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ID Date Authordown Type Category Subject
  31   Mon Sep 27 17:01:53 2021 ranaGeneralHeat LoadMariner cooldown model status + next steps

How about a diagram so that we can understand what this model includes?

  52   Tue May 10 18:29:11 2022 ranaGeneralSuspensionMariner Suspension Cryo shield Install / Removal steps

Transformers Optimus GIF - Transformers Optimus Prime - Discover & Share  GIFs



  60   Thu Jul 7 15:20:04 2022 ranaGeneralOptical Contactingsome useful links

For our optical contacting, Jennifer and I are starting out with glass (microscope slides), with the setup in the EE shop next to the drill press (photos from Jennifer to follow).

Some interesting links:

  • https://www.laserfocusworld.com/optics/article/16546805/optical-fabrication-optical-contacting-grows-more-robust is a write up on contacting, and the link to Dan Shaddock's paper is also useful (need to sign up to get the acutal TSP writeup)
  • Thesis on Silicon Bonding (https://escholarship.org/uc/item/5bm8g42k)
  • https://youtu.be/qvBoGoh_-AE
  7   Wed Mar 17 21:24:27 2021 gautamGeneralDesign specsSilicon TM dichroic coatings for phase I

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 T=50ppm at the second wavelength (which isn't the harmonic) which is different from the PR3 reqs. This kind of repetitive structure with fewer arbitrary thicknesses may be easier to manufacture (and the optimizer may also converge faster since the dimensionality of the space to be searched is smaller). 

Cool starfish 🌟 . What is the interpretation of the area enclosed by the vertices? Is that the (reciprocal) cost? So the better solution maximizes the area enclosed?


Attachment 2 shows the stack. Surprisingly not as crazy (or maybe I have internalized the old "crazy" as "normal")

  38   Mon Oct 11 15:22:18 2021 YehonathanGeneralGeneralMicrocomb alternatives

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 pulses) to allow for f-2f interferometry.

Microcombs are a fancy way of generating combs. They are low-power-consuming, chip-scale, have a high repetition rate, and are highly compatible with Silicon technology. While these are huge advantages for industry, they might be disadvantageous for our purpose. Low-power means that the output comb will be weak (on the order of uW of average power). Microscopic/chip-scale means that they suffer from thermal fluctuations. High rep-rate means we will have to worry about tuning our lasers/comb to get beat notes with frequencies smaller than 1GHz.

Alternatively, and this is what companies like Menlo are selling as full-solution frequency combs, we could use much less fancy mode-locked lasers emitting 50fs - 1ps pulses and broaden their spectrum in a highly nonlinear waveguide, either on a chip or a fiber, either in a cavity or linear topologies. This has all the advantages:

1. High-power (typically 100mW)

2. Low rep-rate (typically 100MHz)

3. Relatively cheap

4. "Narrowband" mode-locked lasers are diverse and can come as a fiber laser which offers high stability.

As a proof of concept, I used this generalized Schrodinger equation solver python package to simulate 1d light propagation in a nonlinear waveguide. I simulated pulses coming out of this "pocket" laser (specs in attachment 1) using 50mW average power out of the available 180mW propagating in a 20cm long piece of this highly nonlinear fiber (specs in attachment 2).

The results are shown in attachments 3-4:

Attachment 3 shows the spectrum of the pulse as a function of propagation distance.

Attachment 4 shows the spectrum and the temporal shape of the pulse at the input and output of the fiber.

It can be seen that the spectrum is octave-spanning and reaches 2um at moderate powers.

One important thing to consider in choosing the parameters of the laser and fiber is the coherence of the generated supercontinuum. According to this paper and others, >100fs pulses and/or too much power (100mW average is roughly the limit for 50fs pulses) result in incoherent spectra which is useless in laser locking or 1f-2f interferometry. These limitations apply only when pumping in the anomalous dispersion regime as traditionally have been done. Pumping in an all-normal (but low) dispersion (like in this fiber) can generate coherent spectra even for 1ps pulses according to this paper and others. So even cheaper lasers can be used. ps pulses will require few meter-long fibers though.



  2   Thu May 21 12:10:03 2020 StephenGeneralResourcesOngoing Mariner Resources

Ongoing points of updates/content (list to be maintained and added)
Mariner Chat Channel
Mariner Git Repository
Mariner 40m Timeline [2020-2021] Google Spreadsheet

  5   Fri Mar 5 11:05:13 2021 StephenGeneralDesign specsFeasibility of 6" optic size in CAD

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?

--> Using the representation of the MOS structure as-is, there is about 1" of clearance between the bottom panel of the first/internal shield under the 6" case, compared with 2" of clearance in the 4" case. This is not very scary, and suggests that we could use a 6" optic size.

2) Any other concerns at this point?

--> Not really, there are degrees of freedom to absorb other issues that arise from the simple 4" --> 6" parameter shift

EASM posted at https://caltech.app.box.com/folder/132918404089


  13   Fri May 7 09:57:18 2021 StephenGeneralEquipmentOverall Dimensions for Mariner Suspension Test Chamber Concept

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".

Stephen's offsets suggest a true shield footprint of 14" x 14" with an overall height of 24".

With generous clearances on all sides, a test chamber with a rectangular footprint internally of about 38" x 32" with an internal height of 34" would be suitable. This scale seems similar to the Thomas Vacuum Chamber in Downs, and suggests feasibility. It will be interesting to kick off conversations with a fabricator to get a sense for this.

This exercise generated a few questions worth considering; feel welcome to add to this list!

  • do we need to have the suspended snout(s)?
  • are we studying an ITM or ETM (or both)?
  • relays or other optical components on the baseplate?
  • angles of optical levers?
  • off center mounting?
  • two doors for front/back access?


  17   Wed Jun 30 16:21:53 2021 StephenGeneralDesign specs 

[Stephen, Koji]

WIP - check layout of 60 cm suspension in chamber at 40m, will report here

WIP - also communicate the

  18   Wed Jul 7 16:32:27 2021 StephenGeneralEquipmentOverall Dimensions for Mariner Suspension Test Chamber Concept

WIP - Stephen to check on new suspension dimensions and fit into 40m chamber

  23   Thu Aug 26 17:40:41 2021 StephenGeneralSuspensionSelecting MOS-style frame

[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).

 - We looked at a scaled-up SOS (WIP, lots of things broke, just notice the larger side plates and base - see Attachment 1) and we were not super excited by the aspect ratio of the larger side plates - didn't look super stiff - or the mass of the base.

 - We noted that the intermediate mass will need OSEMs, and accommodating those will be easier if there is a larger footprint (as afforded by MOS).

MOS-style it is, moving forward!

Also, Checked In to PDM (see Attachment 2 - filename 40mETMsuspension_small-shields.SLDASM and filepath \llpdmpro\Voyager\mariner 40m cryo upgrade ) the current state of the Mariner suspension concept assembly (using MOS). Other than updating the test mass to the 6" configuration, I didn't do any tidying up, so I'm not perfectly satisfied with the state of the model. This at least puts the assembly in a place where anyone can access and work on it. Progress!

  3   Fri Jun 5 11:13:50 2020 RaymondGeneralHeat LoadSteady state heat load example

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 is the BS, left is the beam tube/ETM chamber -- hence the lower absored laser power (solid line) absorbtion (PR power + no HR coating absorption). 


  • Emissivities are listed outside the cartoon.
  • Shields consist of polished aluminum outer surfaces and high emissivity inner surfaces. 
  • 1 W input power, 50 W power recycling, 30 kW cavity power
  • All shields held at 77K 
  • IS snout radius is equal to TM radius
  • 20 ppm/cm bulk silicon absoprtion, 5 ppm coating absorption


  • Steady state condition, where the shields are able to be cooled/held to 77K
  • Holes punched into the inner shield for stops, magnets, etc are assumed to shine RT light onto 123K TM
    • This is very conservative, MOS will stablize at some temp and the OS should block ~all vacuum chamber radiation not funneled through inner shield snout

Missing or wrong

  • [M] Contribution of MOS conduction and emission on the outer shield heat budget
  • [M] Inner shield 
  • [W] OS inner surface currently modelled as one surface seeing incident RT light, need to accomodate the view factor of each of the 5 high e sides to the open maw of the OS
  • [M] Conduction through shield masses, how efficient is it to link them with straps
  • [M] no AR coating absorption 
  • [M/W] Cold finger cooling power from room temp shield to 77K cryocooler ('wrong' label because 61W is only the heat load once shields are cooled):
    • Worst case to reach: 1.5m connection between tank flange and shield (from flange at bottom of the tank)
      • Phosphorous deoxidized copper:  5 cm diameter
      • ETP copper:  3.5 cm diameter
    • Best case: 0.5m connection, from flange at level of OS
      • Phos deox Cu: 3 cm diameter
      • ETP Cu: 2 cm diameter
    • ​​​q_{\text{conductive}} = \frac{A}{L} \left[\int_{4\, \text{K}}^{T_2} \lambda(T) dT - \int_{4\, \text{K}}^{T_1} \lambda(T)dT \right]
  30   Fri Sep 24 13:12:00 2021 RadhikaGeneralHeat LoadMariner cooldown model status + next steps

*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 parameters of the TM and snout were updated to the values recently verified by Nina. To summarize, the model considers the following heat sources onto the testmass (Pin):

- laser absorption by ITM bulk (function of incident laser power, PR gain, and bulk absorption)

- laser absorption by ITM HR coating (function of incident laser power and HR coating absorption)

- radiative heating from room-temp tube snout (function of snout radius and length, and TM radius)

The heat transfer out of the testmass (Pout) is simply the sum of the radiative heat emitted by the HR and AR faces and the barrel. Note that the script currently assumes an inner shield T of 77K, and the inner/outer shield geometric parameters need to be obtained/verified.

Nina and Paco have been working towards obtaining tabulated emissivity data as a function of temperature and wavelength. In the meantime, I created the framework to import this tabulated data, use cubic spline interpolation, and return temperature-dependent emissivities. It should be straightforward to incorporate the emissivity data once it is available. Currently, the script uses room-temperature values for the emissivities of various materials. 

Future steps:

- Incorporate tabulated emissivity data

- Verify and update inner/outer shield dimensions





  32   Wed Sep 29 16:15:19 2021 RadhikaGeneralHeat LoadMariner cooldown model status + next steps

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 - equation found in Cengel Heat Transfer) is calculated to be 0.022. The parameters used in the model are noted in the figure.

Attachment 2 is a simplified diagram that includes the heating/cooling links to the test mass. At 123K, the radiative cooling power from the inner shield (at 77K) is 161 mW. The radiative heating from the snout opening is 35 mW, and the laser heating (constant) is 101.5 mW. Due to the tiny view factor betwen the snout opening and the test mass, most of the heat emitted by the opening does not get absorbed. 

The magnitudes of heating and cooling power can be seen in Attachment 3. Lastly, Attachment 4 plots the final cooldown curve given this model. 

My next step is to add the outer shield and fix its temperature, and then determine the optimal size/location of the inner shield to maximize cooling of the test mass. This is question was posed by Koji in order to inform inner shield/outer shield geometric specs. Then, I will add a cold finger and cryo cooler (conductive cooling). Diagrams will be updated/posted accordingly.

  37   Tue Oct 5 17:46:14 2021 RadhikaGeneralHeat LoadMariner cooldown model status + next steps

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, which is what we want. The expanded diagram can be seen in Attachment 1. 

I wanted to find the optimal choice of inner shield area (AIS) to maximize the radiative cooling to the test mass. I chose 5 values for AIS (from ATM to AOS) and plotted the test mass cooldown for each in Attachment 2. The radiative coupling between the inner shield and test mass is maximized when the ratio of the areas, ATM/AIS, is minimized. Therefore, the larger AIS, the colder the test mass can be cooled. Even though choosing AIS close to AOS increases the coupling between the 2 shields, the resulting heating from the outer shield is negligible compared to the enhancement in cooling.

I chose AIS = 0.22 m2 to model the inner shield and test mass cooldown in Attachment 3. The test mass reaches 123 K at ~ 125 hours, or a little over 5 days. I have pushed the updated script which can be found under mariner40/CryoEngineering/MarinerCooldownEstimation.ipynb.

  42   Fri Oct 15 13:45:55 2021 RadhikaGeneralHeat LoadMariner cooldown model status + next steps

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 to 123K is ~125 hrs or over 5 days for TM length=150mm (unchanged from [37]), but choosing TM length=100m increases this time to ~170 hrs or ~7 days. (Note that these times/curves are derived from choosing an arbitrary inner shield area of 0.22 m2, but the relative times should stay roughly consistent with different IS area choices.)

  43   Fri Oct 15 14:31:15 2021 RadhikaGeneralHeat LoadMariner cooldown model status + next steps

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 negligible. Cooldown time to 123K is ~100 hrs, just over 4 days. I've kept IS area set to 0.22 m2 moving forward.

Attachment 2: TM/IS cooldown, considering 2 lengths for the test mass. Choosing l=100m instead of 150mm increases cooldown time from ~100 hrs to ~145 hrs, or 6 days.

  4   Thu Mar 4 17:04:52 2021 PacoGeneralDesign specsSilicon TM dichroic coatings for phase I

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 are some of the top picks.


For ETM, the target transmissivities are 5.0 ppm @ 2128.2 nm and 50.0 ppm @ 1418.8 nm. After different combinations of differential evolution walkers, numbers of layers, thickness bounds, a couple of different optimization strategies, the optimum design has consistently converged with 19 - 26 layer pairs (total of 38 - 52 layers). The picks are based on the sensitivities, E_field at the boundary, and a qualitatively uniform stack (discarded "insane-looking" solutions). The top picks in Attachment 1 may be a good starting point for a manufacturer. In order of appearance, they are:

  1. ETM_210218_1632
  2. ETM_210222_1621
  3. ETM_210302_1210
  4. ETM_210302_1454


For ITM, the target transmissivities are 2000 ppm @ 2128.2 nm and 50.0 ppm @ 1418.8 nm (critically coupled cavity for AUX). The lower trans for 2128.2 nm made this easier faster to converge, although the number of thin film layers was equally centered about ~ 50 layers. Haven't explored as much in the parameter space, but the top picks in Attachment 2 are decent for approaching manufacturer. In order of appearance, they are:

  1. ITM_210303_1806
  2. ITM_210204_1547
  3. ITM_210304_1714
  6   Wed Mar 17 19:51:42 2021 PacoGeneralDesign specsSilicon TM dichroic coatings for phase I

Update on ETM

New optima are being found using the same basic code with some modifications, which I summarize below;

  1. Updated wavelengths to be 2128.2 nm and 1418.8 nm (PSL and AUX resp.)
  2. 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)
  3. There is now a "starfish" plot displaying the optimized vector cost. Basically, the scores are computed as the inverse of the weighted final scalar costs, meaning the better stats reach farther out in the chart. One of these scalar costs does not actually belong to the optimization (stdevL) and is just a coarse measure of the variance of the thicknesses in the stack relative to the average thickness.
  4. Included a third wavelength as transOPLV (for the OPLEV laser) which tries to get R ~ 99 % at 632 nm
    1. Imagine,... a third wavelength! Now the plots for the transmissivity curves go way into the visible region. Just for fun, I'm also showing the value at 1550 nm in case anyone's interested in that.
  5. Adapted the MCMC modules (doMC, and cornerPlot) to check the covariance between the transmissivities at 2128 and 1418 for a given design.
  6. Reintroduced significant weights for TO noise and Brownian noise cost functions (from 1e-11 to 1e-1) because it apparently forces solutions with lower thickness variance over the stack (not definitive, need to sample more)

Still working to translate all these changes to ITM, but here are samples for some optimum.

  • Attachment 1 shows the spectral reflectivity/transmissivity curves with a bunch of labels and the transparent inset showing the starfish plot. Kind of crazy still.
  • Attachment 2 shows the stack. Surprisingly not as crazy (or maybe I have internalized the old "crazy" as "normal")
  • Attachment 3 shows a very simple corner plot illustrating the covariance between the two main wavelengths transmissions.
  8   Wed Mar 24 17:36:46 2021 PacoGeneralDesign specsLeast common multiple stacks and varL cost

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 work as planned for m=6, 3, and 2.

- While the target transmissivities are reached with comparably fewer layers using this method, the sensitivity and the surface E field are affected and become suboptimal. The good thing is we can do the old way just by setting Ncopies = 0 in the optimization parameters yaml file.

- An example of such a coating is in Attachment 1.

- I decided to just add the 'varL' scalar cost to the optimizer. Now we minimize for the variance in the coating stack thicknesses. As a target I started with 40% but will play with this now.


  9   Wed Mar 24 17:42:50 2021 PacoGeneralDesign specsSilicon TM dichroic coatings for phase I

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 in which the scalars are displayed... enlightened


Cool starfish 🌟 . What is the interpretation of the area enclosed by the vertices? Is that the (reciprocal) cost? So the better solution maximizes the area enclosed?


  10   Fri Apr 2 19:59:53 2021 PacoGeneralDesign specsDifferential evolution strategies

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 at every iteration. From the scipy.optimize.differential_evolution docs, this "val represents the fractional value of the population convergence".

Attachment 1 shows a modest collection of ~16 convergence trajectories for ETM and ITM as a function of the iteration number (limited by maxiter=2000) with the same targets, weights, number of walkers (=25), and other optimization parameters. The vertical axis plots the inverse val (so tending to small numbers represent convergence).

tl;dr: Put simply, the strategies using "binary" crossover schemes work better (i.e. faster) than "exponential" ones. Will keep choosing "best1bin" for this problem.

  15   Fri Jun 4 11:09:27 2021 PacoGeneralDesign specsHR coating tolerance analysis

The HR coating specifications are:

ETM Transmission specs
2128.2 nm 5.0 ppm \pm 2 ppm
1418.8 nm 50.0 ppm \pm 2 ppm


ITM Transmission specs
2128.2 nm 2000.0 ppm \pm 200 ppm
1418.8 nm 50.0 ppm \pm 2 ppm


  • Main constraint: Relative arm finesses @ 2128.2 nm should not differ by > 1%.
  • Secondary constraint: Relative arm finesses @ 1418.8 nm may differ, but the ETM and ITM pair should ensure critically coupled cavity to benefit ALS calibration PD shot noise.

Just took the finesse of a single arm:

\mathcal{F} = \frac{\pi \sqrt{r_1 r_2}}{1 - r_1 r_2}

and propagated transmissivities as uncorrelated variables to estimate the maximum relative finesse. Different tolerance combinations give the same finesse tolerance, so multiple solutions are possible. I simply chose to distribute the relative tolerance in T for the test masses homogeneously to simultaneously maximize the individual tolerances and minimize the joint tolerance.

A code snippet with the numerical analysis may be found here.

Tue Jun 8 11:52:44 2021 Update

The arm cavity finesse at 2128 nm will be mostly limited by the T = 2000 ppm of the ITM, so the finesse changes mostly due to this specification. Assuming that the vendor will be able to do the two ETM optics in one run (x and y), we really don't care so much about the mean value achieved in this run as much as the relative one. Therefore, the 200 ppm tolerance (10% level) is allowed at the absolute level, but a 20 ppm tolerance (1% level) is still preferred at the relative level; is this achievable?. Furthermore, for the AUX wavelength, we mostly care about achieving critical coupling but there is no requirement between the arms. Here a 20 ppm tolerance at the absolute level should be ok, but a 2 ppm tolerance between runs is highly desirable (although it seems crazier); is this achievable?

  19   Tue Jul 27 11:38:25 2021 PacoGeneralDesign specsDOPO single pass PDC efficiency

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.

The parameters use an effective nonlinear coefficient "d_eff" of 4.5 pm/V, and assume we have reached the perfect (quasi) phase matching condition where delta_k = 0 (e.g. we are at the correct crystal operating temperature). The wavelengths are 1064.1 nm for the pump, and 2128.2 nm for degenerate signal and idler. The conversion efficiency here is for the signal photon (which is indistinguishable from the idler, so am I off by a factor of 2?)...

Attachment 1 shows the single pass conversion efficiency "eta" as a function of the pump power. This is done for a set of 5 minimum waists, but the current DOPO waist is ~ 35 um, right in the middle of the explored range. What we see from this overestimates is an almost linear-in-pump power increase of order a few %. I have included vertical lines denoting the damage threshold points, assuming 500 kW / cm ^2 for 1064.1 nm (similar to our free-space EOMs). As the waist increases, the conversion efficiency tends to increase more slowly with power, but enables a higher damage threshold, as expected.

At any rate, the single-pass downconversion efficiency is (over)estimated to be < 5 % for our current DOPO waist right before the damage threshold of ~ 10 Watts, so I don't think we will be able to use the amplified pump (~ 20-40 W) unless we modify the cavity design to allow for larger waist modes.

The important figure (after today's group meeting) would be a single pass downconversion efficiency of ~ 0.5 % / Watt of pump power at our current waist of 35 um (i.e. the slope of the curves below)

  24   Thu Sep 9 11:25:30 2021 PacoGeneralDesign specsRerun HR coatings with n,k dispersion


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.

Basically, all features are still present in both spectral transmission plots, which is consistent with the relatively flat dispersions from 1 to 3 um in Silica and Tantala thin films, but the index corrections of a few percent from low-temperature estimates to room-temperature measured (?) dispersions are able to push the HR transmission up by a few (2-3) times. For instance, the ETM transmission at 2128.2 nm goes up by ~ 3. The new number is still well below what we have requested for phase I so this is in principle not an issue.

A secondary change is the sensitivity (the slope around the specified wavelength) which seems to have increased for the ETM and decreased for the ITM. This was another consideration so I'm running the optimizer to try and minimize this without sacrificing too much in transmission. For this I am using the stack as a first guess in an attempt to run fast optimization. Will post results in a reply to this post.

  25   Thu Sep 9 20:42:34 2021 PacoGeneralDesign specsRerun HR coatings with n,k dispersion


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 dispersion, I intentionally optimized for a lower T such that we intentionally overshoot.

The results are in Attachment #1 and Attachment #2.

  28   Sun Sep 19 18:52:58 2021 PacoGeneralDesign specsHR coating emissivity

[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 the real part only). We used cubic interpolations of the silica and tantala thin film dispersions found here for wavelengths in the 1 to 100 um range. This allowed us to recompute the field amplitude reflectivity and transmissivity over a broader range. Then, we used the imaginary part of the index of refraction and the thin film thicknesses to estimate the absorbed fraction of power from the interface. The power loss for a given layer is exponential in the product of the thickness and the extinction coefficient (see eq 2.6.16 here) . Then, the total absorption is the product of all the individual layer losses times the transmitted field at the interface. This is true when energy conservation distributes power among absorption (=emission), reflection, and transmission:

1 = \epsilon + R + T

The resulting emissivity estimate using this reasoning is plotted as an example in Attachment #1 for the ETM design from April. Two things to note from this; (1) the emissivity is vanishignly small around 1419 and 2128 nm, as most of the power is reflected which kind of makes sense, and (2) the emissivity doesn't quite follow the major absorption features in the thin film interpolated data at lower wavelengths (see Attachment #2), which is dominated by Tantala... which is not naively expected?

Maybe not the best proxy for emissivity? Code used to generate this estimates is hosted here.

  33   Fri Oct 1 11:52:06 2021 PacoGeneralDesign specsHR coating emissivity

[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 I don't quite understand is the discontinous jump at ~ 59 um ... 

  34   Fri Oct 1 12:01:24 2021 PacoGeneralDesign specsTM Barrel coating emissivity

[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:

  1. *| Air || SiO2 x 800 nm || Ta2O5 x 5 um || Silicon |*
  2. *| Air || Ta2O5 x 10 um || Sio2 x 20 nm || Silicon |*
  3. *| Air || SiO2 x 100 nm || TiO2 x 1 um || Silicon |*

Attachments # 1-3 show the emissivity curves for these simple dielectric stacks. Attachment #4 shows the extinction coefficient data used for the three different materials. The next step is to validate these results with tmm, but so far it looks like TiO2 might be a good absorbing film option.

  36   Fri Oct 1 14:11:23 2021 PacoGeneralDesign specsTM Barrel coating emissivity

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.

  47   Fri Nov 5 11:51:50 2021 PacoGeneralDesign specsEstimate of in-air absorption near 2.05 um


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.

Then, in Attachment #2, I estimate the broadened spectrum around 2.05 um and compare it against one produced by an online tool using the 2004 HITRAN catalog.

For the broadened spectrum, I assumed 1 atm pressure, 296 K temperature (standard conditions) and a nominal CO2 density of 1.96 kg/m^3 under this conditions. Then, the line profile was Lorentzian with a HWHM width determined by self and air broadening coefficients also from HITRAN. The difference between 2050 nm and 2040 nm absorption is approximately 2 orders of magnitude; so 2040 nm would be better suited to avoid in-air absorption. Nevertheless, the estimate implies an absorption coefficient at 2050 nm of ~ 20 ppm / m, with a nearby absorption line peaking at ~ 100 ppm / m

For the PMC, (length = 50 cm), the roundtrip loss contribution by in-air absorption at 2050 nm would amount to ~ 40 ppm. BUT, this is nevery going to happen unless we pump out everything and pump in 1 atm of pure CO2. So ignore this part.

Tue Nov 9 08:23:56 2021 UPDATE

Taking a partial pressure of 0.05 % (~ 500 ppm concentration in air), the broadening and total absorption decrease linearly with respect to the estimate above. Attachment #3 shows the new estimate.

For the PMC, (length = 50 cm), the roundtrip loss contribution by in-air absorption at 2050 nm would amount to ~ 1 ppm.

  48   Tue Nov 16 11:47:54 2021 PacoGeneralDesign specsEstimate of in-air absorption near 2.05 um


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 conclusions -->

The PMC loss by background, pressure broadened absorption lines at 2049.9 nm by CO2 is < 1 ppm.

The results posted here are reflected in the latest notebook commit here.

  67   Mon Jul 18 18:34:29 2022 PacoGeneralDesign specsHR coating update

I've been running the HR coating optimization for mariner TMs. Relative to the specifications found here we now are aiming for

  • ITM HR coating of 2000 ppm @ 2050.15 nm, and 1000 ppm @ 1550 nm
  • ETM HR coating of 25 ppm @ 2050.15 nm, and 1000 ppm @ 1550 nm.

Both the PSL and AUX cavity finesses range the few couple of thousands, and the goal is not to optimize the coating stack for noise, but more importantly for the transmission values and tolerances. This way we ensure the average finesse and differential finesse requirements are met. Anyways, Attachment #1-2 shows the transmission plots for the optimized coating stacks (so far). Attachments #3-4 show the dielectric stacks. The code still lives in this repository.

I'm on the process of assessing the tolerance of this design stacks against perturbations in the layer thicknesses; to be posted in a follow-up elog.

  68   Fri Jul 22 13:36:55 2022 PacoGeneralDesign specsHR coating update

Here are some corner plots to analyze the sensitivity of the designs in the previous elog to a 1% gaussian distributed perturbation using MCMC.

Attachment #1 shows the ETM corner plot 

Attachment #2 shows the ITM corner plot.

I let the indices of both high and low index materials vary, as well as the physical thicknesses and project their covariances to the transmission for PSL and AUX wavelengths.

The result shows that for our designs it is better to undershoot in the optimization stage rather than meet the exact number. Nevertheless, 1% level perturbations in the optical thickness of the stack result in 30% deviations in our target transmission specifications. It would be nice to have a better constraint on how much each parameter is actually varying by, e.g. I don't believe we can't fix the index of refraction to better than 1%., but exactly what its value is I don't know, and what are the layer deposition tolerances? These numbers will make our perturbation analysis more precise.

  12   Tue Apr 27 12:28:43 2021 Nina Vaidya & Shruti MaliakalGeneralDesign specsArm Cavity Design 2021

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) gives --> R_c = 58.4 with very slightly different peaks and  energy distribution in the modes

1) Range of R_c is 57 to 60, for some reason lower values of R_c in the range are giving error --> debug this 

2) Find how sensitive the model is for 1% change in R_c value

3) Make sure the side bands are not resonating

  14   Fri May 7 17:50:31 2021 Nina Vaidya & Shruti MaliakalGeneralDesign specsArm Cavity Design 2021 update

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.

For length, 38+0.5% = 38.19 (with RoC 56.2) not ideal, peak is close (48.8kHz) but maybe ok? @Rana thoughts? and 38-0.5% = 37.81 (with RoC 56.2) works well.

To summarise the design:

RoC = 56.2 +/- 1%

L = 38 +/- 0.5%

  1   Thu May 21 11:51:44 2020 KojiGeneralGeneralMariner Elog Test

The first entry of the Mariner elog post

  16   Tue Jun 22 22:28:09 2021 KojiGeneralDesign specsTest Mass wedge design

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 1deg was assumed as a reference. For the other wedge angle, simply multiply the new number (in deg) to the indicated values for the displacement and angle.

- Attachment 2 shows the simplified layout of the test masses for the calculation of the wedge angle. Here the ITM and ETM are supposed to be placed at the center of the in-vacuum tables. Considering the presence of the cryo baffles, we need to isolate the pick-off beam on the BS table. There we can place a black glass (or similar) beam dump to kill the AR reflection. For the ETM trans, the propagation length will be too short for in-vacuum dumping of the AR reflection. We will need to place a beam baffle on the transmon table.

- I've assumed the cavity parameter of L=38m and RoC(ETM)=57m (This yields the Rayleigh range zR=27m). The waist radii (i.e. beam radii at the ITM) for the 2128nm and 1418nm beams are 4.3mm and 3.5mm, while the beam radii at the ETM are 7.4mm and 6.0mm, respectively,

- Attachment 3: Our requirement is that the AR reflection of the ALS (1418nm) beam can be dumped without clipping the main beam.
If we assume the wedge angle of 0.5deg, the opening of the main and AR beams will be (2.462+4.462)*0.5 = 3.46 deg. Assuming the distance from the ETM to the in-air trans baffle is 45" (=1.14m), the separation of the beams will become 69mm. The attached figure shows how big the separation is compared with the beam sizes. I declare that the separation is quite comfortable. As the main and AR beams are distributed on both sides of the optic (i.e. left and right), I suppose that the beams are not clipped by the optical window of the chamber. But this should be checked.
Note that the 6w size for the 2128nm beam is 44mm. Therefore, the first lens for the beam shrinkage needs to be 3" in dia, and even 3" 45deg BS/mirrors are to be used after some amount of beam shrinkage.

- Attachment 4 (Lower): If we assume the same ITM wedge angle of 0.5deg as the ETM, both the POX/POY and the AR beams will have a separation of ~100mm. This is about the maximum acceptable separation to place the POX/POY optics without taking too much space on the BS chamber.

- Attachment 4 (Upper): Just as a trial, the minimum ITM wedge angle of 0.36deg was checked, this gives us the PO beam ~3" separated from the main beam. This is still comfortable to deal with these multiple beams from the ITM/

  20   Fri Aug 6 04:34:43 2021 KojiGeneralGeneralTheoretical Cooling Time Limit

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?

m\,C_p(t)\,T'(t) = -\epsilon\,\sigma A\,[T(t)^4 - 0^4]

T(0) = T_0

Then assume the specific heat is linear as

C_p(t) = c_{p0} T(t)

The actual Cp follows a nonlinear function (cf Debye model), but this is not a too bad assumption down to ~100K.

Then the differential equation can be analytically solved:

T(t) = T_0 \left( 1 + t/t_0 \right )^{-1/2},

where the characteristic time of t0 is

t_0 = \frac{m c_{p0}}{2\,\epsilon\,\sigma A\,T_0^2 }.

Here T_0 is the initial temperature, cp0 is the slope of the specific heat (Cp(T_0) = c_p0 T_0). epsilon is the emissivity of the test mass, sigma is Stefan Boltzmann constant, A is the radiating surface area, and m is the mass of the test mass.

Up to the characteristic time, the cooling is slow. Then the temperature falls sqrt(t) after that.

As the surface-volume ratio m/A becomes bigger for a larger mass, in general, the cooling of the bigger mass requires more time.

For the QIL 4" mass, Mariner 150mm mass, and the Voyager 450mm mass, t0 is 3.8hr, 5.6hr, and 33.7hr respectively.

  • If the emissivity is not 1, just the cooling time is expanded by that factor. (i.e. The emissivity of 0.5 takes x2 more time to cool)
  • And if the shields are not cooled fast or have a finite temperature in the end, of course, the cooling will require more time.
  • 1.25 t0 and 8 t0 tell us how long it takes to reach 200K and 100K.

This is the fundamental limit for radiation cooling. Thus, we have to use conductive cooling if we want to accelerate the cooling further more than this curve.

  21   Tue Aug 17 17:48:57 2021 KojiGeneralEquipmentCrackle SW model

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.

  29   Fri Sep 24 11:02:41 2021 KojiGeneralGeneralActuation Feedback Model and Noise

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
    opts.PhaseWrapping = 'on';

  • We evaluated the open-loop transfer function of the system. For this purpose, we added the monitor point ('F') at the actuator and cut the loop there like:
    sys = connect(P, S, W, ADC, Winv, A2, DWinv, Dinv, DAC, DW, D, R, C, {'xg' 'nADC', 'nDAC', 'nd', 'nth'}, 'xt', {'F','VDAC'});
  • We played with the loopgain (Ga2). When Ga2 is a positive number, the loop was stable. We had to shift the low pass cut-off frequency from 10Hz to 12Hz to make the damping of the 2nd peak stable.
  45   Wed Nov 3 02:52:49 2021 KojiGeneralSuspensionMariner Sus Design

All parameters are temporary:

Test mass size: D150mm x L140mm
Intermediate mass size W152.4mm x D152.4mm x H101.6mm
TM Magnets: 70mm from the center

Height from the bottom of the base plate
- Test mass: 5.0" (127mm) ==> 0.5" margin for the thermal insulation etc (for optical height of 5.5")
- Suspension Top: 488.95mm
- Top suspension block bottom: 17.75" (450.85mm)
- Intermediate Mass: 287.0mm (Upper pendulum length 163.85mm / Lower pendulum length 160mm)

- IM OSEMs: Top x2 (V/P)<-This is a mistake (Nov 3 fixed), Face x3 (L/Y/P), Side x 1 (S)
- TM OSEMs: Face x4
- OSEM insertion can be adjusted with 4-40 screws

To Do:
- EQ Stops / Cradle
(Nov 3 50% done)
- Space Consideration: Is it too tight?
- Top Clamp: We are supposed to have just two wires
(Nov 3 50% done)
- Lower / Middle / Upper Clamps & Consider installation procedure
- Fine alignment adjustment
- Pendulum resonant frequencies & tuning of the parameters
- Utility holes: other sensors / RTDs / Cabling / etc

- Top clamp options: rigid mount vs blade springs
- Top plate utility holes
- IM EQ stops

Discussion with Rana

- Hoe do we decide the clear aperture size for the TM faces?
- OSEM cable stays
- Thread holes for baffles

- Light Machinery can do Si machining
- Thermal conductivity/expansion

- The bottom base should be SUS... maybe others Al except for the clamps

- Suspension eigenmodes separation and temperature dependence


# Deleted the images because they are obsolete.

  46   Thu Nov 4 00:42:05 2021 KojiGeneralSuspensionMariner Sus Design

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.

- Some EQ stops were implemented. Not complete yet.

  51   Thu May 5 19:56:25 2022 KojiGeneralSuspensionMariner Suspension Cryo shield Install / Removal steps

Does this work? Is this insane?

  54   Thu Jun 16 19:43:36 2022 KojiGeneralSuspensionTable for Mariner Suspension Cryo

- B246/QIL Skyhook

  • Find the base of Skyhook. It should be in the storage room (B246). Stephen contacted Chub for lab access. Done
  • Assemble Skyhook with the base and check the stability/safety/capacity/height/etc


  • Ask Paco to move the delicate instruments from the table. Done
  • Bring Skyhook to DOPO. The chamber seems already vented.
  • Find the way to place the cap on the floor safely and cleanly. => Stephen
  • Open the cap and then remove the crackle interferometer. Wrap it with something and place it somewhere in the room. How? => Stephen
  • Move the base to a dolly or something. Then put a cap on the base. => It'd be better to ask Caltech Transp for the chamber transportation.
  • Do we have to temporarily remove the laser safety curtain?

- OMC Lab

  • We probably need to separate the optical table and the base. Ask Caltech Transp to check how the work should be done.
  • Do we have to temporarily move anything on the way?
  • The table can be rolled out to the corridor and then rolled in to the CAML.


  • Remove the grey rack and push the desk to the East.
  • Place the optical table.
  • Place the rack close to the table.
  55   Thu Jun 23 21:11:03 2022 KojiGeneralSuspensionTable for Mariner Suspension Cryo

Table moving effort in the OMC lab: See https://nodus.ligo.caltech.edu:8081/OMC_Lab/412


  57   Sat Jul 2 09:22:39 2022 Juan GeneralGeneralProgress update

I've completed one coil driver board. 
Hopefully next week I can finish the other 2 boards and make the modifications to the sat amp baords. 

  53   Thu Jun 16 14:04:30 2022 JuanGeneralSuspensionTable for Mariner Suspension Cryo

Today we looked at possible locations for where we will be setting up Mariner Suspension and Cryo chamber. The first option was the far left table in the CAML lab but it seems that there is going to be an issue with height clearance, so we have come up with another solution which takes a table from Koji's lab which is 3'x4' ft and moving it into CAML lab in the back right of the lab. To move the table we may need to call facilities to help us because we will most likely need to take the table apart to get it out of the lab. The aisle space in Koji's lab is about 43 inches, but the doorway, which is the tightest space, is 35 inches.

After we have set up the table in CAML we are planning on moving the Chamber in DOPO-lab to CAML. We plan to use skyhook with has a load limit of 500lbs/227kg this should be more than enough to move the chamber. We still need to get the wheeled base for skyhook we are in the works in doing so. 

Also, We want to remove the previous setup from the chamber and leave it at DOPO-lab. Stephen is going to figure out how to keep it clean (sort of). Besides these transportation logistics, I am also working on the electronics as an immediate task and the electrical arrangement in the chamber.

to do list
        - Check the table height
        - Check the chamber height (base/cap)
        - Check how much the chamber cap needs to be lifted (so that we can remove it)
        - Is the weight capacity sufficient?


  56   Mon Jun 27 08:22:22 2022 JuanGeneralGeneralGeneral Update/ Need to do task

I've managed to cut and crimp wires for the power board for coil driver. I will begin adding components to the coil driver board.

- Add Components to Coil Driver board 

 - Replace some Sat Amp Componetns

- Still working on moving optical table to CAML

- Unsure if cryochamber has been cleaned and moved

  58   Tue Jul 5 21:06:47 2022 JuanGeneralGeneralWork Update

Update of my current work I have finished one coil driver board and started on the last two that I need here is the progress and Ideally, I'll finish by tomorrow. 

ELOG V3.1.3-