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ID Date Authorup Type Category Subject
  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.
[C1:PEM-ACC_MC1_X]
chnnum=15014
gain = 10

etc.
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.

grecord(ai,"C1:PSL-PMC_PMCTRANSPD")
{

  field(LOW,"0.98")
  field(LOLO,"0.93")
  field(HIGH,"1.15")
  field(HIHI,"1.3")

}

- - - -

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

IMG_0215.JPGIMG_0214.JPG

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

Note:
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.

(KA)

  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.

IMG_0628.JPG

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.

 fsm.png

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:

Untitled.png

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!

13031.png13031_200.png13031_200b.png

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

  10841   Tue Dec 23 20:50:39 2014 rana, kojiUpdateIOOSeven transfer functions

Today we decided to continue to modify the TTFSS board.

The modified schematic can be found here: https://dcc.ligo.org/D1400426-v1 as part of the 40m electronics DCC Tree.

What we did

1) Modify input elliptic filter (L1, C3, C4, C5) to give zero and pole at 30 kHz and 300 kHz, respectively. L1 was replaced with a 1 kOhm resistor.  C3 was replaced with 5600 pF. C4 and C5 were removed. So the expected locations of the zero and pole were at 28.4 kHz and 256 kHz, respectively. This lead filter replaces the Pomona box, and does so without causing the terrible resonance around 1 MHz.

2) Removed the notch filters for the PC and fast path. This was done by removing L2, L3, and C52.

At this point we tested the MC locking and measured the transfer function. We successfully turned up the UGF to 170kHz and two super-boosts on.

3) Now a peak at 1.7MHz was visible and probably causing noise. We decided to revert L2 and adjusted C50 to tune the notch filter in the PC path to suppress this possible PC resonance. Again the TF was measured. We confirmed that the peak at 1.7MHz is at -7dB and not causing an oscillation. The suppression of the peak is limited by the Q of the notch. Since its in a weird feedback loop, we're not sure how to make it deeper at the moment.

4) The connection from the MC board output now goes in through the switchable Test1 input, rather than the fixed 'IN1'. The high frequency gain of this input is now ~4x higher than it was. I'm not sure that the AD829 in the MC board can drive such a small load (125 Ohms + the ~20 Ohms ON resistance of the MAX333A) very well, so perhaps we ought to up the output resistor to ~100-200 Ohms?


Also, we modified the MC Servo board: mainly changed the corner frequencies of the Super Boost stages and some random cleanup and photo taking. I lost the connecting cable from the CM to the AO input (unlabeled).

  1.  The first two Super Boost stages were changed from 20k:1k to 10k:500 to give us back some phase margin and keep the same low freq gain. I don't really know what the gain requirement is for this servo here at the 40m. The poles and zeros were chosen for iLIGO so as to have the frequency noise be 10x less than the SRD at 7 kHz.
  2. The third Super Boost (which we never used) was changed from 10k:500 to ~3k:150 (?) just in case we want a little more low freq gain.
  3. There was some purple vestigial wiring on the back side of the board with a flying resistor; I think this was a way to put a DC offset in to the output of the board, but its not needed anymore so I removed it.

 

  11343   Tue Jun 2 21:22:07 2015 rana, kojiConfigurationIOOAOM inserted in beam and aligned

We spent an hour today to put the AOM back in the beam before the PMC and verified that the diffraction is working.

  1. The fuse holder was missing from the rack. We inserted a 5A fuse. We expect that the quiesscent draw is < 0.5 A. The power is from the +24V Sorensen supply.
  2. The alignment was tricky, but we optimized it as well as we could in translation and the RZ direction. Its a fixed mount still.
  3. We noticed that according to the datasheet, the polarization is wrong! It wants S-Pol light and we're giving it P-Pol. How come no one noticed this? We expect that the efficiency is reduced because of this. We (Steve) need to brainstorm what kind of mount we can use there to mount it at 90 deg to the plane of the table.
  4. The lens after the AOM has f = +400 mm. The distance from the AOM to the lens is ~800-900 mm so its not so terrible. However, if someone were to put the AOM halfway between the turning mirrors there, the beam diffraction would be canceled.
  5. The AOM input impedance seems to be 50 Ohm as advertised. The previous Koji entry claim of 25 Ohm is mysterious. We checked the Ohmage by sending a signal into the AM input of the AOM using the DS345 which as a 50 Ohm output. 1 Vpp from the DS345 made 1 Vpp on the input of the AM input as measured by Oscope connected by T with high impedance setting.
  6. With 0.5 V offset and a 1 Vpp signal, we get ~20-25% modulation of the power.sad
  7. We have left it running with a 4444.4 Hz modulation and a small amplitude. This is to see if we can use this to measure the cavity poles of the MC and the arms.
  8. We noticed some hash on the Teed input monitor. It was backstreaming of the RF drive. Whoever uses this thing in an ISS feedback ought to make sure to put an RF choke between the servo and this AOM driver.

We also removed a 50/50 pickoff mirror which was used to take one of the NPRO -> EOM polarizer reject beams and send it across the table into a floppy dump. Its now hitting a closer floppy dump. Let's stop using these crappy anodized aluminum flappers anywhere, Steve.

We also noticed that the PMC REFL path uses a W1 from CVI to send the PMC reflection to the REFL RFPD. The dim beam from the AR coated surface is being used rather than the bright beam from the uncoated surface. Ooops. Steve, can you please order another W1 for 1064 from CVI, but get it with a 2-3 deg wedge angle? This one has a wedge which is too small.

  11361   Mon Jun 15 22:36:40 2015 rana, kojiUpdateGreen LockingBeatBox Assay: not looking good

Because the ALS beatbox schematic is out-of-date and misleading, we pulled the box to photograph the current implementation and figure out how to proceed. The box is out on the EE bench right now. Schematic Doc added to 40m Document tree: https://dcc.ligo.org/LIGO-D1102241. Some notes:

  1. The soldering on this board is pretty messy and there are a lot of flying wire and flying component hacks. I wouldn't trust all of the connections.
  2. The GV-81 RF amps in the front end are both stuffed. The 1 dB compression point is 19 dBm, so we want to use them below 10 dBm output. They have a gain of +10.5 dB, so that means they should not be used with and input to the beatbox of more than -10 dBm. Otherwise there will be nonlinear noise generation.
  3. Not stuffed: U1-Comparator, A1-attenuator, U2-splitter.
  4. Why is the filter after the mixer only 2nd order?? That's not a valid filter choice in any RF world. How much do we want to cut off the 2f mixer output before sending into our low noise, audio frequency (and prone to downconversion) amplifier? The Mini-Circuits amplifiers would have given us >60 dB attenuation in the stop band. This one is only going to give us 20-30 dB when the beat frequency is low. Get rid of diplexer. The schematic claims that its just one pole?? Seems like a 2nd order LP filter to me.
  5. The modified schematic (see Koji elog 8855) shows that an OP27 is used for the whitening stage. The current noise of the OP27 with the 3k resistor makes the OP27 current noise dominate below 1 Hz. And what is going on with that filter capacitor choice? We never want to use these tiny things for sensitive filter applications. (cf. Sigg doc on resistor and capacitor choice, the noise reduction book by Ott, H&H, etc.). That's why we have the larger metal-poly, paper, mylar, etc. caps sitting around.

Probably we ought to install a little daughter board to avoid having to keep hacking this dead horse. Koji has some of Haixing'g maglev filter boards. Meanwhile Koji is going to make us a new beatbox circuit in Altium and we can start fresh later this summer.

Interesting link on new SMD cap technology.

Photos of circuit as found

  11363   Fri Jun 19 01:24:26 2015 rana, kojiUpdateGreen LockingBeatBox Assay: not looking good

We had decided a few days ago, to bypass the IF part of the BeatBox board and put some of the Haixing Maglev generic filter boards in there so that we could get more whitening and also have it be low noise.

Tonight we wondered if we can ditch the whole BeatBox and just use the quad aLIGO demod box (D0902745) that Rich gave us a few years ago. Seems like it can.

But, it has no whitening. Can we do the whitening part externally? Perhaps we can run the RF signals from the output of the beat RF Amps over to the LSC rack and then put the outputs into the LSC Whitening board and acquire the signals in the LSC ?

  12639   Wed Nov 23 17:48:16 2016 rana, kojiUpdateIOOHow bad is the McWFS?

Medium.


Previous elog entries on this:

  14730   Fri Jul 5 23:28:52 2019 rana, kruthiSummarySUSETMX unstuck by shaking the stack

We unstuck ETMX by shaking the stack. Most effective was to apply large periodic human sized force to the north STACIS mounts.

At first, we noticed that the face OSEMs showed nearly zero variation.

We tried unsticking it through the usual ways of putting large excitations through AWG into the pit/yaw/side DOFs. This produced only ~0.2 microns of motion as seen by the OSEMs.

After the stack shake, we used the IFO ALIGN sliders to get the oplev beam back on the QPD.

The ETMX sensor trends observed before and after the earthquake are attached.

** plots deleted; SOMEONE, tried to take raster images and turn them into PDF as if this would somehow satisfy our vetor graphics requirement. Boo. lpots must be actual vector graphics PDF

  8741   Tue Jun 25 00:28:52 2013 rana, manasaUpdateLSCArm Cavity scan with X-ALS after ALS servo upgrade

[Rana, Manasa]

ALS noise suppressed to 1KHz/rtHz. 1kHz RMS.

Plot 1: Scan of X arm by changing offset into Phase Tracker -> Xarm loop. Filter bank ramp time set to 120 s + using a 30 mHz low pass filter. IR beam is aligned to x arm, but not well.

Plot 2: ALS error signal with loop open (BLUE), closed with old filters (PURPLE), and with new, better boost (RED).

Plot 3: Bode plot of new boost (FM10), v. old, sad boost (1:50 pole:zero). RMS is now less than 1 kHz or ~50 pm. (in your face, Kiwamu!)

Changes made to the ALS servo:

1. C1ALS-TRX 

ALS-TRX has been calibrated to read from 0-1 instead of counts in 1000 s. Calibration factor = 1/4500 = 0.00022

2. C1ALS_BEATX_FINE

Old antiwhitening filter has been removed. Added LPF at 1000Hz to remove glitches at high frequencies.

3. C1ALS-BEATX_FINE_PHASE

No changes made.

4. C1ALS-XARM

FIlter FM5 modified. 1000:1 changed to 3000:1

5. Offset for ALS scan were given through C1ALS_OFFSETTER1 with LPF50m enabled.

 

The filter modules of the servo were:

 ALS1.png

ALS2.png

ALS3.png

 

 Next:

Check PZT out range for ALS. Figure out what the deal is with ALS SLOW servos.

Add DQ channels for ALS.

Automatic ALS up script (enable and disable phase tracker included).

 

 

  3173   Wed Jul 7 22:52:38 2010 rana, nancyConfigurationIOObad length control offset for the MC

Rana found out that a connection was bad in the shown place, due to which the MEDM screen was showing bad offset for length control.

Basically, the offset slider value would not go into the system because of that bad connection, and was locking the mode cleaner at the wrong location.

  9089   Fri Aug 30 01:01:28 2013 rana, nicSummaryComputer Scripts / ProgramsaLIGO Noise Budget code installed and running

Chris Wipf has been developing a new Noise Budget code that allows us to use our existing Simulink models to handle all of the noise transfer functions. This is mainly by being clever about avoiding the numerical pitfalls that we encounter when doing linearization of Simulink models (e.g. linmod or linmod2).

Screen_Shot_2013-08-30_at_1.00.02_AM.png

In this model, the optical plant is done with analytic TFs using the formulae from the Sigg Frequency Response doc. The big Orange block has just the DAC and some simple pendulum TFs. The upper section contains the simulated digital system: input matrix, digital filter TFs, and output matrix. The digital filters are just based on my memory of iLIGO. The CARM path is made to be fast to approximate the high gain of the Common Mode servo. Without this high gain the PRC optical plant is unstable due to the right half plane zeros. This simple model is used just so that we could see the NB work on a multi-loop system. For the next steps of getting it to work for the 40m, we will use the Optickle TFs instead of analytic functions and also load the digital filters directly from the FOTON files. For the LLO DRMI, we'll add some simplified version of the SUS Simulink models for triples and quads.

 

Yesterday, Nic and I took my old iLIGO IFOmodel.mdl Simulink model and added the new NB hooks that allowed us to use the new code. The screenshot below is from a run of this code:

1) Figure 1 shows the DARM Noise budget. So far we have included shot noise in DARM, CARM, MICH, & PRC. Radiation pressure noise on the ITMs and ETMs. Coating thermal noise on all mirrors.

2) Figure 2 shows the breakdown of how each of the shot noises at each port couple to the DARM readout. The RED trace is the AS port DC readout shot noise. The GREEN trace is the MICH shot noise feeding through the MICH loop and being mostly cancelled by the scalar MICHdamp feedforward path.

3) Figure 3 shows that we've set the coating thermal noise to be equal on all 4 TMs.

4) Figure 78754 is a set of Bode plots of the open loop gains of the 4 LSC loops (inferred from the closed loop TF). Also plotted is the residual MICH2DARM TF (with the MICHdamp cancellation path ON).

5) Figure 9911123 are the step responses of the LSC loops: step inserted at the error point and response measured just after the excitation point.

The editor window on the left shows how simple the NB code is to use once the Simulink model has had all the hooks added to it.

  1888   Tue Aug 11 23:55:04 2009 rana, richSummaryOMCQuantum Efficiency and Dark Current measurements of eLIGO Photodiodes

Rich Abbott, Rana

Summary: We found that the 3mm InGaAs photodiodes from eGTRAN which are being used for the DC Readout in eLIGO are bad. The QE is ~50%. We will have to replace them ASAP.

Valera and Nic Smith have pointed out out a factor of ~2 discrepancy between the estimated power transmission to the dark port in H1 and L1. So we decided to measure the QE of the accused diodes.

 The data of the QE and dark current are attached here.

We used a 1064 nm CrystaLaser (which does not have a very stable power output). We attenuated the light with an ND1.0 for all measurements.

The photocurrent is estimated by reading out the voltage across one leg of the differential drive of the DC PD preamp. The photocurrent goes across a 100 Ohm resistor and then through 2 gain of  1 stages to get to this testpoint, so the overall transimpedance gain is 100 Ohms for this measurement.

By far, the Ophir power meter is the biggest source of error. Its absolute calibration is only 5% and the variation across the sensor face is ~5%. There are some hot and not hot spots on the face which can make even more variation, but we tried to avoid these.

We also inserted the power meter very close to the time when we read the voltage, so that the photocurrent and power estimates are made within 10 seconds of each other. This should reduce the error from the laser's power fluctuations.

All diodes still had the glass case on. We measured the reflected power to be ~5-7% of the incident power. This reflected power is NOT accounted for in these estimates.

 

Punch line: The eGTRAN diodes that we currently use are definitely bad. The JDSU and EG&G 2mm diodes have a better QE. We should immediately purchase 3 mm versions and get them cut and measured to be ready for the Sep. 1 commissioning surge.

  2095   Thu Oct 15 02:38:10 2009 rana, robUpdateOMCDark Port Mode Scan using the OMC

Bottom trace is proportional to the OMC PZT voltage - top trace is the transmitted light through the OMC. Interferometer is locked (DARM- RF) with arm powers = 80 / 100. The peaks marked by the cursors are the +(- ?) 166 MHz sidebands.

  2101   Fri Oct 16 03:16:50 2009 rana, robSummaryLSCfunny timing setup on the LSC

While measuring the Piezo Jena noise tonight we noticed that the LSC timing is setup strangely.

Instead of using the Fiber Optic Sander Liu Timing board, we are just using a long 4-pin LEMO cable which comes from somewhere in the cable tray. This is apparent in the rack pictures (1X3) that Kiwamu has recently posted in the Electronics Wiki. I think all of our front ends are supposed to use the fiber card for this. I will ask Jay and Alex what the deal is here - seems like to me that this can be a cause for timing noise on the LSC.

We should be able to diagnose timing noise between the OMC and the LSC by putting in a signal in the OMC and looking at the signal on the LSC side. Should be a matlab script that we can run whenever we are suspicious of this. This is an excellent task for a new visiting grad student to help learn how to debug the digital control system.

  2118   Mon Oct 19 14:48:15 2009 rana, robSummaryElectronicspiezo jena measuring box
Attached is the schematic of the Piezo Jena driver measuring box made in a Pomona box:
                2.2 uF
In ----o-------- | | --------o-------- Out
       |                     |
       _                     |
       _  1uF                R  7.5 kOhms
       |                     |
       |                     |
      GND                   GND
The 1 uF cap is there to simulate the piezo and the 2.2 uF and 7.5k resistor ac couple the signal for the spectrum analyzer. They give a ~10 Hz corner frequency.
  2311   Mon Nov 23 00:46:09 2009 rana, robUpdatePSLISS RIN: Its too high by 10x

This plot shows the RIN as measured by the ISS. Its ~2 x 10^-7, whereas its supposed to be more like 3 x 10^-8.

The ISS has DC coupled RIN channels (with a _F suffix) and AC coupled RIN channels (with a _FW suffix). By using a swept sine, Rob determined that the AC coupled channels have an AC coupling pole at ~80 Hz. The attached plot uses this and then has the overall gain adjusted to match with the _F channels below 10 Hz.

The _F channels can be converted directly into RIN by just dividing the spectra by the mean value of the time series. The dark offset of these channels is small and so this only introduces a ~5-10% calibration error.

Question #1: Why is the RIN so bad? According to the MEDM screen, the photocurrent on the MON/SENS PDs is 1.9/1.3 mA. That's sort of low, but should still allow us to get 5x10^-8 in RIN.

Question #2: Does it make an effect on the current DC Readout work? IF so, should we try to fix up the ISS in a temporary way? Since the in-loop and out-of-loop detectors are completely coherent, all of the noise is likely just unsuppressed noise from the laser. We are unable to increase the gain because of the high frequency noise from the NPRO.

 

Let's remember to replace this ISS with a new one that can drive an AOM. Need a volunteer to get us a new ISS.

 

  2125   Tue Oct 20 11:38:10 2009 rana, rolfUpdateAdaptive Filteringextra delay and noise in PEM -> ASS/OAF system

An email from Rolf about the delay in the 110Bs:

"...we do take the ~2msec pipeline delay into account when we send the data to DAQ. If I remember correctly, the delay is about 39 samples. On startup, the first 39 samples are 'thrown away', such that, from then on, data lines up with the correct time (just read 2msec later then Penteks)."

  3052   Sun Jun 6 08:08:05 2010 rana, sanjitSummaryElectronicsCapacitor Bridge Test

To get a feel for the Capacitive Bridge problems, we setup a simple bridge using fixed (1 nF) caps on a breadboard. We used an SR830 Lock-In amplifier to drive it and readout the noise.

CapacitanceBridge.png

We measured the cap values with an LCR meter. They were all within a few % of 0.99 nF.

With a 0.5 V drive to the top of the bridge, the A-B voltage was ~2 mV as expected from the matching of the capacitors.

(** Note about the gain in the SR830: In order to find the magnitude of the input referred signal, one has to divide by G. G = (10 V)/ Sensitivity. 'Sensitivity' is the setting on the front panel.)

  1. Directly measuring from Vs to ground gives 0.5 V, as expected. This is done to verify the calibration later on.
  2. Shorting the A and B wires to ground gives ~0 V and lets us measure the noise. On the spectrum analyzer it was ~400 nV/rHz at 100 Hz and rising slowly to 4 uV/rHz at 100 mHz. In this state, the sensitivity was 10 mV, so the overall gain was 1000. That gives an input referred level of ~0.4 nV/rHz at the input.
  3. Hooking up now to A-B: the signal is ~10x larger than the 'dark' noise everywhere. 2 uV/rHz @ 100 Hz, 10 uV/rHz @ 10 Hz, 50 uV/rHz @ 1 Hz. The spectrum is very non-stationary; changing by factors of several up and down between averages. Probably a problem with the cheapo contacts in the breadboard + wind. The gain in this state was still 1000. So at 1 Hz, its 50 nV/rHz referred to the input.

To convert into units of capacitance fluctuation, we multiply by the capacitance of the capacitors (1 nF) and divide out by the peak-peak voltage (1 V). So the bridge sensitivity is 50e-9 * 1e-9 = 5 x 10^-17 F/rHz.

If we assume that we will have a capacitive displacement transducer giving 1 nF capacitance change for a 0.1 mm displacement, this bridge would have a sensitivity of 5 x 10^-12 m/rHz @ 1 Hz. We would like to do ~50-100x better than this. The next steps should be:

  1. Solder it all together on a PCB to have less air current sensitivity and decent contacts.
  2. Use a low-noise FET input. Since the impedance of the bridge is ~5 kOhms at this frequency, we are probably current noise limited.
  3. Estimate the oscillator amplitude noise sensitivity.
  1601   Mon May 18 19:44:52 2009 rana, steveConfigurationVACCryo Pump turned off and valved off: 1 beer can only
I was seeing some excess noise in the ETMY oplev yaw and so we turned off the cryo and restarted c1vac2 to get the turbo pump channels back.

The RGA was also turned off to protect its innocence and we are now running on the single beer can Turbo (TP3). The pressure has risen
from 1e-7 to 2e-5 torr. We'll probably level off at 5e-5 overnight and that's fine for now.

Unfortunately, the VM1 valve, which is between the RGA and the main volume, keeps getting turned off by our interlock software
to protect the RGA. Probably because our Vac screen shows the RGA 'Normal' even though the power is off and the record is invalid (white;
although the MEDM screen doesn't show it white).

I also moved Steve's secret Vacuum control screen from the target/ directory to the correct medm directory (with all the other Vacuum
screens) and added it to the SVN.
  2598   Fri Feb 12 14:19:28 2010 rana, steveHowToloreInternational Fax

Steve showed me how to send an international fax today:

  1. Load paper.
  2. Dial:   011 - (country code) - number
  3. Press START (either the black or color option)
  4. wait for the screaming fax noise
  5. Done

 

  3284   Sat Jul 24 13:13:41 2010 rana, steve, albertoUpdateGeneralInitial Crane Inspection reveals flaws: wiring and oil

The guy from KroneCrane (sp?) came today and started the crane inspection on the X End Crane. There were issues with our crane so he's going to resume on Monday. We turned off the MOPA fur the duration of the inspection.

  1. None of our cranes have oil in the gearbox and it seems that they never did since they have never been maintained. Sloppy installation job. The crane oiling guy is going to come in on Monday.
  2. They tried to test the X-End crane with 2500 lbs. (its a 1 ton crane). This tripped the thermal overload on the crane as intended with this test. Unfortunately, the thermal overload switch disabled the 'goes down' circuit instead of the 'goes up' circuit as it should. We double checked the wiring diagram to confirm our hypothesis. Seems the X-End crane was wired up incorrectly in the first place 16 years ago. We'll have to get this fixed.

The plan is that they will bring enough weight to test it at slightly over the rating (1 Ton + 10 %) and we'll retry the certification after the oiling on Monday.

  3573   Wed Sep 15 01:27:52 2010 rana, steve, valeraUpdatePSLFSS cables connected

- connected the TTFSS cables (FSS fast goes directly to NPRO PZT for now)

- measured the reference cavity 21.5 MHz EOM drive to be 17.8 dBm

-  turned on the HV for the FSS phase correcting EOM (aka PC) drive

- connected and turned on the reference cavity temperature stabilization

- connected the RefCav TRANS PD

- fine tuned the RefCav REFL PD angle

  4281   Mon Feb 14 00:39:21 2011 rana, sureshUpdateElectronicsVCO Frequency Noise Measurement with the MFD

We hooked up the VCO Driver output to the MFD. We adjusted the levels with attenuators to match up to the Level 7 mixer that's being used.

The mixer the input to the SR560 is going in to the XARM_COARSE_OUT channel and the SR560 (AC coupled, Low Noise, G=1000, LP@1kHz) 600 Ohm output goes into XARM_FINE_OUT.

We calibrated these channels by putting in a 10 mVpp sine wave at 0.22 Hz into the Wideband Input of the VCO Driver box (which has been calibrated to have 1.75 MHz/V for f < 1.6 Hz). This should correspond to 17.5 kHz_pp.

To increase the sensitivity, we also added a 140 ft. BNC cable to the setup. We also added some extra short cable to make the overall phase shift be ~90 deg and zero out the mixer output.

I used the time series data in DTT to then calibrate the channels by changing the GAIN field in their filter modules. So now the DAQ channels are both calibrated as 1 count/Hz.

 

  3640   Fri Oct 1 21:34:14 2010 rana, taraUpdatePSLHigh Voltage Driver added to TTFSS -> NPRO

Quote:

We added the Thorlabs HV Driver in between the FSS and the NPRO today. The FSS is locking with it, but we haven't taken any loop gain measurements.

This box takes 0-10 V and puts out 0-150 V. I set up the FSS SLOW loop so that it now servos the output of FAST ot be at +5V instead of 0V. This is an OK

temporary solution. In the future, we should add an offset into the output of the FSS board so that the natural output is 0-10 V.

I am suspicious that the Thorlabs box has not got enough zip to give us a nice crossover and so we should make sure to measure its frequency response with a capacitive load.

 

 We measured the Thorlabs HV Driver's TF today. It is quite flat from 1k to 10k before going up to 25 dB at 100k,

and the response does not change with the DC offset input.

 

The driver is used for driving the NPRO's PZT which requires higher voltage than that of the previous setup.

We need to understand how the driver might effect the FSS loop TF, and we want to make sure that the driver

will have the same response with DC input offset.

 

Setup

 

We used SR785 to measure the TF. Source ch was split by a T, one connected to Driver's input, another one connected to the reference (ch A). See fig2.

The driver output was split by another T. One output was connected to NPRO,

another was connected to a 1nF capacitor in a Pomona box, as a high pass filer (for high voltage), then to the response (ch B)

 The source input is  DC offset by 2V which corresponds to 38 V DC offset on the driver's output.

The capacitance of the PZT on the NPRO is 2.36 nF, as measured by LC meter.

 

 The result shows that the driver's TF is flat from 1k to 10k, and goes up at higher frequency, see fig1.

 

The next step is trying to roll of the gain at high frequency for PZT. A capacitor connected to ground might be used to roll off the frequency of the driver's output.

We will inspect the TF at higher frequency (above 100 kHz) as well.

            

  3641   Mon Oct 4 06:47:46 2010 rana, taraUpdatePSLHigh Voltage Driver added to TTFSS -> NPRO

Inside the FSS box, the FAST path has a ~10 Hz pole made up from the 15k resistor and the 1 uF cap before the output connector.

This should be moved over to the output of the driver to make the driver happy - without yet measuring the high frequency response,

it looks like to me that its becoming unhappy with the purely capacitive load of the NPRO's PZT. This will require a little surgery inside

the FSS box, but its probably justified now that we know the Thorlabs box isn't completely horrible.

 

  3542   Wed Sep 8 00:01:07 2010 rana, valeraUpdatePSLPMC update

We ran the cables for the PMC: The RF cable for the 35.5 MHz drive was cheap and so we swapped the 29.5 MHz cable for it.

There now remain 1 RG-174 cable to drive the FSS PC (21.5 MHz) and 3 Heliax for the Kiwamu Tri-Mod EOM (11, 29.5, and 55 MHz).

We also changed the BLACK HV drive cable for the RED one (previously used for the MZ). All HV cables MUST be RED.

The BLACK cable is now used for the PMC_REFL DC.

The Heliax cables are routed onto the table - it remains a Alberto/Kiwamu job to strain relieve them and attach them to the TriMod box and EOM in the morning.

The PMC is locked and we did some partially bootless alignment and mode-matching. It locks easily on a TEM00 mode (with very poor visibility), but the

rest of the beam train can now be aligned while Valera does the PMC matching mambo.   

 

  4792   Mon Jun 6 23:56:16 2011 rana, valeraConfigurationSUSETMX/ETMY OSEM whitening

 We measured the OSEM PD whitening transfer function of the ETMX OSEM UL whitening stage (D000210) by comparing the input signal to the whitening amplifier (single pin LEMO monitor) to the output signal - both were piped into the DAQ. The transfer function was close to constant 0 dB/180 deg independent of the whitening switch selection (FM1 filter engaged/disengaged)  up to ~20 Hz where we run out of coherence. All other ETMX and ETMY spectra at the input of the digital whitening compensation don't change when the whitening is switched on/off so by induction we conclude that all the ETMX/ETMY OSEM PD hardware whitening filters are not on.

  12573   Wed Oct 19 18:32:25 2016 rana, yinziUpdatePSLRefCav thermal control: heater is dead

We wanted to re-activate the Heater for the reference cavity today to use it as a testbed for PID autotuning and the new heater driver circuit that Andrew is working on for the coating thermal noise experiment.

Unfortunately, it seems that the large power supply which is used for the heater is dead.sad Or maybe I don't remember how to use it?

The AC power cord was plugged in to a power strip which seems to work for IO chassis. We also tried swapping power strip ports.

We checked the front panel fuses. The power one was 3 Ohms and the 'bias' one was 55 Ohms. We also checked that the EPICS slider did, in fact, make voltage changes at the bias control input.

Non of the front panel lights come onfrown, but I also don't remember if that is normal.

Have those lights been dead a long time? We also reconnected the heater cable at the reference cavity side.

  1314   Mon Feb 16 22:58:51 2009 rana, yoichiConfigurationSUSHysteresis in SUS from Misalignments
WE wondered if there was some hysteresis in the SUS alignments. When we leave the optics misaligned for a
long time it seems to take awhile for the optic to settle down. Possibly, this is the slow deformation of
the wires or the clamps.

The attached PNG shows the plot of the bias sliders for a few days. You can see that we misalign some of the
optics much more than the others. This must be stopped.

Kakeru is going to use his nearly complete optical lever calibrations to quatify this by stepping the optics
around and measuring the effect in the optical lever. Of course, the misalignment steps will be too large to
catch on the OL, but he can calibrate the align-sliders into radians to handle this.
  1425   Wed Mar 25 01:37:35 2009 rana, yoichiSummaryIOONo Reference Cavity Required
We were wondering if we need to have a reference cavity. One possible reason to have one is to reduce the free running
frequency noise by some level so that the MC can handle it. According to my manifesto,
the free running noise of the laser is (10 kHz / f) Hz/rHz. The mode cleaner loop gain is sufficient to reduce this to
0.001 Hz/rHz everywhere below 1 kHz - radiation pressure noise and coating thermal noise limit the mode cleaner below
these levels.

So, since it seems like the reference cavity is superfluous (except for the 1 - 10 kHz band), we unlocked it and locked the
MC by feeding back directly to the laser.

In the old set up, the low frequency feedback is to MC2 and the high frequency to the VCO which actuates the FSS which
drives the NPRO PZT and the Pockel cell.

In this new way, we take the MC board's output to the VCO (the TNC monitor point) and send that to the TEST IN1 of the FSS
box. The FSS box then splits the drive to go to the PZT and the PC path. We also turned off the 40:4000 filter in the MC
board and inverted the sign of the MC FAST path.
Good settings for acquisition:
MC INPUT GAIN = 6 dB
40:4000        Disable
FAST polarity  MINUS
VCO Gain       -3 dB
MC LIMITER     Disable

FSS TEST1      TEST
FSS CG         -3 dB
FSS FG         13 dB

After our initial locking success, we realized that the new MC-FSS loop is conditionally stable: the old loop relied on
the 40 kHz refcav pole to make it stable. The new loop has a 4 kHz pole and so the phase lag in the MC-PZT path is too
much. We need to build a passive lead filter (40 kHz : 4 kHz) in a Pomona box to compensate.

There are several more issues:

- I think this will make the whole CM servo handoff easier: there is no more handoff.

- This will make the lock acquisition fringe velocity higher by a factor of the arm/mc length (40 m / 13 m) since
the frequency will be slewing around along with MC2 now. However, Jenne's FF system ought to take care of that.

- Having the laser frequency stabilized to the MC during lock acquisition will make all of the error signals quieter
immediately. This can only be good.

- If we can make this work here, it should translate to the sites directly since they have exactly the same electronics.
ELOG V3.1.3-