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Chapter 5:
Electronic Holographic Interferometry and Its Photographic Origin
The modern personal computer has transformed the field of holographic interferometry almost beyond recognition.When it was first discovered, holographic interferometry was a direct outgrowth of photographic holography and required that photographic holograms be recorded of any object under analysis. The resulting interferograms, while visually striking and pictorially revealing, eventually presented problems in practical use because the applications of mechanics to which this new technique was relevant required numerical measurements. The problem of converting pictorial fringes to numerical analysis was not an easy one to solve. Whereas the displacements that corresponded to fringe centers were known from the wavelength of the light used and the angles of illumination and observation, physically locating these fringe centers in the photographs of fringe patterns was a tedious task that was compounded by the need to interpolate between these data points. Furthermore, the time delay associated with photographic recording of holograms was a serious impediment to many applications. Advances in computers with advances in video technology have overcome both of these obstacles. This chapter presents the current state of the art in holographic interferometry and describes the critical elements in its history that have made this possible.
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