Coherent diffusion of partial spatial coherence

TL;DR

This paper extends the theory of partially coherent light propagation to include coherent diffusion, demonstrating experimentally and analytically how speckle patterns maintain coherence under diffusion in warm vapor, akin to diffraction.

Contribution

It introduces a diffusion analogue of the Van Cittert-Zernike theorem and experimentally studies speckle coherence propagation in diffusing atomic media.

Findings

Speckle coherence propagates similarly under diffusion and diffraction.

An analytic diffusion model explains experimental results.

Coherent diffusion of speckles is demonstrated in warm vapor.

Abstract

Partially coherent light is abundant in many physical systems, and its propagation properties are well understood. Here we extend current theory of propagation of partially coherent light beams to the field of coherent diffusion. Based on a unique four-wave mixing scheme of electro-magnetically induced transparency, an optical speckle pattern is coupled to diffusing atoms in a warm vapor. The spatial coherence propagation properties of light speckles is studied experimentally under diffusion, and is compared to the familiar spatial coherence of speckles under diffraction. An analytic model explaining the results is presented, based on a diffusion analogue of the famous Van Cittert-Zernike theorem.