Lawrence Livermore National Laboratory

Researchers Uncover Potential New Realm in Laser-driven Science

A novel method of harnessing lasers and plasmas may give researchers innovative ways to explore outer space as well as to examine bugs, bones, and tumors back on Planet Earth.

LLNL physicist Félicie Albert led an international team pursuing this new regime in laser research, which was described in a Physical Review Letters (PRL) paper published online on March 31. PRL is a journal of the American Physical Society.

Albert and the team spent more than two years experimenting with new techniques to generate x rays capable of probing the size, density, pressure and composition of highly transient states of matter such as those found in the cores of planets and in fusion plasmas. Plasmas make up 99 percent of the known universe.

Felicie Albert and the Betatron Team at the Jupiter Laser FacilityMembers of the Betatron X-ray Team with the Titan Laser target chamber in the Laboratory’s Jupiter Laser Facility (from left): Jessica Shaw, Clément Goyon, Alison Saunders, Will Schumaker, Brad Pollock, Nuno Lemos, Félicie Albert, and Scott Andrews.

The researchers studied betatron x-ray radiation, emitted when electrons are accelerated to relativistic energies and wiggle in the plasma wave produced by the interaction of a short, intense laser pulse with a gas.

Traditionally, this source has been well studied for laser pulses with femtosecond (quadrillionth of a second)-long durations. To study betatron x-ray emission at the intensities and pulse durations relevant to larger-scale laser facilities, such as LLNL’s Advanced Radiographic Capability (ARC) laser, the researchers conducted an experiment on the Titan Laser at the Laboratory’s Jupiter Laser Facility. There they observed betatron x-ray radiation driven by much longer, picosecond-duration laser pulses.

Image of an X-ray BeamA view of the x-ray beam as seen through a thin filter during the experiment.

“For me a picosecond is forever!” Albert joked. While picoseconds measure time in trillionths of a second, that’s slow to a researcher who prefers even shorter laser pulses.

The experimental work shows that the new radiation source holds great promise for undertaking applications at international large-scale laser facilities, where it potentially could be used for x-ray radiography and phase contrast imaging of laser-driven shocks, absorption spectroscopy, and opacity measurements.

Joining lead author Albert on the paper, “Observation of Betatron X-Ray Radiation in a Self-Modulated Laser Wakefield Accelerator Driven with Picosecond Laser Pulses,” were LLNL colleagues Nuno Lemos, Brad Pollock, Clément Goyon, Arthur Pak, Joseph Ralph and John Moody along with collaborators from the University of California-Los Angeles, the SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory, the University of California-Berkeley, and the University of Lisbon in Portugal.

“This was a very big team effort,” said Albert, who noted that the results did not reveal themselves immediately as in some experiments, and that it took the team a lot of analysis and hard work to uncover the new regime.

They note in their paper the wide variety of potential uses of the technology: Betatron x-ray radiation driven by short-pulse lasers has been used for biological and medical purposes, such as x-ray phase contrast imaging of insects and hard x-ray radiography of bone. Its unique properties also make it suitable for studying the dynamics of high-energy-density plasmas and warm dense matter—a state near solid densities—and temperatures found in the cores of giant planets like Jupiter and in inertial confinement fusion plasmas.

Albert’s work is supported by the LLNL Laboratory Directed Research and Development Program and the Department of Energy Office of Science’s Early Career Research Program. Her paper on the wide-ranging potential for light sources based on laser-plasma acceleration was among the most popular downloads of 2016 published by the international publishing giant, IOP (Institute of Physics) Science, and will be featured throughout 2017 for free download.