise level (~ 1e-17 m/rtHz for this setup.) Noise characterization will be considered next, but from

a quick test of tapping, seismic is the dominating source.

  210   Thu May 26 18:58:56 2011 Mingyuan, TaraDailyProgressCreakNoise from AD734

 

 

 

 

 

We figure out the offset issue of the chip AD 734. We measured the noise of chip AD 734 with 50 ohm input terminated.

The noise is shown below for two chips we are using and noise from spectrum analyzer is attached for reference.

The noise of AD 734 is about 1 uV/root(Hz) at around 50 Hz. The sensitivity of of the chip should be:

dV*dV/10 = 1 uV/root(Hz)  =>  dV ~ 3 mV/root(Hz)

We are not sure about that we understand the noise propagation through the chip correctly.  

  211   Thu May 26 19:39:48 2011 taraDailyProgressCrackleAD734 squaring circuit

By mingyuan, tara

We figured out the offset problem in AD734 chips, the box for squaring and multiplying signals is finished.

 

          The problem from the previous circuit was that the ground from the signal was grounded with the load ground. This time the load ground is separated from the signal ground, Z2 is grounded to load groundThese corrections fix the offset problem and the maximum allowed input ( was 0.6 V.) Now the input can be up to 10V. The output, Z, is (X1-X2)x(Y1-Y2)/10 as described in the datasheet. Now the chip are connected as shown below.

 

IMG_1607.JPG

 

          We are thinking about not using the default denominator (/10) for a multiplying chip (we certainly need it for squaring chips, otherwise the output will rail), because after the signals (from PD and driving voltage) are squared, their dc levels are ~3 V. When the two are multiplied together, the voltage output drops to 3x3/10 = 0.9 V. So if we can have denominator = 1, the signal will be larger. However, we have to understand how the noise in the chip works first. See Mingyuan's entry about input referred noise of the chip ,it is roughly 3 mV/rtHz. If the SNR remains constant regardless of the denominator, we might not need to worry about it.

  212   Fri May 27 17:00:28 2011 Mingyuan, TaraDailyProgressCrackleData readout

 

 

Today we measured the current system noise by the signal squaring and multiplier system we built.
The interferometer is quite stable now and the phase could be stable for more than half hour.
The plates are droven by 2 Hz 3 Vpp sinusoid signal with 4 V offset in common mode.
The signal From PD is band passed by SR560 with 200 gain and squared by AD 734 chip.
The driving signal is also band passed by S560 and squared by another AD 734 chip.
The two squared signal are multiplied by one AD 734 chip. The signal from multiplier is feed
to spectrum analyzer. We also measured the noise spectrum without driving plates. The results look the same.
The signal is very sensitive to talking and walking nearby the table. We suspect that the seismic noise dominates the noise.
The possible noise source:

  • shot noise
  • seismic noise
  • Thermal noise of the plates
  • Thermal noise of the mirror
  • PZT noise and rubbing
  • Air flowing
  • Laser power fluctuation
  • Laser frequency noise
  • noise from AD 734
  • noise from other electronics

 

Tara will upload the plots later.

  213   Fri May 27 20:32:18 2011 taraDailyProgressCrackleData readout

By Mingyuan Tara

We measured the FFT of the demodulated signal from chopping technique. We did not see much. The background noise is still too high.

      With everything ready, we used chopping technique to measure crackling noise. We measure the PSD from the demodulated signal between a) the mirrors being driven at 2Hz, and b) background noise, when the system was at rest, no driving force applied to the mirrors. We did this to check if we can see any signal due to crackling noise/ rubbing noise/ pzt noise or any noise originated from the driving mechanism or not. The result is not quite clear, we see a few peaks from the driven system around 40 Hz, but we have yet to confirm and identify them.

     ==setup==

        The setup is shown in the diagram below. For each bandpass through SR560, we added the gain to the signal as much as possible without railing the signal. Note that in this setup we did not bandpass the signal from PD after we square it , as shown in previous entries. Because Mingyuan did not understand why would we need to and I could not answer him properly, so I agreed to let him have it his way.

      

    crackle_choppig_2011_05_27.pdf

          When we measured the data from the driven system (red curve in the plot), the setup is as shown in the diagram. However, for background measurement (blue curve in the plot), we want to keep the DC supply provided by the function generator to the pzt so that the sensitivity of the signal remain the same. Hence, we used a second function generator to send in similar driving voltage to the squaring box, while the first function generator was set to the dc output voltage to supply the pzts, no sinusoidal output.   (We made a mistake by just unplugging the Vdrive to the pzt and to the squaring box, and the noise level dropped so much.) 

==result==

demod.png

     The red and blue curve shows the psd of the demodulated signal when the blades were driven, and the static case respectively. The peak at 4 Hz that presents in both cases are from the square of the driving signal at 2Hz.

     There are a few  peaks around 36 - 40 Hz when the blades were driven. We could not see this in the SR785 monitor because the monitor was so faint. I just saw this after I plotted the data.  The peaks might come from some resonances in the setup. We expect crackling noise to be more broad band. We will confirm and identify the source of the peak to make sure that we can see some signal from the driving (it can be rubbing between metal, pzt noise, crackle.)

We will repeat the same measurement, and try changing driving frequency/ amplitude, to see if the signal changes or not.

  214   Mon May 30 02:09:53 2011 Vladimir DergachevDailyProgressTiltmeterNoise spectrum after cleaning
First useful spectrum after cleaning. It appears to be at least as good as before. This plot uses pre-cleaning calibration - it should not have changed too much, I'll try doing another calibration after collecting more data.
  215   Tue May 31 17:49:47 2011 Mingyuan, TaraDailyProgressCreakdata readout

 

 

To have the ability of controlling the phase, we need adjust DC voltage of one of the PZTs independently.
We use the function generator to generate AC driving with a DC offset for one of the PZTs and use a OP270
chip to add the driving signal with another DC voltage for another PZT. By changing this DC voltage, we can
control the phase of interference signal. We adjust the voltage to put the PD intensity in the middle to have
the best sensitivity.
We did the same measurement as last time to check the peaks we observed. By use the same condition, we do see
a few extra peaks while the plates are being drovn at 2 Hz. We also changed the driving frequency to 0.7 Hz and
did the same measurement. The results looks different.
  Tara will upload the data later.

 
  216   Tue May 31 19:33:00 2011 taraDailyProgressCrackledata readout

By mingyuan, tara

We built a simple voltage summing circuit for adding DC level to the pzt. This circuit allows us to fine tune the inteferometer's differential arm length, so that we can operate at the fringe's maximum slope. Then we checked the peaks we observed from last time. It turned out to be harmonics from the common mode from driving.

 

The circuit schematic is shown below. The result Vout = Vin1 + Vin2. 

adding_circuit.png

 

The adding circuit is used as shown in the schematic (highlighted in yellow.)

crackle_choppig_2011_05_31.pdf

 *Later, we can use this summing circuit in a feedback control loop for locking the interferometer.

Then we used this circuit in the setup and repeat the measurement to check the peaks we observed last time. With the same setup, we observed the peaks again, but they probably are harmonics from 4Hz from common mode motion which was not perfectly cancelled.

 readout.png

 

 

     We repeated the measurement again with 0.7 Hz driving, and the peaks disappeared. The signal between driving and not driving the arms are very similar. The shape of the PSD changes slightly because of the lower amplitude of the driving signal, as we low pass the signal at 0.1 Hz.

readout2.png

We do need a seismic isolation and vacuum chamber. Right now, sound from people speaking in the lab can disturb the measurement.

 

 a few things we have to consider soon, before we use the maraging steel blades pulled down by a mass block in the experiment.

1) how should we push the blades?  capacitor plate? magnetic coil?

2) When can we move and get a better table, so that we can decide on seismic isolation stage.

3) We have to start looking for vacuum bell jar for the experiment.

4) lock the interferometer?

5) will we get an npro laser for the experiment?

  218   Mon Jun 20 12:11:49 2011 Larisa ThorneDailyProgressCrackleCrackling simulations

I should begin this ELOG with the warning that this is the first time I've ever used MATLAB...

 

 

First item on the agenda is to create a simulation which models the displacement due to the crackling noise on the blade spring. This can be done using MATLAB in just a few lines and generates a plot (see first attachment).

For this simulation, I picked random numbers for the constants, which is why it wil likely look a little funny. 

t =       1:0.1:100;  %time range

fdrive =  0.1   % driving frequency

MaxA =    2    %maximum amplitude

alpha =   1          %some constant

deltax =  MaxA.*sin(2.*pi.*fdrive.*t)

k0 =      1   % spring constant

Force =   k0.*deltax    %driving force

noise =   rand(1,1001); %some random noise function: our crackling noise?

k =       k0+noise.*alpha.*deltax;

dx =      Force./k

crackle = dx-deltax;  % crackling noise measured in terms of displacement

 

 

The next step is to attend to chopping. The second attachment is the circuit I drew to do this, but it differs a bit from what I've seen posted on this ELOG here. Which one is right??

From what I understand, the first simulation (above) results must be injected into the beginning of the top part of this circuit (coming from the PD). Then the signal needs to be bandpassed, squared, bandpassed again, the mixed with a source signal and time averaged to isolate the noise. On the subject of bandpassing: I've been reading up on trying to do this in MATLAB. There seem to be a few suggestions on the Internet, but none of them have worked for me...(then again, I'm probably doing it wrong). The crackling plot shows displacement at a range of frequencies, but I imagine that the chopping circuit will have more to do with voltages. How does this translate?

 

 

TO DO list:

-- Try to create a bandpass filter in MATLAB

-- Try to create a mixer in MATLAB

 

 

  219   Mon Jun 20 17:26:37 2011 Larisa ThorneDailyProgressCrackleCrackling simulations

The rest of the chopping circuit has been designed (see first attachment). 

***NOTE: adjustments have been made to the crackling circuit, where the AC source signal is NO LONGER BEING SENT THROUGH THE SIGNAL SQUARER)

 

Because there are four "outputs", there will be four plots generated. There is a number at the "output" of each in the first diagram attached, which I associated with its corresponding plot number. Here is a sample of the MATLAB code I used for Circuit 1:

fs = 500;

ts = 1/fs;

t = (0:ts:100); %time vector

k0 = 2; %ideal spring constant

fdrive = 0.1; %driving frequency

Amp = 1; %max amplitude

dist = Amp*sin(2*pi*fdrive*t); %spring position

vel = 2*pi*fdrive*Amp*cos(2*pi*fdrive*t); %spring velocity

noise_t = rand(1,50001)*2-1; %noise function

Force = k0*dist; %ideal spring force

alpha = 0.5;

k = k0 + noise_t.*alpha.*k0.*(dist./Amp); % k = k0 + dk

dx = (k - k0).*dist/-k0;

crackle = dx/(alpha*Amp); % = noise*sin^2(2*pi*fdrive*tt)

 

%Bandpass#1 

[B1,A1] = butter(2,[10 100]/(fs/2));

y1 = filter(B1,A1,crackle);

 

%squared signal

ysq = y1.^2;

 

%Bandpass#2

[B2,A2] = butter(2,[10 200]/(fs/2));

y2 = filter(B2,A2,ysq);

 

 

 

 

 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 

%%%Circuit1%%%

 

 

%Source

Vsin = sin(2*pi*fdrive*t);

 

%Doubled source

V1 = 2.*Vsin;

 

%Mixer

ymix1 = y2.*V1; 

 

%Low Pass Filter

[B3,A3] = butter(2,0.1); % error message when fc not within (0,1)

ylpf1 = filter(B3,A3,ymix1);

 

  220   Tue Jun 21 13:32:02 2011 Larisa ThorneDailyProgressCrackleQ and dampening measurements

 We went down to the SUS lab and ran some tests to get measurements we could use to calculate the Q and b (dampening factor/constant?) of the blade springs.

 

The setup was fairly simple (see attachment below): a laser beam was set up such that its path to a photo diode would be interrupted by the movement of a mass (which was attached to the spring blade). The resulting wave function as seen through an oscilloscope hooked up to the PD would give us the necessary data to calculate Q and b.

Given these sets of data, we can reference (this) to find that Q=4.53 f0 T1/2. Here T1/2 is the "decay by half life of amplitude", or the time it takes for the amplitude to be half of when it begins, and can be checked by plugging into the equation and seeing if the resulting expression is true: Amplitude( T1/2)/ Amplitude(t@0) = 1/2 .

 

 

 

 

TO DO list:

 

 

-- Take the oscilloscope data and figure out how to calculate  T1/2, so that Q can be calculated

-- Think about how to calculate b

 

 

  221   Tue Jun 21 14:53:29 2011 Vanessa AconDailyProgressCrackleMatlab simulation of Chopping

Our project is to set up a basic Michelson interferometer to measure and characterize the crackling in blade springs.  That crackling signal will likely be buried under other sources of noise and other parts of the signal, so we will use a chopping technique to extract the crackling signal.  We first set up a Matlab simulation of the chopping technique using a constructed "crackle" signal.  The code and explanation of that simulation are attached.

ETA: changed such that crackle = delta x(t), not delta x(t) - x(t).

  222   Tue Jun 21 16:06:51 2011 Larisa ThorneDailyProgressCrackleBlade plots and Q/b calculation thoughts

I figured out how to plot the graphs given data points gathered by the oscilloscope.Results have been published below.... 

NOTE: there are two blades ("Romulus" and "Remus"). There are two plots per blade: the one with the noticeable sinusoidal shape will be used for Q calculation (see here), whereas the one which looks like a compressed version thereof helps us see how the amplitude of the oscillations decreases over time, exhibiting the "damped" motion, from which we will somehow calculation b.

 

I had an idea for calculating T1/2: if Amplitude( T1/2)/ Amplitude(t@0) = 1/2 . is true, then I just need to find a maximum in the y values (in the voltage data for the graph, since it is not a smooth function), find the closest minimum, then take the difference. This would give me some point near where the amplitude is at "zero". Then all that would have to be done is to find the corresponding x values (time, in seconds) to this maximum and middle "zero" point, and subtract these time values to get the T1/2 value. It's pretty tricky to implement in MATLAB.

Somehow that doesn't seem right though. If one tried to visualize that, wouldn't it seem like we were just measuring the time interval it takes to get through 1/4 of the wave's period? I don't think I understand what is meant by T1/2....

  223   Thu Jun 23 11:26:50 2011 Larisa ThorneDailyProgressCrackleA little noise budgeting

Today we started to set up the experiment which will eventually allow us to characterize the noise of the blade spring crackling. The configuration was an analog of the final configuration, where a controlled voltage over a PZT was used as the driving force on the ETMX only.

 

The first plot, labeled "Spectrum 1" represents the power spectral density plot of the all the noises prevalent in the configuration (i.e., seismic noise, shot noises, fluctuations due to air currents, etc).

"Spectrum 2" is similar, except that the only noise present is 'dark noise', which is the extra signal the PD gets when the laser beams are blocked from hitting it. This 'dark noise' can be thought of as some sort of background noise.

 

By observation, we can compare the orders of magnitude at which both the sum noise and dark noise curves exist.... Spectrum 1 is around the order of ~10-3 to 10-2  whereas Spectrum 2 is around the order of ~10-5. This confirms that the dark noise occurs within the range of values of the sum noise.

 

  224   Thu Jun 23 12:18:15 2011 Vanessa AconDailyProgressCrackleMeasuring resonant frequency and Q factor of the blade springs

 Measurements taken on June 21.

  225   Thu Jun 23 12:26:09 2011 Vanessa AconDailyProgressCrackleInitial Set-up: Noise Budget

Data taken June 22

We measured our initial set-up (with mirrors on PZTs, not masses on springs) noise and found a conversion factor from volts on the spectrum analyzer to meters (distance moved by the mirror).

Notes: I'm assuming that peak in the dark noise is from the lights, even though we have a plastic bin around the set-up.  Also, I used the most common wavelength value for HeNe lasers (from wikipedia).  I will confirm this value later.

ETA: Noise curves have been added for the PZT set-up.  Different curves are at different AC amplitudes and AC frequencies.  The curves do not change much in the 10-100Hz range, with varying low AC frequencies).

  226   Thu Jun 23 12:59:46 2011 Larisa ThorneDailyProgressCrackleNoise budget curve, updated version

 I have made some adjustments to my noise curve from earlier.

 

 

 

The graphs have been consolidated into one, with appropriate scaling. You will notice the y axis has been adjusted by a conversion factor, as we want meters/SQRT(Hz), not Volts/SQRT(Hz).

 

Let deltaV=fringe amplitude from minimum to maximum, as seen on the oscilloscope when there is no driving force on the mirrors =638mV

Let deltaL=difference in Michelson X and Y arms =(wavelength of the He-Ne laser)/4

Let the conversion factor = [deltaV] / [deltaL]

Since most commercial He-Ne lasers produce a laser at wavelength of 633nm (Googled this), the conversion factor=4.031595577E6 in Volts/meter.

 

  227   Fri Jun 24 13:50:01 2011 Larisa ThorneDailyProgressCrackleDriven Noise curves

 Unlike in the earlier post, the configuration (specifically, the PZTs....we will switch tot the actual blade experiment soon) were driving the circuit.

 

Below are the resulting power spectrum density plots. Each represents the same basic configuration, but at different conditions (both driving frequency f and voltage amplitude Vamp could be adjusted).

Three conditions were tested:

  1. f=0.1Hz, Vamp=2V
  2. f=0.2Hz, Vamp=2V
  3. f=0.2Hz, Vamp=3V

For the first two plots, the same conversion factor to get from V/SQRT(Hz) to the desired units of meters/SQRT(Hz). Conversion=2.578199052E6 Volts/meter. Since the voltage amplitude was changed during the third test, the conversion factor had to be adjusted to conversion=3.892575039E6  Volts/meter. [If there is any confusion on how these were calculated, reference the post here]

The fourth plot superimposes all three previous plots.

 

  228   Fri Jun 24 15:44:23 2011 Larisa Thorne and Vanessa AconDailyProgressCrackleCrackling setup, with blades

Laser paths have been added in red (note: these are by no means all of the laser paths, only the ones that allow me to show the end test mass configuration)

Currently only one of the end test masses has a mirror attached...

 

The problem is that the mirrors attached to the blade springs are not on a plane that is parallel to the plane of the optics table, so the reflected beam does not follow the same path back. Rana mentioned at some point that perhaps it would be a better idea to affix the mirrors to the bottoms of the masses holding the blade springs down. I think that sounds like a more viable option.

ETA:  Added initial signal readouts from the photodiode with the mass moving, and with the mass stationary (zoomed in).  Notice that when the mass is moving there is some high frequency signal (300-500Hz) contained inside a larger wave packet (about 3.33Hz).  Possibly one signal is from the change in Lx and Ly in the Michelson setup, while the other is due to the slight changes in angle of the mirror on the spring, thus changing the level of overlap between the two recombining beams.  

However, even when holding the mass stationary we see the 300-500Hz signal.  Possibly some of that was from air currents / overhead lights / etc, because we were not yet able to put the plastic cover over the entire setup with the springs in the way.  More likely however is that the short amount of free spring that exists between the clamp for the mass and the clamp for the mirror is oscillating at its own frequency that is very difficult to damp, even when the mass is stationary.  We will try then to design a setup that positions the mirror on the bottom of the mass, rather than in a separate part of the blade spring.

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