ABSTRACT
The earliest approach to “digital holography” sought to calculate numerically the complex wave front scattered by a virtual object [1,2]. By combining this wave front with a virtual reference beam, the resultant interference pattern could be calculated within a given medium. From the mid-1960s onwards, researchers used a combination of printing and photographic reduction methods to produce crude synthetic holograms from such calculated patterns. The technique of numerically synthesising and then physically encoding the interference pattern corresponding to a virtual object has today come to be known as computer-generated holography (CGH). The availability of comparatively cheap computational power has led to CGH now being used routinely to record high-quality transmission holographic gratings encoding either image or non-image data using electron beam lithography. Modern techniques allow the mass replication of such gratings for applications such as holographic security features and holographic optical elements (HOEs).
