13 - Control of scattering interaction in disordered two-dimensional arrangements of silicon nanoparticles

We aspire to obtain complete control of the complex reflection and transmittance properties of optical nanosurfaces - two-dimensional arrangements of scattering nanoparticles - with near-zero absorption loss and subwavelength lateral resolution.A cornerstone of this research is a strong interaction of light with matter, which is commonly observed for a periodic modulation of the nanosurface permittivity, e.g., by periodic arrangements of scattering nanoparticles across a surface. The coherent built-up of many scattering events allows controlling the optical response and entails the observation of high quality optical resonances. However, the necessary long-range interaction is often detrimental for harvesting such resonances in applications. The optical response is sensitive to the external illumination and cannot be controlled across an extended spectrum. Introducing disorder into such structures can overcome these problems, but the resulting nanosurfaces usually suffer from notable loss of response strength. Moreover, controlling the optical response with high spatial resolution is not possible.To bypass this obstacle, the required strong light-matter interaction can also be achieved with scattering nanoparticles that exhibit an individual resonant response to an external field. This type of response is for example supported by nanoparticles made from high permittivity dielectrics, e.g. semiconductors at frequencies below the band edge. Compared to plasmonic nanoparticles they are appealing since they do not suffer from absorption, leaving scattering as the only remaining source of loss.However, controlling the optical response of arrangements of such high-permittivity nanoparticles at small length scales poses a challenge, as the mutual radiative interaction among all nanoparticles causes the optical response to explicitly depend on the arrangement of other nanoparticles at distances far apart. Here, we suggest adjusting the distance across which long-range interaction is observed by introduction of a tailored disorder to the arrangement of the scattering nanoparticles.

Moreover, tailored disorder not just in the position but also in the geometry of individual nanoscatterers allows to control both the far- and the near-field interaction. Applying these concepts to nanosurfaces composed of scattering nanoparticles with an individually tailored scattering response, e.g. where the electric and magnetic dipolar contribution are of same (complex) amplitude, will provide us with full control of the wave front of the reflected and transmitted light from such disordered nanosurfaces. Combined with the high efficiency of the individual nanoscatterer, we have access to a plethora of highly efficient, flat and lightweight optical devices including planar lenses, beam-shapers, beam deflectors, and holograms. To reach this project goal, we have combined theoretical and experimental expertise, both for the fabrication and the characterization.