Imaging through Diffusing Media by Image Parametric Amplification

Abstract

Imaging through thick diffusing media requires selection of the least scattered light, because ballistic light is only transmitted up to a few millimeters. Hence, temporal gating, i.e. isolation of the front part of a femto or a picosecond pulse appears as a promising tool to form images of objects embedded in thick media, like tumors in human breast. We have used parametric image amplification to obtain images with a time gate duration of about 20 ps. At first, we used latex beads solutions, whose diffusing properties are well known, to characterize the method and its dynamic range for selection of the ballistic light. In a second step, objects embedded in biological tissues, like chicken meat, were imaged. The best results have been obtained by forming the image without lenses, by exploiting the fact that the idler is phase-conjugated with respect to the signal in the transverse directions, while it propagates forward. A 1 cm³ piece of liver embedded in a 4 cm thick chicken breast tissue has been detected.