Développement de traitements multidiélectriques pour les lasers de haute puissance à impulsions femtosecondes

The peak power handling capability of ultra-short pulse lasers is a main concern for new facilities, like those for the European ELI project (Extreme Light Infrastructure) which aims at providing worldwide scientists the possibility to study matter at unexplored energetic levels. In these last generation laser systems, the characteristics of the beam become extreme as it get closer to the experimental chamber: diameter enlarged to a tenth of centimeters, duration reduced to a few femtoseconds, energy amplified up to hundred joules, etc. The last components of the laser chain require very tight optical performances with the highest laser-induced damage threshold in order to durably propagate the beam while keeping its properties (intensity, spectrum, duration, wave front, etc). Some of these components, like mirrors, are designed from dielectric materials deposited with evaporative process under vacuum. This work is a study of the laser resistance of thin film materials in order to design and manufacture mirrors compatibles with the propagation of high peak power laser beams.L'Europe et sa communauté scientifique développent et construisent des lasers de ultra-haute puissance uniques au monde, notamment au travers du projet ELI (Extreme Light Infrastructure). Cette nouvelle génération de lasers à impulsions ultra-brèves permettra aux chercheurs du monde entier d'étudier la matière dans des domaines énergétiques et temporels encore inexplorés. Dans de tels systèmes lasers, plus le faisceau se rapproche de la chambre d'expérience, dans laquelle il est focalisé sur une cible, plus ses caractéristiques deviennent extrêmes : son diamètre est élargi jusqu'à plusieurs dizaines de centimètres, sa durée est réduite à quelques femtosecondes, son énergie est amplifiée au-delà d'une centaine de joules, etc. Les derniers composants optiques de la chaîne laser doivent être conçus pour permettre la propagation durable du faisceau en conservant l’ensemble de ses caractéristiques (intensité, spectre, durée, front d’onde, etc). C’est pourquoi ils requièrent des performances optiques remarquables associées à une résistance au flux laser maximale. Certains de ces composants, comme les miroirs, sont conçus à partir d’empilements de matériaux diélectriques déposés par procédé d’évaporation sous vide. Au cours de ces travaux, la résistance au flux laser de ces matériaux en couches minces a été étudiée pour aboutir au design et à la production de miroirs compatibles avec le transport des faisceaux à haute puissance crête

Femtosecond laser-induced damage threshold of electron beam deposited dielectrics for 1-m class optics

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Laser induced damage threshold of a hybrid mirrors designed for broadband operation in HiLASE beam distribution system

International audienc

Electron-beam deposited materials for high-reflective coatings: Femtosecond LIDT

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Femtosecond laser-induced damage threshold of electron-beam deposited materials for broadband high-reflective coatings on large optics

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Polishing and coating of a F1250mm 90° off-axis parabola for PW lasers

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Zero-contrast grating filters for pixelated applications in the mid-IR range

International audienceSummary form only given. Pixelated filters are of great interest for spatial applications because they compare favourably with traditional filter-wheel multi-spectral imagers in terms of weight and footprint. The thin film technology, which is mainly used to produce filters in the mid-IR range is limited when it comes to fabricating pixelated designs, because the thickness of the stacks in two neighbouring pixels would be different, leading to intricate fabrication steps even though some original methods exist [1]. It has been shown recently that zero-contrast gratings (ZCG) can be used to implement bandpass transmission filters [2]. They consist of a partially-etched high-index material on a low-index substrate. The main advantage is that the central wavelength of the filter can be adjusted simply by modifying the lateral dimensions of the patterns, not the thickness of the high-index layer. However these filters possess 2 major limitations. First, they have a low angular tolerance which limits the smallest possible pixel size. Secondly, their bandwidth is only of few nm which restricts too much the incident flux. Indeed, since the total incident flux is divided along both spectral and spatial dimensions in multi-or hyper-spectral imagers, there is only little flux into each channel.In this paper we report a simple and efficient method to design narrowband transmission filters as well as the first use of a doubly-corrugated grating in order to increase both the bandwidth and angular tolerance of a ZCG. The design method relies on both analytical and empirical relations with very little numerical optimization conducted using Rigorous Coupled Wave Analysis (RCWA)

Ultra-short pulse laser-induced damage thresholds of broadband high-reflective and low dispersive coatings

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Laser-induced damage thresholds of high-reflective coatings for PW lasers

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