Digital in-line holographic microscopy is a captivating imaging method for industrial applications where large volumes of fluids are to be imaged with microscopic resolution. The lensless holographic in-line imaging setup with a point light source, also known as the Gabor setup, can be built up with just a few, fairly low cost, components. In-line holography is well suited for imaging large volumes with a low concentration of scattering particles as most of the light emitted from the point source should pass through the image volume unscattered. The large depth of field of in-line holographic microscopy makes it possible to image larger volumes with comparable resolutions than what can be achieved with traditional light microscopy methods using low magnification objectives. Despite the many advantages gained over traditional microscopic methods by the use of holographic imaging for large volumes, so far it has only been widely utilized in biological and particle image velocimetry studies. The large depth of field of the holographic microscope permits simultaneous imaging of particles located at different depths without the need for mechanical scanning, and allows the use of large diameter fluidic channels which are not as prone to clogging and enable higher flow rates than smaller fluidic channels. In this paper, we present a digital in-line holographic microscope based measurement principle for measuring the solid particle content of fluids. The method proposed is demonstrated on bio-oil samples whose solid contents are less than 0.01 weight percentage.
A setup and algorithm for 4D tracking of microscopic particles is proposed. The particles in certain volume are detected
automatically and their coordinates as well as magnitude and phase distributions saved. The saved data can be used to
analyze the number, spatial distribution, size, speed and track of the particles. Calculations show that it is possible to
measure the 3D position of a particle having a speed as high as 10 m/s. Experiments from 15 to 2000 fps show that high
quality video reconstruction of 1 and 6 μm particle flow is possible at least upto particle density of 200
particles/hologram.
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