Ji-Ping Zou

Recent progress on LULI high power laser facilities

LULI is actively involved in laser developments to continuously upgrade its facilities. We will report on the optimization of the dynamic wavefront control for the LULI2000 facility and on the first phase of the LULI PW project (200J, 1ps). We will also present the ELFIE project, the upgrade of the 100TW system, including an energy enhancement and the development of a short-pulse high-energy OPCPA beam line.

CPA compression gratings with improved damage performance

Volume holographic gratings and ion-etched dielectric diffraction gratings have been designed with the goal of improving the efficiency and damage threshold when used in CPA laser compression scheme. Two damage threshold measurement techniques have been implemented, including one method based on the statistical distribution of damage fluences. We first tested samples with submillimeter laser spots in the subpicosecond regime. We could demonstrate large sample gratings in a complete CPA configuration with over 96% efficiency per pass and a damage threshold twice the one observed on gold coated gratings.

Improvement of the LULI high-energy CPA laser system focusability and repetition rate using an adaptive optical system

We have implemented on the LULI 100 TW laser facility a closed-loop Adaptive Optics system composed of a large aperature dielectric coated deformable mirror and a home-made shearing interferometer. Significant results have been obtained with this system: not only the beam focusability has been improved to a Strehl ratio of 0.9 but it has also been kept at this level for a sequence full-energy shots, with a repetition rate of 20 minutes, through systematic compensation of the cumulative thermal load generated in the large disk amplifiers.

Pulse compression below 40fs at 1μm: The first step towards a short-pulse, high-energy beam line at LULI

We present the upgrading project ELFIE (Equipement Laser de Forte Intensit? et Energie) based on the 100TW mixed Nd:glass CPA laser system at 1?m at LULI, which includes an energy enhancement and the development of a short-pulse, high-energy, good temporal contrast beam line (50fs/5J). We report the first experimental step towards the short-pulse, high-energy beam line: spectral broadening above 60nm from 7nm and temporal pulse compression below 40fs from 300fs at 1?m through a Krypton-filled hollow fiber compressor.

High focusability performance obtained on the LULI 100TW laser facility by use of a dielectric coated deformable mirror

We demonstrate the wave-front correction of the LULI 100TW, 300 fs/30 J high power laser facility for a sequence of shots. Excellent beam focusability close to diffraction limit has been obtained using an adaptive optic system, composed of a large aperture dielectric coated deformable mirror and a home-made shearing interferometer. This correction allows to produce reproducible focal spots with Strehl ratios close to 0.9 at a repetition rate of a shot every 20 minutes, despite of wave front distortions generated by cumulative thermal effects in the large disc amplifiers.

Dynamic phase masks for focal spot optimization and shaping of cw and high-power laser beams

Summary form only given.In the last few years, many solutions have been implemented to correct the wavefront of intense laser beams. Most of them use an adaptive mirror to achieve this correction. At LULI, we have developed in collaboration with Thomson-CSF a liquid-crystal optically addressed electro-optical valve (OAEOV) approach to induce phase shifts onto the beam. Coupled with an achromatic three-wave lateral shearing interferometer (ATWLSI), it provides an improved correction due to its high resolution. We managed to correct the wavefront of our 100-TW Nd:glass laser down to the fluctuation level.

Adaptive optics technique for wavefront correction of multi-terawatt Nd:glass laser chain

Summary form only given. Ultra intense laser systems with peak power in the 10 TW-1 PW range are difficult to focus close to the diffraction limit because of spatial phase aberrations. Reaching this goal is an important task when trying to get the highest possible intensity (typically >10/sup 20/ w/cm/sup 2/). In this paper, we describe an adaptive optics (AO) technique which has significantly improved the wavefront quality of the LULI 100 TW CPA Nd:glass laser. This AO system relies on a feed-back loop coupling a wavefront sensor and a wavefront corrector.