Good work for the oplev noise simulations. Here are some comments/questions:
(A) The noise looks suppressed but the open-loop transfer function doesn't look so good, because it doesn't have sufficient phase margins at the UGFs (0.01 and 10 Hz).
I guess it is better to have a phase margin detector in your code so that the code automatically rejects a bad phase margin case.
Actually since the number of data points are finite, the rms detector in the simulation can not always find a sharp loop oscillation.
(B) The resultant poles and zeros seem canceling each other but the filter still has a structure. Is something wrong ?
Pole 1 frequency = 0.0497181 Hz
Pole 2 frequency = 2.01809 Hz
Zero 1 frequency = 0.0497181 Hz
Zero 2 frequency = 2.01809 Hz
The servo for aligning the Y arm is working fine with the coarse gain coefficients.
However then I found the ASS_Xarm servo was not healthy.
So the next step is to refine the X arm servo in C1ASS.
+ With the ETMY oplev the Y arm became quieter after we recovered the oplev whitening filter (#5523)
+ The Y arm alignment scripts can be run from the usual C1IFO_CONFIGURE screen.
It will servo the spot positions on ITMY and ETMY, and align the input beam pointing. It brings the Y arm power to about 1.
+ The X arm servo is doing something funny. It doesn't bring the arm power up to 1.
I thought the X arm didn't need any modifications because the X arm servo doesn't include PZT1 and PZT2.
So it maybe a simple bug (for example, some switches are disable and so on)
As a suspension test I am leaving all of the suspensions restored and damped with OSEMS but without oplevs
According to the spectra, all of the suspensions had been damped with the OSEMs. The peaks around 1Hz are reasonably suppressed.
However the spectra from ITMX showed a noise floor at very high level. This is because of strange jumps in the signal of the UL shadow sensor.
I will check some analog circuits for the UL sensor.
(ITMX shadow sensors)
Here is the spectra of the ITMX shadow sensors taken during the damping test (#5534)- -
The UL sensor shows a unacceptable amount of noise.
Additionally I checked the time series of the ITMX shadow sensors and found ONLY the UL sensor frequently showed strange jumps in data.
Here is an example of the time series showing a jump ONLY in the UL sensor.
It is possible that the jumps are coming from some circuits, since the rest of the sensors (including the oplevs) don't detect the same jump.
Currently the damping of the ITMX suspension is intentionally disabled for the noise investigation.
The issue on the ITMX UL sensor has been fixed. It was because of a loose connection in the sensor signal path.
After the fix, the sensor responses completely changed and the suspension became unable to be damped with the new matrix.
At the moment the ITMX suspension is damped by the default input matrix.
we should do the free swinging test once again.
The loose connection was found on the rear side of the 1X5 rack.
There is an adapter card on the rear side, where the driver and sensor signals are combined into a single cable.
I pushed the sensor cable (bottom right in the picture) and the noise disappeared.
Note that I changed the labels on the adapter cards from the old X/Y convention to the new one.
After fixing the loose cable the ITMX suspension became unable to be damped.
So I put the input matrix back to the default and it immediately started damping happily. It means our new matrix is not valid any more.
Here is the latest noise spectra of the ITMX sensors damped with the default input matrix.
As usual all of them are limited by the ADC noise above 20 Hz. (ADC noise is plotted in purple curve)
During the work I also pushed not only ITMX ones but also the cable for the rest of the optics in the adapter cards.
Then PRM became unable to be damped, so it implies the PRM suspension also used to be the same situation.
The input matrix of PRM has been also back to the default.
The lock of PRMI wasn't so robust although it could stay locked for more than 10 minutes.
There have been 2-3Hz spikes in everywhere. It needs to be investigated.
+ Diagnosis on the suspensions.
+ Check the beam centering on the RFPDs.
+ Check the f2a filters on PRM and BS.
+ Health check of the suspensions by locking some cavities and measuring the noise spectra for comparison.
+ Trying to use another signal port other than AS55.
The attached picture below is an example of the REFLDC and POXDC signals in time series.
This was when PRCL and MICH were locked by REFL33_I and AS55_Q respectively.
Note that when PRMI is unlocked, REFLDC goes to ~ 5000 counts and POXDC goes within ADC noise of ~ 1 counts.
According to the POP camera it looked like something was oscillating in the YAW direction which coincided with the spikes.
I tried finding any suspicious angular motions in the ITMs, BS and PRM olevs, but none of them showed the 2-3 Hz feature.
Somehow some DAQ channels for C1SUS have disappeared from the DAQ channel list.
Indeed there are only a few DAQ channels listed in the C1SUS.ini file.
I ran the activateDQ.py and restarted daqd.
Everything looks okay. C1SUS and C1PEM were restarted because they became frozen.
The channels for IPPOS had been assigned in a wrong way.
Because of this, C1:ASC-IP_POS_X_Calc corresponds to the actual vertical motion and C1:ASC-IP_POS_Y_Calc is for the horizontal motion.
We should fix the database file to get the correct vertical/horizontal corrdinate.
Now the C1ASS servos are working fine.
However at the end of the scripts sometimes it changes the DC force (e.g. C1:SUS-ITMX_PIT_COMM and so on) by a wrong amount.
So for this bug, it misaligns the suspensions a lot. I will take a look at the script tomorrow.
We found that the C1LSC.ini and C1IOO.ini file had been refreshed and there were a few recorded channels in the files.
So we manually recovered C1LSC.ini file using the daqconfig GUI screen.
For the C1IOO.ini file we simply replaced it by the archived one which had been saved in 22nd of September.
Then we restarted daqd.
[Suresh / Kiwamu]
The c1lsc and c1sus machine were rebooted.
- - (CDS troubles)
After we restarted daqd and pressed some DAQ RELOAD buttons the c1lsc machine crashed.
The machine didn't respond to ssh, so the machine was physically rebooted by pressing the reset button.
Then we found all the realtime processes on the c1sus machine became frozen, so we restarted them by sshing and typing the start scripts.
However after that, the vertex suspensions became undamped, even though we did the burt restore correctly.
This symptom was exactly the same as Jenne reported (#5571).
We tried the same technique as Jenne did ; hardware reboot of the c1sus machine. Then everything became okay.
The burt restore was done for c1lsc, c1asc, c1sus and c1mcs.
- - (ITMX trouble)
During the trial of damping recovery, the ITMX mirror seemed stacked to an OSEM. The UL readout became zero and the rest of them became full range.
Eventually introducing a small offset in C1:SUS-ITMX_YAW_COMM released the mirror. The amount of the offset we introduced was about +1.
The MICH and PRCL motions have been measured in some different configurations.
According to the measurements :
+ PRCL is always noisier than MICH.
+ MICH motion becomes noisier when the configuration is Power-Recycled Michelson (PRMI).
The next actions are :
+ check the ASPD
+ check the demodulation phases
+ try different RFPDs to lock MICH
Thank you for the summary.
I think now you are getting into a phase where you should start doing some quantitative and careful checks.
1. Calculate how much light will be reflected from the cavity if the alignment is perfect.
2. Investigate where those kHz oscillations are coming from.
3. Estimate how much the 1.1 kHz corner frequency in LPF will reduce the phase margin around 10 kHz.
4. Calculate the estimated amplitude of the PDH signal.
5. Compute how big the gain of the PDH box should be.
This is a kind of summary of what I have worked on this week.
[Mirko / Kiwamu]
We have reviewed the AM issue and confirmed the ratio of AM vs. PM had been about 6 x103.
The ratio sounds reasonably big, but in reality we still have some amount of offsets in the LSC demod signals.
Next week, Mirko will estimate the effect from a mismatch in the MC absolute length and the modulation frequency.
Please correct us if something is wrong in the calculations.
According to the measurement done by Keiko (#5502):
DC = 5.2 V
AM @ 11 and 55 MHz = - 56 dBm = 0.35 mV (in 50 Ohm system)
Therefore the intensity modulation is 0.35 mV / 5.2 V = 6.7 x 10-5
Since the AM index is half of the intensity modulation index, our AM index is now about 3.4 x 10-5
According to Mirko's OSA measurement, the PM index have been about 0.2.
As a result, PM/AM = 6 x 103
* DC power = 5.2V which is assumed to be 0.74mW according to the PDA255 manual.
*AM_f1 and AM_f2 power = -55.9 dBm = 2.5 * 10^(-9) W.
Found the Marconi for the 11 MHz source had been reset to its default.
=> reset the parameters. f = 11.065910 MHz (see #5530) amp = 13 dBm.
Interferometer became lockable. I checked the X/Y arm lock, and MICH lock, they all are fine.
The following optics were kicked:
MC1 MC2 MC3 ETMX ETMY ITMX ITMY PRM SRM BS
Sun Oct 2 02:13:40 PDT 2011
They will automatically get back after 5 hours.
Just a quick report.
The AS55 signal contains more noise than the REFL signals.
Why ? Is this the reason of the instability in PRMI ?
I locked the Power-Precycled ITMY with REFL33.
As shown in the plot above, I compared the in-loop signal (REFL33) and out-of-loop signals (REFL11 and AS55).
All the signals are calibrated into the displacements of the PR-ITMY cavity by injecting a calibration peak at 283 Hz through the actuator of PRM.
AS55 (blue curve) showed a structure around 3 Hz and higher flat noise below 1 Hz.
The input matrices of ETMX, ITMX and PRM have been newly inverted.
Those were the ones having some troubles (see #5444, #5547).
After a coarse adjustment of the damping Q factors, they look damping happily.
Before running the peakFit scripts, I woke up the nds2 sever process on Mafalda because it hasn't been recovered from the power outage.
To start the nds2 process I followed the instruction by Jamie (#5094).
Then I started requesting the data of the last night's free swinging test (#5594)
However the NDS2_GetData command failed everytime when data with long duration were requested.
It maybe because some of the data are missing in sometimes, but I haven't seriously checked the data stored in fb.
So for the reason, I had to use a short duration of 1200 sec (default is 3600 sec). That's why spectra look noisier than usual.
My goal of today was to lock PRMI without using AS55 and it is 50% successful.
The sideband-resonance PRMI (SB-PRMI) was locked with REFL33_I and REFL55_Q for the PRCL and MICH control respectively.
The carrier-resonance PRMI wasn't able to be locked without AS55.
(it looked no clean MICH signals at the REFL ports.)
The motivation of not to use AS55 came from the suspicion that AS55 was injecting some noise into MICH (#5595).
So I wanted to try another RFPD to see if it helps the stability or not.
The lock of SB-PRMI was quite stable so that it stayed locked more than 30 minutes (it ended because I turned off the servos.)
Then I briefly tried DRMI while PRCL and MICH kept locked by the same control loops, namely REFL33_I and REFL55_Q.
The lock of MICH and PRCL looked reasonably robust against the SRCL fringes, but wasn't able to find a good signal for SRCL.
I think I am going to try locking DRMI tomorrow.
- - settings
Demod phase for REFL55 = -45.3 deg
Demod phase for REFL33 = -14.5 deg
Whitening gain for REFL55 = 4 (12 dB)
Whitening gain for REFL33 = 10 (30 dB)
MICH gain = 100
PRCL gain = 8
+ I removed an iris on the ITMY table because it was in the way of POY. See the picture below.
+ I found that burtrestore for the ETMX DC coil forces were not functional.
=> currently ETMX's "restore" and "mislalign" buttons on the C1IFO_ALIGN screen are not working.
=> According to the error messages, something seemed wrong on c1auxex, which is a slow machine controlling the DC force.
The input matrix of IPPOS were fixed so that the horizaontal motion correctly shows up in X and the vertial is Y.
(what I did)
+ The data base file, QPD.db, were edited.
QPD.db is a part of the c1isxaux slow machine and it determines the input matrix for deriving the X/Y signals from each quadrant element.
+ The previous input matrix was :
X = (SEG1 + SEG4) - (SEG2 + SEG3)
Y = (SEG1 + SEG2) - (SEG3 + SEG4)
+ The new matrix which I set is :
X = (SEG1 + SEG2) - (SEG3 + SEG4)
Y = (SEG1 + SEG4) - (SEG2 + SEG3)
The new matrix is a just swap of the previous X and Y.
+ Then c1isxaux was rebooted by :
+ The I did the burt restore it to this morning.
[Mirko / Jenne / Kiwamu]
Just a quick update. All the realtime processes on the c1lsc and c1sus machine didn't run at all.
Somehow the c1xxxfe.ko kernel module, where xxx is x04, x02, lsc, ass, sus, mcs, pem and rfm failed to be insmod.
The timing indicators on the c1lsc and c1sus machine are saying NO SYNC.
- According to log files (target/c1lsc/logs/log.txt)
insmod: error inserting '/opt/rtcds/caltech/c1/target/c1lsc/bin/c1lscfe.ko': -1 Unknown symbol in module
- dmesg on c1lsc (c1sus also dumps the same error message):
[ 45.831507] DXH Adapter 0 : sci_map_segment - Failed to map segment - error=0x40000d01
[ 45.833006] c1x04: DIS segment mapping status 1073745153
DXH dapter is a part of the Dolphine connections.
When a realtime codes is waking up, the code checks the Dolphin connections.
The checking procedure is defined by dolphin.c (/src/fe/doplhin.c).
According to a printk sentence in dolphin.c the second error message listed above will return status "0" if everything is fine.
The first error above is an error vector from a special dolphin's function called sci_map_segment, which is called in dolphin.c.
So something failed in this sci_map_segment function and is preventing the realtime code from waking up.
Note that sci_map_segment is defined in genif.h and genif.c which reside in /opt/srcdis/src/IRM_DSX/drv/src.
[Koji / Kiwamu]
We did several tests to figure out what could be a source of the computer issue.
The Dolphin switch box looks suspicious, but not 100% sure.
(what we did)
+ Removed the pciRfm sentence from the c1x04 model to disable the Dolphin connection in the software.
+ Found no difference in the Makefile, which is supposed to comment out the Dolphin connection sentences.
==> So we had to edit the Makefile by ourselves
+ Did a hand-comilpe by editing the Makefile and running a make command.
+ Restarted the c1x04 process and it ran wihtout problems.
==> the Dolphin connection was somehow preventing the c1x04 process from runnning.
+ Unplugged the Dolphin cables on the back side of the Dolphin box and re-plug them to other ports.
==> didn't improve the issue.
+ During those tests, c1lsc frequently became frozen. We disabled the automatic-start of c1lsc, c1ass, c1oaf by editting rtsystab.
==> after the test we reverted it.
+ We reverted all the things to the previous configuration.
The He-Ne laser which has been used for the PRM and BS oplevs were found to be dead.
According to the trend data shown below, it became dead during the dolphin issue.
(During the dolphin issue the output from the oplev QPDs are digitally zero)
I found again the ini files had been refreshed.
I ran the activateDQ.py script (link to the script wiki page) and restarted the daqd process on fb.
The activateDQ.py script should be included into the recompile or rebuild scripts so that we don't have to run the script everytime by hands.
I am going to add this topic on the CDS todo list (wiki page).
It turned out the noise in AS55 was due to a clipping. After fixing the clipping the noise successfully went down.
I was going to briefly check the clipping and go ahead locking DRMI, but for some reason I couldn't stop myself from working on this issue.
Here is a plot of the noise spectra taken before and after fixing the clipping.
The configuration of this measurement is exactly the same as that I did before (#5595)
+ Locked power-recycled ITMY so that the AS beam is bright enough to work with.
+ Shook BS at 1 Hz in the YAW direction
+ Looked around the AP table with an IR viewer and searched for a clipping moving at 1Hz.
+ Found the first lens in the AS beam path has clipped the beam at the upper side. A tiny portion of the beam was clipped.
+ Corrected the beam height to 4 inch by steering the very first mirror.
+ Raised the height of the lens because it was about 3.5 inch or so.
+ Found the lens had a scratch (~1 mm size ) at 1 cm blow the center on the surface.
=> I tried finding a spare 2 inch lens with a long focul length, but I couldn't find it,
So I left the lens as it is, but we should buy some 2 inch lenses just in case like this.
+ Replaced the 1 inch beam splitter by 2-inch 99% BS so that most of the light goes into the RFPD and a little bit goes into the camera.
DRMI has been locked using the same RFPD selection as the old days (i.e. AS55_I, AS55_Q and REFL_I).(#4760)
But remember : this is just a beginning of several measurements and tests to characterize the central part.
Here is a list of the measurements and actions :
- 3f locking related
+ Listing up the necessary RFPDs and their installations.
+ Calibration of the SRM actuator => this is necessary to convert the sensing matrix into unit of [counts/m] or [W/m].
+ Measurement of the sensing matrix => check the performance of 3f signals. Also diagonalization of the LSC sensing matrix
+ Diagonalization of the output matrix.
+ Noise characterization of 3f PDs => confirm the noise are low enough to keep the lock of the central part
- Power-recycling gain issue related (#5541)
+ Estimation of the mode matching efficiency => maybe we can use power-recycled ITMs to estimate it (?)
+ Implementation of auto alignment servos and scripts for MICH, PRCL and SRCL. => integrate it to the existing ASS model
+ Search for a possible loss factor
Yesterday Koji was claiming that the rms monitor of ULSEN on ETMY didn't well go down.
Indeed something bad is happening on ULSEN of ETMY.
I guess it could be a loose connection.
(The unit of Y axis in the plot is not true. Don't believe it !)
The SRM oplevs were found to be oscillating because of a small phase margin.
I reduced the gains to the half of them. The peak which Steve found today maybe due to this oscillation.
The SRM bounce peak 18.33 Hz. Suresh helped me to retune filter through Foton, but we failed to remove it.
The AC response of the SRM actuator has been calibrated.
For a comparison, the length fluctuation of Signal-Recycled ITMX (SRX) and ITMY (SRY) have been measured.
Roughly speaking the length motion of SRX and SRY are as loud as that of PRCL.
Some details about the measurement and data analysis can be found in the past elog entry (#5582).
In the process of converting the raw spectra to the calibrated displacements the SRM actuator was assumed to have a resonance at 1Hz with Q = 5.
(Notes on SRX/Y locking)
+ PRCL is always noisier than MICH.
The efficiency of the mode matching (MM) to PRC (Power-Recycling Cavity) has been estimated by using the interferometer.
The estimated MM efficiency is about 74 % when losses in the cavity are assumed to be zero.
Here are the measured values in REFLDC
Anyways the estimated MM efficiency with the sidebands effect included and without loss effect is
MM efficiency = 73.7 +/- 1.7 % (1 sigma error) or +/- 8.7 % (5 sigma error)
"^2"s are missing in the second equation, but the calculation results seem correct.
PRX and PRY have different mode matching because of the Michelson asymmetry.
Are individually estimated mode matching indicates any sign of reasonable mode mismatch?
(The difference can be very small because the asymmetry is not so big.)
- Thank you for the correction. The missing square operation has been added correctly on the last entry (#5639).
The response of the BS actuator in a low frequency regime has been measured.
+ With free swinging MICH, the sensor (AS55_Q) was calibrated into counts/m.
=> The peak-peak counts was about 110 counts. So the sensor response is about 6.5x108 counts/m
+ Locked Michelson with AS55_Q and the signal was fedback to BS.
+ Set the UGF high enough so that the open loop gain below 10 Hz is greater than 1.
+ With DDT's swept sine measurement, C1:LSC-MICH_EXC was excited with a big amplitude of 40 counts.
+ Took a transfer function from C1:LSC-MICH_OUT to C1:LSC-MICH_EXC.
+ Calibrated the transfer function into m/counts by dividing it with the sensor response.
I think the precision due to the loop gain uncertainty is something like 0.1% at 0.1 Hz. It's not the issue.
The real issue was the loud motion of MICH, which degrades the coherence of the measurement.
Also last night I tried the fringe hopping technique and gave it up for several reasons.
(uncertainty due to the loop gain)
(Effect from the MICH motion)
This seems like an error prone method for DC responses due to the loop gain uncertainty. Better may be to use the fringe hopping method (c.f. Luca Matone) or the fringe counting method
The TRY (TRansmitted light from Y arm ) path was a bit realigned because there had been a small clipping.
This clipping was introducing offsets on the error signals of the C1ASS servo.
During I was running the C1ASS servo on the Y arm I found every time after the auto-alignment is done there still remained a slight offset in the beam pointing,
I looked at the CCD camera which looks at the transmitted light and then introduced an intentional misalignment in ETMY in order to find an obvious clipping.
Indeed there was a clipping in horizontal direction. I checked through the optics on the Y end optical bench.
On the second mirror (beam splitter) the beam was on a very edge. So I steered the first steering mirror to fix it,
In addition to that an iris which is placed between the first and second mirror was also clipping the beam,
So I fully opened the aperture of the iris.
An update on calibration of the BS actuator : A fitting has been done.
- status update on LSC activity :
The measurement of the LSC sensing matrix has begun. But no useful results yet.
The measurement script (#4850) ran pretty well after I did some modifications to adopt the script to the latest LSC model.
However the SNR weren't so great particularly in REFL33 in the PRMI configuration.
So I will tune the amplitude of excitations and integration times tomorrow.
Currently the excitation is at 238.1 Hz, where no disturbing structures are found in the spectra.
The lock of DRMI wasn't stable enough to measure the sensing matrix. Failed.
PRMI and SRMI were okay and in fact they could stay locked robustly for a long time.
I added a new option in the C1IFO_CONFIGURE screen so that one can choose Signal-Recycled Michelson in carrier resonant condition.
Additionally the orthogonalization of the I-Q signals on REFL55 should be done because it hasn't been done.
Anyway, things are working now:
Good job ! Thank you so much
To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.
I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.
Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.
Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.
I made some attempts to measure the sensing matrix of the central part.
I could measure the matrix in the PRMI configuration but wasn't able to measure the matrix in the DRMI configuration.
=> I will report the result of the PRMI sensing matrix tomorrow.
The main reason why I couldn't lock DRMI was that the suspensions were touchy and especially the SRM suspension wasn't good.
Some impacts due to the feedback during the lock acquisition completely kicks SRM away.
The watchdogs' RMS monitor on SRM easily rang up to more than 10 counts once the acquisition started.This is quite bad.
Also the stability of the PRMI lock was strongly depending on the gains of the PRM oplevs.
I guess I have to revisit the vertex suspensions more carefully (i.e. f2a coupling, actuator output matrix, damping gains, input matrices, oplev filters)
otherwise any LSC works in the vertex will be totally in vain.
[Suresh / Koji / Rana / Kiwamu]
Last night we had a discussion about what we do for the RFAM issue. Here is the plan.
1. Build and install an RFAM monitor (a.k.a StochMon ) with a combination of a power splitter, band-pass-filters and Wenzel RMS detectors.
=> Some ordering has started (#5682). The Wenzel RMS detectors are already in hands.
2. Install a temperature sensor on the EOM. And if possible install it with a new EOM resonant box.
=> make a wheatstone bridge circuit, whose voltage is modulated with a local oscillator at 100 Hz or so.
3. Install a broadband RFPD to monitor the RFAMs and connect it to the StochMon network.
=> Koji's broadband PD or a commercial RFPD (e.g. Newfocus 1811 or similar)
4. Measure the response of the amount of the RFAM versus the temperature of the EO crystal.
=> to see whether if stabilizing the temperature stabilizes the RFAM or not.
5. Measure the long-term behavior of the RFAM.
=> to estimate the worst amount of the RFAM and the time scale of its variation
6. Decide which physical quantity we will stabilize, the temperature or the amount of the RFAM.
7. Implement a digital servo to stabilize the RFAMs by feeding signals back to a heater
=> we need to install a heater on the EOM.
8. In parallel to those actions, figure out how much offsets each LSC error signal will have due to the current amount of the RFAMs.
=> Optickle simulations.
9. Set some criteria on the allowed amount of the RFAMs
=> With some given offsets in the LSC error signal, we investigate what kind of (bad) effects we will have.
The following optics were kicked:
Wed Oct 19 04:22:53 PDT 2011
I made some efforts to fix the situation of SRM but it is still bad.
The POS motion wasn't well damped. Something is wrong either (maybe both) sensing part or actuation part.
I am going to check the sensing matrix with the new free swinging spectra (#5690)
When I was trying to lock SRMI I found that the fringes observed at the AS camera didn't show spatial higher order modes, which is good.
So I thought the SRM suspension became quiet, but it actually wasn't. Because the RMS monitor of the SRM OSEMs already went to about 30 counts.
At the same time the opelev error signals were well suppressed. It means some DOFs which were insensitive to the oplev were ringing up, namely POS and SIDE.
According to the LSC error signal and the ASDC signal, I believe that the POS was going wild (although I didn't check the OSEM spectra).
+ Readjusted the f2a filters (see the attachment).
+ Tried to eliminate a coupling between the POS and SIDE drives by tweaking the output matrix.
=> In order to eliminate the coupling from the POS drive to SIDE sensor, I had to put a comparable factor into an element.
So it might be possible that the POS sensor was showing the SIDE signal and vice versa.
In order to check it I left SRM free swinging (#5690).
Kiwamu removed the 18.3 Hz ocsillation by turning down the oplev servo gain.
Status update on dichroic mirror:
I got the specification sheet of an aLIGO 2" dichroic mirror from Lisa.
This is the one from ATF. It has low loss, a high R for 1064 nm and high T for 532 nm. So it matches our needs.
Based on this sheet we may reset some of the parameters in the specification (e.g. incident angle and etc.,) and will get a quote from ATF.
We will buy 3 of them, including 1 spare. First I need to review the specification.
The SRM input matrix has been readjusted.
However still there is the unwanted coupling from the POS drive to SIDE signal and from the SIDE drive to POS signal.
Some of the sub-suspension screens need labels to describe what those row and column are.