Fabien Reversat

MAPS: a turbulence simulator for MCAO

The Multi-Atmospheric Phase screens and Stars (MAPS) instrument is a powerful tool that has been developed in the framework of the ESO Multi-conjugate Adaptive optics Demonstrator project (MAD). It allows emulating a 3D evolving Paranal-like atmosphere as well as up to 12 sources in a 2 arc minutes field of view, as seen at a Nasmyth focus of one of the VLT. It will be used to perform advanced laboratory tests on MAD before its shipment to Chile. In this paper we present the opto-mechanical design of MAPS. This one simulates the characteristics of the VLT focus and achieves a high Strehl Ratio over the whole Field of View in the visible as well as in the infrared. A curved entrance plate crowded with fibers emulates various stars configurations including real sky asterisms. In order to simulate the atmosphere, three rotating Phase Screens are placed in the beam and conjugated with different altitudes. Those are glass plates dig in their surface in a way that the beam passing through is distorted as it would be by an atmospheric turbulent layer. In this poster we also present the process of research that lead to the choice of a reliable technique to imprint the aberrations into the screens, their properties and expected performance.

Development of diffractive antireflection structures on ZnSe for high power CO2 laser applications

The unavoidable absorption of thin films used in antireflective coatings forms a permanent bottleneck in the development of optics for high power laser applications. A valid alternative would be the micro-structuring of the optics surface, realizing a diffraction grating which emulates the functioning of an Anti-Reflection thin film layer. Due to the absence of film material, this diffractive structure would not contribute to the overall absorption of the optics. This paper investigates the practical limits of this strategy, applied to zinc selenide as low absorption infrared substrate material.

Beams homogenization to pump Petawatt class Ti:Sapphire crystals

We have tested two optical solutions to homogenize the spatial profile of nanosecond pump beams to be used for a Petawatt Ti:Sapphire. Simulations and experiments will be presented for microlens arrays and random phase plate.

Laser damage on diffractive optics

Laser damage studies are made on a phase mirror used for laser beam shaping in high power laser applications. The phase mirror is composed of a glass substrate with defined patterns to encode a phase, on top of which a multilayer mirror is deposited. We describe in this paper the LIDT obtained (at 1064nm, 6ns) and the laser damage test procedure, adapted to the geometry, that has been used. A morphologic analysis of the damage sites is made with Nomarski and Atomic Force Microscopy, to obtain information on the damage initiation and its localization on the structured component. The results are completed with simulations of the electric field within the multilayer by using a wave propagation computer code. We obtain localization and values of the light intensification occurring in the structure, that we correlate to experimental measurements.