Sensing particle-nonsphericity with digital holography

We simulate digital in-line holograms of individual particles wavelengths in size to demonstrate that signatures derived from the holograms can enable the differentiation of homogeneous spherical particles from homogeneous and slightly nonspherical particles. The concept is based on the symmetry of the reconstructed image, an approximation of the particle’s near-field light distribution, and the symmetry of the hologram structure itself as expressed by its autocorrelation. Spherical particles show reflection symmetry in these hologram signatures. Particles that are nonspherical in shape by a degree that is less than the holographic image-resolution appear essentially spherical in their image but show asymmetry in either their near-field light distribution or the hologram autocorrelation. We suggest that the analysis may have use in applications where differentiation between liquid spherical droplets and nonspherical particles is needed, perhaps in aerosol studies.