PERSISTENCE, creativity, luck, and old-fashioned hard work are the essential elements of any success story. They were all present in abundance during the development and use of Livermore's Petawatt laser. They had to be, because the project faced some formidable technical challenges. It 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. The prospect of doing laser experiments at an irradiance over ten thousand times greater than had ever been achieved made the project too exciting to pass up.|
Seven years later, 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.
To produce petawatt (quadrillion-watt) pulses, the development team had to produce diffraction gratings much larger and more advanced than what was the state of the art. Such gratings manipulate the delivery and distribution of laser light so that powerful laser pulses don't self-focus and damage the laser optics. The gratings necessary for the Petawatt laser simply didn't exist because they had to contain millions of grooves, each only a fraction of a micrometer wide, and be nearly an order of magnitude larger than any grating previously produced. Moreover, these gratings had to exhibit extremely high diffraction efficiency and operate at a power density much higher than had ever been achieved.
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 fabrication of diffractive optics. 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.
The discovery that laser-damage mechanisms are different at very short pulse durations led to an important new application for lasers. Livermore researchers found that materials machined with ultrashort laser pulses are virtually undamaged, because those pulses are too brief to transfer heat or shock to the materials. This discovery is 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.
The scientific discoveries emerging from Petawatt laser experiments will be analyzed for years to come. Although the Petawatt laser was developed originally to perform basic research on the fast ignitor concept for inertial confinement fusion, physicists Mike Perry and Joe Sefcik proposed its use as a source of intense, high-energy x-radiation. As they were demonstrating the Petawatt laser's utility as an intense x-ray source to support the Department of Energy's Stockpile Stewardship Program-to protect the viability of the nation's nuclear stockpile-Livermore scientists observed 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. These discoveries are described more fully in the article beginning on p. 4.
The Petawatt laser was shut down at the height of its use in May 1999 because the Nova laser facility in which it was housed was being closed to make room for the National Ignition Facility. However, the discoveries enabled by the Petawatt laser will continue to be pursued at new petawatt-class laser facilities under construction in Germany, France, England, and Japan.