C. Sauteret

Synthetic aperture compression scheme for a multipetawatt high-energy laser.

High-energy petawatt lasers using the chirped-pulse amplification technique require meter-sized gratings to limit the beam fluence on the surface of the grating. An alternative, studied by many groups, is a mosaic grating consisting of smaller, coherently added gratings. We propose what we believe to be a new compression scheme consisting of beam phasing instead of grating mosaic phasing. This synthetic aperture compression scheme allows us to control the beam thanks to a unique segmented mirror equipped with three degrees of freedom. With this configuration, the beam is divided into small subapertures adapted to the classical grating size. After compression, these subapertures are coherently added before the focusing stage. Therefore the alignment processes are simplified.

Chromatism compensation of the PETAL multipetawatt high-energy laser

High-energy petawatt lasers use series of spatial filters in their amplification section. The refractive lenses employed introduce longitudinal chromatism that can spatially and temporally distort the ultrafast laser beam after focusing. To ensure optimum performances of petawatt laser facilities, these distortions need to be corrected. Several solutions using reflective, refractive, or diffractive optical components can be addressed. We give herein a review of these various possibilities with their application to the PETAL (Petawatt Aquitaine Laser at the Laser Integration Line facility) laser beamline and show that diffractive-based corrections appear to be the most promising.

Multi-petawatt high-energy laser project on the LIL facility in Aquitaine

A Multi-Petawatt High-Engergy laser coupled to the LIL (MPWHE-LIL) is under construction in the Aquitaine Region in France. This facility will be open to academic community. Nd:glass laser chain and Chirped Pulse Amplification (CPA)technique makes possible to deliver high energy. Optical Parametric Chirped Pulse Amplification (OPCPA) for pre-amplification and new compression scheme will be implemented. The MPWHE-LIL will deliver output energy of 3.6 kJ in 500 fs on target corresponding to more than 7 PW. The PW laser facility linked to UV-60kJ-ns beam from LIL, will give new scientific research opportunities.

Optimization of the dynamic wavefront control of a pulsed kilojoule/nanosecond-petawatt laser facility

The wavefront aberrations in a large-scale, flash-lamp-pumped, high-energy, high-power glass laser system can degrade considerably the quality of the final focal spot, and limit severely the repetition rate. The various aberrations induced on the Laboratoire pour lUtilisation des Lasers Intenses (LULI), laser facility (LULI2000) throughout the amplification are identified and analyzed in detail. Based on these analyses, an optimized procedure for dynamic wavefront control is then designed and implemented. The lower-order Zernike aberrations can be effectively reduced by combining an adaptive-optics setup, comprising a bimorph deformable mirror and a four-wave lateral shearing interferometer, with a precise alignment system. This enables the laser chain to produce a reproducible focal spot close to the diffraction limit (Strehl ratio approximately 0.7). This allows also to increase the repetition rate, initially limited by the recovery time of the laser amplifiers, by a factor of 2 (one shot per hour). The proposed procedure provides an attractive alternative for dynamic correction of the wavefront aberrations of a laser facility as complex as the LULI2000.

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.

Delay interferometric single-shot measurement of a petawatt-class laser longitudinal chromatism corrector

In this paper we present a self-referenced interferometric single-shot measurement technique that we use to evaluate the longitudinal chromatism compensation made by a diffractive lens corrector. A diffractive lens with a delay of 1 ps is qualified for a 60 mm beam aperture. This corrector was implemented on the Alisé Nd:glass power chain. We qualify the corrector and the Alisé power chain chromatism, demonstrating the potential of this measuring principle as well as the interest of diffractive lenses to correct longitudinal chromatism of petawatt-class lasers.

3D numerical model for a focal plane view in case of mosaic grating compressor for high energy CPA chain

An important issue, mosaic grating compressor, is studied to recompress pulses for multiPetawatt, high energy laser systems. Alignment of the mosaic elements is crucial to control the focal spot and thus the intensity on target. No theoretical approach analyses the influence of compressor misalignment on spatial and temporal profiles in the focal plane. We describe a simple 3D numerical model giving access to the focal plane view after a compressor. This model is computationally inexpensive since it needs only 1D Fourier transforms to access to the temporal profile. We present simulations of monolithic and mosaic grating compressors.

Spatial and temporal coherence characterization of a smoothed laser beam

We present a new method for measuring coherence characteristics of the speckles obtained with a smoothed laser. This technique allows us to measure both spatial transverse and temporal characteristics, of hot spots by spatial autocorrelation.

The Petawatt Laser Glass Chain at LULI: Technical Issues and First Results

We present the Petawatt Laser facility project at LULI, from the front end diode-pumped regenerative amplifier, delivering 60 mJ at 1 Hz, to the main power amplifiers and compact compressor based on high-damage-threshold dielectric gratings. This facility will offer a unique combination of a Petawatt laser synchronized with a 1 kJ long-pulse laser, a 100 TW laser, and three 100 J ns lasers.

High-intensity laser-plasma experiments at LULI

This paper reviews the highlights of the high intensity laser-plasma experiments achieved with the six-beam and the 100 TW LULI laser facilities, as well as the progress of the LULI 2000 project. This covers fields of laser fusion, equations of state, hgih energy particle emission, atomic physics, X-ray production and laser developments.