The intensity and phase reconstructed from digital in-line holograms by the convolution approach are analyzed. Distortions of particle images depending on their position in the plane transverse to the optical axis are identified. For this purpose, the object fields of numerically simulated particle holograms as well as of experimental data are reconstructed. The results of three-dimensional correlations of numerical and experimental data are superior when the numerically generated reference volumes are adapted to the transverse locations of the particle. Thus, proof is given that the characteristics of a particle image change distinctly with the transverse position of the particle and that the numerical model successfully simulates these changes. Hence, this knowledge can be integrated in future particle position detection algorithms.
In digital holographic particle image velocimetry, hologram truncation is a very prominent problem when the projection of the particle position to the sensor is close to the sensor edge. Using the convolution approach to reconstruct such a hologram yields a deformed particle image compared to a particle image resulting from a particle with a projection to the center of the sensor. This Letter shows that the deformation complicates particle position detection based on an algorithm originally developed for analog holography by Choo and Kang, and later applied to digital holography by Yang and Kang. This algorithm is refined for the detection of particle positions from the deformed images and applied to numerical and experimental data.
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