Methods of Digital Holography

Digital holography is the analysis and synthesis of wavefronts by means of digital computers. Here analysis means the construction of images of objects and the measurement of their physical characteristics by recording and measur- ing the wavefronts scattered by these objects. The synthesis is the reconstruc- tion of a wavefront of an object which is specified numerically. Problems involving the analysis and synthesis of wave fronts arise frequently in modem science and engineering. These are the problems encountered in the use of electromagnetic and sound waves to peer into the interior of various objects, the problems of the visual display of information in general, and the problems of measuring the characteristics of radiating systems, devising optical apparatus for signal processing, and developing hybrid electrooptic computer systems. Solutions are being sought for these problems through research in holography. The use of digital computers to analyze and synthesize wavefronts is an alternative to the analog methods, which include the methods of physical holography. The digital approach potentially has the advantages which are inherent in the digital technique for signal processing: the processing is highly accurate and absolutely reproducible; the characteristics of the processing or the processing algorithm itself can be changed in a simple way; complicated nonlinear and logic conversions can be carried out; the results are accessible; and it is easy to modify the process at any stage. Digital methods are particularly suitable where quantitative results are required.