arXiv subjects

D. Lacoste

Publications and source records attributed to D. Lacoste.

28 records · Page 2Linked to original sources

arXiv2004

Geometric depolarization in patterns formed by backscattered light

We formulate a framework for the depolarization of linearly polarized backscattered light based on the concept of geometric phase, {\it i.e} Berry's phase. The predictions of this theory are applied to the patterns formed by backscattered light between crossed or parallel polarizers. This theory should be particularly adapted to the situation in which polarized light is scattered many times but predominantly in the forward direction. We apply these ideas to the patterns which we obtained experimentally with backscattered polarized light from a colloidal suspension.

cond-mat.dis-nn↗

arXiv2002

Phase Transitions in Lyotropic Nematic Gels

In this paper, we discuss the equilibrium phases and collapse transitions of a lyotropic nematic gel immersed in an isotropic solvent. A nematic gel consists of a cross-linked polymer network with rod-like molecules embedded in it. Upon decreasing the quality of the solvent, we find that a lyotropic nematic gel undergoes a discontinuous volume change accompanied by an isotropic-nematic transition. We also present phase diagrams that these systems may exhibit. In particular, we show that coexistence of two isotropic phases, of two nematic phases, or of an isotropic and a nematic phase can occur.

cond-mat.soft↗

arXiv2001

Effective index of refraction, optical rotation, and circular dichroism in isotropic chiral liquid crystals

This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependance of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric $P$ is much shorter than the wavelength of the light $λ$, an approximation which has been made in previous studies of this problem. The theoretical predictions are supported by comparing them with experimental spectra of the optical activity in the BP III phase.

cond-mat.soft↗

arXiv2001

Phase transitions in a ferrofluid at magnetic field induced microphase separation

In the presence of a magnetic field applied perpendicular to a thin sample layer, a suspension of magnetic colloidal particles (ferrofluid) can form spatially modulated phases with a characteristic length determined by the competition between dipolar forces and short-range forces opposing density variations. We introduce models for thin-film ferrofluids in which magnetization and particle density are viewed as independent variables and in which the non-magnetic properties of the colloidal particles are described either by a lattice-gas entropy or by the Carnahan-Starling free energy. Our description is particularly well suited to the low-particle density regions studied in many experiments. Within mean-field theory, we find isotropic, hexagonal and stripe phases, separated in general by first-order phase boundaries.

cond-mat.soft↗

arXiv2000

Transport mean free path for Magneto-Transverse Light Diffusion: an alternative approach

This article presents a derivation of the transport mean free path for magneto-transverse light diffusion, $\ell^*_\perp$, in an arbitrary random mixture of Faraday-active and non-Faraday active Mie scatterers. This derivation is based on the standard radiative transfer equation. The expression of the transport mean free path obtained previously from the Bethe-Salpether equation, for the case where only Faraday-active scatterers are present,is recovered. This simpler formulation can include the case of homogeneous mixtures of Faraday-active and non-Faraday active scatterers.

cond-mat.dis-nn↗

arXiv2000

Photonic Hall Effect in ferrofluids: Theory and Experiments

An experimental and theoretical study on the Photonic Hall Effect (PHE) in liquid and gelled samples of ferrofluids is presented. The ferrofluids are aqueous colloidal suspensions of Fe(_{2})CoO(_{4}) particles, which can be considered as anisotropic and absorbing Rayleigh scatterers. The PHE is found to be produced by the orientation of the magnetic moments of the particles, as is also the case for the Faraday effect. The dependence of the PHE with respect to the concentration of the scatterers, the magnetic field and the polarization of the incident light is measured in liquid and in gelled samples and is compared to a simple model based on the use of a scattering matrix and the single scattering approximation.

cond-mat.soft↗

arXiv1999

Coherent Backscattering of light in a magnetic field

This paper describes how coherent backscattering is altered by an external magnetic field. In the theory presented, magneto-optical effects occur inside Mie scatterers embedded in a non-magnetic medium. Unlike previous theories based on point-like scatterers, the decrease of coherent backscattering is obtained in leading order of the magnetic field using rigorous Mie theory. This decrease is strongly enhanced in the proximity of resonances, which cause the path length of the wave inside a scatterer to be increased. Also presented is a novel analysis of the shape of the backscattering cone in a magnetic field.

cond-mat.mes-hall↗

arXiv1999

Stokes parameters for light scattering from a Faraday-active sphere

We present an exact calculation for the scattering of light from a single sphere made of Faraday-active material, to first order in the external magnetic field. We use a recent expression for the T-matrix of a Mie scatterer in a magnetic field to compute the Stokes parameters in single scattering that describe completely flux and polarization of the scattered light.

cond-mat.mes-hall↗

arXiv1999

Transport Mean Free Path for Magneto-Transverse Light Diffusion

We derive an expression for the transport mean free path $\ell^*_\perp$ associated with magneto-transverse light diffusion for a random collection of Faraday-active Mie scatterers. This expression relates the magneto-transverse diffusion in multiple scattering directly to the magneto-transverse scattering of a single scatterer.

cond-mat.mes-hall↗

arXiv1999

Optics of a Faraday-active Mie Sphere

We present an exact calculation for the scattering of light from a single sphere made of a Faraday-active material, into first order of the external magnetic field. When the size of the sphere is small compared to the wavelength the known T-matrix for a magneto-active Rayleigh scatterer is found. We address the issue whether or not there is a so called \em Photonic Hall Effect - \em a magneto-transverse anisotropy in light scattering - for one Mie scatterer. In the limit of geometrical optics, we compare our results to the Faraday effect in a Fabry-Perot etalon.

cond-mat.mes-hall↗