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Petawatt Power

March 28, 2000

In 1993, scientists at the Lawrence Livermore National Laboratory began in earnest to develop a high energy, Petawatt (quadrillion-watt) laser with the aim of proving that it could be used as a "fast ignitor" for capsules of fusion fuel. The fast ignition concept is to separate the usual target implosion into two stages: the familiar compression stage to assemble the fuel at high density, followed by a very rapid ignition stage using a separate "fast ignitor" Petawatt laser. The technique theoretically reduces the total energy needed for fusion ignition by a large factor.

After demonstrating the technology of the Petawatt laser at smaller scale, LLNL converted one of the NOVA laser's ten beams into a 680 Joule Petawatt. The facility operated until May 27, 1999 when NOVA was shut down to make way for the National Ignition Facility prototype.

George Miller, LLNL Associate Director for National Security and recently named Associate Director for NIF Programs, commented that the Petawatt "was considered to be such a high-risk undertaking that, although initially proposed in 1987, work on it did not begin until 1993, when funding was provided by Livermore's Laboratory Directed Research and Development program." "Seven years later," he said, "it is clear that the science and technology that emerged through developing the Petawatt laser will benefit the scientific community, U. S. industry, and the Laboratory for years to come." Miller said that "to produce petawatt pulses, the development team had to produce diffraction gratings much larger and more advanced than what was the state of the art." "The development of facilities and know-how to manufacture these gratings has made Livermore into one of the world's centers for the development and manufacture of diffractive optics," he said, noting "Since completion of the Petawatt gratings, we have developed diffractive optics for laboratories throughout the world, numerous companies, and several government agencies, as well as for Livermore's next superlaser, the National Ignition Facility." Miller said that the Petawatt research led to discoveries about short pulse laser-damage mechanisms to materials that "are now being applied in the Lifetime Extension Program for stockpiled weapons, and we are refining the technology for use in large-scale commercial and defense applications." Among the many scientific discoveries, he noted observations on "laser-initiated nuclear reactions, high energy electron production, and the formation of positron-electron pairs and proton beams far brighter than those produced by any accelerator."

Although Livermore's Petawatt laser is no more, Miller said LLNL would be collaborating on new Petawatt facilities under construction in Germany, France, England and Japan.

Livermore's Mike Perry has led the Petawatt effort as Associate Program Leader for Short Pulse Lasers. He noted that "a primary spinoff from the Petawatt laser program has been the development of ultrashort-pulse lasers for high-precision laser cutting and machining. He said, "Brent Stuart and others first observed the laser's cutting capabilities during early research on the laser damage threshold for a variety of optical materials." He said, "This discovery was put into practical use in developing the first femtosecond laser cutter for use as a precision cutting tool in dismantling weapons at DOE's Y-12 Plant (in Oak Ridge,TN)." Other uses of the technology will include the production of thin films and medical surgery, he said.

General Atomics recently announced that Perry will join the firm as Director of Lasers and Optics Science and Technology. They said, "He will play a central role in developing and implementing GA's strategic objectives in the fields of optics and lasers and their applications to government missions and the commercial arena." Perry thus joins former LLNL Associate Director for Lasers Mike Campbell, who was recently appointed Vice President, Laser and Inertial Fusion Programs at GA.