Fabrication of binary phase diffusers for space-variant processing
Techniques have previously been described for holographically representing space-variant systems. By spatially sampling the input plane and using phase mask diffusers to encode the multiple reference beams, one can sequentially record holograms exhibiting a minimal amount of crosstalk. Gold-coded binary phase masks have been shown to have good correlation properties with known cross-correlation bounds. This thesis describes a technique which generates phase masks using a laser scanner computer generated hologram (CGH) writing f a c i l i t y at a wavelength of 4579A. Methods for determining the proper resist thickness to achieve the necessary 180 degree phase shift between adjacent cells in a mask include analyzing the data taken by an interference microscope and quantitative analysis of the dc component present in the Fourier spectrum of the mask. Comparisons of the effectiveness of the phase masks with that of ground-glass were obtained using two different tests. First, the phase masks were used in a space-variant processor, and the results of the multiplexed holograms were compared to those obtained earlier using a ground-glass diff user. Secondly, computer-generated holograms were made using the phase masks as diffusers and the results were compared with those previously obtained using amplitude masks.