It seemed that the ETMY watchdog tripped early Sunday morning.
The reason is not known. I just looked at ETMX, but it seemed fine.
I called the control room just in case someone is working on the IFO.
Also I did not see any elog entry to indicate on going work there.
So, I decided to reset the watchdog for ETMY. And it is working fine again.
I checked the state of the whitening filters for the ETMY shadow sensors.
Result : They've been OFF (i.e. flat response).
(measurement and setup)
I measured the transfer functions of the whitening board (D000210) by looking at the signal before and after the whitening stage.
The whitening board handles five signals; UL, UR, LR, LL and SD, and there are five single-pin lemo outputs for each signal on the front panel.
A good thing on those lemo monitors is that their signals are monitored before the whitening stages.
Rana suggested me to use these signals for the denominator of the transfer functions and consider the sensor signals as excitation signals.
So I plugged those signals into extra ADC channels via an AA-board and measured the transfer functions.
In the measurement the coherence above 4 Hz was quite small while the suspension was freely swinging.
Therefore I had to excite the ETMY suspension by putting random noise in a frequency band from 5 Hz to 35 Hz to obtain better coherence.
The response is flat over frequency range from ~ 0.2 Hz to ~40 Hz, see the plot below.
According to the spectrum of each signal the measurements above 10 Hz are just disturbed by the ADC noise.
If the whitening filters are ON, a pole and zero are expected to appear at 30 Hz and 3 Hz respectively according to the schematic, but no such features.
I acquired a second full pair of Host interface board cards (one for the computer and one for the chassis) from Rolf (again, 2nd generation - the bad kind).
However, they exhibited the same symptoms as the first one that I was given.
Rolf gave a few more suggestions on getting it to work. Pull the power plugs. If its got slow flashing green lights, just soft cycle, don't power cycle. Alex suggested turning the IO chassis on before the computer.
None of it seemed to help in getting the computer talking to the IO chassis.
I finally decided to simply take the ETMX IO chassis and place it at the Y end. So for the moment, ETMY is working, while ETMX is temporarily out of commission.
We also made the necessary cables (2x 37 d-sub female to 40 pin female and 40 pin female to 40 pin female) . Kiwamu also did nice work on creating a DAC adapter box, since Jay had given me a spare board, but nothing to put it in.
Attachment #1 shows that the ITMX, ETMY and beamsplitter Oplev light levels have decayed significantly from their values when installed. In particular, the ETMY and ITMX sum channels are now only 50% of the values when a new HeNe was installed. ELOG search revealed that ITMY and ETMX HeNes were replaced with newly acquired units in March and September of last year respectively. The ITMX oplev was also replaced in March 2019, but the replacement was a unit that was being used to illuminate our tourist attraction glass fiber at EX.
We should replace these before any vent as they are a useful diagnostic for the DC alignement reference.
Adjusted focus on ETMYF camera so that the IR beam is in focus.
3. Replaced Ygreen REFL camera with ETMYT camera to see transmitted beam mode.
The camera that Yuta means in his elog from last night/this morning is the scattering camera at the Yend. The reason (I think) that he had to do this is that Manasa and Jan took the cable for the ETMYT camera, and were using it for their scattering camera. They mention in elog 8072 that they installed a camera, but they didn't say anything about having taken the ETMYT cable. This is the kind of thing that is useful to elog!
Anyhow, I have removed the Watec that belongs with the scattering setup, that Yuta borrowed, and put it back on the scattering table-on-a-pedestal. I then realigned the usual ETMYT camera (that Yuta moved out of the way to install the borrowed Watec), and put the ETMYT cable back to its usual place, connected to the Sony camera's box on the floor.
tl;dr: ETMYT camera is back to original state.
EDIT later: I put the Watec back, since it is more sensitive to IR, so now we have a Watec in the regular ETMYT place.
I've applied first contact to both the ETMs. They're now ready to be suspended. I've also cut up some lengths of the new wire and put them in the oven for a 12 hour 70C bake.
Unless we want the AR surface to also have a small F.C coat until the optic is in the vacuum chamber, I think I will proceed with re-suspending the ETMs..
David and I were thinking about changing the non-polarizing beam splitter in the EUCLID setup from 50/50 to 33/66 (ref picture). It serves as a) a pickoff to sample the input power and b) a splitter to send the returning beam to a photodetector 2 (it then hits a polarizer and half of this is lost. By changing the reflectivity to 66% then less (1/3 instead of 1/2) of the power coming into it would be "lost" at the ref photodetector 1, and on the return trip less would be lost at the polarizer (1/6 instead of 1/4).
I took this opportunity of EX downtime to change the supply voltage for the AA unit (4-pin LEMO front panel) in 1X9 from +/-5V to +/-15V. Inside the AA board are INA134 and DRV135 ICs, which are rated to work at +/-18V. In the previous state, the inputs would saturate if driven with a 2.5Vpp sine wave from a DS345 func. gen. After the change, I was able to drive the full range of the DS345 (10Vpp), and there was no saturation seen. This AA chassis is only used for the OSEM signals and also some ALS signals. Shadow sensor levels and spectra are consistent before and after the change. The main motivation was to not saturate the Green PDH Reflection signal in the digital readout. The steps we took were:
Steve and I restored the power to the EX AUX electronics rack. The power strip on the lowest shelf of the AUX rack now goes to another power strip laid out vertically along the NW corner of 1X9. The EX green locks to the arm just fine now.
I worked on characterizing the green PDH setup at EX, as part of the ALS noise budgeting process. Summary of my findings:
The main motivation was to get the residual frequency noise of the EX laser when locked to the X arm cavity - but I'll need the V/Hz PDH discriminant to convert the in-loop error signal to frequency units. The idea was to look at the PDH error signal on a scope and match up the horn-to-horn voltage with a model to back out said discriminant, but I'll have to double check my model for errors now given the large mismatch I observe in reflected power.
I decided to use the more direct method, of disconnecting feedback to the EX laser PZT, and then looking at the cavity flashes.
Attachment #1 shows the cavity swinging through two resonances (data collected via oscilloscope). Traces are for the demodulated PDH error signal (top) and the direct photodiode signal (bottom). The traces don't look very clean - I wonder if some saturation / slew rate effects are at play, because we are operating the PD in the 30 dB setting, where the bandwidth of the PD is spec-ed as 260 kHz, whereas the dominant frequency component of the light on the PD is 430 kHz.
The asymmetric horns corresponding to the sideband resonances were also puzzling. Doing the modeling, Attachment #2, I think this is due to the fact that the demodulation phase is poorly set. The PDH modulation frequency is only ~5x the cavity linewidth, so both the real and imaginary parts of the cavity reflectivity contribute to the error signal. If this calculation is correct, we can benefit (i.e. get a larger PDH discriminant) by changing the demod phase by 60 degrees. However, for 230 kHz, it is impractical to do this by just increasing cable length between the function generator and mixer.
Anyway, assuming that we are at the phi=30 degree situation (since the measurement shows all 3 horns going through roughly the same voltage swing), the PDH discriminant is ~40 uV/Hz. In lock, I estimate that there is ~60 uW of light incident on the PDH reflection photodiode. Using the PD response of 0.2 A/W, transimpedance of 47.5 kohm, and mixer conversion loss of 6dB, the shot-noise limited sensitivity is 0.5 mHz/rtHz. The photodiode dark noise contribution is a little lower - estimated to be 0.2 mHz/rtHz. The loop does not have enough gain to reach these levels.
PDH discriminant (40 uV/Hz, see this elog)
Some time ago, I had done an actuator calibration of ITMX. This suspension hasn't been victim to the recent spate of suspension problems, so I can believe that the results of those measurement are still valid. So I decided to calibrate the in-loop error signal of the EX green PDH loop, which is recorded via an SR560, G=10, by driving a line in ITMY position (thereby modulating the X arm cavity length) while the EX green frequency was locked to the arm cavity length. Knowing the amount I'm modulating the cavity length by (500 cts amplitude sine wave at 33.14159 Hz using awggui, translating to ~17.2 kHz amplitude in green frequency), I demodulated the response in C1:ALS-X_ERR_MON_OUT_DQ channel. At this frequency of ~33 Hz, the servo gain should be large, and so the green laser frequency should track the cavity length nearly perfectly (with transfer function 1/(1+L), where L is the OLG).
The response had amplitude 5.68 +/- 0.10 cts, see Attachment #1. There was a sneaky gain of 0.86 in the filter module, which I saw no reason to keep at this strange value, and so updated to 1, correcting the demodulated response to 6.6 cts. After accounting for this adjustment, the x10 gain of the SR560, and the loop suppression, I put a "cts2Hz" filter in (Attachment #2). I had to guess a value for the OLG at 33 Hz in order to account for the in-loop suppression. So I measured the OLTF using the usual IN1/IN2 method (Attachment #3), and then used a LISO model of the electronics, along with guesses of the cavity pole (18.5 kHz), low-pass filter poles (4x real poles at 70 kHz), PZT actuator gain (1.7 MHz/V) and PDH discriminant (40 uV/Hz, see this elog) to construct a model OLTF. Then I fudged the overall gain to get the model to line up with the measurement between 1-10kHz. Per this model, I should have ~75dB of gain at ~33Hz, so the tracking error to my cavity length modulation should be ~3.05 Hz. Lines up pretty well with the measured value of 4.7 Hz considering the number of guessed parameters. The measured OLG tapers off towards low frequency probably because the increased loop suppression drives one of the measured inputs on the SR785 into the instrument noise floor.
The final calibration number is 7.1 Hz/ct, though the error on this number is large ~30%. Note that these "Hertz" are green frequency changes - so the change to the IR frequency will be half.
Attachment #4 shows the error signal in various conditions, labelled in the legend. Interpretations to follow.
G=10 or G=100?
wrong assumption - i checked the gain just now, it is G=10, and is running in the "low-noise" mode, so can only drive 4V. fixed elog, filter.
Note: While working at EX, I saw frequent saturations (red led blinking) on the SR560. Looking a the error mon signal on a scope, it had a pk-to-pk amplitude of ~200mV going into the SR560. Assuming the free-swinging cavity length changes by ~1 um at 1 Hz, the green frequency changes by ~15 MHz, which according to the PDH discriminant calibration of 40 uV/Hz should only make a 60 mV pk to pk signal. So perhaps the cavity length is changing by 4x as much, plausible during daytime with me stomping around the chamber I guess.. My point is that if the SR560 get's saturated (i.e. input > 13000 cts), the DQ-ed spectrum isn't trustworthy anymore. Should hook this up to some proper whitening electronics
Attachment #1 shows the drift of the polarization content of the light from EX entering the BeatMouth. Seems rather large (~10%). I'm going to tweak the X end fiber coupling setup a bit to see if this can be improved. This performance is also a good benchmark to compare the PSL IR light polarization drift. I am going to ask Steve to order Thorlabs K6XS, which has a locking screw for the rotational DoF. With this feature, and by installing some HWPs at the input coupling point, we can ensure that we are coupling light into one of the special axes in a much more deterministic way.
There was no green light even though the EX NPRO was on. I checked the doubling oven temperature controller and found that its power cable was loose on the rear. I reconnected it, and now there is green light again.
I have been puzzled as to why the duty cycle of the EX green locks are much less than that of the EY NPRO. If anything, the PDH loop has higher bandwidth and comparable stability margins at the X end than at the Y end. I hypothesize that this is because the EX laser (Innolight 1W Mephisto) has actuation PZT coefficient 1MHz/V, while the EY laser (Lightwave 125/126) has 5MHz/V. I figure the EX laser is sometimes just not able to keep up with the DC Xarm cavity length drift. To test this hypothesis, I disabled the LSC locking for the Xarm, and enabled the SLOW (temperature of NPRO crystal) control on the EX laser. The logic is that this provides relief for the PZT path and prevents the PDH servo from saturating and losing lock. Already, the green lock has held longer than at any point tonight (>60mins). I'm going to leave it in this state overnight and see how long the lock holds. The slow servo path has a limiter set to 100 counts so should be fine to leave it on. The next test will be to repeat this test with LSC mode ON, as I guess this will enhance the DC arm cavity length drift (it will be forced to follow MCL).
Why do I care about this at all? If at some point we want to do arm feedforward, I thought the green PDH error signal is a great target signal for the Wiener filter calculations. So I'd like to keep the green locked to the arm for extended periods of time. Arm feedforward should help in lock acquisiton if we have reduced actuation range due to increased series resistances in the coil drivers.
As an aside - I noticed that the SLOW path has no digital low pass filter - I think I remember someone saying that since the NPRO controller itself has an in-built low pass filter, a digital one isn't necessary. But as this elog points out, the situation may not be so straightforward. For now, I just put in some arbitrary low pass filter with corner at 5Hz. Seems like a nice simple problem for optimal loop shaping...
gautam noon CNY2018: Looks like the green has been stably locked for over 8 hours (see Attachment #1), and the slow servo doesn't look to have railed. Note that 100 cts ~=30mV. For an actuation coefficient of 1GHz/V, this is ~30MHz, which is well above the PZT range of 10V-->10MHz (whereas the EY laser, by virtue of its higher actuation coefficient, has 5 times this range, i.e. 50MHz). Supports my hypothesis.
THIS CALCULATION IS WRONG FOR THE OVERCOUPLED CAV.
Mode-matching efficiency of EX green light into the arm cavity is ~70*%, as measured using the visibility.
I wanted to get an estimate for the mode-matching of the EX green beam into the arm cavity. I did the following:
This amount of mode-matching is rather disappointing - using a la mode, the calculated mode-matching efficiency is nearly 100%, but 70% is a far cry from this. The fact that I can't improve this number by either tweaking the steering or by moving the MM lenses around suggests that the estimate of the target arm mode is probably incorrect (the non-gaussianity of the input beam itself is not quantified yet, but I don't believe this input beam can account for 30% mismatch). For the Y-arm, the green REFL DC level is actually higher when locked than when ITMY is misaligned. WTF?? Only explanation I can think of is that the PD is saturated when green is unlocked - but why does the ADC saturate at ~3000cts and not 32000?
This data is almost certainly bogus as the AA box at 1X9 is powered by +/-5VDC and not +/-15VDC. I didn't check but I believe the situation is the same at the Y-end.
3000 cts is ~1V into the ADC. I am going to change the supply voltage to this box (which also reads in ETMX OSEMS) to +/-15V so that we can use the full range of the ADC.
gautam Apr 26 630pm: I re-did the measurement by directly monitoring the REFLDC on a scope, and the situation is not much better. I calculate a MM of 70% into the arm. This is sensitive to the lens positions - while I was working on the EX fiber coupling, I had bumped the lens mounted on a translational stage on the EX table lightly, and I had to move that lens around today in order to recover the GTRX level of 0.5 that I am used to seeing (with arm aligned to maximize IR transmission). So there is definitely room for optimization here.
I installed a 10% BS to pick off some of the light going to the IR fiber, and have added a Thorlabs PDA55 PD to the EX table setup. The idea is to be able to monitor the power output of the EX NPRO over long time scales, and also to serve as an additional diagnostic tool for when ALS gets glitchy etc. There is about 0.4mW of IR power incident on the PD (as measured with the Ophir power meter), which translates to ~2500 ADC counts (~1.67V as measured with an Oscilloscope set to high impedance directly at the PD output). The output of the PD is presently going to Ch5 of the same board that receives the OL QPD voltages (which corresponds to ADC channel 28). Previously, I had borrowed the power and signal cables from the High-Gain Transmon PD to monitor this channel, but today I have laid out independent cabling and also restored the Transmon PD to its nominal state.
On the CDS side of things, I edited C1SCX to route the signal from ADC Ch28 to the ALS block. I also edited the ALS_END library part to have an additional input for the power monitor, to keep the naming conventions consistent. I have added a gain in the filter module to calibrate the readout into mW using these numbers. The channel is called C1:ALS-X_POWER_OUT, and is DQed for long-term trending purposes.
The main ALS screen is a bit cluttered so I have added this channel to the ALS overview MEDM screen for now..
The EX PDH setup had what I thought was insufficient phase and gain margins. So I lowered the gain a little - the price paid was that the suppression of laser frequency noise of the end laser was reduced. I actually think an intermediate gain setting (G=7) can give us ~35 degrees of phase margin, ~10dB gain margin, and lower residual unsuppressed AUX laser noise - to be confirmed by measurement later. See here for the last activity I did - how did the gain get increased? I can't find anything in the elog.
During our EX AM/PM setups, I don't think we bumped the PDH gain knob (and I hope that the knob was locked). Possible drift in the PZT response? Good thing Shruti is on the case.
Is there a loop model of green PDH that agrees with the measurement? I'm wondering if something can be done with a compensation network to up the bandwidth or if the phase lag is more like a non-invertible kind.
The closest thing I can think of is here.
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 went through the wiring of the c1auxex crate today to disentangle the pin assignments. The full detail can be found in attachment #1, #2 has less detail but is more eye candy. The red flagged channels are now marked for removal at the next opportunity. This will free up DAQ channels as follows:
This should be enough for temperature sensing, NPRO diagnostics, and even eventual remote PDH control with new servo boxes.
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.
Bad wording, sorry. Should have been channels in excess of ETMX controls. I'll add the others to the list as well.
Updated channel list and wiring diagram attached. Labels are 'F' for 'Front' and 'R' for - you guessed it - 'Rear', the number identifies the slot panel the breakout is attached to.
I'd like to confirm that the IR ALS scheme will work for locking. The X-arm performance so far has been encouraging. I want to repeat the characterization for the Y arm. So I inspected the layout on the EY table, and made a list of characterization tasks. The current EY beam routing is difficult to work with, and it will definitely benefit from a re-do. However, I don't know how much time I want to spend re-doing it, so for a start, I will just try and couple some amount of light into a fiber and bring it to the PSL table, and see what noise performance I get.
Attachment #1: Photo of the current beam layout. The powers indicated were measured with the Ophir power meter.
Attachment #2: A candidate mode-matching solution, given the constraints outlined above. It isn't great, with only 85% modematching even theoretically possible. The lenses required are also pretty fast lenses. But I think it's the best possible without a complete overhaul of the EY layout. I'm still waiting for the lens kit to arrive, but as soon as they get here, I will start this work.
Steve was calibrating the load cells at the EY table with the crane - we didn't get through the full procedure today, so the area near the EY table is kind of obstructed. The 100kg donut is resting on the floor on the North side of the EY table and is still connected to the crane. There are stopper plates underneath the donut, and it is still connected to the crane. Steve has placed cones around the area too. The crane has been turned off.
[steve, rana, gautam]
Rana pointed out that the OSEM cabling, because of lack of a plastic shielding, is grounded directly to the table on which it is resting. A glass baking dish at the base of the seismic stack prevents electrical shorting to the chamber. However, there are some LEMO/BNC cables as well on the east side of the stack, whose BNC ends are just lying on the base of the stack. We should use this opportunity to think about whether anything needs to be done / what the influence of this kind of grounding is (if any) on actuator noise.
Steve also pointed out that we should replace the rubber pads which the vacuum chamber is resting on (Attachment #1, not from this vent, but just to indicate what's what). These serve the purpose of relieving small amounts of strain the chamber may experience relative to the beam tube, thus helping preserve the vacuum joints b/w chamber and tube. But after (~20?) years of being under compression, Steve thinks that the rubber no longer has any elasticity, and so should be replaced.
While Chub is making new cables for the EY satellite box...
While the position of the reflector could possibly be optimized further, since we are already seeing a temperature gradient on the optic, I propose pushing on with other vent activities. I'm almost certain the current positioning places the optic closer to the second focus, and we already saw shifts of the HOM resonances with the old configuration, so I'd say we run with this and revisit if needed.
If Chub gives the Sat. Box the green flag, we will work on F.C.ing the mirrors in the evening, with the aim of closing up tomorrow/Friday.
All raw images in this elog have been uploaded to the 40m google photos.
[chub, bob, gautam]
We took the heavy door off the EY chamber at ~930am.
Waiting for the table to level off now. Plan for later today / tomorrow is as follows:
While restoring OSEMs on ETMY, I noticed that the open voltages for the UR and LL OSEMs had significantly (>30%) changed from their values from ~2 years ago. The fact that it only occurred in 2 coils seemed to rule out gradual wear and tear, so I looked up the trends from Nov 25 - Nov 28 (Sundance visited on Nov 26 which is when we removed the cage). Not surprisingly, these are the exact two OSEMs that show a decrease in sensor voltage when the OSEMs were pulled out. I suspect that when I placed them in their little Al foil boats, I shorted out some contacts on the rear (this is reminiscent of the problem we had on PRM in 2016). I hope the problem is with the current buffer IC in the satellite box and not the physical diode, I'll test with the tester box and evaluate the problem further.
Chamber work by Chub and gautam:
With Chub's help, I've setup a mini cleanroom at EY - Attachment #1. The HEPA unit is running on high now. All surfaces were wiped with isopropanol, we can wipe everything down again on Monday and replace the foil.
Couple IR light into fiber with good MM at EY
As part of characterization, I wanted to calibrate the EY uPDH error point monitor into units of Hz. So I thought I'd measure the PDH horn-to-horn voltage with the cable to the laser PZT disconnected. However, I saw no clean PDH fringe while monitoring the signal after the LPF that is immediately downstream of the mixer IF output. I then decided to measure the low pass filter OLTF, and found that it seems to have some complex poles (f0~57kHz, Q~5), that amplify the signal by ~x6 relative to the DC level before beginning to roll-off (see Attachment #1). Is this the desired filter shape? Can't find anything in the elog/wiki about such a filter shape being implemented...
The actual OLTF looks alright to me though, see Attachment #2.
filter Q seems too high,
but what precisely is the proper way to design the IF filter?
seems like we should be able to do it using math instead of feelins
Izumi made this one so maybe he has an algorythym
I got confused. Why don't we see that too-high-Q pole in the OLTF?
I'm not sure - maybe it was measurement error on my part, I will double check. Moreover, the EX and EY boxes don't seem to use identical designs, if one believes the schematics drawn on the Pomona boxes. The EY design has a 50ohm input impedance in the stopband, whereas the EX doesn't. Maybe the latter needs a Tee + 50ohm terminator at the input?
Judging by the schematics, the servo inputs to both boxes are driving the non-inverting input of an opamp, so they see high-Z.
I got confused. Why don't we see that too-high-Q pole in the OLTF?
Rana and I discussed this alogrythym a bit today - here are some bullet points, I'll work on preparing a notebook. We are still talking about a post-mixer low pass filter.
Here are some loop transfer functions. I basically followed the decomposition of the end PDH loop as was done in the multi-color metrology paper. There is no post-mixer low pass filter at the moment (in my model), but already you can see that the top of the phase bubble is at ~10 kHz. Probably there is still sufficient phase available at 30 kHz, even after we add an LPF. In any case, I'll use this model and set up a cost function minimization problem and see what comes out of it. For the PZT discriminant, I used 5 MHz/V, and for the PDH discriminant, I used 40 uV/Hz, which are numbers that should be close to what's the reality at EY.
(i) Note that there could be some uncertainty in the overall gain (VGA stage in the servo).
(ii) For the cavity pole, I assumed the single pole response, which Rana points out isn't really valid at ~1 MHz, which is close to the next FSR
(ii) The PZT response is approximated as a simple LPF whereas there are likely to be several sharp features which may add/eat phase.
I'll work on preparing a notebook.
Chloe has been to the lab twice to start up her investigations in acoustic noise coupling to mirrors. The general idea for the setup is a HeNe laser bouncing off a mirror and onto a QPD, whose signal provides a measure of beam displacement noise. The mirror will be mounted and excited in various ways to make quantitative conclusions about the quality of different mounting schemes.
We have set up the laser+mirror+QPD on the SP table, and collected data via SR560s->SR785, with the main aim of evaluating the suitability of this setup. The data we collected is not calibrated to any meaningful units (yet). For now, we are just using QPD volts.
Chloe collected data of vertical displacement noise for the following schemes: Terminated SR785 input, Terminated SR560 inputs, Laser centered directly onto the QPD, Laser shining on mirror centered on QPD, laser/mirror/qpd with some small desktop speakers producing white noise from http://www.simplynoise.com. Data shown below.
I can't believe that SR785 can have such a low input noise level (<1nV/rtHz). Review your calibration again.
It is also described in the manual that SR560 typically has the input noise level of 4nV/rtHz, although this number depends on which gain you use.
There was an earthquake around 2:30 am. Now all the mirrors except SRM are damped.