Two-dimensional light, or plasmons, can be triggered when light
strikes a patterned metallic surface. Plasmons may well serve as a
proxy for bridging the divide between photonics (high throughput of
data but also at the relatively large circuit dimensions of one micron,
or one thousandth of a millimeter) and
electronics (relatively low throughput but tiny dimensions of tens of
nanometers, or millionths of a millimeter).
One might be able to establish a hybrid discipline,
plasmonics, in which light is first converted into plasmons, which
then propagate in a metallic surface but with a wavelength smaller
than the original light; the plasmons could then be processed with
their own two-dimensional optical components (mirrors, waveguides,
lenses, etc.), and later plasmons could be turned back into light or
into electric signals.
To show how this field is shaping up, here
are a few plasmon results from that great international physics
bazaar, the March Meeting of the American Physical Society,
which took place last week in Baltimore.
1. Plasmons in biosensors and cancer therapy:
Naomi Halas (Rice
University, firstname.lastname@example.org) described how plasmons excited in the surface
of tiny gold-coated, rice-grain-shaped particles can act as powerful,
localized sources of light for doing spectroscopy on nearby
The plasmons' electric fields at the curved ends of
the rice are much more intense than those of the laser light used to
excite the plasmons, and this greatly improves the speed and
accuracy of the spectroscopy. Tuned a different way, plasmons on
nanoparticles can be used not just for identification but also for
the eradication of cancer cells in rats.
2. Plasmon microscope:
Igor Smolyaninov (University of Maryland,
email@example.com) reported that he and his colleagues were able to
image tiny objects lying in a plane with spatial resolution as good
as 60 nm (when mathematical tricks are applied, the resolution
becomes 30 nm) using plasmons that had been excited in that plane by
laser light at a wavelength of 515 nm. In other words, they achieve
microscopy with a spatial resolution much better than diffraction
would normally allow; furthermore, this is far-field
microscopy -- the light source doesn't have to be located less than a
light-wavelength away from the object.
This work is essentially a
Flatland version of optics. They use 2D plasmon mirrors and lenses
to help in the imaging and then conduct plasmons away by a
3. Photon-polariton superlensing and giant transmission:
Shvets (University of Texas, firstname.lastname@example.org) reported on his use of
surface phonons excited by light to achieve super-lens (lensing with
flat-panel materials) microscope resolutions as good as
one-twentieth of a wavelength in the mid-infrared range of light.
He and his colleagues could image subsurface features in a sample,
and they observed what they call "giant transmission," in which
light falls on a surface covered with holes much smaller than the
wavelength of the light.
Even though the total area of the holes is
only 6 percent of the total surface area, 30 percent of the light got through,
courtesy of plasmon activity at the holes.
4. Future plasmon circuits at optical frequencies:
(University of Pennsylvania, email@example.com) argued that
nano-particles, some supporting plasmon excitations, could be
configured to act as nm-sized capacitors, resistors, and
inductors -- the basic elements of any electrical circuit.
The circuit in this case would be able to operate not at radio (1010
Hz) or microwave (1012 Hz) frequencies
but at optical (1015 Hz) frequencies.
This would make possible the miniaturization and direct processing
of optical signals with nano-antennas, nano-circuit-filters,
nano-waveguides, nano-resonators, and may lead to possible
applications in nano-computing, nano-storage, molecular signaling,
and molecular-optical interfacing.