Abstract

We describe and analyze a system comprising a confocal scanning system, a coherent spatial filtering system, followed by detection, and then a second spatial filtering system. In this method, an object is embedded in an inhomogeneity, in particular, a diffusing material. A point source of light scans across the front surface of the diffuser. Transmitted light illuminates the object, embedded within the diffuser. The light emerging from the diffuser is imaged onto a detector, in front of which is a slit that moves in synchronism with the illuminating beam, or alternatively, the inhomogeneity object structure moves in synchronism with the photographic emulsion. Since the illuminating source is coherent and remains so during its passage through the diffusing material, a coherent spatial filtering operation is possible and is performed at the focal plane of the first imaging lens. The emerging light falls on a detector, which could be a photographic plate, or preferably, a real time recording material such as a liquid or photorefractive crystal device. The detector thus makes a coherent-to-incoherent conversion. The next step is to undo the blurring effect of the diffuser process by a restoration filter that is essentially of a high pass nature. Because of the recording process, the overall process is not linear; thus, the restoration process may not, in general even in a noise-free system, lead to a perfect reconstruction.

© 1989 Optical Society of America