Dark speckle imaging of colloidal suspensions in multiple light scattering media

Quasielastic multiple light scattering experiments have been performed on suspensions of particles in brownian motion embedded inside a solid turbid medium. The photon transport mean free path of the suspension and of its solid environment where adjusted to be identical. We show that by selecting a minimum intensity spat of the speckle pattern generated by the solid medium, it is possible to visualize objects which would be undetectable with common optical techniques. Our results are shown to be in agreement with a diffusion theory for the location of strongly absorbing objects inside multiple scattering media.