Brownian Motion in a Speckle Light Field: Tunable Anomalous Diffusion and Deterministic Optical Manipulation

TL;DR

This paper develops a theory for particle motion in speckle light fields, revealing tunable anomalous diffusion and enabling deterministic optical manipulation, with potential applications in guiding and sorting particles.

Contribution

It introduces a universal theory for Brownian motion in speckle potentials and demonstrates how to control diffusion and perform optical manipulation using speckle properties.

Findings

Tunable anomalous diffusion from subdiffusion to superdiffusion.

Identification of a universal timescale for particle motion in speckles.

Potential for simple, cost-effective optical manipulation techniques.

Abstract

The motion of particles in random potentials occurs in several natural phenomena ranging from the mobility of organelles within a biological cell to the diffusion of stars within a galaxy. A Brownian particle moving in the random optical potential associated to a speckle, i.e., a complex interference pattern generated by the scattering of coherent light by a random medium, provides an ideal mesoscopic model system to study such phenomena. Here, we derive a theory for the motion of a Brownian particle in a speckle and, in particular, we identify its universal characteristic timescale levering on the universal properties of speckles. This theoretical insight permits us to identify several interesting unexplored phenomena and applications. As an example of the former, we show the possibility of tuning anomalous diffusion continuously from subdiffusion to superdiffusion. As an example of the latter, we show the possibility of harnessing the speckle memory effect to perform some basic deterministic optical manipulation tasks such as guiding and sorting by employing random speckles, which might broaden the perspectives of optical manipulation for real-life applications by providing a simple and cost-effective technique.