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  SUS Lab eLog, Page 36 of 37  Not logged in ELOG logo
ID Date Authorup Type Category Subject
  25   Mon Oct 29 11:07:22 2007 waldmanSoftware InstallationOMCSoftware install on OMS
[Alex, Sam]

We spent a little time this morning working on OMS and getting things restarted. A few changes were made. 1) We put openmotif on OMS so that the burtrb doesn't throw that crappy libXm any more. 2) We upgraded OMS to a 32 kHz sampling rate from 2 kHz. All the filters will have to be changed. We also added a PDH filter path to maybe feedback PDH signals cuz that will be cool. Maybe someday I will write up the very cool channel adding procedure.
  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.
  37   Wed Oct 31 09:45:28 2007 waldmanOtherOMCResolution to DAQland saga
[Jay, Sam]

We did a rough accounting for the linear delay this morning and it comes out more or less correct. The 10 kHz 3rd order butterworth AA/AI filter gives ~90 degrees of phase at 6 kHz, or 42 microseconds. Taken together, the two AA and AI filters are worth 80 microseconds. The 1.5 sample digital delay is worth 1.5/32768 = 45 microseconds. The remaining 160 - 125 = 35 microseconds is most likely taken up by the 64 kHz to 32 kHz decimation routine, assuming this isn't accounted for already in the 1.5 sample digital delay.

It remains to be seen whether this phase delay is good enough to lock the laser to the OMC cavity
  42   Wed Oct 31 23:55:17 2007 waldmanOtherOMCQPD tests
The 4 QPDs for the OMC have been installed in the 056 at the test setup. All 4 QPDs work and have medm screens located under C2TPT. The breadboard mounted QPDs are not very well centered so their signal is somewhat crappy. But all 4 QPDs definitely see plenty of light. I include light and dark spectra below. QPDs 1-2 are table-mounted and QPD 2 is labeled with a bit of blue tape. QDPs 3-4 are mounted on the OMC. QPD3 is the near field detector and QPD4 is the far field. In other words, QPD3 is closest to the input coupler and QPD4 is farthest.

Included below are some spectra of the QPDs with and without light. For QPDs 1 & 2, the light source is just room lights, while 3&4 have the laser in the nominal OMC configuration with a few mWs as source. The noise at 100 Hz is about 100 microvolts / rtHz. If I recall correctly, the QPDs have 5 kOhm transimpedance (right Rich?) so this is 20 nanoamps / rtHz of current noise at the QPD.
  43   Thu Nov 1 01:28:04 2007 waldmanOtherOMCFirst digital lock of OMC
[Pinkesh, Sam]

We locked a fiber based NPRO to the suspended OMC tonight using the TPT digital control system. To control the laser frequency, we took the PZT AI output and ran it on a BNC cable down the hallway to the Thorlabs HV box. The Thorlabs is a singled ended unit so we connected the AI positive terminal only and grounded the BNC to the AI shield. We could get a -6 to 1.5 V throw in this method which fed into the 10 k resisotr + 9 V battery at the input of the HV box. The HV out ran to the NPRO PZT fast input.

We derived our error signal from a PDA255 in reflection with a 29.5 MHz PDH lock. The signal feeds into one of the unused Tip/Tilt AA channels and is passed to the PZT LSC drive through the TPT_PDH1 filter bank. In the PZT_LSC filter we put a single pole at 1 Hz which, together with the phase we mentioned the other night (180 degrees at 3 kHz) should allow a 1 kHz-ish loop. In practice, as shown below, we got a 650 Hz UGF with 45 degrees of phase margin and about 6 dB of gain margin.

The Lower figure shows the error point spectrum with 3 settings. REF0 in blue shows lots of gain peaking at 1.5 kHz-ish, just where its expected - the gain was -40. The REF1 has gain of -20 and shows no gain peaking. The current trace in red shows some gain peaking cuz the alignment is better but it also has included a 1^2:20^2 boost which totally crushes the low frequency noise. We should do a better loop sweep after getting the alignment right so we can see how much boost it will really take.

Just for fun, we are leaving it locked overnight and recording the PZT_LSC data for posterity.
  58   Fri Nov 2 12:18:47 2007 waldmanSummaryOMCLocked OMC with DCPD
[Rich, Sam]

We locked the OMC and look at the signal on the DCPD. Plots included.
  59   Sat Nov 3 16:20:43 2007 waldmanSummaryOMCA good day's work

I followed up yesterday's test of the PZT with a whole mess of characterizations of the PZT control and finished the day by locking the OMC with a PZT dither lock and a 600 Hz loop. I haven't analyzed any of the data yet, so its not calibrated in physical units and etc. etc. etc. Since a lot of the sweeps below are of a "drive the PZT, look at the PDH signal" nature, a proper analysis will require taking out the loop and calibrating the signals, which alas, I haven't done. Nonetheless, I include all the plots because they are pretty. The files included below are:

  • DitherLock_sweep: Sweep of the IN2/IN1 for the dither lock error point showing 600 Hz UGF
  • HiResPZTDither_sweep: Sweep of the PZT dither input compared to the PDH error signal. I restarted the front end before the sweep was finished accounting for the blip.
  • HiResPZTDither_sweep2: Finish of the PZT dither sweep

More will be posted later.
  60   Sun Nov 4 23:22:50 2007 waldmanUpdateOMCOMC PZT and driver response functions
I wrote a big long elog and then my browser hung up, so you get a less detailed entry. I used Pinkesh's calibration of the PZT (0.9 V/nm) to calibrate the PDH error signal, then took the following data on the PZT and PZT driver response functions.:

  • FIgure 1: PZT dither path. Most of the features in this plot are understood: There is a 2kHz high pass filter in the PZT drive which is otherwise flat. The resonance features above 5 kHz are believed to be the tombstones. I don't understand the extra motion from 1-2 kHz.
  • Figure 2: PZT dither path zoom in. Since I want to dither the PZT to get an error signal, it helps to know where to dither. The ADC Anti-aliasing filter is a 3rd order butterworth at 10 kHz, so I looked for nice flat places below 10 KHz and settled on 8 kHz as relatively harmless.
  • Figure 3: PZT LSC path. This path has got a 1^2:10^2 de-whitening stage in the hardware which hasn't been digitally compensated for. You can see its effect between 10 and 40 Hz. The LSC path also has a 160 Hz low path which is visible causing a 1/f between 200 and 500 Hz. I have no idea what the 1 kHz resonant feature is, though I am inclined to point to the PDH loop since that is pretty close to the UGF and there is much gain peaking at that frequency.
  63   Mon Nov 5 14:44:39 2007 waldmanUpdateOMCPZT response functions and De-whitening
The PZT has two control paths: a DC coupled path with gain of 20, range of 0 to 300 V, and a pair of 1:10 whitening filters, and an AC path capacitively coupled to the PZT via a 0.1 uF cap through a 2nd order, 2 kHz high pass filter. There are two monitors for the PZT, a DC monitor which sniffs the DC directly with a gain of 0.02 and one which sniffs the dither input with a gain of 10.

There are two plots included below. The first measures the transfer function of the AC monitor / AC drive. It shows the expected 2 kHz 2d order filter and an AC gain of 100 dB, which seems a bit high but may be because of a filter I am forgetting. The high frequency rolloff is the AA and AI filters kicking in which are 3rd order butters at 10 kHz.

The second plot is the DC path. The two traces show the transfer function of DC monitor / DC drive with and with an Anti-dewhitening filter engaged in the DC drive. I fit the antidewhite using a least squares routine in matlab constrained to match 2 poles, 2 zeros, and a delay to the measured complex filter response. The resulting filter is (1.21, 0.72) : (12.61, 8.67) and the delay was f_pi = 912 Hz. The delay is a bit lower than expected for the f_pi = 3 kHz delay of the AA, AI, decimate combination, but not totally unreasonable. Without the delay, the filter is (1.3, 0.7) : (8.2, 13.2) - basically the same - so I use the results of the fit with delay. As you can see, the response of the combined digital AntiDW, analog DW path is flat to +/- 0.3 dB and +/- 3 degrees of phase.

Note the -44 dB of DC mon / DC drive is because the DC mon is calibrated in PZT Volts so the TF is PZT Volts / DAC cts. To calculate this value: there are (20 DAC V / 65536 DAC cts)* ( 20 PZT V / 1 DAC V) = -44.2 dB. Perfect!

I measured the high frequency response of the loop DC monitor / DC drive to be flat.
  79   Wed Nov 7 14:01:31 2007 waldmanOmnistructureOMCFrequency and Intensity noise
One of the biggest problems I had using the PZT to lock was excessive noise. I did a little noise hunting and found that the problem was the cable running from the rack to the laser fast input. As a reminder, the laser has a 4 MHz / volt fast input. We require about 300 MHz to go one FSR, so there is a Thorlabs HV box between at the NPRO fast input which takes 0-10 V -> 0-150 V. The 150 V HV range is worth about 600 MHz of NPRO frequency.

OLD SETUP: Single side of DAC differential (10 Vpp) -> 9V in series with 10 kOhm -> 10 kOhm input impedance of Thorlabs HV -> NPRO

We used the single side of the DAC differential because we didn't have a differential receiver. This turned out to be a bad idea because the cable picks up every 60 Hz harmonic known to man kind.

NEW SETUP: Digital conditioning -> DAC differential (digitally limited to 0 - 1 V) -> SR560 in A-B mode gain 10 (0 - 10 V output)-> Thorlabs HV -> NPRO.

This has almost no 60 Hz noise and works much, much better. Moral of the story, ALWAYS USE DIFFERENTIAL SIGNALS DIFFERENTIALLY !

Note that I may be saturating the SR560 with 10 V output, Its spec'd for 10 Vpp output with 1 VDC max input. I don't know whether or not it can push 10 V out....
  86   Fri Nov 9 00:01:24 2007 waldmanOmnistructureOMCOMC mechanical resonances (Tap tap tappy tap)
[Pinkesh, Aidan, Sam]

We did a tap-tap-tappy-tap test of the OMC to try to find its resonances. We looked at some combination of the PDH error signal and the DCPD signal in a couple of different noise configurations. The data included below shows tapping of the major tombstone objects as well the breadboard. I don't see any strong evidence of resonances below the very sharp resonance at 1300 Hz (which I interpret as the diving board mode of the breadboard). If I get free, I 'll post some plots of the different breadboard resonances you can excite by tapping in different places.

(The "normalized" tapping response is abs(tap - reference)./reference.)
  107   Mon Dec 17 19:39:52 2007 waldmanLaserOMCFiber seems to be broken
The 50 m fiber running from Rana's lab to 056 seems to be broken. I can't get any light through it to save my life. A 5 meter fiber couples like child's play. I think we should acquire a fiber coupler - then I will couple light into the 5 m fiber that works fine and couple it to the 50 m fiber and prove that its broken. Only then will I go pull the installed fiber from the 40m clean room.

  109   Wed Dec 19 23:09:43 2007 waldmanLaserOMCOMC relocked
The OMC has been relocked in preparation for final diode alignment, final QPD aligment, and adding the beam blocks. The mode matching is really terrible, so it makes alignment a little difficult because there is a high, high order mode close to the 00 that is making problems for the vertical alignment.

  110   Wed Dec 19 23:10:27 2007 waldmanComputingOMCFramebuilder broken
The framebuilder on OMS isn't doing anything. I can't get data using dataviewer or DTT. Thankfully, I can still use an analog scope to get data.

  112   Thu Dec 20 19:11:40 2007 waldmanComputingOMCHoWTO build front ends
For instance, to build the TPT front end code.

  • Save your file /cvs/cds/advLigo/src/epics/simLink/tpt.mdl
  • go to /cvs/cds/advLIGO on the TPT machine
  • do make clean-tpt tpt install-tpt
  • do rm /cvs/cds/caltech/chans/daq/C2TPT.ini (this step is needed because the DAQ install code isn't quite right at the time of this writing.
  • do make install-daq-tpt
  • run starttpt to restart the tpt computer.

  113   Thu Dec 20 19:12:11 2007 waldmanLaserOMCStressful reattachment of heater
Photos may follow eventually, but for now here's the rundown. I scraped the heater clean of the thermal epoxy using a clean razor blade. Then I stuffed a small piece of lint free cloth in the OTAS bore and wrapped the OMC in tin foil. With a vacuum sucking directly from the face of the OTAS, I gently scraped the glue off the OTAS aluminum. I wiped both the OTAS and the heater down with an isoproponal soaked lint-free cloth. I put a thin sheen of VacSeal on the face of the heater, wiping off the excess from the edges with a cloth. Then I clamped the heater to the OTAS using 2" c-clamps from the tombstone back to the heater front, making sure the alignment of the OTAS was correct (connector on the absolute bottom, concentric with the OTAS outer diameter). I added a second clamp, then beaded the outside of the joint with a little bit extra VacSeal, just for kicks. I'll leave it covered at least overnight, and maybe for a day or two.

  114   Sat Dec 22 18:05:07 2007 waldmanLaserOMCHeater bonding (almost) successful
The heater is now (re)bonded to the OTAS using VacSeal instead of the thermal epoxy. Unlike the expensive high-quality epoxy, VacSeal has supported 4 cycles of connector on/off.

Unfortunately, I didn't bond the heater as straight onto the aluminum as I had hoped. The connector is still about 5 degrees from the vertical so that the connector body sticks up close to the beam (but not as close as it might be. The mode matching is sooooo terrible (because I used an unlabeled lens) that it is impossible to identify the little bit of scattered light coming off the connector. Some of it could be (and probably is), junk light. I believe the closest approach of the connector is ~3 mm, but in the event we measure the finesse to be low, we might want to consider reworking the connector to get it down out of the beam.
  115   Sun Dec 23 17:21:57 2007 waldmanLaserOMCQPD3 centering
In the current cabling scheme, QPD3 is the Far field QPD mounted to the breadboard. With the cavity on a "pretty good alignment" I can physically move the QPD and get the signals to go +/- 1. In other words, I can physically move the QPD to zero its signal, which is the whole purpose of this test. The QPD matrix looks like [1 1 1 1; 1 1 -1 -1; 1 -1 -1 1]; Pitch looks right, yaw might be backwards. Note that the QPD is in a "plus" orientation.

I can center QPD4, the "near field" QPD just fine as well. In this configuration.

One caveat going forward - This alignment is going to be a real pain. In order to be in the linear range of the QPD, we need to be +/- omega/10 or something. In other words, with our 500 micron waist size, we need to get within 50 microns. We should get a translation stage made for this.
  116   Sun Dec 23 18:40:12 2007 waldmanLaserOMCDCPD centering
I can use a CCD camera and a macro lens to see the transmitted cavity beam on the DC photodiodes. I don't know which camera b/c there is no name on it, but it is a square edged camera with a 1/4-20 thread on the mount and has a many pinned cable running to a PS-12SU power supply. I also don't know which macro lens, but tis C-mount, about 4 inches long by 1.5 inches diameter with zoom, focus and f-stop adjustments (all unmarked).

When I look at the face of the transmitted PD, I see the three pins behind the diode chip on the left side. I can move the PD such that the beam is centered on the diode, but this is all the way to one side of the radiator clearance holes. When I maximally misalign the diode, the beam overlaps the diode edge on the side of the feed thru pins.

For the reflected DCPD, I cannot center the beam. Viewing the face of the PD with the two visible feedthru pin son the left side of the diode chip, the beam is low to the left and I cannot center it. I will try again tomorrow with the radiator with the oversize thru holes and see if I can center it. I think it may be a good idea to use an oversized radiator on the transmitted DCPD as well.
  117   Wed Dec 26 15:46:22 2007 waldmanLaserOMCDCPD centering
I used the drilled out radiator with both DCPDs and confirmed that I could center the beams. I also found the reflected beams and confirmed that a) there is clearance for the beamdumps and b) the location of the beams. Note that by some freak of fate, the transmitted DCPD ghost beam is only at about +15mm above the breadboard. I should mount the beamdump a bit low to accomodate it.

I can use a CCD camera and a macro lens to see the transmitted cavity beam on the DC photodiodes. I don't know which camera b/c there is no name on it, but it is a square edged camera with a 1/4-20 thread on the mount and has a many pinned cable running to a PS-12SU power supply. I also don't know which macro lens, but tis C-mount, about 4 inches long by 1.5 inches diameter with zoom, focus and f-stop adjustments (all unmarked).

When I look at the face of the transmitted PD, I see the three pins behind the diode chip on the left side. I can move the PD such that the beam is centered on the diode, but this is all the way to one side of the radiator clearance holes. When I maximally misalign the diode, the beam overlaps the diode edge on the side of the feed thru pins.

For the reflected DCPD, I cannot center the beam. Viewing the face of the PD with the two visible feedthru pin son the left side of the diode chip, the beam is low to the left and I cannot center it. I will try again tomorrow with the radiator with the oversize thru holes and see if I can center it. I think it may be a good idea to use an oversized radiator on the transmitted DCPD as well.
  118   Wed Dec 26 22:39:52 2007 waldmanLaserOMCDCPD beam dumps
I manufactured 2x 1" x 1" black glass beam dumps by vac-sealing the appropriate sized squares to DCPD tombstones. I then locked the cavity and looked at where the DCPD reflections went. The REFL DCPD is no problem, but the choices for the TRANS DCPD aren't so hot. As shown in the enclosed photos, the three options are ugly. I lean towards option 1, but the other two are possibilities as well.

To be clear,

Option 1: beam dump close to the PD at an angle to the beam splitter. Spot is centered on the dump and a little of the tombstone hangs off the edge

Option 2: beam dump close to the PD, parallel to the beam splitter. In order to get the spot on the black glass, the tombstone is very close to the beamsplitter. (This option might be more attractive if the tombstone is rotated 180 degrees.) The tombstone doesn't hang off the edge.

Option 3: We can catch the beam after the beam splitter if we hang the tombstone significantly off the edge, like by half. You'll see in the photos

  120   Fri Jan 25 22:08:45 2008 waldmanLaserOMCOMC ready for shipment
The OMC has been boxed in its spiffy black box and is ready for shipment.

We mounted the OMC in its frame, removing any loose mechanical parts and tightening up the nylon tipped set screws. Then we swaddled each optic in tin foil and lint free cloth before wrapping the whole thing in a double layer of the shiny stuff. Finally we wrapped the whole kaboodle in a double layer of ameristat before shoe-horning (literally) it into the box. The package is about 1/4" too long, so it required some effort to get it into the box, and will doubtless require similar effort to remove it.

The OMC in its box was left on top of its shipping container in 056.
  750   Tue Nov 19 22:29:39 2013 xiaoyueDailyProgressCrackleHysteresis Test Set Up

Attending: EricG, Gabriele, Xiaoyue

We installed two steel blades with different stiffness. By changing the hanging weight we are leveled the two arms, also the two end mirrors roughly. Leveling the whole stage by a more careful balancing of bearing weight, or does it matter much to the noise issue was left as an open question.

Eric walked me through the control system including the matlab program, emdm interfacing, foton, data viewer, striptool, diagnostic test tool, cymac terminal for signal generation. For every new system, a transfer function should be investigated by sweeping the driving frequency; or we can drive with a range of frequencies and extract the information from the output using Fourier analysis, but the coherence function exhibited a poor correlation (<<1, in a random fashion) between input and output signal when we tried this method.

We went through Eric’s python code for hysteresis analysis. We are driving the system on(+) – off – on(-) – off series with the sign indicating the direction of the driving force. The time interval between consequent actions is half an hour. We set it to run two cycles for each of the three levels of driving voltages.

  752   Thu Nov 21 22:58:51 2013 xiaoyueDailyProgressCrackleOptical Setup

Gabriele and I set up a rough Michelson interferometer alignment.

Matlab model -- Gabriele


Side view (left) Top view (right)


where the maroon beams are reflected from end mirrors. 

We tilted both of the 45 degree mirrors to deviate the reflected beam with an angle from incoming beams to bypass mirror 1(M1), to be detected by photodiode (PD).

Also it should be noted that the two end mirrors (ENDM1, ENDM2) have height difference of 1cm approximately, so we differentiate the optical path lengths of the two arms accordingly.

The alignment procedure is listed briefly as below:

- prepare the first mirror with a horizontal beam using irises.

- prepare a vertical reference using two irises aligned with a home-made plumb bob. 

- Align the 45 degrees inclined mirrors for vertical beams.

- Make sure the end mirrors are horizontal by overlapping incoming and reflected beams

- Roughly align the entire setup with beams superimposed

- Tweak the 45 degrees mirrors to separate the beam with a small angle (but large enough to bypass M1)

- Recenter or decenter mirrors to extract the symmetric port 

- Install photodiodes and beam dumps

(We may want to order more visible range mirrors / D-cut mirror / D-cut mirror mounts.)

  753   Tue Nov 26 01:03:45 2013 xiaoyueDailyProgressCrackleSystem Installed

Attending: Eric, Gabriele, Xiaoyue

We overlapped the two arms by first eliminate the fringes as much as possible. However the angular motion of the suspended mirrors kept bringing the fringes in. Then we did finer aligning by maximizing the signal amplitude, making sure a good overlapping is giving magnificent interference (either constructive or destructive). A beating envelope was observed.

Then we installed the system into the chamber. Then we went through the procedures to generate the transfer function for the damping loop. We forgot to turn off the damping which at the beginning raised very strange phase behavior. As people walked around affected the signal a lot, we decided to pump the chamber overnight. 

  772   Wed Feb 12 11:13:01 2014 xiaoyueDailyProgressCrackleseismic noise coupling characterization

In order to study the current setup better to improve the design of the 2nd version experiment, I did some seismic coupling analysis. The plan is to shake the optical table with a white noise (5V, pre-amplified with a bandwidth 10-1k Hz, input 0.5A, 2V) mini-shaker (B&K type 4810), while the motion of the table is monitored by a 3-axis accelerometer. A full description of the seismic noise picture should include analysis of the coupling from table motion to Mich signal, bench (damped by rubbers) inside the chamber to Mich signal, and we also want to characterize different coupling from bench to different optical elements.

The first and easiest thing I tried is to characterize the transfer function between table vibration and Mich signal. The table was shaken in x, y, and z directions separately, with hopefully three linearly independent measurements of a_x, a_y, and a_z measured for each 1hr shaking. In this way we built matrix [a_xx, a_xy, a_xz; a_yx, a_yy, a_yz; a_zx, a_zy, a_zz] where the additional index indicates the shaking direction. With [e_x, e_y, e_z] for each shaking measured by servo, simply solve [a_xx, a_xy, a_xz; a_yx, a_yy, a_yz; a_zx, a_zy, a_zz][T_x, T_y, T_z] = [e_x, e_y, e_z] will give us the transfer function along x, y and z. 


The picture is plotted with coherence between a_ii (where i is the driving direction) and mich signal is larger than 0.8. the result seems to agree with our expectation that the seismic noise transfer function follows the power law trend. 

However, the coherence is very bad. I tried increasing the noise power by limiting bandwidth to 10 - 300 Hz and inputing 0.8A 3.0V to the shaker). From the result of the z-drive result, the coherence in low frequency range is improved a lot, so I am going to finish the three-axial analysis. While the last trial of data is fit by 1/f^2, the later trial is better fit by 1/f^3, but this kind of fit is tricky. There are many resonances and it is difficult to judge which fit is the best. 



I tried superimposing the two and they are similar where both of them have good coherence.


I also did analysis (keep data with coherence > 0.8) for the coupling from directly the bench motion to optical elements. I mounted another mini-accelerometer on the newport mirror mount and clamp it to the table like what we did inside the chamber.


x has a generally higher level because the accelerometer is mounted along x-direction on the mirror mount. It seems that the transfer function is much smaller than one, which probably indicates a difference in calibration between the two signals. I will at some point mount the accelerometer one next to the other and measure the relative calibration, which should be simply a flat transfer function. 

Another problem here is that I got very bad coherence at low frequency. I have no good explanation why there seems to be a high-pass cutoff around 30 Hz, but we definitely need to push the measurement down to 10 Hz. 

  773   Wed Feb 12 18:02:01 2014 xiaoyueDailyProgressCracklestress-strain info about maraging steel blades

I got a chance to talk with Norna about the strain range we are in for our maraging steel blades:

We typically load the blades to a stress level of 800 MPa to 1000MPa. The upper value there is approx. 55% of the yield stress which is ~1.9 GPa. The Young’s modulus E = 186 GPa.

—> strain rate = d/dt [ (F sin(wt) + F0) / E ] = (wF/E) cos(wt) —> maximum rate = wF/E = (2 pi 0.125 Hz) (800 counts ~ 1um deflection) / 186 GPa

400 MPa ~ 1mm deflection

4 kPa ~ 1um deflection

—> max rate = 1.689e-08 /second

Also, the triangular shape gives equal stress along the length of the blade when loaded.

In addition, as [1996 Dahmen] "Hysteresis, avalanches, and disorder-induced critical scaling: A renormalization-group approach" shows a relationship between hysteresis and crackle, on page 14 878 they show how a model scaling hysteresis loop area with r, where r is associated with the average avalanche size: A_sing ~ r^(2-alpha) (MFT :alpha =0), I am thinking maybe materials with larger hysteresis loop area would generate crackling noise more “easily”. If this is the case, a good candidate would be the AISI 1085, which is also called music wire; it’s a high carbon steel. 


Reference: [1998 Beccaria] "The creep problem in the VIRGO suspensions: a possible solution using maraging steel"

  774   Fri Feb 21 11:36:56 2014 xiaoyueDailyProgressCrackleSeismic noise coupling to optical elements

I took the calibration line for the two accelerometers by mounting the small one rigidly next to the 3-axial seismometer and shake to get calib =  transfer function G (w/ coh<0.8=NAN). I also solved the problem where we lost information in low frequency range by correcting the frequency axis -- I used wrong sampling frequency because I did not notice that DMPA_IN1 has sampling frequency of 1/4*8192 while the ACCX_OUT channel is 1/2*8192.

After all the debugging, the coupling transfer function looks like:


with resolution of 0.02 Hz, and 2^8 averages (# of hanning windows)

I characterized two different mirror mount configurations -- setup 1 & 2, see figure below -- for comparison. setup2 seemes less robust as expected — as it has an extra post & post-holder joint.


Now the setup is ready for further seismic coupling characterization of different optical elements that we might consider using in the upgraded version of experiment.


  776   Tue Feb 25 23:16:51 2014 xiaoyueDailyProgressCrackleSeismic coupling to different opto-mechanics

I took some measurement for several combinations of opto-mechanics during the weekend:



The structure around 20Hz is unwanted, and we suspect it's due to the resonance of optical bench. 
Also, there seems to be a non trivial dependence of the structure there on the post length. For example, the shortest one (0.5”) has a large structure, then there is no data for the 1” one, the 1.5” shows no structure, the 2” is large, the 3" is small again and the 4” is large again. Irene Fiori from Virgo [2013 Fiori] argued that the contact surface between the components might play a role.

In this case we repeat the measurements on the small plate on rubber, instead of shaking the whole table.


Use DTT to have a live view of the changes:
1. test on the rubber plate —> structure at 20 Hz disappears, seems like the 20 Hz is the bench resonance frequency
2. test by tightening clamps —> structure around 1kHz moves to higher frequency
3. test by tightening mirror to post —> structure at high frequency becomes smaller

Below is an example for change#2, where after tightening the clamp, the green ref. curve (power spectrum of ACC#2) shifts to the red one.


The transfer function is smooth and flat, up to 300Hz.

  777   Wed Feb 26 16:53:22 2014 xiaoyueDailyProgressCrackleNewport Suprema vs. Thorlabs Polaris

From the latest measurements, it seems that Thorlabs Polaris mirror mount will work better for our purpose:


We suspect the better junction between mirror mount and the post be the explanation for the smoother /flatter transfer function of TP (Thorlabs Polaris) series. Also, there is a trend that shorter post works better for the TP series. NS (Newport Suprema) has a similar trend except for .5’ post, which has more bumpy structures probably due to the poor clamping. 


  783   Fri Apr 11 01:33:28 2014 xiaoyueDailyProgressCrackleOSEM electronics PD calibration

I wired the electronics up according to the satellite amplifier circuit diagram from document LIGO-T040106-01-K.


As the OSEM available have LED SME2470 and PD SMD2420 same as the amplifier is designed for. For simplicity I skipped the voltage regulator part  and supply reverse voltage for PD, current for LED using DC voltage supplies. Also, since I am reading Vout uisng a multimeter, no high-current buffer is included in my testing circuit. Another thing to note is that instead of LT1124ACN8 operated at +/- 15V I used OPA604AP operated at +/- 12V, because it's the op amp I found in lab at hand..

I first used a hand-cut aluminum flag, mounted on a translational stage, for calibration. I set reverse voltage as 10V, LED current 35 mA. 


By cutting the beam I expected to obtain a symmetric Erf funciton-like Vout vs. flag position data, but as is shown in the figure, trial 2, I got long nonlinear tail for the other half of the data tr, along with the fact that I cannot completely block the light. I trimmed the flag a little bit to make the edge sharper and collected the data as trial 3.

I chose three different fits to analyze the linear behavior range:


linear range (mm)

center V_out (V)

sensitivity (V/mm)













My first guess for the cause of bad shape is the poor quality of my hand-cut flag. Also Gabriele suggested that probably the op amp was saturated at high V_out range.

I changed the flag from the arbitrarily cut square into a slim metallic post, and I decreased the LED current a little bit to ensure the V_out is below 10V to avoid saturation.


In this trial I am able to get a much better — in sense of both symmetry and linear range — response. The maximum linear range I am able to fit is 0.8 mm with a sensitivity of 6V/mm.

  785   Fri Apr 25 15:38:20 2014 xiaoyueDailyProgressCrackleOSEM electronics PD calibration

I measured the noise for the circuit using SR785, at 10Hz 15 avgs to be 16.14 nVpk2 /Hz ~ 1e-08 m /sqrt(Hz) at .1'' flag position, which is the midway of our linear range. However compared to the noise value of 1e-10 m/sqrt(Hz), tested in LIGO-T040106-01-K, our noise is higher by 2 order of magnitude.

The most probable source of the excess noise is the fact that I am not using a stabilized current supply for the LED. I added in an adjustable voltage regulator LM317T (as I didn't find a precision 10V reference at hand) and it pushed the noise down to 15.92 pVpk2 /Hz ~ 1e-10 m /sqrt(Hz).


  786   Mon Apr 28 00:49:09 2014 xiaoyueDailyProgressCrackleOSEM PD firnal circuit and noise characterization

 Zach designed a wonderful circuit for us, and I wired it up according to the schematics:



For the two OPA140, which I didn’t find in lab I used OP27E instead, and I used two [R = 150, 3W] in series to substitute for [R13 = 270, 1W]. The original PD readout, without the 2-stage whitening, is very low at only 0.166 V with full LED exposure, thus I changed R16, the transimpedance load from 470 to 27k to give a max 9.9V voltage output. The value was determined by a potentiometer but finally substituted with a metal film resistor for noise concern. I also added a 1nF to the feedback of transimpedance for oscillation attenuation. 

I re-calibrated the linear range to be 1.143 mm with sensitivity of 5.5V/mm at center voltage of 5.4245 V. Using AC coupling input configuration and measure two channels with channel 2 shorted as a reference, the RMS noises at a mid-way flag position are measured as below in units of m /sqrt(Hz) :






noise floor





output RMS





RMS before whitening






The performance is in expectation expect that low frequency range (<1Hz) is behaving weird. I measured the transfer function of one 0.75-75 Hz whitening stage to confirm the noise amplification after two-stage whitening.  


To make the analysis more organized I should interface the signal analyzer ASAP..

  787   Tue May 13 02:08:49 2014 xiaoyueDailyProgressCracklecrackle1 seismic, laser intensity and shot noise

I measured the typical optical table motion using the wilcoxen accelerometers, and fed it through the transfer function I measured before for the seismic noise estimation.

I also measured the laser intensity noise along with the shot noise. First I opened the chamber and blocked one arm of the beam to decouple the laser noise from other noises that can rise from the asymmetry of Michelson configuration. Also to make sure my data is understandable, I confirmed that the photodiode is not saturated by plotting out the beam power vs. output voltage curve, using a half waveplate + PBS (Thorlabs PBS101A) in front of the fibre input.


Then I used SR785 (interfaced with Q's help) to analyze the laser noises, with the experimental shot noise value extrapolated at high frequency level off floor: mean of the floor RIN_ns  = 1.2282e-07/sqrt(Hz). While the incoming beam power P is measured as 0.275 mW we convert to obtain: ns = RIN_ns * P = 1.2282e-07*0.275e-3 =  3.3776e-11 W/sqrt(Hz), which agrees with the theoretical value ns_t = sqrt( 2hvP ) = sqrt(2*6.62e-34 [J*s]*(3e8[m/s]/633e-9[m])*0.275e-3[J/s])  = 1.31e-11 W/sqrt(Hz). 

Then I did the unit conversion for laser noises, from V/sqrt(Hz) to m/sqrt(Hz),

DataViewer PDBOUT = 2720 count  ~ ocilloscope = 1.50V with 1Mohm termination

Gmich = 1.5e11 count /m

(___ V/sqrt(Hz)) * 1/1.50V*2720 count /(1.5e11 count/m) = (___ )*1.2089e-08 m/sqrt(Hz)


I took laser noises in frequency intervals for finer line-width resolutions. Also it should be noted that I observed 20kHz (and its harmonics) peaks now and then, and I have no clue where they are from -- I got rid of them one time by short-circuiting A of Channel2, terminating all B's with 50ohm caps, but it's not replicable..

  789   Wed Jun 11 00:40:50 2014 xiaoyueDailyProgressCrackleEBSD map for maraging steel blade sample

I did an Electron Backscatter Diffraction (EBSD, please refer to http://www.ebsd.com for more background information) analysis for the maraging steel (18% Ni Grade 250) blade sample.


To generate this map, BCC and FCC structures were used as the model. It was found that BCC structure is the best fit. Then the high resolution map with pixel size of 0.03 um was taken.

We should use the pole figures as a color key to interpret the map -- it tells us how the grains are orientated in the sample. Since the sample is thin and flat we care only about the Z0 direction, which is the direction normal to the blade surface. For example the greens correspond to grains with zone axis (101) facing up along Z0.


The next step is to choose a good grain with single slip geometry, within which to make a pillar with at least 1 um diameter for compression test.

  801   Thu Jul 3 01:09:38 2014 xiaoyueDailyProgressCrackleSS Blade Response


The goal is to design a damping loop for the newly installed stainless steel blades.

We measured the transfer function for the blade response:



A comparison with the old maraging steel blades measurements can be found in Elog 757 and 587.

We modeled the transfer function and try to compensate the 2nd peak at ~10 Hz using a inverse function drive, however it did not work well. We doubted that the seismic noise is responsible for the problem, because seismic noise can excite the torsion / lateral tilting mode that cannot be damped / controlled by the coil drive, which only takes care of the vertical motion of the blades. To check the guess we took measurement of the coherence function of the seismic signal and the shadow sensor readout while common excitation is on for a sweep sine measurement:


In the Coherence Function measurement Z, Y, X table data correspond to the seismic noises measured by the 3-axial Wilcoxon accelerometer. The Z post data was taken by the seismometer mounted directly on the post.

The high coherence ~10 Hz indicates that we might be able to improve the compensator design with better management of the cables -- now they are hanging and touching freely on the vacuum chamber wall -- i.e. routing the cables such that there is no direct path from chamber motion to motion of the second stack, and closing the lid.

  802   Wed Jul 9 17:19:15 2014 xiaoyueDailyProgressCrackleEBSD map for maraging steel blade sample

As the small grain size (max ~ 5 um) measured in the last maraging steel sample was skeptical for well annealed steel, I annealed the other non-annealed maraging steel sample under the condition described in E0900023-v12: 450 C for 100 hrs, however in air but not in inert gas atmosphere. I did another EBSD analysis for the self-annealed sample:


Although the data quality is not good mainly because of relatively poor polishing, we should still see that the grain size is actually really large (max ~ 50 um). It indicates that the last sample is not well annealed as it's claimed to be. I plan to double-check by taking a look at the grains of the original non-annealed sample. 

On the side I characterized the carbon steel sample:


It should be noted that the Z inverse pole figure (color key) stays the same for all measurements (green 101, blue 111, red 001).


I did an Electron Backscatter Diffraction (EBSD, please refer to http://www.ebsd.com for more background information) analysis for the maraging steel (18% Ni Grade 250) blade sample.


To generate this map, BCC and FCC structures were used as the model. It was found that BCC structure is the best fit. Then the high resolution map with pixel size of 0.03 um was taken.

We should use the pole figures as a color key to interpret the map -- it tells us how the grains are orientated in the sample. Since the sample is thin and flat we care only about the Z0 direction, which is the direction normal to the blade surface. For example the greens correspond to grains with zone axis (101) facing up along Z0.


The next step is to choose a good grain with single slip geometry, within which to make a pillar with at least 1 um diameter for compression test.


  804   Sat Jul 12 01:11:41 2014 xiaoyueDailyProgressCrackle2D FFT for EBSD Map

I made a 2D FFT for the EBSD images using matlab



 Seems like a rather qualitative analysis. Is there any way you can make a 2D FFT of this so that we can see what the distribution of grain sizes are? What are typical sorts of grain size analysis people do in order to get quantitative comparisons?

 where the left one is for the as-received maraging steel sample, right for the self-annealed sample.


and a selected cross-section for direct comparison:


Yet from the plots I can only infer that a more scattered plot is corresponding to a smaller "grain components". May need more study on typical analysis, and here is an EXAMPLE how other people did it.

  809   Wed Jul 16 12:48:09 2014 xiaoyueDailyProgressCrackleEBSD for SS340, Grain Size Distribution

I did EBSD for Stainless Steel 340:


I also did a grain size analysis in their manager-data software, which directly gives us histogram of grain sizes. It should be noted that different statistics would lead to different results, but still it should allow us to compare the grain information quantitatively between different materials.



  813   Thu Jul 24 12:35:36 2014 xiaoyueDailyProgressCrackleSingle Crystalline Cu micropillar

Will the tiny modulation bring about crackles is a long lasting question for me. Since driving at force above the pinning barriers is the fundament to generate dislocation slip, I am thinking about using some well-studied material and investigate if, and how the small amplitude perturbation can overcome the threshold with time. My idea is to

1. take some characteristic stress-strain curves -- for literature comparison, basically to make sure my data makes sense

2. load the pillar close to yielding; this may be difficult because the smaller the sample, the more stochastic nature its mechanical property would carry, mainly because of the large statistical fluctuation caused by small ensemble of dislocations.

3. hold the indenter tip at the load, but apply oscillations using a built-in method used for measuring contact stiffness, and look for slip events over time.

I luckily inherited a single crystalline Cu sample. I electropolished the surface using electrolyte consists of 110 mL 85% phosphoric acid, 40 mL nitric acid, 50 mL 99.7% acetic acid, with applied voltage = 1.5V, current = 100 mA, T(heat stage) = 60 C. When reacting the solution gave off terrible yellow smoke and the solution turned from transparent to green and then to blue.. It should be noted that the reacted solution has a much higher temperature than target temperature 60 C because the process is exothermic, but it somehow worked, giving me smooth shiny sample surface. I tried FIBing pillars yesterday but with the current voltage /current I got some pudding-shape pillars... I need to consult people about the right working condition for Cu.

  819   Mon Aug 4 18:00:17 2014 xiaoyueDailyProgressCracklemicro cantilever

I made a micro-cantiliver out of SS340, single grain. Relocating the EBSD grain map in SEM is tricky, I used a self-defined coords system. However I will put the sample back for a EBSD analysis after making full use of this area:


The cantilever is of size 860 nm * 6 um which mimics the real blade in ratio width : length = 1:7.


I also made a micro-pillar (1 : 2.5 um) in order to compare the nano-pillar compressions to the nano-cantilever bending to see how the signature is different when the strain gradients are present.


Tests will be conducted soon. 

  820   Tue Aug 5 10:41:05 2014 xiaoyueDailyProgressCrackleMichelson Locked


From last Thu we are no longer able to lock the Michelson. Today we tried first with 0.5 gain instead of 1, and we added a resonant gain around 10 Hz, where the error signal showed a large peak. This gave us a reasonable lock. From there we measured and fit the plant transfer function and re-designed the compensators for the structures above 100 Hz. Applying the new compensator we were able to lock the Michelson fairly robust, increasing the gain to 2 (unity gain frequency at about 150 Hz)


It should be noted that if we keep increasing the gain to 3, there appeared to be some unstable structure around unity gain frequency. We also tried to increase gain at the other three resonance frequency peaks but it kicked the system to be unstable; we finally decided to use the simplest version of boost. An allipticlowpass filter at 600 Hz was also applied because high frequency resonances were getting unstable.

Now the lock acquisition procedure is:

1. Switch local damping on

2. Engage filters "lock", "notch1810"

3. Ramp up the gain to 0.5

4. Engage “Resgain”, “compensator1/2/3”

5. Ramp up the gain to 2

6. Engage the low pass and additional resonant gains at 30 Hz: “lowpass” and “boost”

We updated the autolocker accordingly. We started a data taking with common driving at 800 counts

  823   Thu Aug 7 12:13:32 2014 xiaoyueDailyProgressCrackleHunt ghost beam

Yesterday we vented the chamber and located a secondary beam on SYPD. We pushed it away from the sensing region by re-centering the main beams on both PDs. We were thinking of using iris to block the spurious beam but it clipped the reflection beam. Also we took care of two undamped beams that were dumped on the chamber wall. This helped a lot with the bump feature saw around 400-500 Hz.

After all of these tweaks the lock still worked! We increased the loop gain at ~11 Hz and ~16 Hz and this suppressed the resonance peaks seen in the error signal spectrum. When we were ready to do more adjustment the cables (taped on the wall) fell and we are going to fix it and pick everything up again today.


Xiaoyue, Gabriele 

The data collected during the night were not very good, since the interferometer kept unlocking very often. We can't get any crackle data out of them.

We then tweaked a bit more the interferometer, remeasured and refitted the high frequency compensators. We also cleaned all mirrors. We noticed that the shape of the high frequency structure changed after the cleaning, but they did not change if we moved the beam centering on the end mirrors, by realigning the Michelson to a different point.

We see a strange noise spectrum, in the form of a bump up to 400-500 Hz. This reminds us of spurious interference with a ghost beam. It also seems (but we are not so sure) that the size of the bump changes with the alignment. So, we maybe have some ghost beam interfering with our main beam. We checked that the bump is the same in both AP and SP photodiodes.

We're leaving the autolocker on, to check the lock robustness over night. We also replugged all seismometers, since we suspect that lock losses might eb caused by seismic shocks.


  829   Wed Aug 13 13:08:25 2014 xiaoyueDailyProgressCracklemicromechanical analysis of yielding

I compressed a pillar (D = 1.1 um, H = 2.5 um, made out of SS304 single grain) using G200 nanoindenter.


Using inflection point I got F_yield  = 0.3 mN, and knowing the pillar diameter to be 1 um we can estimate yield stress ~ 0.3 mN / pi (0.55 um)^2 = 316 MPa

However a more conventional definition for yielding point is the “0.2% offset” where people draw a line with slope of elasticity from 0.2% strain, and find the first cross over to be the yielding ~ 0.4 mN/ pi(0.55um)^2 = 421 MPa


I would also love to compare the pillar compression data with the indentation data.


In order to extrapolate yield stress information I need to convert the load vs. depth data to stress vs. strain ones. It involves a better knowledge of the indenter tip, as so far I got contradicting result from projected area function calibration and the tip radius claimed in the spec sheet (max projected area exceeds the claimed tip area). Also I need to learn more about how to find the actual “contact height” which excludes the non-plastic indentation from the machine loading depth.

  830   Sat Aug 16 17:16:05 2014 xiaoyueDailyProgressCrackleCOMSOL simulation

I used COMSOL to compute the stress distribution on our blades. I set fixed constraint and a boundary load on the block clamp surfaces as demonstrated in the figure. In simulation I used extremely fine free tetrahedral mesh. The first principle stress contour is plotted. We see that we have large amount of blade areas that are bearing stress over 80% of the micro mechanical yielding (~250 MPa).


  832   Wed Aug 20 21:17:34 2014 xiaoyueDailyProgressCrackleIncreasing driving amplitude

We were able to collect seven hours of data using driving amplitude 800 counts last night, and the first analysis of the data in a narrow quiet band does not show statistical difference between driving on and off states. We plan to take data with larger driving amplitude. I compared the error signal power spectrums for several candidate amplitudes and there are no distinctive features showing up. Also the system have stayed locked for ~20 mins with common drive amplitude being 1600 counts, so I updated the code and we are going to collect data with double the driving amplitude tonight. 


  833   Fri Aug 22 09:50:01 2014 xiaoyueDailyProgressCrackleCrackle2 born

 [Gabriele, Xiaoyue] We checked all the mechanical parts received. Although there are some problems, Crackle2 are officially born!


 And I updated my wallpaper:


  836   Wed Sep 3 10:28:34 2014 xiaoyueDailyProgressCrackleSign of non-linear noise

Before we had trouble locking the Michelson for long periods of hours. We found that the problem lies in the autolocker script which checks if the IFo is locked with two conditions: RMS of error signal below threshold, and also RMS of correction below threshold. But the threshold of the correction was set to 1500, which is less than our driving amplitude. Therefore the autolocker at some point believes the IFO is unlocked because the correction gets too large. We increased the correction threshold to 5000 and then it stayed locked without problems.

Thus for the past week we have collected data with driving amplitude of 2400, 3000, 4000, and within certain quiet bands, all of them are showing a sign of non-linear noise being modulated at 2FQ, which agrees with our prediction for a crackling noise due to the fast driving change. We are going to take  more data with various of driving amplitudes and see if there's a correlation between the noise and the driving power. For an expedient comparison, I analyzed the three data set in band 548 - 570 Hz. 


We believe that the 1FI noise is due to misalignment. It should be noted that analyzing different bands, different hours, will give different results for the 2FQ modulation. Also we should question why the sign of the noise power could flip.

  840   Wed Sep 10 10:39:46 2014 xiaoyueDailyProgressCrackleCrackle1 driving amplitude calibration

I first double checked if we are driving in a linear range.


Blade A

Blade B

Drive Amplitude (counts)

Shadow Sensor Reading (counts)

Oscilloscope Reading of SS output (mV)

Shadow Sensor Reading (counts)

Oscilloscope Reading of SS output (mV)


























Then using Eric's calibration (Elog 601) I calculated 1.97 nm /count for blade A and 1.59 nm /count for blade B. It should be noted that we have set DRVA gain = -1, DRVB gain = -1.19, so the effective driving is (0, 1, 2, 3, 4)k * 1.19 counts.

ELOG V3.1.3-