Measurements of strong correlations in the transport of light through strongly scattering materials

Abstract

In this thesis, we study light transport through multiple scattering random photonic materials. Light incident on such materials undergoes many scattering events before exiting the material. The relation between the incident and the transmitted fields is determined by the optical transmission matrix of the material. If one knows this matrix, one can send a pre-designed field to the scattering material to get the desired transmitted field. According to theory, light transport through scattering materials takes place via open transmission eigenchannels with transmission coefficient close to 1. If one can design an incident field that couples only to the open transmission eigenchannels, one can get unity transmission through a scattering material. The theory also predicts that the number of open transmission eigenchannels is small. This leads to the transmitted fields to be a superposition of a small number of independent fields and makes them correlated. One can study these correlations by studying optical transmission matrices of scattering materials. A large part of this thesis is devoted to measuring and analyzing optical transmission matrices of strongly scattering random photonic materials, in particular random photonic ZnO nanoparticles and GaP nanowire ensembles. As the scattering becomes stronger, the number of open transmission eigenchannels becomes even smaller, making the transmitted fields even more strongly correlated. When a large enough portion of the transmission matrix is measured, these correlations show up in the singular value histograms of the measured transmission matrices. We study singular value histograms of the measured matrices and observe correlations. We also demonstrate retrieving the scattering strength of the GaP nanowire ensemble from the measured transmission matrix. Moreover, we study intensity fluctuations in the speckle transmitted through random photonic ZnO nanoparticle media. We observe that the measured speckle intensity histogram is in line with predictions of theory. Finally, we describe an experiment where we control light transport through a random photonic TiO2 paint layer using wavefront shaping with binary amplitude modulation. We blocked the portion of the field that interferes destructively with the rest of the field at a pre-determined target area behind the scattering sample, creating a bright spot at the target.