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ID Date Author Typedown Category Subject
  388   Wed Nov 10 20:04:13 2010 taraSummaryPMCoptical gain vs Vrf for side bands

 I checked that the optical gain in PMC loop increases as the power in the sideband increases. The result is 10.7 dB/V.


This measurement is for checking how much gain (in optical path) will we get from changing power in the side bands.

The excitation is sent to EXT DC channel on PMC. Reference signal is at HV mon, response is picked up at Mix mon.

This TF includes PZT and OPT paths, PZT TF should remain the same independent from the side band power.


I vary the RF voltage, and adjust the gain slider for maximum stability.  The gain setup should not matter

in the TF part we are measuring as long as the loop is stable.


I measured the gain at 3 different frequencies, 290.8 Hz, 1.035 kHz, 5.09 kHz where the TF look reasonable and smooth.

(The loop UGF is ~ 500-900 Hz, Thus the data at 1k and 5 kHz are nicer than that of 290 Hz)

 the slopes from each fit are


290 Hz 10.3 dB/V
1.035 kHz 10.72 dB/V
5.09 kHz 10.84 dB/V


The results are fairly linear in our region (RF between 4.8 to 5.9 V). The gain slider for this voltage range is between 13 - 20 dB.

At higher RF voltage, PMC_RCTRANSPD starts to drop significantly.

At lower RF voltage, the gain is too low.


This means we can increase the gain in OPT TF up to 10 dB by adjusting RF voltage (increase side band power)

Attachment 1: dBvsV.png
  389   Wed Nov 10 22:36:59 2010 taraSummaryPMCcurrent PMC's OLG TF

The current plot for PMC's OLG TF is plotted below. The RF V is 6V, Gain slider is 14 dB.


The UGF is 820 Hz with phase margin (PM) = 180 - 53 = 127 degree.


At higher gain slider setup, the system starts to oscillate. One possible cause is the peak near 10^4 Hz which

might be the PZT's resonance frequency.

Without the notch the total gain we can increase will be limited by the peak.

I'll make a notch to damp it down.

The current spec will be ~20dB notch at 12.5 kHz, FWHM ~1kHz


From current setup, the optical TF should be + 16.5 dB flat, and the gain added by the gain slider is +14 dB.

previous setup we have opt TF = -5 dB and +30 dB from gain slider.

So we have improved the overall gain by ~5 dB and to UGF increased from 530 to 830 Hz.


Attachment 1: TF_2010_11_10.png
  424   Fri Dec 10 01:14:08 2010 taraSummaryRefCavRCAV/ACAV poles

I analyzed the pole for RCAV and ACAV from 2010_12_06 entry. ACAV has a pole at  54 kHz, RCAV pole is at 38kHz.


Cavity pole = FWHM/2. Knowing cavity pole and FSR, we can calculate a cavity's finesse (= FSR/ pole). These values

will be used when we simulate the TF of the system

We amplitude modulated the laser intensity via EAOM, and measured the TF between RCAV_trans_PD and PMC for RCAV pole.

Since PMC's pole is ~2 MHz and ACAV/RCAV poles should be around 35 MHz, PMC won't effect much on our measurement.


Cavity is 0.2032 m long -> FSR = c/2L = 738 MHz, then


ACAV's Finesse = FSR/FWHM = 6835

RCAV's Finesse =  9710



Attachment 1: acav_pole.png
Attachment 2: rcav_pole.png
  425   Fri Dec 10 12:07:34 2010 FrankSummaryRefCavRCAV/ACAV poles

very interesting. ACAV was a brand new cavity when we installed it, coming from the same batch as all other LIGO refcavs. When we unpacked the cavity from the original REO tube you could smell the softeners from the plastic. It was sitting more than 10 years in that tube. But as this is/was the only spare cavity we had no choice and installed it. Later i forgot to check the real finesse as the scans showed a finesse close to what it should be and we never spent time on that again.


I analyzed the pole for RCAV and ACAV from 2010_12_06 entry. ACAV has a pole at  54 kHz, RCAV pole is at 38kHz.


Cavity pole = FWHM/2. Knowing cavity pole and FSR, we can calculate a cavity's finesse (= FSR/ pole). These values

will be used when we simulate the TF of the system

We amplitude modulated the laser intensity via EAOM, and measured the TF between RCAV_trans_PD and PMC for RCAV pole.

Since PMC's pole is ~2 MHz and ACAV/RCAV poles should be around 35 MHz, PMC won't effect much on our measurement.


Cavity is 0.2032 m long -> FSR = c/2L = 738 MHz, then


ACAV's Finesse = FSR/FWHM = 6835

RCAV's Finesse =  9710




  434   Mon Dec 20 00:08:57 2010 JanSummaryPEM2-day seismic analysis

One of my DAQs (18bit, 1V range, NI 6289) in the seismo lab is recording data from a T240 broadband seismometer on the PSL table. Here, I am going to present plots for the first two days of data taking. I think that there are a couple of interesting features that should eventually be explained using additional seismometers.

The first datum is taken shortly after 2010-12-18 00:00 UTC. The seismometer is oriented along the sides of the table. If I am not mistaken, then the long side of the table should be approximately parallel to the East-West cardinal.



2010-12-18 (Saturday UTC, Friday/Saturday PT)

The plot that I like to look at first is my "hourline" plot. It is inspired by ancient seismology print-out styles. It shows 24h of displacement. Each hour is represented by 200 data points per channel properly filtered. The absolute value of the plot has no information. Different normalizations are chosen at different days to make the largest displacement of the day still fit without intersecting other hour lines. What you can see here is that the vertical channel is very stationary and weaker than the horizontals. The disturbances within the first hours is Tara working at or near the table and causing strong tilts. We will see more detail in this plot at the next day.


The next step is usually to look at the spectra. I like to produce quiet-time and total-time averages. I need to apologize about the labeling. I just noticed that there is still "ASD" on the y-axis. An amplitude spectral density would have different units (m/s/Hz). So these are root power spectral densities (sometimes also called linear spectral densities). In any case, the quiet-time spectrum is just barely below the global NHNM (new high-noise model) of Peterson. This is scary. If your measurement depends on seismic noise, then look for another lab. Characteristic for near coast sites is the double peak at oceanic microseismic frequencies (also seen at the Virgo site). Now, the higher-freq one is not easy to explain. I can only imagine that there is evanescent coupling of ocean wind waves (which do not produce significant microseisms far from the coast) to ocean bottom near the coast. The lower-freq peak is the usual ocean swell, freq doubled peak. You can also see Tara's low-freq tilts comparing the two plots. We will be able to understand more about the >1Hz spectrum in following plots.


The H/V ratio is the ratio of horizontal spectra to the vertical spectrum. It can tell you a lot if you know the seismic speed. If you don't know seismic speeds, then it can still be helpful to identify local anthropogenic sources. A seismic field "randomizes" over large propagation distances, which means that it loses its inital polarization (elliptical for Rayleigh and linear for body waves in many cases). The PSL ratios are not much different for the two horizontal directions. It is difficult to say what it means, but my first guess would be that all structures in the ratios are not due to source characteristics, but due to site characteristics (layers that cause resonances, the table itself,...). But it could also be related to sources.Only a seismic array can help here.


I am only showing two of the three spectral histograms. The level of spectral variation is actually lower than expected (low-freq tilts are the exception). The fact that you don't see much blue in the two plots tells you that the seismic field is quite stationary (well, at least in relation to its high absolute value). I have absolutely no explanation for this. I am very curious to observe the variations over longer periods of time. Especially the vertical displacement is surprisingly stationary. We will see this better in the time frequency plots.


I usually look at normalized time-frequency plots, but the unnormalized versions seem more exciting to people who don't look at them very often. Again, only two out of three channels. You can see many of the features that we also found in earlier plots (tilts, ocean microseisms, high-freq disturbances). Aparently, the near-coastal wind must have lost some strength during these 24h. Its peak was losing power at evening (keep in mind the 8h time difference). I don't understant part of the >10Hz vertical spectrum. What disturbance (small bandwidth) is losing power over night?

Plot11_2010-12-18.jpg Plot13_2010-12-18.jpg

Finally, I plotted a few particle trajectories. There is a low-freq plot with horizontal data <1Hz. It was taking during night when Tara had already left. So the polarization is natural. Although together with the other three plots (>20Hz, all three channels combinations) I get the idea that this polarization could be because of the table. One should eventually compare with data taken from the ground. I intend to program a trajectory histogram since there is more informaition in the high-freq plots than can be represented in these plots. So stay tuned. It requires a serious effort (a seismic array) to understand seismic polarization if you don't have any other site-specific information. Anyway, polarization is already interesting and can be used to give you a factor 2 in (seismic-noise limited) sensitivity if you orient your suspension system along the right direction! On the PSL table, you should avoid alignment parallel to the short side.






  435   Mon Dec 20 00:59:21 2010 JanSummaryPEMPlots of seismic data 2010-12-19

 2010-12-19 (Sunday UTC, Saturday/Sunday PT)

I am only going to point out a few differences or similarities to the previous day. The next plots that I intend to post are long-term (weekly, or monthly) plots. If people want to look at daily plots, then they can ask me. I have them on my PC.

The hour-lines plot seems to tell us that there is more going on than the day before, but remember that it is plotted with a different normalization. It is much quieter in fact. Still, as on the previous day, the real action can only be seen in the horizontals. It is almost exclusively underground luxury to observe horizontals that are as weak as the vertical.

Quiet-time and total-time spectra are more similar than on the previous day. What I find noteworthy is that the H/V ratios haven't changed much.

Weekend histograms are even more stationary (not surprisingly).

There is again this peculiar near-10Hz feature that goes away during night (although it stays in the horizontal...).

I was a little suprised to see particle trajectories to be very similar to the ones on the previous day. I always thought of surface seismicity of something that must vary strongly in terms of seismic sources.








  443   Mon Dec 27 10:10:39 2010 JanSummaryPEMWeekly plots; T240 on PSL table

I am just posting the time-frequency plots for a week-long summary. The data was collected between 2010-12-18 UTC 00:00 and 2010-12-25 UTC 00:00 (7 full days). Although least important to us, I am always most fascinated by the natural (microseismic) sources and not so much by anthropogenic (microtremor) sources. You could go on now and generate bifrequency plots, ultra-low frequency spectral variations and so on. These results would help to distinguish natural sources from local disturbances and can help to identify signals that are much weaker than the spectral density.

I will continue to acquire the data from the table for another week. Then I will move the seismometer from the table to the ground just for a day or so to check what the table does to the particle trajectories. Then it will go back to my lab.


Attachment 1: Plot8.jpg
  447   Mon Jan 10 13:28:36 2011 JanSummaryPEMWeekly plots; start date 2010-12-25

These two plots are just for completeness. In a few minutes I will be able to post the plots for the third week, which could be more interesting since it contains the transition from table to ground. I don't understand why the low-frequency disturbance is "out of phase" with the high-frequency one. It's maybe the last sign of Tara before he left, so he seems to be out of synch with the rest of the world.


  448   Mon Jan 10 14:27:11 2011 JanSummaryPEMWeekly plots; starting date 01/01/2011

 So I don't know what's going on, but the table is doing something really terrible. Maybe it vibrates as a response to ventilation, whereas the coupling of ventilation to ground is comparatively weak. Anyway, this is the end of PSL seismic measurements. Data will be kept on one of the machines in 058f. In principle, I could convert the data into frames and copy it to another location, but it may be too much work. I can always easily produce .mat files with averaged spectra etc. Let me know.


  455   Wed Jan 26 20:21:57 2011 FrankSummaryElectronics EquipmentACAV RFPD modified

The ACAV RFPD stopped working this afternoon. It had high current consumption on the +15V supply, causing the supply to drop down to 2.3V.
I turned out that the logic IC (U8, see schematic) was broken and so the +5V (internally regulated) caused the high current flow which is supplied from the +15V.
I removed U8 entirely as we don't need it. Pin7 of U2 can be left open according to the datasheet in order to enable the device. Diode is now working again.

Already yesterday we made several changes in order to make the RFPDs for both cavities the same. Basically more DC and AC gain.
Attached the modified schematic (only page 1) for ACAV RFPD. Changes are in red.



  460   Mon Jan 31 21:40:50 2011 Frank, TaraSummaryDAQnew channel for frequency counter added

We added a new channel C3:PSL-FSS_FREQCOUNT which contains the analog output of the SR620 frequency counter connected to the beat photodiode.


  • C3:PSL-FSS_FREQCOUNT is connected to CH6 of the first 3123 card, connector P3 (first D-SUB). This is also J4 of the PSL x-connect.
  • Added channel entry in fss.db database. Sampling rate is 10Hz.  Scaled from -10 to 10V in unit  "volts" as we don't know which settings we will use later.
  • Also added channel to daqd. restarted daqd. Manual restart of daqd as controls using script requires password for controls.
    That shouldn't be so but i was to lazy to search for the bur


Counter output is 0 to 8V, right now used in relative mode which means zero frequency deviation equals 4V. Current gain for first test is 100kHz/V.

  469   Thu Feb 3 14:25:18 2011 FrankSummaryBEATFrequency counter time series

2 stretches of data taken at the following UTC times:

11/2/2 23:18:19  duration: ~9min

11/2/2 23:22:50  duration: ~9min

units for data: volts  SCALE: 10kHz/V


Here a screenshot for the first stretch from dataviewer:


 here the data: freqcounter_timeseries.dat

 we didn't take longer timeseries with more range as the resolution is so bad that it couldn't be used to extract a spectrum down to mHz .

RAW data can be accessed via or SSH-login and doing the usual.
Channel name is C3:PSL-FSS_FREQCOUNTER



  476   Mon Feb 7 18:13:31 2011 FrankSummaryVCOVCO tuning - fitted function

tried to fit  the tuning of the VCO in order to calibrate the VCO tuning voltage into frequency shift.
I've only fitted it down to -4.3V using 5 degrees as there is no change in frequency below that point anymore.
Will add an EPICS software channel which contains the calibrated data.

Linear model Poly5:
     f(x) = p1*x^5 + p2*x^4 + p3*x^3 + p4*x^2 + p5*x + p6
       p1 =   0.0005513
       p2 =   -0.003731
       p3 =   -0.005932
       p4 =    -0.02587
       p5 =       1.406
       p6 =       79.99


Using 9 degrees the fit is not as good in the valid region for the 5 degrees, but covers the entire range from -5V to 5V

Linear model Poly9:
     f(x) = p1*x^9 + p2*x^8 + p3*x^7 + p4*x^6 +
                    p5*x^5 + p6*x^4 + p7*x^3 + p8*x^2 + p9*x + p10
       p1 =   4.16e-006
       p2 = -1.095e-006
       p3 =  -0.0003138
       p4 =   0.0003221
       p5 =    0.007185
       p6 =    -0.01047
       p7 =    -0.05412
       p8 =    0.006482
       p9 =       1.498
       p10 =       79.97


  477   Mon Feb 7 20:33:00 2011 FrankSummaryVCOcalibrated VCO monitor signal now available

channel name is C3:PSL-ACAV_VCOMON_CAL, calibrated in MHz using the fifth order polynomial equation at the moment.
Unfortunately the field length for the EPICS CALC record is limited (but not mentioned anywhere in the manual !) so the 9th order equation is too long

will change that later to 2 channels for calculating parts of the equation each and then finally combining those parts in a third record to C3:PSL-ACAV_VCOFREQ

  478   Tue Feb 8 00:03:02 2011 FrankSummaryVCOcalibrated VCO monitor signal now fully available

the configuration is currently running with a softIOC in /caltech/target/SoftIOC/ on fb2, the database is PSL.db.
Will move that on the VME crate when we reboot the crate the next time.

Currently two channels are defined: C3:PSL-ACAV_VCOMON_CAL and C3:PSL-ACAV_VCOFREQ

C3:PSL-ACAV_VCOMON_CAL contains the polynomial fit for the VCO monitor voltage, which is good for -4.3V to 5.0V in tuning voltage.
To extend the range down to -5V i've used a second calc function named
The frequency value where the polynomial function crosses the measured function of the VCO tuning is about 71.6MHz.
As the tuning range ends here the change in frequency for even smaller tuning voltages is almost zero.
So the second function simply checks if the frequency is greater. If so, the output is the polynom. If smaller the value is fixed to 71.6MHz.

Both channels are written to the frames from now on.



        field(SCAN,".1 second")
        field(DESC,"VCO frequency")

        field(SCAN,".1 second")
        field(DESC,"VCO frequency")
        field(CALC," A>B?A:B")

  480   Tue Feb 8 10:41:59 2011 FrankSummaryBEATcavity drift within 24h

i analyzed  the data taken with the short cable and compared it to the signal from the tuning input to the VCO.
I used the 9.order polynomial fit from yesterday to convert the VCOMON voltage into absolute VCO frequency.
The beat frequency is then twice that frequency.

On the other hand the cable-delay technique was sampled with channel FREQCOUNT.
I've measured the peak voltage of the amplified mixer response to be about 4.52V.
The frequency change which corresponds to peak-to-peak change in output signal (see yesterdays entry) i've used is the smallest value i measured ( 6.42MHz).

Using the sampled data, divided by 4.52V, taking sin-1 of that and multiplying it by 6.41MHz /2 gives the measured frequency change.
As i don't get an absolute frequency from that measurement i added an offset of 151.5MHz (this information is from the VCO's absolute frequency) in order to compare the fluctuations with the VCO signal.

RESULT:  beat signal fluctuations over a long period of time can be measured using the VCO feedback signal.
                Both signals absolutely agree except for the region where the mixer signal is at it's peak and so the slope is close to zero and so the uncertainty is too large.

Here the plot:



t0 = tconvert('02/06/2011 10:10:00');
dur = 3600*24*1;

chans = {...

y1 = get_trend(chans{1},'minute',t0,dur);
y2 = get_trend(chans{2},'minute',t0,dur);

y1.data = y1.mean;
y2.data = y2.mean;

y1.data = 2*fittedmodel2(y1.data);
y2.data = 151.5-asin(y2.data./4.52).*3.21;

t1 = linspace(0,dur,dur*y1.rate)';
t2 = linspace(0,dur,dur*y2.rate)';

plot(t1,y1.data, 'r',t2,y2.data, 'b')
xlabel({'time [s]'});
ylabel({'beat frequency [MHz]'});

  486   Thu Feb 10 00:21:55 2011 FrankSummaryBEATcomparison VCO feedback signal and "cable technique"

data taken at 02/06/2011 10:10:00 UTC, duration = 24h

updated plots:



data files:






structure of data files like this:

y1 =
   name: 'C3:PSL-ACAV_VCOMON'
   min: [1440x1 double]
   mean: [1440x1 double]
   max: [1440x1 double]
   rate: 0.0167
   start: 981022215
   duration: 86400
   data: [1440x1 double]

raw data in min/mean/max
calibrated (mean) data in data

  490   Thu Feb 10 16:45:32 2011 FrankSummaryElectronics Equipmentultra low-noise pre-amps

some old designs i've built some years ago using the cheaper DIP versions of the matched BJT pairs from Analog Devices.

Designs are DC-coupled, gain 1000 as they were designed for measuring the noise of photodetectors.
Given values are not 100% what i've used later, only for drawing the schmatics (e.g. gain setting resistors or compensation), but order of magnitude is right.

Eagle-files + Documentation:








  508   Tue Feb 22 22:38:18 2011 FrankSummaryComputersFB2 rebooted

this afternoon the framebuilder (and/or the NDS server) stopped for unknown reasons. We could see real data with Striptool but the framebuilder only saw old, non-changing EPICS values and was still writing them.
Rebstarting the daqd didn't help so i rebooted fb2 and the problem was gone. For some reason we have to manually start daqd und nds, but not a big deal every 6month or so. I also restarted the SoftIOC still running on fb2 which provides the calibrated VCO feedback signal

  514   Thu Feb 24 16:36:06 2011 FrankSummaryLaserPMC re-aligned, EOAM re-alligned , power adjusted

I re-aligned the PMC, same for the electro-optic amplitude modulator (EOAM). I also adjusted the power levels everywhere up to the PMC for maximum performance.

I also had to re-adjust the PMC phase. Startup-setting was 2.29V but had to be 3.29V! Error signal is 2.46Vpp at mixer mon.

Power is set to 20mW transmitted through the PMC when modulation is off. Power can be adjusted behind the PMC as it was setup before.
Power modulation is +/-1.5mW around 20mW with max on function generator (~15%).

  517   Mon Feb 28 09:48:27 2011 FrankSummaryRefCavACAV PID parameters wrong

 after rebooting yesterday the ACAV heater was railing over night.
Today i figured out that the integrater value in the startup skript had the wrong sign!
Changed the entry according to Tara's post last week. Now temp controller is working again.

  518   Mon Feb 28 09:51:15 2011 FrankSummaryEnvironmentsockets at computer desk fixed

Tom from the electrical workshop fixed the two sockets at the computer desk.
We also checked the other sockets as they were labeled wrong,so we didn't know which circuit breaker they go to.
Re-labeled the sockets.

All circuit breakers are located in the main panel in the ATF lab.

  532   Fri Mar 4 00:44:43 2011 FrankSummaryNoiseBudgetcable delay setup - noise floor ?

Why i did this: When measuring the beat signal with the PLL and the cable-delay setup simultaneously we didn't see correlation between both techniques.
We realized that we can't measure the current noise level using the (short) cable. However the estimated "noise floor" for the setup was much below.
So something must be wrong:

So i checked the noise floor of the cable setup again -  it looks like i don't know how to determine the real noise floor for the setup:

I've set up a simple cable delay measurement setup using a Marconi, a power splitter and a +7dBm mixer. Marconi power is +10dBm, so LO is +7dBm.
Cable is 3 feet or so. Mixer signal is filtered (LP 1.9MHz) and terminated (50Ohm) before amplified with the battery-powered FET preamp.
I measured the noise floor by terminating the RF input of the mixer. Changing the input range and so the phase noise of the LO does not change the my "noise floor".

Then i measured the output for different input range settings of the Marconi starting from 1MHz down to 1kHz.
Here the result (not calibrated to frequency noise, only absolute voltage noise levels i measured, but does not matter for what i wanted to see):


For 1MHz and 500kHz input range everything looks OK at high frequencies. The characteristic bump at high frequencies is highly visible.
The low frequency noise looks different to what we measured before using the PLL, but that's not the problem right now.
Starting with 100kHz the measurement limit is reached but still above the "noise floor" with a terminated input.
So how do i measure the "real" noise floor without using a super low-noise oscillator?

Here the frequency noise of the same Marconi measured using the PLL:


will try tomorrow using the long cable...

  534   Fri Mar 4 14:52:00 2011 FrankSummaryEnvironmentHVAC system fixed

i called them every day in the past and told them that something is wrong with the HVAC system of the labs but the didn't fix that.
So i called them today again and asked them to come and get in touch with me so that i can show them what's wrong.

So this afternoon a guy showed up and i showed him where the thermostats are, where the cold air is usually coming out and how it was before.
He first suggested that the HEPA filters might be the issue and asked me when we replaced it the last time.
So i said to him that it's pretty unlikely that all of them in three labs are bad from one day to another and that there is no cold air coming out anywhere.
He finally measured the temperature everywhere using one of those infrared thermometers and realized that all of the HVAC system has constant 78F anywhere in the labs.

He finally tracked it down to a hose usually connected to the main cold air valve of the system which was loose hanging around.

He connected it back and now we have cold air again

Temperature is rapidly decreasing from 81F at the moment.

  660   Thu Aug 18 23:12:42 2011 RaphaelSummaryFSSsimulink just about done. Feedback appreciated.

So over the whole summer, I've put together, little by little, the simulink model for the path that locks the laser to the reference cavity. I'm going to attach the matlab files in a zip folder. I've tried my best to comment as best as possible and to make the programs as robust as I could possibly think of.

I am also attaching the LISO models to the TTFSS paths and for the fits to the measured PZT and EOM Actuator transfer functions. I'm going to list the links of past elogs that refer that mention these fits. I'm also going to attach the fits themselves.


EOM Actuator Measurement Procedure

PZT and EOM Actuators Fit

A more complete description of my measurements can be found in my surf report

I am still not satisfied with these fits and would like some feedback in improving them. I am most worried about my measured EOM Actuator transfer function fit.

Attachment 1: fss_simulink.zip
Attachment 2: fss_LISO.zip
Attachment 3: eom_measured_vs_fitted.jpg
Attachment 4: PZT_TF_measured_vs_fitted.jpg
Attachment 5: PZT_Actuator_Gain_measured_vs_fitted.jpg
Attachment 6: PZT.jpg
Attachment 7: EOM.jpg
Attachment 8: EOMHV.jpg
  661   Fri Aug 26 20:52:16 2011 RaphaelSummaryElectronics EquipmentRFPD characerization

Here is the measured transimpedance of the RFPD.


I measured this by taking the optical transfer function using the Jenne Laser. The setup is shown below:


I needed to readjust my measured optical transfer function to account for the difference in power between the two diodes. Before, I assumed that all the energy that I measured using the ophir powermeter at the points before the photodiode was not actually going into the photodiode. For the tested photodiode, I got 89% of the voltage that I was supposed to measure if I used the quantum efficiency from the data sheet and no loss. The predicted measurement was calculated using the equation V=P*QE*l*e/(h*c)*Z, where V is the dc voltage output, P is the incident power on the photodiode, l is the wavelength, and Z is the DC transimpedance. However, I only measured 49% of the predicted dc voltage from the reference photodiode. This is most likely because not all of the light is hitting the reference photodiode. The diode is quite small, and I was unsuccessful in focusing the light on the diode even further. So I decided to just use the dc voltage and calculate the photocurrent. I can then use the ratios of the photocurrent to adjust for the difference in power of the incident beams. I can do this because the responsivities are just about the same and I'm going to assume the losses in both diodes are equal. I then multiply by the transimpedance of the reference photodiode to obtain the transimpedance of the tested photodiode. A much more cohesive, clear, and eloquent explanation for obtaining the transimpedance will be included in my final report :>] (I'm a bit tired now :>[ ).

Here is the characterization of the shot noise and the input referred noise floor at 35.5MHz.


I made two different types of fits and obtained two different answers for the transimpedance and for the shot noise intercept. I should also note that the parameter fittings seem to change (not exactly sure by how much) when I took more and more data, i.e., the parameters fittings didn't seem to be converging to a single number.

So in the end, we have 3 different answers for the transimpedance at 35.5MHz: Z= 1231, Z=1297, and Z=1397. I also have two different answers for the shot noise intercept: i_int=0.41mA, 0.48mA. For the shot noise measurement, I am inclined to say that I would trust the fit with the green and orange line the most, just because the shot noise has to be proportional to 2ei_dc, so we only had to figure out one parameter (which was done by finding the intersect between the input referred noise level and the line that forms from the shot noise).

However, I guess we should be a little bit more conservative and say that the shot noise intercept can be as high as 0.48mA. For the Z intercept, I am inclined to say that I would trust the same fit just because it was really the only parameter in this fit and the shot noise has to follow that line. So maybe Z=1397. I perhaps assumed to many things when I calculated the transimpedance from the optical transfer function, such as equal responsivities, equal losses, and that the referenced PD transimpedance is accurate. However, I don't really know how accurately shot noise can be measured. Perhaps the optical transfer function is more reliable in obtaining the transimpedance.

Sorry for the rambling. I'm a bit tired. Also, sorry this took so long. I basically spent two weeks trying to figure out why my shot noise measurement wasn't following theory and why my two measurements contradicted each other. It was a matter of hunting down two factors of two :<[.

  679   Fri Sep 16 22:15:03 2011 FrankSummaryFoamthermal insulation added

when playing with the setup i've noticed that we are actually very sensitive to temperature fluctuations (more than i expected), so the absolute length (or CTE?) must be more different than we expected. So i've added the thermal insulation, drilled four new holes in the end caps, connected the temp sensors etc. Thermal control loop is running now. Made some changes to channels (mostly range limiuts, warning levels etc) and added four new software channels which i will use to generate absolute calibrated temp signals. The difference between the sensors is about 1K. I know it does not matter for the stabilization but i hate it as you never know if you have a gradient or degraded sensor or so...

I'ver started heating it up to 26.5C (you may ask why this number: laziness -  actually i've started the heater before finishing the insulation and that was the actual temperature at the time i finished it). The LO for the AOM already increased to 70.6MHz (from 64MHz). So my guess is that once we reach 30C we are back in range for the iLIGO VCO.

Will change the temperature over the weekend in a couple of steps to measure the temperature sensitivity  (differential length change with temp). This will tell us how good the thermal stability has to be to not be limited by thermal fluctuations. We then can make a decision on further things like second, external box, passive foam or metal box with active control etc..

  702   Mon Oct 10 21:30:45 2011 Tara, FrankSummarySeismicsecond leg replaced

we have replaced the second leg which was leaking. It could be that the legs are simply to old and the rubber got brittle. As far as i know the table has never been operated floating as it had the suspended reference cavity on it since the beginning. We operate at around 85 PSI, maximum operational pressure is specified at 100PSI so that should be OK. The second leg started leaking after one day of floating operation. We disassembled one today to have a close look but we can't really tell where the leak is. We will check with some pressure to see what's broken within the next few days. Let's see what the other legs do in the near future. We still have plenty of "spares", as Aidan bought two new sets (taller ones) for the old tables in the TCS lab. So we have 8 short ones which are currently not used (and seem to be newer than the ones we currently have). And they still work as passive legs.

  703   Wed Oct 12 00:53:40 2011 Tara, FrankSummarySeismicsecond leg replaced

As the table was floated, we measured the noise from error point again.


     We tried to determine if the noise bump we saw were from the window, so we place an extra window in front of a mirror [add fig] and compare to the noise when there was no window. The results are not different that much.

     From a quick look, by adjusting the input power, from 1mW to 10mW. The shape of the noise from error point changes substantially. This could be come from RFAM or scattering.  I'll measure the noise vs input power after I optimize everything first. RFAM, beam splitter, back reflection have to be optimized.



  705   Thu Oct 13 02:36:58 2011 Tara, FrankSummarySeismicsecond leg replaced

After optimized everything, I repeated the measurement that was done in this entry (noise at detection point). There is some improvement, the result is shown below.


==What have been done==

By "optimize everything", I meant:

  1. The Faraday Isolator was installed back in the setup, and optimized for maximum isolation. [add pic]
  2. Beam splitter and quarter wave plate sets (for double passed AOM and cavities) were optimized for minimum back reflection.
  3. EOM with half wave plate were adjusted for minimum RFAM (reduced by ~ 20 dB)
  4. Beam alignment to the cavities: visibility are up to 93% for both cavities now.

 Measurement Recap:  We want to check the noise from scattering noise or RFAM at the detection point, so we measure the noise at error point when the beam reflected off the cavity, or a mirror in front of the chamber (cf entry:700). We also want to see the dependent on power input, so we chose 10mW, 5mW and 1mW input power.

    Below are measurements from error point (Mixer out) which are calibrated to absolute frequency noise through the slope of error signal from each setup (power input of 10mW, 5mW and 1mW)


==Comments for the results==

  1.    The noise level when the beam reflected off the cavity goes down when we float the table and optimize everything ( red, green, blue are lower than pale pink (result from 2011_10_07).
  2.    The noise level when the beam reflected off the cavity do not change much with input power ( red, green, blue are about the same)
  3.    At 1mW the noise at high frequency (above 50Hz)  raises up for both cases (reflected off cavity / mirror) I'm not sure what happens. The calibration seems to be ok since the noise level at low frequency matches the results from 5mW and 10mW setup.
  4.    Seismic stack's resonant frequency at 6.7 Hz shows up more clearly after RFAM/ back reflection are minimized.


To Do: We will check the beat signal tomorrow. There should be improvement, since optics are optimized and the table is floated.

Attachment 2: plot_2011_10_12.fig
  744   Thu Dec 1 22:00:53 2011 FrankSummaryRFAMEOM foam insulation (2nd generation) and temp stabilization

below some pictures of the second generation of EOM foam insulation for the room temp cavities. The main idea behind this version was to get a foam box with large enough, particle free beam holes which is following the EOM while being aligned. So this version's reference plane is the top of the EOM. The foam box consists of two different foams. One is the very stiff, old yellowish polyurethane foam used as the top plate. The main EOM insulation is the same white packing foam as used for the 40m version.


The tubing for the holes are parts from the Push-to-Connect Tube Fittings used for our air distribution for the table.


To electrically insulate the RF connection from the aluminum tape on the outside i've build a small insulated SMA extension.


For the heater i used the same 1" x 1" Kapton heater as used at the 40m. I have two temp sensors attached to the case of the EOM, one 1k Platinum RTD and one 100k NTC. The NTC has a much higher sensitivity. The RTD is currently used for temp calibration.


I've had a sample of one of the TeamWavelegth WTC3243  temp controllers which i used for a first try. They claim something like 2mK/24h stability but i don't know anything about their noise. My test board has an on-board reference which is currently used for the setpoint, but it also comes with an external analog input. Output current can be individually limited for positive and negative direction (when using a TEC). For use with a heater one of them is simply tuned to zero. The chip only has P and I but also comes with an "actual temp" monitor output (error-point monitor, but there is no out-of-loop sensor). Below a picture of the test setup.


  753   Thu Dec 8 15:59:21 2011 FrankSummaryPMCrealignment

started realigning everything from scratch and calibrate all channels right. PMC optical power channels need re-calibration.

input beam to PMC: 28.9mW
PMC transmitted beam: 23.4mw
transmission trough curved mirror: 1.63mW

--> only 81% visibility (87% including back mirror leakage), but should be enough for what we want to do. Don't know the loss mechanism (didn't investigate)

  754   Thu Dec 8 20:28:06 2011 taraSummaryPMCrealignment

A reminder for Frank about the setup, 

  • The AOM's case on RCAV beam path is not screwed down to the body, so it will be blocking the beam.
  • The height for Faraday isolator behind the PMC is not correct, i think only ~80% of the power is transmitted. I haven't had it fixed yet
  • When I measured the visibility of RCAV, I scanned the cavity and minimize the dip as seen on the REFL RFPD. I got sth ~90% transmission, but when I measured the actual tranmitted power, the visibility is lower than that, maybe only~ 75%.
  • There is some weird reflection on ACAV RFPD, I'm not sure if it comes from the window or not.
  755   Thu Dec 8 21:06:10 2011 FrankSummaryPMCrealignment

thanks, for the info.

I only did the PMC so far as i has to fix the daq and add the new channels. What's the problem with beam height of the isolator? Is the beam too low or the mount too high? Do you know?


A reminder for Frank about the setup, 

  • The AOM's case on RCAV beam path is not screwed down to the body, so it will be blocking the beam.
  • The height for Faraday isolator behind the PMC is not correct, i think only ~80% of the power is transmitted. I haven't had it fixed yet
  • When I measured the visibility of RCAV, I scanned the cavity and minimize the dip as seen on the REFL RFPD. I got sth ~90% transmission, but when I measured the actual tranmitted power, the visibility is lower than that, maybe only~ 75%.
  • There is some weird reflection on ACAV RFPD, I'm not sure if it comes from the window or not.


  759   Fri Dec 9 06:32:24 2011 TaraSummaryPMCrealignment

The V-block's height is a bit too high. The beam height is very close to 3".


thanks for the info.

I only did the PMC so far as i had to fix the daq and add the new channels. What's the problem with beam height of the isolator? Is the beam too low or the mount too high? Do you know?




  760   Fri Dec 9 11:49:17 2011 FrankSummaryDAQdaqd problems (which turn out to be not critical)

Talked to Alex about the daqd and it's strange behavior on our machine.

  1. The first thing is that the daqd did not show up as a process even it was running. According to Alex this happens because we only write about 100 EPICS channels so they cpu load is so small that it does not show up all the time so you can easily miss it. The safest way to find out if it's running is to try to telnet into it on port 8087 and check the status.
  2. We have the following error message in our log file (since a long time ago):
    A call to "assert (pE == &entry)" failed in ../../cds/project/daq/fb2/exServer.h line 346
    EPICS Release EPICS R3.14.10- $R3-14-10-RC2$ $2008/10/10 15:01:51$.
    E-mail this message to the author or to tech-talk@aps.anl.gov
    Calling epicsThreadSuspendSelf()

    This happens because it's trying to start an epics ioc using a wrong version of the epics library. We tried different version but couldn't fix it. Looks like the easiest solution would be to re-compile the daqd.
  3. Error message: failed to rename file; errno 2
    This means it can't rename the current frame file it is writing to which can have several reasons. Most often it does not have the rights to do so and a second option is that if the daqd is already running but invisible and you try to start (another) one there is no exception catching for that case and those two processes create a conflict because they try to create/write to the same file.
  4. If you want to grab data using the dataviewer you get the following message even if data exists
    read(); errno=9
    read(); errno=9
    T0= some time and length of data
    No data output

    Unknown problem. Even the data exists and can be grabbed using different command line tools to directly access the frames the dataviewer does not get data. A second weird behavior is that if you request let's say 60 seconds it request 120 seconds. Should not be like that but that's a dataviewer problem.
  783   Thu Jan 12 16:04:05 2012 TaraSummaryPMCIsolator base, EOM base's height

As mention in the previous corresponding entry, the height of the base for the faraday isolator is not correct. I removed the thing from the table and measure its height again in order to have it fixed. It has to be cut by 3/128 inch from the base (see figure below). The groove for the isolator is well leveled. I got the same height for both ends. I'll bring it back to machine shop tomorrow.


There are other mechanical parts I need to fix:

  • Broadband EOM's base: Frank noticed that it is a bit too high, and the 4- axis stage height has to be adjusted close to minimum which is not good for mechanical stability.
  • New design for EOM base: If we decide to go for two EOMs for 1)adding side band, and 2) feedback, we need some space for installing the second extra EOM. With the current EOM base design, it takes up to much space along the beam path, so I might need to make a new EOM base.
  • RFPDs' base: Now they are only a plastic post. We will need a sturdier design.
  • Base for dual periscope

I'll try to have these parts before we open the chamber to change the seismic stage.

  788   Thu Jan 19 17:27:35 2012 FrankSummarySafetyStolen Items

More and more stuff got taken from the lab without telling us and now REALLY delay things:

  1. entire Newport lens kit (in wooden box), AR-coating for 1064nm
  2. entire spool of RG405
  3. resonant New Focus EOM, 24.5MHz (resonant PDs and Wenzel OCX are still here)


  792   Mon Jan 23 01:49:30 2012 FrankSummaryElectronics EquipmentRFPD work

modified one of the photodiodes from LLO to be used as one of the RFPDs in our setup for locking the cavities. Changes are documented in the pdf (all files are on svn in data folder from 1/21/2012 and 1/22/2012).

  • Had to cut traces of the pcb to add a coil for the resonance circuit as there is no adjustable inductor with the right footprint with the large value we need for 14.75MHz (~3.5uH). Same for the notch which is not exactly at 29.5MHz, but adjusting that makes it impossible to adjust the main resonance exactly to 14.75MHz, limited by the range of the coil, as we don't have the right inductors. Coilcraft kits do not contain the values we need. Will order a couple of the right ones for future work.
  • Changed dc gain to 100, so DC output can be used up to 5mA but we are planning to use only ~1mW
  • RF gain is still 10, but might change that later after i checked the noise budget. Might replace the opamp and add a factor of 2 or 3 here if required.
  • PD dark noise is ~60nV/rtHz which is equivalent to 6.5e-12A/rtHz input noise, so shot noise limit equivalent of ~130uA of photocurrent. Confirmed with white light source.



Will continue modifying a second PD for the second cavity.


  833   Fri Feb 17 14:54:36 2012 FrankSummaryBEATmarconi noise measured using delay line

tried to measure the frequency noise of the Marconi using the delay line. Setup is identical to the schematic posted in entry #832.

I've set the LO power to 13.64dBm as it is close to optumum value. The mixer output is terminated with 500Ohms. The slope is 1.1145MHz/V.
Measured the noise at the output using the SR785 and a SR560, gain 1000.

Plot shows the following:

  • SR560, gain=1000 with 50Oms input termination
  • SR560, gain=1000 with 1.9MHz LP-filter and 500Ohms load impedance
  • Mixer output with RF input terminated with 50Ohm, LO still ON
  • Marconi noise with modulation input turned off
  • Marconi noise measured using the delay-line technique (with mod input range 10kHz, turned ON but input terminated with 50Ohms) - noisefloor NOT subtracted
  • Marconi noise measured using the PLL (with mod input range 10kHz, turned ON but input terminated with 50Ohms)


  • SR560 is currently not limiting the performance
  • The noise floor even with FM tuning input turned OFF is too high, but far above the rest of the equipment noise floor
  • We can barely see the additional phase noise from the Marconi with 10k input range turned ON - no way to see the noise of input ranges 1k or below at the moment. Reason unknown. Noise level is higher as predicted from the ideal setup (see elog entry #825)


Attachment 2: noise_budget.fig
  837   Fri Feb 24 04:10:41 2012 KojiSummarySeismicNew stack transfer function / ringdows

[Frank and Koji]

1) Stack vertical transfer functions

We have attached a KISTLER accelerometer on the stack.
The accelerometer was epoxied on a low-outgassing kapton tape while the tape is attached on the stack.

The table was shook by either a PZT or impact-hammering by a fist.

The new resonant freqs are 10.5 and 35Hz in stead of previous 15Hz and 55Hz.
This provides us an additional isolation by factor of ~10 above 20Hz

2) Stack pitching mode identification

Location of the accelerometer on the stack was swept from the center to the edge of the plate.
The difference of the transfer functions gives us the idea where are thepitch resonances.
It seems that the resonant frequencies in pitch are 20 and 60Hz

3) Ringdown measurement of the other modes

In order to check the resonant freq of the other modes, the stack was excited by a finger
in longitudinal, yaw-rotational, and transverse directions.

The results: longitudinal 3.1Hz, rotational 5.2Hz, transverse 2.7Hz


Attachment 1: vertical_tf_comparison.pdf
Attachment 2: vertical_pitch_tf.pdf
Attachment 3: ringdown_time_series.pdf
  879   Sun Mar 11 22:40:33 2012 ranaSummaryNoiseBudgetThermal Noise calculation using gwincDev

 I recalculated the thermal noises using the specific layer structure of silica/tantala that was used to get a 300 ppm reflectivity. This is not based on an REO data sheet, but just based on using lambda/4 layers with a lambda/2 silica cap on top. I used the minimum total number of layers required to get better than 300 ppm. In reality, REO may have used another couple of pairs to get it correct.

 I have used phi_SiO2 = 1e-4 and phi_tantala = 2.3e-4. I've asked Gregg Harry and Matt Abernathy to give us updated numbers.

The noise plot below shows that the thermo-optic noise at 100 Hz - 1 kHz is not insignificant, but also not dominant.

The bad news is that the Brownian noise is lower than we've been using in the usual Noise Budget plots (like Tara's last one). So, if my calculation is correct, we're not as close to the real coating noise as we thought...

Next step is to compare the calculations to find out the difference (this means you Tara, don't let Frank stop you). My code is committed to the iscmodeling CVS at MIT:   iscmodeling/coating/iRefCav/. It requires the whole gwincDev/ tree in order to run.

Attachment 1: RefCav_R.png
Attachment 2: RefCav_TOnoise.png
  883   Tue Mar 13 16:29:43 2012 ranaSummaryNoiseBudgetThermal Noise calculation using gwincDev

I looked around in some of the papers for a better estimate of the Q for the different coating materials. From


I get new numbers (I think the numbers I used in the previous calculation were too modern). The numbers from this 2004 CQG article are

phi_silica  = 0.00004 +/- 0.00003 

phi_tantala = 0.00042 +/- 0.00004

which are lower for silica and higher for tantala than what I used before.

  885   Tue Mar 13 23:44:02 2012 ranaSummaryNoiseBudgetThermal Noise calculation using gwincDev

  I have updated the plots using the more correct loss angles for the silica and tantala - attached are the plots. The overall Brownian noise has gone up by ~20% since the noise was always dominated by the tantala before.

In order to be honest, I suggest that we plot the Brownian noise using some of these confidence intervals - the yellow region indicates what I think the 2*sigma limits are.

You'll have to run the code yourself if you want to put these traces into your Noise Budget plots.

Attachment 1: RefCav_TOnoise.png
  886   Wed Mar 14 00:21:42 2012 FrankSummaryNoiseBudgetThermal Noise calculation using gwincDev

i will get a copy from Jamie tomorrow and edit our current noise budget file to replace our simple calculations with the updated gwinc calculations. I have to update the plot for the proposal anyway and want to make it look good (and right). The current version of the proposal contains a placeholder only.


  I have updated the plots using the more correct loss angles for the silica and tantala - attached are the plots. The overall Brownian noise has gone up by ~20% since the noise was always dominated by the tantala before.

In order to be honest, I suggest that we plot the Brownian noise using some of these confidence intervals - the yellow region indicates what I think the 2*sigma limits are.

You'll have to run the code yourself if you want to put these traces into your Noise Budget plots.


  887   Wed Mar 14 17:31:51 2012 taraSummaryNoiseBudgetThermal Noise calculation using gwincDev

The discrepancies between in GWINC code and our code are  different values of phi_perp/ phi_perpendicular, and the simplification of the formula.


The coating thermal noise from Rana's plot is about a factor of sqrt(2) lower from the usual code we have been using. The reasons are that

  1. We use different values of phi_perp and phi_para. Values from GWINC phi_perp/phi_para are 1.3e-4/1.7e-4,  ours are 1.7e-4/3.1e-4. This is the main reason why the results do not agree
  2.  Our code uses a simplified Thermal noise formula, where all the terms with 1- sigma are ~ 1 see [fig.1], but another simplified version[fig.2] that keeps one more term of 1-sigma gives a result that agrees with that from GWINC.  With the same parameters, the better simplified version (with term 1-sigma) gives the result smaller than that of the exact formula by only ~ 1%.
  3.  Also, the temperature we use in the code is 35 C, while the temperature in GWINC is 20 C. This contributes to 5% reduction from our result.



fig1: excerpt from Harry etal. Class Quantum Grav 19 (2002) 897-917



 fig2. excerpt from Harry etal. www.ligo.caltech.edu/docs/P/P060072-00.pdf

  902   Fri Apr 6 01:36:39 2012 Tara, FrankSummaryNoiseBudgetACAV loop changes

summary of all changes made and more detailed plots will be posted soon, so check back later

writing in progress

  • replaced New Focus power supply for RFPD with Agilent power supply (+/-15V)
  • added isolation transformer between mixer LO and main splitter of 14.75MHz LO
  • changed gain of input stage from PDH-box from 10 to 20
  • replaced thickfilm resistors in input stage with thin film ones
  • added offset potentiometer to input opamp
  • added 25MHz HP-filter to AOM driver/amplfier

ACAV loop is now completely free from line harmonics and the in-loop level dropped to ~10nV/rtHz (includes 7nV/rtHz from analyzer). Mixer dark noise is ~25nV/rtHz.

  913   Fri Apr 13 13:35:37 2012 Tara, FrankSummaryNoiseBudgetPDH readout noise level verification

we re-checked the electronic noise level for each PDH loop and also checked how the noise level rises with a shot noise limited light source (halogen bulb) using the exact same setup as we use daily.
Before we had only checked the individual parts, e.g. the shot noise limit of our RF-PD, not including the rest of our setup (mixer, LO or filter stages). This was just to confirm that nothing is broken and our PDs are still OK.

Measurements were taken right after the mixer / LP-filter, but still connected to PDH servo. This is OUT1 of the common path of the TTFSS-box  and the input on the front of our ACAV PDH servo. We blocked the laser and adjusted the power of the bulb and measured the electronic noise floor using the SR785. The dark noise spectrum is the one already shown in the last noise budget. Below the plots of noise level, measured around 500Hz (100 avgs, wide marker) vs different photocurrents of the PDs. DC impedance is 2kOhms, regular DC level for RCAV is 1.7V and 1.47V for ACAV. RF-impedance is the same as measured some time ago for those diodes. Data in folder 4/11/2012 on svn.

SN_RCAV.png  SN_ACAV.png

Conclusion: New measurements agree very well with the old measurements. So our PDs still work fine and there is no excess noise in our readout we missed.

  918   Mon Apr 16 15:35:15 2012 Frank, TaraSummaryNoiseBudgetmechanical resonances

we mapped the mechanical resonances in our system using two techniques :

  1. tapping each optical component and check spectrum for excited modes. This technique is difficult as we usually excite a lot of other mechanical modes nearby as well.
  2. exciting everything with white noise (loudspeaker) and then add damping on individual components and checking spectrum which modes we reduce. Very precise but you have to start with the dominant wants and damp them first to see the smaller ones nearby.

resonance frequency is attached to each component. Green background behind numbers means we could verify the frequency using both techniques. Yellow means measured using tapping but could not see using the damping technique as the contribution to the beat signal is to weak. Input optics needs to be checked and finalized. Picture is temporary only.

beatboard_resonances.jpg PDH.jpg

  920   Mon Apr 16 18:17:05 2012 Frank, TaraSummaryNoiseBudgetmechanical resonances

I was told at JILA that anything less than 3/4" thick is lame.

This place has thick stuff:


Don't worry about the cost of the plastic - if it helps the noise, we have the money.

ELOG V3.1.3-