Abstract

With raster scan devices, the spot size is usually about equal to the spacing between addressable points. Examples include E-beam lithography systems and spatial light modulators. Methods for synthesis of digital holograms that have evolved for use with vector plotters, where the spot size is much greater than the step size, cannot make full use of the resolution of these devices. The most faithful encoding of the wave front at the hologram is achieved by processing each addressable point individually, using as many samples from the wave front as there are points in the hologram. We may distinguish three classes of synthesis techniques based on the type of processing involved. In order of increasing computational demand, these are (1) point-to-point spatially periodic, memoryless processing, (2) spatially recursive and possibly spatially periodic processing, and (3) iterative processing. We compare several methods from these three categories in terms of diffraction efficiency and fidelity of the reconstructed image. As a quantitative measure of fidelity, we consider the mean-squared and maximum errors between the optimally scaled reconstruction and the object. These measurements are based on both digitally reconstructed holograms and optical reconstruction of holograms synthesized using an E-beam lithography system and a Litton iron-garnet spatial light modulator.

© 1985 Optical Society of America