Scattering is the key
Allard P. Mosk
Random scattering of light, which takes place in paper, paint and biological tissue is an obstacle to imaging and focusing of light and thus hampers many applications. At the same time scattering is a phenomenon of basic physical interest as it allows the study of fascinating interference effects such as open transport channels [1,2]. These are complex field patterns which propagate through strongly scattering materials without loss or backscattering. The open channels fit the nanostructure of the scattering medium like a lock and key, which enables high-security authentication and communication protocols. These protocols exploit both the complexity of a scattering material and the unclonability of the quantum state of a photon [3,4].
Imaging through scattering media has been transformed by the use of computers to control the light and process the data. Scattering “lenses” made of high-index materials allow wide-field speckle-illumination microscopy with a resolution approaching 100 nm , by the use of phase-retrieval algorithms. More advanced machine learning algorithms that process the scattered light patterns pave the way to new methods to recognize and classify objects that cannot be directly imaged.