Torrey and Daniel 10/3/2023

We measured the laser power coming out of the seeder to see if a Newport 10D20DM.8 could serve as a filter to image the light coming out of the amplifier. We measured the power incident, transmitted, and reflected for a few angles of incidence.

Data:

~<5 degree AOI:

Incident: 26.1 mW

Transmitted: 4.25 uW (0.00016 of the incident power is transmitted)

Reflected: 26.04 mW (0.9977 of the incident power is reflected)

Implied Absorption: 0.06 mW (0.0023 of the power is absorbed)

45 degree AOI:

Incident: 26.06 mW

Transmitted: 10.99 uW (0.00042 of the incident power is transmitted)

Reflected: 26.09 mW (more power is seemingly reflected than incident; some small measurment error)

Implied Absorption: 0 mW (none of the power is absorbed)

The conclusion is that the mirror's OD is between 3.4 and 3.8 depending on the AOI. This should work very well with a amplifier of 5 W, giving around 2 mW of transmission with little absorption and an easy to block reflected beam.

One complication is the back of the Newport 10D20DM.8 is frosted, potentially making the beam hard to profile.

After having assembled the dark box for the SNSPD, Boris has taken the SNSPD to JPL to wire bond the physical sensor to the newly assembled PCB and box. I worked with Jamie to learn how to solder the pins and SMA connectors to the PCB, and finalize the dark box by filling the pin holes with black epoxy. I will post updated images of the final outcome this week.

As for uncertainty measurements for the Yokogawa system (here-11226) I have begun writing automated scripts for running specific measurements outlined in the paper (attachment 2) which detail how to calculate and measure the uncertainty of the Yokogawa system. Thus far I have attained one of the primary plots for the calibration factor for the power meter based on wavelength (see attachment 1). 

Next I will need to check that the powermeter script auto-calibrates the power meter to the correct wavelength before each measurement and will repost more in-depth results. After, I will make a long accurate measuement of the callibration factor plot and save the data to be integrated (and updated when needed) in the script such that any measurment made on the system will take callibration factors from this dataset and integrate them into the overall uncertainty calculation (as seen in the paper attached). 

I will then be running a script to do the same process for changes in laser output power. Lastly, the uncertainties for the attenuators and optical switches will be calibrated accordingly with the previous measurements included respectively. The final script will allow a user to make a PCR curve and based on the set conditions (attenuation value, optical switches in use, and laser output power) will calculate the uncertainty of each measurement accordingly. 

I screwed down the sled with the laser to the breadboard and aligned the laser into the bowtie cavity. The laser is centered through the input port, onto the crusher, and out of the 3rd port. The beam was diverging, so I then added a 1 m focal length lens before the final steering mirror. This lens did not affect the allignment of the beam. The beam is roughly 2 mm while hitting the crusher mirror and has a smaller, unmeasured waist after leaving the bowtie cavity. I plan on making some measurments next.

[Sander, Daniel, Torrey]

As discussed in group meeting, we tested the "mirror crusher" (the device that applies a force on a mirror in the filter cavities in order to change the radius of curvature of the optic, for wavefront control) yesterday. We first measured the beam profile and fit the data to the equation,

\[w^2(z) = w_0^2 + M^4 \left( (\frac{\lambda}{\pi w_0} \right)^2 (z-z_0)^2 \] ,

to get an approximate beam waist and location to use in the next step. The result for which can be found here.The optical layout of the system can be found here. We then wrote a quick code in Finesse to simulate the system, one for with a flat mirror, and then one for a curved mirror. The results for these can be found in the images attached labelled flat and curved respectfully. In the tables, the number of interest is under the w column, at the point n1.p1.i. This just corresponds to an arbitary point in space (where the scanning slit was placed). The difference of these values, and the estimated change in beam size from the crusher is then 38.1 microns. The actual measured change was (x,y): (17, 110). This discrepancy could come from the beam not being centered on the mirror being pushed on. Note that the model doesn't exactly agree with some of the experimental data in otherways, i.e. the expected beam diameter at the measurement point from the model is roughly 2 mm, where as the measured was ~2.7mm. I will update this post as the model is improved.

Additional improvements/iterations to be made:

-Maximize beamsize on optic thats being pushed on. Locate the waist some distance away. Then push on the mirror and see how the waist location changes.

-Improve collimation out of fiber. It is not collimated in the slightest, see here. We recently purchased a collimator that you can adjust along the z-axis to improve this. Will swap it out.

Here are the current layouts of the B102 space and a highly cleaned version of the renovation plans. These are for thinking through large-scale configurations. Let's keep live versions in https://wiki.mccullerlab.com/Main/Layouts and in the dropbox in GQuEST/Layout_Mockups (for now).

See photos!

See attached files!

For the Thermal Shields, I added some new coldheads, added radiation to the copper bar assuming it sees the bath everywhere, and added some code to evalute time to heat with some heaters. This last bit of code is super wierd and non-deterministic, so don't trust the graphs if they don't look physical.

I also wrote some brief code calculating what kind of thermal gradients the beamsplitter can support given some laser power is absorbed by the optic. A 12.5 K/W accross a 10 mm long, 2 mm side length square spoke. Assuming 0.1 W is absorbed, this is 1.25 K.

One consideration: will one part of the optic heat up more that another due to radiation from an inner shield at 242 K? I believe the answer is no given a uniform optic thickness, since both power abosrbed and thermal mass are proportional to area. This ignores how the beam splitter holder reduces how much certain parts of the beamsplitter see the inner shield. Because the total power on the optic is 0.2 W, this approximation doesn't need to be examined further and we should only worry about the laser power's effect on introducing gradients.

I added a copper bar that goes from the coldhead to the breadboard which holds the beamsplitter. I also added a much more realistic model of the cryocooler with a variable lift (the amount of power than can be removed from the bar as a function of temperature) After modeling different coldheads and layers of shields, it is quite apparent the time to cool to 123 K doesn't really depend on how much shielding there is unless the cryocooler lift is barely more than the power lost to the bath. This makes sense analytically.

Depending on the amount of shielding, there are between 4.3 W and 8.7 W lost to the bath at equilibirum.

Attached is a table with different coldheads and levels of shielding. {}:{}:{} means that coldhead couldn't cool the beamsplitter to 123 K. Note: values might not exactly line up due to changing parameters. I have some uncertainty to picking an emissivity depending on context. Luckily this level of accuracy isn't needed.

Next steps are getting quotes on the thermal shields and coldheads. We should get a coldhead with at least 20 W of lift near 123 K.

I have been working in Maria's Lab with Boris and Andrew to get familiar and create updates for the new machines they have for measuring SNSPD characteristics.

Here are the details of our work so far and the first measurements we have done on the currently loaded SNSPD's.

Basic set of procedures:

First calibrating the fibers loss must be done Unplug from the SNSPD DIFF-2/3 fiber port

    Use:

          Python PhotonRateYokogawa.py -CAL

Then perform the fiber switches as directed in the code Follow on screen instructions to swap between fibers 3+ times Add the new "cfactor" variable to the yaml file (PhotonRate.yml) under "cfactor" Plug the cable back into the DIFF-2/3 fiber port To set a photon rate using the script

    Use:

         Python PhotonRateYokogawa.py -P

For PCR Measurements: Use PCR Yaml to setup the start and end bias ramp values Use the KEYSIGHT_55320A.yaml to setup the ramping threshold values Use the IsolatedVSourceServer.yaml to setup the diff output being used Set the min and max bias current levels and threshold levels in the yaml's by manually adjusting the bias current while checking the spikes on an oscilascope

     Once all setup Use:

        Python pcrCurveVarint.py

This will allow us to run the ramping threshold levels for the photon counter For Dark Count Measurements Keep almost all variables the same but we will take out the fiber for the laser and cap the SNSPD port, then we will increase the integration time for each bias voltage step Run the same code: Python pcrCurveVarint.py

Code for running these scripts will soon be uploaded to the gitlab as we finalize our changes.

Attachment 1: raw plots for readout from DIFF2 and DIFF3 for photon counts.

Attachment 2: Dark Count plot for DIFF2 and DIFF3 (port is covered with a cap)

Attachment 3: Efficiency plot (difference of counts - dark counts divided by total photon input)

Attachment 4: SNSPD pulse response from oscilloscope. Red line is the threshold used for triggering a count on the counter.

Next Steps:

1. Calculating uncertainties and measuring uncertainties for the new system (power meter, laser, attenuators and optical switch).

2. Redo the plots and add the uncertainties to the data.

3. Place GQuEST SNSPD into dark box and cryostat and take Dark Counts measurement

4. Characterize efficiency of the GQuEST SNSPD

Photon Counting for GQuEST presentation given on 9/6/2023 to Marias group.

Talk went well please let me know if you need any images from the slides.

PDF is attached, here is the link: Photon Counting for GQuEST 

Attached are some GQuEST SolidWorks Photos

Using simple trig, assuming there is some temperature gradient accross the beam splitter mount:

Delta Theta/Delta T = alpha*L/h, where alpha is the coefficient of thermal expansion, L is the length of the beam splitter in the beam axis, and h is the distance accross which the temperature gradient exists.

For the aluminum beam splitter, alpha = 2.34*10^-5 at RT and is a bit below that value near 123 K, L = 1.25 in, and h = 4.5 in.

This gives Delta Theta/Delta T = 6.5 urad/K

Setup:

I calculate the conduction and radiation from my SolidWorks assembly to figure out how much power our cryostat needs and how long it will take to cool everything. 

All units are metric.

There are 4 seperate elements with (a constant temperature within the element) and 7 conduction pathways. The 4 elements are the breadboard+beamsplitter mount (labeled "bread"), the inner shield (labeled "inner"), the outer shield (labeled "outer"), and the vacuum chamber (labeled "bath"). The 7 pathways are the following

bread+bath: conduction and radiation

bread+inner: radiation

inner+outer: radiation

inner+bath: conduction

outer+bath: conduction and radiation

I use SolidWorks and a little bit of analytic calculation to figure out the conductances. 

After calculating the coupling coefficients, I set up 3 ODEs to get the time dependence. I have some code to give me the exact time it takes to reach 123 K. From the equilibrium results, I calculate each pathway's power and the total power lost to the bath.

Results:

At equilibrium, 4 W are lost to the bath. This is the minimum power required to cool the beamsplitter, but we are going to need more to cool it in a reasonable timeframe.

If we go with a 25 W cryohead, which I think is very possible between 123 and 294 K, it takes nearly 8 hours to cool the beamsplitter and breadboard. It takes a little over a day for the inner shield to reach equilibrium and 2-3 days for the outer shield to reach equilibirum.

Using the Pfeifffer Vacuum Calculator, I am evaluating what pump can handle the entire 0.5 m GQuEST Vacuum Setup.

Parameters:

Calculated volume: 0.145 m³

Calculated surface: 2.6 m²

Desorption rate: 1e-9 mbar*l/(s*cm²)

Leak rate: 3e-9 mbar*l/s

Using a 6 m³/s scroll through a 1 m, 50 mm diameter tube, it should only take ~7 minutes to reach 1 Torr.

Using a 300 L/s turbo through a DN 100 connected directly to the source, it will take around 30 hours to reach 10^-8 Torr.

Using a 80 L/s turbo through a DN 63 connected directly to the source, it will take 4 days to reach 10^-8 Torr.

Unless the 300 L/s turbo were prohibitively expensive, I would therefore advocate for a 6 m³/s scroll and a 300 L/s turbo.

Dropping a couple resources here for mode matching, at least how I've done it in the past. Looks like we will need to do some of these calculations in the next few weeks so if you haven't done it I would start here.

1. Calculate the approximate beam waist position. Attached is an example of that. Use a beam profiler to measure the beam size at multiple locations and this script will calculate the approximate beam waist position.

2. Download some form of mode matching tool. Lee has one he prefers, I use this: http://www.sr.bham.ac.uk/dokuwiki/doku.php?id=geosim:jammt It's called jaMMT (just another Mode Matching Tool).

3. Input your calculated waist position, the lenses you have available for mode matching, the preferred location of the new waist, etc, and this program will do the rest. Happy to show people how to do this in more detail in person. It is a pretty easy program to use though.

Happy Mode Matching.

Brief calculation to evaluate the displacement of a mass from sound waves. All units are metric except Lp, which is the sound pressure level in db. I assume F = d * m * ω²

[Ian, Sander]

We attempted to measure seismic noise in various locations using the Wilcoxon accelerometer. We used an AlphaLab LNA10 (see photo) to amplify the signal from the accelerometer, and acquired the data downstream of the amplifer with the Moku:Go. 

The problem we found is that the amplifier seems to introduce noise in the measurement that obfuscates the signal from the accelerometer. This can be seen by comparing spectra obtained with the accelerometer connected through the amplifier vs. having just the amplifier connected (i.e. having nothing connected to the amplifier input). The measured spectra in the two cases are almost indistinguishable at amplifier gains of 10 and 100.

The attached spectra are for measurements with gain=1000, where the red traces (input 1) are the measurements of the channel with the amplifier, and the blue trace (input 2) is a reference measurement of an unconnected Moku input. The faded red trace is with the accelerometer connected through the amplifier, the bright red trace is with just the amplifier. The accelerometer was oriented vertically (z-direction).

Further indication that the LNA10 introduces signifcant noise is found by comparing the spectra here to those in entry 11284, which have very different frequency dependences. Those spectra were taken without an amplifier (I think?).