CEA Cesta

About: CEA Cesta is a facility organization based out in Le Barp, France. It is known for research contribution in the topics: Laser & Laser Mégajoule. The organization has 647 authors who have published 649 publications receiving 8667 citations. The organization is also known as: Centre d'études scientifiques et techniques d'Aquitaine & Le Cesta.

Coherent emission of light by thermal sources

Abstract: A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle--the so-called Wolf effect. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.

Etude théorique et numérique d'une hiérarchie de modèles aux moments pour le transfert radiatif

Abstract: Resume Nous appliquons ici le principe de minimisation d'entropie a l'equation de transfert radiatif. Comme dans le cadre des equations cinetiques classiques, nous obtenons a l'aide de ce principe une hierarchie de systemes aux moments fermes. Chaque systeme de la hierarchie est hyperbolique, possede un flux limite par la vitesse de la lumiere et dissipe localement l'entropie. Nous analysons plus particulierement les proprietes du premier systeme de la hierarchie.

Discrete velocity model and implicit scheme for the bgk equation of rarefied gas dynamics

Abstract: We present a numerical method for computing transitional flows as described by the BGK equation of gas kinetic theory. Using the minimum entropy principle to define a discrete equilibrium function, a discrete velocity model of this equation is proposed. This model, like the continuous one, ensures positivity of solutions, conservation of moments, and dissipation of entropy. The discrete velocity model is then discretized in space and time by an explicit finite volume scheme which is proved to satisfy the previous properties. A linearized implicit scheme is then derived to efficiently compute steady-states; this method is then verified with several test cases.

Polishing-induced contamination of fused silica optics and laser induced damage density at 351 nm.

Abstract: In this paper we study the effect of contamination induced by fabrication process on laser damage density of fused silica polished parts at 351 nm in nanosecond regime. We show, owing to recent developments of our raster scan metrology, that a good correlation exists between damage density and concentration of certain contaminants for the considered parts.