Stirring of the propagation and the absorption of light in complex nanophotonic media

This thesis presents experimental investigations into the propagation of light inside both disordered and ordered complex photonic systems. The experimental results are interpreted using theoretical and numerical models. One of the main focus of this thesis is to determine experimentally and theoretically the distribution of the energy density inside a scattering medium when the incident wavefront is optimized. As a starting point, we calculated the energy density inside a 2D waveguide with disorder and decomposed the energy density in terms of the eigenfunctions of the diffusion equation. We found that very few eigenfunctions (e.g M = 1 for an open transmission channel and M = 7 for shaped waves) are remarkably su�fficient to reconstruct the energy densities. The fact that the reconstruction can be accomplished with a few number shows that the energy density inside the scattering is similar to the diffusion eigenfunctions. A rigorous theoretical proof of this similarity is, however, still an open challenge at this time. One approach is to derive the energy density as a function of depth based on the principle of conservation of flux and the known total transmission. We have measured the total stored energy and the depth-dependent energy density inside three-dimensional scattering media. The energy density was probed using fluorescent nanoparticles distributed inside the sample. The experimental data reveal that the total stored energy is enhanced using wavefront shaping in agreement with theoretical prediction and numerical simulations. Our result can be used to control the color of white LED. A white LED has a blue LED that illuminates phosphor particles, which both scatter and absorb blue light and re-emit in the red wavelengths [92]. Optimizing on the blue light will increase the blue content of the white LED as well as the red, since the total energy stored is enhanced. On the other hand, the red content of the white LED can be increase by optimizing on only the red re-emitted.