Plasmons in Flatland..Seeing the Light in two dimensions

[Guest guest]

The American Institute of Physics Bulletin of Physics News

Number 770 March 23, 2006 by Phillip F. Schewe, Ben Stein

 

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 relatively large circuit dimensions---1 micron) and

electronics (relatively low throughput but tiny dimensions---tens of

nm). 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 APS March Meeting, which took place last week in

Baltimore.

1. Plasmons in biosensors and cancer therapy: Naomi Halas (Rice

Univ., halas) 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

bio-molecules. The plasmons's 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 (Univ. Maryland,

smoly) 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

waveguide.

3. Photon-polariton superlensing and giant transmission: Gennady

Shvets (Univ. Texas, gena) 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% of the total surface area, 30% of the light got through,

courtesy of plasmon activity at the holes.

4. Future plasmon circuits at optical frequencies: Nader Engheta

(Univ. Pennsylvania, engheta) 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 (10^10

Hz) or microwave (10^12 Hz) but at optical (10^15 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.

 

From the very very Large to the very very Small, and moving rather

fast/slow, the people found themselves stuck right here in the middle

of things....bob