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Nanoparticle arrays control light

18 Jun 2007

Light can be guided and manipulated at the nanoscale using "plasmonics physics", according to new calculations by US researchers. Maxim Sukharev and Tamar Seideman of Northwestern University have also shown that they can create nanoscale light sources that have controllable coherence and polarization properties. Such sources could be important for making a variety of all-optical nanodevices, from sensors and switches to superlenses and information storage devices.

Using a genetic algorithm and parallelized codes that numerically solve Maxwell's equations of classical electrodynamics, Sukharev and Seideman have shown that coherent properties of so-called plasmons – collective oscillations of conductive electrons in metal nanoparticles – can be used to control light propagation. Using the example of a T-junction composed of silver nanospheres, the researchers demonstrated that the polarization of light alone can be used to manipulate the propagation path of light through the spheres. This simple scheme could be used as an optical nanoswitch, or inverter, which would operate far below the diffraction limit.

The researchers also showed that incident light can be trapped by plasmonic crystals (periodic arrays of nanoparticles). Moreover, depending on the geometry of the crystal, the light can be focused and guided in a wavelength-sensitive fashion.

"Another result, which I expect to carry interesting implications in several fields, is the opportunity to create nanoscale light sources with controllable coherence and polarization properties," Seideman told nanotechweb.org. "Such sources could potentially extend the established and growing field of coherent optical control from the macro- into the nano-world."

The ability of the researchers to pre-design plasmonic nanodevices with desired functionalities may also have practical applications. "The ability to numerically not only predict the optical response, but also design the nanoconstruct so as to have desired properties, is necessary to develop all-optical nanodevices. These range from sensors and switches to superlenses and information storage devices," said Seideman. "We are fascinated by the possibility of controlling the pathways of light waves at array intersections, trapping and funnelling light in tiny plasmonic crystals, and designing functional devices based on wave interference concepts."

The team now hopes to develop ultrafast elements based on nanoplasmonic physics. Other projects include making intense nanoscale coherent sources with controllable polarization, studying the dynamics of single atoms and molecules in the presence of plasmon-driven electromagnetic fields and designing hybrid nanostructures, composed of metals and semiconductors, with predetermined optical properties.

The researchers reported their work in J. Phys. B: At. Mol. Opt. Phys.

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