1. ABSORBER COATINGS FOR
MID-INFRARED
ASTROPHYSICS
DAHLIA BAKER1, EDWARD WOLLACK2 , KARWAN ROSTEM2,3
1. COE COLLEGE, DEPARTMENT OF PHYSICS
2. OBSERVATIONAL COSMOLOGY LAB, NASA GODDARD SPACE FLIGHT CENTER
3. DEPARTMENT OF PHYSICS AND ASTRONOMY, THE JOHNS HOPKINS UNIVERSITY
2. • Physics and Mathematic Major
• Physics Club and Outreach
• Studied Computational Biophysics,
moving on to Planetary Science research
ABOUT ME
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3. BACKGROUND
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• HIRMES - High Resolution Mid-InfrarEd Spectrometer
• Functioning in the 20-200 micrometer range
• Eliminate
• SOFIA – Stratospheric Observatory for Infrared Astronomy
4. APPROACH
• Goals
• Create a material that absorbs stray light
• Lightweight, easy applicable
• Known dielectric function
• What is this?
Describes the electric response to incident radiation
• Diffusively reflects rather than specularly reflects
• Withstand cryogenic temperatures (µK)
• First Step- Characterize the materials
• Dielectric functions
• Second Step- Matlab Model
• Model each sample layer with found dielectric function
• Third Step- Manufacturing
• Create sample plates
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6. SAMPLES
Sample Letter
Thickness
of Epoxy
(µm) Final Layer Count Composition (Layer Order)
A 579 2 Epoxy, Z306
B 644 3 Epoxy, Z306, K1
C 449 3 Epoxy, K1, Z306
D 505 4 Epoxy, K1, Z306, K1
E 707 1 Epoxy
F 494 2 Epoxy, K1
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7. DIELECTRIC CHARACTERIZATION
Frequency response data taken with a microwave network vector analyzer
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Transmission through waveguide
Reflection from sample
• Periodic structure of reflection shows
constructive and destructive interference
• Shows the “true density” as seen by an
incident electromagnetic wave
• Loss is due to dielectric properties of
microspheres, scattering due to geometry
is not considered
8. THE MODEL
Material Thickness (µm) Dielectric (-)
Aluminum 500 1+ 1x108i
Epoxy 377H 500 7.4 + 0.4i
3M K1
Microspheres 100 1.1 + 0.002i
Aeroglaze Z306 50 2.6 + 0.6i
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Response vs. Wavelength
9. RESULTS
• Conclusions
• Our proposed material can be
manufactured at a small scale
• Model predicts correct response
• Drawback – model cannot predict
response from diffuse scattering
due to microspheres
• Further Studies
• Measure optical
frequency-dependent
response with a Fourier
Transform Spectrometer
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Transmittance vs. Frequency for Epoxy
Reflectance vs. Frequency for Epoxy
12. ACKNOWLEDGEMENTS
NASA and Collaborators
I would like to give special thanks to the Observational
Cosmology Lab at NASA Goddard Space Flight Center and my
mentors
Edward J. Wollack Karwan Rostem
For their support of my project:
• Dave Chuss and Riley McCarten,
Villanova University
• Paul Mirel, Observational Cosmology Lab,
NASA GSFC
• Kyle Johnson, George Washington University
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Editor's Notes
Black surfaces are necessary for the type of wavelength attenutation that’s required by a high-functioning absorptive coating. They’re applied for the inside of telescope baffles, like the hubble, on the domes of ground based observatories, and in every day imaging techniques such as the inside of a camera lens baffle. The point is to take incident light and eliminate the reflections so that there cannot be any ordered stray light
The geometry and the material surfaces make a object "black" -- dielectrics on their own are not perfectly absorbing. Once the dielectric properties are known -- the geometry can be specified to achieve a desired level of performance. Would discuss what light can do -- it can be reflected, absorbed, transmitted, or scattered -- the outcome is set by the boundary conditions and the geometry of the structure.
In this case, we use dielectrics to absorb specific wavelengths. The materials we used are specifically chosen for their polarizability and how much energy they can absorb.
Talk about the mid-infrared range (next slide)
Discussing the point of each aspect, why they matter to the purpose of the product and what results we hope to see
graphine in 377H provides loss in dielectric matrix -- 301 epoxy is the binder and is used to dilute 377H to the desired sC filling fraction silica tailors the coefficient of thermal expansion so the material can be cooled without damage K1 microspheres roughens the surface and dilutes the media to lower the reflectance Z306 serves as an anti-reflection coatings improves short wavelength absorptance
The actual samples we created
Would recommend showing and discussing waveguide measurement of microspheres -- this provides a measurement of the "true density" of the microspheres as seen by an incident electromagnetic wave. The dielectric value derived from this measurement at 1icm (30GHz) will be used to inform the concentration used in the final mixture. The "true density" of the particles (0.11gm/cm^3) differs from the bulk density of the powder (0.07gm/cm^3) measured with the scale -- in practice the "true density" will be used to compute the effective index of the media when the air voids in the powder are replaced by epoxy
Here I could talk about Kyle’s code, and how you use the dielectric functions to calculate how much absorptance/reflectance would come from the material. Drude dispersion model and transmission line theory. The materials simply act as impedance to the signal
