Yesterday we could lock the Michelson again without much problems (elog to come). The high frequency is limited by laser intensity noise and acoustic noise.
Today I’d like to try to close the chamber with the bell jar, even though we can’t pump down. We’ll route the cables through the aluminum foil that closes the flanges.
The goals are:
- to see if we can reduce air currents (low frequency motions) and improve acoustic noise
- more important, to see how the table moves with the bell jar and if we can keep a good Michelson alignment when we close
In particular, if the second point turns out to be critical, we could install the Crackle1 pico motors to the left side Michelson arm folding mirror.
More things to do:
- measure intensity noise on each PD blocking the other arm (maybe scaling linearly the input power, just to be sure that we are seeing intensity noise and not PD dark noise or electronic noise), estimate the coupling to the Michelson sensitivity (what is the maximum residual RMS motion of the Michelson we can tolerate?)
- measure the power on each PD, so we can estimate the shot noise level
- measure the photodiode signal electronic noise (which is likely ADC noise). Can we improve things with a whitening for the moment being, while we wait for the new photodiodes?
- yesterday I clamped an accelerometer on top of the support structure. We should use it to estimate the contribution of seismic noise to the Michelson displacement signal. Maybe we can try to shake the table and see if we can measure a seismic noise TF, to see if the suspension is working properly.
- more or less related, we should measure accurately the resonance of the two test blades, and see how different they are.
- finally, we should compute a projection of the suspension and blocks damping noise
It has been observed during the last week that the suspension OSEM signals tend to drift. Here is a trend of all OSEMs during last night. I smoothed the traces since Saikanth was performing some swept sine injections (maybe with too large amplitude...)
So it appears that the suspension OSEMs drifted quite a lot over the whole night, some of them going almost out of the linear range. However, the block OSEM signals didn't change significantly: this would indicate that the breadboard remained vertical, since the blocks haven't moved with respect to the breadboard. The only way to reconcile these two pictures is to assume that the breadboard translated, but didn't rotate over the night. Which would make sense, assuming the table tilted a bit: the breadboard always stays vertical (gravity wins) but it will shift a bit laterally.
I used Saikanth's sensing matrix (eq. 6 of his second report) to reconstruct the motion in translation and angles:
This is not exactly as expected, but close. It turns out that roll and yaw stayed constant, while pitch changed quite a lot. At the same time the breadboard mostly translated in Y. Clearly what the suspension OSEM measure is the tilt and translation of the breadboard with respect to the support structure, which also tilts with the table. So the plot above seems to indicate that we had a tilt of the optical table mostly in the pitch direction.
Just for fun, here is a comparison of the best noise spectrum of Crackle1 (in vacuum), and the latest one from Crackle2, still in air and with temporary feedthough.
Today we had problem in damping the suspension. We saw that both B and D loop were oscillating at high frequency. After a lot of investigations, we measured the plant transfer function of the B actuation, and found a very surprising response like a simple resonance at 55 Hz. Since we couldn't figure out the origin of this, we lifted the bell jar out and checked that nothing was touching. As a last resort, we checked the B magnet and found it very loose: just touching it was enough to detach it.
So, that's what happens when a magnet is loose.
I once had the similar magnet issue ten years ago at TAMA. At the time, a loose magnet actually produced a lot of crackling noise.
Attachment1: 4.5Hz actuation on a coil (lower curve), DARM error (upper curve). At a particular pulling force of that magnet, a glitch happens.
Attachment2: The sensitivity curve with a loose magnet. The magnet produced a huge upconversion noise with resonance at 150Hz and 4kHz.
Update for what followed:
In process of finding out what the problem with B was, we removed OSEMs one by one to see if the peak around 55Hz persisted. This is because we suspected some magnet was touching the inside of an OSEM. However, we did realize that magnet B was loose, and we fixed it.
In our process of recentering, coil F got broken, and we had to replace OSEM F with a new one. After recentering all 6 OSEM, we tried to turn on damping again, but this time, the sign of B seemed to be wrong, and the loop became unstable. This was unexpected and strage, because we hadn't messed with B like we did with F, and the sign could not have changed all of a sudden. (It is possible, though, that it was because we plugged the terminals in the reverse way when we checked the coil driver circuit...)
So, that's what happens when a magnet is loose.
The following information will be useful to properly compute the moments of inertia and the position of the center of mass of the suspended breadboard.
I stripped the bread board Solidworks model of everything, except the breadboard (with H shaped reinforcement on the back), the OSEMs with supports and the clamps. Blocks are removed (for some reason Solidworks is still showing the left block in the drawing, but it'snot there since the X position of the center of mass is 0, so the system is symmetric).
The attached figure shows all the data reconstructed by Solidworks. Here are the main informations (coordinates are with respect of breadboard geometric center, front surface, z axis is downward, x to the right, y out of front)
Total mass: 13.96 kg
Center of mass position: X = 0.00 mm, Y = 5.73 mm, Z = -16.36 mm
Moments of inertia with respect to coordinate origin: Ixx = 209000, Iyy = 491000, Izz = 304000 kg mm^2
[Xiaoyue, Eric, Gabriele]
Presently we have four cables coming out of the chamber.
The pinout of the 26 pins cables are the following
Pin 1 coil common ground
Pins 2-7 coil signals
Pins 8-9 LED power supplies
Pin 10 OSEM PD common ground
Pin 11-16 OSEM signals
Pin 17-19 Thorlabs photodiodes power supplies
Pin 20 Thorlabs photodiodes common ground
Pin 21-22 Thorlabs photodiode signals (21 AP, 22 SP)
Pin 23-26 Translation stage
We are going to redistribute this on the three DB25 connectors in the feedthough and on one DB9:
DB25_1: Cable 1 pins 1-16 (blocks OSEMs)
DB25_2: Cable 2 pins 1-16 (suspension OSEMs)
DB25_3: Cable 1 pins 23-26 (translation stage) and Cable 3 (picomotors)
DB9_1: Cable 1 pins 17-22 (photodiodes)
The aurolocker has been failing for the last ~9 hours, so at 3:05pm I disabled it. Maybe the Michelson is too misaligned to acquire the lock.
Last night we ran into the situation where we could not connect to NDS server anymore.
After a old-fashioned reboot, CyMAC showed a warning sign: “this computer has only 0 bytes disk space remaining". Eric came in to help wipe old frames, releasing ~13% free space on the disk. We also changed the wipe time from 6 am everyday to every 6 hours, and we tuned the percent of data to keep from 85 down to 80%.
With enough free space we tried connecting to NDS again but found IOP process overloaded once in a while, like reported before with the BIOS enabled serial port (entry 1105). Finally we found it's again the BIOS setting problem. After changing the "SERIAL ATTRIBUTION" setting from "ON" to "SOL" (referring to LIGO wiki) we no longer have observable overloading problem. Now the system is running as normal, but we lost all medm parameters.
Added Suspension TF measurement templates and script here. Gabriele told me he will take care of moving it to the appropriate folder on the workstation/cymac2. These are the most important templates that I leave behind.
I was looking for MATLAB scripts on my PC to be put in documentation, but I realized that MOST (apart from what I've already added to LIGOShare) of those are too specific to the trials I was doing, the formats I was using, etc. I felt that they won't be any useful to anybody else; but there's one script that could be useful, and it is generic enough to be modified for multiple purposes. Uploaded it here; these don't have to be moved anywhere else since these are just MATLAB scripts. Most of the other functions/wrapper I had built earlier are already on Dropbox in the MATLAB library here.
Note: green items are completed
2015-08-06 Xiaoyue: added 5 seconds sleep after lock is acquired to wait for control signal transient: autolocker takes the trasient as a lock on wrong fringes.
KR2-BBOARD_LOCK_SERV_OUT transient when lock is aquired
2015-08-19 Gabriele: changed idle state to unlocked, set apart reset_function() from reset state: every time the autolocker is disabled, it will break lock, reset the lock filters and histories, reset PD from whitened to unwhitened signals, and switch on all damping loops. We assume everytime we disable the lock, we want an unlocked, damped state.
The attached figure shows the trend of the suspension shadow sensor signals, calibrated in microns, during most of yesterday and this morning. At about time -2.5 hours I started realigning and recentering the suspension OSEMs, so you can see that right before time 0 hours the signals are all around zero. At time 0 hours we put back the bell jar an started the pump down. There is large motion of the signals, that's over in basically one hour. Some of them moved really far from zero. After the initial fast change, the trend is rather slow. At about time +6 Hours Xiaoyue pumped the legs, and the signals moved to a different value, not necesserely better.
After that the trend is quite slow, and probably linked to daily temperature variations.
I suggest we don't pump the legs anymore for some time, and see how the signals settle down. I had the impression in the past that when we leave the legs alone, their pressure drops from 6 bar down to about 5-5.5 and stay stable there. This pressure is good for us. It's also important to understand if the trend we see is a constant drift of the legs, or simply due to daily temperature changes.
Vent started at 1:45pm LT and done in 5 minutes. Attached trends of the suspension OSEM signals, not calibrated. The shift is not very large, so most of the motion we saw yesterday was due to the belljar weight.
At 2:10 LT we removed the belljar. As visible in the trends, we didn;t see large changes in the signals as the one we say yesterday after putting the bell jar on and pumping.
Venting started at 1:15pm LT. Chamber open after 10 minutes.
Cleaned all optics.
Attached plot shows that the suspension and the blocks are free.
Chamber closed at 3:00pm LT.
Pumping started at 3:03pm LT.
Pump stopped at 4:45pm LT. Pressure is 234 mTorr.
It turned out that all block OSEM LEDs are off. Maybe I disconnected somthing while cleaning the chamber floor. However, even without block damping, we can lock. Low frequency sensitivity is not great, but at least the scattered light is no more there.
At 5:15pm LT I left the interferomter locked, with autolocker active.
Here are some drawings of the new roll-decoupling stage for the suspension that we're going to build soon.
All coordinates are relative to the front surface of the breadboard, origin is on the lower right corner (looking at the optics side). X increases from right to left, Y increases moving away from the board toward the observer, Z increases going up. All dimensions in millimeters. Uncertaints are of few millimiters.
* Estimated from the suspension point position and the roll resonant frequency f0 = 0.57 Hz. From Solidworks the total mass is about 27 kg and the moment of inertia is 0.88 kg m^3. So the suspension point is 43 mm above the center of mass.
Block suspension wires 106 mm
From board to Roll Decoupling Stage (RDS) 77 mm
From RDS to Blades: Left 96 mm, Right 83 mm
From Intermediate stage (IS) to blades: Front 122 mm, Back 129 mm, Right 128 mm, Left 125 mm
For future reference, here is the datasheet of the photodiodes we are using: C30665
The wires are:
white = ground
blue = anode
green = cathode
Last night all locks were lost after about 1 hour, due to a 4.7 Hz instability slowly rising. This might be caused by the new actuation splitting scheme.
I measured about 0.3 mW impinging on the QPD. This gives a SUM signal of about 9 V.
However, the numbers do not check out. If I trust Koji's elog and the QPD datasheet I have
SUM = 0.3 mW x 0.05 A/W (responsivity at 1064 nm) x 10e3 (transimpedance) = 150 mV
Forgetting about this, with 0.3 mW total I get about 9/4 = 2.25 V for each quadrant. So I can increase the power by a factor 6-7 more (2 mW) before I saturate the single quadrants (the sum will be saturated, but that's not important). I increased th power on the QPD up to about 1mW and saw no saturation in the X and Y signals.
With the present input power configuration, there are about 0.5 mW impinging on the diode. So we could increase by a factor about 4 more the power on the PD.
I think a good power would be 1 mW on the QPD.
There were a couple of SR560 in the lab which I notice have been unplugged for months. Since this slowly degrades the batteries and causes us to spend money/time to replace them, I have moved these to the EE shop and put them on charge.
please plug these in whenever they are not in use
Progress: the board and components arrived and assembled. Some obvious mistakes are fixed on the next version in Altium.
Next: how to test the board? i.e. How to connect the test instruments (such as spectrum analyzer, DC power supply) to the board? We need connector converters (from BNC to headers female & from BNC to 9 pin D shape male). Or do we have better ways to test it?
Note: Altium footprints for WIMA capacitors are created. Altium test point component is created. These might be useful in the future.
Progress: The reason why the board from oshpark did not work is found. The board has 6 layers, but Oshpark only make 2 or 4 layer boards. They just ignored two layers (the two ground layers) so there is no ground at all on the board.
Some known issues is fixed in the new board (capacitor footprint, connector in the wrong direction). The new board will arrive next Wednesday.
Some good quality connectors are made - next board will be ready to test once arrived.
Next: I plan to put other components into Altium by Wednesday.
We ordered the board from Screaming Circuits and chose to provide the component ourselves. However, the parcel we ordered from Verical was lost by Fedex on its way to Screaming Circuits. The original delivery date was delay from late May to June 13.
Once the board arrives, we will test the board - TF, noise etc. Any others?
I think I shorted somewhere near the RTN testpoint on the board today while testing it. I saw some sparks. After that the board becomes non-responsive - it is not responding to whatever signal I send in. I will use another board and go on with testing.
I placed the two beam profilers with the two laptops and chargers right inside the Crackle lab, as requested by Paco.
Note: Please don't try to connect these old Windows to the network. We just extract the data via USB etc, and that's all the connection we allow.
Shruti took back the beam profilers today AM to Cryo.
Shruti: returned to Gabriele's office
Today entered lab ~ 09:00. Over the weekend I coded a PySerial wrapper for the thorlabs MDT694B single channel piezo controller. I spent some time testing and debugging the code but it now works fine (tested on Linux, python=3.8.6 and PySerial=3.4-4). The wrapper refers to the manual available here. The code is available in the labutils repo
Wow! This is really cool! I didn't realize that this small box has such many remote capabilities.
We have this piezo controller everywhere in the labs and your code gives us a lot of opportunities to implement process automation.
Borrowed 1 (new focus) broadband EOM from CTN for temporary use in Crackle (2 um OPO exp)
On Monday, tested a 1998 (Rev. 0) RFPD originally found in Crackle (serial #010). Looks like it was first resonant at 24.493 MHz, but was later tuned for 14.75 MHz. I used the AG4395A network analyzer in CTN following the procedure in the previous ELOG post, splitting R output into the test input of the RFPD. Driving at up to -10dBm, couldn't see any resonant feature in the TF below 150 MHz. Tuning the inductor L1 made no difference. The regulator (U3 and U4 near bottom right in picture below) outputs were nominal.
I borrowed a flat response (DC to 125 MHz) PD from CTN lab (New Focus 1811) along with its power supply for short term use.
Below are some photos of the aformentioned RFPD. I added some kapton to keep dust off the PD.
QIL elog entry: QIL/2524
Photos, please, because we don't allow a free-rolling cylinder in a lab.
Borrow both beam profilers and laptops from WB 264A.
- Noticed that the cavity transmission peaks @ 1064 nm were much wider than originally estimated by the dopo cavity design notebook suggesting a lower Finesse. So using the PDH error signal, and knowing the EOM sidebands are at 36 MHz estimated the current DOPO cavity linewidth to be 19.5 MHz, well in excess of the target 10.4 MHz.
- Updated the crystal AR coating specs from Raicol (R < 0.3% @ 1064/2128), but more importantly, I included the absorption coefficient of KTP, alpha=0.005/cm (often quoted as < 0.01 / cm) into the roundtrip loss and the design now gives 17.97 MHz. So, given the uncertainty in the absorption coefficient of the NL crystal, and all the coatings in the experiment, this adjustment might be enough to explain this observation.
Drew some new mounting scheme for the DOPO cavity; main revisions with respect to the current mount are -->
Attachment 1 illustrates the design; shows three views of the same assembly.
Concerns: mechanical noise from side mounted mirrors ... for this, there could be a solid piece which makes a rigid connection between the two mirrors (that's why they are upside down) and perhaps between the two tall posts (so S-shaped as viewed from the top)? Still working on this.
I am suspicious that this is not the true tilt noise, but instead the in-the-loop spectrum as before. Is this corrected for the loop shape an the tiltmeter's mechanical response?
I will attach the data from this elog (Wed Sep 07):
->micerror090502.data: Michelson error signal (Through a high pass filter:10Hz, gain=1000.)
->spenoise0905.data: The noise of spectrum analyzer (The input connects to ground through 50 ohm.)
->sr5noise0905.data: The noise of SR560 (high pass filter: 10Hz, gain=1000. The input connects to ground through 50 ohm. The output connects to spectrum analyzer.)
->gnuspe.plt: Gnuplot script file
In these data files, the first sequence is frequency, and the second sequence is the output voltage.
->michnoisem.data: Michelson error signal.
->pdnoisem.data: The signal from PD with laser off.
->lasernoisem.data: The intensity noise of laser.
->gnuspe.plt: Gnuplot script file
In these data files, the first sequence is frequency, the second sequence is the calibrated value [mater], the third sequence is the value before calibration [volt], and the fourth sequence is just the number.
Here I make an estimate of the gas damping for the maglev.
The damping rate:
I use the formula given by Cavalleri et al. presented in the article titled Gas damping force noise on a macroscopic test body in an infinite gas reservoir [PLA 374, 3365–3369 (2010)]. According to Eq. (18) in their paper, the viscous damping coefficient for a rigid body is given by
Here p≈10^5Pa is the air pressure, S is the surface area of the rigid body (≈ 0.05m^2 the floating plate in our case), m_0≈28 is the air molecular mass, T≈273K is the environmental temperature. Plug in the number, we get
Given mass of the floating plate to be around 0.56 kg, we get mechanical damping rate to be:
which is very large. This means the floating plate is an strongly over-damped oscillator if the resonant frequency is around the design value of 0.1Hz. To have a quality factor of even order of unity, we need to pump down by one hundredth of the air pressure.
The displacement noise:
We can use the fluctuation-dissipation theorem to estimate the displacement noise. The force spectrum is given by
The displacement noise around the mechanical resonant frequency reads:
Given a resonant frequency to be around 0.1 Hz, we have
This is smaller than the seismic noise which is approximately three orders of magnitude higher.
If I hold up a piece of paper in the lab, I can see it move because of the air currents. Since the maglev and a piece of paper have roughly the same resonant frequency, I think your estimate is not covering the whole picture.
I made an estimate for frequency noise requirement for a laser that can be used in crackle experiment. With some assumptions, I came up with df = 3x102 [Hz/rtHz ] for the requirement.
The two beams from both arms are recombined at the output port of a Michelson interferometer. If it is operated at dark port, the output signal will be linear with the differential length between the two arms.
some assumptions in the calculation:
This will be a requirement for the planned ecdl.
Is a HeNe laser good enough? I'm not sure about HeNe frequency noise level, and I haven't found it in literature that much. I checked here,see fig 5, HeNe f noise is not so bad compared to NPRO noise (10^4 /f Hz/rtHz).This feels a bit counter intuitive. But if it is real, it should be ok for the measurement around 100 Hz and above.
The hall effect sensor is quite noisy, and I am trying to find where the noise comes from. The first I tried today is to measure the power spectrum and coherence among three hall effect sensors (in the vertical direction). Here is the result:
(the unit for the power spectrum density is in digital volt per root hertz.)
I do not quite understand why there is almost no coherence (apart from the 60Hz power line), even though the power spectra are almost identical among these sensors.
Can someone shed some light where the issue is? Is the noise non-stationary or what?
--------Another measurement with fewer average---------------------
It seems that when the number of average is small, the coherence is large, an indication of non-stationary?
I'm having trouble getting good TF estimates from Wiener filtering, I think because the ranges of high coherence are kind of narrow. Additionally, given that the displacement spectra of the table and of my ifo looked like the stack wasn't doing much, I was suspicious that my inattention to cabling led to a mechanical short of the stack.
So: I ripped everything out and put the accelerometers directly on the stacks!
Here are some displacement spectra, and a vertical "TF"s of the stacks obtained by dividing the noise spectra.
In the 1 plate case, I had the chamber lid open, which led to the broad peak at ~120 Hz.
In any case, I see peaks at ~9Hz And ~24Hz and more isolation that I was getting before. I'm going to put things back together much more carefully.