Tech Briefs Magazine - August 2023 - 39

Strengthening Electron-Triggered Light Emission
A new method can produce a hundredfold increase in light emissions from a type of
electron-photon coupling.
Massachusetts Institute of Technology, Cambridge, MA
A
wavelength of visible light is about
1,000 times larger than an electron,
so the way the two affect each
other is limited by that disparity. Now,
researchers have come up with a way
to make much stronger interactions
between photons and electrons possible
- in the process producing a hundred-fold
increase in the emission of
light from a phenomenon called
Smith-Purcell radiation.
The findings, reported in the journal
Nature, show that using a beam of electrons
in combination with a specially
designed photonic crystal - a slab of
silicon on an insulator, etched with
nanometer-scale holes - could theoretically
predict stronger emission by
many orders of magnitude than would
ordinarily be possible in conventional
Smith-Purcell radiation.
from the electron to a group of photons
- or vice versa. Whereas conventional
light-electron interactions rely on producing
light at a single angle, the photonic
crystal is tuned in such a way that
it enables the production of a whole
range of angles.
Researchers have found a way to create much stronger
interactions between photons and electrons, in the process
producing a hundred-fold increase in the emission
of light from a phenomenon called Smith-Purcell radiation.
(Image: Courtesy of the researchers/MIT)
ciently (e.g., terahertz waves, ultraviolet
light, and X-rays).
Unlike other such approaches, the freeelectron-based
method is fully tunable; it
can produce emissions of any wavelength
by adjusting the size of the photonic structure
and the speed of the electrons - ideal
for making sources of emission at wavelengths
that are difficult to produce effiAccording
to the team, the basic principle
involved could potentially enable far
greater enhancements using devices specifically
adapted for this function.
The approach is based on a concept
called flatbands, and the underlying principle
involves the transfer of momentum
" If you could actually build electron
accelerators on a chip, " said Professor
Marin Soljačić, " you could make much
more compact accelerators for some of
the applications of interest, which
would still produce very energetic electrons.
That obviously would be huge.
For many applications, you wouldn't
have to build these huge facilities. "
The new system could potentially
provide a highly controllable X-ray
beam for radiotherapy purposes, said
MIT postdoc Charles Roques-Carmes.
Also, the system could be used to generate
multiple entangled photons - a quantum
effect that could be useful in the creation
of quantum-based computational and
communications systems.
For more information, contact Abby
Abazorius at abbya@mit.edu; 617-2532709.
Nanoscale
3D Structure to Control Light
This technique could lead to significantly more efficient optical devices, advancing
technological applications in communications and more.
The Pennsylvania State University, University Park, PA
M
etamaterials, made up of small, repeated
structures engineered to produce
desired interactions with light or
sound waves, can improve optical devices
used in telecommunications, imaging and
more. But the functionality of the devices
can be limited by the corresponding design
space, according to Lei Kang, Assistant
Research Professor of Electrical Engineering
at Penn State.
Kang and interdisciplinary collaborators
from Penn State and Sandia National Laboratories
leveraged three dimensions of
design space to create and test a metamaterial
with robust optical properties.
" It's not easy to efficiently explore design
space for 3D metamaterial components,
or unit cells, " Kang said. " But we
Tech Briefs, August 2023
have developed a variety of complex optimization
techniques in our lab, and
our collaboration with Sandia National
Laboratories has allowed for fabrication
of very complex 3D structures at the
nanometer scale. This unique combination
of advanced capabilities provides a
good strategy to explore 3D unit cells
that can lead to sophisticated metamaterial
functionalities. "
One such functionality is enabling asymmetric
transmission of light, in which light
waves exhibit different power levels dependent
on their direction of travel through a
material. Realization of this phenomenon
for light with an electric field oscillating in
a specific direction - called linear polarization
- has often required bulky compowww.techbriefs.com
nents
due to design challenges, according
to Kang. He said a nanoscale device permitting
asymmetric transmission of linearly
polarized light could lead to significantly
more efficient optical devices, advancing
technological applications in communications
and more.
To identify an ideal unit cell design, the
team developed a computational optimizer
based on a genetic algorithm, which
identifies new configurations by mimicking
natural selection, with both self-designed
and commercial software to target
robust performance within set parameters.
Applying this approach to a 3D space
presented unique obstacles and benefits
when designing the optimizer. Generating
designs in an additional dimension, while
39
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