Reflection, transmission, absorption, diffraction and gain in plasmonic-photonic Ag-capped monolayers of dye-doped nanospheres

Summary form only given. Numerical 3D simulations of plasmonic-photonic systems with periodicity d~λ under oblique incidence are challenging in the visible spectral range. Many interacting modes, strong dispersion of the metal, as well as the complex geometry and sharp features resulting in hot spots have to be included. Different phases of temporal harmonics require significant modifications of conventional broadband FDTD approaches. For this reason quantitative modeling of such structures is usually restricted only to the normal incidence (θ=0°) reflection R, transmission T and extinction E=1-R-T. To find the absorption A, which is important in active nanoplasmonic and metamaterial devices, one has to take into account the often neglected diffraction D.To come around these problems, we use a frequency domain solver with multi-mode Floquet port excitation and unit cell boundary conditions; blended edges, an adaptive tetrahedral mesh, experimental optical parameters of metals, and the parallelization capabilities of the CST MWS® software. In this way, E can be subdivided into A and D on both sides of the structure. Using this flexible framework, we model self-assembled monolayers (ML) of polystyrene (PS) nanospheres (diameter d=390 nm) on a glass support, covered by 40 nm of Ag (Fig. 1c). Such hybrid plasmonic-photonic crystal slabs are interesting because of their ability to manipulate and redirect light and ease of manufacturing over areas of up to some mm2 [1]. Gain is introduced into the system when optically pumped fluorescent dyes (absorption/emission maxima at 468/513 nm) are embedded into PS spheres.In our system the extraordinary transmission (EOT, Fig. 1a, red curve) exists without any holes in the structure (Fig. 1c). Its angular dispersion does not follow simple plasmonic model. The polarization conversion (s↔p, by several %) is observed for T and R, when the plane of incidence does not have mirror symmetry, and f- r D even in symmetric cases (Fig. 1b). The polarization, azimuthal orientation of the incident plane (angle ij in Fig. 1) and irradiation direction strongly influence R, T and D, and to a lesser extent A. Furthermore, for dyedoped PS spheres with realistic dye concentrations, Lorentzian gain leads to compensation of A, EOT values T>1, as well as enhancement in R and D. Higher concentrations lead to further amplification and line narrowing typical for the approach to lasing threshold (Fig. 1d).