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International audience; Scattering of coherent light from a disordered material produces a complex distribution of intensity known as a speckle pattern. Speckle patterns are not as random as they appear at first glance. Their statistical properties exhibit universal features, as already recognized in the first paper on laser speckle. The existence of short-range and long-range spatial correlations in speckles has been shown to be fundamental in wave physics. It has also led to the emergence of novel approaches for imaging through scattering media.

International audience; Is there a bright spot in the shadow of an opaque disk? Nearly 200 years ago, Augustin Fresnel and François Arago’s remarkable answer to this question validated the wave theory of light and inaugurated the modern theories of diffraction. Today, their renowned experiment can be easily reproduced using lasers and cameras. Far beyond its historical interest, the experiment is a versatile platform to illustrate the main concepts of optical physics, including diffraction, interference, speckle, and Fourier optics.

Shape deviations of spur gears obtained by using Electronic Speckle Pattern Interferometry are compared with the results of numerical simulation. The dual illumination method produces a speckle pattern by simultaneous illumination of a sample by two laser waves symmetrically in the direction of observation. Two images obtained, respectively, before and after deformation are subtracted to obtain the field of displacement. Furthermore, a study of meshing stiffness was performed for different types of setting for an internal gear.

Optical techniques using single wavelength lasers allow precise study of the superficial displacements of deeper anatomical structures through direct mechanical pull. Two techniques have been used in this study: 1. Double exposure speckle photography. Since 1980 the relationship between the surface displacements and minimal traction applied to the transverse processes of the spine, either unilateral or bilateral, was studied in an attempt to simulate muscular action exerted at this level. 2. Computerised speckle interferometry. This allowed analysis of the deformations between the lumbar vertebrae under vertical compression, shear or torsion outside the usual anatomical planes. This preliminary study outlines the mechanical behaviour and the plasticity of the vertebral structures but has been performed on only a few anatomical specimens thus not allowing statistical analysis. This would require a larger series.

We briefly present experimental as well as theoretical results on measurements of spatial coherence of ultrasonic pulsed waves in random scattering media, particularly composite materials. We show that a given medium can behave either coherently or incoherently depending on the orientation of the ultrasonic beam, and what this implies in terms of characterization, speckle reduction and defect detection