1 September 2002
Light beams for mini measurements
Boulder, Colo.—A sharply focused, laserlike beam of extreme ultraviolet (EUV) light has University of Colorado researchers believing scientists and engineers will for the first time measure and manipulate objects at the scale of nanometers, or billionths of a meter.
Size has been a major hurdle when developing, or even seeing, the components for next-generation computers and nanoscale machines because the objects can be smaller than the waves of light illuminating them. While electron microscopes and other scanning devices can view the small structures, many critical measurements require optical microscopes, and optics are limited by the wavelength of their light sources.
"This pioneering research could have a profound impact on science and technology for years to come," said Filbert Bartoli, a program manager in the NSF Engineering Directorate's Division of Electrical and Communications Systems.
Researchers said the EUV light, which has a wavelength of only tens of nanometers, can pulse in shorter bursts than any other system on the planet, a critical property for measuring fast interactions among small particles. It also has a tight focus that is difficult to achieve with other EUV sources.
"EUV will share in the richness of opportunities that nanotechnology has to offer, permitting interactions at the level of a single molecule," said Bartoli. As nanotechnology and computer chip manufacture advance, there is going to be an increase in demand for better measurement tools. "We're getting better and better at fabricating these structures, but it does little good if we cannot measure them," he said.
Margaret Murnane and Henry Kapteyn of JILA led the team. The researchers developed the short-wavelength light source using a device that could fit on a dining room table. The NSF and the Department of Energy support the project.
The researchers used a process called high harmonic generation (HHG) to produce the EUV light. Researchers fire a visible-light laser into a gas, creating a strong electromagnetic field. The field ionizes the gas, separating electrons from their parent atoms.
The electrons recollide with the ionized gas atoms and oscillate back and forth within the electromagnetic field. As a result, a well-synchronized stream of photons, boosted up to a high-energy, extreme ultraviolet wavelength, fires out of the system. The end product is basically a multimegawatt laser.
The EUV beam is so focused that in the right system, it could produce the smallest diameter laserlike beam in the world: 20 to 30 times smaller than a more common, helium neon laser and several hundred times more intense, the researchers said.
Preexisting EUV lasers are more powerful and better for certain applications. But in the other laser designs, the properties of the gas change during HHG, and the light does not stay tightly focused. A variety of factors can worsen the effect.
The JILA team used a visible-light laser that can fire in bursts as short as a femtosecond (a quadrillionth of a second), yet the breakthrough development is a "structured waveguide" that confines the target gas and keeps the EUV beam steady and tightly focused. The resulting conversion of visible laser light into EUV wavelengths is more than 100 times more efficient than other laser designs, the researchers said.
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