In taking a photograph, an image of the object is formed on a plane where some photosensitive material (e.g., a photographic plate) is kept. The photosensitive material reacts to the intensity of light falling on it and consequently, after developing and fixing of the photographic plate, one obtains a permanent record of the intensity distribution that existed at the plane occupied by the photographic plate when it was exposed. In this process, the phase distribution that existed in the plane of the photographic plate is completely lost. Thus, if the amplitude distribution at the plane of the photographic plate was, say, A(x, y) exp [iφ(x, y)], where A(x, y) and φ(x, y) are real functions of x and y (the x-y plane being the plane of the photograph), then the recorded pattern is proportional to ∣A(x, y)eiφ(x, y)∣2= A2(x, y). Thus, the phase information, which is contained in φ(x, y), is lost. In contrast, the principle of holography, which we are going to develop in this chapter, is one in which not only the amplitude distribution but also the phase distribution can be recorded.
KeywordsPlane Wave Focal Plane Spherical Wave Object Point Reference Wave
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