I don't know what exactly is going on, but MC became flaky and it's been frequently unlocked.

I have turned off the MC WFS servo to check if the WFSs are doing something bad. But it still tends to be unlocked without the WFS servo.

Right now it doesn't stay locked for more than 10 min.

       Locking plan            

Here is a plan in my mind and these are basically the details of the gantt chart (#6143):

• (1 day task) Measurement of the recycling gains of the RF sidebands with the PRMI and DRMI configuration, using POP22/110 RFPD.
  • I need to have confidence that I am really locking the DRMI with SRC resonating to 55 MHz.
  • Also those values will enable us to estimate losses and mode matching again (maybe ?).
• (3-4 days task) Measurement of the sensing matrix using the multiple-LOCKIN system.
  • Write a script to automatically measure the sensing matrix. This must be easy.
    • The results will enable us to diagonalize the input matrix and therefore it eventually gives more solid lock of the DRMI
    • Also it will give us the optical gains of 3f signals. So this is actually a step toward the 3f signal check.
• (3-4 days task) Noise budgeting on the 3f signals
  • This is a very important part of the DRMI characterization because the results will tell us whether we can hold the DRMI lock with a sufficient SNR or not.
  • If it turns out that they don't have good SNRs, we then have to come up with some ideas to improve the SNRs.
• (Extra fun task depending on schedule) 3f DRMI lock + Y arm ALS
  • If the beat-box electronics are not available by the time when the work above are completed, I will do this fun task.
  • Probably it is better to start preparing the common mode servo electronics because it will be needed anyway.

The dynamic power normalization system has been modified such that the normalization happen after the LSC input matrix.

Both the c1scx and its IOP realtime processes became out of sync.

Initially I found that the c1scx didn't show any ADC signals, though the sync sign was green.

Then I software-rebooted the c1iscex machine and then it became out of sync.

For tonight this is fine because I am concentrating on the central part anyway.

No we can't do that because the c1scx model is not working properly.

If you look into the real time controller screen you will find what I mean.

[John / Kiwamu]

 We found that some of the suspensions channels (for example C1:SUS-BS_POS_IN1 and etc) were not accessible from dataviewer for some reasons.

So far it seems none of the channels associated with c1sus are accessible from dataviewer.

[John / Kiwamu]

 We tried to figure out what is causing spikes in the REFL33 signal, which is used to lock PRCL.

No useful information was obtained tonight and it is still under investigation.

(Background)

 One thing preventing us from doing smooth measurements of the noise budget and the sensing matrix is some sharp spikes in the LSC error signals.

For example when we lock PRMI with REFL33 and AS55 fedback to PRCL and MICH respectively, both the REFL33 and AS55 signals show some spikes in time series.

Those spikes then bring the noise spectra higher than how they should be.

So for the reason, taking the noise budget doesn't give us much information about the interferometer rather than there are spikes.

Also the sensing matrix measurement has been suffered from those spikes, which excite the impulse responses of the low pass filters in the LOCKIN detection systems a lot.

(What we did)

 We looked into the actual analog signals to see if there are indeed spikes or not before they are acquired to the ADCs.

But we didn't find any corresponding spikes in the signals that are after the mixers.

It maybe because the signals we looked into didn't have high enough SNR because they were coming out from the monitor lemo outputs on the demod boards.

 Then we thought the spikes are from the whitening circuits, due to some kind of saturation.

We decreased the gain of the whitening filters by a factor of 10, but it didn't help and the spikes were still there.

[John / Valera / Kiwamu]

 We installed a new weapon, an optical spectrum analyzer in the AS port.

Like we used to do in the old days, two BNC cables were newly laid down and they bring the output of the OSA to the control room to monitor the spectrum with an oscilloscope.

(Some notes)

The photo diode of the OSA was replaced by a Thorlab PDA100A to amplify the signals.

The carrier peak is at about 6.9 V and the f1 and f2 sidebands peaks are at about 40 mV when the beam is in straight shot (everything is misaligned except ITMY and BS).

According to a rough calculation, those numbers correspond to a modulation depth of about 0.16 or so.

The depth agree with what Mirko measured before (#5519)

A very strange thing is going on.

The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.

This noise shows up even when the beam is single-bounced back from PRM ( the rest of the suspensions are misaligned) and it's very repeatable.

Any idea ?? Am I crazy ?? Is PRM making some fringes with some other optics ??

(background)

(Glitch is related to the PRM POS actuation)

(Possible scenario)

I did a quick test to check a hypothesis that PRM is interfering with some other optics in the single bounce configuration.

I shook all the suspensions (except the MC mirrors) at 3 Hz in POS, PIT and YAW with an amplitude of 1000 counts.

No effects were found in the REFL demod signals.

So it is NOT a fringe effect caused by the other suspended mirrors.

AWG is not working. This needs to be fixed.

I could set the channel and the parameters in the AWGGUI screen, but it never inject signals to the realtime system.

I have slightly rotated the lambda/2 plate, which is used for attenuating the REFL beam's power on the AS table

because the plate had been at an unusual angle for investigation of the glitches since last Thursday.

It means the laser power going to the coating thermal noise setup has also changed. Just keep it in mind.

 Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.

Looking at it through an IR viewer, I saw the REFL beam hitting one of the biggest dust particles on that mirror.

This dust particle maybe causing the glitches or maybe not.

Anyway because it's always better to have clean mirrors, I will wipe the steering mirror in this evening and check the presence of the glitches again.

Actually awg works fine without any problems when the excitation channels belong to the c1lsc machine.

It seems that the awg doesn't inject signals on the channels of the c1sus machine, for example C1:SUS-BS_LSC_EXC and so on.

I wiped both surfaces of the REFL second steering mirror.

However no improvements. The glitches still remain.

(Pic.1 before wiping, Pic.2 after wiping)

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 (The measurement)

1.  Preparation : calibration of the MC2 actuator as a frequency actuator (for more details, see the next section)
2.  Set the interferometer to the single-bounce configuration such that the beam directly is reflected back from PRM
3.  Take spectra of REFL11_I without driving any optics. This spectra tells us how quiet the noise normally is.
4.  Drive MC2_POS at 10 Hz with an amplitude of 10000 counts so that we can see the high frequency up conversion noise
   • The frequency was chosen such that the excitation is out of the local damping bands
   • The amplitude was chosen to be as big as possible until the MC unlocked
   • With this drive, the laser frequency should change by 20 MHz peak-peak at 10 Hz.
5.  Record the noisy spectrum when the MC2_POS was driven.
6.  Drive PRM instead of MC2 at 10 Hz.
   • Adjust the amplitude of the excitation such that the cut-off frequency of the up conversion noise matches with that of the MC2 driven case.
   • The amplitude was found to be 1700 - 2000 counts, this uncertainty is currently limiting the precision of the optical distance estimation.
   • With this amount of the drive, PRM moves by 0.8 um peak-peak at 10Hz.
7. Estimate the optical length based on the amount of the drives for PRM and MC2.
   • Estimate the FSR using the following relation df/FSR = dx/ (lambda/2). => FSR = 17 MHz
   • Since FSR = c/ (2L),  L = c/(2 FSR) = 9.5 m or so

(Calibration of the MC2 actuator)

I searched for a scattering body in the REFL path.

According to the result the REFL path on the AS table is innocent.

The idea of the search method is given as follows:

•   Put a 1/10 ND attenuator at the origin of the REFL path on the AS table.
•   Of course this reduces the signal level by the same factor of 10 in the REFL11_I demod signal.
•   If the scattering body is in the REFL path the up conversion noise will be smaller by a factor of 100 because the scattered light go across the attenuator twice.

I realigned the incident beam to PMC at 23:30. The transmitted light went up from 0.78 to 0.83.

Also I decreased the HEPA level down to 20 % for the night time locking.

One of my goals in this week is : measurement of the current best ALS noise budget.

Last night I took a new noise spectra of the Y arm ALS, which is shown in the attached figure below.

The displacement of the arm cavity observed from the IR PDH is at 66 pm in rms. In the measurement the arm length was stabilized with the ALS technique.

Here is a new time series plot showing how stably ALS can control the arm length.

In the middle of the plot the cavity length was held at the resonance point for ~ 2 min. and then it passed through the resonance point to show the full shape of the PDH signal.

Apparently the PDH signal is now quieter than before (#6133)

I have realigned the beam pointing to PMC. The transmitted light increased from 0.74 to 0.83.

The misalignment was mainly in pitch.

I did some more stuff for the Y arm ALS and updated the noise budget:

After the works, the rms displacement improved a little bit, so it is now at 24 pm in rms.

Though, it turned out that the MFD's ADC is now limiting the noise in a frequency band of 200 mHz - 5 Hz.

So tonight I will increase the gain of the whitening filter to push down the ADC noise more.

(What I did)

 + added the DAC noise and comparator noise based on measurements.

 + redesigned the servo filter shape to suppress the seismic noise below 10 Hz.

 The attached plot below shows the newly designed open loop transfer function together with the old one for a comparison.

UGF is at 120 Hz and the phase margin is about 27 deg.

• FM7 = resonant gain (17)
• FM6 = resonant gain (3)
• FM5 = zero(1) * pole(500)
• FM4 = pole(1) * zero(40.) * 40.
• FM3 = pole(1) * zero(40.) * 40.
• FM2 = pole(0.001)*zero(1)*1000.

Surprisingly increasing the gain of the whitening filter didn't improve the noise curve.

It suggests that the ADC noise is not the limiting factor below 10 Hz.

Indeed the glitches show up in the analog demodulated signals. So it is not an issue of the digital processing.

With an oscilloscope I looked at the I/Q monitor outputs of the LSC demodulators, including REFL11, REFL33, REFL55, POY11, AS55 while keep locking the carrier-resonant PRMI.

I saw some glitches in REFL11, REFL55 and AS55. But I didn't see any obvious glitches in REFL33 and PO11 because the SNR of those signals weren't good enough.

(some example glitches)

The attached plot below is an example shot of the actual signals when the carrier resonant PRMI was locked.

The first upper row is the spectrogram of REFL11_I, REFL55_I, REFL33_I and AS55_Q in linear-linear scale.

The second row shows the actual time series of those data in unit of counts.

The bottom row is for some DC signals, including REFLDC, ASDC and POYDC.

You can see that there are so many glitches in the actual time series of the demod signals (actually I picked up the worst time chunk).

It seems that  most of the glitches in REFL11, REFL33 and AS55  coincide.

The typical time scale of the glitches was about 20 msec or so.

Note that the PRMI was locked by REFL33 and AS55 as usual.

During the Y arm ALS I found that the noise of the AS55 demod signal was worse than that of POY11 in terms of the Y arm displacement.

There is a bump from 500 mHz to 100 Hz in the AS55 signal while POY11 didn't show such a structure in the spectrum.

The plot below is the noise spectra of the Y arm ALS. The arm length was stabilized by using the green beat-note fedback to ETMY.

In this measurement, POY11 and AS55 were served as out-of-loop sensors, and they were supposed to show the same noise spectra.

In the plot It is obvious that the AS55 curve is louder than the POY curve.

After I recovered the lock of PMC, I found that the PMC transmission was quite low. It was about 0.26 in the EPICS display.

I zeroed the PSL temperature feedback value which had been -2.3 and then the PMC transmission went back to a normal value of 0.83.

I believe it was because the PSL was running with two different oscillation modes due to the big temperature offset.

I did a fine alignment on the Y end green setup. The green light became able to be locked again.

I went through various IFO configurations to see if there are glitches or not.

Here is a summary table of the glitch investigation tonight. Some of the cells in the table are still not yet checked and they are just left blank.

        Low finesse PRMI      

The low finesse PRMI configuration is a power-recycled MIchelson with an intentional offset in MICH to let some of the cavity power go through MICH to the dark port.

To lock this configuration I used ASDC plus an offset for MICH and REFL33 for PRCL.

The MICH offset was chosen so that the ASDC power becomes the half of the maximum.

In this configuration NO glitches ( a high speed signal with an amplitude of more than 4 or 5 sigma) were found when it was locked.

Is it because I didn't use AS55 ?? or because the finesse is low ??

Also, as we have already known, the up conversion noise (#6212) showed up -- the level of the high frequency noise are sensitive to the 3 Hz motion.

Here is a hypothetical scenario which could make the glitches in the LSC error signals. It can be considered as a 4 step phenomenon.

        (1) up conversion noise due to a large motion at 3 Hz

   => (2) rms level exceeds the line width (a.k.a. linear range) in some LSC sensors

   => (3) unlocks some of the DOFs  in a moment

   => (4) glitches due to the short unlock.

- - plan  - -

 In order to check this hypothesis the low finesse PRMI must serve as a good test configuration.

What I will do is to gradually decrease the offset in MICH such that the finesse of PRMI becomes higher.

And at each different finesse I will check the spectra, glitch rate, and etc.

[Rana / Kiwamu]

We tried to set some parameters for the suspension drift monitor but the old matlab script, which automatically sets the values, didn't run because it uses the old mDV protocol.

The attached link below is a description about the script.

https://wiki-40m.ligo.caltech.edu/Computers_and_Scripts/All_Scripts#Drift

It needs to be fixed or upgraded by pynds.

[Steve/ Kiwamu]

 We found that the laser had completely shut off for ~ 4 hours even with all the PSL doors closed.

We are guessing it is related to the interlock system and Steve is working on it to fix it.

I gave up tonight's locking activity because the MC can't stay locked.

It seems that somehow the seismic noise became louder from about 1:00 AM.

I walked around the outside of the 40-m building to see what's going on, but no one was jumping or partying.

I am leaving the MC autolocker disabled so that the laser won't be driven crazy and the WFS won't kick the MC suspensions.

The attachment is a 3-hour trend of the seismometer outputs and the MC trans.

[ Koji / Kiwamu ]

The frequent unlock of the MC are most likely unrelated to ground motion.

Although the reason why MC became unstable is still unclear.

There are two facts which suggest that the ground motion and the MC unlock are unrelated :

(1) It turned out that the seismometer signals (C1:PEM-SEIS-STS_AAA ) have a big cross talk with the MC locking signals.

    For example, when we intentionally unlocked the MC, the seismometer simultaneously showed a step-shaped signals, which looked quite similar to what we have observed.

    I guess there could be some kind of electrical cross talk happening between some MC locking signals and the seismometer channels.

    So we should not trust the signals from the STS seismometers. This needs a further investigation.

(2) We looked at the OSEM and oplev signals of some other suspended optics, and didn't find any corresponding fluctuations.

    The suspensions we checked are ETMX, ETMY, ITMX and MC1.

     None of them showed an obvious sign of the active ground motions in the past 24 hours or so.

I have measured the sensing matrix of PRMI.

It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control.

The data is coming soon.

I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts.

Smells like something is very wrong.

Measured sensing matrix

        Some obvious things:

•  REFL11 : The separation angle between MICH and PRCL is narrow and it is far from the ideal 90 degree. This doesn't agree with the simulation.
•  REFL33:  The MICH and PRCL signals are almost degenerated in their demodulation phase.
•  REFL55 :  It shows non-90 degree separation. This doesn't agree with the simulation.
•  REFL165 : The separation is close to 90 degree, but the signals are small. And I am not sure if the MICH signal is real or just noise.
•  AS55 : Somehow it shows a nice 90 degree separation, but this result doesn't agree with the simulation.

Expected sensing matrix from a simulation

Measurement

•  Locked PRMI with the carrier anti-resonating in PRCL.
•  Adjusted the control gains for both the MICH and PRCL control to have UGFs at ~ 100 Hz.
•  Put a 30 dB notch filter  in each control servo at 283.1 Hz where an excitation signal will be.
•  Excited PRCL and MICH at different time via the realtime lockng in the LSC front end. The amplitude is 1000 counts and the frequency is at 238.1 Hz.
  
  • For the MICH excitation, I have coherently and differentially excited ITMs
•  Used DTT to take a transfer function (transfer coefficients at 283.1 Hz) from the lockin oscillator to each LSC demodulated signal.
  • Including AS55I/Q, REFL11I/Q, REFL33I/Q, REFL55I/Q and REFL165I/Q.
•  Calibrated the obtained transfer functions from unit of counts/counts to V/m using the actuator response (#5637)

I updated the table which I posted some time ago (#6231). The latest table is shown below.

It seems that the glitches show up only when multiple DOFs are locked.

Interesting thing is that when the low finesse PRMI is locked with a big MICH offset (corresponding to a very low finesse) it doesn't show the glitches.

Qualitatively speaking, the glitch rate becomes higher as the finesse increases.

I will try SRMI tomorrow as this is the last one which I haven't checked the presence of the glitches.

I found that the DC monitor of the REFL165 was showing 9 V regardless of how much laser power goes to the diode.

I am worried about whether the RF output is also broken.

It needs to be checked and I will leave this to Suresh as one of his morning tasks.

Sometimes ago I reported that there have been a kind of upconversion noise when PRM was excited (#6211).

This time I found another one, which showed up when BS was excited.

Assuming this is related to some kind of scattering process and also assuming this is from the same scattering body as that for the PRM driven case,

we may be able to localize and perhaps identify the scattering body.

(Measurement Condition)

(Noise spectrum)

The MC became crazy again.

It seems that there were corresponding steps in the OSEM signals. Look at the one-day trend posted below.

[Koji / Kiwamu]

 The MC is now back to normal. The beam pointing to the interferometer is good.

There were two different issues :

• A mechanical mount was in the MC WFS path.
• There were some loose connections in the SUS rack

Slid have we the position of the mechanical mount. Nicely the WFS beam go through now.

And also I pushed all the connectors associated with the MC SUS OSEMs in the SUS rack.

After pushing the connectors, the MC1 OSEM readouts dramatically changed, which actually more confused us.

As shown in the 3 hours trend below, the OSEM readouts have changed a lot (shown in the middle of the plot with arrows). Some bumps after the steps correspond to our alignment efforts.

I locked the PRMI with the AS55I and Q combination.

It seems the glitche rate decreased,

but I am not 100 % sure because the rest of the demod signals (i.e. REFL11 and etc) were showing relatively big signals (noise ?), which may cover the glitches.

Also the optical gain of PRCL at AS55I doesn't agree with my expectation based on the obtained sensing matrix (#6283).

It looks too low and lower than the measured sensing matrix by a factor of 50 or so.

I will continue working on this configuration tomorrow and then move on to the SRMI locking as a part of the glitch hunting activity.

[ Den / Kiwamu]

 We have realigned the MC suspensions so that the WFS servos are smoothly engaged.

Now it seems working fine. The beam pointing to the interferometer also looks okay.

The WFSs control kept failing to engage the servos because of large misalignments in the MC suspensions.

When the TEM00 was locked, the transmitted light was only about 1200 counts and the reflected light was about 2.8 counts.

We tweaked MC1, MC2 and MC3.

I tried the "Yarm + PRMI" configuration to see what happens.
The Y arm was locked at a resonance and held with the ALS technique.
On the other hand, the X arm was freely swinging.

I briefly tried severl demod signals to calm down the central part, but didn't succeed.
Now I feel I really want to have the X arm locked with the ALS technique too.
Give me the beat-box !

The attached screen shot shows the transmitted light of both arms as a function of time.
TRY is always above 1, since it was kept at a resonance.
Sometimes TRY went to 50 or so.

PZT1, the one with Koji's custom mid-HV driver (#5447), is getting degraded.

The movable range in the pitch direction became narrower than what it used to be (maybe a factor of 3 estimated by looking at the beam spots).

I think we should raise the priority level of the active TTs for the next vent.

I have been having a feeling that the PZT1 response is getting smaller since the end of the last year, but now I am confident

because I could see the difference between the movable ranges of Yaw and Pitch, and they used to have approximately the same amount of the movable ranges.

Right now this is not a serious issue as the beam pointing determined by the MC alignment is so good that the Pitch range doesn't rail.

I won't be surprised if it becomes completely immovable in 3 month.

Two new BBPDs have been installed on the PSL table.

The first one was installed by Koji a few days ago, and I stalled the second one today.

They will serve as beat-note detectors for the green locking.

Next step : I have to lay down a long SMA cable which goes from the BBPD to the IOO rack.

I tried SRMI. The glitch rate wasn't as high as that of PRMI but it happened once per 10 sec or so.

Last night I tried the "Y arm + central part" locking again. Three different configuration were investigated :

•  Y arm + DRMI
•  Y arm + PRMI
•  Y arm + MICH

In all the configurations I displaced the Y arm by 20 nm from the resonance.

As for the DRMI and PRMI configurations I wasn't able to acquire the locks.

As for the MICH configuration, the MICH could be locked with AS55. But after bringing the Y arm to the resonance point the lock of MICH was destroyed.

I did a quick calculation to see if the offset of the arm length which I tried last night was reasonable or not.

The conclusion is that the 20 nm offset that i tried could be a bit too close to a resonance of the 55 MHz sidebands.

A reasonable offset can be more like 10 nm or so where the phases of all the laser fields don't get extra phases of more than ~ 5 deg.

The attached plot shows where the resonances are for each sideband as a function of the displacement from the carrier's resonance.

The red solid line represent the carrier, the other solid lines are for the upper sidebands and the dashed lines are for the lower sidebands.

The top plot shows the cavity power and the bottom plot shows how much phase shift the fields get by being reflected by the arm cavity.

Apparently the closest resonances to the the main carrier one are that of the 55 MHz sidebands, and they are at +/- 22 nm.

So if we displace the arm length by 22 nm, either of the 55 MHz sidebands will enter in the arm cavity and screw up the sensing matrix for the 55 MHz family.

I tried the Yarm + PRMI configuration again.

The PRMI part was locked, but it didn't stay locked during the Y arm was brought to the resonance point.

I will post the time series data later.

(locking of the PRMI part)

Tonight I was able lock the PRMI when the arm was off from the resonance by 10 nm (#6306).

This time I used REFL11Q to lock the MICH instead of the usual AS55Q because the MICH didn't stay locked with AS55Q for some reason.

The PRCL was held by REFL33I as usual.

Also I disabled the power normalization for the error signals because it could do something bad during the Y arm is borough to the resonance.

In order to reduce the number of the glitches, PRM was slightly misaligned because I knew that the lower finesse gives fewer glitches.