HOLOGRAPHY: FINCH holography uses incoherent illumination

摘要

Incoherent-light holograms are potentially useful in three-dimensional (3-D) outdoor and astronomical imaging, as well as fluorescence holographic microscopy. Although 3-D computed holograms have been created by taking multiple images of incoherently illuminated objects from multiple points of view, this process is slow and many images are needed. Another technique, scanning holography, uses a point detector to integrate the light intensity from Fresnel zone plates that are mechanically scanned over the object. Although the process produces a Fresnel hologram (obtained as a correlation between the object and the zone-plate patterns), it is also relatively slow. Using a variation of Fresnel holography, researchers at the Johns Hopkins University Montgomery County Campus Integrated Imaging Center (Rockville, MD) have implemented a new and faster method of recording holograms. The method, called Fresnel incoherent correlation holography (FINCH), uses incoherent illumination. Instead of using mechanical scanning or movement, the technique records on a CCD three sequential images of light reflected by a 3-D incoherently illuminated object that have propagated through a diffractive optical element (DOE). The three recorded holograms use a different phase factor of the DOE and are then superposed in the computer, resulting in a Fresnel hologram that reveals the physical features of the 3-D object.