Stirring of the propagation and the absorption of light in complex nanophotonic systems
| Abstract | This thesis presents experimental investigations into the propagation oflight inside both disordered and ordered complex photonic systems. Theexperimental results are interpreted using theoretical and numericalmodels. One of the main focus of this thesis is to determineexperimentally and theoretically the distribution of the energy densityinside a scattering medium when the incident wavefront is optimized. Asa starting point, we calculated the energy density inside a 2D waveguidewith disorder and decomposed the energy density in terms of theeigenfunctions of the diffusion equation. We found that very feweigenfunctions (e.g M = 1 for an open transmission channel and M = 7 forshaped waves) are remarkably suffficient to reconstruct the energydensities. The fact that the reconstruction can be accomplished with afew number shows that the energy density inside the scattering issimilar to the diffusion eigenfunctions. A rigorous theoretical proof ofthis similarity is, however, still an open challenge at this time. Oneapproach is to derive the energy density as a function of depth based onthe principle of conservation of flux and the known total transmission.We have measured the total stored energy and the depth-dependent energydensity inside three-dimensional scattering media. The energy densitywas probed using fluorescent nanoparticles distributed inside thesample. The experimental data reveal that the total stored energy isenhanced using wavefront shaping in agreement with theoreticalprediction and numerical simulations. Our result can be used to controlthe color of white LED. A white LED has a blue LED that illuminatesphosphor particles, which both scatter and absorb blue light and re-emitin the red wavelengths. Optimizing on the blue light will increase theblue content of the white LED as well as the red, since the total energystored is enhanced. On the other hand, the red content of the white LEDcan be increase by optimizing on only the red re-emitted. |
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| Authors | O. S. Ojambati |
| Year of publication | 2016 |
| Date published | 09/2016 |
| Journal | Thesis advisors: W. L. Vos, A. Lagendijk, and A. P. Mosk |
| School | University of Twente |
| Keywords | correlations, diffusion, disordered media, photonic crystal, transmission eigenchannels, Wavefront shaping |