This is a follow up to my previous elog entries on SRCL non-stationary noise subtractions (45403 and 45508), and to the recent observations that SRCL noise contribution to DARM is closer than predicetd by the noise budget (either from coherence 45785 or from a direct noise injection 45792).

I further developed the technique described in 45403 and 45508 to identify and model non-stationary noise couplings. Now I can directly estimate a parametric, realizable and stable linear filter for each coupling. More details on the algorithm and the results during a SRCL noise injection will follow.

For now, since the linear term is still dominant, I restrict the analysis to a linear and stationary coupling from SRCL_IN to CAL-DELTA_EXTERNAL. Using 600 seconds of quiet data (no noise injection) starting at GPS 1228461018, I can reconstruct the optimal transfer function from SRCL to DARM in order to cancel out all of the SRCL noise. The plot below shows the result, the blue traces are absolute values (y axis on the left) and the yellow traces are phase (y axis on the right). The dots show the coupling factors computed in the frequency domain using the direct approach described in 45403. The solid lines are the "parametric" couplings: in other words the algorithm tries to minimize a weighted band-limited RMS in a band between 20 and 400 Hz, by modeling the coupling as stable, realizable 10th order rational function. To be clear, it's not a fit to the frequency domain reconstruction, but rather a direct fit to the data cross spectral densities.

I can then convert the poles and zeros of this optimal coupling function to a IRR filter and perform a time domain subtraction. The result, shown below, confirms the level of SRCL noise in DARM predicted either by BruCO coherence 45785 or by Rana's injection 45792. 

The last attached plot shows the coherence between DARM and SRCL before and after the time domain subtraction.

For reference, here's the transfer function from LSC-SRCL_IN1 to CAL-DELTAL_EXTERNAL (all poles and zeros frequencies in Hz). Note that both signals have been normalized by subtracting the mean value [mean(SRCL) = 0.00159, mean(DELTAL) = -9.800e-9] and dividing by the standard deviation [std(SRCL) = 3.131, std(DELTAL) = 1.503e-5):

Z =    [  73.27096456+274.9515352j ,   73.27096456-274.9515352j ,
          -1.09403038+269.468058j  ,   -1.09403038-269.468058j  ,
        -166.83658568  +0.j        ,   -0.8012538 +162.2435469j ,
          -0.8012538 -162.2435469j ,   -7.08797763+133.8045331j ,
          -7.08797763-133.8045331j ,   -3.15622979+134.12022151j,
          -3.15622979-134.12022151j,    0.9151632 +130.36107968j,
           0.9151632 -130.36107968j,   -1.42267922+119.98903183j,
          -1.42267922-119.98903183j,   -1.20138561 +97.64824832j,
          -1.20138561 -97.64824832j,   12.51635674 +30.96586879j,
          12.51635674 -30.96586879j,   27.66665614  +0.j        ]

P =    [  -2.14932791+268.49097597j,   -2.14932791-268.49097597j,
        -121.14272574+208.73233613j, -121.14272574-208.73233613j,
          -0.91968157+162.46027366j,   -0.91968157-162.46027366j,
         -51.9247949  +97.84796774j,  -51.9247949  -97.84796774j,
         -12.82120671+136.99086962j,  -12.82120671-136.99086962j,
          -0.96319905+136.92492285j,   -0.96319905-136.92492285j,
          -1.4837154 +128.24815143j,   -1.4837154 -128.24815143j,
          -0.60056718+120.09145053j,   -0.60056718-120.09145053j,
          -0.48652029 +97.30282541j,   -0.48652029 -97.30282541j,
         -15.69466233 +33.36645134j,  -15.69466233 -33.36645134j],

K = 3.079408216222647

   Added 150ml water to the crystal chiller. Water level in the diode chiller was OK. Both filters are clean and clear. No other issues or concerns noted.  

All plots look to be nominally ok. Chiller level steps coincide with Tuesday maintenance work.

Weekend Commissioning:  25 W work, looking at PI Modes (Seb & Terra)

Tues Maintenance Work Summary:  Stay in Laser Hazard & 4Hrs (i.e. end at noon)

• PSL/IO
  • PZT swap by  Jason, Cheryl, Keita (no other PSL work can go on until this work done!  Coordinate with HAM3 ISI work, if needed)
  • DBB work by Jason
  • Robert would like to do measurements after PZT swap
  • Dust Monitor move in Diode room (Jeff B)
• HAM3 ISI Noise Hunting of ~1Hz thing (Hugh)
  • IMC need to go OFFLINE if this happens, so will need to coordinate with PSL work.
• CDS: 
  • ESD work at EX & EY
  • Temperature sensors into PCal to look for noise
• Model Work
  • OMC Model Change (Keita)
  • HAM4/5/6 HEPI & ISI model updates (Hugh)
  • TCS Model Change:  Simulation fix (Danny)
  • LSC POPDC channels (Daniel)
  • ECAT CS 4 Only Beckhoff Restart (Daniel)
• PCal Work:  Calibration & Tune Up.  Start with EY.  (Rick)
• VAC
  • MY hammer drilling, extra vehicle traffic
  • MX annulus ion pump (this week)

Safety:  Be careful with icy conditions!

Just so that other people are aware, I've made ndscope templates for the violin mode drive and monitors.  They're accessible from both my locking screen and the normal violin mode overview screen.

TITLE: 12/10 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Commissioning
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    Wind: 4mph Gusts, 3mph 5min avg
    Primary useism: 0.03 μm/s
    Secondary useism: 0.37 μm/s

Light snow outside on ground from last night, but no issue driving/walking around parking lot (a little foggy on Rt 10).
QUICK SUMMARY:

• Terra & Seb have been here overnight for AMD (Acoustic Mode Damper) measurements.

Craig, Terra, Dan

Here's some observations from today on issues with locking, overall the alignment doesn't seem great and I'm not sure what we're doing wrong:

We ran initial alignment several times today. However, during MICH dark align the WFS seem to be taking us to something other than the symmetric elephant shape we usually have. We checked the phasing of AS45_B today and it all seemed fine. We touched up BS in either PRMI or check mich fringes if it wouldn't even lock that. Seems suspicious.

DRMI has been taking a long time to lock, PRMI seems fine, flashes look good.

Doing initial alignment of the arms has also been troublesome, getting good flashes in green has been more difficult than before, Y-arm has been particularly temperamental.

Getting through ENGAGE_REFL_POP_WFS was bit of a rollercoaster each time, PRC1 and PRC2 made some large detours.

We managed to get up to nominal low noise once for a few hour lock. The final lock didn't look very good though, there was a steady 0.6Hz oscillation in the PRG/RF18/arm powers that wouldn't die down, although it was stable overzealous commissioning brought it down.

We're trying to get it locked so Terra can do some PI work, however it's not looking likely at the moment.

I was skeptical about the SRCL noise in the noise budget, so I checked it again. I think it is pretty close.

Its a simple method, but should be accurate. SRCL_FF left on in the Guardian set state in NLN.

1. Turn on broadband noise excitation in SRCL2_EXC with AwgGui.
2. Adjust calibration of SRCL_OUT in DTT until the SRCL_OUT trace matches DARM.
3. turn off excitation to see how the ambient SRCL compares to DARM.

From this exercise I get the attached plot. Looks like its very close in the 40-90 Hz band. Options:

1. better low pass filtering; Downside: this is hard and will make the loop more unstable.
2. lower the SRCL gain: could be fine, but we don't yet know what the allowed SRCL error signal fluctuations are. i.e., how much can the SRC length fluctuate before it goes nonlinear or ruins the WFS signals?
3. improve the sensing noise: more power, more modulation depth, less electronics noise. Do we have a SRCL noise budget?

Sheila, Dan Brown, Rana

Because DRMI acquisition has been slow, we looked at the phasing of REFLAIR which is what we use to acquire DRMI. 

By injecting a 132 Hz line in PRM with notches on in MICH and SRCL, we measured that in DRMI the phase of REFLAIR 45 should be 112 degrees to minimize PRCL in the Q phase (currently 97), and for REFLAIR 9 the phase should be 8 degrees to minimize PRCL in the Q phase (currently -23 degrees).  

We reverted these changes since we lost lock and had trouble reacquiring with the new phases.  We didn't get a chance to measure the POP9I to SRCL element, but that would be the next step if we want to try to use these phases for DRMI acquisition.   

Terry and I quickly set up a 1811 on the CLF beam to check for seeding, and we see that our level of 3MHz sidebands on the CLF (which will be at the interferomter carrier frequency) is similar to what was seen at LLO 37945

Details:

We put the 1811 (AC coupled version) in place of the CLF rejected diode.  We used the half wave plate in front of the PBS to reduce the power here.  Once the diode was in we set the waveplate so that we saw 495 +/- 5mV of DC output (transimpedance 10V/mA) and measured the RF (+/- 1dBm for all):

-75dBm at 3.127 MHz
-75dBm at 200 MHz
-75.8 dBm 203.128 MHz  

Comparing this to LLO, we are getting 4 times more DC power, and about 6dBm more 3MHz signal, so that means that relative to the carrier our seeding power level is similar to LLO.  We haven't moved the RF amplifiers, feedthroughs, or attentuators as was done at LLO, which is consistent with the LLO results.  

While we were doing this measurement, I must have bumped the PBS in the CLF path which is very loose in it's mount, misalinging the fiber input  Terry tightened the mount, and we were able to find the beam in reflection off the OPO by carefully adjusting the PBS mount.  Then we used the two steering mirrors in front of the fiber coupler to maximize the transmission.  We found while doing this that the CLF launch diode was misaligned, and it looks like this has been misaligned for more than 20 days.  The beam is now aligned onto the diode.  Terry measured 4mW going towards the fiber, and the fiber launch diode reports 3.75mW towards the fiber.  The CLF Trigger diode reports 1 mW coming out of the chamber.  

Summary:

We were able to lock the squeezing angle using the 3MHz signal from the OMC DCPD's, and we have caused a few lockloses.  We have found that our locking scheme is introducing a lot of noise, so our next step is to lock the OPO length to the laser frequency.  

Locklosses:

In our first attempt we used the interferometer locked at 2W DC readout to look for the LO error signal.  We caused a lockloss then, and so we then changed to working with the interferometer locked on RF and the OMC locked.  We caused a couple of other locklosses this afternoon, one when the interferometer was locked on RF and the OPO became unlocked with the beam diverter open.  After this we added closing the beam diverter to the OPO guardian DOWN state, and the state CHECK_EOM (which we enter when the TTFSS EOM is railed).  

After successfully locking the squeezer angle, we transitioned to DC readout.  When we attempted to close the beam diverter we lost lock, which we also don't understand.  

We have been injecting ~10uW of CLF (measured on SQZT6), which gives us about 10 dBm of RF on the 3MHz demod.  We are wondering if this is too much and might be part of our lockloss problems.  We tried reducing it by a factor of 2.  

Locking:

Nutsinee will post details of the squeezing angle lock configuration that we used tonight, even though we don't plan to keep using this scheme. 

The basic steps:

• allow the laser temperature servo to bring the beatnote close to the correct frequency. (OPO guardian in down state)
• Lock the squeezer laser to the OPO using the TTFSS (OPO guardian to OPO_LOCKED_CLF)
• Lock the CLF using it's guardian.  
• We then could see that the frequency of the 3 MHz sidebands were not quite right.  We wrote an epics servo, which zeros the difference between the squeezer vs PSL sample (ref cavity) beatnote and twice the IMC VCO frequency, using the timing system frequency readbacks (which update once per second).  This is currently in the guardian called SQZ_PLL in a state called CHECK_BEATNOTE_2, but it will be moved somewhere else and given a more descriptive name.  This can hold us within 100kHz of the correct frequency.  
• We sent the 3MHz signal to both the OPO PZT and the additive offset of the TTFSS.  The additive offset was needed because of a large peak in the noise at around 1 kHz, which is similar to what was seen with the homodyne locking.  Because our locking scheme where the laser follows the OPO (rather than the other way around) introduces a lot of noise, especially at high frequencies, we have a lot of phase noise which means that we need a bandwidth higher than we can get with the PZT only to lock the squeezing angle.  For this reason we introduce an offset in the OPO PDH locking, which allowed us to lock but is obviously terrible. 
• Injecting squeezing in the IFO with this situation resulted in adding a lot of noise.  (See first attachment)

Uncontrolled squeezing:

• The interesting thing is that when we left the beam diverter open but blocked the CLF field and let the squeezing angle rotate, it actually rotates slowly and the large added noise is gone. The second attachment shows the same reference as the first, but with two traces captured with 4 exponential averages at 1Hz, 75% overlap, one showing close to the highest noise that we saw and one showing close to the lowest noise that we saw.  This seems like squeezing and anti-squeezing based on how flat the noise is, but there are two things that are surprising.  While it might be possible that this isn't anti-squeezing at all, it continued for more than 10 minutes without drifting away.  (We were sitting with CLF blocked and the beam diverter open from 4:45 to 4:55, with the OPO locked and the slow servo keeping it's frequency approximately correct.)
  • The level of anti-squeezing seems too high.  Looking between 1100Hz and 11400 Hz, this is almost 17dB of anti-squeezing.  Nutsinee measured the non linear gain to be 3.6, so with our expected total efficiency of 80%, we would expect at most 8dB of anti-squeezing.  (I know, this sounds like I am making a factor of 2 mistake, but I don't think I am.  I'm attaching the dtt file and my script in case anyone wants to double check.)  You might think that the extra noise we see is just some additional noise that we are adding with the squeezer other than anti-squeezing, but at times the noise level drifts down to just a few dB above shot noise. 
  • This squeezing angle is rotating slowly.  With a nonlinear gain of 3.7 and the efficiency of 80%, this would mean that over the 2 seconds of the low noise measurement the squeezing angle only rotated by about 610 mrad, which would be about 100nm of path length change.   We should compare this with the calibrated squeezing angle error signal which Nutsinee will post, but it seems strange that we needed 10's of kHz bandwidth to lock the squeezing angle with  such a slowly drifting system.  

I believe I have found a relevant bug report and a work around for various issues using the 'Terminator' terminal emulator program, including:

1. New terminals were placed behind existing terminals.
2. Opening a new terminal on a workspace that did not already have a terminal open on it would move an already existing terminal from another workspace to the workspace that the new terminal was opened on.

The bug report is here: https://bugs.launchpad.net/terminator/+bug/1508531

The work around is mentioned in one of the comments. Edit your ~/.config/terminator/config file and add 'dbus=False' under [global_config]. For example:

[global_config]
	dbus=False
[keybindings]
[profiles]
  [[default]]
    scrollback_infinite = True
[layouts]
  [[default]]
    [[[child1]]]
      type = Terminal
      parent = window0
    [[[window0]]]
      type = Window
      parent = ""
[plugins]


This seems to have resolved the issues mentioned above for me.