Observation of fluctuations of the local density of states in disordered photonic media

Local density of states (LDOS) uniquely describes the available optical eigenmodes in which photons can exist at a specific spatial location. The LDOS controls the spontaneous emission, which is a fundamental phenomenon associated with the creation of light from the source. In disordered photonic media, the average LDOS is independent of the photonic properties, and only scales with the effective refractive index. Instead, strong sample- to-sample fluctuations of the LDOS are the characteristics of a disordered medium. Qualitative calculations of the fluctuations of the LDOS were previously made in the contexts of the nonlinear sigma model and the intensity correlations in speckle patterns. To date, however, there have not been any experiments to confirm this theory. This paper investigates spontaneous emission of emitters in the disordered photonic media. Time-resolved measurements on single polystyrene spheres incorporated with dye molecules, which are embedded inside a disordered layer of ZnO nanoparticles, are done. Fluorescence images of single fluorescent spheres embedded in a 4.8 mum-thick layer of ZnO pgiment at a depth of 2.5 mum are obtained.