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ID Date Author Type Category Subject
  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)

Attachment 1: singlepass_eff_overest.pdf
singlepass_eff_overest.pdf
  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

  Draft   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

  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/

Attachment 1: wedge.pdf
wedge.pdf
Attachment 2: Layout.pdf
Layout.pdf
Attachment 3: ETM.pdf
ETM.pdf
Attachment 4: ITM.pdf
ITM.pdf
  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

Analysis

  • 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?

  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%

Attachment 1: Arm_Cavity_Design_05072021_with_tolerances.pptx
Attachment 2: HOMhelper.py
def add_cavmodel(kat, T=0.001, Loss=5e-6, theta=60, L_rt = 2*12.240, R_c = 20, f1 = 11e6, gamma1 = 0, f2 = 55e6, gamma2 = 0):
    '''
    T: Transmission of mirror (ITM)
    Loss: Loss of mirror ETM
    L_rt: Round trip length of cavity
    R_c: Radius of curvature of ETM
    
    '''
    
    
... 98 more lines ...
Attachment 3: Arm_HOManalysis.ipynb
{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 376,
   "metadata": {},
   "outputs": [],
   "source": [
    "from pykat import finesse\n",
    "from pykat.commands import *\n",
... 825 more lines ...
Attachment 4: HOMplot.py
import numpy as np
import scipy.constants as scc
import matplotlib as mpl, matplotlib.pyplot as plt
from matplotlib import cm

plt.rcParams.update({'text.usetex': False,
                     'lines.linewidth': 2,
                     'font.family': 'serif',
                     'font.serif': 'Georgia',
                     'font.size': 22,
... 132 more lines ...
  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?

 

Attachment 1: mariner_suspension_test_chamber_concept.jpg
mariner_suspension_test_chamber_concept.jpg
  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

Attachment 1: Arm_Cavity_Design_04232021.pptx
Attachment 2: Arm_HOM_optimization.ipynb
{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Mariner: Higher Order Mode Analysis of Arm Cavities for Phase-I trial\n",
    "\n",
    "This notebook contains a study of mode-matching for optical Fabry-Perot cavities using Finesse\n",
    "\n",
... 943 more lines ...
  11   Fri Apr 23 10:41:22 2021 AidanGeneralDesign specs2 um photodiode requirements

MCT HgCdTe requirements: https://docs.google.com/spreadsheets/d/1lajp17yusbkacHEMSobChKepiqKYesHWIJ6L7fgr-yY/edit?usp=sharing

 

  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.

Attachment 1: diffevostrategies.pdf
diffevostrategies.pdf
  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

Quote:

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?

 

  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.

 

Attachment 1: ETM_Layers_210323_0925.pdf
ETM_Layers_210323_0925.pdf
  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?

Quote:

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

  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.
Attachment 1: ETM_R_210317_1927.pdf
ETM_R_210317_1927.pdf
Attachment 2: ETM_Layers_210317_1927.pdf
ETM_Layers_210317_1927.pdf
Attachment 3: ETM_nominal_cornerPlt.pdf
ETM_nominal_cornerPlt.pdf
  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

 

Attachment 1: 4in_from_20210305_easm.png
4in_from_20210305_easm.png
Attachment 2: 6in_from_20210305_easm.png
6in_from_20210305_easm.png
  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.

ETM

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

ITM

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
Attachment 1: ETM_coating_candidates.pdf
ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf ETM_coating_candidates.pdf
Attachment 2: ITM_coating_candidates.pdf
ITM_coating_candidates.pdf ITM_coating_candidates.pdf ITM_coating_candidates.pdf ITM_coating_candidates.pdf ITM_coating_candidates.pdf ITM_coating_candidates.pdf
  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). 

Parameters: 

  • 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

Assumptions

  • 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]
Attachment 1: Heat_Load_Sketch.pdf
Heat_Load_Sketch.pdf
  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
 

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

The first entry of the Mariner elog post

ELOG V3.1.3-