Researchers at the University of Iceland, Harvard University, the University of Cologne and the Fraunhofer Institute Jena have demonstrated net optical amplification in a plasmonic waveguide. Achieving such a macroscopic propagation of surface plasma waves is critical for the detection and characterization of cells, virus particles or single molecules.
Surface plasmons, traveling along the interface between a metal and a dielectric, allow confining optical energy to volumes that are significantly smaller than those accessible with conventional dielectric waveguiding structures, such as optical fibers. Tightly focused optical energy can be used as a 'nano-probe' that provides valuable measurements, and the tight confinement of the optical field promises optical devices with reduced dimensions. But under normal circumstances, optical energy travels over very short distances in plasmonic waveguides before it is absorbed due to Ohmic loss in the metal.
The team of researchers developed a structure that provides sufficient amplification to overcome the intrinsic absorption of a plasmonic waveguide. A structure consisting of an ultra-thin gold film was embedded in a highly fluorescent polymer, and optically pumped by an ultrafast laser source. The structure channels the light generated by the fluorescent polymer to the plasmonic waveguide. As the plasmonic wave travels along the waveguide, its intensity is increased by stimulated emission of the optical energy stored in the fluorescent polymer.
- Malte C. Gather et al, Nature Photonics, 4, 457 - 461, 2010.