The effect of flow motion on a volume hologram written in a fluid medium is studied. The hologram is written in a sensitized fluid by either thermal absorption or the photochromic effect or by other mechanisms. After being written, the hologram is deformed because of the motion of the supporting fluid. The effect of several representative fluid motions on the hologram deformation, i.e., a plane shear flow and a symmetric plane jet, is found by solving the associated convection-diffusion equation. The effect of diffusion on the fading of the hologram is also studied for several diffusion rates corresponding to different hologram-writing mechanisms. The result of the calculation is the determination of the new shape and intensity of the hologram as functions of time. The analysis is carried out entirely in the Fourier domain, where the convection–diffusion equation is solved more easily. The output is therefore given in terms of spatial Fourier components that represent the deformed and convected hologram. The use of volume holograms for the determination of velocity gradients corresponding to small-scale fluid motion is discussed. In this paper we describe the deformation process that the hologram undertakes under the effect of fluid motion. In part II of this series [ J. Opt. Soc. Am. A 5, 1297 ( 1988)] we describe a method for predicting the diffracting characteristics of strained holograms. That method directly incorporates the results presented here.
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