The University Record, September 14, 1992

U-M, French scientists race to create most powerful laser beam

By Sally Pobojewski
News and Information Services

Scientists at the U-M and the French National Atomic Energy Commission have achieved another breakthrough in the international race to create the world’s most powerful beam of laser light.

The first scientific report of the laser beam breakthrough was made by the French group directed by C. Sauteret at the Ultrafast Phenomenon Conference held in June in Antibes, France.

The 55-terawatt beam of laser light was produced in April at the Centre d’Etudes de Limeil-Valenton in Limeil, France. (One terawatt is equivalent to one trillion watts.) The beam was produced using the Centre’s P-102 laser with a laser amplification technique and a second pre- amplifing laser developed by Gerard A. Mourou, professor of electrical engineering and computer science, and his co-

researchers.

“The 55-terawatt laser pulse far exceeds last year’s record of 30 terawatts set by researchers at Japan’s Osaka University,” says Henri Doucet, director of the Centre.

During the brief laser burst, researchers are able to produce the power of 55 terawatts—the equivalent of 100 times the total electrical power generated annually in the United States.

“The laser beam can be focused over a spot smaller than the cross-section of a human hair to produce extremely high power densities,” Mourou says.

The most immediate application of the new technology will be to expand basic scientific knowledge, according to Mourou. “We currently know very little about what happens when extremely intense laser beams interact with matter,” he said.

“Our preliminary experiments show that shooting high-powered laser pulses through plasma—a state of matter made up of atomic nuclei and free electrons—creates shock waves capable of accelerating electrons close to the speed of light in very short distances,” notes Donald P. Umstadter, assistant research scientist in electrical engineering and computer science.

This could lead to the development of table-top, laser-powered particle accelerators, according to Umstadter. Currently, physicists must build massive, expensive laser accelerators to produce the speeding beams of electrons and powerful electric fields required to smash atoms into subatomic particles.

Another potential application for supercharged laser beams, according to Mourou, is development of an X-ray laser capable of observing the molecular and atomic action of living cells.

“With power densities of this magnitude, it also may be possible to use short laser pulses to trigger thermonuclear fusion reactions at lower pressures than are required by current inertial confinement fusion technology,” Umstadter says.

Inertial confinement fusion systems, designed to produce nuclear energy from a controlled fusion reaction, are being developed at several laboratories in Europe and Japan. In these systems, thermonuclear fuel must be compressed to densities 1,000 times greater than liquid density until the thermonuclear reaction begins spontaneously. Producing the extremely high pressures and temperatures required to trigger the reaction, however, is difficult and expensive.

The secret to the record-breaking power levels produced by the French laser is a technique called “chirped pulse amplification,” which was first developed by Mourou and his associates. With this technique, laser pulses are first produced in short bursts of a fraction of one picosecond or about one-trillionth of a second. The duration of the pulses are then stretched out by 1,000 times before they enter the laser’s amplifier. After amplification, the pulse is compressed back into the original fraction of a one-picosecond burst.

Using this technique and the P-102 laser, the same team of French and American scientists with the help of researchers from the CEA-Saclay produced a 20-terawatt beam on May 17, 1990. Since then, U-M researchers and their French colleagues have developed new laser pre-amplification techniques for producing shorter and therefore more powerful laser pulses.

“Our ultimate goal—and we see no limits in the technology to prevent us from achieving it—is to push the power of the beam to 1,000 terawatts,” said Jacques Coutant, department head at the Centre. “With hard work and cooperation between scientists working on both sides of the Atlantic, we believe we will attain that goal.”

The French/U-M laser research experiment was funded by the French National Atomic Energy Commission and the U-M. Scientists assisting with the experiment from the Centre d’Etudes de Limeil-Valenton, under the direction of Christian Sauteret, include Claude Rouyer and Stephano Seznec, with the assistance of Arnold Migus from ENSTA-LOA. Participating researchers from the U-M Ultrafast Science Laboratory include Yves Baudoin, John Scott Coe, Jeff Squier and Jean-Luc Tapie.