Digital in-line holography (DIH) is advantageous due to simple optical system, high space bandwidth utilization and high stability. Furthermore, it can deliver 3D spatial coordinates and the size distribution of particles in a volume from a single hologram, and 3D trajectories and velocities from sequential holograms. These advantages make it extensively used in solid particles, liquid or gaseous particles and biological particles , and brings Digital In-line Particle Holography (DIPH). However, DIPH suffers from speckle noise , and considerable efforts have been devoted to mitigating the speckle noise. All these works solved the problem of the speckle noise by designing post-processing algorithms. We proposed a novel approach which mitigates the speckle noise by increasing the signal-to-noise ratio (SNR) . It is achieved via the joint design of optical systems and post-processing algorithms, and the SNR is enhanced by combining several holograms captured under different illumination angles. The experimental results show that the proposed scheme performs significantly better than the normal scheme in terms of SNR and false-detection-ratio, and can be easily extended into single-shot imaging.
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