Exploiting scattering media for exploring 3D objects

Scattering media, such as diffused glass and biological tissue, are usually treated as obstacles in imaging. To cope with the random phase introduced by a turbid medium, most existing imaging techniques recourse to either phase compensation by optical means or phase recovery using iterative algorithms, and their applications are often limited to two-dimensional imaging. In contrast, we utilize the scattering medium as an unconventional imaging lens and exploit its lens-like properties for lensless three-dimensional (3D) imaging with diffraction-limited resolution. Our spatially incoherent lensless imaging technique is simple and capable of variable focusing with adjustable depths of focus that enables depth sensing of 3D objects that are concealed by the diffusing medium. Wide-field imaging with diffraction-limited resolution is verified experimentally by a single-shot recording of the 1951 USAF resolution test chart, and 3D imaging and depth sensing are demonstrated by shifting focus over axially separated objects. By exploiting the lens-like properties of a scattering medium, scientists have imaged objects concealed by a diffuse material. Alok Kumar Singh and co-workers from the University of Stuttgart in Germany performed imaging based on speckle intensity correlation but with the important addition of a reference point source near the object to be imaged. The object is illuminated with spatially incoherent light, which is scattered by a suitable medium, such as a diffuser or piece of chicken breast. An image sensor then detects the resulting two-dimensional speckle intensity patterns. Experiments with a USAF standard test target demonstrated that the approach can deliver diffraction-limited spatial resolution. Three-dimensional imaging is possible by capturing a series of speckle patterns with the image sensor at different axial positions.