Because the objective of holography is to perform phase retrieval from a recorded hologram, this chapter discusses how this can be achieved using analog holographic techniques. Conventional analog holography entails physical re-illumination of the hologram of the object with a reading beam and finding the 3D real or virtual image. Numerical phase retrieval methods are also addressed that unwrap the computed (and thus always modulo 2p) phase to determine the exact phase change of the image. In holographic interferometry and phase-shifting holographic interferometry, the phases from different states of an object can be compared to yield information about the 3D deformation of the object.
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