Synthetic Holography for Optical Testing

Abstract

—Computer Generated Holograms (CGH’s) have been used for the testing of aspherical surfaces. The CGH acts as a reference element in an interferometric configuration. The CGH’s may be generated either by coding both amplitude and phase or by coding only the phase of the wavefront. It may be safely assumed that the wavefronts encountered during testing are of uniform amplitude and hence the methods using only phase coding for the generation of the hologram are of more relevance to testing. We have modified the procedure by Birch et al for generating CGH. This modified procedure along with the concept of aberration balancing extends the capability of the CGH; even steep aspherics can be tested. The CGH’s have been generated for the wavefront from a plano-convex lens both for its axial and off-axial positions. The results of the experiments indicate that the CGH and provide a reference wavefront to an accuracy better than λ/10. An analysis of the errors introduced during fabrication and use of the CGH has been presented.