Digital recording and numerical reconstruction of holograms: reduction of the spatial frequency spectrum

Abstract

Direct recording of Fresnel holograms on a charge-coupled device and their numerical reconstruction is possible if the maximum spatial frequency of the holographic microstructure is adapted to the spatial resolution of the detector array. The maximum spatial frequency is determined by the angle between the interfering waves. For standard CCDs with spatial resolutions of ;100 lines/mm, the angle between ref- erence and object wave is limited to a few degrees. This limits the size of the objects to be recorded or requires a great distance between object and CCD target. A method is described in which the primary object angle is optically reduced so that objects with larger dimensions can be re- corded. The principle is demonstrated for the example of deformation analysis. Two Fresnel holograms, which represent the undeformed and the deformed states of the object, are generated on a CCD target, stored electronically, and the wave fields are reconstructed numerically. The interference phase can be calculated directly from the digital holograms, without generating an interference pattern. As an application of this method, we present the transient deformation field of a plate that is loaded by an impact. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: digital holography; hologram interferometry; numerical hologram reconstruction; charge-coupled devices.