The concept of cross density of states characterizes the intrinsic spatial coherence of complex photonic or plasmonic systems, independently on the illumination conditions. Using this tool and the associated intrinsic coherence length, we demonstrate
unambiguously the spatial squeezing of eigenmodes on disordered fractal metallic films, thus clarifying a basic issue in plasmonics.
We present numerical calculations of the Local Density of Optical States (LDOS) in the near field of disordered plasmonic films. The calculations are based on an integral volume method, that takes into account polarization and retardation effects, an
d allows us to discriminate radiative and non-radiative contributions to the LDOS. At short distance, the LDOS is dominated by non-radiative channels, showing that changes in the spontaneous dynamics of dipole emitters are driven by non-radiative coupling to plasmon modes. Maps of radiative and non-radiative LDOS exhibit strong fluctuations, but with substantially different spatial distributions.
We establish a fundamental relationship between the averaged density of states and the extinction mean free path of wave propagating in random media. From the principle of causality and the Kramers-Kronig relations, we show that both quantities are
connected by dispersion relations and are constrained by a frequency sum rule. The results are valid under very general conditions and should be helpful in the analysis of measurements of wave transport through complex systems and in the design of randomly or periodically structured materials with specific transport properties.
