Sensing the Position of a Single Scatterer in an Opaque Medium by Mutual Scattering

Tracking the position of a single particle within opaque samples is a major challenge in optics. It is usually done by sending a single beam of waves to a target and studying the scattered waves, as in typical X-ray experiments for weakly interacting samples. The recent development of multiple-beam techniques such as optical wavefront shaping, where light scattering with multiple properly phased incident beams, has opened new potential for research of strongly interacting opaque samples. In this work, we show that mutual scattering is a powerful method to detect the displacement of a single scatterer in an optically dense sample of many (up to
$\mathrm{N}=1000)$
similar scatterers. We illustrate that our multiple-beam technique provides speckle patterns with an angular sensitivity at least 10 times higher than the traditional one-beam techniques and can be a powerful tool in imaging and metrology applications.