Physiology of Behavior

Digital holography (DH) has emerged as one of the most effective coherent imaging technologies. The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields, from quantitative phase imaging to optical metrology and 3D display technologies, to name a few. Like many other digital imaging techniques, DH must cope with the issue of speckle artifacts, due to the coherent nature of the required light sources. Despite the complexity of the recently proposed de-speckling methods, many have not yet attained the required level of effectiveness. That is, a universal denoising strategy for completely suppressing holographic noise has not yet been established. Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community. This review article provides a broad discussion about the noise issue in DH, with the aim of covering the best-performing noise reduction approaches that have been proposed so far. Quantitative comparisons among these approaches will be presented.

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Strategies for reducing speckle noise in digital holography

In this paper, we present the design, fabrication and optical characterization of computer-generated holograms (CGH) encoding information for light beams carrying orbital angular momentum (OAM). Through the use of a numerical code, based on an iterative Fourier transform algorithm, a phase-only diffractive optical element (PO-DOE) specifically designed for OAM illumination has been computed, fabricated and tested. In order to shape the incident beam into a helicoidal phase profile and generate light carrying phase singularities, a method based on transmission through high-order spiral phase plates (SPPs) has been used. The phase pattern of the designed holographic DOEs has been fabricated using high-resolution Electron-Beam Lithography (EBL) over glass substrates coated with a positive photoresist layer (polymethylmethacrylate). To the best of our knowledge, the present study is the first attempt, in a comprehensive work, to design, fabricate and characterize computer-generated holograms encoding information for structured light carrying OAM and phase singularities. These optical devices appear promising as high-security optical elements for anti-counterfeiting applications.

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Design, fabrication and characterization of Computer Generated Holograms for anti-counterfeiting applications using OAM beams as light decoders

Comparative appraisal of global and local thresholding methods for binarisation of off-axis digital holograms

We record simultaneously interferometric out-of-focus images and digital in-line holograms of liquid and frozen water droplets. We show that the analysis of speckle-like out-of-focus images allows a quantitative estimation of the size of the particles which is corroborated by numerical reconstruction of holograms recorded simultaneously. Interferometric out-of-focus imaging could be extended to the characterization of ice in clouds in the atmosphere.

Size determination of mixed liquid and frozen water droplets using interferometric out-of-focus imaging

ew Tech n iq u es in D ig ial H o lo g ap h y E d ied b y P acal P iart This book is devoted to special techniques in digital holography. The authors establish a synthetic state of the art of important advances in the field of digital holography. They are interested in detailing advances related to fundamentals of digital holography, in-line holography, digital color holographic metrology, digital holographic microscopy, infrared holography and special techniques in full-field vibrometry.

New Techniques in Digital Holography

Vesicles are simplified models of living cells such as red blood cells. Hydrodynamical effects lead to a specific structure of the suspension that is analyzed by digital holographic microscopy on earth and in microgravity conditions.

Minetti Christophe

Papers

New Techniques in Digital Holography

Dynamic of a vesicle suspension under shear flow by digital holographic microscopy