 Wed Nov 17 09:27:04 2021, Jiri Smetana, General, General, Lagrangian Model - Translation & Pitch 
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I've been having a look at the transfer functions for the translation and pitch of both masses. I'm attaching the plot of all input-to-output
transfer functions of interest so far. Here I've identified the pitch resonances of the two masses (one each) as well as the two pendulum modes. I
need to now investigate if they occur in the correct places. I have confirmed the DC response by directly solving the statics problem on paper. |
 Wed Dec 15 06:43:43 2021, Jiri Smetana, General, General, Lagrangian Model - Translation & Pitch
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I've checked the validity of my state space model in a couple of ways so that we have confidence in the results that it gives. I've checked the
DC gain of the transfer functions where it is non-zero. I did this by solving the static balance of forces problem in the extended body model by hand to
get the DC CoM position as well as the pitch angle of both masses. In the previous ELOG entry I didn't quite do this for all transfer functions so |
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Fri Nov 5 11:51:50 2021, Paco, General, Design specs, Estimate of in-air absorption near 2.05 um
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[Paco]
I used the HITRAN database to download the set of ro-vibrational absorption lines of CO2 (carbon dioxide) near 2.05 um. The lines are plotted
for reference vs wavenumber in inverse cm in Attachment #1. |
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Tue Nov 16 11:47:54 2021, Paco, General, Design specs, Estimate of in-air absorption near 2.05 um
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[Paco]
There was an error in the last plot of the previous log. This was correctly pointed out by rana's pointing out that the broadening from air
should be independent of the CO2 concentration, so nominally both curves should coincide with each other. Nevertheless, this doesn't affect the earlier |
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Wed Nov 3 02:52:49 2021, Koji, General, Suspension, Mariner Sus Design
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All parameters are temporary:
Test mass size: D150mm x L140mm
Intermediate mass size W152.4mm x D152.4mm x H101.6mm |
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Thu Nov 4 00:42:05 2021, Koji, General, Suspension, Mariner Sus Design
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Some more progress:
- Shaved the height of the top clamp blocks. We can extend the suspension height a bit more, but this has not been done.
- The IM OSEM arrangement was fixed. |
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Tue Oct 26 08:09:08 2021, Jiri Smetana, General, General, Lagrangian Suspension Model - Extended Body
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I've been testing out the extended body lagrangian models and I'm trying to understand the ground motion and force coupling to the test mass
displacement. I've compared the two point-mass model to the extended model and, as expected, I get very similar results for the ground coupling. Attachment
1 shows the comparison and asside from more agressive damping of the point-mass model making a small difference at high frequency, the two models look |
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Fri Sep 24 13:12:00 2021, Radhika, General, Heat Load, Mariner cooldown model status + next steps
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*Note: the current modeling script can be found at: CryoEngineering/MarinerCooldownEstimation.ipynb
Nina pointed me to the current mariner cooldown estimation script (path above) and we have since met a few times to discuss upgrades/changes.
Nina's hand calculations were mostly consistent with the existing model, so minimal changes were necessary. The material properties and geometric |
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Mon Sep 27 17:01:53 2021, rana, General, Heat Load, Mariner cooldown model status + next steps
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How about a diagram so that we can understand
what this model includes? |
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Wed Sep 29 16:15:19 2021, Radhika, General, Heat Load, Mariner cooldown model status + next steps
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Attachment 1 is a geometric diagram that reflects the current state of the ITM cooldown model, introduced in [30].
The inner shield is assumed to be held at 77K for simplicity, and 2 heat sources are considered: laser heating, and radiative heating from the room-temperature
snout opening. The view factor Fij between the snout opening and test mass (modeled as 2 coaxial parallel discs separated by length L - |
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Tue Oct 5 17:46:14 2021, Radhika, General, Heat Load, Mariner cooldown model status + next steps
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Building on [32], I added a copper cold finger to conductively cool the inner shield, instead
of holding the inner shield fixed at 77K. The cold finger draws cooling power from a cyro cooler or "cold bath" held at 60K, for simplicity.
I added an outer shield and set its temperature to 100K. The outer shield supplies some radiative heating to the inner shield, but blocks out 295K heating, |
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Fri Oct 15 13:45:55 2021, Radhika, General, Heat Load, Mariner cooldown model status + next steps
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I used the same model in [37] to consider how test mass length affects the cooldown. Attachment
1 plots the curves for TM length=100mm and 150mm. The coupling between the test mass and inner shield is proportional to the area of the test mass, and
therefore increases with increasing length. Choosing l=100mm (compared to 150mm) thus reduces the radiative cooling of the test mass. The cooldown time |
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Fri Oct 15 14:31:15 2021, Radhika, General, Heat Load, Mariner cooldown model status + next steps
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I reran the cooldown model, setting the emissivity of the inner surface of the inner shield to 0.7 (coating), and the emissivity of the outer surface
to 0.03 (polished Al). Previously, the value for both surfaces was set to 0.3 (rough aluminum).
Attachment 1: TM cooldown, varying area of the inner shield. Now, the marginal improvement in cooldown once the IS area reaches 0.22 m2 is |
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Tue Oct 12 12:49:42 2021, Jiri Smetana, General, General, Damping Loop (Point-Mass Pendulums)
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Now that I have correct phase and amplitude behaviour for my MIMO state space model of the suspension and the system is being correctly evaluated as
stable, I'm uploading the useful plots from my analysis. File names should be fairly self-explanatory. The noise plots are for a total height of 550
mm, or wire lengths of 100 mm per stage. I've also attached a model showing the ground motion for different lengths of the suspension. |
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Thu Oct 14 04:17:36 2021, Jiri Smetana, General, General, Damping Loop (Point-Mass Pendulums) 8x
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Here are the DAC and residual displacement spectra for different suspension heights ranging from 450 mm to 600 mm. I aimed to get the Q of the lower
resonance close to 5 and the DAC output RMS close to 0.5 V but as this was just tweaking values by hand I didn't get to exactly these values so I'm
adding the actual values for reference. The parameters are as follows: |
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Tue Oct 12 12:44:44 2021, Jiri Smetana, General, General, New Damping Loop Model
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I've ironed out the issues with my MATLAB model so that it now shows correct phase behaviour. The problem seems to arise from infinite Q poles where
there is an ambiguity in choosing a shift of +/- 180 deg in phase. I've changed my state space model to include finite but very high Q poles to aid
with the phase behaviour. The model has been uploaded to the GitLab project under mariner40 -> mariner_sus -> models -> lagrangian. |
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Mon Oct 11 15:22:18 2021, Yehonathan, General, General, Microcomb alternatives
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Following our discussion at the Friday JC meeting, I gathered several resources and made a small simulation to show how frequency combs might be generated
on platforms other than microcombs or mode-locked lasers.
Indeed, frequency combs generated directly from a mode-locked laser are expensive as they require ultra-broadband operation (emitting few fs |
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Fri Oct 1 12:01:24 2021, Paco, General, Design specs, TM Barrel coating emissivity
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[Paco, Nina, Aidan]
We ran our stack emissivity calculation on different AR stacks to try and make a decision for the TM barrel coatings. This code has yet to be
validated by cross checking against tmm as suggested by Chris. The proposed layer structures by Aidan and Nina are: |
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Fri Oct 1 13:24:40 2021, Aidan, General, Design specs, TM Barrel coating emissivity
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I have to question whether this passes a sanity test. Surely in the case of Stack 2, the 10um thick Ta2O5 will absorb the majority of the incident radiation
before it reaches the SiO2 layer beneath. It should at least be similar to just absorption in Ta2O5 with some Fresnel reflection from the AIr-Ta2O5
interface. |
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Fri Oct 1 14:11:23 2021, Paco, General, Design specs, TM Barrel coating emissivity
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Agree with this. Quickly running tmm on the same "stacks" gave the Attachment
#1-3. (Ignore the vertical axis units... will post corrected plots) and extend the wavelength range to 100 um. |
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Sun Sep 19 18:52:58 2021, Paco, General, Design specs, HR coating emissivity
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[Paco, Nina]
We have been working on an estimate of the wavelength dependent emissivity for the mariner test mass HR coatings. Here is a brief summary.
We first tried extending the thin film optimization code to include extinction coefficient (so using the complex index of refraction rather than |
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Fri Oct 1 11:52:06 2021, Paco, General, Design specs, HR coating emissivity
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[Paco, Nina, Aidan]
Updated the stack emissivity code to use the Kitamura paper fused silica dispersion which has a prominent 20 um absorption peak which wasn't
there before... (data was up to 15 um, and extrapolated smoothly beyond). The updated HR stack emissivities are in Attachments #1 - #2. A weird feature |
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Wed Sep 15 09:15:21 2021, Jiri Smetana, General, General, Actuation Feedback Model and Noise
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I've implemented a more extensive feedback model that uses proper conversions between metres, volts, counts etc. and includes all the (inverse) (de)whitening
filters, driver, servo and noise injections in the correct places. I then closed the loop to obtain the transfer function from horizontal ground motion
and each noise source to test mass displacement. I tuned the servo gain to reduce the Q of both resonances to ~20. |
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Thu Sep 16 10:02:47 2021, Jiri Smetana, General, General, Actuation Feedback Model and Noise
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Here's the DAC voltage spectrum with its associated RMS.
Also, for clarity, this model is for a lossless point-mass double pendulum system with equal masses and equal lengths of 20 cm.
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Fri Sep 24 11:02:41 2021, Koji, General, General, Actuation Feedback Model and Noise
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We had a meeting with the code open in ZOOM. Here are some points we discussed:
The code requires another file ground.m. It is attached here.
The phase of the bode plots were not wrapped. This can be fixed by applying the "PhaseWrapping" options as |
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Thu Sep 9 11:25:30 2021, Paco, General, Design specs, Rerun HR coatings with n,k dispersion
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[Paco]
I've re-run the HR coating designs for both ETM and ITM using interpolated dispersions (presumably at room temperature). The difference is
shown in Attachment #1 and Attachment #2. |
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Thu Sep 9 20:42:34 2021, Paco, General, Design specs, Rerun HR coatings with n,k dispersion
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[Paco]
Alright, I've done a re-optimization targetting a wider T band around 2128 nm. For this I modified the scalar minimization cost to evaluate
the curvature term (instead of the slope) around a wide range of 10% (instead of 1%). Furthermore, in prevision of the overall effects of using the updated |
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Thu Aug 26 17:40:41 2021, Stephen, General, Suspension, Selecting MOS-style frame
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[Koji, Stephen]
Kind of a silly post, and not very scientific, but we are sticking to it. During our check in today we discussed Mariner suspension frame design
concept, and we chose to proceed with MOS-style (4 posts, rectangular footprint). |
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Tue Aug 24 08:15:37 2021, Jiri Smetana, General, General, Actuation Feedback Model
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I'm posting a summary of the work I've done on the Lagrangian analysis of the Mariner suspension design and a state space model of the actuator
control loop. The whole feedback mechanism can be understood with reference to the block diagram in attachment 1.
The dynamics of the suspension are contained within the Plant block. To obtain these, I derived the system Lagrangian, solved the Euler-Lagrange |
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Tue Aug 17 17:48:57 2021, Koji, General, Equipment, Crackle SW model
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As a kickoff of the mariner sus cryostat design, I made a tentative crackle chamber model in SW.
Stephen pointed out that the mass for each part is ~100kg and will likely be ~150kg with the flanges. We believe this is with in the capacity
of the yellow Skyhook crane as long as we can find its wheeled base. |
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Fri Aug 6 04:34:43 2021, Koji, General, General, Theoretical Cooling Time Limit
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I was thinking about how fast we can cool the test mass. No matter how we improve the emissivity of the test mass and the cryostat, there is a theoretical
limitation. I wanted to calculate it as a reference to know how good the cooling is in an experiment.
We have a Si test mass of 300K in a blackbody cryostat with a 0K shield. How fast can we cool the test mass? |
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Tue Jul 27 11:38:25 2021, Paco, General, Design specs, DOPO single pass PDC efficiency
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Here is a set of curves describing the single-pass downconversion efficiency in the 20 mm long PPKTP crystals for the DOPO. I used the "non-depleted
pump approximation" and assumed a plane-wave (although the intensity matches the peak intensity from a gaussian beam). Note that these assumptions
will in general tend to overestimate the conversion efficiency. |
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Fri May 7 09:57:18 2021, Stephen, General, Equipment, Overall Dimensions for Mariner Suspension Test Chamber Concept
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Koji, Stephen
Putting together Koji's design work with Stephen's CAD, we consider the size of a test chamber for the Mariner suspension.
Koji's design uses a 6" x 6" Si optic, with an overall height of about 21.5". |
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Wed Jul 7 16:32:27 2021, Stephen, General, Equipment, Overall Dimensions for Mariner Suspension Test Chamber Concept
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| WIP - Stephen to check on new suspension dimensions and fit into 40m chamber |
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Wed Jun 30 16:21:53 2021, Stephen, General, Design specs,
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[Stephen, Koji]
WIP - check layout of 60 cm suspension in chamber at 40m, will report here
WIP - also communicate the |
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Tue Jun 22 22:28:09 2021, Koji, General, Design specs, Test Mass wedge design
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The ETM wedge of 0.5deg will allow us to separate the AR reflections. We will be OK with the ITM wedge of 0.5deg
too. 0.36 deg for ITM is also OK, but not for the ETM.
- Attachment 1 shows the deflection of the 2128mn and 1418nm beams by the test mass wedge. Here, the wedge angle of |
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Thu Mar 4 17:04:52 2021, Paco, General, Design specs, Silicon TM dichroic coatings for phase I
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Have been using the 40m Coatings repo code by Gautam (with some modifications
to make dichroic designs under Ta2O5_Voyager), as well as the parameters
compiled in the Mariner wiki for Silica-tantala thin films. Here |
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Wed Mar 17 19:51:42 2021, Paco, General, Design specs, Silicon TM dichroic coatings for phase I
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Update on ETM
New optima are being found using the same basic code with some modifications, which I summarize below;
Updated wavelengths to be 2128.2 nm and 1418.8 nm (PSL and AUX resp.)
The thickness sensitivity cost "sensL" previously
defined only for 2128 nm, is now incorporating AUX (1418 nm) in quadrature; so sensL = sqrt(sens(2128) ** 2 + sens(1418)**2)
There is now a |
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Wed Mar 17 21:24:27 2021, gautam, General, Design specs, Silicon TM dichroic coatings for phase I
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I guess you have tried it already - but does enforcing the stacks to be repeating bilayer pairs of the same thickness fail miserably? When doing
this for the PR3 optic @1064nm, I found that the performance of a coating in which the layers are repeating bilayers (so only 2 thicknesses + the cap and
end are allowed to vary) was not that much worse than the one in which all 38 thicknesses were allowed to vary arbitrarily. Although you are aiming for |
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Wed Mar 24 17:36:46 2021, Paco, General, Design specs, Least common multiple stacks and varL cost
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Update on ETM/ITM coating design;
- Following what seemed like a good, intuitive suggestion from Anchal, I implemented a parameter called
Ncopies, which takes a stack of m-bilayers and copies it a few times. The idea here was to have stacks where m is the least
common multiple of the wavelength fractional relation e.g. m(2/3) = 6 so as to regain some of the coherent scattering in a stack. Unfortunately, this didn't |
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Fri Apr 2 19:59:53 2021, Paco, General, Design specs, Differential evolution strategies
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Differential evolution strategies 'benchmarking' for thin film optimization
Since I have been running the ETM/ITM coatings optimization
many times, I decided to "benchmark" (really just visualize) the optimizer trajectories under different strategies offered by the scipy.optimize
implementation of differential evolution. This was done by adding a callback function to keep track the convergence=val |
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Fri Jun 4 11:09:27 2021, Paco, General, Design specs, HR coating tolerance analysis
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The HR coating specifications are:
ETM Transmission specs
2128.2
nm
5.0 ppm 2 ppm
1418.8 |
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Wed Mar 24 17:42:50 2021, Paco, General, Design specs, Silicon TM dichroic coatings for phase I
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Yeah, the magnitudes are the inverse weighted scalar costs (so they lie on the appropriate relative scale) and indeed larger enclosed areas point to
better optima. I would be careful though, because the lines connecting the scalar costs depend on the order of the vector elements (for the plot)... so
I guess if I take the cost vector and shuffle the order I would get a different irregular polygon, but maybe the area is preserved regardless of the order |
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Fri May 7 17:50:31 2021, Nina Vaidya & Shruti Maliakal, General, Design specs, Arm Cavity Design 2021 update
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Here are the final slides with all the results on the Arm Cavity Design, please review.
For RoC of 56.2 +/- 1% things are working well. Tolerance of 0.5% will be better however, 1% is still working; as long as we do not want any
peaks ~50kHz away. |
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Tue Apr 27 12:28:43 2021, Nina Vaidya & Shruti Maliakal, General, Design specs, Arm Cavity Design 2021
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Rana’s code: R_c = 57.3
-->New code with optimization: sweeping through a range of R_c, using a cost function that puts value on peak height, distance of the peaks
from the zero order, and mode number. This cost function can be edited further to adapt to more aims (Slides attached). Currently (code attached) |
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Fri Apr 23 10:41:22 2021, Aidan, General, Design specs, 2 um photodiode requirements
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MCT HgCdTe requirements: https://docs.google.com/spreadsheets/d/1lajp17yusbkacHEMSobChKepiqKYesHWIJ6L7fgr-yY/edit?usp=sharing
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Fri Mar 5 11:05:13 2021, Stephen, General, Design specs, Feasibility of 6" optic size in CAD
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6" vs 4" optic size comparison using CAD - worth hopping into the 3D geometry using the link below, but also posting a couple of images below.
1) We can adjust all parameters relating to the suspension frame except the beam height. Is there enough clearance under the optic for the internal
shield? |
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Fri Jun 5 11:13:50 2020, Raymond, General, Heat Load, Steady state heat load example
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Attached is a cartoon partial view into the heat load experienced by the Mariner assembly.
The omnigraffle file with more explicit arrow labelling in the 'layers' tab is available here.
The dashed red lines along to top represent vacuum chamber radiation incident on all sides of the OS/IS, not just from the top. Off picture to the right |
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Thu May 21 12:10:03 2020, Stephen, General, Resources, Ongoing Mariner Resources
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Ongoing points of updates/content (list to be maintained and added)
Mariner Chat Channel
Mariner Git Repository |
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Thu May 21 11:51:44 2020, Koji, General, General, Mariner Elog Test
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| The first entry of the Mariner elog post |