Attached is a plot of the diffracted power versus offset slider position.
With the current slider setting of 6.35, we are diffracting around 3 W of
light.  Even if the output power of the laser was only 100 W, this would
be 3% not the indicated ~15%.  However we know the output power of the laser
is greater than 100 W, so obviously the percent diffracted light is even less
than 3%.

   This is noticeably less than when the ISS was last tuned up.  Back then a
slider setting of 6.35 would diffract about 7 W.  Although nothing has changed
hardware-wise, it is possible that the 80 MHz source for the ISS AOM is no
longer providing the ~32 dBm, or the AOM driver is deteriorating.




Jason/Peter

With the pre-modecleaner unlocked the output of the locking photodiode was between
-1.070 V and -1.080 v.  Locked was between -170 mV and -185 mV.  This gives the
pre-modecleaner visibility to be between 83% and 84%.


Jason/Peter

Attached are measurements of the ISS transfer function performed after a
minor alignment adjustment to the ISS AOM.  These were taken with the gain
slider at 6 dB and 9 dB.  The offset slider was left at 6.35.

    With the gain slider at 6dB the UGF is about 54 kHz; 9 dB 70 kHz.
However there is considerable peaking in the noise spectrum.  The free-running
noise is also attached.

    All measurements were taken with PDA which was the in-the-loop sensor
at the time.  The reference signal was at -2.00.  At this setting the measured
DC output of PDA was -8.70 V.



Jason/Peter

Attached are the transfer function measurements of the FSS taken yesterday afternoon.
The first two plots are taken with the common gain at 16 dB and fast gain of 22 dB.
The second measurement (C16F22-2) I think was affected by the modecleaner trying to
acquire lock, which might explain the notch-like feature just past 200 kHz.  The
UGF in both measurements is about 195 kHz.

    The third measurement, taken with a common gain of 20 dB and a fast gain of
22 dB is, I suspect, also affected by the modecleaner trying to acquire lock.



Jason/Peter

This is as far as I have been able to get the IFO tonight. I tried to set the intent bit, but it will not engage. I have set the Ops Observatory Mode to Observing.

Ross and I are the only ones in the control room. The last lock was lost at ENGAGE_ISS_2ND_LOOP from a pringle mode on ETMY.

[Everyone]

We have determined (a few hours ago) that flipping the ESD bias sign on ETMX does not allow us to lock ALS DIFF.  Jeff has looked through the settings, and everything is flipped to match the bias sign as appropriate, but we're still not able to lock.  It looks like a crossover is unstable, or something like that.  For now, we have reverted the ETMX ESD bias to its pre-Tuesday state, which has facilitated locking.  Team SUS will look into this later.

The ISS is much better behaved now that the alignment work was done.  However the FSS gain change was making the IMC loop very nearly unstable, and we lost lock during the power-up twice due to this instability.  Sheila and Keita will post their measurements that discovered and fixed this issue.

We have so far been able to power up to 40W once, but it looks like a PI rang up pretty quickly.  Carl will post details, but this is a new mode that hasn't been a problem previously, so it does not yet have damping settings.

At this time, it looks like there is no problem in getting to 40W, and other than PI damping we should be able to get all the way to low noise.

If Carl is unable to find damping settings relatively quickly, we may choose to instead only go to 20W for tonight, so that we can get to low noise and set the intent bit.  Stay tuned for more updates...

Jenne, Sheila, Keita, Peter and Jason are here. The work in the PSL enclosure has completed for now. The IFO has made it to DC readout twice, but lost lock on increase power. Keita and Sheila are taking measurements related to the FSS.

After a lot of alarms going off including a message from Jim, I discovered that most of the DMT processes had skidded to a dead standstill. The problem seems to have been that the broadcast frames had increased their length so that the data buffer lengths had to be increased also. The buffer lengths are now updated and the SenseMonitor outputs should now be working again. 

Yet again, Please! Let me know, preferably in advance, any time the broadcast frame list is changed.

Dan, Jim, Dave:

we tried several things today to try to make h1fw0 more stable. These are:

reintroduction of h1ldasgw2 to take NDS traffic away from h1ldasgw0 (leaving it only used by h1fw0)

upgrade the network link between h1fw0 and h1ldasgw0 from a cat5e 1GE to a fiber opitcs 10GE using borrowed intel 10GE cards from LDAS

reconfigure fw0 to not write commissioning frames

power cycle fw0 and ldasgw0

these changes have not made fw0 any more stable. fw1 continues to be more stable, some of its restarts were coincident with fw0 restarts (within several minutes)

The measurements of HARD loops with different laser powers were posted before (alog 27864, 27885, 27920).

We found that the big discrepancies between the measurements and modeling for Pitch are caused by a mistake in the simulation. I fixed it and replotted the measurements at 10w and 40w (37w actually) as below.

Now the modeling curves fit the measurements much better. In the 10w plots, the black dots are measurements without the optical levers servos on for the ETMs, and the red ones are measurements with OL on for all the TMs. (The blue curves are the modeling results, which assume only OL on for ITMs.)

Took advantage of laser being down (aLOG #28142 & 28145) to change the water filters in the chiller room. 
Swapped out the Diode Chiller filter. The filter looked fine, but changed it out anyway to see if this had any effect on the rising PSL chiller pressures. 
Did not change the Chrystal Chiller filter. The filter bracket is poorly mounted to the wall and is coming loose. Need to secure the filter bracket to the wall before unscrewing the filter canister.         

J. Kissel, E. Goetz

Having a few new breakthrough ideas on the UIM actuation system (see LHO aLOG 24914), we explored whether we are modeling the [m/N] L1/UIM force to L3/TST displacement transfer function incorrectly. This was done by driving the UIM out to 600 [Hz] and measuring the response in DARM. Not only did we find the expected-but-not-yet-modeled wire violin modes at ~330 [Hz], 420 [Hz], and some at ~500 [Hz], but we found several bending-mode resonances at 111 [Hz] and 166 [Hz]. Indeed, upon first glance, we think the 111 [Hz] resonance is the remaining missing frequency dependence that explains the turn-up seen at 100 [Hz] in all previous measurements of the UIM to TST transfer function.

We'll process in more detail some time in the future, but check out the attached screen shots and be amazed at how not 1/f^6 the L1 to L3 transfer function is.

--------
We'd started by exciting the L1 stage via awggui in a broad-band fashion such that we could catch all of the wire violin mode frequencies watching DARM. As Evan mentions, we had suspected that these wire resonances -- documented in T1300876 -- were the source of the deviation from 1/f^6, and they'd just not been included in the SUS dynamical model -- [[EDIT -- Brett has now included them in the model, and they are a non-negligible effect; see LHO aLOG 24915]]. This broadband TF is shown in the first attachment. Black is the with excitation ON, and red is ambient (to distinguish the ~505 [Hz] fiber violin modes from the ~495 [Hz] TOP to UIM wire violin modes, and the Beam Splitter violin modes & 331.7 [Hz] calibration line from the Sus. Point to TOP wire violin modes). Only the peaks of the wire violin mode resonances are visible above the DARM noise; driving them any higher breaks the IFO's lock.

Just in case, we drove down to the same ~80 [Hz] region, and BINGO! We also found new, unexpected resonances at 166 [Hz] and even as low as 111 [Hz]! (see second and third attachments) Our best guess for the source of these resonances are imperfect actuators. Perhaps the bending of the L-bracket that mounts the OSEM coil to the reaction chain's UIM (see D060375, see page 1 for the total assembly, lock at pg 14 for the L-bracket). Though, if it were these L brackets, I'd suspect there would be 4 independent resonances... also it doesn't look like enough moving mass to have resonance frequencies as low as ~100 [Hz]... dunno, will think more.

Finding something at 111 [Hz], we then took a careful swept sign measurement covering it, and indeed, it looks strikingly like another piece of the UIM puzzle. (see 4th attachment). We also grabbed a PCAL to DARM transfer function over this frequency vector, so we can turn the TF into an absolute calibration later.

For future reference, the templates for the swpet sine TFs are here:
/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/PostO1/H1/Measurements/FullIFOActuatorTFs/
2016-01-12_L1toDARM_FullLock.xml
2016-01-12_PCALYtoDARM_FullLock.xml

and I attach screenshots of the awggui sessions used to excite L1 and PCAL in a broad-band fashion (DARM_IN1 ASDs during the broad-band excitations were taken using the standard wall FOM for DARM).