HIGH-ENERGY PHYSICS: LULI laser aims for petawatt output

For two decades, the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) at the école Polytechnique (Palaiseau, France) has been the center of research in France for laser-created plasmas and inertial-confinement fusion.

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For two decades, the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) at the école Polytechnique (Palaiseau, France) has been the center of research in France for laser-created plasmas and inertial-confinement fusion. The facility contains one of the world's largest lasers, a six-beam 100-TW Nd:glass laser, which is at the disposal of European researchers. The Commissariat à l'Energie Atomique (CEA; Paris, France), which has its own lasers—the Phebus, a two-beam Nd:glass laser delivering energy of 20 kJ at 1.06 µm and 5 kJ at 0.35 µm in 1-ns pulses, and the older Octal laser—is now dismantling them to concentrate its efforts on its Megajoule laser program, intended for research on thermonuclear weapons. The dismantling of the CEA's Octal and Phebus lasers will substantially increase the importance of LULI to researchers.

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Right. Central to the amplification scheme for the LULI 2000 nanosecond laser is a series of rod and disk amplifiers. Spatial filters maintain beam quality, while Faraday rotators minimize damaging back-reflections.

Research at the LULI program must remain at a high scientific level, according to Arnold Migus, the LULI director. The LULI 2000 program was designed to meet needs of the scientific community, which include access to high-power picosecond and femtosecond pulses. Initiated in 1999, the LULI program will be in force until 2006 and will include the construction of a nanosecond laser (Nano 2000) and a picosecond laser (Pico 2000).

The importance of this program led the CEA and the Centre National de la Recherche Scientifique (Paris, France) to enter into a partnership in 1998 with the École Polytechnique and the Université Paris (Paris, France). A commitment by the CEA to donate the dismantled Phebus laser components to LULI has given the project a boost, resulting in a proposal by école Polytechnique to build a new laser facility.

The LULI 2000 nanosecond laser installation will include two Nd:glass laser beamlines equipped with rod amplifiers and 208-mm-diameter phosphate-glass disk amplifiers producing 1.053-µm pulses having 1 kJ energy and 1 ns duration (see figure on p. 26). Also included will be four Nd:glass beamlines for diagnostics, two laboratories that encompass the laser-beam foci, and an enclosure containing laser oscillators, preamplifiers, and devices for shaping beam pulses. Once the Nano 2000 laser is complete, the Pico 2000 will be brought into operation. The picosecond laser will deliver 1-kJ, 1-ps pulses having petawatt peak power.

"After LULI 2000, the laser installations will grow not in volume, but in accuracy and reliability, in order to be more open to the applications developed in partnership with industry," says Migus. This change in emphasis will lead to the lasers operating at a higher repetition rate, an endeavor led by the Laser Ultra-Courts et Intense, et Applications (LUCIA) project. Integral to LUCIA is the development of high-intensity diode-pumped lasers. The resulting high repetition rate will benefit materials processing, x-ray lithography, and scientific applications that include the use of ultrashort x-rays to dynamically study inert and living matter. Average power of the diode-pumped lasers will reach the kilowatt level.

Roland Roux

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