rougher, improving its ability to scatter light and enhancing the
“The light-extraction efficiency enhancement is very sensitive
to the dimension of the protuberances,” Yi said. More research is
needed to see whether there are benefits to adding more, he said.
During lab experiments, Yi discovered that adding the thin film
to the scintillator of an x-ray mammographic unit increased the
intensity of the emitted light by as much as 175 percent compared
with the output of a traditional scintillator.
The work appeared in Optics Letters ( http://dx.doi.org/10.1364/
OL. 37.002808) and represents a proof-of-concept evaluation of
the use of the moth eye-based nanostructures in medical imaging
materials. It also could be applied to various light-emitting
devices, Yi said.
Metamolecules switch handedness under light
Controlling the chirality of artificial molecules could
enable advances in communications and biomedical
imaging. Top, a scanning electron microscope image
of optically switchable chiral terahertz metamolecules. Bottom, the purple, blue and tan colors
represent the gold meta-atom structures at different
layers; two silicon pads are shown in green. Images
courtesy of Xiang Zhang et al, Berkeley Lab.
BERKELEY, Calif. – A new technique
that uses light to change the “handedness”
of artificial molecules could benefit terahertz technology applications from biomedical research to ultrahigh-speed communications and homeland security.
Using a light beam, the chirality of artificial molecules has been switched from a
right-handed orientation to a left-handed
one for the first time. Chirality is the distinct left or right orientation, or handedness, of some types of molecules – meaning it can take one of two mirror-image
forms. Called enantiomers, the right- and
left-handed forms of such molecules can
exhibit strikingly different properties; for
example, one enantiomer of the chiral
molecule limonene has a lemon scent,
while the other smells of orange.
The ability to observe or switch a molecule’s chirality using terahertz electromagnetic radiation is a coveted asset in high
“In electromagnetism, chirality or opti-
cal activity arises from the coupling be-
tween the electric and magnetic responses
of the materials,” said Xiang Zhang, one
of the leaders of the research and a princi-
pal investigator with the US Department
of Energy’s Lawrence Berkeley National
Laboratory’s Materials Sciences Div.
“However, in natural materials, the mag-
netic response is extremely weak at THz
and optical frequencies, and as a result,
the chirality is also very weak.”
Using terahertz metamaterials engi-
neered from nanometer-size gold strips
with air as the dielectric, Zhang and a
multi-institutional team of colleagues from
Los Alamos National Lab and the Univer-
sity of Birmingham in the UK fashioned a
delicate artificial chiral molecule that they
incorporated with a photoactive silicon
medium. By performing photoexcitation of
their metamolecules with an external light
beam, they observed dynamically con-
trolled handedness flipping in the form of
circularly polarized emitted terahertz light.