Abstract

It has been recently demonstrated¹ that the ballistic component (photons that arrive first) through random media can be separated in time from the diffused scattering component. This report addresses time-resolved two-dimensional imaging of the ballistic signal emanating from point and plane objects located in turbid media. We used an ultrafast Kerr gating system, consisting of a mode-locked ps glass laser, a CS2 Kerr shutter, and a two-dimensional change-coupled device camera with 600400 spatial resolution to record the images. A pair of 200 m point sources separated by 400 m in water solution with scattering beads, was resolved using a fluorescence time gating. A U.S. Air Force bar-test chart was placed inside the water solution filled with beads at OD = 4. The diffused and ballistic signals from the chart were imaged at different times. At T = 0, we obtained a clear bar image with the spatial resolution 500 m. These key observations are the result of ballistic photons arriving first at the Kerr gate. When the gating time was delayed, the images broadened and blurred. The time difference between the ballistic and the diffusive scattering components was measured to be 15 ps.

© 1990 Optical Society of America