Linear and nonlinear optical properties of metallic photonic crystals and pseudo/negative index materials

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Metallic photonic crystals can be composed of regular arrays of metallic nanoparticles on a waveguide. Strong coupling by light, especially through this underlying waveguide, leads to collective states. These states consist of localized particle plasmons and extended polaritonic excitations, similar to cavity polaritons in a semiconductor microcavity. We have two goals in our project: (a) We would like to understand and describe the linear optical properties of the coupled light-particle-plasmon system, especially the optical transmission and reflection properties that differ substantially from the spectra of individual metal nanoparticles. For example, we found strong Fano resonances as a sign of interference between a narrow resonance and a continuum. What exactly is the nature of these interfering states, and how are they coupled? What determines the coupling strength? Do these coupled systems form a complete photonic bandgap? What determines the size of the normal-mode coupling? (b) The coupled system exhibits a new type of excitations, so-called particle-plasmon-waveguide-polaritons. What is the lifetime of these excitations, what is their dephasing time? We want to study these coherent properties using nonlinear femtosecond spectroscopy, e.g., autocorrelation spectroscopy. Is it possible to tailor the dephasing times of the coupled system? Can we quantify the radiative and nonradiative contributions to the dephasing rate? Meeting these challenges will yield a fundamental and more complete understanding of the linear and nonlinear optical properties of collective excitations in metallic photonic crystals.