A system for forming an image of an object in a turbid medium comprises a light
source for producing a coherent light beam of a selected frequency that is divided
by a beamsplitter into a reference beam directed along a first optical path and
a signal beam directed along a second optical path where the object to be imaged
is located. The signal beam impinges upon the object and reflects back toward the
beamsplitter. The reference beam is modulated to shift its frequency. A mirror
reflects the reference beam back toward the beamsplitter for combination with the
signal beam to produce an output optical signal. A photodetector receives the output
optical signal from the beamsplitter and produces an electrical signal having a
frequency related to shifts in frequency between the reference beam and the signal
beam and having an amplitude proportional to the image intensity. A heterodyne
detector connected to the photodetector produces a beat signal when the first and
second optical paths have matching lengths so that the location of the point on
the object where the signal beam reflected can be determined. By scanning the signal
beam across the object, the system determines locations of a number of points on
the object sufficient to form its image.