Should measure the S-matrix using a bi-directional coupler.

[Paco, Radhika]

Today we tried to pick up from [1920] by repeating the sweep measurements across RF frequency, at 3 dBm (max power). We noticed that the 0th order signal would dip around the expected value, consistent with the plot in [1920]. However, there was no signal from the 1st order. Clearly diffraction was occurring as seen by the dip in 0th order, but nothing was coming out of the 1st order port. We spent some time debugging by swapping the photodetector inputs / playing with the PD gains / performing power cycles, but got no insight into the issue. 

We suspected the 1st order fiber coming out of the AOM might be damaged, since it loops around fairly tightly. After giving it more slack, we still saw no signal. We wanted to test the fiber, so we took an unused output of the 50-50 beamsplitter and fed it into the 1st order port, effectively running the AOM in reverse. We hooked up the input and 0th order ports to the photodiodes and did not observe any signal. From here we were more convinced that the 1st order fiber may have seen some damage. 

For next steps, we can still use the existing fiber setup to take measurements of relative intensity noise (RIN), using the 0th order output of the AOM. I plan to do this in the next few days. Meanwhile, Paco is looking into ordering parts for a free space setup. We found a free-space AOM at 1064nm that seems promising, and we will work to transition the setup accordingly. 

I took a relative intensity noise (RIN) measurement of the ECDL, by feeding the 0th order output of the AOM to the SR785. The RF power driving the AOM was set to 0 dBm. The RIN at 1 Hz is about 3x10^-5, which is consistent with informal measurements we took on 08/13. From my understanding this noise looks pretty low, which is good. I will consult with Paco and add more discussion or conclusions, if any.

[Paco,  Radhika]

Uninstalled the fiber AOM and temporarily removed the third fiber 2x2 port beamsplitter. We are now using this free-space AOM. Then, I managed to launch one of the outputs of the second fiber beamsplitter into free space using a F220APC-1550 fixed collimator. The beam clears the  AOM aperture nicely and lands on the other side.

This AOM operates at a RF frequency of 35 MHz, so we set up a sweep on the Marconi to cover a window of 35 MHz +- 15 MHz. Using an IR detector card, we looked for evidence of 1st-order diffraction (from the setup geometry, the 1st order beam should have been visibly discernable). We first scanned the AOM across yaw but did not notice diffraction. Then, Paco lowered the height of the fixed collimator and we repeated scanning across yaw. We eventually saw the beam "jump" - diffraction! We adjusted yaw until we recovered both 0th and 1st order beams, at 50/50 intensity.

In summary, the free-space AOM works and we have managed to see 1st order diffraction. Next steps will be to quantitatively measure this diffraction while sweeping across RF frequency and power.

[Paco, Radhika]

We had previously noticed that the ECDL laser power seemed weaker compared to when we originally set it up and tested it. Today Paco opened it up and tweaked the grating inside to obtain a max power of 3 mW. This way, we could better resolve the 0th and 1st order beams coming out of the AOM.

Since we don't yet have a lens to send the collimated 1st-order beam to fiber, we connected a power meter to detect the beam and hooked it up to the oscilloscope. We noted peak diffraction at around 38.5 MHz (rough estimate). Using the inverse relationship between laser wavelength and the RF frequency , and the fact that the AOM is designed to operate at 1550 nm at 35 MHz, we calculated that the ECDL wavelength should be ~1409 nm. Of course this is a rough estimation, but it is a quick validation that we are indeed operating near 1418 nm. 

[Paco, Radhika]

Last Friday we received a new lens to direct the AOM 1st-order beam from free space into a fiber cable. We mounted the lens and connected a fiber cable into the photodiode, and tried to align the lens and see a jump in the oscilloscope. We were not able to do so and wrapped up for the day.

Today we continued aligning the lens with the fine adjustment on the mount, and eventually saw signal on the scope! Hooray, done with free space. We then prepared for eventually taking a heterodyne beat note measurement and hooked up the appropriate inputs/outputs to the beamsplitters. We added in the 50-50 beamsplitter that takes in the 1st order diffracted beam along with the beam from the delay line as inputs. We passed one of the outputs to the photodiode and had to retweak the freespace-to-fiber lens until we recovered signal on the scope, and we saw the beatnote signal.

Next, while Paco is out of town I will continue to work towards making a frequency noise measurement. We made a roadmap today:

I will demodulate the beat note using a mixer and a 35 MHz LO sourced from the Marconi. The result will be a 2f cosine term, along with a much lower frequency term which encloses the frequency noise information. This will be passed through a low-pass filter to get rid of the first high-frequency term. The remaining time-domain signal will be passed to the SR785 to obtain a spectra of the frequency noise. Calibration will need to be performed to obtain the right units for the spectra, Hz²/Hz (or Hz/rtHz). 

Attachment 1 is a diagram of the current setup for measuring ECDL frequency noise. Since the last update, I have fed the beat note signal to a mixer, using a 35 MHz LO sourced from the Marconi. The resulting demodulated signal is passed to a low-pass filter, removing the 2f sinusoidal term (any trace of the frequency difference) and leaving behind a low-frequency term containing frequency noise information of the original beam (accumulated over the length of delay line).

I took spectra of the resulting signal using the SR785 (Attachment 2). Note that these units are still in V/rtHz, since the signal has not been calibrated to the appropriate units for frequency noise, Hz/rtHz. Finding the calibration term will involve study of delay line frequency discrimination. 

[Paco, Radhika]

Beatnote recovery

Restarted ECDL characterization last Friday. After some lab cleanup, and beatnote amplitude optimization we borrowed Moku Lab from Cryo lab to fast-track phase noise measurements. Attachment #1 shows a sketch of our delayed self-heterodyne interferometer. The Marconi 2023A feeds +7 dBm to a  ZHA-3A amplfier which shifts the frequency of the laser in one of the arms using a free space AOM. The first order is coupled back into a fiber beamsplitter to interfere with a 10 m delay line beam.

Improved beatnote detection

The 38.5 MHz beatnote was barely detectable before when using PDA20CS2 because at unity (lowest) gain stage, the bandwidth was only 11 MHz... We instead switched to an FPD310-FC-NIR type which has a more adequate high-frequency response. Attachment #2 shows the beatnote power spectrum taken with Moku Lab spectrum analyzer. The two vertical lines indicate (1) the heterodyne beatnote frequency and (2) the "free spectral range" indicating the actual delay in the MZ arms, which is calibrated to  = 9.73 m (using 1.46 for n, the fused silica fiber index).

Phase meter and freq noise calibration

We then tried using the phase meter application on the Moku. The internal PLL automatically detected the 38.499 MHz center frequency and produced an unwrapped RF phase timeseries (e.g. shown in Attachment #3). The MZ interferometer gives an AC signal

oscillating at , i.e. the angular beatnote frequency. The delay (calibrated above) characterizes the response of the MZ relating the RF phase noise spectrum to the optical phase noise spectrum. The RF phase obtained through the phase meter has a fourier transform

So the optical phase spectral density is related to the rf phase spectral density by a transfer function   Then, the RF & optical phase power spectral densities are related by   or

Then, because the instantaneous laser frequency is ,  in fourier domain  the frequency and phase PSDs are related by the magnitude square of this transfer function like

Following this prescription, we compute an estimate for the frequency noise ASD (square root of the PSD) shown in Attachment #4. The frequency noise estimated by this method has several contributions and *does not* necessarily represent the free-running ECDL frequency noise.

Next steps

• Noise budgeting (experiment)
• Control loop (open/closed) models

We want to have a simple low noise circuit to drive the LED. Our plan is to use the AD587 followed by a filter/buffer.

Requirements:

from 0.1-10 Hz, produce less RIN in the LED light than shot noise by a factor of 3.

With 35 mA of LED drive, we get ~35 uA of photocurrent (no magnet/flag). The shot noise of 35 uA is ~3.5 pA/rHz.

So the RIN from shot noise is 1e-7. So we shoot for a RIN of 3e-8 from the LED.

The AD587 voltage reference has a relative noise of 1e-7 at 0.1 under very good conditions (perhaps our vacuum system will be so kind). So we have to get a factor of 3 filtration at 0.1 Hz.

The following circuit should it for us: its a 2nd order Butterworth implemented in a Sallen-Key configuration. The noise is reasonable and the cutoff frequency is so low (0.03 Hz) because of the latest in capacitor technology.

We can buy metal poly caps which are as large as 47uF and have a reasonable physical size and tolerance and noise.

On page 2 of the plot you can see that the noise performance of this filter is limited by the input voltage noise of the FET opamp (op1) (AD743 - soon to be obsolete). The noise of the BUF634 (op2) is insignificant in this configuration. What we really need to make this good is a part with just as good of an input current noise spec as the AD743 but 3x less voltage noise at 0.1 Hz. I offer one cookie to whomever can find an opamp that fits those parameters.

These images show the circuit diagram (left) and the proto setup (right):

update: added a 230 Ohm series resistor between the BUF634 output and the LED to step the voltage down to the 1.7V that the LED wants.

I found a Quad Opamp OP497 (neither dual nor single!), but this is not enough to expel AD743.
Dis-continuation of OP497 is also close except for one SMD package.

AD743 (reference):
LF Voltage Noise: 0.38 V pp, 0.1 Hz to 10 Hz
Voltage Noise: 2.9 nV/√Hz @ 10 kHz
Current Noise: 6.9 fA/√Hz @ 1 kHz

OP497:
LF Voltage Noise: 0.3 V pp, 0.1 Hz to 10 Hz
Voltage Noise: 15 nV/√Hz @ 1kHz
Current Noise: 5 fA/√Hz @ 1kHz

Not having much luck. I found the LT1028, which has 10x better low-frequency voltage noise (35 nVpp, 0.1 Hz to 10 Hz), but its current noise is worse by a ridiculous factor of 1000:

The situation is well illustrated in the following application note of Analog Devices:

Low Noise Amplifier Selection Guide for Optimal Noise Performance

Even though the graph is created for 1kHz, it is very clear that AD743
has superb performance for high source impedance purposes:
combination of low current noise and low voltage noise.

If the source impedance of Rana's circuit (400kOhm@DC) are reduced to 20K or so,
OP-27 type OPamp can come into the scope. However this means we need to use 10 times
larger capacitors. This is almost impossible for now, though innovation on the caps
can change the situation.

LT1028 is an AD797 type opamp. This works greatly with the smaller source impedance.

 Last night, I was going to retake the noise measurement with the added elements that Rana suggested, but instead I spent a ridiculous amount of time trying to figure out what is going on with my Sallen-Key filter. I now know a lot more about their limitations, but am still at a loss as to what is happening in this case. The problem is that no one seems to be using a corner frequency anywhere near this low (at least not anyone trying to explain these filters). The following is a comparison of an ideal 2nd-order Butterworth filter and a real one using an LT1464.

The filter behaves as expected a ways past the corner frequency, rolling off at 40 dB/decade. As the signal increases in frequency, the capacitors' impedances decrease, until (at point 'b'), they fall below the output impedance of the amp, causing the response to climb at 40 dB/decade. This happens for a short while, until the unity-gain bandwidth frequency (~ 1-10 MHz, 4 MHz for the AD743) of the op amp is reached, and the filter can attenuate no more ('c'), so the response flattens out to 0 dB/decade.

Different component values affect the high-frequency behavior of the filter, as shown below.

This makes sense, since with smaller capacitors it takes a higher frequency to fall below the output impedance of the amp. In any case, though, the final flatline always happens near the UGB frequency. The following is a plot of the transfer functions I measured (also in last post). I did not change the C values--only the R's--so the corner frequency is different in each case. What I observe is some R-dependent maximum attenuation, which sets on well before the 4-MHz UGB frequency of the AD743. The strangest part is that for small enough R this maximum "attenuation" is actually a positive gain.

I suppose it is not a huge deal, as I can increase the stopband attenuation as R while only increasing the Johnson noise as 2 * sqrt(R), but it would be nice to get some insight into what 's going on.

NOTE: While it appears that the high-frequency flatline in the other plots occurs for a different reason, it still seems to be R-dependent. I could not find any explanation for what determines this asymptotic behavior.

 The SR785 I am using for the AOSEM noise measurements (the one that was in the TCS lab) doesn't seem to want to boot up all the way. After sitting at the "Backup OK" screen for ~30 secs, a dialog box pops up reading "WaitDone Error", after which the machine reboots. This continues forever.

I remember this having happened when I first liberated it from the TCS lab a few weeks ago. I turned the thing off for a while and it eventually worked just fine. I tried the same thing now and it didn't work. I am going to give it another go in the morning.

Has anyone experienced this error before?

Same thing happened when I went in this morning. I left it for a while (on this time) and it seems to be working. We might want to have this machine looked at.

 This is some data measured in the ATF (by Zach) for 2 fixed mirrors on the bench, and gives some idea of what mechanical vibration noise you can expect.  You'll need to scale this for the number of mirrors in your own setup.  You can add this to your noise budget by including the following lines in your Matlab code:

load gyro_single-arm_noise_calibrated.txt;

f_mech_noise = gyro_single_arm_noise_calibrated(:,1); % frequency vector for plotting mechanical noise

SA_x_noise = gyro_single_arm_noise_calibrated(:,2); % gyro single-arm noise calibrated to meters

In Elog 256, we showed that the 1" magnets have a mean of 106 Gauss with a variance of 12.8 Gauss.
The question would be if we want to have an imbalance of 1% how many magnets we need to buy.Here
Here we will make an estimate by assuming that the distribution of strength is Gaussian---a reasonable assumption
given what we have measured. The distribution would simply be

with and . Through numerical integration, one can find out the probability content for the
magnet strength falling into [105, 107] (within the 1% error around the mean)  is 0.062. Therefore, if we want
to have 4 matched magnets that have 1% error around the mean, the number of magnets we need to order is
approximately 4/0.062 = 64. Since we have already got 12, extra 50 would be enough (the quantity that we order
today), unless we are not lucky.

Steve: I asked  K&J  Magnetics to select matched pairs of 4, but they declined.

  Mac OSX Lion came out pretty recently and COMSOL 4.2 [at the time of the writing] does not successfully install on these OSes. There's two issues in general - the first issue is that Lion changed the way some of the paths work (that COMSOL depends on) and COMSOL will throw seemingly unrelated errors in trying to start up.

I want to include laser frequency noise in my noise budget, so we discussed making a very asymmetric Michelson in yesterday's meeting, to try and make a measurement of the laser I'm using. I sat down to do the calculation of relating the PD voltage PSD to frequency noise, but tripped up a bit. Looked for references, and couldn't find anything that didn't dive straight into optical cavities, etc. I realized that a Michelson is essentially a delay line, and found an old HP doc called "Phase Noise Characterization of Microwave Oscillators" which talks about delay lines.

The key difference was that I was initially modeling frequency noise as f(t)=f0 + df(t), whereas using a field that oscillates as sin(2 pi f t + d phi (t)) is much more fruitful. 

I translated the math into things I'm used to thinking about and wrote a quick note which I'm attaching here. Once we get the lab cleaned up after the hold drilling, I'm going to set up a measurement to quantify the frequency noise of my laser. 

 Series resonance still there, but I've gotten a lock with an RMS only a bit higher than my previous best . UGF around 130Hz. 

Was able to keep the Michelson locked for 20 minutes, so I'm making a loop TF measurement, and then setting it up to run as long as it can overnight. Here's a (totally uncalibrated) spectrum! 

I've turned the PD gains up by 10dB since ELOG 677, which is why the RMS seems WAY higher, when in fact it is only somewhat higher. 

Assuming the thing will stay locked for an appreciable amount of time, many things will follow tomorrow....

After moving to the shorter legs, we had to go through a lot of iterations to get the setup to working stage; As far as the suspension system goes, there were problems with the alignment: positioning and centering of the suspension and block OSEM. We kept knocking off magnets once in a while, and some times the intermediate mass stage itself was not leveled. The following steps, in the same order, were and should be followed in future for hassle-free alignment and recentering.

1. First, move all OSEMs off the mounts so that there's no knocking off while the breadboard moves. That is, no magnet should be inside of the OSEM.
2. Start with filling pressure in all the table legs to 6bar. Note that this only keeps the table parallel to the floor, but NOT perpendicular to gravity. But we will work with this.
3. Obviously, the intermediate mass stage is NOT going to be leveled (i.e. perpendicular to gravity). This can be easily verified using a spirit (bubble) level. The task then is to adjust the tilts of the suspension blades such that the bubble is centered in two mutually perpendicular directions. This ensures that the whole of the setup is nearly perpendicular to gravity even though the table is not.
4. One can now move on to recentering all OSEMs. In the latest round of recentering, we had knocked off magnets while trying to recenter. The process would become simple if one did the following:
   • Align and recenter suspension OSEM first, with the blocks free. It is easier to move the OSEM mount itself than to remove and reposition the magnet!
   • In case of any magnet falling off, use superfast glue - one that dries up quickly. Also, wherever possible, a smart method described here can be put to use to recenter it perfectly.
   • While aligning the block OSEMs, extra care must be taken not to shake the breadboard too much because that would knock off the suspension magnets. 
   • As usual, all shadow sensor output counts must be around 8000.

Currently, we have a working "local" damping feedback. This works, and we know it. And so, this forms our "backup plan" while we transition towards a new and better damping system. Especially while attempting to take TF measurements with driving matrix implemented, one must ensure that all necessary changes/modifications to the interface are done before initiating measurements. This post talks about the things to be done in order to start such TF measurements, and things to be done after such measurements are done. It assumes that the user starts with "local" damping turned on and working.

1. Starting from when "local" damping is turned ON, the first step is to turn OFF "local" damping - both suspension and block damping. This can be done by opening the SUSP_CTRL_X (etc.) medm screens and turning OFF outputs.
2. After outputs are turned OFF, inputs and all filters are to be turned OFF. The gain in each case is to be set to 1.
3. For some d.o.f., it might happen that a positive offset might give a negative shift in the sensed displacement/rotation. In such a case, the sign of the gain must be flipped.
4. Next, driving (and sensing) matrices are to be changed from identity to the desired ones.
5. While using DTT/AWG to measure/excite, care must be taken to use SUSP_CTRL_X_EXC (and so on) for excitation, SUSP_CTRL_X_IN1 (and so on) for sensing.
6. Care must be taken while choosing amplitudes of excitation: these are no longer coil amplitudes. One might want to look up the driving matrix, till one gets used to numbers in this domain.
7. Start measurements.

Once measurements are done:

1. First, before modifying anything else, outputs in SUSP_CTRL_X (and so on) screens are to be turned OFF.
2. Then, gains can be brought back to earlier set values, and input and filters can be turned ON.
3. Driving (and sensing too, if needed) matrix should be set to identity.
4. Only after that can "local" damping be turned ON again.

If I find time before I leave, I will write a script to change all of this by one click. That can save some time, but more importantly: it is safer. Often, it can happen that one turns ON "local" damping without changing all settings back properly. For instance, one might turn ON "local" damping without changing the driving matrix back to identity; this makes the breadboard shake like crazy, and potentially knock off magets! The motivation, hence, is to make it easier and safer.

Our work today was relatively easy since I was able to properly clamp down the breadboard efficiently. In this configuration it is almost rigidly connected to ground. Here is the procedure:

1. get all magnets out of the OSEMs
2. secure the blocks with the newly installed stops
3. secure the bottom of the breadboard with the two screws
4. rest the intermediate stage on the four stops
5. add two blocks of rubber per side, as shown in the figure. One block sits between the side of the breadboard and the support structure. The other block sits behind the breadboard, between the back and the transverse arm. The safety stops installed in the support structure are loosened and pushed back, until they press on the breadboard and squeeze a bit the rubber. Then they are tightened again. 

In this configuration we could work on the breadboard without problems. It's not moving even when you work on screws.

Background: The design of the DAC noise monitor is in the PCB design stage - I am trying to put the circuit on the PCB board in Altium. We use three power voltages to drive the op amps in the circuit: -15 V. +15 V. We also need power ground and signal ground. This circuit is going to replace a part of a big PCB board with other existing circuits.

Question: What are the layers used by the existing design? The DAC noise monitor needs to fit with other parts, so they have to share the same layers. Is there a PCB layout file for the existing design?

In case of absence, I will start with a signal layer, a -15V power layer, a +15V power layer, a power ground, and a signal ground. I googled a bit and they say the cost will be high and five layers might be more than what we want. Besides, I am not sure about the sequence of the layers either. I will start with this in order to proceed in Altium before we figure out what we need to do:

TOP

Signal layer

+15V power

Power ground

Signal ground

-15V power

BOTTOM

How much sense does it make?

I proceeded as described below. The routing is completed. All the signal routing is completed. One thing worries me is that I am afraid the signal ground and power ground is yet separated. I do have two internal planes for signal ground and power ground. Should they be connected to the same power input (so that they are just two planes with the same source)? Altium treats all the ground as one net GND. If the answer to the question is yes, I need to figure out how to get Altium separate them. In Altium, you can specifiy which net you connect to, but I did not figure out how to specify which layer. (Maybe I need to create a separated GND net, like PGND/SGND for that?) 

Here is a summary file with the schematics and PCB design: NoiseMonitor.pdf

Also, this is the link to the Wiki page, with more details about this work: https://wiki-40m.ligo.caltech.edu/Electronics/NoiseMonitor

As per Chris's suggestions, I replaced the capacitors with surface mount ceramic capacitors, doubled the trace width to 0.5mm and adjusted the routings accordingly. New PCB layout is attached.

I forgot to connect the outputs of U1 and U2. It is fixed. I also run the design rule check and verified that all the connections are made. I separated the power ground and signal ground as well. The summary PDF is updated below.

you can just use some BNC clip doodles (mini grabbers, etc). Go directly from the test equip (scopes, analyzers) to the pins on the board. Or if you are able to mount the D-sub connectors, you can use a breakout board. Can borrow from the 40m if you don't have them in WB.

 I've turned the main turbo back on and aligned the readout now.  The vacuum is already down to 1e-6torr.  It seems that the the offset pin on the bottom of the mass is causing the fiber to move a lot as the isolation mass rotates.  The movement does not appear much to the eye, but is taking up most of our readout range at the moment.

We can wait to see if this motion dies down.  If not we may be forced to replace this intermediate mass with one where the pin is in the center.

Today we brought a rack from Drever lab to 050 W Bridge. This rack will be used for crackle experiment.

   We start setting up the experiment, and we need a rack for electronics equipment, so with Steve's help we got one from Drever lab. We cleaned the rack before brought it in the lab, so there should be no dust.

Next, we will find a lock-in amplifer, maybe a function generator to drive the system.

We plan to work on the experiment on

Tuesdays  afternoon

Thursdays afternoon

Fridays afternoon.

I took the liberty of tidying up the Crackling table a bit.

The Cryo people left us a friendly reminder to "get our own shit": they had found many parts from their own experiment being used or lying around on our Crackling table. Parts belonging to the Cryo experiment are labeled with a dot of gold nail polish. I'm fairly sure I found, switched out and put away all these gold-dotted parts that were lying around on our Crackling table as I was cleaning up.

 The lab floor is being mopped tomorrow. Perhaps this would be a good time to clean/put stuff away? (I did start on this a little last week, but much can still be done)

 [Rana, Steve, Alastair, Zach, Larisa, Vanessa]

We went over to the old Drever lab (in the room with the Synchrotron) for some sort of vacuum tank/glass bell jar to house our crackle experiment. 

The vacuum tank we brought back (currently parked outside the Crackling lab room on a cart) has ~1' diameter and a few glass ports, presumably which we will shine the laser through. This tank is interesting in that it was designed or perhaps originally modified to run on its side instead of standing straight up.

We brought some other items back from the lab as well:

--function generators (x2)

--SR560 (x4?)

--amps (x2, different kinds)

--lock-in amplifiers (x2 that need function generators, x1 that works on its own)

--SR785 (x1)

--tapped aluminium stacks (x2)

We took the SR785 to replace our SR780, which is now in the EE lab(?). Most of the SR560s are also in our lab, as well as one of the function generators and the standalone lock-in amplifier.

TO DO:

Because of the addition of this lab equipment, as well as the newly "cleaned" state of the labroom, we should look into getting some more storage space....specifically: 19" shelves for the Crackling racks, and some NIM racks, both of which Rana informs me we can get from the 40m lab.

Also need to think about acquiring softer rubber stops for separating the two stacks. The black rubber stops we found in the Drever lab are quite hard (presumably made for steel, whereas our stacks are aluminum.

see entry here

[Eric Q, Zach]

Per Rana's request, we ordered some parts for the C³ (Coating, Crackle, Cryo) lab last week. The parts will ship today. Here is the PO:

The bottom of the cryostat contains a chamber where the main components of the experiment will be contained. This space is cylindrical in nature with heighth = 5.6cm and diameter = 13cm. In addition, the cylinder has two inner lips which create an inner diamter = 11.4cm. Furthermore, hole spacing for the screws that will attach the apparatus to the cryostat is approximately 1cm.

Also, we are working with a square window through which a laser will pass. The opening is an embedded circle with diamter 2.7cm and the square itself having length = 5.5cm.

We went into the Ogin  future Crackle Lab and found a few things that looked like vacuum pumps. There are two roughing pumps (one has the words LEAKS written on it), and most of a turbo pump. They all look like replacement parts for the presumably working pump setup that is hooked up the the thermal noise chamber in that room.

link

I put the new HV feedthrough on the cantilever dewar. I borrowed the heat tape from the CTN lab and I am going to bake the chamber over the weekend at 80 deg C, it's currently pumping and heating up.

 cantilever dewar is baking at 80C and pressure is being recorded to C5:VAC-P2_PRESSURE. data logging started at gps time 1065570956. (4:55pm local time Friday).

pressure trend during bake

Cryo cantilever dewar.

Here is the pressure trend (30 hours) after turning off my heat tape.

It quickly drops to ~ 1 x 10^-5 torr. Before the bake, it was never getting below 4 or 5 x10^-5 torr.

Because of this success, and because no work will be done on this chamber for the next week and a half. I will keep baking to further remove contamination.

New bake started at 1065921266.

This is the pressure trend when I close off the valve between the pump line and the cryostat. I am not totally sure how to interpret this, but the fact that the pressure didn't go much lower (like the 10^-6 region) when the pump is only pumping the line makes me think that there may be a leak in my line. Something to investigate.

Today I started preparing for the displacement of the electronic rack far from the optical table.

I built two new long cables, thas as far as I can tell are exactly equal to the old (shorter) cables. The suspension OSEM signals are working well (including damping and driving), but the block OSEMs are not working properly. In particular Z1, Z2 and X1 (at least) are not showing good signals. I haven't checked the picomotors and the photodiodes yet.

Vent started at 11:55am LT

Chamber open at 1:15pm LT

[Federico, Gabriele]

The problems we had on Friday seems related to failures in the DAC. We checked all the DAC channels without sending any signal. All DACs have low offsets (few mV) except for channels 12 and 13 which output 2.236 V and 1.250 V.

Here is the workaround: we are no more using channels 12 and 13, now the corresponding signals, X2 and Y2 coils, are connected respectively to channels 0 and 8.

TEST_DAC1 is still connected to channel 7, while TEST_DAC2 is now connected to channel 15

This morning I moved the old Crackle1 rack out of the lab (we're going to use it in the C.Ri.Me. lab) and I substituted it wtih a cart.

Johannes and I have taken the following equipment from the crackle lab to the 40m between Friday, June 1, and Sunday, June 3 2018. 

• 1 Lightwave M126N-1064-200 NPRO (S/N 259) + controller unit. Measured power output was 320mW.
• 1 AcoustoOptic Modulator, box was labelled "TNI Isomet AOM 1205C-843"
• 1 AcoustoOptic Modulator RF driver, box was labelled "AOM Modulator Driver Model 232A-1"
• 1 broadband EOM (Unlabeled, but looks like the NewFocus)
• 1 Faraday isolator (Unlabeled)

Apart from the NPRO which was taken from the optical bench, everything else was taken from the storage cabinet by the lab entrance.

The gratings and aspheric lenses glued on the mounts were delivered to the lab on Thu.

The powermeter controler + S401C head was lent from OMC Lab. Returned to OMC Jul 15, 2020 KA