I successfully steered out the two output beams from BHD BS to ITMY table today. This required significant changes on the table, but I was able to bring back the table to balance coarsely and then recover YARM flashing with fine tuning of ITMY.

• The counterweights were kept at the North end of the table which was in way of one of the output beams of BHD.
• So I saved the level meter positions in my head and removed those counterweights.
• I also needed to remove the cable post for ITMY and SRM that was in the center of the table.
• I installed a new cable post which is just for SRM and is behind AS2. ITMY's cable post is next to it on the other edge of the table. This is to ensure that BHD board can come in later without disturbing existing layout.
• I got 3 Y1-45P and 1 Y1-0 mirror. The Y1-0 mirror was not installed on a mount, so I removed an older optic which was unlabeled and put this on it's mount.
• Note that I noticed that some light (significant enough to be visible on my card) is leaking out of the 45P mirrors. We need to make sure we aren't loosing too much power due to this.
• Both beams are steered through the center of the window, they are separating outside and not clipping on any of the existing optics outside. (See attachment 1, the red beam in the center is the ITMY oplev input beam and the two IR beams are the outputs from BHD BS).
• Also note that I didn't find any LO beam while doing this work. I only used AS beam to align the path.
• I centered the ITMY oplev at the end.

Next steps:

• LO path needs to be tuned up and cleared off again. We need to match the beams on BHD BS as well.
• Setup steering mirrors and photodiodes on the outside table on ITMY.

[Yuta, Paco, Anchal]

We measured

(a) BHDC_DIFF sensitivity to BS dither for a set of MICH offsets.

Configurations

• MICH locked with AS55_Q
  • The MICH offset was varied below
• LO_PHASE locked with BH55_Q
  • Balanced DCPD_A and DCPD_B by applying a digital gain of 1.00 to DCPD_A
  • Changed the BH55 demod angle to 140.07 deg to minimize BH55_I
• BS dither at 311.1 Hz
  • Use newly added HPC_BS Lockins to readback the demodulated signals

Results & Discussion

The analysis was done with the '/cvs/cds/rtcds/caltech/c1/Git/40m/scripts/CAL/BHD/BHD_DIFFSensitivity.ipynb' notebook.

Attachment #1 shows the main result showing the sensitivity of various demodulated error signals at 311.1 Hz for a set of 21 MICH offsets. We noted that if we didn't randomize the MICH offset scan, we observed a nonzero "zero crossing" for the offset.
Note that, although LO_PHASE loop was always on to control the LO phase to have zero crossing of BH55_Q, actual LO phase is not constant over the measurement, as MICH offset changes BH55_Q zero crossing.
When MICH offset is zero, LO_PHASE loop will control the LO phase to 0 deg (90 deg away from optimal phase), and BHDC_DIFF will not be sensitive to MICH, but when MICH offset is added, BHDC_DIFF start to have MICH sensitivity (measurement is as expected).
For BHDC_SUM, MICH sensitivity is linear to MICH offset, as it should be the same as ASDC, and does not depend on LO phase (measurement is as expected).
For BH55_Q, MICH sensitivity is maximized at zero MICH offset, but reduces with MICH offset, probably because LO phase is also being changed.

[Anchal, Paco, Yuta]

Attachment #1 is the same plot as 40m/17303 but with MICH sensitivity for ASDC and AS55 also included (in this measurement, BH55 demodulation phase was set to 140.07 deg to minimize I fringe).
Y-axis is now calibrated in to counts/m using BS actuation efficiency 26.54e-9 /f^2 m/counts (40m/17285) at 311.1 Hz.
2nd X-axis is calibrated into MICH offset using the measured AS55_Q value and it's MICH sensitivity, 8.81e8 counts/m (this is somehow ~10% less than our usual value 40m/17294).
ASDC have similar dependence with BHDC_SUM on MICH offset, as expected.
AS55_Q have little dependence with MICH offset on MICH offset, as expected.

This plot tells you that even a small MICH offset at nm level can create MICH sensitivity for BHDC_DIFF, even if we control LO phase to have BH55_Q to be zero, as MICH offset shifts zero crossing of BH55_Q for LO phase.

Notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/BHD/BH_DIFFSens_pydemod.ipynb

Attachment #2 is the same plot, but BH55 demodulation phase was tuned to 227.569 deg to have no MICH signal in BH55_Q (a.k.a measurement (c)).
In this case, LO phase will be always controlled at 0 deg (90 deg away from optimal), even if we change the MICH offset, as BH55_Q will not be sensitive to MICH.
In this plot, BHD_DIFF have little sensitivity to MICH, irrelevant of MICH offset, as expected.
MICH sensitivity for BH55_I is also constant, which indicate that LO phase is constant over this measurement, as expected.

Notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/BHD/BH_DIFFSens_pydemod.ipynb

Attachment #3 is the same plot, but BH55 demodulation phase was tuned to 70 deg.
This demodulation phase was tuned within 5 deg to maximize MICH signal in BHD_DIFF with large MICH offset (20).
In this case, LO phase will be always controlled at 90 deg (optimal), even if we change the MICH offset, as BH55_Q will not be sensitve to LO carrier x AS sideband component of the LO phase signal.
In this plot, BHD_DIFF have high sensitivity to MICH, irrelevant of MICH offset (at around zero MICH offset it is hard to see because LO_PHASE lock cannot hold lock, as there will be little LO phase signal in BH55_Q, and measurement error is high for BHD_DIFF and BH55 signals).
MICH sensitivity for BH55_I and BH55_Q is roughly constant, which indicate that LO phase is constant over this measurement, as expected.

These plots indicate that BH55 demodulated at MICH dither frequency can be used to control LO phase robustly at 90 deg, under unknown or zero MICH offset.


Notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/BHD/BH_DIFFSens_pydemod.ipynb

LO phase delay:
 From these measurements of demodulation phases, I guess we can say that phase delay for 55 MHz in LO path with respect to MICH path (length difference in PR2->LO->BHDBS and PR2->ITMs->AS->BHDBS) is

2*(227.569-70(5)-90)-90 = 45(10) deg

 This means that the length difference is (omegam=5*2*pi*11.066195 MHz)

c * np.deg2rad(45(10)+360) / omegam = 6.1(2) m   (360 deg is added to make it close to the design)

  Is this consistent with our design? (According to Yehonathan, it is 12.02 m - 5.23 m = 6.79 m)

  Attachment #4 illustrates signals in BH55.

Next:
 - Lock LO PHASE with BH55 demodulated at MICH dither frequency (RF+audio double demodulation), and repeat the same measurement
 - Finer measurement at small MICH offsets (~1nm) to see how much MICH offset we have
 - Repeat the same measurement with BH55_Q demodulation phase tuned everytime we change the MICH offset to maximize LO phase sensitivity in BH55_Q (a.k.a measurement (b)).
 - What is the best way to tune BH55 demodulation phase?

I looked into the issue that Yehonathan reported with the BI channels. I found the problem was with the .cmd file which sets up the Modbus interfacing of the Acromags to EPICS (/cvs/cds/caltech/target/c1auxey1/ETMYaux.cmd).

The problem is that all the channels on the XT1111 unit are being configured in Modbus as output channels. While it is possible to break up the address space of a single unit, so that some subset of channels are configured as inputs and another as outputs, I think this is likely to lead to mass confusion if the setup ever has to be modified. A simpler solution (and the convention we adopted for previous systems) is just to use separate Acromag units for BI and BO signals.

Accordingly, I updated the wiring plan to include the following changes:

• The five EnableMon BI channels are moved to a new Acromag XT1111 unit (BIO01), whose channels are configured in Modbus as inputs.
• One new DB37M connector is added for the 11 spare BI channels on BIO01.
• The five channels freed up on the existing XT1111 (BIO00) are wired to the existing connector for spare BO channels.

So, one more Acromag XT1111 needs to be added to the c1auxey chassis, with the wiring changes as noted above. I have already updated the .cmd and EPICS database files in /cvs/cds/caltech/target/c1auxey1 to reflect these changes.

I added a new XT1111 Acromag module to the c1auxey chassis. I sanitized and configured it according to the slow machines wiki instructions.

Since all the spare BIOs fit one DB37 connector I didn't add another feedthrough and combined them all on one and the same DB37 connector. This was possible because all the RTNs of the BIOs are tied to the chassis ground and therefore need only one connection. I changed the wiring spreadsheet accordingly.

I did a lot of rewirings and also cut short several long wires that were protruding from the chassis. I tested all the wires from the feedthroughs to the Acromag channels and fixed some wiring mistakes.

Tomorrow I will test the BIs using EPICs.

I tested the digital inputs the following way: I connected a DB9 breakout to DB9M-5 and DB9M-6 where digital inputs are hosted. I shorted the channel under test to GND to turn it on.

I observed the channels turn from Disabled to Enabled using caget when I shorted the channel to GND and from Enabled to Disabled when I disconnected them.

I did this for all the digital inputs and they all passed the test.

I am still waiting for the other isolator to wire the rest of the digital outputs.

Next, I believe we should take some noise spectra of the Y end before we do the installation.

There was some work done on the Acro crate this morning. Unclear if this is independent, but I found that the IMC servo board IN1 slider doesn't respond anymore, even though I had tested it and verified it to be working. Patient debugging showed that BIO1 (and only that acromag unit with the static IP 192.168.114.61) doesn't show up on the subnet in c1psl. Hopefully it's just a loose network cable, if not we will switch out the unit in the afternoon. 

Jon is going to make a python script which iteratively pings all devices on the subnet and we will put this info on an MEDM screen to catch this kind of silent failure.

[Mirko,Jenne]

Created 5-band BLRMS for seismometer data (Gur1, Gur2 and STS1 each in x,y,z respectively) and accelerometer 1 through 6.

Bands are:
0.1Hz-0.3Hz
0.3Hz-1Hz
1Hz-3Hz
3Hz-10Hz
10Hz-30Hz
each with a fitting 4th order butterworth bandpass.

Data is recorded at 256Hz as e.g. C1:PEM-ACC1_RMS_RMS_0p3_1_OUT_DQ. For the 75 channels we have that corresponds to the data rate of just 1.2 16kHz channels.

c1pem execution time increased fom 6-7us to 15-16us out of 480us available.

I fixed up the seismic.stp file for the StripTool display:

1. All BLRMS channels now have a y-axis range of 3 decades. So they all are displaying the same relative changes.
2. So the 0.01-0.1 Hz band which is all over the place is real, sort of. Masha says that it is due to the seismometer signal being dominated by noise below 0.1 Hz. She is going to fix this somehow.
3. I changed the samping time from 1 sec. to 10 sec. to make the traces less fuzzy.
4. We (Masha / Liz) should harmonize the colors of this file with what's on the summary pages.

The BLRMS are totally crazy today!  I'm not sure what the story is, since it's been this way all day (so it's not an earthquake, because things eventually settle down after EQs).  It doesn't seem like anything is up with the seismometer, since the regular raw seismic time series and spectrum don't look particularly different from normal.  I'm not sure what's going on, but it's only in the mid-frequency BLRMS (30mHz to 1Hz).

Here are some 2 day plots:

Its an increase in the microseismic peak. Don't know what its due to though.

 I have finally plugged GUR1 back in....it is down at ETMY for now, since that's where the cable was.  BLRMS are back up on the projector.

[ericq, gautam]

BLRMS filters have been set up for the coil outputs and shadow sensor signals. The signals are sent to the C1PEM model from C1MCS, where I use the library block mentioned in the previous elog to put the filters in place. Some preliminary observations:

1. The entire operation seems to be computationally quite expensive - just for the 3 IMC mirrors, the average CPU time for C1PEM increased from ~50 usec (before any changes were made to C1PEM) to ~105 usec just as a result of installing 420 filter modules with no filter coefficients loaded (3 optics x 10 channels x 14 filter banks) to ~120 usec when all the BP and LP filters for the BLRMS blocks have been loaded and turned on (Attachment #1). Eric suggested that it may be computationally more efficient to do this without using the BLRMS library part - i.e. rather than having so many filter modules, do the RMS-ing using a piece of C code that essentially just implements the same SOS filters that FOTON generates, I will work on setting this up and checking if it makes a difference. The fact that just having empty filter modules in the model almost doubled the computation time suggests that this approach may help, but I have to think about how to implement some of the automatic checks that having a filter bank in place gives us, or if these are strictly necessary at all...
2. While restarting the C1PEM model, we noticed that some of the optics were shaking - looking at the CPU timing signals for all the models on C1SUS revealed that both the C1SUS model and the C1MCS model were geting overclocked when C1PEM was killed (see the sharp spikes in the red and green traces in Attachment #2 - the Y scale in this plot is poor and doesnt put numbers to the overclocking, I will upload a better screenshot that Eric took once I find it). The cause is unknown.
3. Yesterday, I noticed that when C1PEM was restarted, the states of the filter bank switches were not reverted to their states in the SDF tables. They are showing up as changes, but it is unclear why we have to manually revert them. I have also not yet added the states of the newly installed filters (BPs and LPs for the MC BLRMS blocks) to the SDF tables. 

Unrelated to this work: we cleaned up the correspondence between the accelerometer numbers and channels in the C1PEM model. Also, the 3 unused ADC blocks in C1PEM (ADC0, ADC1 and ADC2) are required and cannot be removed as the ADC blocks have to be numbered sequentially and the signals needed in C1PEM come from ADC3 (as we found out when we tried recompiling the model after deleting these blocks).

In order to be consistent with the naming conventions for the new BLRMS filters, I made a library block that takes all the input signals of interest (i.e. for a generic optic, the coil signals, the local damping shadow sensors, and the Oplev Pitch and Yaw signals - so a total of 12 signals, unused ones can be grounded). The block is called "sus_single_BLRMS". Inside the block, I've put in 12 BLRMS library blocks, with each input signal going to one of them. All the 7 outputs of the BLRMS block are terminated (I got a compiling error if I did not do this). The idea is to identify the optic using this block, e.g. MC2_BLRMS. The BLRMS filters inside are called UL_COIL, UR_COIL etc, so the BLRMS channels will end up being called C1:SUS-MC2_BLRMS_UL_COIL_0p01_0p03 and so on. I tried implementing this in C1PEM, but immediately after compiling and restarting the model, I noticed some strange behaviour in the seismic rainbow STS strip in the control room - this was right after the model was restarted, before I attempted to make any changes to the C1PEM.txt file and add filters. I then manually opened up the filter bank screens for the RMS_STS1Z bandpass and lowpass filters, and saw that the filter switches were OFF - I wonder if this has something to do with these settings not being updated in the SDF tables? So I manually turned them on and cleared the filter hitsory for all 7 low pass and band pass filter banks, but the traces on the seismic striptool did not return to their nominal levels. I manually checked the filter shapes with Foton and they seem alright. Anyways, for now, I've reverted to the C1PEM model before I made any changes, and the seismic strip looks to be back at its normal level - when I recompiled and restarted the model with the changes I made removed, the STS1Z BLRMS bandpass and lowpass filters were ON by default again! I'm not sure what I'm doing wrong here, I will investigate this further. 

As discussed in a Wednesday meeting some time ago, we don't need to be writing channels from BLRMS filter modules to frames at 16k (we suspect this is leading to the frequent daqd crashes which were seen the last time we tried setting BLRMS up for all the suspensions). EricQ pointed out to me that there conveniently exists a library block that is much better suited to our purposes, called BLRMS_2k. I've replaced all the BLRMS library blocks in the sus_single_BLRMS library block that I made with there BLRMS_2k blocks. I need to check that the filters used by the BLRMS_2k block (which reside in /opt/rtcds/userapps/release/cds/common/src/BLRMSFILTER.c) are appropriate, after which we can give setting up BLRMS for all the suspensions a second try...

 We should make screens like this for the LSC signals, errors, ALS, etc.

I copied Mirko's PEM BLRMS block, and made it a library part.  I don't know where such things should live, so I just left it in isc/c1/models.  Probably it should move to cds/common/models.  To make the oaf compile, you have to put a link in /opt/rtcds/caltech/c1/core/branches/branch-2.1/src/epics/simLink , and point to wherever the model is living. 

I then put BLRMSs on the control signals coming into the OAF, and after the Correction filter bank in the Adapt blocks, so we can check out what we're sending to the optics.

Today I worked with the BLRMS channels, re-triangulated the seismometers (the STS is now on the very end of the Y-arm, while the GUR2 is on the X-arm - this GUR2 cable will need to be either extended or replaced - Jenne and I will look at parts tomorrow), and added 0.01 - 0.03 Hz and 0.03 - 0.1 Hz RMS channels (However, the MEDM files for these are not yet complete - I will finish these tomorrow) in order to be able to better see earthquakes. I also did some things for the neural network project, including beginning Simulink tutorials so that I can run my code by applying a force on a damped harmonic oscillator + white noise until it stops.

I will explain the methodology behind the new RMS filters tomorrow morning, when the seismometers have settled down and I can make coherence plots.

I'll post a better E-log tomorrow when it's not 2 in the morning.

I laid down the floor a BNC cable from the Y End table to the BNC Chamber. The cable runs next to the east wall.

I'm leaving the cable because it can turn useful in the future.

I'm tying the end of the cable to a big threaded steel rod on the side of the BS chamber.

I've also labeled as TRY

 [Yuta, Steve, Manasa]

There are cables piled up around the access connector area which have been victims of stampedes all the time. I have heard these cables were somehow Den's responsibility. 

Now that he is not around here:

I found piled up bnc's open at one end and with no labels lying on the floor near the access connector and PSL area. Yuta, Steve and I tried to trace them and found them connected to data channels. We could not totally get rid of the pile even after almost an hour of struggle, but we tied them together and put them away on the other side of the arm where we rarely walk.

There are more piles around the access connector...we should have a next cleanup session and get rid of these orphaned cables or atleast move them to where they will not be walked on.

 I've checked that the 2pin lemo connector that was run some time ago from the LSC rack to the MC board does indeed transmit signals. To try and evaluate its suitability I did the following:

• Generated a 5mVpp 1.3kHz signal with an SR785 and fed that into CM board In1, all boosts off, 0dB AO gain. 
• Both BNC and LEMO connected to CM servo out
• One of BNC or LEMO connected to IN2 of MC servo, input gain of 30dB but disabled, OUT2 switched to AO and fed to Agilent spectrum analyzer. 
• Terminated MC IN2 for comparison. 

No real difference was seen between the two cases. The signal peak was the same height, width. 60Hz and harmonics were of the same amplitude. Here are the spectra out to 200k, they are very similar. 

Mode cleaner was locked during this whole thing. This may interfere with the measurement, but is similar to the use case for the AO path. If ground loop / spurious noise issues keep occurring, it will be worthwhile to examine the noise of the CM and MC servo paths, inputs and outputs more carefully. 

This evening, Gautam helped me with setting up the apparatus for calibrating the GigE for BRDF measurements.
The SP table was chosen to set up the experiment and for this reason a few things including a laser and power meter (presumably set up by Steve) had to be moved around.

We initially started by setting up the Crysta laser with its power source (Crysta #2, 150-190 mW 1064 laser) on the SP table. The Ophir power meter was used to measure the laser power. We discovered that the laser was highly unstable as its output on the power meter fluctuated (kind of periodically) between 40 and 150 mW. The beam spot on the beam card also appeared to validate this change in intensity. So we decided to use another 1064 nm laser instead.
Gautam got the LightWave NPro laser from the PSL table and set it up on the SP table and with this laser the output as measured by the same power meter was quite stable.

We manually adjusted the power to around 150 mW. This was followed by setting up the half wave plate(HWP) with the polarizing beam splitter (PBS), which was very gently and precisely done by Gautam, while explaining how to handle the optics to me.
 On first installing the PBS, we found that the beam was already quite strongly polarized as there seemed to be zero transmission but a strong reflection.
With the HWP in place, we get a control over the transmitted intensity. The reflected beam is directed to a beam dump.
I have taken down the GigE(+mount) at ETMX and wired a spare PoE injector.
We tried to interface with the camera wirelessly through the wireless network extenders but that seems to render an unstable connection to the GigE so while a single shot works okay, a continuous shot on the GigE didn’t succeed.

The GigE was connected to the Martian via Ethernet cable and images were observed using a continuous shot on the Pylon Viewer App on Paola. 

We deliberated over the need of a beam expander, but it has been omitted presently. White printer paper is currently being used to model the Lambertian scatterer. So light scattered off the paper was observed at a distance of about 40 cm from the sample.
While proceeding with the calibrations further tonight, we realized a few challenges.

While the CCD is able to observe the beam spot perfectly well, measuring the actual power with the power meter seems to be tricky. As the scattered power is quite low, we can’t actually see any spot using a beam card and hence can’t really ensure if we are capturing the entire beam spot on the active region of the power meter (placed at a distance of ~40cm from the paper) or if we are losing out on some light, all the while ensuring that the power meter and the CCD are in the same plane.

We tried to think of some ways around that, the description of which will follow. Any ideas would be greatly appreciated.

Thanks a ton for all your patience and help Gautam! :) 

More to follow.. 

Power meter only needed to measure power going into the paper not out. We use the BRDF of paper to estimate the power going out given the power going in.

From what I understood froom my reading, [Large-angle scattered light measurements for quantum-noise filter cavity design studies(Refer https://arxiv.org/abs/1204.2528)], we do the white paper test in order to calibrate for the radiometric response, i.e. the response of the CCD sensor to radiance.‘We convert the image counts measured by the CCD camera into a calibrated measure of scatter. To do this we measure the scattered light from a diffusing sample twice, once with the CCD camera and once with a calibrated power meter. We then compare their readings.’

But thinking about this further, if we assume that the BRDF remains unscaled and estimate the scattered power from the images, we get a calibration factor for the scattered power and the angle dependence of the scattered power!

With this idea in mind, we can now actually take images of the illuminated paper at different scattering angles, assume BRDF is the constant value of (1/pi per steradian), 

then scattered power Ps= BRDF * Pi cosθ * Ω, where Pi is the incident power, Ω is the solid angle of the camera and θ is the scattering angle at which measurement is taken. This must also equal the sum of pixel counts divided by the exposure time multiplied by some calibration factor. 

From these two equations we can obtain the calibration factor of the CCD. And for further BRDF measurements, scale the pixel count/ exposure by this calibration factor.  

NOTE: The potentiometers on the bread board circuit box (the one I have been using with the signal generator, DC power, LED displays, and pulse switches) is BROKEN!

The potential across terminals 1 and 2 (also 2&3) fluctuates wildly and there dial does not affect the potential for the second potentiometer (the one with terminals 4, 5, and 6).

This has been confirmed by Koji and Jaimie.  PS I didn't break it! >____<

NEVERTHELESS, using individual resistors and the 500 ohm trim resistor, I have managed to get the current versus forward voltage plot for the Hamamatsu L9337 Infared LED

I labeled all the newly installed flanges and connected the in-air cables (40m/16530) to appropriate ports. These cables are connected to the CDS system on 1Y1/1Y0 racks through the satellite amplifiers. So all new optics now can be damped as soon as they are placed. We need to make more DB9 plugs for setting "Acquire" mode on the HAM-A coil drivers since our Binary input system is not ready yet. Right now, we only have 2 such plugs which means only one optic and be damped at a time.

[Rana, Diego]

We manually realigned the BS and PRM optical levers on the optical table.

I have restored the damping of BS and PRM. Today is janitor day. He is shaking things around the lab.

BS & PRM oplev is restored. Note: the F -150 lens was removed right after the first turning mirror from the laser. This helped Rana to get small spot on the qpd.

It also means that the oplev paths are somewhat different now.

Using PRX, I remeasured the relative actuation strengths of the BS and PRM to see if the PRM correction coefficient we're using is good. 

My result is that we should be using MICH -> -0.2655 x PRM + 0.5*BS.

This is very close to our current value of -0.2625 x PRM, so I don't think it will really change anything.

Measurement details:

The reason that the BS needs to be compensated is that it really just changes the PRM->ITMX distance, lx, while leaving the PRM-ITMY distance, ly, alone. I confirmed this by locking PRY and seeing no effect on the error signal, no matter how hard I drove the BS. 

I then locked PRX, and drove an 804Hz oscillation on the BS and PRM in turn, and averaged the resultant peak heights. I then tried to cancel the signal by sending the excitation with opposite signs to each mirror, according to their relative meaured strength.

In this way, I was able to get 23dB of cancellation by driving 1.0 x PRM - 0.9416 * BS. 

Now, in the PRMI case, we don't want to fully decouple like this, because this kind of cancellation just leaves lx invarient, when really, we want MICH to move (lx-ly) and PRCL to move (lx+ly). So, we use half of the PRM cancellation to cancel half of the lx motion, and introduce that half motion to ly, making a good MICH signal. Thus, the right ratio is 0.5*(1.0/0.9416) = 0.531. Then, since we use BS x 0.5, we divide by two again to get 0.2655. Et voila.

I tried to reduce BS 3.3 Hz motion with local damping. 3.3 Hz probably comes from the stack, but I want to reduce this because PRMI beam spot is moving in this frequency.
I tried it by putting some resonant gains to oplev servo and OSEM damping servo, but failed.

What I learned:
  1. BS OSEM input matrix diagonalization looks impressively good. Below is the spectra of oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without damping (REF is without). You can see mechanical resonances are well separated. Also, damping servos don't look like they are adding noise at 3.3 Hz.


  2. 3.3 Hz motion is not stationary. Amplitude is sometimes high, but sometimes low. Amplitude changes in few seconds. You can even see 3.3 Hz in the dataviewer, too.

  3. I set new oplev gains. I lowered them so that UGFs will be ~ 2.5 Hz. I turned ELP35 on.

C1:SUS-BS_OLPIT_GAIN = 0.2 (was 0.6)
C1:SUS-BS_OLPIT_GAIN = -0.2 (was -0.6)

  4. All OSEM sensors feel about the same amount of 3.3 Hz motion.

  5. OLPIT and OLYAW reduces if you put 3.3 Hz resonant gain to oplev servo, but it is maybe not true since they are in-loop error signals. You can't see the difference from OSEM sensors. Below is oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without 3.3 Hz resonant gain (REF is without).

It is not as dramatic as PRMI, but I could see BS 3.3 Hz motion at AS and REFL when MI is locked at dark fringe.
Below is uncalibrated spectra of REFLDC and ASDC when
  Red: MI is locked at dark fringe
  Blue: there's no light (PSL shutter closed)

We have to do something to get rid of this.

[Anchal, Paco, Yuta]

BS Oplev Path

• The changed position of PRM (40m/16863) meant that BS oplev path is getting clipped by the PRM SOS tower.
• We had to move BSOL ~ 16 cm North and ~ 1.7 cm East.
• This means that the BS Oplev input beam is now coming behind TT2 instead of infront of it.
• We also had to align the beam such that input and returning beam are colinear.
• This meant we, had to change the mount of the upstream beamsplitter in the in-air table so that we can use that for separating the return beam.
• Again, we should order 2 inc visible BS for this path.
• Half of the return beam is making its way all the way back to the laser head. I'm not sure if that can be an issue for our oplev loops.
• We kept the SRM Oplev path same using irises on the table.

PRM Oplev

• Again, due to changed position of PRM and BS Oplev, it became very hard to setup oplev for PRM.
• We found a special position which allows us to catch returning beam through the center of the window.
  • But this returning beam is not prompt reflection from PRM, it is reflection of the HR surface.
  • We are hitting about ~5 mm from the edge of PRMOL mirror (because we cannot move the mirror anymore south to avoid clipping BS and SRM input oplev beams)
  • We put in a 1.1m focal length lens in the input beam to narrow the beam on PRMOL so that it doesn't clip
• We did not put any lens for the return beam. The sensitivity of this oplev might be low due to slighlty bigger beam on the QPD than others (SRM, BS). We can revisit and insert a lens later if required.

Interferometer alignment and PRM alignment

• The work on BS table did not change the table balance much. We got back the alignment pretty much instantly.
• We were able to maximize the arm transmissions.
• Then we used a beam card with hole to check for reflection from PRM and used PRM (mostly pitch correction) to get the return beam back in same way.
• This recovered REFL beam on the camera. We used REFLDC signal to align PRM better and maximized it.
• We centered BS, SRM and PRM oplevs after this point.

LO beam mode correction and spatial overlap

• We tried changing the distance between LO3 and LO4 to get a better output LO beam.
• We also tried to swap the LO4 mirror with the spare mirror but we had the same result.
• Eventually, we decided to move LO3 back to East and LO4 to the west edge of the table. This made the beam sizes comparable.
  • Future exercise: We think that LO1 or LO2 might be significantly off-spec in their ROCs which might cause this issue.
  • We should rerun the calculations with the ROC values of LO1 and LO2 written in the datasheets and figure out the correct LO3-LO4 length required.
  • We can make this change in the next vent if required.
• After the beam sizes were looking approximately similar but more iterations of changing length and realigning are required.

Remaining tasks before pumpdown

• Push/pull too bright/dark OSEMs in the SOSs (40m/16865).
• Finish LO beam mode correction and spatial overlap.
• Center all oplevs, note all beam positions on camera, and note down all DC PD values at proper alignment.

I calibrated the BS oplev PIT and YAW error signals as follows:

1. Locked X-arm, ran dither alignment servos to maximize transmission.
2. Applied an offset to the ASC PIT/YAW filter banks. Set the ramp time to something long, I used 60 seconds.
3. Monitored the X arm transmission while the offset was being ramped, and also the oplev error signal with its current calibration factor.
4. Fit the data, oplev error signal vs arm transmission, with a gaussian, and extracted the scaling factor (i.e. the number which the current Oplev error signals have to be multiplied by for the error signal to correspond to urad of angular misalignment as per the overlap of the beam axis to the cavity axis.
5. Fits are shown in Attachment #1 and #2.
6. I haven't done any error analysis yet, but the open loop OL spectra for the BS now line up better with the other optics, see Attachment #3 (although their calibration factors may need to be updated as well...). Need to double check against OSEM readout during the sweep.
7. New numbers have been SDF-ed.

The numbers are:

BS Pitch     15  /  130    (old/new)     urad/counts

The numbers I have from the fitting don't agree very well with the OSEM readouts. Attachment #1 shows the Oplev pitch and yaw channels, and also the OSEM ones, while I swept the ASC_PIT offset. The output matrix is the "naive" one of (+1,+1,-1,-1). SUSPIT_IN1 reports ~30urad of motion, while SUSYAW_IN1 reports ~10urad of motion.

From the fits, the BS calibration factors were ~x8 for pitch and x12 for yaw - so according to the Oplev channels, the applied sweep was ~80urad in pitch, and ~7urad in yaw.

Seems like either (i) neither the Oplev channels nor the OSEMs are well diagonalized and that their calibration is off by a factor of ~3 or (ii) there is some significant imbalance in the actuator gains of the BS coils...

[Suresh / Kiwamu]

 Adjustment of the OSEMs on BS has been done.

All the bad suspensions (#5176) has been adjusted. They are waiting for the matrix inversion test.

The AS spot on the camera was oscillating at ~3 Hz. Looking at the Oplevs, the culprit was the BS PIT DoF. Started about 12 hours ago, not sure what triggered it. I disabled Oplev damping, and waited for the angular motion to settle down a bit, and then re-enabled the servo - damps fine now...

[JC]

Lately, I have been working on a 3d sketch of the BS OPLEV Table on SolidWorks. This is my progress so far, a few of the components I will have to sketch myself, such as the HeNe laser and photodiodes. This will just be a general layout of the HeNe laser, optics, and photodiodes.

As part of the hunt why the X arm IR transmission RIN is anomalously high, I noticed that the BS Oplev Servo periodically kicks the optic around - the summary pages are the best illustration of this happening. Looking back in time, these seem to have started ~Nov 23 2020. The HeNe power output has been degrading, see Attachment #1, but this is not yet at the point where the head usually needs replacing. The RIN spectrum doesn't look anomalous to me, see Attachment #2 (the whitening situation for the quadrants is different for the BS and the TMs, which explains the HF noise). I also measured the loop UGFs (using swept sine) - seems funky, I can't get the same coherence now (live traces) between 10-30 Hz that I could before (reference traces) with the same drive amplitude, and the TF that I do measure has a weird flattening out at higher frequencies that I can't explain, see Attachment #3.

The excess RIN is almost exactly in the band that we expect our Oplevs to stabilize the angular motion of the optics in, so maybe needs more investigation - I will upload the loop suppression of the error point later. So far, I don't see any clean evidence of the BS Oplev HeNe being the culprit, so I'm a bit hesitant to just swap out the head...

The BS SIDE damping gain seemed too low. The gain had been 5 while the rest of the suspensions had gains of 90-500.

I increased the gain and set it to be 80.

I did the "Q of 5" test by kicking the BS SIDE motion to find the right gain value.

However there was a big cross coupling, which was most likely a coupling from the SIDE actuator to the POS motion.

Due to the cross coupling, the Q of 5 test didn't really show a nice ring down time series. I just put a gain of 80 to let the Q value sort of 5.

I think we should diagonalize the out matrices for all the suspensions at some point.

Summary : 

I have been working on analyzing the seismic data obtained from the 3 seismometers present in the lab. I noticed while looking at the combined time series and the gain plots of the 3 seismometers that there is some error in the calibration of the BS seismometer. The EX and the EY seismometers seem to be well-calibrated as opposed to the BS seismometer.

The calibration factors have been determined to be :

BS-X Channel: 

BS-Y Channel: 

BS-Z Channel:

Details :

The seismometers each have 3 channels i.e X, Y, and Z for measuring the displacements in all the 3 directions. The X channels of the three seismometers should more or less be coherent in the absence of any seismic excitation with the gain amongst all the similar channels being 1. So is the case with the Y and Z channels. After analyzing multiple datasets, it was observed that the values of all the three channels of the BS seismometer differed very significantly from their corresponding channels in the EX and the EY seismometers and they were not calibrated in the region that they were found to be coherent as well. 

Method :

Note: All the frequency domain plots that have been calculated are for a sampling rate of 32 Hz. The plots were found to be extremely coherent in a certain frequency range i.e ~0.1 Hz to 2 Hz so this frequency range is used to understand the relative calibration errors. The spread around the function is because of the error caused by coherence values differing from unity and the averages performed for the Welch function. 9 averages have been performed for the following analysis keeping in mind the needed frequency resolution(~0.01Hz) and the accuracy of the power calculated at every frequency. 

1. I first analyzed the regions in which the similar channels were found to be coherent to have a proper gain analysis. The EY seismometer was found to be the most stable one so it has been used as a reference. I saw the coherence between similar channels of the 2 seismometers and the bode plots together. A transfer function estimator was used to analyze the relative calibration in between all 3 pairs of seismometers. In the given frequency range EX and EY have a gain of 1 so their relative calibration is proper. The relative calibration in between the BS and the EY seismometers is not proper as the resultant gain is not 1. The attached plots show the discrepancies clearly : 

• BS-X & EY-X Transfer Function : Attachment #1
• BS-Y & EY-Y Transfer Function : Attachment #2

          The gain in the given frequency range is ~3. The phase plotting also shows a 180-degree phase as opposed to 0 so a negative sign would also be required in the calibration factor. Thus the calibration factor for the Y channel of the BS seismometer should be around ~3. 

• BS-Z & EY-Z Transfer Function : Attachment #3

The mean value of the gain in the given frequency range is the desired calibration factor and the error would be the mean of the error for the gain dataset chosen which is caused due to factors mentioned above.

Note: The standard error envelope plotted in the attached graphs is calculated as follows :

         1. Divide the data into n segments according to the resolution wanted for the Welch averaging to be performed later. 

         2. Calculate PSD for every segment (no averaging).

         3. Calculate the standard error for every value in the data segment by looking at distribution formed by the n number values we obtain by taking that respective value from every segment.

Discussions :

The BS seismometer is a different model than the EX and the EY seismometers which might be a major cause as to why we need special calibration for the BS seismometer while EX and EY are fine. The sign flip in the BS-Y seismometer may cause a lot of errors in future data acquisitions. The time series plots in Attachment #4 shows an evident DC offset present in the data. All of the information mentioned above indicates that there is some electrical or mechanical defect present in the seismometer and may require a reset. Kindly let me know if and when the seismometer is reset so that I can calibrate it again. 

The response of the BS actuator in a low frequency regime has been measured.

(Measurement)

 + 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.

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

An update on calibration of the BS actuator : A fitting has been done.

(Fitting)

(Fitting result)

Q and I aligned the BS such that we were hitting the center of ETMX. The ETMX cage does not have OSEM setscrew holes on the front, so it is not possible to put the targets that Steve made on this optic.  So, I put the freestanding ruler in front of the optic, with the edge of the ruler at the center (as viewed from above) of the optic.  Then Eric steered the BS until we were hitting the 5.5" mark, and roughly half of the beam was obscured by the ruler.

We then aligned ITMX such that the prompt reflection was colinear with the incoming beam. 

I checked the 2 spots through the BS, heading to the AS port.  (2 spots since MICH hasn't been locked / finely aligned yet).  They were being clipped on the 2nd output PZT.  I adjusted the knobs of the first output PZT to center the spots on the 2nd PZT.  Note that the output PZTs' power is still off, and has been off for some unknown length of time.  I had found them off when prepping for the vent a week or two ago.  So the current alignment depends on them staying off.  We don't really need them on until we're ready to employ our OMC.

The beams now look nicely unclipped on the AS camera, and we're aligning MICH.

I've measured seismic and acoustic noise on BS and AS tables. It seems that horizontal motion of BS table is ~1.5-2 times more then AS table in the frequency range 5-50 Hz.

Edit by Den: this was POI table, not BS!