Researchers capture first laser-driven, high-resolution CT scans of dense objects

The findings, published this week in Optica, describe the science and engineering behind this new radiographic imaging capability and its potential benefits to a range of industries, from aerospace to additive manufacturing. 

The project is a years-long collaboration between researchers at CSU's Departments of Electrical and Computer Engineering and Physics and Los Alamos National Laboratory, with participation from AWE in the U.K. 

"This demonstration is just the beginning," said Reed Hollinger, an assistant professor at CSU and lead author of the study. "We are using the CSU-built ALEPH laser to generate extremely bright X-ray sources to do high-resolution X-ray radiography and CT. As we develop our new facility, our goal is to ramp this into something that can make a broad impact."

The team's approach offers a fast and non-destructive way to obtain a detailed view inside dense structures, such as rocket components and turbojet engines. With growth in additive manufacturing, the new technology could greatly enhance quality control while preserving the integrity of 3D-printed parts. 

Next-generation laser-driven imaging at Colorado State University

Current industrial CT scanners are not only massive and costly, but they produce images with millimeter scale resolution. The team's laser-driven approach generates a much smaller X-ray source, enabling significantly higher resolution without decreasing the energy of the X-rays.

"A small spot MeV X-ray source is the single largest lever that is potentially available for improving high resolution MeV X-ray imaging," said James Hunter of Los Alamos National Laboratory, who collaborated with Hollinger on the study. 

The method, rich in physics, uses a petawatt class laser focused to an intensity of 1021 Wcm-2 to accelerate a beam of electrons to a few million volts over a few microns in space -- smaller than the width of a human hair. The electrons in the beam collide with heavy atoms in the target, causing them to slow down and convert their kinetic energy to X-rays. These X-rays have significantly higher energy than those found in traditional X-ray tubes used in hospitals. The increased X-ray energy is necessary to penetrate dense objects like the turbine blades shown in the study. 

"For perspective, the energy of a traditional hospital X-ray source is only tens of thousands of volts as opposed to our X-ray source, which is millions of volts," said Hollinger, who is part of the Walter Scott, Jr. College of Engineering at CSU. 

Each X-ray pulse only lasts for a few trillionths of a second, enabling time-resolved radiography of objects moving at incredible speeds.

"For example, we could one day capture high-resolution 3D images of the inside of a jet engine while it's operating. Currently, there are no other X-ray sources that can do this," said Hollinger. 

The CSU team's work is part of a larger vision to leverage high-intensity laser sources for a wide range of uses, from studying inertial fusion energy to generating bright beams of GeV electrons and MeV x-rays. It is one of the many technologies that researchers aim to scale up using the expanded capabilities of the university's new Advanced Technology Lasers for Applications and Science (ATLAS) Facility, set to come online in late 2026.