Null detection of ballistic photons for locating objects buried in turbid media.

We describe an optical system in which a vibration induced to a laser probe beam combined with a half-blocked photodiode allows determination of the position and width of objects buried in turbid media. Our system is based on the detection of an AC signal which drastically decreases under the presence of an obstructing buried object. We describe the technique and include experimental results showing that the system is capable of detecting 2 mm wide objects buried at depths up to 3 cm from the front surface of a sample simulating scattering properties of soft tissue. [ABSTRACT FROM AUTHOR]