The EPICS process on the c1ioo front end had died mysteriously. As a result, MC autolocker wasn't working, since the autolocker control variables are EPICS channels defined in the c1ioo model. I restarted the model, and now MCautolocker works.

I'm working near 1X5 and there is an SR785 adjacent to the electronics rack with some cabling running along the floor. I plan to continue in the evening so please leave the setup as is.

During the course of this work, I noticed the +15V Sorensen in 1X6 has 6.8 A of current draw, while Steve's February2018 label says the current draw is 8.6A. Is this just a typo?

Steve: It was most likely my mistake. Tag is corrected to 6.8A

I'm still in the process of electronics characterization, so the SR785 is still hooked up. MC3 coil driver signal is broken out to measure the output voltage going to the coil (via Gainx100 SR560 Preamp), but MC is locked.

I setup a basic MEDM screen for remote control of the PLL.

The Slow control voltage slider allows the frequency of the laser to be moved around via the front panel slow control BNC.

The TTL signal slider provides 0/5V to allow triggering of the servo. Eventually this functionality will be transferred to the buttons (which do not work for now).

The screen can be accessed from the PSL dropdown menu in sitemap. We can make this better eventually, but this should suffice for initial setup.

Summary:

In the IMC actuation chain, it looks like the MC1/MC3 de-whitening boards, and also all three MC optics' coil driver boards, are showing higher noise than expected from LISO modeling. One possible candidate is thick film resistors on the coil driver boards. The plan is to debug these further by pulling the board out of the Eurocrate and investigating on the electronics bench.

Why bother? Mainly because I want to see how good the IR ALS noise is, and currently, the PSL frequency noise is causing the measurement to be worse than references taken from previous known good times.

Details:

Sometime ago, rana suggested to me that I should do this measurement more systematically.

• Attachments #1, #2 and #3 show noise measurements in various conditions for MC1, MC2 and MC3 respectively.
• In the above three attachments, I stitched together multiple spans from the SR785, and so the bin-width is different. The data is downloaded from the analyzer normalized by the bin-width (PSD units).
• The roll-off at ~800Hz in the orange trace for MC1 and MC3 is consistent with an 800 Hz LPF that was used for anti-image filtering from the old 2 kHz era.
• While it may look like the analog de-whitening isn't being switched on in some of these plots, I confirmed by transfer function measurement that it is indeed switching.
• Data used to make these plots are in Attachment #4. Unfortunately, the code requires some of my personal plotting libraries and so I'm not uploading it.
• Sketch of measurement setup is shown in Attachment #5. It is not indicated in the schematic, but the SR560 was operated in battery mode for this measurement.
• For MC1, I did the additional measurement of terminating the LEMO input to the coil driver and measuring (what should have been) just the coil driver electronics noise. But this measurement doesn't look very clean, and hence, the decision to pull the board out to continue debugging.
• While at 1X6, Rana tightened the LEMO connectors going to MC1. We should opportunistically do MC2 and MC3 as well.
• Some changes to be made:
  • Thick film ---> thin film.
  • Reroute HPF-ed back-plane Vmon output to the front panel LEMO.

I've now restored all the wiring at 1X6 to their state before this work.

I guess it's fine for now while we are still finalizing the setup at EX, but we should eventually line up the seismometer axes with the IFO axes. Is there a photo of the orientation of the seismometer pre heater can tests? If not, probably good to make some sort of markings on the granite slab / seismometer to allow easy lining up of these axes...

Since we've been hijacking channels like there is no tomorrow for the AUX-PLL setup, I'm documenting the channel names here. The next time c1psl requires a reboot, I'll rename these channels to something more sensible. To find the channel mapping, Koji suggested I use this. Has worked well for us so far... We've labelled all pairs of wires pulled out of the cross connects and insulation taped the stripped ends, in case we ever need to go back to the original config.

I have pulled out MC1 coil driver board from its Eurocrate, so IMC is unavailable until further notice. Plans:

1. Thick film --> Thin Film
2. AD797 --> Op27
3. Remove Pots in analog actuation path.
4. Measure noise
5. Route HPF signal (UL DAQ Mon) to front panel. I think we should use the SMA connectors. That way, we have DC and AC voltage monitors available for debugging.

If there are no objections, I will execute Step #5 in the next couple of hours. I'm going to start with Steps 1-4.

This work is now complete. MC1 coil driver board has been reinstalled, local damping of MC1 restored, and IMC has been locked. Detailed report + photos to follow, but measurement of the noise (for one channel) on the electronics workbench shows a broadband noise level of 5nV/rtHz () around 100Hz, which is lower than what was measured here and consistent with what we expect from LISO modeling (with fast input terminated with 50ohm, slow input grounded).

• Marked up schematic + photo post changes uploaded to DCC page.
• There was a capacitor in the DAQ monitor path making a 8kHz corner that I now removed (since the main point of this front panel HPF monitor point is to facilitate easy coil driver noise debugging, and I wanted to be able to use the SR785 out to high frequencies without accounting for an additional low pass). Transfer function from front panel LEMO input to front panel LEMO monitor is shown in Attachment #1.
• Voltage noise measured at DB25 output (with the help of a breakout cable and SR560 G=100) with front panel LEMO input terminated to 50ohm, Bias input grounded, and pin1 of U21A grounded (i.e. watchdog enabled state) is shown in Attachment #2. This measurement was taken on the electronics bench.
• Inside the lab (i.e. coil driver board plugged into eurocrate), the noise measured in the same way looks identical to what was measured in elog13870.
• I tried repeating the measurement by powering the board using an bench power supply and grounding the bias input voltage near 1X6, and the strange noise profile persists. So this supports the hypothesis that some kind of environmental pickup is causing this noise profile. Needs more investigation. 

In any case, if it is indeed true that the optic sees this current noise, the place to make the measurement is probably the Sat. Box. Who knows what the pickup is over the ~15m of cable from 1X6 to the optic.

All models on the c1lsc front end were dead. Looking at slow trend data, looks like this happened ~6hours ago. I rebooted c1lsc and now all models are back up and running to their "nominal state".

Summary:

1. The DFD noise floor is ~0.5Hz/rtHz at 100Hz (see Attachment #2).
2. I cannot account for the measured noise floor of the DFD system. The Marconi noise and the AA noise contributions should be neglibible at 100Hz.
3. This SURF report would lead me to believe that the delay line cable length is 50m. But my calibration suggests it is shorter, more like 40m (see Attachment #1). I had made some TF measurements of the delay sometime ago, need to dig up the data and see what number that measurement yields.

Details and discussion: (diagrams to follow)

• Delay line linearity was checked by driving the input with Marconi, waiting for any transient to die down, and averaging the I and Q inputs to the phase tracker servo (after correcting for the daughter board TF) for 10 seconds. The deg/MHz response was then calculated by trigonometry. Not sure what to make of the structure in the residuals, need to think about it.
• DFD noise was checked by driving the DFD input with a Marconi at 50MHz, RF level = 8dBm, which are expected parameters for nominal ALS operation. In this configuration, I measured the spectrum of the phase tracker output. I then used the calibration factor from the above bullet to convert to Hz/rtHz.
• The electronics noise contribution of the daughter board was calibrated to Hz/rtHz by using the Marconi to drive the DFD input with a known FM signal (mod depth ~0.05), and using the SR785 to measure the power of the FM peak. This allows one to back out the V/Hz calibration constant of the delay line. I tweaked the carrier frequency until the ratio of power in I channel to Q channel (or the other way around) was >20dB before making this measurement.
• I have no proof - but I suspect that the whole host of harmonics in the noise spectrum is because the 1U AA chassis sits directly on top of some Sorensen power supplies. These Sorensens power the frequency distribution box in the LSC rack, so the simplest test to confirm would be to turn off the RF chain, and then Sorensens, and see if the peaky features persist.

Summary:

• DC light power incident on beat PD is ~400uW from the PSL and ~300uW from EX.
• These numbers are consistent with measured mating sleeve and fiber coupler losses.
• However, I measure an RF beatnote of 80mVpp (= -18dBm). This corresponds to a mode matching efficiency of ~15%, assuming InGaAs efficiency of 0.65A/W.

I find this hard to believe.

Details:

• I took this opportunity to clean the fiber tips on the PSL table going into the BeatMouth.
• PSL light power going into the BeatMouth is 2.6mW. Of which ~400uW reaches the Beat PD (measured using my new front panel monitor port).
• Similarly, 1mW of EX light reaches the PSL table, of which ~300uW reaches the Beat PD.
• The RF amplifier gain is 20dB, and RF transimpedance is 50 ohms.
• Using the (electrical) 20dB coupled port on the front panel, I measured a beat signal with 8mVpp. So the actual beat note signal is 80mVpp.

Discussion:

As I see it, the possibilities are:

1. My measurement technique/calculation is wrong.
2. The beat PD is broken has optoelectronic different that is significantly different from specifications.
3. The non-PM fiber lengths inside the beat box result in ~15% overlap between the PSL and EX beams. Morever, there is insignificant variation in the electrical beat amplitude as monitored on the control room analyzer. So there is negligible change in the polarization state inside the BeatMouth.

I guess #3 can be tested by varying the polarization content of one of the input beams through 90 degrees.

A couple of months ago, I took 21 measurements of the delay line transfer function. As shown in Attachment #2, the unwrapped phase is more consistent with a cable length closer to 45m rather than 50m (assuming speed of light is 0.75c in the cable, as the datasheet says it is).

Attachment #1 shows the TF magnitude for the same measurements. There are some ripples consistent with reflections, so something in this system is not impedance matched. I believe I used the same power splitter to split the RF source between delayed and undelayed paths to make these TFs as is used in the current DFD setup to split the RF beatnote.

[rana,gautam]

Summary:

Last night, Rana fact-checked my story about the coil driver noise measurement. Conclusions:

1. There is definitely pickup of strong lines (see Attachment #1. These are hypothesized to come from switching power supplies). Moreover, they breathe. Checkout Rana's twitter page for the video.
2. The lines are almost (but not quite) at integer multiples of 19.5 kHz. The cause of this anharmonicity is to be puzzled out.
3. When the coil driver board is located ~1m away from the SR785 and the bench supply powering it, even though the lines are visible in the spectrum, the low frequency shape does not show the weird broad features I reported here. The measured noise floor level is ~5nV/rtHz, which is consistent with LISO noise + SR560 input noise (see Attachment #2). However, there is still some excess noise at 100 Hz above what the LISO model leads us to expect. 
4. The location of the coil driver board and SR560 relative to the SR785 and the bench power supply I used to power the coil driver board can increase the line heights by ~x50. 
5. The above changes the shape of the low frequency part of the spectrum as well, and it looks more like what is reported in elog13870. The hypothesis is that the high frequency lines are downconverted in the SR560.

Note: All measurements were made with the fast input of the coil driver board terminated with 50ohms and bias input shorted to ground with a crocodile clip cable.

Next steps:

The first goal is to figure out where this pickup is happening, and if it is actually going to the optic. To this end, I will put a passive 100 kHz filter between the coil driver output and the preamp (Busby Box instead of SR560). By getting a clean measurement of the noise floor with the coil driver board in the Eurocrate (with the bias input driven), we can confirm that the optic isn't being buffeted by the excess coil driver noise. If we confirm that the excess noise is not a measurement artefact, we need to think about were the pickup is actually happening and come up with mitigation strategies.

RXA: good section EMI/RFI in Op Amp Applications handbook (2006) by Walt Jung. Also this page: http://www.electronicdesign.com/analog/what-was-noise

[koji, gautam]

We noticed quite a strong burning smell in the office area and control room ~20mins ago. We did a round of the bake lab, 40m VEA and the perimeter of the CES building, and saw nothing burning. But the smell persists inside the office area/control room (although it may be getting less noticeable). There is a whining noise coming from the fan belt on top of the office area. Anyways, since nothing seems to be burning down, we are not investigating further.

Steve [ 10am 5-31 ] we should always check partical count in IFO room

Service requested 

Seems like as a result of my recent poking around at 1X6, MC3 is more glitchy than usual (I've noticed that the IMC lock duty cycle seems degraded since Tuesday). I'll try the usual cable squishing voodo.

gautam 8.15pm: Glitches persisted despite my usual cable squishing. I've left PSL shutter closed and MC watchdog shutdown to see if the glitches persist. I'll restore the MC a little later in the eve.

Jon informed me that there are some EPICS channels that JoeB's camera server code looks for that don't exist. I thought Jigyasa and I had added everything last year but turned out not to be the case. I followed my instructions from here, did the trick. While cleaning up, I also re-named the "*MC1" channels to "*ETMX", since that's where the camera now resides. New channels are:

C1: CAM-ETMX_ARCHIVE_INTERVAL (Archival interval in minutes)
C1: CAM-ETMX_ARCHIVE_RESET (Reset Archival interval in minutes)

C1: CAM-ETMX_CONFIG_FILE (Config file)
 

Summary:

I wanted to recover the DRMI locking. Among other things, Jon mentioned that his mode spectroscopy can be done in the DRMI config. But I was foiled last night by a rogue waveplate in the AS beampath, and today evening, I noticed the resurfacing of this problem. Clearly, this is indicative of some issue in the analog whitening electronics, as the DC light level on the AS55 PD is consistent with previous measurements. Moreover, last time, the problem "fixed itself" so I don't know what exactly the problem was in the first place. I'll try doing the same test in the linked elog tomorrow. As a quick test, I cycled through the whitening gains (0-45dB) to see if it was some stuck ADC register, but that didn't fix the problem.

The problem seems to be with REFL55 only - I am able to lock the PRMI with carrier resonant without any issues, and the error signal levels are consistent with what I remember them being while the PRMI is swinging around. AS55 lives on the same whitening board and doesn't seem to suffer from the same probelms.

Decided to do the check tonight, but as Attachment #1 shows, no real red flags from the whitening gain side.

As it happened last time, the problem apparently fixed itself - somehow the act of me disconnecting the cables and reconnecting them seems to solve the problem, need to think about this.

Anyway, DRMI was locked a few times tonight. I got in a good long stretch where I ran some sensing lines and collected some data, analysis tomorrow. I am going to center the vertex oplevs as an alignment reference for now. A major source of lockloss seems to be angular instability - see for example this video grab of POP:

Could be due to noise injection from the noisy PRM Oplev HeNe, or just TT mirror angular motion (I couldn't get the PRC angular FF going tonight).

We have the appropriate heatsink - I'd like to minimize interference with the main beam wherever possible.

If damage to the fiber is a concern, I think it's better to use a PBS + waveplate to attenuate the power going into the fiber. When the AOM switching is hooked up to CDS, it's easy to imagine a wrong button being pressed or a wrong value being typed in.

It would probably also be good to have a pickoff monitor for the NPRO DC power so that we can confirm its health (in the short run, we can hijack a PSL Acromag channel for this purpose, as we now do for FSS_RMTEMP). I don't know that we need an EOM for the PLL, as in order to get that going, we probably need some fast electronics for the EOM path, like an FSS box. 

STEVE: I ordered the right heatsink for the acousto after Koji pointed out that the vertical fins are 20% more efficient. Why? Because hot air rises. It will be here in 3-4 days.

[johannes, gautam]

1. Johannes aligned the single bounce off the ITM into the AUX fiber on the AS table, and also the AUX beam into the fiber on the PSL table.
   • Mode matching isn't spectaular anywhere in this chain.
   • But we have 2.6mW of light going into the SRM with the AOM deflection into the 1st order beam (which is what we send into the IFO) maximum.
2. We set up some remote capabilities for the PLL and Marconi frequency (=PLL setpoint) control.
3. Motivation was to try and lock DRMI, and look for some resonance of the AUX beam in the SRC.
   • We soon realized this was a way too lofty goal.
   • So we decided to try the simpler system of PRMI locked on carrier.
   • We were successfully able to sweep the Marconi setpoint in up to 20kHz steps (although we can only move the setpoint in one direction, not sure I know why now).
   • Then we decided to look for resonances of the AUX beam in the arm cavity.
   • Still no cigar
     
4. Plus points:
   • PLL can be reliably locked remotely.
   • Marconi freq. can be swept deterministically remotely.
5. Tomorrow:
   • Fix polarization issues. There is some low freq drift (~5min period) of the power incident on the fiber on the PSL table which we don't understand.
   • Verify MM into IFO and also into fiber at PSL table.
   • Do mode spectroscopy.

I was wondering why the PMC modulation sidebands are showing up on the control room analyzer with ~6dB difference in amplitude. Then I realized that it is reasonable for the cabling to have 6dB higher loss at 80 MHz compared to 20 MHz.

[steve, gautam]

We added the following channels to C0EDCU.ini and restarted the daqd processes. Channels seem to have been added successfully, we will check trend writing later today. Motivation is to have a long term record of annulus pressure (even though we are not currently pumping on the annulus).

C1:Vac-PASE_status

C1:Vac-PASV_status

C1:Vac-PABS_status

C1:Vac-PAEV_status

C1:Vac-PAEE_status

plot next day

For some time now, I've been puzzled by the unreliability of the ASS_X dither alignment servo. Leaving the servo on, TRX often begins to decay to a lower value, and even after freezing the dither at the maximum TRX values, I can manually align the mirrors to increase TRX. We have suspected some kind of clipping in the TRX path that is responsible for this behaviour. Today I decided to investigate this a bit further. To have the arm locked and to inspect the beam, we have to change the locking trigger - TRX is what is normally used, but I misaligned the Y arm completely, and used AS110 as a trigger instead. There is some strangeness in the triggering topology, but this deserves a separate elog.

Once the arm was locked (and relocks using the AS110 trigger in the event of an unlock), I was able to trace the beampath on the EX table with an IR card. The TRX beam is rather large and weak, so it is hard to see, but as best as I can tell, the only real danger of clipping (or perhaps the beam is already clipped) is on the final steering mirror before the beam hits the (Thorlabs) PD. Steve/Pooja are working on getting a photo of this, and will upload it here shortly. Options to mitigate this:

1. Use the harmonic separator to steer the beam lower, and center it on the 1" steering mirror. However, this could possibly lead to clipping on some of the upstream lenses.
2. Raise the height of the 1" steering mirror by 0.25". However, this would require a custom 3/4" dia post height or some shims, which I am not sure is in line with our optomechanic mounting practises.
3. Use a 2" mirror instead of a 1" mirror.

The EX QPD has stopped working since the Acromag install. If it were working, we wouldn't have to rely on the alternate triggering with AS110 and instead just use the QPD as TRX, while we debug the Thorlabs PD path.

I though that the "C1LSC_TRIG_MTRX" MEDM screen completely controls the triggring of LSC signals. But today while trying to trigger the X-arm locking servo on AS110 instead of TRX, I found some strange behaviour. Summary of important points:

1. Even though the servo was supposed to be triggered on AS110, the act of me blocking the beam on the EX table destroyed the lock. I verified the correlation between me blocking the beam and the lock being destroyed by repeating the blocking at least 10 times at different locations along the beam path (to make sure I wasn't accidentally clipping the Oplev beam for example).
2. Investigating further, I found that me turning off the TRX signal digitally also deterministically led to the X arm lock being lost. To be clear, the TRX DC element in the trigger matrix was 0.
3. Confirmed that TRX wasn't involved in any way in the locking servo (I was checking for normalization of the PDH error signal by the DC transmission value, but this is not done). To do this, I locked the arm, and then turned all elements corresponding to TRX in the PowNorm matrix to 0. Then I disabled the locking servo and re-enabled it, and the lock was readily re-acquired readily.

All very strange, not sure what's going on here. The simulink model diagram also didn't give me any clues. Need's further investigation.

FSS slow wasn't running so PSL PZT voltage was swinging around a lot. Reason was that was c1psl unresponsive. I keyed the crate, now it's okay. Now ITMX is stuck - Johannes just told be about an un-elogged c1susaux reboot. Seems that ITMX got stuck at ~4:30pm yesterday PT. After some shaking, the optic was loosened. Please follow the procedure in future and if you do a reboot, please elog it and verify that the optic didn't get stuck.

I opted for the quickest fix - I raised the height of the offending steering mirror using a 0.25" shim. In the long term, we can get a taller post machined. After raising the mirror height, I then checked the DC centering of the spot on the DC PD using a scope.

Looking at the performance of the X arm ASS, I no longer see the strange oscillatory behaviour I described in my previous post . Moreover, the TRX level was ~1 before be raising the steering mirror - but it is now ~1.2. So we were certainly losing some power.

It isn't clear to me in the drawing where the Agilent is during this measurement. Over 40m of cabling, the loss of signal can be a few dB, and considering we don't have a whole lot of signal in the first place, it may be better to send the stronger RF signal (i.e. Marconi pickoff) over the long cable rather than the weak beat signal from the Transmission photodiode. 

Given the various changes to the IFO config since last Thursday when I was last able to lock the DRMI, I wanted to try once again tonight. However, I had no success. By my judgement, the alignment is fine as judged by looking at mode flashes on the cameras. However, despite following the usual alignment procedures, I did not get a single lock in tonight.

Perhaps we can use a flip mount on the BS that combines the PSL and AUX beams on the AS table, so we have the option of recovering the usual IFO config when we so desire - while Jon needs the SRC locked for his measurement, it would be nice to not have to figure out the correct demod phases etc each time there is a change in the optical setup of the AUX beam.

Unfortunately, this has happened (and seems like it will happen) enough times that I set up a script for rebooting the machine in a controlled way, hopefully it will negate the need to repeatedly go into the VEA and hard-reboot the machines. Script lives at /opt/rtcds/caltech/c1/scripts/cds/rebootC1LSC.sh. SVN committed. It worked well for me today. All applicable CDS indicator lights are now green again. Be aware that c1oaf will probably need to be restarted manually in order to make the DC light green. Also, this script won't help you if you try to unload a model on c1lsc and the FE crashes. It relies on c1lsc being ssh-able. The basic logic is:

1. Ask for confirmation.
2. Shutdown all vertex optic watchdogs, PSL shutter.
3. ssh into c1sus and c1ioo, shutdown all models on these machines, soft reboot them.
4. ssh into c1lsc, soft reboot the machine. No attempt is made to unload the models.
5. Wait 2 minutes for all machines to come back online.
6. Restart models on all 3 vertex FEs (IOPs first, then rest).
7. Prompt user for confirmation to re-enable watchdog status and open PSL shutter.

Why is this happening so frequently now? Last few lines of error log:

I fixed it by running the reboot script.

 [Koji, gautam]

Per this elog, we don't need any AIOut channels or Oplev channels. However, the latest wiring diagram I can find for the EX Acromag situation suggests that these channels are hooked up (physically). If this is true, there are 12 ADC channels that are occupied which we can use for other purposes. Question for Johannes: Is this true? If so, Kira has plenty of channels available for her Temperature control stuff..

As an aside, we found that the EPICS channel names for the TRX/TRY QPD gain stages are somewhat strangely named. Looking closely at the schematic (which has now been added to the 40m DCC tree, we can add out custom mods later), they do (somewhat) add up, but I think we should definitely rename them in a more systematic manner, and use an MEDM screen to indicate stuff like x4 or x20 or "Active" etc. BTW, the EX and EY QPDs have different settings. But at least the settings are changed synchronously for all four quadrants, unlike the WFS heads...

Unrelated: I had to key the c1iscaux and c1auxey crates.

I worked a bit on recovering the DRMI locking again tonight. I decided to shutter the AUX laser on the PSL table at least until I figured out the correct locking settings. As has become customary now, there was a cable in the AS beampath (leading from the AS55 DC monitor to nothing, through the enclosure side panel, it is visible in Attachment #3 in this elog) which I only found after 30mins of futility - please try and remove all un-necessary cables and leave the AS beampath in a usable state after working on the AS table!  In the end, I got several short (~3mins) stretches in tonight, but never long enough to do the loop characterization I wanted to get in tonight, probably wrong gains in one or more of the loops. In the last 30 minutes, the IMC has been frequently losing lock, so I am quitting for now. The AUX laser remains shuttered.

Steve mentioned two unlabelled optics were found at EX, relics from the Endtable upgrade.

• One was a 1" 45 deg p-pol optic (Y1-1025-C-45P), it looks a bit scratched.
• The other was a Beam Sampler (BSF10-C).

These are now labelled and forked down on the SP table.

[koji, gautam]

With Koji's help, I got repeatable and reliable DRMI locking going again tonight - this is with the AS path optics for the spectroscopy measurement in place, although the AUX laser remained shuttered tonight. Results + spectra tomorrow, but here's what I did:

• Initial alignment procedure was as usual - use arms+ASS to align ITMs, and then PRMI carrier+ASS to align PRM and BS.
• Found the appropriate gains and demod phases.
• Measured loop TFs - PRCL is a big mystery. Used these to finalize loop gains.
• Ran some sensing lines.
• Whitened DRMI PDs for a calibrated "low-noise" spectrum (although the coils were not de-whitened).

As I have found before, it is significantly easier to get the locking going post 11pm - the wall Seis BLRMS don't look that much quieter at midnight compared to 10pm, but this might be a scaling issue. I'll do a quantitative assessment next time... Also, Foton takes between 25-45 secs to save an updated filter (timed twice today).

Attachment #1 shows the measured PRCL loop shape. The blue line is meant to be the "expected" loop shape. While the measured loop shape tracks the expectation down to ~100 Hz, I cannot explain the shape below it. I am also not sure what to make of the fact that there is high coherence down to 10 Hz fron IN2 to IN1, but no coherence between EXC/IN2. I confirmed that the low-frequency boost filters were ON during the measurement. I don't understand how a pendulum TF + the digital filters we used can account for the shape below 100Hz.

gautam 11pm: After discussing with Koji, I conclude that the low frequency loop shape is consistent with the excitation amplitude being insufficient below 100 Hz. Coherence is good between In1/In2 because they are the same signal effectively - what we need is coherence between In1 and EXC, which isn't plotted. It is still strange that Coherence between In2/EXC is ZERO....

I want to use the Fiber Coupled laser from the PDFR system to characterize the response of the fiber coupled PDs we use in the BeatMouth. The documentation is pretty good: for a first test, I did the following in this order:

• Removed the input fiber to the 1x16 splitter located in the rack near the OMC chamber.
• Connected aforementioned fiber to a collimator.
• Aligned the output of the collimator onto a razor beam dump.
• Turned on the laser controller - it came on with a TEC temperature of 22.5 C and I_diode 0 mA, and the "output shorted" LED was ON (red).
• Turned up the diode current to 80 mA, since the "threshold current" is stated as 75 mA in the manual. In fact, I could see a beam using an IR card at 30 mA already.
• At 80mA, I measured 3.5 mW of output power using the Ophir.

Seems like stuff is working as expected. I don't know what the correct setpoint for the TEC is, but once that is figured out, the 1x16 splitter should give me 250 uW from each output for 4mW input. This is well below any damage threshold of the Menlo PDs. Then the plan is to modulate the intensity of the diode laser using the Agilent, and measure the optoelectronic response of the PD in the usual way. I don't know if we have a Fiber coupled Reference Photodiode we can use in the way we use the NF1611 in the Jenne laser setup. If not, the main systematic measurement error will come from the power measurement using a Fiber Power Meter.

Summary:

Neither of the Menlo FPD310 fiber coupled PDs in the beat mouth have an optoelectronic response (V/W) as advertised. This possibly indicates a damaged RF amplification stage inside the PD.

Motivation:

I have never been able to make the numbers work out for the amount of DC light I put on these PDs, and how much RF beat power I get out. Today, I decided to measure the PD response directly.

Details:

In the end, I decided that slightly modifying the Jenner laser setup was the way to go, instead of futzing around with the PDFR laser. These PDs have a switchable gain setting - for this measurement, both were set to the lower gain such that the expected optoelectronic response is 409 V/W.

[Attachment #1] - Sketch of the experimental setup. 

[Attachment #2] - Measured TF responses, the RF modulation was -20dBm for all curves. I varied the diode laser DC current a little to ensure I recovered identical transfer functions. Assumptions used in making these plots:

1. NF1611 and FPD310 have equal amounts of power incident on them.
2. The NF1611 transimpedance is 700V/A.

[Attachment #3] - Tarball of data + script used to make Attachment #2.

Conclusions:

• The FPD310 does not have a DC monitor port. 
  • So the dominant uncertainty in these plots is that I don't know how much power was incident on the PD under test.
  • The NF1611 DC power level could be measured though, and seemed to scale with DC pump current linearly (I had only 3 datapoints though so this doesn't mean much).
• Neither PD has transimpedance gain as per the specs.
  • The X PD shows levels ~x10 lower than expected.
  • The Y PD shows levels ~x3 lower than expected.
• I will repeat the measurement tomorrow by eliminating some un-necessary patch fiber cables, and also calibrating out the cable delays.
  • The setup shown in Attachment #1 was used because I didn't want to open up the BeatMouth.
  • But I can pipe the port of the BS not going to the FPD310 directly to the collimator, and that should reduce the systematic uncertainty w.r.t. power distribution between FPD310 and NF1611.

don't use IN_1/IN_2: recall pizza meeting from a few weeks back: use IN1/EXC + Al-Gebra

Do we really have 2 free ADC channels at EX now? I was under the impression we had ZERO free, which is why we wanted to put a new ADC unit in. I think in the wiring diagram, the Vacuum gauge monitor channel, Seis Can Temp Sensor monitor, and Seis Can Heater channels are missing. It would also be good to have, in the wiring diagram, a mapping of which signals go to which I/O ports (Dsub, front panel BNC etc) on the 4U(?) box housing all the Acromags, this would be helpful in future debugging sessions.

[jon, gautam]

Jon is doing some characterization of the AUX laser setup for which he wanted only the prompt retroreflection from the SRM on the AS table, so the PSL shutter is closed, and both ITMs and ETMs are misaligned. The prompt reflection from the SRM was getting clipped on something in vacuum - the ingoing beam looked pretty clean, but the reflection was totally clipped, as I think Johannes aligned the input beam with the SRM misaligned. So the input steering of the AUX laser beam into the vacuum, and also the steering onto AS110, were touched... Also, there were all manner of stray, undumped beams from the fiber on the AS table Jon will post photos.

Before we began this work, we found that c1susaux was dead so we rebooted it.

I think this is because /cvs/cds is getting too big. lsblk reveals:

I believe one of sdc or sdd is connected via SATA while the other is an external USB drive. Maybe we have to get bigger backup disks, but this may be a huge pain to setup as it will involve taking chiara down. Actually, now that I check the backup log, seems like backup is executing successfully - not sure if this is due to my unelogged mounting of sdc (using sudo mount /dev/sdc1 /media/40mBackup) last week, or if this is some LDAS backup. But in any case, seems undesirable that sdb1 is larger than sdc1 or sdd1.

I finally analyzed the sensing measurement I ran on Tuesday evening. Sensing responses for the DRMI DOFs seems consistent with what I measured in October 2017, although the relative phasing of the DoFs in the sensing PDs has changed significantly. For what it's worth, my Finesse simulation is here. 

All optics have been re-aligned. Jon/Johannes will elog about the work today.

Using the numbers from the sensing measurement, I calibrated the measured in-loop MICH spectrum from Tuesday night into free-running displacement noise. For convenience, I used the noise-budgeting utilities to make this plot, but I omitted all the technical noise curves as the coupling has probably changed and I did not measure these. The overall noise seems ~x3  higher everywhere from the best I had last year, but this is hardly surprising as I haven't optimized anything for low noise recently. To summarize:

• DRMI was locked using 1f error signals.
• MICH was controlled using AS55_Q.
• Main difference is that we have a little less (supposedly 10%) light on the AS55 PD now because of the AUX laser injection setup. But the AUX laser was shuttered.
• 1f LSC PDs (REFL11, REFL55 and AS55) had ADC whitening filters engaged in while this data was taken.
• ITM and BS coils were not de-whitened.

I will do a more thorough careful characterization and add in the technical noises in the coming days. The dominant uncertainty in the sensing matrix measurement, and hence this free-running noise spectrum, is that I haven't calibrated the actuators in a while.

I did the measurement with the BeatMouth open today. Main changes:

• Directly pipe the RF output of the Menlo PDs to the Agilent, bypassing the 20dB coupler inside the BeatMouth.
• Directly pipe the unused port of the Fiber Beamsplitter used to send light to the Menlo PD to an in-air collimator, which then sends the beam to the NF1611 reference detector.

So neglecting asymmetry in the branching ratio of the fiber beamsplitter, the asymmetry between the test PD optical path and the reference PD optical path is a single fiber mating sleeve in the former vs a collimator in the latter. In order to recover the expected number of 409 V/W for the Menlo PDs, we have to argue that the optical loss in the test PD path (fiber mating sleeve) are ~3x higher than in the NF1611 path (free space coupler). But at least the X and Y PDs show identical responses now. The error I made in the previously attached plot was that I was using the 20dB coupled output for the X PD measurement .

Revised conclusion: The measured optoelectronic response of the Menlo PDs at 10s of MHz, of ~130 V/W, is completely consistent with the numbers I reported in this elog. So rogue polarization is no longer the culprit for the discrepancy between expected and measured RF beatnote power, it was just that the expectation, based on Menlo PD specs, were not accurate.#2 of the linked elog seems to be the most likely, although "broken" should actually be "not matching spec".

While killing time b/w measurements, I looked on the ITMY optical table and found that the NF1611 I mentioned in this elog still exists. It is fiber coupled. Could be a better substitute as a Reference PD for this particular measurement.

[Jon, Gautam, Johannes]

We did the following today:

1. Dither align arms such that ITMs were reliable arm references.
2. Configure the IFO such that ITMX single bounce was the only visible beam reaching the AS port from the symmetric side - ITMY, both ETMs, PRM and SRM were misaligned.
3. Do coarse alignment on the AS table using the usual near field / far field overlap technique, with "near" and "far" dictated by arm reach on the AS table. In this way, the ingoing AUX beam and the PSL single bounce from ITMX were collimated on the AS table.
4. Lock the AUX / PSL PLL. We expected a beatnote on AS110 at eithe (80-50)=30 MHz or (80+50)=130 MHz. 80 MHz is the AOM driver frequency, while 50 MHz is the PLL offset. (Marconi was actually set to 60 MHz, prolly Keerthana forgot to reset it after some remote experimentation).
5. Beat was found at 30 MHz. 
6. Input steering of AUX beam into the IFO was tweaked to maximize the beat. Johannes claims he saw -35 dBm on AS110 last week. But Jon reported a best effort of ~-60 dBm today. Not sure how to square that circle.
7. Once we were confident that the input of the AUX and PSL beams were well aligned, we decided to do a scan. PRC was chosen as PRMI can be locked but I don't yet know the correct settings for SRMI locking, and DRMI seemed too ambitious for daytime.
   • PRMI was locked on carrier.
   • Jon can comment more here, but the measurement with AM sidebands does not rely on any beatnote on the AS110 PD, it is just looking for coupling of the AM sideband into the IFO from the AS port at resonant frequencies of the PRC.
   • For a coarse sweep, we swept from 1-60 MHz, 801 points, and the IF bandwidth was set at 30 kHz on the AG4395.
   • Transfer function being measured was the ratio of AM signal detected at AS110 PD, to RF drive applied to the AOM driver.
   • We were expecting to see dips separated by the PRC FSR (~25 MHz, since the PRC RT length is ~12.5m), when the AM sideband becomes resonant in the PRC.
   • But we saw nothing. Need to think about if this is an SNR problem, or if we are overlooking something more fundamental in the measurement setup.

This measurement seems like a fine candidate to trial the idea of looking for the FSRs (and in general, cavity resonances) of the PRC in the phase of the measured TFs, rather than the amplitude.

Yesterday, I moved the following optics:

1. Lens in front of AS110 PD.
2. BS splitting light between AS110 and AS55.

After moving these components around a bit, I locked them down once I was happy that the beam was pretty well centered on both of them, and also on AS110 and AS55 (measured using O'scope with single bounce from one ITM, other optics misaligned).

The beam was close to clipping on the lens mentioned in #1, probably because this wasn't checked when the 90-10 BS was installed for the AUX laser. Furthermore, I believe we are losing more than 10% of the light due to this BS. The ASDC (which is derived from AS55 PD) level is down at ~110cts as the Michelson is fringing, while it used to be ~200 cts. I will update with a power measurement shortly. But I think we should move ahead with the plan to combine the beam into the IFO's AS mode as discussed at the meeting last week.

Unrelated to this work, but c1psl and c1iscaux were keyed. 

ASDC has something weird going on with it - my main goal yesterday was to calibrate the actuators of ITMX, ITMY and BS using the Michelson. But with the Michelson locked on a dark fringe, the ASDC level changed by up to 50 counts seemingly randomly (bright fringe was ~1000 cts, I had upped the whitening gain to +21dB), even though the CCD remained clearly dark throughout. Not sure if the problem is in the readout electronics or in the PD itself.

Summary:

The actuator (pendulum) gains for the Beam Splitter and the two ITMs were measured to be:

BS: 9.54 +/- 0.05 nm/ct [100 ohm series resistor in coil driver board]

ITMX: 2.44 +/- 0.01 nm/ct [400 ohm series resistor in coil driver board]

ITMY: 2.44 +/- 0.02 nm/ct [400 ohm series resistor in coil driver board]

Counts here refers to DAC counts at the output of the coil filter banks (as opposed to counts at the LSC servo output). The dominant (systematic) uncertainty (which isn't quoted here) in this measurement is the determination of the peak-to-peak swing of the dark port sensor, AS55_Q. I estimate this error to be ~1ct/33cts = 3%. These values are surprisingly consistent with one another once we take into account the series resistance.

Details:

The last time this was done, we used ASDC to do the measurement. But I don't know what signal conditioning ASDC undergoes (in PD or in readout electronics). In any case, in my early trials yesterday, ASDC was behaving unpredictably. So I decided to do redo the measurement.

[Attachment #1]- Flowchart describing the calibration procedure.

[Attachment #2] - AS55_Q output while the Michelson was freeswinging. I had first aligned the ITMs using ASS. The peak-to-peak value of this corresponds to . So we know AS55_Q in terms of cts/m of MICH displacement.

[Attachment #3] - Magnitudes of transfer function from moving one of the MICH optics, to the now calibrated AS55_Q. Fits are to a shape , with  being the fitted parameter. Coherence during the measurement is also plotted.

• Note that the excitation is applied to the channels C1:SUS-<optic>_LSC_EXC, for <optic> in [BS, ITMX, ITMY]. But since my de-whitening board re-work to remove the analog x3 gain, there is a digital x3 gain in the coil driver filter banks. So while the calibration numbers given above are accurate, be aware that when using them for sensing matrix measurements etc, you have to multiply these by x3.
• Furthermore, moving the BS by results in a Michelson length change of , and this has been factored into the above number.

Next Steps:

1. Now that I have a calibration I trust more, re-analyze my DRMI sensing matrix data. Actually the sensing response numbers aren't significantly different from what I have been assuming. It's just that in terms of counts applied at the LSC input of a suspension, there is a digital x3 gain that has to be explicitly factored in.
2. Calibrate POX and POY by locking the arms and driving the now calibrated ITMs by a known number of counts.
3. Calibrate the ETMs, and MC1/MC2/MC3 by looking at calibrated POX/POY.
4. Lock DRMI, and calibrate SRM and PRM.

Reference:

[1] - http://www.phys.ufl.edu/~bernard/papers/CQG20_S903.pdf

Motivation:

1. I want to use the QPD at POP, calibrate it into physical units, and quantify the amount of angular jitter in the PRC (which I claim is what limits DRMI stability atm).
2. I want to revive the PRC angular feedforward to try and mitigate this a bit. But is feedforward even the best approach? Can we use feedback using the POP QPD?

POP QPD checkout:

• The POP QPD sits on the ITMX optical table. 
• It is interfaced to the CDS system via an OT301 and then a Pentek whitening stage (z:p = 15:150). 
• The OT301 claims to have a switchable offset nulling capability - but despite my best efforts tonight, I couldn't use the knobs on the front to null the offset (even with the PRC locked on carrier and a strong POP beam on the QPD).
  • We don't have readbacks of the individual quadrants available.
  •  
• So I moved the QPD with the PRC locked, to center the CDS readback of the spot position at (0,0).
• Next step is to calibrate the POP QPD readback into physical units.
  • I'm thinking of using the EricG diode laser for this purpose.
  • I can calibrate counts to mm of displacement on the QPD active area.
  • After which I can use the estimated position to PR2 (from which POP is extracted) to convert this to angular motion.
• I guess I should check for coherence between the POP QPD signal and all angular sensors of PRM/BS/MC1/MC2/MC3 to try and confirm the hypothesis that the folding mirrors are dominating the angular noise of the cavity. Unfortunately we don't have readbacks of the angular positions of TT1 and TT2.
• I moved the POP camera a bit in YAW so that the POP spot is now better centered on the CCD monitor.
• I also wanted to check the centering on the other POP QPD (POP22/POP110/POPDC?) but I think the POPDC signal, used for triggering the PRCL LSC servo, is derived from that PD, so everytime I blocked it, the lock was lost. Need to think of another strategy.
• MC3 has been rather glitchy tonight.
  • So I will wait for a quieter time when I can collect some data to train the WF for angular FF.

Per discussion today eve, barring objections, I will do the following tomorrow morning:

1. Remove ETMX coil driver board from 1X9
   • Change series resistances on the fast path to 2x4k in parallel. One will be snipped off once we are happy we can still lock.
   • Remove AD797s, potentiometers.
   • Thick film-->thin film for important components.
2. Remove ETMX de-whitening board from 1X9
   • Remove x3 analog gain.
   • Thick film-->thin film for important components.