Matthias P. L. Sentis

Experimental validation of the vectorial complex ray model on the inter-caustics scattering of oblate droplets

We report the first experimental validation of the Vectorial Complex Ray Model (VCRM) using the scattering patterns of large oblate droplets trapped in an acoustic field. The two principal radii and refractive index of the droplets are retrieved with a minimization method that involves VCRM predictions and experimental light scattering patterns. The latter are recorded in the droplet equatorial plane between the primary rainbow region and the associated hyperbolic-umbilic diffraction catastrophe. The results demonstrate that the VCRM can predict the fine and coarse stuctures of scattering patterns with good precision, opening up perspectives for the characterization of large non-spherical particles.

Physical-optics approximation of near-critical-angle scattering by spheroidal bubbles

A first-order approximation is derived for the near-critical-angle scattering of a large spheroidal bubble illuminated by a plane wave propagating along the bubble axis of symmetry. The intensity of the far-field scattering pattern is expressed as a function of the relative refractive index and the two radii of curvature of the spheroidal bubble at the critical impact point.

Photonic jet reconstruction for particle refractive index measurement by digital in-line holography

A new and computationally efficient approach is proposed for determining the refractive index of spherical and transparent particles, in addition to their size and 3D position, using digital in-line holography. The method is based on the localization of the maximum intensity position of the photonic jet with respect to the particle center retrieved from the back propagation of recorded holograms. Rigorous electromagnetic calculations and experimental results demonstrate that for liquid-liquid systems and droplets with a radius > 30µm, a refractive index measurement with a resolution inferior to 4 × 10-3 is achievable, revealing a significant potential for the use of this method to investigate multiphase flows. The resolution for solid or liquid particles in gas is expected to be lower but sufficient for the recognition of particle material.

Droplet sizing and mixture fraction measurement in liquid–liquid flows with rainbow-angle diffractometry

The capabilities and resolution of the rainbow technique were extended to estimate the size distribution and composition of droplets in liquid-liquid systems. For these droplets, essentially characterized by a low relative refractive index (m≈1.001-1.20), the first-order rainbow is localized in the near-forward to sideways region. It exhibits an unusually higher contrast in the parallel polarization due to the vicinity of the rainbow and the Brewster angles. A numerical study revealed that a few thousand to ten thousand droplets were necessary to obtain reliable estimations of the first moments of typical droplet size distributions when the diffractometer is operated as an ensemble averaging technique. The importance of the accuracy of the light scattering model and the inverse methods used are also documented. Experimental results performed on free-rising submillimeter to millimeter droplets of various compositions showed that a global resolution of 1% to 5% of their mean diameter and about 1.6×10-4 of the dispersion on their refractive index (i.e., 3% in the mixture fraction of oily droplets in water) could be achieved, which enhances the perspectives on mixing and extraction studies in liquid-liquid systems.

Organic photo sensors for multi-angle light scattering characterization of particle systems

Organic Photo Sensor (OPS) technology allows printing on conformable plastic-like substrates complex-shaped, arbitrarily-sized and pre-aligned photosensitive elements. This article reports, to the best of our knowledge, the first investigation to implement this emerging technology for Multi-Angle Light Scattering (MALS) characterization of nano- and microparticle suspensions. Monte Carlo and Lorenz-Mie theory calculations as well as preliminary experimental results on latex suspensions clearly demonstrate the potential of the proposed approach.

Impact of the pulse contrast ratio on molybdenum K α generation by ultrahigh intensity femtosecond laser solid interaction

We present an extended experimental study of the absolute yield of Kα x-ray source (17.48u2009keV) produced by interaction of an ultrahigh intensity femtosecond laser with solid Mo target for temporal contrast ratios in the range of 1.7u2009×u2009107–3.3u2009×u2009109 and on three decades of intensity 1016–1019u2009 W/cm². We demonstrate that for intensity Iu2009≥u20092u2009×u20091018u2009 W/cm² Kα x-ray emission is independent of the value of contrast ratio. In addition, no saturation of the Kα photon number is measured and a value of ~2u2009×u20091010 photons/sr/s is obtained at 10u2009Hz and I ~1019u2009 W/cm². Furthermore, Kα energy conversion efficiency reaches the same high plateau equal to ~2u2009×u200910−4 at Iu2009=u20091019u2009 W/cm² for all the studied contrast ratios. This original result suggests that relativistic Ju2009×u2009B heating becomes dominant in these operating conditions which is supposed to be insensitive to the electron density gradient scale length L/λ. Finally, an additional experimental study performed by changing the angle of incidence of the laser beam onto the solid target highlights a clear signature of the interplay between collisionless absorption mechanisms depending on the contrast ratio and intensity.

On the size and morphological characterization of needle-shaped TiO2 nanoparticles in suspension

We report the work in progress to develop a non invasive and fast optical method allowing characterizing the concentration, aspect ratio and mean size of acicular, nanorod and nanotube shaped particles. This method is based on the analysis of the spectral extinction of nanoparticles illuminated by polarized-light and whose orientation can be controlled by means of electrostatic and/or hydronamical forces. T-Matrix calculations and preliminary experimental results illustrate some aspects and features of this method.

Light Scattering by Large Bubbles

This review highlights the various electromagnetic methods, geometrical and physical optics approximations developed so far in the literature to predict the light scattering properties of large bubbles in an optically dilute regime. The underlying problematic is essentially linked to the characterization of bubbly flows or, more generally, multiphase flows, where most optical diagnostics are based on the analysis of the scattering diagrams, caustics and singularities with interferometric or diffractometric techniques.

Development of Optical Techniques for Multiphase Flows Characterization

Optical methods for investigating multiphase flows are reviewed and discussed in the scope of the development of apparatus convenient for nuclear fuel reprocessing. Indeed, the various processes implemented (e.g. leaching, solvent extraction, filtration, crystallization, etc.) involve either liquid/gas, liquid/liquid and/or liquid/solid flows. Besides the adaptation of classical techniques, such as PIV and image processing, that have been used to quantify velocity fields and particles size distribution in flat-tank reactors, a typical design used in the nuclear industry to mitigate criticality issues, more innovating techniques are currently developed. The latter open the way to the measurement of less usual, although equally important measurements, such as the droplet composition in a liquid-liquid extraction column, and mass transfer rate in multiphase flows.Copyright