High power diode-pumped solid-state laser operation in the bounce amplifier geometry

Imperial Users onl

Modeling of damage in unidirectional ceramic matrix composites and multi-scale experimental validation on third generation SiC/SiC minicomposites

International audienceThe purpose of this paper is to experimentally validate a 1D probabilistic model of damage evolution in unidirectional SiC/SiC composites. The key point of this approach lies in the identification and validation at both local and macroscopic scales. Thus, in addition to macroscopic tensile tests, the evolution of microscopic damage mechanisms - in the form of matrix cracks and fiber breaks - is experimentally analyzed and quantified through in-situ scanning electron microscope and computed tomography tensile tests. A complete model, including both matrix cracking and fiber breaking, is proposed on the basis of existing modeling tools separately addressing these mechanisms. It is based on matrix and fiber failure probability laws and a stress redistribution assumption in the vicinity of matrix cracks or fiber breaks. The identification of interfacial parameters is conducted to fit the experimental characterization, and shows that conventional assumptions of 1D probabilistic models can adequately describe matrix cracking at both macro- and microscopic scales. However, it is necessary to enrich them to get a proper prediction of ultimate failure and fiber break density for Hi-Nicalon type S fiber-reinforced SiC/SiC minicomposites

Caractérisation expérimentale de l'endommagement dans les minicomposites SiC/SiC

National audienceLes composites SiC/SiC sont étudiés pour leur usage potentiel comme matériau de gainage dans les réacteurs nucléaires de génération future. Afin de valider un modèle multiéchelle d'endommagement à l'échelle microscopique, une caractérisation expérimentale de l'endommagement à l'échelle du toron est mise en œuvre. Des essais de traction in-situ sur minicomposite permettent d'obtenir des données statistiques sur la cinétique d'apparition des fissures matricielles et l'évolution de leur ouverture en fonction de la contrainte. Ces observations de surface sont complétées par des observations microtomographiques réalisées à l'ESRF sur un minicomposite en traction. L'analyse des images 3D permet alors d'étudier la propagation des fissures matricielles au sein du minicomposite. Les ruptures de fibres sont également observables grâce à cette technique d'observation

High power diode-pumped solid-state laser operation in the bounce amplifier geometry

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Adaptive optics with a thermally activated mirror for the correction of phase front disturbances in high-power laser systems

In a solid state laser system high pump powers can result in strong temperature gradients affecting the phase front of the beam due to deformation and locally varying refractive indices in the active medium. A dynamic correction process is desirable in order to compensate distortions at different pumping powers. Here we present an adaptive optics (AO) system applicable to high power beams. Main component of the system is a mirror that consists of a colored glass absorbing below 900 nm and a coating which is highly reflective above 950 nm. It can be heated and deformed by the intensity distribution of an 808 nm beam that has been modulated via a DMD. The resolving capacities of the AO have been analyzed and measures taken to improve them. In the next step, the performance of the AO correcting an incoming wave modified with defined distortions will be investigated. In future, the system will be implemented into a thin-disk amplifier to compensate phase aberrations of the active medium. The current status of the project is presented

High energy laser sources for space debris detection

The large and rising number of space debris particles in low earth orbit (LEO) is posing an increasing danger to LEO satellites and the ISS. For example, even sub-centimeter particles can cause significant damage to solar panels; cm-class objects can destroy satellites. In the medium term, this threat can limit the use of popular orbits that have a high density of space debris. A first step in dealing with space debris entails locating and tracking even small debris objects with high precision to calculate orbital data and evaluate the threat they pose to satellites. After an initial passive optical detection of particles, a ground-based, high energy laser is required to obtain precise distance information through time-of-flight measurements. For this purpose, a 1 J, 1 kHz laser system with good beam quality based on thin-disk laser amplifiers is under development. Here we present the current status of the experiment and give an overview of the planned laser setup