The concept of diffusion is widely used to study propagation of light through multiple scattering media such as clouds, interstellar gas, colloids, paint, and biological tissue. Such media are often called random. This terminology is, however, misleading. Notwithstanding its complexity, the process of wave (e.g. light, sound, electron wave, etc) propagation is deterministic – i.e. given the exact position of scattering centers and the amplitudes of the impinging waves, one can uniquely determine the precise pattern of wave field throughout the system. This pattern can be represented in the basis of eigenchannels of multiple-scattering medium that are based on singular value decomposition of a suitably defined transmission/reflection/absorption matrix, and coupling into different eigenchannels can lead to such a diverse transport behaviors as perfect transmission/reflection/absorption.
The universal bimodal distribution of singular values of transmission matrix in lossless diffusive systems underpins such celebrated phenomena as universal conductance fluctuations, quantum shot noise in condensed matter physics, and enhanced transmission in optics and acoustics. In contrast to the distribution of singular values, the corresponding eigenchannels, are sensitive to the geometry – a specific choice of boundary conditions, placement of macroscopic inhomogeneities in the system, etc. In lossy systems, absorption and its spatial distribution represent the additional degrees of control. In this talk, we will demonstrate effective approaches to modify the eigenchannels in a deterministic way, opening up new opportunities for controlling energy distribution inside complex media via wave-front shaping.