Depth-of-focus reduction for digital in-line holography of particle fields

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Poor axial precision caused, in part, by large depth of focus (ꞇ) has been a vexing problem in extraction of particle position from digital in-line holograms. A simple method is proposed to combat this depth-of-focus difficulty. The method is based on decoupling of size and position information. With d , ∆, and λ being particle diameter, CCD pixel size, and the wavelength, respectively, our main theoretical result is the reduction of ꞇ from ꞇ ~ d2 / λ to ꞇ ~ ∆2 / λ for particles of known size. This result is confirmed in laboratory experiments with holograms of calibrated glass spheres.

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© 2005 Optical Society of America. Publisher’s version of record: https://doi.org/10.1364/OL.30.001303

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Optics Letters