Since the first introduction of the basic concepts of the hologram and the holographic process by Gabor, extensive advances have occurred in the techniques associated with the formation of the hologram, the materials used for recording the hologram, and the suggested applications of the various techniques. A hologram is, as explained in Chapters 25 and 26, the record of an interference pattern formed between a field (optical, acoustical, microwave, etc.) of interest and a known or reproducible background or reference field. When this record, the hologram, is illuminated with a beam equivalent to the reference field, the original field of interest can be recreated. Thus, both the amplitude and phase of the field of interest are stored and recreated, whereas normally, of course, if the field of interest is recorded alone, only the amplitude is stored and the field information is then restricted to the autocorrelation of that field.
Initially, despite the intriguing nature of the process itself, only limited positive results were obtained in the application of this unique invention. Nevertheless, some very important scientific results were obtained that provided the fundamental understanding of the process.
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