Vadim Markel

Associate Professor of Radiology and Bioengineering

PENN ENGINEERING, School of ENGINEERING and APPLIED SCIENCE - Philadelphia, PAMetal Nanoparticle Chains as Optical Waveguides

ABSTRACT: The conventional optical waveguides such as optical fibers are made of transparent dielectrics. In order to support a propagating mode, the transverse dimension of the fiber must be larger than approximately one half of the wavelength. At the optical and near-IR frequencies, this condition places a practical limit on miniaturization of integrated optical devices. Therefore, development of novel optical elements of subwavelength size requires an alternative choice of materials. Currently, there exists a considerable interest in using the ``plasmonic materials'', that is, nanostructured high-conductivity metals. In particular, a waveguide can be realized as either a metal nanowire or a chain of metal nanoparticles. If the phase velocity of a polarization wave propagating along a chain is lower than the speed of light in the host medium, the electromagnetic field is exponentially localized near the chain. Such exponentially localized excitations are known as the surface plasmon polaritons (SPPs). In the absence of geometrical defects or irregularities, the SPPs propagate without radiative losses or scattering.A fascinating property of light transport in nanoparticle chains is that mechanical contact of the nanoparticles is not required. Nanoparicles in an chain can be viewed as miniature ``beacons'', which transmit the optical excitations along the chain. Another interesting feature is the exceptional tunability. There are almost limitless possibilities to vary the nanoparticles' shape as well as the chain composition and design and, by doing so, to vary the SPP propagation distance and dispersion law. The latter is of primary importance. The dispersion curve of a good waveguide must be approximately linear in a certain range of frequencies, which, in turn, determines the waveguide's bandwidth.

These and other topics relevant to the waveguiding properties of metal nanoparticle chains will be discussed in my talk.