Light imaging in a scattering medium, using ultrasonic probing and speckle image differencing

摘要

Coherent light is projected through a scattering medium. The light emerging from the medium is a superposition of a multitude of scattered wavelets, each of which represents a specific scattering path. These wavelets are projected onto a diffuse reflecting surface (the viewing plane of a two-dimensional photodetector array) where they interfere with each other, giving rise to a speckle pattern. By introducing a focused ultrasound pulse into the medium, the position of the scatterers are changed at a known location (probe region) in the medium, and this causes a change in the speckle pattern. By comparing speckle images before and after the scatterers are moved, the light absorption properties of the probe region can be measured even though multiple scattering interferes with direct imaging of the region.