Three-dimensional shape recognition using computer-generated holograms and temporal light-in-flight technique.

Visualization of light propagation and light in flight are general names for viewing a pulse of light traveling through an optical system. Abramson suggested [Appl. Opt. 30, 1242 (1991)] the use of light-in-flight techniques for holographic comparison of different objects. His system is based on sending picosecond pulses in such a sequence that, if the object has the desired shape, all the scattered light arrives simultaneously at an ultrafast detector. The result is that the shortness of the detected pulses is a measure of the similarity between a holographically recorded master object and the test object. The reference hologram is recorded from a master surface, which is not always available. This method suffers from low-contrast results. A computer-generated-hologram technique is suggested and mathematically analyzed. This technique overcomes the low-contrast problem, and a master object is not needed.