No abstract

In the previous design, the maximum drive radiation temperature was 4 MK or 350 eV (Holstein 1996). Different beam configurations gave roughly the same uniformity with the NIF-size cavity. Our best configuration used four cones of beams illuminating three rings. An integrated 2D simulation pointed out that the symmetry was good enough to reach a gain of ten. Two evolutions took place in the design of our MJ laser. We moved from a capsule adapted to 4 MK (L1000) to another one adapted to 3.5 MK (L1215) in order to minimize the parametric instabilities (the cavity size is almost the same). This new capsule also has a better hydrostability according to the “classical modelling” (Lindl 1995). The second evolution is a simplification of the target chamber. We restricted ourselves to two major configurations for indirect drive (two-ring and three-ring configurations). Therefore, only three cones of beams are necessary instead of five cones in the first design. Finally, the number of holes in the chamber is 80 instead of 100.

The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 jim). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT densitỹ 100 p 0 (fio liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.

Low levels of intensity noise in semiconductor lasers is a key feature for numerous applications such as high resolution spectroscopy, fiber-optic sensors, signal distribution in broadband analog communications as CATV, and more generally for microwave photonics systems. In particular, a DFB laser with very low relative intensity noise (RIN) levels from 0.1 to 20 GHz is a key component as it correspond to the whole frequency bandwidth of interest for radars. Several approaches have been reported but most suffer from the compromise between RIN level and power out level and stability, with RIN level in the range -150 dB.Hz -1 to -155 dB.Hz -1 in this frequency range [1,2]. We report here results from a new AlGaInAs DFB laser developed at 3S PHOTONICS. Excellent device performance is observed across an operating range from the laser threshold up to the thermal roll-over. Pure longitudinal single mode at 1545 nm is obtained over the whole current operating range with side mode suppression ratio higher than 50dB. The maximum output power reaches up to 130 mW. In these conditions, RIN levels below -160 dB.Hz -1 is obtained in up to 20 GHz. These are the best results to our knowledge combining such high single mode output power with such low RIN level in the frequency range 0.4-20 GHz.