Below is an updated table of mean and standard deviation values for the data taken from GDS, SLM, and the ratio GDS / SLM with imaginary parts rescaled by adding 1.0 (~the magnitude of the kappas):

                                   SLM mean         SLM std          GDS mean          GDS std             ratio mean            ratio std

Re(kappa_tst)             0.8920              0.0068            0.8915                0.0058              0.9995                  0.0044

Im(kappa_tst)             -0.0158             0.0039            -0.0145               0.0014              1.0014                   0.0042

Re(kappa_pu)             0.8961              0.0080            0.8956                0.0059              0.9995                  0.0067

Im(kappa_pu)             -0.0050            0.0056            -0.0034              0.0022               1.0017                   0.0061

kappa_c                      1.1115                0.0094            1.1168                 0.0087               1.0048                  0.0078

f_c                               354.2332         2.9296            345.0556           2.3106               0.9742                   0.0104


Here are covariance matrices and correlation coefficient matrices between SLM and GDS:

       Covariance                          Correlation

Re(kappa_tst)
1.0e-04 *
    0.4618    0.3208                  1.0000    0.8163
    0.3208    0.3345                 0.8163    1.0000

Im(kappa_tst)
1.0e-04 *
    0.1507    0.0012                   1.0000    0.0211
    0.0012    0.0210                   0.0211    1.0000

Re(kappa_pu)
1.0e-04 *
    0.6385    0.3128                 1.0000    0.6636
    0.3128    0.3480                 0.6636    1.0000

Im(kappa_pu)
1.0e-04 *
    0.3140    -0.0036               1.0000   -0.0293
   -0.0036    0.0495               -0.0293    1.0000

kappa_c
1.0e-04 *
    0.8895    0.4464               1.0000    0.5464
    0.4464    0.7502               0.5464    1.0000

f_c
    8.5828   -0.0252              1.0000   -0.0037
   -0.0252    5.3387              -0.0037    1.0000

Updated plots are attached as well.

Here are the BruCo scan on SRCL/PRCL/MICH on the other good time.

I picked up Oct. 24, 08:00 UTC as the other good time.

SRCL: https://ldas-jobs.ligo-wa.caltech.edu/~youngmin/BruCo/PRE-ER10/H1/Oct24/H1-SRCL-1161331217-600/

PRCL: https://ldas-jobs.ligo-wa.caltech.edu/~youngmin/BruCo/PRE-ER10/H1/Oct24/H1-PRCL-1161331217-600/

MICH: https://ldas-jobs.ligo-wa.caltech.edu/~youngmin/BruCo/PRE-ER10/H1/Oct24/H1-MICH-1161331217-600/

The results are updated using new excluded channel lists.

It looks like the coherence of the IMC WFS with the SRCL error signal is mostly above 80 Hz, where our jitter is similar to what it was during O1 according to the IMC WFS (spectra in the alog that Lisa links ). 

I looked at the coherence of the two sensors used for the SRCL error signal, POP45 I and POP9I, and we can see that POP 9I has more coherence with the IMC WFS at the frequencies where we think accoustic motion of mounts on the PSL table dominate the jitter. 

More strange stuff, when we look at the PDA and PDB photodetectors of the first loop in the ISS. In the attached plot, the current traces are with a PMC offset of 3.28mV, reference traces 1-15 are with a 3.58mV offset and reference traces 16-19 are with a 2.98mV offset. With a positive offset change we see a some degradation in PDA at high frequencies, whereas PDB sees significantly less noise. For a negative offset PDA gets a tad bit better and PDB gets worse. Overall PDB shows up to an order of magnitude change in its noise level, whereas PDA only shows up to a factor of 2, going the opposite way. The PMC gain was high and 28dB.

Here is the throughput as function of the offset with a Lorentzian as a fit. The parameters are 0.761, 3.28mV and 4.59mV for the amplitude, offset and HWHM, respectively. Looks like the demodulated signal is only ~9mV pk-pk.

(Keita writing as Sheila)

For those of you who are interested, Daniel's measurement doesn't mean that the noise behavior (in length locking and in intensity noise) makes sense.

(Now writing as myself.)

According to T0900577 (select ilspmc_servo3.pdf) the output of TUF-3 mixer is amplified by a DC gain of 4 and sent to a summation amplifier that has a gain of 10 for the demod and a gain of 1/100 for the offset.

The offset signal seems to be calibrated to represent the offset in the OUTPUT of the summation amplifier (i.e. +-100mV when the offset from DAC is +-10V). Update: I was deceived by HOPR and LOPR of he signal on MEDM being 100 and -100, but the calibration filter of this channel of this gain is just 3.2k, so the number should represent the equivalent offset after the gain of 4 but before the gain of 10.

So this 9mVpp is after the gain of 40 total, the demod right after the mixer should be ~9mV/4/10=230uVpp.

Update: The demod right after the mixer should be ~9mV/4=2.3mVpp.

If this is true this is excessively small and cannot be good, and I wonder if the demod phase is correct or if this is an expected signal level. If this is as designed, can't we increase the modulation depth upstream or something?

(The main document in the above DCC is so-called PDF Portfolio, which is just a document containing all pdfs listed in "other files". If you're on Linux workstations the pdf in the above DCC appears as if it's just a one-page document promoting Adobe product, but if you're using evince document viewer, change "thumbnails" on the left panel to "attachments", and you can select whichever file in the portfolio to view).

Looking at the RF chain:

• The output of the RF amp in the CER is 13 dBm
• There is a 2 dB attenuator in the CER
• Assuming 1 dB cable loss
• There is a 20 dB attenuator at the PSL rack panel

Therefore, the drive to the modulator seems to be -10 dBm, or 71 mV rms. A standard New Focus 4004 EOM has a modulation coefficient of 25 mrad/V. So the estimated modulation depth is around 1 mrad.

The mixer readbacks are flawed and just see ADC noise. They could use a gain of 200 to get above the ADC noise. Proposed values:

• N7: OP27
• R33: 1K
• R11: 200K
• R12: 0
• C4: 33p
• J2: remove

[Travis, Jenne]

We tried chasing alignments a little bit, but also can't get the transmitted power above 0.95ish.  Travis suggested looking at the laser itself.  In the attached screenshot you can see that the green DC power measured at the end station dropped suddenly, at a time corresponding to the drop in transmitted power.  Why would the power drop like that?  Were there things going on at the end station around the 24th?

Betsy, Jason, Travis, Kiwamu,

After some investigation and tentative adjustments, the situation did not improve after all. We still have no idea what happened.

In the end, we restored all the suspensions back to where they were before the maintenance and steered the IM3 yaw to obtain a value of +0.2 in IM4_TRANS_YAW.

[Some conclusions]

• We don't think the PSL pointing has changed according to the irises in the PSL.
• The MC2 trans loop (DOF3) seems to bring us to the same point as before according to the beam spots on the wall of the PSL booth (see the attached picture).
• The behavior this time seems to be different from the old mysterious behavior we had seen in 2014 (15650) in the sense that restoring all the suspensions did not bring us back to the same IM4 QPD position this time. 

[Summary of the activities]

• We went into the PSL and checked the beam spot on two iris locations.
  • One right below the bottom periscope (which I think was installed for allocation of the PZT mirror last year, 17976). And the other at the transmission of the bottom periscope mirror which Cheryl installed a long time ago.
  • Both of them seemed extremely good and therefore we found no indication of misalignment.
• We restored all the suspensions to where they were before the maintenance by using the witness sensors.
• We went into IOT2L and steered some optics.
  • The beam seemed higher everywhere by a few mm which is consistent that we have some misalignment in yaw. Although, since it was so small that we decided not correct for it.
  • We centered the beam on REFL LSC diode and the two WFS diodes. The LSC diode was aligned manually by steering the beam splitter in front. The WFSs were aligned using the picomotors. All of them were done when the IMC was unlocked.
  • Re-adjusted some beam dumps, trying to catch stray light without approaching too close to the main beam.
• Checked the beam spots on the PSL wall by opening the PSL light pipe. See the attached picture.
  • Out of three beam spots, two were found to be unchanged. The other one was different by a few mm. I have no idea what this means and how yesterday's activity impacted on these locations (30867).

[Summary of the shift]

The following tables summarize the alignment before the alignment and after our investigation and adjustments.

Summary table for pitch

Summary table for yaw

As I was writing these values, I noticed that the the beam waist location of the IMC translated by roughly 0.5 mm according to equation (4) in P1000135. I have no idea how we ended up introducing this translation in the IMC eigen axis without changing the input beam line determined by the PSL periscope mirror and the MC2 spot position. As expected, we compensated whatever the misalignment by introducing a +182 urad offset to IM2. If this compensation by IM3 is not perfect (and probably this is true in reality), this will result in a different spot position on PRM. The rest of the interferometer should be fine in principle.

Jenne, Sheila, Kiwamu,

In addition, we did a brief test in order to distinguish whether this is due to a change in the PLS pointing or something in the suspensions.

We conclude that misalignment in PSL (if any) don't explain what we see on IM4_TRANS. Again, we still don't have an idea of what happened.

[The test]

We restored all the suspensions back to the values listed above. We disabled the IMC ASCs so that they don't pull the suspensions to whatever the points they want to park. The idea is that with the restored suspension, we should get back to the same value on IM4_TRANS if all the misalignment was due to something in the PSL. If the spot on IM4_TRANS does not come back to the old location, then something in the chamber must have changed.

[Results]

Initially, the yaw signal of IM4_TRANS was about -0.4 counts before we restored the suspensions. After the restoration, the value became -0.1 which is closer to what it was (+0.2). However, obviously we did not fully come back to the old value on IM4_TRANS. This means that misalignment in PSL alone can not explain the situation right now. Something else likely in the chamber must have moved.

This result motivated us not to touch the PSL. Instead we decided to move IMs to recover a high recycling gain in the interferometer (30910).

Open FRS Ticket 6527.

I'll look at this as soon as I can. Apologies for leaving before full recovery to be able to catch and address this.

Spectra look much better too! Attached are times from before Oct 11 maintenance work (blue), just after Oct 18 maintenance work (green), and this morning after the clipping had been fixed (red). Note that the amplitude of the 331.9 Hz has returned to the O1 amplitude.

A trend of the mean power level over the last 10 days is also attached. The calibration discrepancy between TX and RX PD is likely now reduced. Previously, as identified by Shivaraj (LHO aLOG 30845), the discrepancy was ~4%. Now the discrepancy is less than ~1% as the end of the trend indicates.

After going through my notes, the following should also be logged.

VCO S1200563 is outfitted with a PLL board.  This board is attached to the existing board via an SMA-T connector on the Low Noise VCO Board.  This connector was very loose when we opened up the chassis, and the end that is supposed to connect to the PLL board was disconnected and wedged between two VCO modules.  The SMA was very loose here.  We showed Richard this and he advised us to remove the SMA-T and the SMA jumper cable which was disconnected, we then used an SMA cable torque wrench to ensure proper torque on the connectors.

When we worked on the 2nd PLL VCO chassis (S1200564), we noticed that the SMA-T was torqued, and the SMA jumper was attached to the PLL board.

By "on" I assume that the electronics are energized (i.e. the fan is running) but not the filament?

That is correct, Kyle.

Note to self: check the front-end calculations of the uncertainty and coherence of these lines before and after this change after the IFO reverted back to 25 [W] input power. 
Example checks: 
   - do the calculations show the expected decrease in coherence / increase in uncertainty? 
   - how much was the uncertainty / coherence when the SNR was so high? 
   - do we like that level of uncertainty? did it reveal more real optical parameter changes instead of noise?

Delayed update, these changes were accepted in the SDF today (Oct. 26, 2016, ~10:20 PDT).