Ice crystal habits from cloud chamber studies obtained by in-line holographic microscopy related to depolarization measurements

SNR enhancement in in-line particle holography with the aid of off-axis illumination

The digital in-line particle holography suffers from speckle noise, for which considerable efforts have been devoted in order to mitigate it by designing post-processing algorithms. This paper proposes a novel approach, which mitigates the speckle noise by increasing the signal-to-noise ratio (SNR). It involves the joint design of optical systems and post-processing algorithms, and enhances the SNR by combining several holograms captured under different illumination angles. The experimental results show that the proposed scheme performs better than the normal scheme in terms of SNR and false-detection-ratio.

Phase retrieval method for digital holography with two cameras in particle measurement

This paper presents a phase retrieval method for digital holography with two high-speed cameras in particle measurement. The conditions for recording two holograms are derived theoretically. We focus in particular on the distance between the two holograms. The relative misalignment of the two holograms is also evaluated by numerical simulations. Finally, we experimentally compared settling particles reconstructed by the presented method and the Gabor method.

Design of an in-line, digital holographic imaging system for airborne measurement of clouds

We discuss the design and performance of an airborne (underwing) in-line digital holographic imaging system developed for characterizing atmospheric cloud water droplets and ice particles in situ. The airborne environment constrained the design space to the simple optical layout that in-line non-beam-splitting holography affords. The desired measurement required the largest possible sample volume in which the smallest desired particle size (∼5 μm) could still be resolved, and consequently the magnification requirement was driven by the pixel size of the camera and this particle size. The resulting design was a seven-element, double-telecentric, high-precision optical imaging system used to relay and magnify a hologram onto a CCD surface. The system was designed to preserve performance and high resolution over a wide temperature range. Details of the optical design and construction are given. Experimental results demonstrate that the system is capable of recording holograms that can be reconstructed with resolution of better than 6.5 μm within a 15 cm(3) sample volume.