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ID Date Authorup Type Category Subject
  11905   Mon Jan 4 14:45:41 2016 rana, eq, kojiConfigurationComputer Scripts / Programsnodus pwd change

We changed the password for controls on nodus this afternoon. We also zeroed out the authorized_keys file and then added back in the couple that we want in there for automatic backups / detchar.

Also did the recommended Ubuntu updates on there. Everything seems to be going OK so far. We think nothing on the interferometer side cares about the nodus password.

We also decided to dis-allow personal laptops on the new Martian router (to be installed soon).

  11303   Mon May 18 17:42:14 2015 rana, ericQUpdateGeneralsome status

Today at 5 PM we replaced the east N2 cylinder. The east pressure was 500 and the west cylinder pressure was 1000. Since Steve's elogs say that the consumption can be as high as 800 per day we wanted to be safe.

  1. We closed the black valve before the regulator and closed the valve on the cylinder.
  2. We unscrewed the brass fill line to the cylinder.
  3. We unchained the cylinder and put in the dolly (and attached the chains on there).
  4. We rolled in a fresh cylinder from outside using the red dolly (it should have chains).
  5. We put it in place, hooked up the chains, and screwed on the brass nozzle with the large adjustable wrench (need to put a non-adjustable here).
  6. Opened up the cylinder valve.
  7. Opened up the black valve.
  8. New east pressure reading is 2500 PSI. Regulated N2 pressure is 68 PSI.

1) Checked the N2 pressures: the unregulated cylinder pressures are both around 1500 PSI. How long until they get to 1000?


  11315   Tue May 19 18:55:12 2015 rana, ericQUpdateGeneralsome status

After one day the pressures are east/west = 2200/450 PSI



  1. New east pressure reading is 2500 PSI. Regulated N2 pressure is 68 PSI.


  10418   Thu Aug 21 02:42:17 2014 rana, ericqConfigurationGreen LockingGain changes on Green Y PDH

[rana, ericq]

We spent time trying to relieve the Yend green PDH of it troubles. 

We realized that the mixer in the PDH setup (mini circuits ZAD-8+), wants 7dBm of LO to properly function. However, we use one function generators output, through a splitter, to give signals to the laser PZT and the mixer LO. 

We don't want 7dBm of power hitting the laser PZT, though. The summing node that adds the servo output to the sideband signal was supposedly designed to do some of this attenuation. Rana measured that 10Vpp out of the function generator resulted in 20mVpp on the fast input to the NPRO, after the summing node. Hence, the 0.09V setting was only resulting in something like 0.2mV hitting the PZT. The PZT has something like 30 rad/V PM response, meaning we only had ~0.006 rad of modulation. 

Now, the function generator is set to 2 Vpp, meaning 4 mVpp hitting the PZT, meaning ~0.12 radians of modulation. The mixer is now getting +7dBm on its LO, and the PDH traces look much cleaner. However, the PDH error signal is now something like 100mVpp, which is much bigger than the PDH board is designed for, so there is now a 10dB attenuator between the reflection PD DC block and the RF input to the mixer. 

Here are screenshots of the Inmon channel (which has a gain of ~20) showing a sweep through some PDH signal, and the error signal while in green lock. Huge 60Hz harmonics are still observed. 



Regarding these 60Hz issues, we need to make sure that we remove all situations where long BNCs are chained together with barrel connectors, or Ts are touching other ones. We also should glue or affix the pomona summing box to the shelf, so that its not just laying on the floor.

The concrete next step is to go fiddle with things, and see if we can get the 60Hz noise to go away, then measure the PDH loop and noises again. Hopefully, this should make the ALS much more reliable. 

  9329   Fri Nov 1 19:09:01 2013 rana, evanConfigurationPSLPMC reflected beam nonsense

 While looking at the PMC REFL beam for the AOM diffracted beam, we noticed that although only one beam exists between the PMC and the first steering mirror, there are two afterwards and they both go to the PMC REFL  RFPD!!! This is madness. We only want one beam on our PDH diode.

The reason that we have two beams is that that first steering mirrors is actually a (W1-PW-1025-UV-1064-45P) non-wedged window with an AR coating on only one side. So two beams come out of it. There is a terrible and floppy and illegal anodized aluminum dump close to this beam which *someone* probably intended to use as a "scraper" to get rid of one of the beams.

Black anodized aluminum is a horrible beam dump material at 1064 - its about as grey as Steve's chair. And its so soft that it scatters light back into the PMC and makes more acoustic noise. And it is mounted so poorly (only one screw) that it can easily be bumped and twist and miss the beam. Punchline: only use anodized aluminum dumps for stray light around cameras or for HeNe for OL. Its NOT allowed anywhere where we care about interferometry of NIR beams.

It was also set to dump the dimmer beam. On Monday, we should order ~5 W1 and get them with a wedge of 1-2 deg. Then we use a black glass dump for the dim beam and orient the bright one to hit the REFL camera and the PMC REFL PD.

For the weekend, I have adjusted the crappy grey aluminum flapper to catch the bright beam so that the PMC REFL image no longer shows the interference fringe of two beams. Lets see how the PMC drifts over the next 3 days.

  12646   Tue Nov 29 17:46:18 2016 rana, gautamFrogsComputer Scripts / Programsgateway PWD change

We found that someone had violated all rules of computer security decency and was storing our nodus password as a plain text file in their bash_profile.

After the flogging we have changed the pwd and put the new one in the usual secret place.

  12911   Mon Mar 27 20:41:21 2017 rana, gautamUpdatePSLPMC DAQ assay for feed-forward integration

We are thinking to use the PMC signals to help us in figuring out the feedback / feedforward stuff and making it better.

Today we scoped out the PMC DAQ channels (which were never re-hooked up after the Joe/Jamie CDS upgrade 6 years ago).

There is a 4-pin LEMO connector on the front panel which gives

  1. the error signal (after the 4th order, post-mixer lowpass and a OP27 buffer with a 17 kHz low pass)
  2. the feedback voltage to the PZT, after a resistive divide by 50

Both of these signals are buffered by the AD620 inst amp configured with a gain of 1. In the green scope trace, you can see that there's a ~110 MHz signal strongly evident there. In the spectrum analyzer screen shot there is a instrument noise trace and then a PMC error point trace. You can see that all the peaks are ony there when I connect to the servo board instead of a Terminator. This RF noise is mainly the higher harmonics of the 35.5 MHz modulation getting there. It seems to be in both the error and control DAQ outputs, and a question is whether or not it is also in the servo electronics.

I also attach a close up of the servo board in the region of the post-mixer LC low pass filtering. I think its supposed to be 4th order cutoff at 1 MHz, but maybe the caps are busted or there's a way for the RF from the mixer to bypass the filters and get into the main servo path?

In the medium term, we probably want to use the new PDH servo that Rich is making. Need to buy/make a HV driver to use, but that should be easy.

  13316   Mon Sep 18 15:00:15 2017 rana, gautamFrogsComputer Scripts / Programsgateway PWD change

We implemented the post-SURF-season nodus password change today.

New password can be found at the usual location.

  15173   Wed Jan 29 03:05:47 2020 rana, gautamUpdateSUSMC misalignments / sat box games

In the last couple days, as the IMC ringdowns have been going on, we have noticed that the MC is behaving bad. Misaligning, drifting, etc.

Gautam told me a horror story about him, Koji, and melted wires inside the sat boxes.

I said, "Its getting too hot in there. So let's take the lids off!"

So then we:

  1. Removed the lid (only 4 screws were still there)
  2. cut off some of the shield - ground wires and insulated them with electrical tape
  3. squished the IDC connectors on tightly
  4. left it this way to see if MC would get better - certainly the painfully hot heatinks inside the box were now just 110 F or so

After some minutes, we saw no drifting. So maybe my theory of "hot heatsink partially shorting a coil current to GND through partially melted ribbon cable" makes sense? IF this seems better after a month, lets de-lid all the optics.

Let's look at some longer trends and be very careful next to MC2 for the next 3 days! I have put a dangerous mousetrap there to catch anyone who walks near the vacuum chamber.

gautam: the grounding situation per my assessment is that the shield of all the IDC cables are connected to a common metal strip at 1X5 - but in my survey, I didn't see any grounding of this strip to a common ground.

  15849   Sun Feb 28 16:59:39 2021 rana, gautamUpdateLSCmore PRMI checks here: what it is ain't exactly clear

On Friday evening we checked out a few more things, somewhat overlapping with previous tests. All tests done with PRMI on carrier lock (REFL11_I -> PRC, AS55_Q-> MICH):

  • check that PRC drive appropriately minimizes in REFL55_Q. I:Q ratio is ~100:1; good enough.
  • put sine waves around 311 and 333 Hz into PRCL and MICH at the LSC output matrix using awggui and LSC osc. not able to adjust LSC/OSC output matrix to minimize the MICH drive in REFL_I.
  • measured the TF from BS & PRM LSC drive to the REFL55_I/Q outputs. very nearly the same audio frequency phase, so the problem is NOT in the electronics || mechanical transfer functions of the suspensions.


Further questions:

  1. is this something pathological in the PRMI carrier lock? we should check by locking on sidebands to REFL55 and REFL165 and repeat tests.
  2. Can it be a severe mode mismatch from IMC output to PRMI mode? the cavity should be stable with the flipped folding mirrors, but maybe something strange happening. How do we measure the mode-matching to the PRC quantitatively?
  3. huge RAM is ruled out by Gautam's test of looking at REFL demod signals: dark offset vs. offset with a single bounce off of PRM (with ITMs mis-aligned)
  4. if there is a large (optical) offset in the AS55_Q lock point, how big would it have to be to mess up the REFL phase so much?
  5. what is going on with the REFL55 whitening/AA electronics?

unrelated note: Donatella the Workstation was ~3 minutes ahead of the FE machines (you can look at the C0:TIM-PACIFIC_STRING on many of the MEDM screens for a rough simulacrum). When the workstation time is so far off, DTT doesn't work right (has errors like test timed out, or other blah blah). I installed NTP on donatella and started the service per SL7 rules. Since we want to migrate all the workstations to Debian (following the party line), lets not futz with this too much.

gautam, 1 Mar 1600: In case I'm being dumb, I attach the screen grab comparing dark offset to the single bounce off PRM, to estimate the RAM contribution. The other signals are there just to show that the ITMs are sufficiently misaligned. The PRCL PDH fringe is usually ~12000 cts in REFL11, ~5000cts in REFL55, and so the RAM offset is <0.1% of the horn-to-horn PDH fringe.

P.S. I know generally PNGs in the elog are frowned upon. But with so many points, the vector PDF export by NDS (i) is several megabytes in size and (ii) excruciatingly slow. I'm proposing a decimation filter for the export function of ndscope - but until then, I claim plotting with "rasterized=True" and saving to PDF and exporting to PNG are equivalent, since both yield a rasterized graphic.

  9925   Wed May 7 23:09:06 2014 rana, jamieSummaryComputer Scripts / ProgramsOttavia back on network

After Jamie fixed the third party repo issue with Ottavia, he was able to upgrade it to Ubuntu 12.04 Precise Pangolin. But its network stopped working.

I tried to fix its issues by ifconfig and GUI, but what it really wanted was for me to put the network cable back into its eth0 slot. The eth1 network card appears not be working anymore.

All seems fine now. Next I will mount the shared user disk from linux1 and put in a .bashrc.

  553   Mon Jun 23 19:33:01 2008 rana, jenneUpdateIOOMC_F Noise check
We looked at the MC_F spectrum because Rob and Yoichi said that it had gone 'all crazy'. It
seemed fine as we looked at it (even with only one boost stage on) so we looked for things
that might be marginal and make it go nuts.

At the error point (Q mon on the demod board and TEST IN1) of the MC Servo board we saw the
old 3.7 MHz signal (comes from the 33 MHz RFAM getting demodulated by the 29.5 MHz MC LO)
and thought that this might cause some worries. So we installed Jenne's passive elliptic
low pass which has a 3.7 MHz zero.

This wiped out the 3.7 MHz noise but we were not able to re-create the extra frequency noise
so its unlikely to have fixed the main problem. However, we leave it in because its good. If
there is a need to revert it, we have left hanging on the side of the rack the old cable which
was a SMA->TNC making a direct, unfiltered connection between the MC Demod board and the MC
servo board.

More before and after results from Jenne tomorrow, but for now here is a calibrated MC_F spectrum
using the new MC_F-Reference.xml template file.

We also noticed that we could make some small effects on the MCF spec by adjusting the PMC gain so
there's probably more hay to be made there using a lead brick and a gain slider. More in Jenne's
  873   Sat Aug 23 09:39:51 2008 rana, jenneUpdatePSLPMC Survey
Jenne, Rana

We scoped out the PMC situation yesterday.

Summary: Not broke. UGF ~ 500 Hz. Needs some electronics work (notches, boosts, LPFs)

Ever since we swapped out the PMC because of the broken PZT of the previous one, the UGF has been
limited to a low value. This is because the notches no longer match the mechanical resonant
frequencies of the body. The old one had a resonance at 31.3 kHz which we were notching using
the LC notch on the board as well as a dangling Pomona box in the HV line to the PZT. The one
has a resonance at ~14.5 kHz which we don't yet have a notch for. Jenne has all the real numbers and
will update this entry with them.

  • Implement the 4th order Grote low pass after the mixer.
  • Replace the AD797 with an OP27.
  • Change servo filter to have a boost (need DC gain)
  • Make a 14.5 kHz notch for the bode mode.
  • Put a 20 lb. gold-foil wrapped lead brick on the PMC.

Here's the link about the modified PMC board which we installed at LHO:
LHO PMC elog 2006
  1978   Tue Sep 8 20:15:33 2009 rana, jenneSummaryPSLRC temperature servo: Heater Voltage noise

We measured the voltage noise of the heater used to control the RC can temperature. It is large.


The above scope trace shows the voltage directly on the monitor outputs of the heater power supply. The steps are from the voltage resolution of the 4116 DAC.

We also measured the voltage noise on the monitor plugs on the front panel. If these are a true representation of the voltage noise which supplies the heater jacket, then we can use it to estimate the temperature fluctuations of the can. Using the spectrum of temperature fluctuations, we can estimate the actual length changes of the reference cavity.

I used the new fax/scanner/toaster that Steve and Bob both love to scan this HP spectrum analyzer image directly to a USB stick! It can automatically make PDF from a piece of paper.

The pink trace is the analyzer noise with a 50 Ohm term. The blue trace is the heater supply with the servo turned off. With the servo on (as in the scope trace above) the noise is much much larger because of the DAC steps.

  9187   Thu Oct 3 00:01:59 2013 rana, jenneHowToLSCsteps to full IFO

In moving now to full IFO locking, there are a number of sub-states to diagnose:

  1. PRMI + 1 arm
  • Measure sensing matrix as arm is scanned into resonance. Compare time series of sensing matrix elements with New LoopTickle simulation. But first, we need more than 1 LOCKIN screen in the LSC! That will allow us to measure all of the elements of front_matrix.jpg simulataneously.
  • Measure 3f PRMI noise spectra as a function of arm position. Look for trouble.
  1. DRMI + 1 arm
  • Same as PRMI above.
  • Want to find why this is unstable sometimes. Make stable for t > 10 minutes.
  • Maybe add some QPD->ASC for SRC angular control, but how? Will this still work after the arms are resonant or will it be swamped by carrier contrast defect? Will Berlusconi ruin all of the Italian gelateria? Only time can tell...
  1. FPMI (non optically recombined) for ALS diagnosis
  2. PRFPMI (iLIGO configuration)
  • this ought to be easier than DRFPMI
  • will let us tell if our ALS is good enough to handle the coupled cavity pole
  1. DRFPMI (aLIGO style)

Which to do first and in what order?

  9188   Thu Oct 3 01:06:48 2013 rana, jenneUpdateSUSoplev XY-plots reflect new calibration

As another proof that sometime is ill with ETMX Optical Lever:

We scanned the ETMX bias in PIT using ezcastep and saw that the OL response is very screwy. In the attached, you can see that the ETMX SUSPIT signal shows that the actual motion is good and linear. In fact, our sus diagonalization is extermely good and there's almost no signal in SUSYAW.

  9191   Thu Oct 3 02:43:34 2013 rana, jenneSummaryLSCPRMI: comparison of 1f and 3f signals w/ calibration

The attached plot shows the spectra of all the REFL signals with the PRMI SB lock.

We excited the ITMY_LSC with 3000 counts. We used the Masayuki calibration of ITMY (5 nm / count * (1/f^2)) to estimate this peak in the REFL spectra.

To correctly scale the REFL spectra we account for the fact that the DTT BW was "0.187 Hz" and we turn off the "Bin" radio box before measuring the peak height with the cursor.

Since the ITMY motion is 3000 * 5e-9 / (580.1 Hz)^2 = 44.6 pm_peak, we want the DTT spectrum of the REFL spectra to report that too.

i.e. to convert from peak height to meters_peak, we use this formula:

meters_peak = peak_height * sqrt(BW) * sqrt(2)

I *think* that since the line shows up in multiple bins of the PSD, we should probably integrate a ~0.5 Hz band around the peak, but not sure. Need to check calibration by examining the time series, but this is pretty close.

Mystery: why are the REFL_I 3f signals nearly as good in SNR as the 1f signals? The modelling shows that the optical gain should be ~30-100x less. Can it be that our 1f electronics are that bad?

Bonus: notice how we have cleverly used the comb of bounce frequencies around the calibration line to determine that REFL11 is clipping!

  9668   Tue Feb 25 00:00:01 2014 rana, jenneUpdateLSCreasons that the REFL signals may be degenerate now

We're exploring some effects which may give some funny macroscopic detuning and cause a near phase degeneracy in the REFL RF signals (see radar plot from Jenne below).

1) Alignment: we centered the oplevs to reduce fluctuations and then tweaked the BS and PRM alignment to build up the power. No significant change in the RF phases of the DOFs.

2) Measuring RAM: we set the dark offsets (by hand since the Masayuki script doesn't really work well anymore) to with 1 counts. We then locked the MC, misaligned the ITMs, and looked at the REFLOUT16 channels using the following command line:

C1:LSC-REFL11_I_OUT16     -12.04
C1:LSC-REFL11_Q_OUT16     -14.34
C1:LSC-REFL33_I_OUT16       0.43
C1:LSC-REFL33_Q_OUT16      -0.28
C1:LSC-REFL55_I_OUT16       2.84
C1:LSC-REFL55_Q_OUT16       5.64
C1:LSC-REFL165_I_OUT16      4.40
C1:LSC-REFL165_Q_OUT16      0.10

So these offsets are small in counts. In meters this corresponds to....less than 3 pm for any of the I signals.

Refl11I = 2.06e-12 meters

Refl11Q = 2.94e-10 meters

Refl33I = 5.28e-13 meters

Refl33Q = 1.07e-11 meters

Refl55I = 2.71e-12 meters

Refl55Q = 3.55e-11 meters

Refl165I = 3.07e-13 meters

Refl165Q = 8.63e-14 meters



3) Next we want to put large offsets into the error points of the loops

4) Change modulation depth

5) Check IMC length (todo for Q/Manasa for Tuesday - Wednesday)

  9669   Tue Feb 25 02:46:38 2014 rana, jenneUpdateLSCChanging PRCL offset changes REFL 165 degeneracy

[Jenne, Rana]

We put offsets in the PRCL and MICH loops, and measured sensing matrices for each condition. 

What we found was that PRCL offsets of order 1/20th a linewidth (calibration to be checked tomorrow) would give significant changes in the angles of the REFL signal sensing matrix elements.  We broke MICH lock before we were able to put in a significant enough offset to see the demod phases change.

Because there are so many plots, I've put them together in a pdf. Each page has a set of radar plots for sensing matrix elements.  On the bottom of each page I note what our MICH and PRCL offset values were, and where the data is saved (in the 40m scripts directory). To see the differences, make sure your pdf viewer is set to single-page, not scrolling.


One major thing that we noted was that putting in a PRCL offset also changed the MICH offset.  When we increased the PRCL offset, we saw the AS port get brighter (but not as bright as when we were putting in large MICH offsets). 

Tomorrow, I need to check the calibrations we were using, to see how many meters we were moving the optics.  Also, Q, Gabriele and I need to meditate and do some modelling to figure out why the length offset could be affecting the degeneracy so strongly. 

  9675   Tue Feb 25 23:38:05 2014 rana, jenneUpdatePEMGUR1 Z channel excess noise: oscillating Z channel

Last night we noticed an excess in the GUR1Z seis BLRMS on the StripTool. It was in the 0.1 - 0.3 Hz band. The rumor in the control room was that "this kind of noise has been showing up at night recently".

AS it turns out, this was not some environmental noise around the 40m at night, but instead its some internal servo oscillation in the GUR1 Z channel. In the Guralp seismometers, each channel is a different mechanical sensor (unlike the STS or T240), so when a single channel gets noisy it doesn't always implicate the others.

My guess is that the oscillation came from the Z channel needing to be recentered. I power cycled the interface box just now. The oscillation had already gone away, but I thought this might reduce the excess noise. Maybe it did, but the effect is tiny. You can see in the oscillation reference that the low frequency noise is high, but in the new trace its still kind of high. Needs to be re-centered correctly with the paddle. Or add a centering button to the interface box.

  9920   Wed May 7 04:01:44 2014 rana, jenneUpdateLSCPRFPMI: Common Mode servo using REFL_DC ON, CARM offset still non-zero
  1. With REFL_DC coupled into the CM board through an SR560 (with an offset subtractor), we were able to transition to use it as the CARM error signal.
  2. We reduced the CARM offset until the arm powers went up to ~13.
  3. We had the AO path turned on and the MCL/AO crossover was ~150 Hz.
  4. We saw the double cavity pole come in from HF down to ~1-2 kHz. The lock stayed stable like this.
  5. We've set the IMC overall gain higher by +4dB in the mcup script. That's -4 dB from Eric's max gain earlier today.
  6. We have some scripts now for this scripts/PRFPMI/ :   camr_cm_down.sh and carm_cm_up.sh
  7. The sequence was ALS -> SqrtInv while digital with CARM -> MC2. Then we digital transition to REFL_DC using the CM board switch to put REFL_DC into the REFL11_I socket.
  8. REFL_DC is noisy, so we upped the SR560 gain by 10 and compensated.

Also, we found the PRM OL off and turned it back on. The ETMY was swinging a lot after lock loss, so we set its SUSPOS damping gain to match the ETMX and it stopped swinging so much.

Next up: more of the same, make this sequence more stable, turn on CARM OSC and watch the LOCKI outputs while we slowly ramp between signals.

Also, what should be the sign of the CARM offset ???

  10396   Thu Aug 14 22:58:59 2014 rana, jenneSummaryGreen LockingALS DIFF tuning

 We've been having trouble tuning the ALS DIFF matrix. Trying to see if the MC2 EXC can be cancelled in ALS DARM by adjusting the relative gains in ALSX and ALSY Phase Tracker outputs.

There's a bunch of intermittent behavior. Between different ALS locks, we get more or less cancellation. We were checking this by driving MC2 at ~100-400 Hz and checking the ALS response (with the ALS loops closed). We noticed that the X and Y readbacks were different by ~5-10 degrees and that we could not cancel this MC2 signal in DARM by more than a factor of 4-5 or so. In the middle of this, we had one lock loss and it came back up with 100x cancellation?

Attached is a PDF showing a swept sine measurement of the ALSX, ALSY, and DARM signals. You can see that there is some phase shift between the two repsonses leading to imperfect cancellation. Any ideas? Whitening filters? HOM resonance? Alignment?

  10708   Thu Nov 13 01:03:28 2014 rana, jenneUpdateSUSOL updates on ITMs and ETMs

 We copied the new SRM filters over onto the OL banks for the ITMs and ETMs. We then adjusted the gain to be 3x lower than the gain at which it has a high frequency oscillation. This is the same recipe used for the SRM OL tuning.

Before this tune up, we also set the damping gains of the 4 arm cavity mirrors to give step response Q's of ~5 for all DOF and ~7-10 for SIDE.

  10807   Wed Dec 17 01:51:44 2014 rana, jenneUpdateASCASS retuned

Did a big reconfig to make the Y-arm work again since it was bad again.

  1. Undid Koji's topology change. The A2L loops now feedback to the arm mirrors to adjust the cavity axis. The cavity transmission signals now feedback to the input beam.
  2. The UGF of the Trans->Input beam servos is ~5-10x higher than the A2L servos.
  3. The Trans loops have a ~10-15 s settling time.
  4. The Input Matrix has been adjusted to fit with our intuition:The ETM tilt moves the beam equally on the ITM and ETM faces.
  5. The Output Matrix has also been adjusted to do like this: we're using an intuitive matrix inverse rather than one based on measurement. It turns out to be a reasonable guess and we can tune this later.
  6. Seems stable with many kinds of steps and misalignments. Seems not reliable if the arm power is less than ~0.5.
  7. Reducing the dither amplitudes to make the power fluctuation less than 5% made it much more stable.

With the arm aligned and the A2L signals all zeroed, we centered the beam on QPDY (after freezing the ASS outputs). I saw the beam going to the QPD on an IR card, along with a host of green spots. Seems bad to have green beams hitting the QPD alogn with the IR, so we are asking Steve to buy a bunch of the broad, dielectric, bandpass filters from Thorlabs (FL1064-10), so that we can also be immune to the EXIT sign. I wonder if its legal to make a baffle to block it on the bottom side?

P.S. Why is the Transmon QPD software different from the OL stuff? We should take the Kissel OL package and put it in place of our old OL junk as well as the Transmons.

  11041   Tue Feb 17 00:24:47 2015 rana, jenneUpdateLSCALS Fool filter updated for more cancellation

Today we measured the TFs again and then updated the filter in the POY -> ALS FF path so as to get 10x better cancellation.

The cancellation went from ~10 dB to ~30 dB. This seems good enough. The new filter 'Comp1' is just constructed by eye. We then had to tune the filter module gain to a few %. Seems good enough for now, but we should really try to understand what it is and why it is the way that it is. In the above plot, the ORANGE trace is the old cancellation and the GREEN one is the new one. The filter TF is attached below - its not special, we made it by presing buttons in FOTON until the TF matched the measured TF of ALSY/LSC-MC_CTRL_FF_OUT.

  2434   Sun Dec 20 21:39:40 2009 rana, jenne, kiwamuUpdateASSOAF Model update and build instructions

After a lot of headache, I got the OAF working again - read on for details.....................

Sometime last week, Jenne, Kiwamu, and I tried to update the OAF model to include the IIR "feed-around" path.

This path is in parallel to the existing FIR-based adaptive FXLMS stuff that Matt put in earlier. The reason for the

new path is that we want to try emulating the same FF technology which has been successful lately at LLO.


However, we were unable to make the ASS work after this work. Mostly, the build stuff worked fine, but we couldn't get DTT

to make a transfer function. The excitation channels could be selected and the excitation would actually start and get all the

way into MC1, but DTT would just hang on the first swep-sine measurement with no time-out error. Clearly our ASS building

documentation is no good. We tried using the instructions that Koji gave us for AAA, but that didn't completely work.


In particular, the 'make-uninstall-daq-ass' command gave this command:

[controls@c1ass advLigo]$ make uninstall-daq-ass
grep: target/assepics/assepics*.cmd: No such file or directory
Please make ass first
make: *** [uninstall-daq-ass] Error 1

re-arranging the order to do 'make-ass' first fixes this issue and so I have fixed this in the OAF Wiki.


The there's the whole issue with the tpchn_C3.par file. This contains all the test point definitions for the ASS/OAF machine. The main

IFO numbers are all in tpchn_C1.par and the OMC is all in tpchn_C2.par. When we do the usual build, in the 'make install-daq-ass' part:

[controls@c1ass advLigo]$ make install-daq-ass
Installing GDS node 3 configuration file
Updating DAQ configuration file

we get this .par file installed in the target area. The ACTUAL param file seems to actually be in /cvs/cds/caltech/gds/param  !!


Of course, it still doesn't work. That's because the standard build likes to point to /cvs/cds/caltech/gds/bin/awgtpman and the one that runs on

linux is actually /opt/gds/awgtpman. So I've now made a file called startup_ass.cmd.good which runs the correct one. However, the default build

will try to start the wrong one and we have to fix the 'startass' script to point to the correct one on each build. Running the correct awgtpman

allows us to get the TP data using tools like tdsdata, so far no luck with DTT.\


UPDATE (23:33): It turns out that it was my old nemesis, NTPD. c1ass had a /etc/ntp.conf file that was pointing at an ntp server called rana113. I

am not an NTP server; I don't even know what time it is. I have fixed the ntp.conf file by making it the same ass c1omc (it now points to nodus). After

this I set the date and time manually (sudo date -s "20 DEC 2009 23:27:45") and then restarted NTPD. It should now be fine even when

we reboot c1ass.


After all of this nonsense, I am able to get TP data from c1ass and take transfer functions between it and the rest of the world !

  2437   Mon Dec 21 02:22:31 2009 rana, jenne, kiwamuUpdateASSOAF Model update and build instructions

This allowed measuring the MC1 -> MCL TF finally. Its mostly flat. Data saved as Templates/OAF/OAF-MCLTF.xml

  2836   Fri Apr 23 21:02:14 2010 rana, joeUpdateLSCStarted dev of LSC FE

Joe and I started working on the new LSC FE control today. We made a diagram of the system in Simulink, but were unable to compile it.

Joe checked out the latest CDS software out of their new SVN and put it somewhere (perhaps his home directory).

We then copied the directory with the .mdl files and the CDS parts library into our real Simulink Model Directory:


Use this and not someplace in Alex or Rob's home directory !

Joe will put in more details on Monday once he figures out how to build the new stuff. Basically, we decided not to support multiple versions of the CDS real time code here. We'll just stay synced to the latest stable ~versions.

I exported the current version of the LSC FE into our public_html/FE/ area on nodus where we will put all of the self-documenting FE diagrams:


To make a web setup like this, you just use the "Export to Web" feature from the top-level Simulink diagram (e.g. lsc.mdl). Choose the following options:


Note: in order to get the web page to work, I had to change the apache httpd.conf file to allow AddType file overriding. Here's the term cap of the diff:

nodus:etc>diff httpd.conf httpd.conf~
< ServerAdmin jenne@caltech.edu
> ServerAdmin aso@caltech.edu
<     AllowOverride FileInfo

  4232   Mon Jan 31 12:40:38 2011 rana, joeUpdateGreen LockingDFD - medm screen

This is a plot showing the old filters and the new ones we added this morning.

The new ones have a Cheby for AC coupling below 10 Hz and then a 500 Hz LP after the mixer. The LP frequency has been increased so that we can use this signal in a feedback loop to the ETM with a ~100 Hz UGF.

  3603   Thu Sep 23 23:24:43 2010 rana, johnny, taraSummaryPSLAM modulate AOM to measure RefCav Thermo-Optic coefficient

Big Johnny and I hacked a function generator output into the cross-connect of the 80 MHz VCO driver so that we could modulate the

amplitude of the light going into the RefCav. The goal of this is to measure the coefficient between cavity power fluctuations and the

apparent length fluctuations. This is to see if the thermo-optic noise in coatings behaves like we expect.


To do this we disconnected the wire #2 (white wire) at the cross-connect for the 9-pin D-sub which powers the VCO driver. This is

called VCOMODLEVEL (on the schematic and the screen). In the box, this modulates the gain in the homemade high power Amp which

sends the actual VCO signal to the AOM.


This signal is filtered inside the box by 2 poles at 34 Hz. I injected a sine wave of 3 Vpp into this input. The mean value was 4.6 V. The

RCTRANSPD = 0.83 Vdc. We measure a a peak there of 1.5 mVrms. To measure the frequency peak we look in

the FSS_FAST signal from the VME interface card. With a 10 mHz linewidth, there's no peak in the data above the background. This signal

is basically a direct measure of the signal going to the NPRO PZT, so the calibration is 1.1 MHz/V.


We expect a coefficient of ~20 Hz/uW (input power fluctuations). We have ~1 mW into the RC, so we might expect a ~20 Hz frequency shift.

That would be a peak-height of 20 uV. In fact, we get an upper limit of 10 uV.

 Later, with more averaging, we get an upper limit of 1e-3 V/V which translates to 1e-3 * 1.1 MHz / 1 mW ~ 1 Hz/uW. This is substantially lower

than the numbers in most of the frequency stabilization papers. Perhaps, this cavity has a very low absorption?

  930   Thu Sep 4 18:02:34 2008 rana, josephbConfigurationPEMAccelerometer gains increased by 10
We increased the Accelerometer gains by 10 by modifying the C1ADCU_PEM.ini file.
gain = 10

The plot shows the before and after for one channel. The ADC noise floor is ~10^-2 counts/rHz in this plot so now
we can do much better noise subtraction.
  882   Mon Aug 25 17:45:34 2008 rana, josephb, robHowToPEMAccelerometer range
Joe shows us by jumping up ~15" in the control rom that the accelerometers are set with not enough gain.

Since this is taken around 5:30 in the evening, so we can take the nearby time series to represent what a
high noise level is. I recommend we up the gain using the ICS-110B .ini file.
  894   Thu Aug 28 19:02:25 2008 rana, josephb, robSummaryComputersbig boot
This afternoon Joe did something with an .ini file (look for his detailed elog entry) and the computers went bad.
RFM network screen not active - filter modules not working.

We went around and booted every machine as has been done before. The correct order for a memory corruption
fixing big boot is the following:

    [1] RESET the RFM switches near the FB racks.
    [2] Power cycle c1dcuepics.
    [3] Power cycle all other crates with real time CPUs:
    c1iscey, daqctrl, daqawg, c1susvme1, c1susvme2, c1sosvme, c1iovme, c1lsc, c1asc, & c1iscex
    [4] Start up all FEs as described in Wiki.
    [5] Burt restore everyone (losepics, iscepics, assepics, omcepics?)
  6034   Tue Nov 29 07:45:56 2011 rana, joshSummaryComputer Scripts / Programs40m Daily News web pages

 As part of the initiative to get a good daily summary page for aLIGO commissioning, Josh is spearheading his Detector Characterization group to produce such web pages for the 40m.

They're starting out with this launching point and then we can add all kinds of other information and plots as we want (e.g. Vac, PEM, Weather, coffee status). If you have suggestions/ideas, just edit this entry and add them, or email Josh directly.

  3014   Sun May 30 13:26:07 2010 rana, kiwamuUpdatePSLnew HIGH-LOW value for PMC_TRANS

We changed the HIGH/LOW values of the PMC_TRANS.

The edited file was updated on the svn.

Since the PMC_TRANSPD was replaced behind the pzt mirror (see the entry), its nominal value were reduced to something like ~1V from the previous value of ~2V.

In the medm screen C1PSL_PMC.adl the PMC_TRAN always indicated red because the value were low compared with the previous one.

We went to /cvs/cds/caltech/target/c1psl, then edited psl.db

- Here are the new parameters we set up in the file.




- - - -

These values are based on ~4days trend of the PMC_TRAN.

Then we manually updated those numbers by using ezcawrite in order not to reboot C1PSL.

So now it nicely indicates green in the medm screen.

  2442   Tue Dec 22 02:50:09 2009 rana, kiwamu, jenneUpdateASSOAF Feedaround ON and doing something good

Kiwamu made the OAF screen functional today - screenshot attached.

After this, I used the measured TF of the MC1 to MCL to filter the signals from the Wilcoxon accelerometers and feed them into the MC.

The noise at 3 Hz went down by a factor of ~3. There's a little excess created at 100 Hz. Its good to see that our intuition about feed-forward is OK.

I did all of the filter calculations by adapting the scripts that Haixing, Valera, and I got going at LLO. They're all in the mDV/extra/C1 SVN.


The Wiener code predicts much better performance from using more than just 2 horizontal accelerometers, but I was too lazy to do more channels today.

I also added the Rai box to the Ranger readout today - the noise at 0.1 Hz went down by a factor of 10 and the noise at 1 Hz is close to 10^-11 m/rHz.

  4331   Sun Feb 20 21:22:33 2011 rana, kiwamu, valeraConfigurationIOOMC Servo Change

For some reason, Kiwamu forced us to change the MC servo electronics today. We are now combining it with the FSS box.

The MC Servo by itself was locking by just driving the NPRO PZT. Becuase of the ~30 kHz mechanical resonances of that system, our badnwidth is limited. To get higher bandwidth, we can either use a wideband frequency shifter like the AOM or just use the ole FSS combo of PZT/EOM. The old MC servo was able to get 100 kHz because it used the AOM.

So we decided to try going through the FSS box. The MC servo board's FAST output now goes into the IN1 port (500 Ohm input impedance) of the TTFSS box. This allows us to use the FSS as a kind of crossover network driving the PZT/EOM combo.

At first it didn't work because of the 5V offset that Jenne, Larisa, Koji, and Suresh put into there, so I cut the wire on the board that connected the power to the summing resistor and re-installed the MC Servo board.

We also removed the old Jenne-SURF 3.7 MHz LP between the MC mixer and servo. Also removed the Kevin-box (1.6:40) stuck onto the NPRO PZT.

We have yet to measure the UGF, but it seems OK. The PCDRIVE is too high (~5-6V) so there is still some high frequency oscillation. Needs some investigation.

* To get the FSS SLOW servo to work (change NPRO temperature to minimize PZT drive onto NPRO) I set the setpoint to 5V in the script so that we operate the FSS box output at 5V mean. I set the threshold channel to point to MC_TRANS_SUM instead of RC_TRANSPD. I also had to fix the crontab on op340m so that it would point to the right scripto_cron script which runs the FSSSlowServo, RCThermalPID.pl, etc. I also had to fix scripto_cron itself since it had the old path definitions and was not loading up the EpicsTools.pm library.

** Also, I was flabbergasted by the dog clamping on the last turning mirror into the MC. Barely touching the mount changes the alignment.

  3556   Fri Sep 10 02:35:30 2010 rana, kiwamu, valera, taraConfigurationPSLupdate

Over the last couple nights we got the beam into the FSS path and all the way to the IMC and out onto the AP table.

Tara and Valera have calculated a mode-matching solution for the reference cavity. It utilizes only a single lens between the AOM and the reference cavity. Valera and Steve will move the reference cavity into place in the morning.

We noticed that the layout was too tight on the end going into the MC and so we adjusted the angle of the final zig-zag. This will put the final mode-matching lens in between the final steering mirrors (which is generally undesirable) but the lens in this case is only f=400 mm. In addition, this lens may provide some more decoupling between the steering mirrors.

The whole layout has to be a little adjusted because of a calculation mistake I made in the mode-matching. I used only the nominal focal lengths from the CVI catalog and not the effective one. For the UV-grade fused silica lenses, the effective focal length is actually 20-30% longer. Today we measured that the "f=200 mm" lens we got is actually f = 238 mm. The BK7 lenses are much closer to the nominal.

We also replaced the Klinger mount ahead of the PMC with a Polanski style so that we could get the PMC REFL beam out without hitting the mount. Valera will continue to refine this section on the weekend.

Tomorrow, we will lock the MC using feedback only to the NPRO. The 0-150 V piezo driver is on the PSL table ready for action.

I also got a LCD video monitor from Frank and hooked it up on the PSL table. If we like this kind of thing, we can get many of them. They are pretty cheap. It would be handy to have 3-4 of them on the PSL and one on every of the ISC tables. They take the standard video for input and need +12V for power. Right now the one in there is looking at the PMC transmission.

The Omnigraffle layout as of tonight is attached.

  1451   Wed Apr 1 23:18:07 2009 rana, kojiSummaryIOONo Reference Cavity Required
Koji sent us a note about our "No Reference Cavity Required" entry. I thought that it nicely summarizes the
whole shebang and so I post it here for its pedagogical value.

Generally, frequency stabilization is a comparison of the two
frequency references.

1. In the conventional case you are comparing the NPRO stability with
the RC stability. The NPRO cavity is short and probably placed in a
less stable environment than that of the RC. Therefore, the PDH
signal only feels the frequency fluctuation of the NPRO, resulting
in the laser PZT fast feedback dominated by the NPRO stability. As
the MC length at low frequency is controlled by the mass feedback,
the resulting laser stability through the MC is virtually limited
by the RC stability.

2. On the other hand, you are comparing the stabilities of the NPRO
crystal and the MC cavity in the direct control configuration. The
stability of the MC at high frequency is better than that of the
NPRO. It is opposite at low frequency, of course, because of the
pendulum motion. The resulting laser stability through the MC is
limited by the MC stability.

3. In the CM servo, the length of the MC is stabilized such that the
arm stability is duplicated to the MC. As a result, your MC servo
compares the stability between the NPRO and the arm cavity. Again
at around 1Hz, the arm cavity is noisier than the NPRO. (This is
true at least TAMA case. I am quite unsure about it in the LIGO
long arm cases.)

One useful consequence is that in those configurations, the laser PZT
feedback at around 1Hz represents the stability of the NPRO, the MC,
and (possibly) the arm cavity, respectively. It was clearly seen
Yoichi's e-log entry 1432. At TAMA we call this signal as "MCPZTfb"
and use this for the diagnostic purposes of the suspended cavities. As
the laser fast PZT is rarely replaced and considered as a stable
actuator, this signal is considered as a good reference at low
frequency which is consistent across various configurations
(e.g. before/after replacement of the suspensions etc). Once the
response and the coefficient are calibrated you can easily convert
this signal to the length displacement.

Another remark: In the direct configuration, the frequency stability
of the beam goes through the MC is determined by the MC stablity. It
means that the beam to the arm has essentially worse stability than
the arm stability by factor of L_arm/L_MC. In the 40m case this factor
is just 3 or so. This is ok. However, for the LIGO 4km arm, the factor
becomes something like 300. This means that if you have 1um_rms of the
MC length fluctuation, the arm PDH feels 300um_rms. (Maybe some extent
less because of the common mode rejection of the MC suspensions.)

Yes, the actuator to the MC length is very strong this time, and
should be able to stop this amount of fluctuation easily... if the
things are all linear. I am not certain whether you can acquire the
lock even by this strong actuator when the arm is crazily swinging,
the PDH signals are ringing all the way, etc, etc...Particularly in
the recycling case!

One possible remedy is a technique developed by the German
necromancers, as always. They used the NPRO cavity as a reference
cavity. They actuate the MC length at low frequency. But I don't know
the exact configuration and how they accomplished the CM hand-off. We
have to ask Hartmut.

The other possibility is your adaptive stabilization of the MC by the
FIR technique. So far I don't know how much stability you can improve
in the LIGO 4km case.

There would be many possibilities like feedforward injection from the
green arm locking signal to the MC length, etc, etc.
  1731   Fri Jul 10 19:56:23 2009 rana, kojiOmnistructureEnvironmentChanged office temp

I have increased the temperature setpoint in the office area by ~0.75 deg F. Figure attached. Also a few days ago I increased the setpoint of the AC in the control room. Looks like the Laser is able to handle the changes in office area temperature so far, but lets see how it fares over the weekend.

  2242   Wed Nov 11 18:43:57 2009 rana, kojiHowToPhotosIlluminated Paintbrush Technique


1/4" exposure, standard room lights                                                                              3" exposure, slowly moving LED bar light from ~60 cm distance

Because of the light behind, the focus was attracted by the far objects...
Evenso the magnet ball looks better in the right picture.

The technique is as follows:
Use longer exposure time, move the LED bar illumination through the area like painting the light everywhere.
It is supposed to provide a picture with more uniform light and the diminished shadow.


  2762   Sun Apr 4 00:21:42 2010 rana, kojiSummaryElectronicsCheckout of EG&G (PARC) preamp model #113, s/n 49135

We tested out the functionality of the EG&G 113 preamp that I found in one of the cabinets. This is one of the ancestors of the SR560 preamp that we are all used to.

It turns out that it works just fine (in fact, its better than the SR560). The noise is below 3nV/rHz everywhere above 30 Hz. The filter settings from the front panel all seem to work well. And the red knob on the front panel allows for continuous (i.e. not steps) gain adjustment. In the high-bandwidth mode (low pass filter at 300 kHz), there is ~35 deg of phase lag at 100 kHz. So the box is pretty fast.


I would easily recommend this above the SR560 for use in all applications where you don't need to drive a 50 Ohm load. Also the battery is still working after 17 years!

There's several more of the this vintage in one of the last cabinets down the new Y-arm.

  3903   Fri Nov 12 00:42:11 2010 rana, kojiUpdateIOOMC alignment

We decided to ignore the computer script outputs for the beam positions and use instead the eyeball method to get the beam into the MC:

  1. Adjust PSL launch beam to get the beam centered on IM1.
  2. Eyeball the beam to hit the center of MC1. We can get this pretty good by using the brackets to get the vertical and using the centering of the input/refl beams to center it horizontally.
  3. Use MC3 suspension to hit the center of MC2. We did this by hitting each of the 3 EQ stop screw heads and triangulating the MC3 bias settings.
  4. Use MC2 bias to hit the center of MC1.
  5. Use MC1 to get good flashes.
  6. Use all 3 MC sus biases to maximize the transmitted light and minimize the REFL DC.

With this rough alignment in place, we leave it to Yuta to finish the coil balancing and the A2L. We will have an aligned MC in the morning and will start the BS chamber alignment.

  4253   Fri Feb 4 23:39:56 2011 rana, kojiUpdateLSCmixer based FD set up for noise test

We set up the mixer based FD to check out its noise performance.

It is being acquired as C1:GCV-XARM_FINE_OUT_DAQ.

We have calibrated it by driving the frequency of the RF signal generator and putting the value into the GAIN field. We got 100 kHz / 5450 counts; the _OUT_DAQ channel is now being recorded in units of Hz. The cable length has been adjusted so that the full mixer output can swing 16 MHz peak-peak before turning over.

Also, we did a lot of cable cleanup around the IO rack. Kiwamu and Suresh's setups were somewhat dismantled. The whole area was too messy and too hacky to be allowed to survive. Our "temporary" setups have a way of becoming permanent holding places for barrels, adapters, duct tape, etc.

  4254   Sat Feb 5 23:03:04 2011 rana, kojiSummaryElectronicsAnalog Frequency Discriminator: splitter + mixer + long cable

This diagram shows the setup of the analog Mixer-Frequency Discriminator (MFD).

The idea is similar to the one of the Schnupp Asymmetry for our Michelson interferometers. The signal from the PD (or any signal source for which you want to know the frequency) is split into two legs; one leg is much longer than the other. The two legs are recombined at a mixer/demodulator. The demodulator output varies sinusoidally with the phase difference of two legs, the same as when we try to measure the phase noise of an oscillator, for example. This is the same concept as the digital frequency discriminator that Aidan and Joe put into the GFD FE system recently.

With a ~1m cable length asymmetry, we get 180 deg of phase shift for a ~100 MHz signal (recall that the speed of light in most of our cables is ~2 x 10^8 m/s). The mixer gives a linear output at 50 MHz (and 150 MHz, 250 MHz, etc.).

This single mixer based setup is fine for most everything we do. In order to get even more resolution, one can just use 2 mixers by splitting the signal with a 4-way instead of 2-way mixer. One setup can have a 0.5-1 m asymmetry to have a large range. The other can have a ~10-30m asymmetry to get a comb of linear readouts.

Typically, we will have some kind of weak signal at the photodiode and will use a 20 or 40 dB gain RF amp to get the signal into the mixer. In this case, the mixer output noise will be at the level of tens of nV/rHz. Any usual low noise audio amplifier (SR560 variety) will be enough to read out the signal.

Why the 50 Ohm terminator? If you look at the specs of the BLP-1.9 filter from Mini-Circuits (its the same for almost all of their LP filters) you see that there's ~90 dB of attenuation above ~30 MHz (where our signals 2*f product will show up). If we use an RF input signal of ~0 dBm, this means that we get a high frequency product of -95 dBm (~10 uVrms) which is OK. But the return loss is 0 dB above 5 MHz - this means that all of the high frequency content is reflected back into the mixer! The 50 Ohm terminator is there to absorb the RF signals coming out of the mixer so as to prevent them from going back into the mixer and mixing with the RF/LO signals. The 50 Ohm terminator does attenuate the DC/audio frequency signals we get out of the mixer by a factor of two, but that's OK since we are not limited by the mixer's thermal noise.

Noise Measurement:

To checkout the noise, we used a 6m RG-58 cable in one leg. We used the DS345 signal generator for the source. We adjusted the frequency to (~21 MHz) give a ~zero mean signal at the demod output. The 6m cable makes the demod output's peak-peak swing correspond to ~16 MHz. We then used an SR560, DC coupled, G=1000, low-noise, 2pole low pass at 1 kHz, to get the signal into the ADC.


The attached plot shows the noise. We have caibrated the digital gain in the channel to make the output into units of Hz. The high frequency noise floor is ~0.3 Hz/rHz and the 1/f knee is at 10 Hz. This setup is already good enough for all of the green locking work at the 40m. In order to make this useful for the reference cavity work or the gyro, we will have to use a longer cable and a lower noise audio amplifier.

As can be seen from the plot, the ADC noise is below the measured noise. The noise of the SR560 with the input terminated is shown in grey - the measured noise of the MFD is very close to this. In order to improve the performance, the next step should be to use a longer cable. There's clearly going to be some trade-off between the temperature dependent effects which come with long cables (dphi/dT gets bigger) and trying to use a high gain ~1 nV/rHz amplfier at the mixer output.

Temperature Drift of the long cable:


This 24-hour minute-trend shows the frequency wander as well as the room temperature. This is not proof of a temperature dependence, but if it is then we get ~3 kHz/deg for the sensitivity. If this is actually the cable and not the amplifier, then we'll have to hunt for a lower tempco cable and put it in a box to isolate it.

  6198   Sat Jan 14 00:50:08 2012 rana, kojiConfigurationIOOTowards coating thermal noise measurement with RefCav / MC beat

Koji asked aloud tonight if we could measure the coating thermal noise of the refcav optics by beating the refcav light with the MC_TRANS light. Then we looked at our calculations for the noises:

Displacement noise of T=200ppm silica/tantala coating on a 1" silica substrate with a 300 micron beam spot = 1e-18 * sqrt(100 Hz / f) m/rHz.

Displacement noise from coating thermal in the MC is roughly smaller by the beam size ratio (1.8 mm / 0.3 mm). Some differences due to 3 mirrors and more layers on MC2 than the others, but those are small factors.

So, the frequency noise from the refcav should by larger than the MC thermal noise by a total factor of (1.8 / 0.3) * (13 m / 8 inches) ~ 400.

Another way to say it is that the effective strain noise in the RC is (1e-18 / 0.200) = 5e-18 /rHz. This translates into (5e-18 * 13) = 6.5e-17 m/rHz in the MC. (in frequency noise its 1.5 mHz/rHz).

I have measured the frequency noise in the LLO MC to be at this level back in 2009, so it seems possible to use our RC + MC to measure coating thermal noise by the length amplification factor and compete with Frank+Tara.


So today we set up the Jenny RC temperature setup to lock the LWE NPRO to the RC and then set up the beat note with the IFO REFL beam on the AS table. By using the 2 laser beat, we are avoiding the VCO phase noise issue which used to limit the PSL frequency noise at ~0.01 Hz/rHz. To do this we have reworked some of the optics on the PSL and AS tables, but I think its been done without disturbing the beams for the regular locking. Beat note has been found, but the NPRO has still not been locked to the RC - next we setup the lockin amp, dither the PZT, and then use the New Focus lock box to lock it to the RC.

You might think that its hard to measure this since the MC has ~1 MHz frequency fluctuations and we want to measure down to 1e-4 Hz. But, in fact, we can just use a 200 m MFD with a LT1128 preamp. Then we use the MFD to stabilize the MC length to the refcav and just use the control + error signal of the MFD setup as the coating thermal noise measurement.


Note: Beat found at ~40deg for the aux laser. The aux laser is on but the shutter is closed.
The AS camera seems to be hosed. Need a bit of alignment. (KA) ==> Fixed. (Jan 15)

  9324   Thu Oct 31 21:22:00 2013 rana, kojiSummaryIOOmodulation beat note in MC servo

I hooked up the 4395 to the MC servo board test out (TP2A) and looked at the spectrum using our new SPAG4395.py script. We noticed a huge peak at ~3.8 MHz and correctly guessed that it was due to the beat between the MC modulation frequency 29.5 MHz and 3*f1 (~33 MHz).

So we tuned the Marconi for the main mod. from 11065910 to 11066099 Hz and saw the beat note disappear (to within the 1 Hz tuning precision of our Marconi).

New MC length tuning method! Alert the LA Times!


My conjecture is that this temperature dependent mismatch between the modulation frequency (f1) and the MC length  is what leads sometimes to our nasty saturating PC DRIVE signal. TBD.

  9760   Fri Mar 28 22:10:00 2014 rana, kojiUpdateSUSrecovery from

* EQ Southeast of LA around 45 minutes ago. Callum and I felt it.

* Koji and I came in to recover. MC suspensions had been mis-aligned. ETMs both tripped their watchdogs.

* As before, the ETMX was stuck in its cage and the UR & LR OSEMs were reading zero V.

* We moved the MC sus back to their OSEM values from 2 hours ago. Koji aligned everything else by just using his chee.

* To shake the ETMX loose, I tried a different tactic than the "Great Balls of Fire". I started giving it 20k steps through the ASCYAW filterbank (with ramping OFF). I used the green light in the X arm video to look at the swinging. Using this as a readback I pumped the OFFSET button on ASCYAW to resonantly swing up the yaw motion. I had to turn the watchdog thresh up to 2000 temporarily. After a couple minutes the ETMX was free.

* We then used the bias sliders to steer it back onto the OL center (which Q nicely lined up for us recently) and then X arm locked in green right away.

Fri Mar 28 22:38:04 2014:  We've just ridden through the 5th aftershock. None of the aftershocks have tripped the watchdogs  but they break the IMC lock.

  10832   Mon Dec 22 21:53:08 2014 rana, kojiUpdateIOOSeven transfer functions

Today we were looking at the MC TFs and pulled out the FSS box to measure it. We took photos and removed a capacitor with only one leg.

Still, we were unable to see the weird, flat TF from 0.1-1 MHz and the bump around 1 MHz. Its not in the FSS box or the IMC servo card. So we looked around for a rogue Pomona box and found one sneakily located between the IMC and FSS box, underneath some cables next to the Thorlabs HV driver for the NPRO.

It was meant to be a 14k:140k lead filter (with a high frequency gain of unity) to give us more phase margin (see elog 4366; its been there for 3.5 years).

From the comparison below, you can see what the effect of the filter was. Neither the red nor purple TFs are what we want, but at least we've tracked down where the bump comes from. Now we have to figure out why and what to do about it.

* all of the stuff above ~1-2 MHz seems to be some kind of pickup stuff.

** notice how the elog is able to make thumbnails of PDFs now that its not Solaris!

  10833   Tue Dec 23 01:55:35 2014 rana, kojiUpdateIOOSeven transfer functions

Some TFs of the TTFSS box

ELOG V3.1.3-