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

International audienceIn 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 damag

Physico-chemical environment of Al impurity atoms in amorphous silica

The physico-chemical environment around the aluminum impurity atoms in commercial Herasil silica is studied by electron-induced X-ray emission spectroscopy. Despite the low concentration of aluminum and the charging effect occurring upon electron irradiation, we have been able to characterize the environment of the Al atoms. We show that the Al atoms are in an octahedral environment, i.e. surrounded by 6 oxygen atoms. The presence of Al clusters, whose metallic character would make them candidates to be ultraviolet absorption centers, is ruled out

Coexistence of an ordered anisotropic phase and a liquid expanded phase in an amphiphilic monolayer

We present an experimental study of a phase transition in a monolayer made of fluorescent amphiphiles. We have combined measurement of surface tension isotherms, ellipsometry and observations by microscopy. We have observed an ordered anisotropic phase coexisting with a liquid phase. The ordered phase is made of elongated domains, whose growth and melting are briefly described.Nous présentons une étude expérimentale d'une transition de phase d'une monocouche d'amphiphiles fluorescents. Nous avons effectué des mesures de pression de surface, d'ellipsométrie et des observations en microscopie. Nous avons observé une phase ordonnée anisotrope en coexistence avec une phase liquide. La phase ordonnée est constituée de domaines allongés dont la croissance et la fusion sont décrites brièvement

L’endommagement des optiques du LMJ : problématique, mécanismes et métrologie

Cet article traite de la problématique de l’endommagement laser sur les installations de fortes puissances. La métrologie mise en œuvre pour mesurer la durée de vie des optiques en laboratoire mais également sur chaîne est exposée. Quelques mécanismes à l’origine de l’endommagement laser sont également présentés ainsi que des solutions mises en œuvre afin de réduire les niveaux d’endommagement

Electron kinetics and emission for metal nanoparticles exposed to intense laser pulses

A kinetic theory for the interaction of laser radiation with metal nanoparticles embedded in a wide-band-gap dielectric is presented. The formalism is based on the integration of the Boltzmann equation for electrons of an open system, adapted to the description of electron losses from the nanoparticle such as thermionic and photoelectric effects. Differential forms of the electron-electron and electron-phonon collision operators are introduced to perform kinetic calculations beyond the nanosecond time scale. This kinetic model, which also includes nanoparticle-matrix energy transfer, is used to calculate laser energy deposition, redistribution, and electron ejection for nanosecond or picosecond laser-pulse durations in a model system for laser damage investigation; gold nanoparticles embedded in SiO2 glass. Though electron-phonon relaxation times are small compared with laser-pulse duration, an important part of the electron population is found to be driven beyond a typical 10 eV energy. These results suggest that laser absorption by a metal nanoinclusion can create a plasma around the particle

Electron kinetics and emission for metal nanoparticles exposed to intense laser pulses

A kinetic theory for the interaction of laser radiation with metal nanoparticles embedded in a wide-band-gap dielectric is presented. The formalism is based on the integration of the Boltzmann equation for electrons of an open system, adapted to the description of electron losses from the nanoparticle such as thermionic and photoelectric effects. Differential forms of the electron-electron and electron-phonon collision operators are introduced to perform kinetic calculations beyond the nanosecond time scale. This kinetic model, which also includes nanoparticle-matrix energy transfer, is used to calculate laser energy deposition, redistribution, and electron ejection for nanosecond or picosecond laser-pulse durations in a model system for laser damage investigation; gold nanoparticles embedded in SiO2 glass. Though electron-phonon relaxation times are small compared with laser-pulse duration, an important part of the electron population is found to be driven beyond a typical 10 eV energy. These results suggest that laser absorption by a metal nanoinclusion can create a plasma around the particle

X-ray spectroscopy study of electronic structure of laser-irradiated Au nanoparticles in a silica film

The electronic structure of gold nanoparticles embedded in a silica film is studied, both before and after irradiation at 355 nm by a laser. The Au 5d occupied valence states are observed by x-ray emission spectroscopy. They show that before irradiation the gold atoms are in metallic states within the nanoparticles. After irradiation with a fluence of 0.5 J/cm2, it is found that gold valence states are close to those of a metal-poor gold silicide; thanks to a comparison of the experimental Au 5d states with the calculated ones for gold silicides using the density-functional theory. The formation of such a compound is driven by the diffusion of the gold atoms into the silica film upon the laser irradiation. At higher fluence, 1 J/cm2, we find a higher percentage of metallic gold that could be attributed to annealing in the silica matrix