Aerospace & Defense Technology - December 2022 - 31

Tech Briefs
250 °C for a VE system. This work has
also produced numerous reactive diluents
and viscosity reducers for VE and
UPE technology based on fatty acids,
lignin, and isosorbide that will maintain
or increase polymer performance
while reducing hazardous emissions.
Biobased lignin-derived resins with
high-bioatomic efficiency that are good
for the lower end of high-performance
composites and most coatings applications
were identified. Furan epoxies
are very promising with good thermomechanical
properties and very high
toughness, making them excellent
candidates for composites and coatings
applications. Higher-performing UPE
resins using isosorbide as an additive
or component were developed, but the
feasibility for scale-up is low due to the
long reaction times required.
This work was performed by John J.
La Scala, Joshua Sadler, Faye R. Toulan,
Anh-Phuong Lam, Christopher Annunziato,
Amod Ogale, Meng Zhang, Annel
Various weapons platforms that use composite materials including the Apache helicopter, the high-mobility
multipurpose wheeled vehicle, Stiletto, F-22, and USS Radford.
Greene, Steven Chambers, Joseph Stanzione
III, Kaleigh Reno, Richard Wool,
Fengshuo Hu, Eric Hernandez, Donghun
Koo, and Giuseppe Palmese for the
Army Research Laboratory. For more
information, download the Technical
Support Package (free white
paper) at mobilityengineeringtech.
com/tsp under the Manufacturing &
Materials category. ARL-0252
MOVPE Growth of LWIR AlInAs/GaInAs/InP Quantum
Cascade Lasers: Impact of Growth and Material Quality on
Laser Performance
The quality of epitaxial layers in quantum cascade lasers (QCLs) has a primary impact on QCL operation,
and establishing correlations between epitaxial growth and materials properties is of critical importance
for continuing improvements in QCL performance.
Massachusetts Institute of Technology, Lexington, Massachusetts
Q
uantum cascade lasers (QCLs) are
compact coherent optical sources
that emit over a wide wavelength range
in the mid- to long-infrared (3-25 µm)
as well as into part of the terahertz
spectrum. With recent developments
of AlInAs/GaInAs/InP QCLs exhibiting
watt-class output power levels at room
temperature in the mid-wave infrared
(MWIR, 3-7 µm) and long-wave infrared
(LWIR, 8-12 µm) regions, QCLs
have become increasingly attractive for
numerous technological applications
including infrared countermeasures,
free-space communications, and chemical
and biological sensing.
As interest in QCLs continues to
grow, so does the desire to improve
performance and understand factors
that may ultimately limit these unique
and complex devices. QCLs are unipolar
devices based on tunneling and
intersubband transitions between
quantum-confined energy states in the
conduction band of a coupled quantum-well
structure. These structures
are designed using band structure engineering
to optimize optical transitions
and electron transport for laser characteristics
such as wavelength, threshold,
power, efficiency, and high-temperature
operation.
Aerospace & Defense Technology, December 2022
mobilityengineeringtech.com
A typical QCL structure consists of a
complex sequence of barrier and quantum
well layers, totaling ~600-1000
layers, with thickness ranging between
0.6 to 6 nm. With the requirement of
so many ultra-thin layers being reproducibly
grown over microns of thickness,
it is not surprising that while
the first proposal to use intersubband
transitions for radiation amplification
was proposed in 1971, it was over 20
years before QCLs operating at cryogenic
temperatures were first demonstrated
in 1994, and another eight years
for room temperature continuous-wave
(cw) operation in 2002.
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Aerospace & Defense Technology - December 2022

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