Petawatt laser probes nature at Texas university

Some things really are bigger in Texas—the petawatt laser built by scientists and engineers at the University of Texas at Austin, for one. “[It] is the highest-power laser in the world,” says Todd Ditmire, director of the Texas Petawatt Laser, which held a ribbon-cutting ceremony on 28 August.

The laser has a peak power of 1.2 PW, or 1.2 × 10¹⁵ watts. New amplification technology, namely, a combination of nonlinear optics and doped glass to amplify a broad range of wavelengths, has shrunk the pulse duration down to 165 femtoseconds, from 600 fs at the only other petawatt lasers yet built—one in the UK and one, since decommissioned, at Lawrence Livermore National Laboratory. The shorter pulse time means target materials can be heated faster “than anything expands,” Ditmire says, “and you can get plasmas with solid—or higher—densities.”

A key area of study will be fundamental properties of such dense plasmas: “Electrical conductivity, the equation of state—the sort of thing that astrophysicists want to know,” says Ditmire. The petawatt laser will also be used to accelerate electrons by having them surf on plasma waves. “We should be able to get to 10 GeV,” says Ditmire. “That’s starting to get into a regime in which high-energy physicists might take notice.” Other lines of research include looking at aspects of inertial confinement fusion and ejecting protons from one material to heat a second target to fusion temperatures.

The first research effort, Ditmire says, will be to focus the beam into a gas of deuterium clusters, a few thousand atoms per cluster. “The laser ejects the electrons, leaving a ball of ions. These ions repel each other and the ball explodes.” The resulting ions can fuse with ions from other exploded clusters. “It’s not interesting for energy production, but it’s a bright burst of fusion neutrons,” he says. The neutrons, he adds, can be used in pump–probe materials studies.

The petawatt’s $15 million tab was footed by the National Nuclear Security Administration through earmarks in energy and water appropriations bills obtained thanks to Texas Republican Senator Kay Bailey Hutchison. “Senator Hutchison has long championed efforts to strengthen innovation and research at our nation’s education institutions,” says aide Courtney Sanders. Hutchison, a member of the Senate Committee on Appropriations, was “proud to help make the project possible through federal funding,” Sanders says. The information gleaned from experiments with the laser will “improve our ability to certify the reliability of the aging US nuclear weapons stockpile without underground nuclear testing,” adds NNSA spokesman John Broehm. “Universities are a great resource to better our understanding of the physics and are independent of NNSA methods and conclusions. … It is extremely helpful to have this outside perspective.”

“Importantly,” says Ditmire, “this is the only petawatt laser on a university campus in the US. It will play a significant role in educating students in high-intensity laser and high-energydensity science.” Although the laser will not be used for classified research, he adds, “NNSA wants us to train good students who could then go work for the weapons labs.” Mechanisms for outside researchers to use the petawatt laser are still being formulated.