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  SUS Lab eLog, Page 33 of 38  Not logged in ELOG logo
ID Date Author Type Categoryup Subject
  1873   Wed Dec 9 18:03:31 2020 PacoDailyProgressGeneralLab organization

In the process of adding a PC/controls, and other related instruments, reorganized items in the lab. Threw out some boxes and stored cabling and unused power dock. Moved the sticky mat and put out large trash bin. Organized electronics rack to which a Sorensen (DCS33-33) power supply was attached. For this, took a 14 AWG wire (should be fine up to 15 A at 115 VAC) and cut plug end. Then connect neutral and live as indicated by the rear of the panel and add chassis ground. Tested DC output voltage of 3 V and it works ok.

There are now two workstations in the lab attached to the same monitor (VGA and DVI ports), and it is ok to ssh from one to the other. They both now have fresh debian 10 installs.

  1897   Tue Jan 26 11:47:12 2021 PacoDailyProgressGenerallow quality PDH error signal

After getting what looked like a decent cavity reflection signal, installed RFPD yesterday. For this, removed the lens that was right before the PD because the RFPD area is large enough, but keep ND filter in place. Powered with +- 18 VDC and monitor DC out on the scope, and RF out is sent to the IF of the mixer in the PDH box. For the LO, split the Marconi RF output and connected the demodulated signal into Ch2 of the scope in hopes that there was an error signal.

A hint of the error signal is present (blue trace below), although deeply buried in line noise (and harmonics up to ~180 Hz) so there really are two things to optimize now -->

  1. Line noise (hunting for ground loops or equipment, e.g. power supplies, analyze LO spectrum before/after splitters, mixers, etc...)
  2. Mode matching (this was the first reaction, as improving the cav refl SNR by means of mode matching makes a better pdh err signal)

Other things attempted so far -->

  • Switched mixers, splitter, and RF cables
  • Bypass the phase shifter completely
  • Scan LO phase
  • Floated RFPD power supply
  • Floated PDH box power supply (really only affecting the phase shifter if anything, though unlikely to matter at this point)
Attachment 1: poor_PDH_err.jpg
  1904   Wed Feb 24 17:42:49 2021 PacoDailyProgressGeneralDOPO locking and SHG

Locking update

The plan during these past few days has been to have fast control loop of the cavity (locked to laser using PZT, which succeeded using SR560s), and slow control loop where the laser temp. actuator is fed back the integrated PZT input to follow the long term cavity drift. For that, have been messing around with the high-level (GUI) API of PyRPL, with basically no success. In fact currently the RedPitaya cannot even replace the SR560 fast controls, which probably has to do with the +- 1 Volt limits on the RP input/output.

Another issue is that any loop gain depends on the REFL power, which will be at some point slowly ramped up to cross the OPO operating threshold, and while there is a (PBS + HWP) knob on how much light is hitting the RFPD, the lock is not yet good enough to keep up with the slow human action.

First light from nonlinear conversion

WIth the cavity locked, and under ~ 220 mW of pump (right before the cavity, i.e. 1.3 Amps of current on the driver), noticed a tiny green dot coming from within the crystal oven. This is pretty great news in terms of phase matching, but not necessarily so in terms of the right parametric conversion process (understanding is that SHG is easier to attain even with single pass). See tiny green spot as caught using phone camera in the attachment.

Attachment 1: shg.jpg
  1911   Thu May 20 17:09:43 2021 KojiSummaryGeneralAnother Heimann Sensor

Another Heimann Sensor / Boston Electronics delivered to Paco.
This unit (purchased May 2020/ / Delivered Aug 5th, 2020) has a FZ-Si window on it.
We don't know how it is.

Attachment 1: P_20210520_151126.jpg
  1930   Tue Jan 10 23:40:17 2023 KojiLab InfrastructureGeneralHeavy item transport - preparation 

See http://nodus.ligo.caltech.edu:8080/Mariner/121

  1931   Thu Jan 12 11:51:49 2023 KojiLab InfrastructureGeneralHow to move the large engine hoist through the narrow door

How to move the large engine hoist through the narrow door

See http://nodus.ligo.caltech.edu:8080/Mariner/122

  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

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.
Attachment 1: CavityRingdown.png
Attachment 2: CavityRingdown.m
% CavityRingdown.m
% Eqn 41 of 
% "Doppler-induced dynamics of fields in Fabry–Perot
% cavities with suspended mirrors", Malik Rakhmanov (2000).
% http://www.ligo.caltech.edu/docs/P/P000017-A.pdf

clear all

% read in ringdown timeseries:
at = importdata('tek00000.csv');
... 121 more lines ...
  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


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):


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.

Attachment 1: Residuals_Spirals.pdf
  563   Tue Aug 21 09:32:52 2012 nicolasDailyProgressNoise BudgetPrototype Cryogenic Cavity Noise

The attached PDF shows the thermal noise of a short, low mass silicon cavity.

The thermal noise uses the gwincdev BQuad suspension noise term, I've disabled all the stages except the last (so it is a simple pendulum). The frequency noise is the noise budget of Dmass' silicon refcav.

The mass is 10g, the cavity length is 0.1m. The ribbons are 2mm by 0.05mm, 0.5m long.

I made them so thin because for some reason the gwinc model starts going nuts with the violin modes at high frequencies. (you can see that above ~150Hz). The frequency where it goes nuts comes down lower if I make them thicker. I don't know what's happening in the model but I guess it's not physical.

So this experiment looks a little like Thomas Corbitt's cantilever, it's not so similar to what would go in LIGO but it makes the thermal noise big enough to be seen above frequency noise.

Attachment 1: cryosus10g.pdf
  567   Wed Aug 29 11:36:46 2012 nicolasDailyProgressNoise Budgetgwinc-dev BQuad model doesn't like thick ribbons

In order to accentuate the thermal noise in a silicon test cavity, it would be nice to make the ribbons a little bit thicker. Sadly, the BQuad thermal noise model seems to explode when the fibers get thicker.

The three plots I will show have the following parameters in common:

4 fibers, single pendulum silicon suspension @120K. 10g mirror mass, 5cm fiber length, 2cm cavity length. The fiber width is 2mm and the fiber thickness varies in the three plots.

The first shows a fiber thickness of 0.05mm. The second has 0.1mm, and the third is 0.2mm.

As one can see, the model sort of goes more and more nuts as the thickness is increased. I don't really understand the model enough to know why this is the case, but it seems that to have a believable noise budget we might need to make a thermal noise model from scratch, rather than using gwincdev.

Attachment 1: shortcryo1.pdf
Attachment 2: shortcryo2.pdf
Attachment 3: shortcryo3.pdf
  568   Wed Aug 29 11:43:55 2012 nicolasDailyProgressNoise Budgetmatlab source

The source for what I've been using to calculate thermal noise.

Attachment 1: protocryo.tar.gz
  632   Fri Apr 26 16:04:56 2013 taraNoise HuntingNoise Budgetfrequency noise requirement for laser used in crackle experiment

I made an estimate for frequency noise requirement for a laser that can be used in crackle experiment. With some assumptions, I came up with df = 3x102 [Hz/rtHz ] for the requirement.

 The two beams from both arms are recombined at the output port of a Michelson interferometer. If it is operated at dark port, the output signal will be linear with the differential length between the two arms.

some assumptions in the calculation:

  • Operating at darkport
  • The laser has frequency = f0 + df  (carrier + noise)
  • mismatch between the two arms is ~ 1mm
  • aim for SNR = 1, no integration time.
  • crackle signal is ~10-15 m/rtHz, this is actually the shot noise limit of the current setup.


This will be a requirement for the planned ecdl.

Is a HeNe laser good enough? I'm not sure about HeNe frequency noise level, and I haven't found it in literature that much. I checked here,see fig 5, HeNe f noise is not so bad compared to NPRO noise (10^4 /f Hz/rtHz).This feels a bit counter intuitive. But if it is real, it should be ok for the measurement around 100 Hz and above.

  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. 


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


Attachment 1: noisebudget.pdf
Attachment 2: diagram.pdf
Attachment 3: DACnoise-comparison.pdf
  1850   Mon Apr 20 22:56:30 2020 ranaDailyProgressNoise BudgetNoisemon:DAC noise analysis from L1 and H1

for some reason the DAC noise estimate is too high, it can't really be so large compared to the real DARM curve (see the noise budget curves from LLO - there are other noise sources besides DAC noise)

some possibilities:

  1. maybe the DAC noise calibration into meters is wrong? I can't tell from the code where this came from. It would be good to put a comment in there.
  2. perhaps most of this noise is actually angular noise. The ASC control signals are adjusted by tuning the digital coefficients (before MASTER_OUT) so that the angle to length coupling is minimized. I think something like this has to be done to remove the angular noise from the DAC noise estimate.
  3. internal saturation of the DAC noise monitor?

I hve modified the code to plot nicer and also to remove some divide by zero problems. There is also still some warnings about other divide by zero - those should probably be fixed by examining how better to handle it when the coherence goes to zero.

Attachment 1: DACnoise-comparison.pdf
Attachment 2: dacNB.zip
  1947   Tue Nov 14 16:14:11 2023 ranaMiscNoise Budgettriples

we only care about PRM, PR2, PR3, BS, SR3, SR2, SRM, so you should eliminate all other optics from the plots.

Then just plot the HSTS to get started and we can see how they compare.

  1948   Tue Nov 14 22:18:15 2023 murtazaMiscNoise Budgettriples

The spectra for damp out for the following optics
- small triples {PR2, PRM, SR2, SRM} (Attachment 1)
- large triples {PR3, SR3} (Attachment 2)
- beamsplitter {BS} (Attachment 3)

For pwelch(), I was not taking into account the DC offset which is why I was getting funky plots (spectral leakage). I corrected for it, no more interpolation anymore!

Edit: I have changed the yaxis label for all plots to counts/rHz for now since I do not know the exact calibration

Attachment 1: Small_Triples_DAMP_OUT_Spectra.pdf
Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf Small_Triples_DAMP_OUT_Spectra.pdf
Attachment 2: Large_Triples_DAMP_OUT_Spectra.pdf
Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf Large_Triples_DAMP_OUT_Spectra.pdf
Attachment 3: BS_DAMP_OUT_Spectra.pdf
BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf BS_DAMP_OUT_Spectra.pdf
  1949   Wed Nov 15 09:48:05 2023 ranaMiscNoise Budgettriples

Can you explain how you calibrated the control signals into displacement units? It would be fine to start if you could just plot them with the y-axis in counts/rHz for now, unless you have good confidence in the calibration.

  1950   Thu Nov 16 13:15:06 2023 murtazaMiscNoise Budgettriples

Small Triple Suspension Trial Filter Design

tldr: From the Damp_OUT spectrum of the small suspensions, PRM had a relatively larger magnitude in the 10-30Hz bandwidth. I thus choose to design filters for them using PRM as a reference.
While designing for PRM, I used the site noise asd (DAMP_IN*(1 + OLG)) given as input to the controller instead of using white noise while desinging them.
The design objectives that were met are as follows:

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth or better
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of ~30 degrees and gain margins of ~3dB or better

The same design principles were used for PRM as for PR3 (explained in this elog). Here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 
Note: I had an an interesting time designing the Roll Mode, bumping the peaks to increase damping on them after setting the UGF at 2.75 would increase the ringdown period. I reverted to using a similar overall "magnitude" that they used at the sites and added notches for reducing noise in the required bandwidth. The new filter still better on the ringdown (15 seconds lesser) so I'll leave it at that for now and make changes if required later. 




Velocity Damping






zpk(0, -2*pi*pair(150, 80), 1)


notch(10,10,5), notch(15,10,9), notch(20,10,11)

bump(4.5, 3, 2)





zpk([0], -2*pi*pair(80, 30), 1)

notch(10,12,5), notch(15,12,6), notch(20,12,7)

bump(4.5, 5, 3.5), bump(0.674, 5, 5)




zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,6.5), notch(15,12,9), notch(20,12,11), notch(25,12,5)

bump(5.5, 2, 1.5)

ellip(6, 3, 30, 2*pi*[24, 30],'stop', 's')



zpk([0], -2*pi*pair(100, 30), 1)

notch(10,12,5), notch(15,12,8), notch(20,12,15)

bump(4.5, 5, 1.4), bump(4, 6, 7)




zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(15,10,7), notch(20,10,10)

bump(1.006, 10, 6), bump(6.5, 10, 2)




zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(15,12,5), notch(20,12,5.5)

bump(1.51, 5, 10), bump(4, 5, 2)

ellip(6, 3, 50, 2*pi*[35, 45],'stop', 's')


The pdfs have been arranged as following for each DOF. (Comparisons are between the site filter design and the trial filter design (need to come up with a better terminology for this)).

  • Attachment 1 shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Attachement 2 shows a comparison of the filter designs in the bandwidth of interest
  • Attachment 3 shows the open loop transfer function (P(s)*C(s)) with phase and gain margin (minimum stability margins)
  • Atttachment 4 shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: L_smallASDnRD1115.pdf
L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf L_smallASDnRD1115.pdf
Attachment 2: L_smallFilter1115.pdf
L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf L_smallFilter1115.pdf
Attachment 3: L_smallComBodeOL1115.pdf
L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf L_smallComBodeOL1115.pdf
Attachment 4: L_smallBodeOL1115.pdf
L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf L_smallBodeOL1115.pdf
  1957   Wed Nov 22 13:58:13 2023 murtazaMiscNoise BudgetLIGO Triple Damping Loops

Small Triple Suspension Trial Filter Design (SR2 Baseline)

tlpr: Referencing the triple noise breakdown from this alog , SR2 has the highest noise amongst the smaller suspensions. I had designed the trial filters eariler using PRM as a baseline, but since the optics couple against DARM loop differently, I am switching to this new baseline
While designing for SR2, I used the site noise asd (seismic noise + sensor noise = DAMP_IN*(1 + OLG)) given as input to the controller instead of using white noise while desinging them. I had to lose out on the ringdown times this time, still doing comparable to the sites. Phase and gain margins almost at design criterion now.
I've also added bumps to account for the "SECRET COSTS" at low frequencies; however, since I had to reduce the gain on the damping filters, they're relatively lower in magnitude than the site filters (most of these peaks are around the mechanical resonances at the lower frequencies; getting similar features in the ringdown could be a good measure of these bumps doing the job although being lower in magnitude, maybe :$).
The site noise asd was produced using a timeseries
obtained from 11/22/2023, 12am PST for a duration of 1 hour
The design objectives that were met are as follows:

  • Lower noise by a factor ~10 in the 10-30Hz bandwidth or better
  • Achieve similar ringdowns for the impulse response
  • Have phase margins of ~30 degrees and gain margins of ~3dB or better

The same design principles were used for SR2 as for PRM (explained in this elog). Here’s the filter design for each DOF. (The electronics gain has not been accounted for here, it must be added to the filter design). The filters work with negative feedback with a gain of 1. 



Velocity Damping






zpk(0, -2*pi*pair(150, 80), 1)





bump(0.67, 5, 10),

bump(4.5, 3, 11)





zpk([0], -2*pi*pair(80, 30), 1)

notch(10,12,4), notch(10,12,3),


notch(20,12,4), notch(20,12,5)

bump(4.5, 5, 3),

bump(0.674, 5, 6)




zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,5), notch(10,12,5),


notch(20,12,10), notch(25,12,10)

bump(0.678, 5, 5),

bump(6, 5, 5)

ellip(6, 3, 30, 2*pi*[24, 30],'stop', 's')



zpk([0], -2*pi*pair(100, 70), 1)

notch(10,12,4), notch(10,12,4),


notch(20,12,5), notch(20,12,5)

bump(1.98, 5, 3),

bump(5, 5, 3)




zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,5), notch(10,10,5),


notch(20,10,5), notch(20,10,6)

bump(1.006, 10, 6),

bump(7, 10, 8)




zpk([0], -2*pi*pair(100, 50), 1)

notch(10,10,3), notch(10,10,2),


notch(20,12,3), notch(20,12,4)

bump(1.52, 7, 18),

bump(4, 5, 5)

ellip(6, 3, 50, 2*pi*[35, 45],'stop', 's')


The pdf has been arranged as following for each DOF. (Comparisons are between the existing site filter design and the trial filter design (sticking to this terminology, psych).

  • Figure 1 shows a comparison of the sensor noise ASD (DOF sensor noise on M1 to DOF Displacement on M3) in the bandwidth of interest and ringdown periods for the impulse response. (FOR Longitudinal DOF, the impulse input was ground, for the remaining DOFs, the input was at M1). 
  • Figure 2 shows a comparison of the filter designs in the bandwidth of interest
  • Figure 3 shows the open loop transfer function (P(s)*C(s)) with phase and gain margin (minimum stability margins)
  • Figure 4 shows a comparison of the open loop transfer functions (P(s)*C(s)).
Attachment 1: Small_Triples_Filter_Design_1122.pdf
Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf Small_Triples_Filter_Design_1122.pdf
  5   Fri Oct 19 16:11:38 2007 pkpOtherOMCOMC PZT response
Sam and I locked the laser to the OMC cavity and looked at the error signal as a function of the voltage applied to the OMC PZT.
Here are two plots showing the response as a function of frequency from 1 kHz to 100 kHz and another high-res response in the region of 4.5 kHz to 10 kHz.
Attachment 1: fullspec.jpg
Attachment 2: 4.5to10.jpg
Attachment 3: 4.5to10.pdf
Attachment 4: fullres.pdf
  6   Sat Oct 20 11:54:13 2007 waldmanOtherOMCOMC and OMC-SUS work
[Rich, Chub, Pinkesh, Chris, Sam]

Friday the 18th was a busy day in OMC land. Both DCPDs were mounted to the glass breadboard and the OMC-SUS structure was rebuilt to the point that an aluminum dummy mass is hanging, unbalanced. The OSEMs have not be put on the table cloth yet, but everything is hanging free. As for the DCPDs, if you recall one beam is 3mm off center from the DCPD tombstone. Fortunately, one DCPD is nearly 3mm offcenter from the case in the right direction, so the errors nearly cancel. The DCPD is too high, so the beam isn't quite centered, but they're close. We'll get photos of the beam positions in someday. Also, the DC gain between the two PDs is, at first glance, different by 15%. DCPD1, the one seen in transmission has 315 mV of signal while DCPD2 has 280 mV. Not sure why, could be because of beam alignment or tolerances in the Preamp or the angle incident on the diode or the QE of the diodes. The glass cans have *not* been removed.
  8   Mon Oct 22 19:27:14 2007 pkpOtherOMCPZT calibration/ transfer function.
We measured the PZT transfer function by comparing the PZT response of the circuit with the cavity in the loop, with that of the circuit without the cavity in the loop. Basically measure the transfer function of the whole loop with the laser/PZT and Op-amps in it. Then take another measurement of the transfer function of everything else besides the PZT and from both these functions, we can calculate the PZT response.

The calibration was done by using the error signal response to a triangular wave of volts applied to the PZT. A measurement of the slope of the error signal , which has three zero-crossings as the cavity sweeps through the sidebands, gives us the Volts/Hz response. In order to derive a frequency calibration of the x axis, we assume that the first zero crossing corresponds to the first side band (-29.5 MHz) and the third one corresponds with the other sideband (+29.5 MHz). And then by using the fact that we know the response of the cavity to a constant frequency shift, we can use the Volts/Hz measurement to calculate the Volts/nm calibration. The slope that was calculated was 3.2e-6 V/Hz and using the fact that the cavity is 1 m in length and the frequency is 1064 nm, we get a calibration of 0.9022 V/nm.

Attachment 1: calib.pdf
Attachment 2: calibpzt2.pdf
Attachment 3: all2.pdf
Attachment 4: noPZT2.pdf
  9   Tue Oct 23 09:01:00 2007 ranaOtherOMCPZT calibration/ transfer function.
Are you sure that the error signal sweep is not saturated on the top ends? This is usually the downfall
of this calibration method.
  14   Thu Oct 25 17:52:45 2007 waldmanOtherOMCOMCs with QPDs
[Rich, Chub, Pinkesh, Sam]

Yesterday we got the QPD, OTAS, and PZT cabling harness integrated with the OMC. We found a few things out, not all of them good. The QPDs went on no problem and could be fairly well aligned by hand. We "aligned" them by looking at all four channels of the QPD on the scope and seeing that there is signal. Since the beam is omega = 0.5 mm, this is a reasonable adjustment. We then connected the OTAS connector to the OTAS and found that the heater on the OTAS was bonded on about 30 degrees rotated from its intended position. This rotated the connector into the beam and caused a visible amount of scattering. This wasn't really a disaster until I removed the connector from the heater and broke the heater off of the aluminum parts of the OTAS. Two steps backwards, one step forward. After the OMC, OMC-SUS integration test we will re-bond the heater to the aluminum using VacSeal. In the meantime, the OMC has been moved to Bridge 056 for integration with the OMC-SUS. More on that as we make progress.
  16   Thu Oct 25 23:35:36 2007 waldmanOtherOMCHang the OMC!
[Pinkesh, Sam]

We tried, convicted and hung the OMC today. The OMC was found guilty of being overweight, and unsymmetrically balanced. The unsymmetry was kind of expected and was corrected with a hefty stack of counterweights positioned over the counterweighting holes. The stacks will be measured at some future date and correctly sized objects machined. The overweightness showed up when the level hanging breadboard was about 5 mm low. This showed up in the board height above the table as well as the OSEM flag positions within their holes. The problem was remedied with a liposuction of the intermediate mass. We removed both small vertical cylinder weights that Chris added, and then we removed the heavy steel transverse weight that can be used to adjust the tip around the long axis (I forgot what its called).

The top of the breadboard ended up about 154 mm off the table. The breadboard is 39 mm thick, and the optics are centered (30 - 12.7) = 17.3 mm below the surface for a as hanging beams height of 154 -39 - 17.3 = 97.7 mm or about an 0.150 inches lower than we were aiming for. Can I get a refund?

We screwed up in multiple ways:
  • The slotted disks that capture the wires do not have the alignment bore used to center the wire in the hole
  • We didn't correctly route the far field QPD cable so it runs funny
  • We didn't have a tool which could be used to get two of the DCPD preamp box mounting screws (which are M3's chub!)
  • We don't have the cable clamps to tie off the electrical cables to the intermediate mass
  • We don't have any of the cabling from the OMC-SUS top to the rack so we can't test anything
  • We haven't uploaded pretty pictures for all to see

We left the OMC partially suspended by the OMC-SUS and partly resting on the installation lab jacks which are currently acting as EQ stops. After we fix the cabling we will more permanently hang it. PS, It looks like the REFL beam extraction will be tricky so we need to get on that....
Attachment 1: IMG_1483.jpg
Attachment 2: IMG_1481.jpg
  19   Fri Oct 26 17:34:43 2007 waldmanOtherOMCOMC + earthquake stops

[Chub, chris, Pinkesh, Sam]

Last night we hugn the OMC for the first time and came up with a bunch of pictures and some problems. Today we address some of the problems and, of course, make new problems. We replaced the flat slotted disks with the fitted slotted disks that are made to fit into the counterbore of the breadboard. This changed the balance slightly and required a more symmetric distribution of mass. It probably did not change the total mass very much. We did find that the amount of cable hanging down strongly affected the breadboard balance and may also have contributed to the changing balance.

We also attached earthquake stops and ran into a few problems:

  • The bottom plate of the EQ stops is too thick so that it bumps into the tombstones
  • The vertical member on the "waist" EQ stops is too close to the breadboard, possibly interfering with the REFL beam
  • The "waist" EQ stops are made from a thin plate that doesn't have enough thickness to mount helicoils in
  • Helicoil weren't loaded in the correct bottom EQ stops
  • The DCPD cable loops over the end EQ stop looking nasty but not actually making contact

However, with a little bit of jimmying, the EQ stops are arrayed at all points within a few mm of the breadboard. Meanwhile, Chub has cabled up all the satellite modules and DCPD modules and Pinkesh is working on getting data into the digital system so we can start playing games. Tonight, I intend to mount a laser in Rana's lab and fiber couple a beam into the 056 room so we can start testing the suspended OMC.
  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.
  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.
Attachment 1: SS.pdf
Attachment 2: SS.gif
  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.
Attachment 1: QPD_SignalSpectrum.pdf
Attachment 2: QPD_SignalSpectrum.gif
  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.
Attachment 1: 071101_PZT_firstLoopSweep.pdf
Attachment 2: 071101_PZT_firstLoopSweep.gif
Attachment 3: 071101_OMC_FirstLock_spectra.pdf
Attachment 4: 071101_OMC_FirstLock_spectra.gif
  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.
Attachment 1: 071102_OMC_LockedDCPD.gif
Attachment 2: 071102_OMC_LockedDCPD.pdf
  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.
Attachment 1: 071103_DitherLock_sweep.png
Attachment 2: 071103_DitherLock_sweep.pdf
Attachment 3: 071103_HiResPZTDither_sweep.png
Attachment 4: 071103_HiResPZTDither_sweep.pdf
Attachment 5: 071103_HiResPZTDither_sweep2.png
Attachment 6: 071103_HiResPZTDither_sweep2.pdf
  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.
Attachment 1: 071103DitherShape.png
Attachment 2: 071103DitherZoom.png
Attachment 3: 071103LSCShape.png
Attachment 4: 071103DitherShape.pdf
Attachment 5: 071103DitherZoom.pdf
Attachment 6: 071103LSCShape.pdf
Attachment 7: 071103LoopShape.pdf
  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.
Attachment 1: 07110_DithertoVmonAC_sweep2-0.png
Attachment 2: 071105_LSCtoVmonDC_sweep4-0.png
Attachment 3: 07110_DithertoVmonAC_sweep2.pdf
07110_DithertoVmonAC_sweep2.pdf 07110_DithertoVmonAC_sweep2.pdf
Attachment 4: 071105_LSCtoVmonDC_sweep4.pdf
071105_LSCtoVmonDC_sweep4.pdf 071105_LSCtoVmonDC_sweep4.pdf
  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....
  82   Thu Nov 8 00:55:44 2007 pkpUpdateOMCSuspension tests
[Sam , Pinkesh]

We tried to measure the transfer functions of the 6 degrees of freedom in the OMS SUS. To our chagrin, we found that it was very hard to get the OSEMs to center and get a mean value of around 6000 counts. Somehow the left and top OSEMs were coupled and we tried to see if any of the OSEMs/suspension parts were touching each other. But there is still a significant coupling between the various OSEMs. In theory, the only OSEMS that are supposed to couple are [SIDE] , [LEFT, RIGHT] , [TOP1, TOP2 , TOP3] , since the motion along these 3 sets is orthogonal to the other sets. Thus an excitation along any one OSEM in a set should only couple with another OSEM in the same same set and not with the others. The graphs below were obtained by driving all the OSEMS one by one at 7 Hz and at 500 counts ( I still have to figure out how much that is in units of length). These graphs show that there is some sort of contact somewhere. I cant locate any physical contact at this point, although TOP2 is suspicious and we moved it a bit, but it seems to be hanging free now. This can also be caused by the stiff wire with the peek on it. This wire is very stiff and it can transmit motion from one degree of freedom to another quite easily. I also have a graph showing the transfer function of the longitudnal degree of freedom. I decided to do this first because it was simple and I had to only deal with SIDE, which seems to be decoupled from the other DOFs. This graph is similar to one Norna has for the longitudnal DOF transfer function, with the addition of a peak around 1.8 Hz. This I reckon could very be due to the wire, although it is hard to claim for certain. I am going to stop the measurement at this time and start a fresh high resolution spectrum and leave it running over night.

There is an extra peak in the high res spectrum that is disturbing.
Attachment 1: shakeleft.pdf
Attachment 2: shakeright.pdf
Attachment 3: shakeside.pdf
Attachment 4: shaketop1.pdf
Attachment 5: shaketop2.pdf
Attachment 6: shaketop3.pdf
Attachment 7: LongTransfer.pdf
LongTransfer.pdf LongTransfer.pdf LongTransfer.pdf
Attachment 8: Shakeleft7Nov2007_2.pdf
Attachment 9: Shakeleft7Nov2007_2.png
  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.)
Attachment 1: Fig1.png
Attachment 2: Fig2.png
Attachment 3: Fig4.png
Attachment 4: Fig2.pdf
Attachment 5: Fig1.pdf
Attachment 6: Fig4.pdf
Attachment 7: ResonanceData.zip
  87   Fri Nov 9 00:23:12 2007 pkpUpdateOMCX and Z resonances
I got a couple of resonance plots going for now. I am still having trouble getting the Y measurement going for some reason. I will investigate that tommorow. But for tonight and tommorow morning, here is some food for thought. I have attached the X and Z transfer functions below. I compared them to Norna's plots - so just writing out what I was thinking -

Keep in mind that these arent high res scans and have been inconviniently stopped at 0.5 Hz Frown.

Z case --

I see two small resonances and two large ones - the large ones are at 5.5 Hz and 0.55 Hz and the small ones at 9 Hz and 2 Hz respectively. In Norna's resonances, these features arent present. Secondly, the two large peaks in Norna's measurement are at 4.5 Hz and just above 1 Hz. Which was kind of expected, since we shortened the wires a bit, so one of the resonances moved up and I suppose that the other one moved down for the same reason.

X case --

Only one broad peak at about 3 Hz is seen here, whereas in Norna's measurement, there were two large peaks and one dip at 0.75 Hz and 2.5 Hz. I suspect that the lower peak has shifted lower than what I scanned to here and a high res scan going upto 0.2 Hz is taking place overnight. So we will have to wait and watch.

Pitch Roll and Yaw can wait for the morning.
Attachment 1: Xtransferfunc.pdf
Xtransferfunc.pdf Xtransferfunc.pdf Xtransferfunc.pdf
Attachment 2: Ztransferfunc.pdf
Ztransferfunc.pdf Ztransferfunc.pdf Ztransferfunc.pdf
  93   Mon Nov 12 10:53:58 2007 pkpUpdateOMCVertical Transfer functions
[Norna Sam Pinkesh]

These plots were created by injected white noise into the OSEMs and reading out the response of the shadow sensors ( taking the power spectrum). We suspect that some of the additional structure is due to the wires.
Attachment 1: VerticalTrans.pdf
VerticalTrans.pdf VerticalTrans.pdf VerticalTrans.pdf VerticalTrans.pdf
  99   Wed Nov 14 07:48:38 2007 nornaOmnistructureOMCOMC Cable dressing
[Snipped from an email]

1) Last Friday Pinkesh and I set the OMC up with only the top three OSEMs and took a vertical transfer function. We had removed the other OSEMs due to difficulty of aligning all OSEMs with the weight of the bench etc bringing the top mass lower than the tablecloth can accommodate. See attached TF.Clearly there are extra peaks (we only expect two with a zero in between) and my belief is that at least some of them are coupling of other degrees of freedom caused by the electrical wiring. Pinkesh and I also noticed the difficulty of maintaining alignment if cables got touched and moved around. So.....

2) Yesterday Dennis and I took a look at how much moving a cable bundle around (with the peak shielding) changed the DC alignment. In a not too precise experiment ( using HeNe laser reflecting off the bench onto a surface ~ 1 metre away) we saw that we could reposition the beam one or two mm in yaw and pitch. This corresponds to ~ one or two mrad which is ~ the range of the OSEM DC alignment. We discussed possibility of removing the cabling from the middle mass, removing the peak and taking it from the bench directly to the structure above. I asked Chub if he could make an equivalent bundle of wires as those from the two preamps to see what happens if we repeat the "moving bundle" experiment. So...

3) Today Chub removed the cabling going to the preamps and we replaced it with a mock up of wire bundle going directly from the preamps to the structure above. See attached picture. The wires are only attached to the preamp boxes weighted down with masses but the bundle is clamped at the top. We repeated the "wiggle the bundle" test and couldnt see any apparent movement ( so maybe it is at most sub-mm). The cable bundle feels softer.

The next thing Chub did was to remove the second bundle ( from photodiodes, heater, pzt) from its attachment to the middle mass and strip off the peek. It is now also going to the top of the structure directly. The whole suspension now appears freer. We discussed with Dennis the "dressing " of the wires. There are some minor difficulties about how to take wires from the bright side to the dark side, but in general it looks like that the wires forming the second "bundle" could be brought to the "terminal block" mounted on the dark side and from there looped up to the top of the structure. We would have to try all this of course to see the wiring doesnt get in the way of other things (e.g. the L and R OSEMs). However this might be the way forward. So...

4) Tomorrow Pinkesh and I will check the alignment and then repeat the vertical transfer function measurement with the two bundles as they are going from bench to top of structure. We might even do a horizontal one if the middle mass is now within range of the tablecloth.
We can then remove preamp cables completely and lay the second bundle of cables on the optical bench and repeat the TFs.

The next thing will be to weigh the bench plus cables. This will allow us to
a) work out what counterbalance weights are needed - and then get them manufactured
b) firm up on how to handle the extra mass in terms of getting the masses at the correct height.

And in parallel Chub will work on the revised layout of cabling.

Looking a little further ahead we can also get some stiffness measurements made on the revised bundle design ( using Bob's method which Alejandro also used) and fold into Dennis's model to get some sanity check the isolation.

I think that's it for now. Comments etc are of course welcome.

Attachment 1: OMC-11-13-07_011.jpg
Attachment 2: VerticalTrans.pdf
VerticalTrans.pdf VerticalTrans.pdf VerticalTrans.pdf VerticalTrans.pdf
  102   Wed Nov 14 16:54:54 2007 pkpUpdateOMCMuch better looking vertical transfer functions
[Norna Pinkesh]

So after Chub did his wonderful mini-surgery and removed the peek from the cables and after Norna and I aligned the whole apparatus, the following are the peaks that we see.
It almost exactly matches Norna's simulations and some of the extra peaks are possibly due to us exciting the Roll/longitudnal/yaw and pitch motions. The roll resonance is esp prominent.

We also took another plot with one of the wires removed and will wait on Chub before we remove another wire.
Attachment 1: VerticalTransPreampwireremovedNov142007.pdf
VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf VerticalTransPreampwireremovedNov142007.pdf
Attachment 2: VerticalTranswiresclampedNov142007.pdf
VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf VerticalTranswiresclampedNov142007.pdf
  105   Thu Nov 15 17:09:37 2007 pkpUpdateOMCVertical Transfer functions with no cables attached.
[Norna Pinkesh]

The cables connecting all the electronics ( DCPDs, QPDs etc) have been removed to test for the vertical transfer function. Now the cables are sitting on the OMC bench and it was realigned.
Attachment 1: VerticaltransferfuncnocablesattachedNov152007.pdf
VerticaltransferfuncnocablesattachedNov152007.pdf VerticaltransferfuncnocablesattachedNov152007.pdf VerticaltransferfuncnocablesattachedNov152007.pdf VerticaltransferfuncnocablesattachedNov152007.pdf
  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.

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