Bringing tunability to ultrafast nanoplasmonics

Abstract

The nanosciences are stimulating the possibility of engineering novel nanophotonics with tunable, tailored properties. In particular, nanocomposites with metallic nanoparticles embedded in an insulating host matrix (as shown in Figure 1), represent a distinctive class of nanoplasmonics: they have specific nonlinear characteristics due to enhancement of the local field. 2 The cost effectiveness of these materials could open up photonic applications in wave mixing, heterodyning, and modulation, and could expand their role in laser applications. In addition, nanoplasmonics could be an integrated component of nonlinear optical (NLO) devices: the global market for NLO materials was estimated at $856.1 million in 2005 and is expected to grow to $1,656 billion by 2009. Since nanoplasmonics are macroscopically isotropic, their nonlinear response is of the third order. The χcomposite(ω) enhancement—which takes place in the neighborhood of the plasmon frequency ωp—has been confirmed experimentally. In addition, they are fast: degenerate four-wave mixing and Z-scan in Au, Ag, and Cu-based nanoplasmonics have given values of about 10 − 10esu with response times on the picosecond scale. Further, because the notions of centro-symmetry and phase matching are not major concerns with these new materials, they should open up new possibilities for NLO nanophotonics. One of the technological challenges has been to fabricate these nanoplasmonics with the additional feature of reversible χcomposite(ω) frequency tunability: tuningωp via an external stimulus. As ωp is proportional to nmeff/2 host(ω), one could anticipate its tunability via the carrier density (n), the effective electronic mass (meff) of the metallic nanoparticles, or through the dielectric function of the dielectric host matrix (ωhost). While the first two of these parameters can be varied by changing the nature of the nanoparticles, the third option requires a radical change in the host matrix. The latter is more effective, as has been illustrated experimentally. Results with gold nanoparticles emFigure 1. Schematic illustration of a composite nanoplasmonic consisting of metallic nanoparticles embedded in a dielectric host matrix. In the neighborhood of the corresponding plasmon frequency, the local field Eloc is enhanced relatively to the excitation electromagnetic field Eexc.