Optics of disordered systems group

Current Interests

Imaging in biological systems: Scattering is a huge problem for non-invasive optical imaging in biological systems, as scattering from the inhomogeneities in the tissue often limit microscopy to the surface of the sample or (at best) to a shallow depth. Optical imaging through a strongly scattering system is currently an unsolved problem, but in recent years several possible approaches were put forward. The line of research I follow is based on the idea that multiple scattered light possesses non-trivial correlations, which can be exploited to extract information from beyond a scattering material.

Analogue computation using light: Nowadays we are used to the idea that computation is synonymous with digital computers, but it wasn't always like that. Analogue computers had a very important role until a few decades ago. Modern technological developments, like the introduction of fast and reliable spatial light modulators, allow us to control light propagation to a degree that was unthinkable just a few years ago, opening the possibility to a revival of analogue computation (or at least hybrid analogue-digital computation) using light to perform selected tasks at the speed of light.

Light scattering in correlated systems: Describing transport in a disordered environment is a complicated task, so it is no surprise that some simplifying assumptions are made. The most common of these assumptions is that the disorder can be modeled as white noise, i.e. all the correlations are neglected. But if we look around us most of what we see definitively does not show a crystalline  kind of order and periodicity, but it is not even white noise. Most of the time things have some degree of randomness, but still have correlations. Understanding how light (or other waves) propagate in a correlated disordered potential is still an understudied problem, which can have very practical applications.

Past interests (that resurface quite often)

Anderson localization: When light scattering gets so strong that successive scattering event can not be treated as independent anymore, interference between different possible paths become dominant and the system has a phase transition from a conductive (diffusive) regime to a localized regime where diffusion-like transport is impossible. This regime is known as Anderson localization. There is a heated debate if Anderson localization of light in 3D is even possible at all, but even Anderson localization in 1D and 2D keeps showing surprising results, even after many years of study.

Anomalous transport: In the textbook case of normal diffusion, particle transport is described as a random walk to which all the steps give the same contribution (Brownian motion). Superdiffusion occurs when the transport is dominated by a few very large steps (Lévy flights). In this regime the variance of the step length distribution diverges and the mean square displacement grows faster than linear with time, leading to what is known as anomalous diffusion.