Non-Gaussian anomalous diffusion of optical vortices

Area of Science:

• Complex Systems Physics
• Optical Physics
• Soft Matter Physics

Background:

• Anomalous diffusion is common in biological and physical systems, deviating from standard Brownian motion.
• Optical vortices have previously only shown Brownian motion in random speckle fields.

Purpose of the Study:

• To experimentally demonstrate anomalous diffusion of optical vortices in complex media.
• To investigate the underlying mechanism and characteristics of this anomalous diffusion.
• To explore the potential applications of optical vortices in microrheology.

Main Methods:

• Utilizing temporally varying speckle patterns from multiple-scattering viscoelastic media.
• Analyzing optical vortex trajectories to identify self-similarity and antipersistent correlations.
• Modulating sample viscoelasticity to control diffusion properties.

Main Results:

• Direct experimental evidence of anomalous subdiffusion of optical vortices was observed.
• The motion exhibits self-similarity and antipersistent correlations, consistent with fractional Brownian motion (FBM).
• Vortex displacements follow a non-Gaussian heavy-tailed distribution, and diffusion properties are tunable via viscoelasticity.

Conclusions:

• Optical vortex diffusion in viscoelastic media is complex FBM but non-Gaussian.
• This finding provides fundamental insights into vortex dynamics and the decoupling of Brownianity and Gaussianity.
• Optical vortices show promise as endogenous tracers for microrheology applications.