Nanolocalization of time-reversed coherent optical fields in random scattering media

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The far field emission pattern of a nanoscale light emitter positioned in a nanoscale random scattering environment contains information about the localized emission. Because of the reciprocity of electromagnetic wave propagation time-reversing the outgoing wave creates an excitation that propagates back to the emitter and localizes on a sub-diffraction limited length scale. In the microwave regime this nanolocalization was recently demonstrated by selectively addressing microwave antennas separated only by λ/30 (G. Lerosey, et al., Science 315 (2007) 1120). Also for the second funding period we propose to experimentally demonstrate nanolocalization of radiation based on time-reversed fields in the visible range of the electromagnetic spectrum. The theoretical and experimental investigations performed in the first funding period have shown that nanotextured layered materials, as they are used in thin film solar cells to increase the absorption efficiency, are well suited to investigate light localization in one dimension. Spectral phase and amplitude of the scattered radiation is characterized by spectral interference measurements and a vector field synthesizer allows back-propagating the time reversed field. Two-photon fluorescence is used to demonstrate that the time reversed fields indeed exhibit spatiotemporal focusing in the layered structure. Comparison with adaptively optimized and unshaped pulses allows estimating the efficiency of nanolocalization via time reversal. Using the same technique, nanoparticle aggregates acting as random optical nanoantennas will be used to demonstrate localization in three dimensions. In addition we will investigate how the nanolocalization is influenced by dissipation in the scattering medium, the polarization degree of freedom and the properties of the nanostructure (resonances in the response, reverberation chamber). Besides the topic of nanolocalization of time reversed fields we will also study the adaptive optimization of light propagation and localization in random scattering media. The model calculations show that in comparison to nanolocalization of time-reversed fields a significantly improved selectivity of the local excitation is expected for adaptively optimized fields. The goal is to demonstrate spatiotemporal excitation control in suitably designed and dye-functionalized random nanoantennas. Besides the topic of nanolocalization of time reversed fields we will also study the adaptive optimization of light propagation and localization in random scattering media. The model calculations show that in comparison to nanolocalization of time-reversed fields a significantly improved selectivity of the local excitation is expected for adaptively optimized fields. The goal is to demonstrate spatiotemporal excitation control in suitably designed and dye-functionalized random nanoantennas.