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ID Date Authorup Type Category Subject
  9861   Sun Apr 27 21:30:59 2014 KojiUpdateLSCALS servo characterization

The measured openloop TF of the ALS servo for each was characterized by a ZPK model.

The openloop TF can be modeled by:

1) Filter TF obtained from foton
2) Actuator response with appropriate assumption
3) Phase tracker closed loop TF
4) Delay caused by the digital control
5) anything else

For 1) ZPK models of the servo filter was obtained from foton. It turned out that the TF of FM5 doesn't match with the ZPK model in foton.
Therefore the TF was exported and fitted with LISO. This seems to be related to the pole frequency (3kHz) which is too close to Nyquist frequency (8kHz).

FM(:,1)  = zero1(f,5).*pole1(f,0.001)*5000;
FM(:,2)  = zero1(f,1).*pole1(f,0.001)*1000;
FM(:,3)  = zero2(f,4.5,1.4619).*pole1(f,0.001).*pole1(f,0.001)*20.2501*1e6;
FM(:,4)  = zero2(f,35,2).*pole2(f,3,3).*zero1(f,3000).*pole1(f,1).*pole2(f,3000,1/sqrt(2)).*pole1(f,700).*zero1(f,10).*zero1(f,350).*136e1;
FM(:,5)  = zero1(f,1).*pole1(f,4.010e3).*pole2(f,17.3211e3,1.242).*zero2(f,18.865e3,100e3);
FM(:,6)  = zero2(f,3.2,0.966775).*pole2(f,3.2,30.572);
FM(:,7)  = zero2(f,16.5,2.48494).*pole2(f,16.5,78.5807).*zero2(f,24.0,2.22483).*pole2(f,24.0,7.03551);
FM(:,8)  = 1;
FM(:,9)  = zero2(f,7.50359,1.07194).*pole2(f,1.43429,0.717146)*27.5653;
FM(:,10) = 1;

dc_gain = 14;

FM1/2/3/5/6/7/9 are used for the control.

For 2), a resonant freq of 0.97 with Q of 5 was assumed.

The model for 3) was obtained by the previous entry.

Now the measured TF was divided by the known part of the model 1) ~ 3) and empirically fitted in LISO.

### XARM ###
pole 392.5021429051 698.1992431753m
zero 42.3128869460k 31.0954443799m
pole 589.2716424428 2.8325268375
factor 8.3430140244
delay 34.7536691023p

### YARM ###
pole 416.2463334253 743.2196174175m
zero 97.9161062704M 114.6703921876m
pole 626.0463515310 2.7671041771

factor 9.0045911761
delay 34.0945727358p

These compensation TF have weird TF. Probably the frequency response of the delay and the analog AA/AI filters without the high frequency data
led the LISO make up this. I'm requesting Masayuki to provide the AA/AI data to make the estimation more reasonable.
For the servo modeling, this is sufficient and we'll go a head.

The results of the OLTF modeling are attached.

Attachment 1: ALSX_OLTF.pdf
Attachment 2: ALSY_OLTF.pdf
  9862   Mon Apr 28 10:24:10 2014 KojiUpdateLSCerror signal characterization

As we now have the loop model, we can characterize the error signals.

We have the following data:

1) Free-running ALS error signals (i.e. phase tracker output) calibrated in Hz (for 532nm) (blue)
2) Controlled ALS error signals calibrated in Hz (for 532nm) (red)
3) ALS error signals measured with X and Y arm locked with the IR PDH. (black)
    This is likely to represent the sensing noise of the beatnote detection

from 2) we can derive the similar quantity as 1)
4) Estimated free-running ALS error signals from the controlled signals (green)


- From 1) and 4) we can see that the phase tracker is not perfectly linear. It seems that fast fringing of the phase tracker is causing upconversion.

- From 2) and 3) the servo loops don't have enough gain between 3Hz and 20Hz. On the other hand they have too much gain bekow 3Hz.

Attachment 1: ALSX_SPE.pdf
Attachment 2: ALSY_SPE.pdf
  9863   Mon Apr 28 10:34:51 2014 KojiUpdateLSCnew ALS servo design

Based on the evaluation of the error signals, the new servo was designed.

- Don't touch the locking filters. (i.e. FM5)
- Sacrifice some phase at 150Hz to increase the gain between 3-20Hz.
- As resonant gains costs the phase without increasing the LF gains, replace them with a poles for the integrators.

FM(:,1) = zero2(f,.5,.7).*pole2(f,0.001,.7)*(0.5/0.001)^2;
FM(:,2) = zero2(f,5,2).*pole2(f,3,3).*pole1(f,1).*zero1(f,5)*5*(5/3)^2;
FM(:,3) = zero2(f,25,.7).*pole2(f,3.2,10)*(25/3.2)^2; % Zero crossing
FM(:,4) = zero2(f,35,2).*pole2(f,3,3).*zero1(f,3000).*pole1(f,1).*pole2(f,3000,1/sqrt(2)).*pole1(f,700).*zero1(f,10).*zero1(f,350).*136e1;
FM(:,5) = zero1(f,1).*pole1(f,4010).*pole2(f,17.3211e3,1.242).*zero2(f,18.865e3,100e3);
FM(:,6) = zero2(f,5,2).*pole2(f,10,2).*pole2(f,16.5,30).*zero2(f,30,2);
FM(:,7) = 1;
FM(:,8) = 1;
FM(:,9) = 1;
FM(:,10) = 1;
dc_gain = 14;

FM1/2/3/5/6 are expected to be used for the control.

FM1: Boost below 0.5Hz. This does not cost the phase margin.
FM2: Increase the gain below 5Hz. This hardly cost the phase margin.
FM3: Boost below 25Hz. This is the main phase cost at UGF. This has a complex pole pair at 3Hz with Q=10 to supress the stack motion.
FM6: zero-pole-pole-zero combination to boost the gain between 5 to 30Hz. This eats the phase margin a little.

Note that the phase tracker gain for the X arm was increased by factor of 2.5.

Attachment 1: ALSX_OLTF_new2.pdf
Attachment 2: ALSY_OLTF_new2.pdf
  9864   Mon Apr 28 10:48:48 2014 KojiUpdateLSCnew ALS servo design: comparison

Comparison of the new and old servo OLTF
The new servo has the same UGF, slightly less phase margin, and more gain between 1.5 and 25Hz.

Attachment 1: ALSX_OLTF_new.pdf
Attachment 2: ALSY_OLTF_new.pdf
  9865   Mon Apr 28 10:59:54 2014 KojiUpdateLSCNew ALS servo design: expected error signals

The expected error signals derived from the estimated free running error signals of the ALS.

1) Previously estimated free-running noise (blue)
2) Previous in-loop ALS error signal (red)
3) Estimated error signal with the new servo (green)
4) Out-of-loop noise of the ALS with the arm controlled with the IR PDH (black)

Now the error signal (green) is expected to be very white.
The suppressed noise between 3 to 20Hz are below the sensing noise level.
There seems a little excess at 24.5Hz and 28Hz. If it is limiting the RMS, we need to take care of them.

Attachment 1: ALSX_SPE_new.pdf
Attachment 2: ALSY_SPE_new.pdf
  9866   Mon Apr 28 11:03:57 2014 KojiConfigurationLSCNew ALS servo implemented for the X arm

The new ALS/LSC servo was implemented for the X arm.

I'll upload more data later but here I make quick remarks:

- We need to give the gain of 12 to have correct UGF with the ALS.

- With this servo, the Xarm PDH lock oscillates with the gain of 0.02. We need to lower the gain to 0.015.
  Also FM trigger should be changed not to trigger unused FMs (FM7/8)

  9867   Mon Apr 28 11:08:11 2014 KojiUpdateLSCNew ALS servo design: expected error signals

Here are the MATLAB scripts and LISO codes for all of these servo analyses

Attachment 1: 140421_ALS_servo.zip
  9874   Tue Apr 29 01:10:16 2014 KojiConfigurationLSCNew ALS servo implemented for the X arm

New ALS servo performance

Attachment 1:

Comparison between the old (orange) and new (red). The new error signal (red) is suppressed like a white noise as expected.

Comparison between the out-of-loop evaluation (black) and the in-loop signal (red). Below 50Hz the out-of-loop is limited by the sensor-noise like something.
This out-of-loop stability was measured with the ALS stayed at the top of the resonance and calibrated the POX11 error signal.

Attachment 2:

New ALS servo with the LSC PDH signal. When the PDH signal is used for the control, FM4 is additionally used.
In this condition, the error signal was measured and calibrated into frequncy noise (Hz/sqrtHz).

By comparing the POX (with the new servo) and POY (with the old servo) signals, one can see that the new servo has better supression below 30Hz with almost no cost at ~100Hz.

Attachment 1: ALSX_SPE.pdf
Attachment 2: ALSX_PDH_SPE.pdf
  9875   Tue Apr 29 10:01:25 2014 KojiConfigurationGeneralnetgpibdata is working again now

I've moved the WB network analyzer to the OMC lab. The 40m network analyzer is not in service for the MC monitoring.
I setup the configuration so that the same command gives us the same spectrum measurement.

  9887   Thu May 1 00:13:21 2014 KojiUpdateLSCALS X beat setup aligned

I saw big misalignment on the GTRX camera, I went to the PSL table and aligned the beat beams.

I disconnected the RF out of the X beat PD and  connect an oscilloscope.
The beat amplitude was 15mVpp at the beginning and is 60mVpp right now.
I checked the alignment on this RF PD and the DC PD as well as the spot on the CCD.

The RF cable was connected again.

Jenne and I ran the ALS and scanned the arm cavity. We had the impression that the noise level of the ALS improved,
but I don't have correctly calibrated measurement. Let's do it tomorrow in the day time.

The Yarm beat alignment look awful. We should align this too.

  9905   Fri May 2 14:31:26 2014 KojiUpdateLSCALS Y beat setup aligned

Please check the X&Y ALS out-of-loop stability. Use fine resolution (BW0.01). Calibrate the POX/POY in Hz.

  9939   Fri May 9 21:18:51 2014 KojiUpdateGreen LockingReverted X green light power

It is actually very tricky to measure the green power at the output of the doubling crystal as the IR often leaks into the measurement.
I checked the green beam powers on the X/Y/PSL tables.

CONCLUSION: There is no green beam which exceeds 5mW anywhere in the 40m lab.

Note: The temperature of the doubling crystal at the X end was optimized to have maximum green power. It was 36.3degC and is now 36.7degC.


When the angles of the wave plates are optimized, we have 539mW input to the doubling crystal.
With the Xtal temperature of 36.7degC, where the green power is maximized, the power right after
the harmonic separator (H.S.) was 9.6mW.

Xtal temp 36.7degC   ~~~


If we believe these 4.69mW and 4.54mW are purely from the green, we have 4.8mW right after the H.S.
This corresponds to the conversion efficiency of 1.6%/W (cf. theretical number 2%/W)

By disabling the heating of the crystal, we can reduce the green light by factor of 60. But still the reading right after the H.S. was 5.3mW

Xtal temp 29.2degC   ~~~

Naively taking the difference, the green beam right after the H.S. is 4.4mW.

In either cases, the green power right after the oven is slightly less than 5mW.


When the angles of the wave plates are optimized, we have 287mW input to the doubling crystal.
With the Xtal temperature of 36.0degC, where the green power is maximized, the power right after
the harmonic separator (H.S.) was 0.86mW.

Xtal temp 36.0degC   ~~~


When the temperature was shifted to 39.2degC, the reading after the H.S. was 70uW. Therefore the contamination by the IR is small
in this setup and we can believe the above reading in 70uW accuracy. This 0.86mW corresponds to the conversion efficiency of 1.2%/W.


The incident IR is 80mW. We have 170uW after the H.S., which corresponds to the conversion efficiency of 2.6%/W. Maybe there is some IR contamination?
From the vacuum chamber total 1mW of green is derivered when both arms are locked and aligned.

Thus the total green power at the PSL table is less than 5mW.

  9992   Mon May 26 07:59:23 2014 KojiUpdateElectronicsAmplifier removed from BeatX path

And the out-of-loop level of the ALSX compared with the previous measurement is ...?


I just realized that I forgot to elog this, but yesterday afternoon I bypassed the amplifier in the BeatX path, and now the X beatnote is about -27dBm.  Arms lock nicely with ALS.


  10001   Wed May 28 19:15:38 2014 KojiUpdateLSCX green broadband PD NOT working

If the PD is the suspect, just pull it from the table and bring it to the PD testing setup.

The transimpedance of the PD should be ~2000 Ohm for both of the RF and DC outputs.

The test setup gives you the systematic opportunity for examination of the signal line.
Check the signal level with the active probe.

Once the broken component is found replace it. You are supposed to have the replacement
components on the blue tower.

  10004   Thu May 29 14:40:17 2014 KojiUpdateLSCHigh Bandwidth power recycled Yarm.

Wait. It is not so clear.

Do you mean that the IFO was locked with REFL11I for the first time?

Why is it still in the "low finesse" situation? Is it because of misalignment or the non-zero CARM offset?

  10012   Mon Jun 9 16:55:31 2014 KojiSummaryElectronicsBBPD D1002969-v8 transimpedence measurement

How is the modulation depth assumed in the calculation?

If you don't know the modulation depth, you can't calibrate the transimpedance of each PD individually.

  10031   Thu Jun 12 11:03:11 2014 KojiFrogsGeneralWorld Cup Soccer 2014


  10038   Fri Jun 13 19:09:44 2014 KojiUpdateIOOA blown fuse found on the euro card crate at 1X2 (IOO) rack.

[Rana Zach Koji]

We tracked down the MC locking issue to be associated with the power supply problem.
Replacing a fuse which had incomplete connection with the new one, the MC started locking.

We still have the MC autolocker not running correctly. This is solely a software problem.

We went down to the IOO electronics rack to investigate the electronics there. After spending
some time to poking around the test points of the MC servo board, we noticed that the -24V
power indicator on the MC demodulator module was not lit. In fact, Steve mentioned on Wednesday
that the -24V Sorensen supply had lower current than nominal. This actually was a good catch
but should have been written in the ELOG!!!

We traced the power supply wires for the crate and found one of the three -24V supply has no
voltage on it. Inspection of the corresponding fuse revealed that it had a peculiar failure mode.
The blown LED was not lit. The connection was not reliable and the -24V power supply was flickering.

We then replaced the fuse.This simply solved all of the issues on the MC servo board. The electronics
should be throughly inspected if it still has the nominal performance or not, as the boards were exposed
to the single supply more than a week. But we decided to try locking ability first of all.

Yes, we now can lock the MC as usual.

Now the newly revealed issue is MC autolocker. It was running on op340m but op340m does not want to run it now.
It should be closely investigated.

Also turning on WFS unlocks the MC. Currently the WFS outputs are turned off.
We need usual align MC / check spot position / adjust WFS QPD spots combo.

  10064   Wed Jun 18 21:37:11 2014 KojiUpdateIOOMC REFL investigation

[Jenne Koji]

We decided to check the situation of the REFL MC beam path.

- No resolution of the weird MC REFL DC increase
- The reflection from the PD was adjusted to hit the beam dump
- The MC WFS paths were aligned again


We found that the reflected beam from the PD was hitting the mount of the beam dump.
So the entire MC REFL path was steered down such that the last steering mirror does not neet to steer the beam.
When the alignment was adjusted so that the reflection from PD hit the beam dump, the beam spot on the small mirror right before the PD
got a bit marginal but it seemed still OK after some tweak.

Then we looked at the reflection value. It is still about 6.5. No change.

As we messed up the entire MC REFL path, we aligned the MC WFS paths again.
This was done with the unlocked MC REFL beam. Once the cavity was locked,
it turned out that it was enough for the WFS too keep the MC locked.

  10065   Wed Jun 18 21:53:48 2014 KojiUpdateElectronicsChanges to the PD frequency response measurement system

Not "hot" current but "photo" current. Is this my bad!?

It was me who told Nichin that the DC transimpedance was 200Ohm. But according to this entry I checked the RF transimpedance of AS55 before.
In my code, the DC transimpedance was defined to be 50Ohm. If we believe it, 30mV corresponds to 0.6mA.


The multimeter readout 30mV finally. Taking the transimpedence as 200ohm approx., the hot current is about 1.5mA.


  10085   Fri Jun 20 19:09:23 2014 KojiUpdateElectronicsTransimpedence measurement-BBPD

Oh, nice! This must be a new technique to have a higher transimpedance by breaking the PD.

Now both BBPDs are showing abnormally high impedance.
(Remember, you have not revised your
previous entry after my pointing out you have a bug in the code.)

You should break down the measurement into each raw numbers for validation.
And if this high impedance is still true, you should point out what is causing of this anomaly.

  10109   Fri Jun 27 20:52:30 2014 KojiUpdateCDSOTTAVIA was not on network

I came in the lab. Found bunch of white EPICS boxes on ottavia.
It turned out that only ottavia was kicked out from the network.

After some struggle, I figured out that ottavia needs the ethernet cable unplugged / plugged
to connect (or reconnect) to the network.

For some unknown reason, ottavia was isolated from the martian network and couldn't come back.
This caused the MC autolocker frozen.

I logged in to megatron from ottavia, and ran at .../scritpt/MC

nohup ./AutoLockMC.csh &

Now the MC is happy.

  10110   Fri Jun 27 23:49:56 2014 KojiUpdateGeneralIR beam found, TTs not aligned well yet

The IR beam was found on the PRM surface, some CCDs, and in the X arm. The TTs are not aligned well yet.

I'm leaving the IFO with the following state.


ITMY/ETMY - aligned to the given green beam. GTRY (no PSL green) 1.0~1.1

ITMX/ETMX - aligned to the green beam. The end PZT for the green beam was steered to have maximum GTRX (0.76 without PSL green)

TT1/TT2 - unknown alignment, TT1/TT2 are related such that the spot is on the POP CCD

PRM - aligned to the given IR beam (i.e. PRM spot on the REFL CCD)

BS - aligned to the given IR beam (i.e. ITMX spot on the AS CCD, The X arm is flashing)


- ITMX was stuck in the suspension. it was caused by the EQ.

- When the X arm was aligned to the green beam, there was no green hitting on the GTRX PD. That's why the end PZT was adjusted.

- In order to earn more range for TT1, C1:IOO-TT1_YAW_GAIN and C1:IOO-TT1_PIT_GAIN were increased to 300 (100 nominal) and the limiter (at 500) were removed.

- The HeNe laser for BS/PRM does not emit the beam even with the driver turned on. Is there a hidden shutter or something? ==> Jenne



- Find the Y arm fringe by moving TT1 and TT2 without loosing the PRM/AS/POP spots.


  10144   Mon Jul 7 18:11:04 2014 KojiUpdateGeneralBeam Waists

- Plots should be directly attached on the elog. (Attaching codes in a zip is OK.)

- Plot legends should not touch or hide any data points.

- Don't exclude data points.

- The model for the beam profile fitting is incorrect: zr and w0 are dependent

- The code needs to be reviewed by someone for refinement.
EricQ, or possibly Jamie, Jenne while he is absent).

  10148   Mon Jul 7 22:18:26 2014 KojiUpdatePSLPMC local oscillator is going wonky

It seems that there is no better chip in MiniCircuits line-up with the same form factor.
ERA-5 is the most powerful one in the ERA (or MAR) series.

If the output is ~0dBm we have MAR-6SM in stock. But I suspect that ERA-5 was driven at the power level close to its saturation (~18dBm).

If we allow different form factors, we have GVA-** or GALI-** in the market and also in the blue tower, in order to gain more performance margin.
If it is difficult to apply them, I would rather use another ERA-5 with enhanced heat radiation.

I'm sure that Downs has EAR-5 replacement.

  10153   Tue Jul 8 15:28:32 2014 KojiUpdatePSLPMC local oscillator is going wonky

Koushik and Koji try to fix the PMC oscillator issue. So we remove the module from the rack.
This means we don't have the PMC transmission during the work.

  10159   Wed Jul 9 00:47:22 2014 KojiUpdatePSLPMC local oscillator is going wonky

Koushik replaced an ERA-5 in the PC path. We put the module back to the rack and found no change.
The epics LO level monitor monitor is still fluctuating from 6~11dBm. We need more thorough investigation
by tracing the signals everywhere on the board.

Despite the poor situation of the modulation, PMC was locking (~9PM). Rana suspect that the PMC demodulation
phase was not correctly adjusted long time. 

Koushik has the measured power levels and the photos of the board. I'll ask him to report on them.

  10179   Thu Jul 10 18:25:18 2014 KojiUpdateGeneralCoupling telescope design

CFC-2X-C has a FIXED focal length of 2mm, but the collimator lens position is adjustable.
I'm not yet sure this affects your calculation or not as what you need is an approximate mode calculation;
once you couple the any amount of the beam into the fiber, you can actually measure it at the output of the fiber with a collimator attached.

  10194   Mon Jul 14 14:28:27 2014 KojiSummaryElectronicsTiming Issues of Mini Circuits UFC-6000: Solved

Looks good. Now you have the internal timer to verify the external clock.
If you can realize the constant rate sampling without employing the external clock, that's quite handy.

  10211   Wed Jul 16 01:35:16 2014 KojiSummaryLSCPython Wavelet peak finding for dramatic ALS - Red Resonance finding speedup

From the last plot:

- Subtracting the offset of 0.0095, the modulation depth were estimated to be 0.20 for 11MHz, 0.25 for 55MHz

- Carrier TEM00 1.0, 1st order 0.01, 2nd order 0.05, 3rd order 0.002, 4th order 0.004

==> mode matching ~93%, dominat higher order is the 2nd order (5%).

Eric: now we have the number for the mode matching. How much did the cavity round-trip loss be using this number?

  10214   Wed Jul 16 02:22:10 2014 KojiUpdateElectronicsTest run of PDFR system

Log-log ... 

  10223   Wed Jul 16 23:02:16 2014 KojiSummaryElectronicsBode Plots and complete Characterization of Frequency Counter

If I assume 1sample delay for 0.1s sampling rate, the delay is Exp[-I 2 pi f T], where T is the sampling period.

This means that you expect only 36 deg phase delay at 1Hz. In reality, it's 90deg. Huge!

Also there are suspicious zeros at ~1.6Hz and ~3Hz. This may suggest that the freq counter is doing some
internal averaging like a moving average.

It would be interesting to apply a theoretical curve on the plot. It's an intellectual puzzle.

  10232   Thu Jul 17 17:39:57 2014 KojiUpdateElectronicsPDFR debugging attempt : REFL11

What is the coupling factor between the RF in and the RF mon of the demodulator?
I don't assume you have the same amount RF power at those two points unless you have an RF amplifier in the mon path.

  10234   Thu Jul 17 22:08:14 2014 KojiUpdateGeneral1X2 Rack Changes

It sounds like the work was done carefully. Even so, Jenne or Manasa have to run the ALS (X and Y) to check if they are still functional.

  10242   Sat Jul 19 20:51:51 2014 KojiUpdateLSCRIN in arm transmission

Your calibration of the ALS signal should be revised.

The phase for the ALS is not an optical phase of the green but the phase of the phase tracker servo output.

The calibration of the phase tracker depends on the cable length of the delay line in the beat box.
It seems that we are based on this calibration. Which gives up ~19kHz/deg.

Or, equivalently, use C1:.....PHASE_OUT_HZ instead.

  10262   Wed Jul 23 11:32:04 2014 KojiUpdateLSCIFO warming up

Alone with the IFO. Started from some conversation with it.

Some ALS trials: Found the Y-end green alignment was terrible. In fact the end green set up is terrible.
Unfixed optics, clipping/fringing in the faraday, unstable suprema mounts which is unnecessarily big.

Eventualy I stopped touching the end alignment. Run ALS to see the stability of the things.
This is a performance confirmation after some touching of the ALS electronics by Manasa/SURFs

The sensing noise levels of the ALSs looks the same as before.

The intensity noise of the transmission was also checked. They are not RIN but very close to RIN
as the DC was the unity for both arms.

The X arm has worse ALS noise level and RIN.
Although I forgot to turn off the HEPA flow at the south bench during the measurement. Gurrr.

Attachment 1: 140722_ALS.pdf
  10285   Tue Jul 29 16:41:54 2014 KojiUpdateLSCMC servo

The MC openloop gains were measured with several conditions
- MC fast/PC crossover was measured to be ~30kHz.
- No feature found in the fast path above 10kHz.


I have been making a circuit to test the crossover between the PZT and PC paths.
This was supposed to allow us to inject a test signal as well as the 5V necessary to offset the voltage for the HV amp.
So far this attempt was not successful although the circuit TF looked just fine. I was wondering what was wrong.

I now suspect that the noise of the circuit was too big. It has ~65nV/rtHz noise level. This corresponds to the external
disturbance of 1~2Hz/rtHz. This is ~10 times larger noise level than the freerun frequency noise.

In the control band the circuit noise is suppressed (cancelled) by the feedback loop.
This is OK when the loop is dominated by the PZT loop. However, if the loop is dominated by the PC path,
the PC path has to work for this compensation.

So what I should do is to remove the low pass filter in the FSS and move it to the downstream of the HV amp.
This way we may be able to reduce the PC path actuation as the noise of the HV amp is also reduced by the LPF.


For the meantime, I used another approach to characterize the MC crossover. I could manage to lock the MC without the PC path.
The openloop was measured with and without the PC path in this low gain setup. In fact the loop was oscillating at 6kHz
due to the low phase margin. Nevertherless, this comparison can let us find where the crossover. The loop gain was also
measured with the nominal condition.

<<Measuerement condition>>

MC IN1 Gain: +19dB
VCO Gain: +3dB
Boosts: No boost / No super boost

FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path disconnected.
(Note that the loop was almost oscillating and the apparent gain may look lower than it should have been)

MC IN1 Gain: +19dB
VCO Gain: +3dB
Boosts: No boost / No super boost

FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path connected.

MC IN1 Gain: +19dB
VCO Gain: +15dB
Boosts: Boost On / Super boost 2

FSS Common Gain: +13dB
Fast Path Gain: +21.5dB
The PC path connected.


Attachment 1: MCservo.pdf
  10291   Tue Jul 29 20:14:10 2014 KojiUpdate40m Xend Table upgradeXarm Green steering mirror upgrade

That was super fast! Great job, Andres and Nic!

  10293   Wed Jul 30 00:42:27 2014 KojiUpdateLSCMC servo

I used an oscillator and an oscilloscope to measure the open loop transfer function at higher frequency than 100kHz.
(I remember that I tried to use Agilent 4375A for this and failed before ... due to low input impedance???)\

Here is the update. It seems that the gain margin is not so large. We should apply low pass to prevent too large servo bump.

Attachment 1: MCservo.pdf
  10300   Wed Jul 30 22:01:24 2014 KojiUpdateLSCMC servo

In fact there is a pomona box between the HV amp and the laser.
It is expected that the combination of the box and the laser PZT (2.36nF by Elog #3640) provides poles at 2.9Hz and 148kHz and a zero at 32Hz.
Basically, the gain of this stage is 0.1 at 10kHz. So the injected noise is reduced by factor of 10. It is just barely OK.
I need a bit more careful design of the output stage for the MC servo.

  10301   Wed Jul 30 23:12:05 2014 KojiUpdateGeneralIFO patrol

- The cable for the beat note was disconnected from the frequency counter and reconnected to the spectrum analyzer.

- PMC/IMC had not been locked for 8 hours. 

- PMC was relocked.

- IMC got immediately relocked. Today IMC relocks very fast.

- Went to the ETMX table. Aligned the oplev beam on the QPD

- The X end green beam was realigned to the cavity.
I can feel that the two mirrors provides quite independent alignment adjustment. VERY NICE.
Green TRX: without PSL Green - 0.612, with PSL green - 0.725

I can clearly see that the mode matching is not ideal. All the higher modes are LG modes!
The input mode is very round.

- Arm cavities were aligned by ASS

- Tested ASX. PZT2 Pitch/Yaw servos run with the previous setting. We still can maximize the transmission by touching PZT1.

- Now Eric joined the activity.

-  Once the beam is aligned what we could lock was LG00/10/20/30.
   We measured the power in LGn0 modes
   LG00: 0.588
   LG10: 0.154
   LG20: 0.053
   LG30: 0.020

   This suggests that the mode-matching ratio is something like 70%

- Q is aligning the PMC. PMC transmission prev 0.783. Basically we could not improve it.
We thought this number can go up to ~0.82 or even ~0.84. We wonder if this comes from the decay of the laser power or reduced visibility?


  10302   Thu Jul 31 01:08:54 2014 KojiUpdateLSCALS stability check

- ALS X/Y arm stability was checked by IR locked arms.

- Basically the stability looks same as before.

Q sez: here are some ALS ASDs (in Hz/rtHz). 

The reference plots are with the arms locked on CARM/DARM with ALS. The main traces are with the arms locked on POX/POY. Alignment affects these traces a fair amount.


The X arm ALS seems no worse for the upgrade, and the PZT actuators do look pretty orthogonal when we play around with the alignment. 

  10306   Thu Jul 31 12:23:38 2014 KojiSummaryElectronicsPZT Calibration

1) Don't be brainless. Redo the fitting of the Y arm. Obviously the fit is not good.

2) How can you explain the value from the ADC bit and range?

e.g. +/-10V range 16bit ADC => 2^16/20 = 3276.8 count/V

  10310   Thu Jul 31 19:37:59 2014 KojiUpdateIOOSuccessful modification of the FSS

Quick note:

Migration of the 10Hz pole from the output stage of the FSS to the pomona box was successful.
This also allowed me to insert my offsetting/summing point circuit.

Trial 1:

- Remove C63 (1uF cap) of the FSS

- Short 500 Ohm in the pomona box

This removed 10Hz pole in FSS and 32 Hz zero in the pomona box.
In total we obtain the gain and range of 3.2 for the fast PZT path.

3x10^2 to 3x10^3 times more filtering of the HV amp noise between 10kHz and 100kHz.

The current maximum gains of the FSS is

Overall +19dB (prev. +13dB)
Fast     +30dB (prev +21.5dB)

Trial 2:

- Insert a summing amplifier between the FSS box and the HV amp.

- This amplifier attenuate the input by a factor of 2, and add 5V. i.e. +/-10V input => 0~10V output.

- This just worked fine.

Trial 3:

- Now the fast gain is nominally +30dB.

- In order to provide more room to play with the fast-PC cross over, I moved the pole freq from 2.9Hz to 9.9Hz
  This was done by replacing a 5kOhm in the pomona box by a 1.5kOhm.

Trial 4:

- I just noticed that the output impedance of the FSS (15.8kOhm) and the input impedance of the summing amp (10k Ohm)
  interfere and gives additional 1/2.58 attenuation in addition to the attenuation in the summing amplifier.
  This yields the output range of the HV amp between 45-105V, instead of 0-150V. This is not nice.

- The output impedance of the FSS box (R46 15.8kOhm) was replaced with 100Ohm.

- Now the PMC unlocks very frequently. This might have come from the PMC locking issue or too much gain of the IMC

Trial 5 (final):

- I suspected that the PMC unlock is caused by too much actuation at the high freq. So I decided to revert the  pomona box change

  10311   Thu Jul 31 21:21:49 2014 KojiFrogselogMicroSoft BingBot is attacking us

Oh, this is cool! Thanks!
I could not figure out how to place robot.txt as it was not so obvious how elogd handles the files in the "logfile" directory.

  10312   Thu Jul 31 21:59:25 2014 KojiBureaucracyGeneralAnts

Don't leave your food on tables and desks!

Also I put the souvenir chocolates in the microwave, just in case.

Attachment 1: P7316690.JPG
  10313   Thu Jul 31 23:19:22 2014 KojiUpdateComputer Scripts / ProgramsSVN bulletin

Did this break "netgpibdata"?

I couldn't download data from SR785. Downloading from AG4395A was OK.

The cause seemed the module for SR785

-rw-rw-r-- 1 controls controls   24225 2014-07-30 18:36 SR785.py

I had a local copy of this file and replaced it with mine. Now netgpibdata start working.
The old one is named SR785.py_bak

-rwxr-xr-x   1 controls staff      12944 Jul 31 23:08 SR785.py

The file size is significantly different from the one we had.

  10314   Thu Jul 31 23:43:00 2014 KojiUpdateIOOModulation frequency adjustment

The main IFO modulation frequency was adjusted to match with the FSR of the IMC.

The new frequency is 11.066128 MHz. This corresponds to the IMC round-trip length of 27.0910 m

This has been done by looking at the peak at 25.845MHz (5* fmod - 29.5MHz) in the MC REFL PD mon.

  10315   Fri Aug 1 00:51:07 2014 KojiUpdatePSLFSSSlowServo update

FSS Slow set point to be zero

op340m:FSS>cat FSSSlowServo
#!/usr/bin/perl -w

# PID Servo for PSL-FSS (Slow)
# Tobin Fricke 2007-01-09

use strict;
#use Scalar::Util qw(looks_like_number);

sub looks_like_number {
    return ($_[0] =~ /^-?\d+\.?\d*$/);  #FIXME

use EpicsTools;

# Parameters
my $process  = 'C1:PSL-FSS_FAST';
my $actuator = 'C1:PSL-FSS_SLOWDC';
#my $setpoint = 5.5;
my $setpoint = 0;
my $blinkystatus = 0;

op340m:scripts>/opt/rtcds/caltech/c1/scripts/PSL/FSS/FSSSlowServo > /cvs/cds/caltech/logs/scripts/FSSslow.cronlog &

  10316   Fri Aug 1 01:29:55 2014 KojiUpdateIOOPMC issue

- PMC suddenly refused to lock.

- Investigated what's wrong

- Finally, I touched RF Output Adjust (C1:PSL-PMC_RFADJ). Then it started locking.

- C1:PSL-PMC_RFADJ was set to 2.0 by rana when we looked at the PMC LO issue.
  Now PMC does not lock with this value. I set it to 6.0 so that the lock is robust.

- Right before I lost PMC locking, I had some difficulty in locking IMC. Of course,  the robustness of the PMC is related to the robustness of the IMC.
  We definitely need to investigate this. (RF powers, open loop TF, etc)

ELOG V3.1.3-