Random scattering of light, e.g., in paint, cloud and biological tissue, is a common process of both fundamental interest and practical relevance. The interference of multiply scattered waves leads to remarkable phenomena in mesoscopic physics such as Anderson localization and universal conductance fluctuations. In applications, optical scattering is the main obstacle to imaging or sending information through a turbid medium. Recent developments of adaptive wavefront shaping and phase recording techniques in optics have enabled the experimental demonstrations of imaging and focusing light through opaque samples. By shaping the incident wavefront, we showed that the total transmission of light through a highly scattering medium can be varied by several orders of magnitude. Such a significant modification of the total transmission is made possible by the mesoscopic correlations. In addition, we demonstrated that coherent illumination and wave-front shaping can be used to make a weakly absorbing cavity perfectly absorbing and to enhance strongly the absorption of a multiple scattering medium. The coherent control of absorption is achieved not by modifying the property of the absorbing medium, but by manipulating the incident light. The potential applications include deep tissue imaging, optical communication, photovoltaics and radiation treatment.

Experimental control of light intensity distribution inside a random scattering system by shaping the incident wavefront. (a) Top-view scanning electron micrograph of a silicon waveguide fabricated by e-beam lithography and reactive ion etching. The left inset shows air holes of diameter 90 nm randomly distributed inside the waveguide. The sidewalls of the waveguide consist of a triangular lattice of air holes that reflect light (right inset). (b, c) Two-dimensional intensity distribution inside the disordered waveguide shown in (a) for a random input field (b) and for the optimized input wavefront for maximum light penetration into the disordered structure. The lower panels depict the cross-section-averaged intensity as a function of penetration depth z.