Modified correlation method to autofocus particles in digital in-line holography

Daniel H. Martínez-Suárez; Alejandro Restrepo-Martínez; Alejandro Mira-Agudelo; Francisco E. López-Giraldo

doi:10.1117/1.OE.56.11.111715

24 August 2017 Modified correlation method to autofocus particles in digital in-line holography

Daniel H. Martínez-Suárez, Alejandro Restrepo-Martínez, Alejandro Mira-Agudelo, Francisco E. López-Giraldo

Author Affiliations +

Optical Engineering, Vol. 56, Issue 11, 111715 (August 2017). https://doi.org/10.1117/1.OE.56.11.111715

Abstract

A method is proposed to automatically evaluate the focal planes of spherical particles. This method compares the correlation coefficients of multiple reconstructed planes relative to a reference plane. The particles are located where a minimum correlation is found, and reconstructions are made using an angular spectrum propagator. The Hough transform is employed to segment the hologram, thereby enabling the detection of circular shapes, such as Airy patterns, and the edges of the particles themselves. The autofocus is improved by creating a correlation matrix using an iterative process, which reduces the computational cost of the particle display processes in their respective focal planes. A theoretical model was studied to estimate the longitudinal and transverse magnifications of the focused particles caused by the influence of aberrations in the reconstruction of digital holograms due to the spherical reference wave used. Experimentally, laser light was used to illuminate 5-_μm latex particles, which was recorded by a CCD camera with a 9.9-_μm pixel size. The reconstructions measured an average particle radius of 71.3±16.3 _μm in the average focal plane, which was estimated to be 60.65±0.22 mm from the hologram where the magnifications were considered.

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Daniel H. Martínez-Suárez, Alejandro Restrepo-Martínez, Alejandro Mira-Agudelo, and Francisco E. López-Giraldo "Modified correlation method to autofocus particles in digital in-line holography," Optical Engineering 56(11), 111715 (24 August 2017). https://doi.org/10.1117/1.OE.56.11.111715

Received: 20 April 2017; Accepted: 24 July 2017; Published: 24 August 2017

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KEYWORDS

Particles

Holograms

Digital holography

Holography

Spherical lenses

Diffraction

Optical engineering

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