Reciprocity-assisted ghost imaging through dynamic random media

Ghost imaging enables the imaging of an object using intensity correlations between a single-pixel detector placed behind the object and a camera that records the light that did not interact with the object. The object and the camera are often placed at conjugate planes to ensure correlated illumination patterns. Here, we show how the combined effect of optical reciprocity and the memory effect in a random medium gives rise to correlations between two beams that traverse the random medium in opposite directions. In a proof-of-principle experiment, we observe such correlations when the beams traverse two thin diffusers separated by a variable distance. We find that the angular width of the region over which the beams are correlated decreases as the distance between the diffusers is increased. We then utilize these correlations to demonstrate a ghost imaging scheme in which the object and camera are placed at opposite ends of the random medium and illuminated by counter-propagating beams that can potentially be emitted by two different sources.