Unwanted laser damage of optical materials, first reported in 1964, continues to limit the output energy and power of pulsed and continuous-wave laser systems. Despite nearly 50 years of research in this area, including tremendous advances in damage-resistant optical materials, interest from the international laser community in laser-damage issues remains high and does not show signs of diminishing.
This interest is evident from the high level of attendance at the annual SPIE Laser Damage symposium. Presentations at the September 2012 event covered various aspects of laser-induced damage and materials for high-power laser development including damage-measurement protocols and standards, damage in optical coatings, damage mitigation, nonlinear optical and laser host materials, photonic bandgap materials, materials characterization, surface and bulk defects, contamination of optical components, and thermal management of high-power lasers.
The SPIE journal, Optical Engineering, has also just published a special section on laser damage research in the December 2012 volume.
One reason for the growing interest in new approaches to laser damage research is the development of novel laser systems and optical materials. For example, new ultrafast and short-wavelength lasers involve new damage effects, and researchers have to deal with specific damage mechanisms not studied before. As a result, laser scientists frequently require non-traditional approaches to characterization of laser-damage resistance.
The preamplifiers of the National Ignition Facility are the first step in increasing the energy of laser beams as they make their way toward the target chamber. NIF recently achieved a 500 terawatt shot, 1000 times more power than the United States uses at any instant in time.
Courtesy Damien Jemison/LLNL
NIF a shining example of laser development
The brightest example of laser development that involves all aspects of laser damage, including its impact on design, operations, and reliability, is the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California (USA). This $3.5 billion project took almost 15 years to start operation of the most powerful laser in the world. Similar projects are under development in France, China, and Japan.
Shining nanosecond laser pulses into a special chamber, the facility has 192 lasers designed to ignite a thermonuclear reaction in a hydrogen target by the formation of hot plasma, releasing as much energy from fusion as could be supplied by several power plants.
This enormous amount of energy could potentially replace many present power facilities that burn coal or oil to produce heat. Although NIF has not yet accomplished its ultimate goal, (An experimental shot in September 2012 produced 1 megajoule of the 1.4–1.8 megajoules needed.) ignition looks like a very special job for high-power lasers that cannot be accomplished by other tools or approaches.
Among the research presented at SPIE Laser Damage was a talk by James A. Pryatel, the cleanliness protocol manager for NIF. Presenters also addressed recent developments in metamaterials and micro-structured surfaces to replace traditional optical elements such as multi-layer optical coatings that control reflection at surface.
SPIE Laser Damage 2012 was co-chaired by SPIE Fellow M.J. Soileau and SPIE members Gregory J. Exarhos, Joseph A. Menapace, Detlev Ristau, and Vitaly E. Gruzdev. Papers presented at the symposium are available in the SPIE Digital Library.
The 2013 symposium will be held 22-25 September in Boulder, CO (USA), with abstracts due in April.
NIF shows power in ongoing experiments
In an experiment last September at the National Ignition Facility (NIF) in California, 192 laser beams were, for the first time, used on a solid target while a suite of 26 diagnostic instruments kept watch.
“From the point of view of showing the facility’s capability, it was spectacular. Everything worked,” NIF director Ed Moses told Nature.com.
The target capsule deliberately wasn’t stocked with the mix of isotopes needed for fusion to occur, Nature reported. The power of the shot was well short of that needed for ignition because of concerns that the optical elements used to focus the beams might be damaged by anything higher.
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