Marc Brunel

Professeur - Université de Rouen

Groupe de recherche :
Interaction laser/particule(s)

On the morphology of irregular rough particles from the analysis of speckle-like interferometric out-of-focus images

Using a simplified description, we show that the 2-dimensional Fourier transform of the speckle-like out-of-focus image of an irregular rough particle is given by the 2 dimensional-autocorrelation of the shape of the particle. Experiments confirm well this result. Using a matrix transfer based-formulation, we further determine the exact scaling factors between both functions, whatever the imaging system is.

M. Brunel, S. González Ruiz, J. Jacquot, J. van Beeck, Opt. Commun. 338, 193-198 (2015)

Interferometric out-of-focus imaging simulator for irregular rough particles

We present the development of an original simulator to predict interferometric out-of-focus patterns created by irregular rough particles. Despite important simplifications of the scattering properties, this simulator allows to predict quantitative properties of the speckle-like patterns : i.e. the dimension of the central peak of the 2D-autocorrelation of the pattern. This parameter can then be linked to the size and the shape of the particle projected on the CCD sensor, in cases where there is no exact theoretical formulation to calculate the scattered intensity. An experimental demonstration is performed with irregular NaCl salt crystals.

M. Brunel, S. Coetmellec, G. Gréhan, H. Shen, J. Europ. Opt. Soc. : Rap. Public. Vol. 9, 14008 (2014).

Long exposure time Digital In-line Holography for the trajectography of micronic particles within a suspended millimetric droplet

Digital in-line holography is used for the three-dimensional tracking of micronic particles in a millimetric droplet. The 3D location of the inclusions is realized through the digital reconstruction of holograms using the 2-Dimensional Fractional Fourier Transform. The trajectory of the particles inside the droplet is obtained using a long exposure scheme.

S. Wichitwong, S. Coëtmellec, D. Lebrun, D. Allano, G. Gréhan, M. Brunel, Opt. Commun. 326, 160-165 (2014).

Interferometric out-of-focus imaging for the 3D tracking of spherical bubbles in a cylindrical channel

We present an original interferometric out-of-focus imaging set-up to track the 3D position and the size of spherical bubbles in a cylindrical channel. Experimental results confirm theoretical predictions. Using a double acquisition, a 3 components velocimetry of bubbles can be performed, simultaneously with size measurements.

H. Shen, S. Saengkaew, G. Grehan, S. Coetmellec, M. Brunel, Opt. Commun. 320, 156-161 (2014).

Digital In-Line holography assessment for general phase and opaque particles

We propose using the circle polynomials to describe a particle’s transmission function in a digital holography setup. This allows both opaque and phase particles to be determined. By means of this description, we demonstrate that it is possible to estimate the digital in-line hologram produced by a spherical particle. The experimental intensity distribution due to an opaque micro-inclusion is compared to the theoretical one obtained by our new model. Moreover, the simulated hologram and reconstructed image of the particle by an optimal fractional Fourier transformation under the opaque disk, quadratic phase, and quasi-spherical phase approximation are compared with the results obtained by simulating holograms by the Lorenz–Mie Theory (LMT). The Zernike coefficients corresponding to the considered particles are evaluated using the double exponential (DE) method which is optimal in various respects.

S. Coëtmellec, W. Wichitwong, G. Gréhan, D. Lebrun, M. Brunel, A.J.E.M. Janssen, J. Europ. Opt. Soc. : Rap. Public., Vol. 9, 14021 (2014).

Determination of the size of irregular particles using interferometric out-of-focus imaging

We present a mathematical formalism to predict speckle-like interferometric out-of-focus patterns created by irregular scattering objects. We describe the objects by an ensemble of Dirac emitters. We show that it is not necessary to describe rigorously the scattering properties of an elliptical irregular object to predict some physical properties of the interferometric out-of-focus pattern. The fit of the central peak of the 2D-autocorrelation of the pattern allows prediction of the size of the scattering element. The method can be applied to particles in a size range from a tenth of micrometers to the millimeter.

M. Brunel, H. Shen, S. Coëtmellec, G. Gréhan, T. Delobel, International Journal of Optics, Article ID 143904 (2014).

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