Frank Dubois

Digital Holographic Interferometry with CO2 Lasers Applied to Aspheric Space Reflectors Testing

Digital holographic interferometry at long infrared wavelengths allows monitoring large deformations of space reflectors during vacuum-thermal testing. We present different optical schemes and an application to the complex case of elliptic reflector.

In-situ holography microscopy of plankton and particles over the continental shelf of Senegal

We present the first results obtained by a newly developed submersible digital holography microscope (DHM), Holoflow@Sea, to enable continuous in-situ monitoring of ocean or fresh water bodies in a less intrusive manner. The microscope features an off-axis configuration with reduced-coherence illumination. The optics is designed to image plankton and particles in the size range 2 μm-200μm within a water volume of 1 mm × 1 mm × 2 mm. The prototype was successfully deployed for the first time over the continental shelf of Senegal during a fisheries survey carried out in March 2013. The objective was to combine several laboratory techniques used for plankton and particle identification (high-performance liquid chromatography, flow cytometry and optical microscopy) on discrete collected samples with DHM images taken in situ at locations with different environmental conditions. Hologram data were acquired inside an upwelling cell, i.e., new water, and along the coast, i.e., old water, as well as off the upwelling cell at the continental shelf border. Preliminary results of holographic reconstruction are encouraging, with the distinctive morphology of some phytoplankton species allowing easy identification to genera level. Challenges are recognised with the identification of small spheroid organisms. Analyses are underway to allow comparison with traditional methods of plankton identification and evaluate the benefit of additional in-situ observations obtained by holography microscopy. The preliminary results already demonstrate the potential of DHM for in-situ studies of plankton and particles.

Automatic three-dimensional localization of micro-particles using digital holographic microscopy

We present a numerical technique for automatic extended focused imaging and three-dimensional analysis of microparticle field observed in a digital holographic microscope working in transmission. We use Fourier method for the extraction of complex amplitude from the single exposition digital holograms. We create a synthetic extended focused image (EFI) using the focus plane determination method based on the integrated amplitude modulus. We apply the refocusing criterion locally for each pixel, using small overlapping windows, in order to obtain a depth map and a synthetic image in which all objects are refocused independent from their refocusing distance. The obtained synthetic EFI allows us to perform image segmentation and object detection. We improve the accuracy of vertical localization using an additional refining procedure in which each particle is treated separately. A successful application of this technique in the analysis of microgravity particle flow experiment is presented.

Refocus Criterion Based on the Phase in the Fourier Domain for Automatically Refocusing in Multispectral Digital Holographic Microscopy: Accuracy and Dependency Study

© 2018 The Author(s). The fast autofocus criterion using the phase in the Fourier domain, suitable for digital holographic microscopy when the complex field is known for at least two distinct wavelengths, is deeply investigated, which allows finer adjustment.

Dynamics of Red Blood Cells in shear flow using digital holographic microscopy with reduced coherence

Red Blood Cells are deformable objects constituting 50% of the blood. Their 3D repartition, in the smallest capillaries especially, leads to complex flow properties. Those properties are studied under shear flow by DHM under microgravity.

Breast Inspection By Diaphanoscopy Improved By Use Of Optical Fiber And Pseudocolor Processing

Optical fiber illumination of a breast gives rise to a contrasted image where flaws conduct to a medical control for cancer inspection similar to other techniques and without any danger. Pseudocolor processing improves the technique.