Holography as a Measuring Tool

Abstract

The advantages of holography over conventional photography for the recording and direct measurement of physical structures are reviewed in terms of depth offield, resolution, angle of view and information storage density. The depth of field is limited by the coherence length of the laser, or its ability to illuminate adequately the subject, and scenes of up to 8 mdepth have been recorded. Information storage on the photographic plate can be as much as 106 times greater than that achieved by conventional photographic means, and a resolution of approximately 1µm at a distance equal to the linear dimensions of the holographic plate can be achieved. Causes of aberration, noise and other distortions are discussed and some of the requirements on laser performance are described. The possibility of applying holographic techniques to the recording of objects in hostile environments such as nuclear reactors is considered.