We demonstrate that holographic speckle-free imaging is possible when a dynamic recording medium, such as a Bi12SiO20 crystal, and a four-wave mixing configuration are used. The method is based on time integration in the conjugate-image plane of N coherent images having an independent speckle pattern. We apply this concept to a real-time optical processing operation. A speckle-free time-averaged interferogram of a vibrating structure is obtained.
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