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2017 NRL REVIEW
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geometries. This fabrication technique could produce 
metamaterials that would withstand high temperature 
and high power, and that, thus, would overcome a 
common weakness of today’s delicate microfabricated 
prototypes, especially at mmW frequencies. Figure 4 
shows a 3D-printed mold for an array of split-ring reso-
nant structures that we made for a scaled-model test 
at an operating frequency near 10 GHz. The structure 
provides the electromagnetic design shape as well as 
structural rigidity and fixturing for the forming of 
functional materials into the mold, which will ultimate-
ly be etched away. 
SUMMARY
  In this research, we developed a new 3D additive 
fabrication method for creating mmW amplifier cir-
cuits in pure electrical-grade copper. We demonstrated 
the use of a commercial high-resolution polymer 3D 
printing process for molding pure bulk copper 3D 
geometries in precise detail. We demonstrated the 
creation of a copper traveling-wave tube amplifier 
circuit designed for 100 GHz operating frequency by 
our 3D-PriME process, and showed the use of a 3D 
nano-printing technology to create amplifier circuit 
molds for operation at over 1,000 GHz. In addition to 
FIGURE 4
3D-printed mold for split-ring resonator type metamaterial.
amplifier circuits, we showed the use of 3D printing 
for exotic structures with engineered electromagnetic 
properties (metamaterials). This research establishes 
the utility of our new method across a variety of com-
mercial 3D printing technologies and electromagnetic 
structure types, and over a range of at least a decade 
in RF frequency spectrum, spanning the mmW and 
terahertz ranges.
 
[Sponsored by the Base Program (CNR funded)]
References

C.D. Joye, A.M. Cook, J.P. Calame, D.K. Abe, A.N. Vlasov, 
I.A. Chernyavskiy, K.T. Nguyen, E.L. Wright, D.E. Pershing, T. 
Kimura, M. Hyttinen, and B. Levush, “Demonstration of a High 
Power, Wideband 220-GHz Traveling Wave Amplifier Fabri-
cated by UV-LIGA,” IEEE Trans. Electron Devices 61, 1672–1678 
(2014).
2
 A.M. Cook, C.D. Joye, J.P. Calame, and D.K. Abe, “3D-Printed 
Mold Electroforming for Microfabrication of W-band TWT 
Circuits,” Proceedings of IEEE 18th International Vacuum Elec-
tronics Conference, London, UK (2017).
3
 R. Engelke, J. Mathuni, G. Ahrens, G. Gruetzner, M. Bednar-
zik, D. Schondelmaier, and B. Loechel, “Investigations of SU-8 
Removal from Metallic High Aspect Ratio Microstructures with 
a Novel Plasma Technique,” Microsyst. Technol. 14, 1607–1612 
(2008).
    
ª
     
                                                                                                

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T H E   A U T H O R S
ALAN M. COOK
 received a B.S. in physics from Arizona 
State University in 2003 and an M.S. and a Ph.D., both in 
physics, from the University of California, Los Angeles, in 
2005 and 2009, respectively. His graduate research demon-
strated a method of generating powerful sub-millimeter-
wave radiation from a strongly-focused electron beam in a 
linear accelerator. In 2009, he joined the Plasma Science and 
Fusion Center at the Massachusetts Institute of Technology, 
where his postdoctoral research focused on nanosecond 
millimeter-wave plasma dynamics and frequency-selective 
photonic crystal electron accelerators. In 2011, he joined 
NRL as a research physicist. His current work focuses on 
microfabrication methods and materials for high-power 
vacuum electronic amplifiers in the upper-millimeter-wave 
frequency range. He is the recipient of a 2012 Dr. Delores 
M. Etter Top Scientists and Engineers of the Year Award, 
an NRL Technology Transfer Award, and an Alan Berman 
Research Publication Award.
COLIN D. JOYE
 received a B.S. in electrical engineering 
and computer science from Villanova University in 2002 
and an M.S. and a Ph.D., both in electrical engineering, 
from the Massachusetts Institute of Technology (MIT) in 
2004 and 2008, respectively. He was a research assistant and 
visiting scientist in the Waves and Beams Division at the 
MIT Plasma Science and Fusion Center from 2002 to 2008. 
In 2008, he joined the former Vacuum Electronics Branch 
at NRL as a Karle Fellow. His research interests include 
millimeter-wave vacuum electron amplifiers and novel 
microfabrication techniques. In 2016, he received the Presi-
dential Early Career Award for Scientists and Engineers. 
He is also the recipient of a 2012 Dr. Delores M. Etter Top 
Scientists and Engineers of the Year Award, an NRL Tech-
nology Transfer Award, and two Alan Berman Research 
Publication Awards.
JEFFREY P. CALAME
 received three degrees in electri-
cal engineering from the University of Maryland, College 
Park: a B.S. in 1985, an M.S. in 1986, and a Ph.D. in 1991. 
His graduate research from 1985 to 1991 involved the 
development of a high peak power gyroklystron, a type of 
multi-megawatt microwave amplifier. From 1992 to 1997, he 
performed postdoctoral research at the University of Mary-
land on microwave amplifiers, the microwave processing of 
materials, and the dielectric properties of ceramics. In 1997, 
he joined NRL as an electronics engineer in the Vacuum 
Electronics Branch, and from 1997 to 2003, he developed 
high average power, wideband millimeter-wave amplifiers 
for radar applications. He is presently Section Head in the 
Electromagnetics Technology Branch, where he performs 
and supervises research on millimeter-wave amplifiers for 
electronic warfare, communications, and radar applications. 
He also performs research on related advanced materials and microfabrication technologies, including microwave absorbing materi-
als, high heat flux cooling, additive manufacturing, and high-peak-power energy storage.

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F. KEITH PERKINS
 received an S.B. in physics from the 
Massachusetts Institute of Technology in 1982 and an M.S. 
and a Ph.D., both in materials science, from the University 
of Wisconsin-Madison in 1988 and 1992, respectively. He 
worked at the University of Wisconsin Synchrotron Radia-
tion Center from 1983 to 1988. He held a National Research 
Council postdoctoral fellowship tenured at NRL from 1992 
to 1995, at the end of which he was converted to a perma-
nent staff member in Electronics Science and Technology 
Division. Since then, his work has included high resolu-
tion lithography, chemical vapor sensors from nanophase 
materials, and growth and applications of carbon nanotubes, 
and he says that he is now surprised to find himself back to 
working on high resolution lithography. He received a Top 
Navy Scientists and Engineers of the Year Award in 2007.

A MIGHTI Flight for
Ionospheric Insight
S
ay you’re flying from Africa to 
South America and you want to 
use geopositioning along the way. 
What’s the likelihood that you’re going to 
face an outage during, say, a nighttime 
flight? Right now, it’s anyone’s guess. 
  The U.S. Naval Research Laboratory 
(NRL) aims to help remove the 
guesswork. NRL scientists have sent 
into space an instrument designed 
to study the Earth’s thermosphere. 
The Michelson Interferometer for 
Global High-resolution Thermospheric 
Imaging (MIGHTI) instrument will help 
researchers better understand space 
variations that contribute to disruptions in 
communications equipment, radar, and 
global positioning systems on Earth. 
  NRL’s MIGHTI instrument was scheduled 
to launch in December 2017 onboard 
NASA’s Ionospheric Connection 
Explorer mission. NRL is one of the 
few places in the country that supports 
the development of satellite sensors 
completely, from concept to execution 
— from the first spark of an idea to the 
reality of a satellite payload, including 
operational data analysis algorithms. The 
MIGHTI instrument is a recent example.

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INTRODUCTION
  Developed by the NRL Space Science Division, the 
Michelson Interferometer for Global High-resolution 
Thermospheric Imaging (MIGHTI) satellite instrument 
is part of NASA’s Ionospheric Connection (ICON) 
Explorer mission. The ICON mission, led by Thomas 
Immel at the University of California, Berkeley, flies a 
suite of instruments designed to explore the mecha-
nisms controlling the environmental conditions in 
space and how they are modified by weather in the 
lower atmosphere. In studying this region where Earth’s 
weather and space weather meet, researchers hope to 
find answers to their questions about how Earth’s upper 
atmosphere behaves, because this part of the atmo-
sphere is essential for the performance of many systems 
that use long-distance radio wave propagation. 
  NRL’s MIGHTI instrument aboard the ICON 
satellite contributes to reaching the mission goals by 
measuring the neutral winds and temperatures in 
the Earth’s low-latitude thermosphere. The MIGHTI 
instrument uses the Doppler Asymmetric Spatial 
Heterodyne (DASH) spectroscopy technique, which 
was co-invented and pioneered by NRL. The payload 
consists of two identical units that observe the Earth’s 
thermosphere with perpendicular viewing directions. 
As the ICON satellite travels eastward and continuously 
images the thermosphere and ionosphere, MIGHTI 
measures the vector components of the vertical wind 
profile. 
From Sensor Idea to Satellite Instrument
C.R. Englert,
1
 C.M. Brown,
1
 K.D. Marr,
1
 and J.M. Harlander
2
  
1
Space Science Division
2
Space Systems Research Corporation (Alexandria, Virginia)
M
otivated by the need to measure altitude profiles of atmospheric wind in the thermosphere/ionosphere region 
from space, the Space Science Division has led the development of an innovative optical technique with advan-
tages over previously deployed instrumentation. Within about a decade (from 2005 to 2016), the new concept, 
patented by the Navy and named the Doppler Asymmetric Spatial Heterodyne (DASH) technique, was matured from an 
idea to a space-qualified payload. The NRL-developed Michelson Interferometer for Global High-resolution Thermospheric 
Imaging (MIGHTI) satellite instrument, the first space-based DASH instrument, is part of the NASA Ionospheric Connec-
tion (ICON) Explorer mission. 
 
The idea of this new type of space-based, high-altitude wind sensor was first demonstrated at NRL with a simple 
bench setup in 2005 and published in 2006. The first monolithic interferometers, which are the “heart” of the sensor, were 
designed and built in the following years. Data analysis techniques were developed, and several ground-based thermo-
spheric wind measurements were conducted in 2010 and 2011 to demonstrate and validate the approach. On the strength 
of these results, the new technique was selected for the wind sensor of the NASA ICON mission. This article describes the 
optical technique and the major milestones of its development. 
  NRL’s MIGHTI is named for Albert Michelson, a 
physicist known for his research on the measurement 
of the speed of light using a related interferometer type. 
More directly, MIGHTI builds on technology previ-
ously used in NRL’s SHIMMER (Spatial Heterodyne 
Imager for Mesospheric Radicals), a payload aboard 
STPSat-1. The NRL MIGHTI team is led by Christoph 
Englert, head of the Geospace Science and Technology 
Branch in the Space Science Division. 
  The MIGHTI instrument has origins in NRL re-
search that reaches back to early 2005. In early 2005, 
our small team at NRL worked with research partners 
at the University of Wisconsin, Madison, and St. Cloud 
State University on the first satellite instrument to use 
a monolithic Spatial Heterodyne Spectrometer (SHS) 
interferometer to measure the mesospheric trace gas 
hydroxyl, or OH, a highly reactive radical and an im-
portant player in atmospheric chemistry. This measure-
ment uses the diffuse fluorescence of OH as seen from 
space on the Earth’s horizon and requires very high 
spectral resolution in a narrow wavelength interval in 
the near ultraviolet, making SHS a good technique for 
this problem.
1
 
  Much as it does in a Fourier Transform Spectrom-
eter (FTS), light coming into an SHS is split into two 
interferometer arms. After being reflected at the ends 
of the arms, the beams are recombined at a beamsplit-
ter, where they interfere constructively or destructively 
(to varying degrees, one way or the other), depending 
on the optical path difference (OPD) introduced by the 

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two arms and the signal wavelength. Measuring the 
resulting intensity for different OPDs allows us to cre-
ate an interferogram, which is equivalent to the Fourier 
transform of the incident spectrum. In a conventional 
FTS, the different OPDs are created by moving mirrors 
in one or both arms, and the interferogram is recorded 
as a function of OPD using a single element detector. 
In SHS, the arms are terminated by tilted diffraction 
gratings, and each grating groove can be considered as 
a separate mirror at different OPD. Thus, by projecting 
the gratings onto an imaging detector, an SHS instru-
ment can record many hundred interferogram samples 
simultaneously. The discrete steps between the grat-
ing grooves also result in a heterodyning effect, which 
allows for low spatial frequencies of the interferogram 
features on the detector while achieving high spectral 
resolution without moving interferometer parts.
  SHS is particularly suitable for applications that re-
quire high resolution over a limited wavelength region 
and diffuse sources. In addition, the “multiplex noise” 
disadvantage, which any FTS must accept, is minimized 
if the source is limited to the signal of interest, without 
a large background signal. 
DOPPLER ASYMMETRIC SPATIAL
HETERODYNE SPECTROSCOPY 
  The above properties of SHS make it suitable for 
measuring the faint signal of naturally occurring air-
glow from oxygen atoms in the Earth’s upper atmo-
sphere. This measurement helps researchers determine 
the local wind speed from the Doppler shift of these 
almost monochromatic emissions. For this problem, 
very small wavelength shifts, on the order of one part 
in 50 million, must be determined from the measured 
interferogram. 
  The thin line in Fig. 1 illustrates the typical interfer-
ogram of a temperature-broadened emission line. The 
interferogram consists of a cosine-shaped signal with 
a bell-shaped envelope due to the fact that the oxygen 
emission line is not monochromatic. The difference 
between this interferogram and an interferogram from 
a slightly Doppler-shifted emission line, which has a 
slightly different cosine fringe frequency, is shown as 
the thick black line. The difference maximizes at a par-
ticular OPD away from the center (OPD=0) location. 
Thus, to measure the wind in the upper atmosphere, 
it is most efficient to build an interferometer that only 
measures an OPD interval in which the measured sig-
nal is most sensitive to the Doppler shift. The resulting 
interferometer is “asymmetric,” with one arm longer 
than the other, giving rise to the name Doppler Asym-
metric Spatial Heterodyne Spectroscopy, or DASH, as it 
is known.
2
 
FIRST BREADBORD, BRASSBOARD, AND 
MONOLITHIC DASH INTERFEROMETERS
  We performed our first demonstration of a DASH 
interferometer in 2005. We modified a breadboard 
SHS interferometer built for a different project but that 
allowed us to easily configure asymmetric arm lengths. 
In this first experiment, shown in Fig. 2, we measured 
the small wavelength changes of laser diodes, and we 
published the concept in 2006.
3
    
  A year later, using NASA support, we started con-
structing a brassboard experiment to measure actual 
Doppler shifts in the near infrared, using laser light 
FIGURE 1
Thin line: Interferogram of a temperature broadened emission 
line. Thick line: difference between this interferogram and one 
for a slightly Doppler shifted line with a slightly different fringe 
frequency. The signal difference is largest around P
OPT
, for 
which the measurement will be most sensitive.
FIGURE 2
Breadboard setup of a Spatial Heterodyne Spectrometer (SHS) 
interferometer with a cubic beamsplitter and two adjustable 
gratings. The grating on the right was translated away from the 
beamsplitter to demonstrate the Doppler Asymmetric Spatial 
Heterodyne (DASH) concept by simultaneously measuring 
small wavelength shifts of two laser diodes. 

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bounced off a spinning, reflective wheel. Furthermore, 
this effort resulted in the first thermally compensated, 
monolithic DASH interferometer (Fig. 3).
4
 Monolithic 
designs are particularly beneficial for spaceflight in-
strumentation, because they are robust and, therefore, 
at low risk of misalignment from vibrations during 
launch. Also, because its design eliminates all moving 
interferometer parts, DASH offers greatly increased 
reliability of spaceflight instrumentation.  
MEASURING REAL WINDS FROM THE 
GROUND
  After successfully demonstrating the DASH tech-
nique in the laboratory, we shifted our focus to another 
milestone: the first measurement of real atmospheric 
winds using the DASH technique. Upper atmospheric 
winds can be measured from the ground using the 
same airglow lines that are observed from space, pro-
vided that there are no clouds blocking the signal from 
the upper atmosphere. In 2009, we began building a 
portable DASH instrument from mainly commercial 
off-the-shelf components (Fig. 4). We performed our 
first ground-based measurements from the rooftop of 
the NRL Space Science Division building, in Washing-
ton, DC, in 2010. The patent for the DASH technique 
was also awarded to the Navy that year. We repeated 
the wind measurements from a much less light-pollut-
ed site in North Carolina in 2011.
5
 These observations 
were conducted simultaneously with a Fabry-Perot 
instrument (the gold standard in devices for ground-
based upper atmospheric wind measurements).
THE PATH TO SPACE
  In 2011, concurrent with running our ground-based 
DASH measurements, we joined researchers at the Uni-
versity of California, Berkeley, in soliciting NASA with 
a proposed ICON mission that would incorporate the 
MIGHTI instrument. In spring 2013, NASA selected 
the proposed ICON mission for spaceflight. As part 
of the ICON proposal activities, and specifically to opti-
mize the MIGHTI sensor design, we continued to study 
key instrument parameters, such as the thermal behav-
FIGURE 4
The portable DASH ground-based instrument positioned on 
a concrete column inside an observation hut with removable 
roof at the Pisgah Astronomical Research Institute in North 
Carolina.
FIGURE 3
(a) First monolithic DASH interferometer. This interferometer 
used a triangular Kösters prism as the beamsplitter, allowing 
the use of only one grating in the parallel interferometer arms. 
(b) Breadboard setup for testing of the monolithic interferom-
eter using a neon hollow cathode lamp as the signal source.

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ior of DASH interferometers.
6
 The finished MIGHTI 
payload was delivered to the ICON project in February 
2016. The complete instrument consists of a calibration 
lamp unit, an electronics unit, and two identical optical 
sensors (Fig. 5(a)) that observe the atmosphere with 
two perpendicular viewing directions. This configura-
tion allows researchers to determine the wind speed 
and direction as a function of altitude, because the 
Doppler shift contains only information on the wind 
velocity component along the viewing direction.
  Figure 5(b) shows the optical bench of one of the 
sensor units during assembly. The optical bench holds 
all of the optical elements, including the interferom-
eter in its holder, on the left, and the imaging detector, 
shown in the yellow enclosure on the right. Figure 
6 shows the MIGHTI interferometers
7
 as they look 
before their integration into the instrument (the photo 
shows two used for flight and a third that is a spare). 
The figure depicts the cubic beamsplitters with the long 
and short interferometer arms attached to the front-left 
and back-left cube sides, respectively. 
CONCLUSION
  In July 2017, MIGHTI was fully integrated and 
tested onboard the ICON satellite.
8
 Figure 7 shows the 
complete spacecraft with the solar panels in the de-
ployed position. The two arrows indicate the locations 
of the two MIGHTI optical sensors. The ICON mission 
was launched in December 2017 from the Reagan Test 
Site at the Kwajalein Atoll, about 2,500 miles west of 
Hawai’i; the launch placed the satellite in a low-inclina-
tion, low-Earth orbit (Fig. 8). ICON is an Explorer-class 
mission, led by the University of California, Berkeley, 
and managed at NASA’s Goddard Space Flight Center 
in Greenbelt, Maryland. ICON is slated for a nominal 
two-year mission but, if all goes well, conceivably could 
be extended to accomplish additional science. The data 
that ICON provides will give atmospheric scientists 
reliable and continuous insight into thermospheric 
and ionospheric processes. NRL’s MIGHTI instrument 
onboard the ICON satellite will contribute to the mis-
FIGURE 6
Monolithic, temperature-compensated interferometers for 
MIGHTI, two for flight and one spare. 
FIGURE 7
Fully integrated NASA Ionospheric Connection (ICON) Explorer 
satellite with deployed solar panels. The locations of the two 
MIGHTI optical sensors are indicated by the arrows. 
FIGURE 5
(a) Solid model of a single optical sensor for the Michelson 
Interferometer for Global High-resolution Thermospheric Im-
aging (MIGHTI) satellite instrument. The optical bench is the 
purple structure. It holds all optical elements of the sensor. 
Light is accepted via the blue baffle. The cyan surface is a 
radiator, which rejects heat generated by cooling the detec-
tor. (b) Optical bench of one of the MIGHTI sensors during 
assembly.
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