Scientists from Lawrence Livermore National Laboratory (LLNL) and the University of California, Irvine have designed a new high-intensity spiral laser that could revolutionise plasma control technologies.
As published in Nature Photonics, the rotating, spring-shaped laser pulse can be tuned over a variety of speeds- including exceeding the speed of light without violating relativity.
Traditional laser beams used to interact with plasma are limited to a single point and pace of interaction, which in turn limits findings for new developments in fusion energy, particle acceleration and astrophysics.
“For a long time, people have used high-power and high-intensity laser pulses to drive plasmas,” said LLNL scientist and lead author Andrew Longman. “But those lasers are almost always in their simplest configuration. It’s basically a round spot—nothing especially interesting. It’s like hitting the plasma with a hammer. We’re interested in laser pulses that are structured in both space and time because they let us do unusual things, like stir the plasma.”
Producing freeform optics down to the nanometer
Using specialised beamsplitters- one containing shorter (“blue”) wavelengths and the other longer (“red”) wavelengths- researchers split a broadband laser into two beams.
Each beam then reflects from a custom, nanostructured mirror, produced by LLNL’s National Ignition Facility and Photon Science directorate.
“For some of these freeform optics, across the entire optic, the difference between the design and the finished part was only about five nanometers,” said author Tayyab Suratwala, the program director for Optics and Materials Science and Technology at LLNL. “We’re talking down to almost the atomic scale.”
After reflecting from the two mirrors, a second beamsplitter recombines the two beams and alignes them precisely in space and time, creating the twisting laser pulse.
“In Ghostbusters, they have the proton packs that fire one beam down the middle and another that spirals around it,” Professor Franklin Dollar, who helped assemble and test the laser at UC Irvine, said. “At high intensities, we only knew how to make the middle beam. Now we can make the spiraling beam too.”
The spiral laser spring has a wide range of potential applications
Simulations using light springs suggest that a table-top scale laser system could generate strong magnetic fields, exceeding 100 teslas, by driving helical plasma waves that behave like tiny electromagnetic coils.
These intense magnetic fields generated in a laboratory setting would give scientists opportunity to explore atom behaviour and the light they emit under extreme circumstances.
“The nice thing was that it was all done on a laser that can just literally fit on your tabletop,” Longman said. “You don’t need to have these large-scale multimillion-dollar lasers in order to do original work.”
Another application is in plasma-based particle acceleration. Simulations suggest that helical plasma waves driven by light springs could prevent electrons outrunning the laser pulse accelerating them, meaning they stay in the accelerating region long enough to reach higher energies.
“We can really crank up the fields for how fast we accelerate particles,” Dollar said. “We can get similar energies to what you might get out of a giant accelerator facility in something like a centimeter.”
