February 18, 2008, Ann Arbor, MI--Researchers from the University of Michigan have demonstrated a Ti:sapphire femtosecond laser that is twice as intense as one they produced in 2004.
The 1.3-micron pulsed laser beam lasts just 30 femtoseconds but measures 20 billion trillion watts per square centimeter. It contains 300 terawatts of power--300 times the capacity of the entire U.S. electricity grid.
This intensity is about two orders of magnitude higher than any other laser in the world can produce, said Victor Yanovsky, a research scientist in the U-M Department of Electrical Engineering and Computer Science who built the ultra-high power system over the past six years. The laser can produce this intense beam once every 10 seconds, whereas other powerful lasers can take an hour to recharge.
"We can get such high power by putting a moderate amount of energy into a very, very short time period," Yanovsky said. "We're storing energy and releasing it in a microscopic fraction of a second."
To achieve this beam, the research team added another amplifier to the HERCULES laser system, which previously operated at 50 terawatts.
HERCULES is a Ti:sapphire laser that takes up several rooms at U-M's Center for Ultrafast Optical Science. Light fed into it bounces like a pinball off a series of mirrors and other optical elements. It gets stretched, energized, squeezed and focused along the way.
HERCULES uses the technique of chirped pulse amplification developed by U-M engineering professor emeritus Gerard Mourou in the 1980s. Chirped pulse amplification relies on grooved surfaces called diffraction gratings to stretch a very short duration laser pulse so that it lasts 50,000 times longer. This stretched pulse can then be amplified to much higher energy without damaging the optics in its path. After the beam is amplified to a higher energy by passing through titanium-sapphire crystals, an optical compressor reverses the stretching, squeezing the laser pulse until it's close to its original duration. The beam is then focused to ultra-high intensity.
In addition to medical uses, intense laser beams like these could help researchers explore new frontiers in science. At even more extreme intensities, laser beams could potentially "boil the vacuum," which scientists theorize would generate matter by merely focusing light into empty space. Some scientists also see applications in inertial confinement fusion research, coaxing low-mass atoms to join together into heavier ones and release energy in the process.
A paper on this research, "Ultra-high intensity 300-TW laser at 0.1 Hz repetition rate," is published online in the journal Optics Express (click here). Yanovsky and Karl Krushelnick are authors of the paper.
Krushelnick is a professor in the departments of Nuclear Engineering and Radiological Sciences, Electrical Engineering and Computer Science, and Physics. Yanovsky is a research scientist in the Department of Electrical Engineering and Computer Science. They are co-principal investigators in the U-M Frontiers in Optical Coherent and Ultrafast Science Center (FOCUS), a National Science Foundation Physics Frontier Center. Krushelnick is also associate director of the Center for Ultrafast Optical Science. The research team for this project also includes Vladimir Chvykov, an associate research scientist in the Department of Electrical Engineering and Computer Science, and Galina Kalinchenko, an assistant research scientist in the Department of Electrical Engineering and Computer Science.