A laser focus on radiation generation

23 May 2007

Will laser-generated radiation one day prove useful in cancer therapy? A UK collaboration aims to find out.

A consortium of UK-based scientists has secured £5 million ($9.9 million) in research funding to turn the concept of laser-generated radiation into a robust, ready-to-go technology. The four-year project, involving researchers from nine separate institutions, could lead to cheaper, simpler solutions for proton and ion radiotherapy. Laser-energized radiation sources could also cut the cost of research into cosmic-radiation exposure from frequent air travel and manned space missions.

Experiments have shown that intense, energetic beams of ionizing radiation can be produced by shining a high-power laser onto a thin target made of metal, plastic or liquid. The type of radiation produced depends on the composition of the target, and the LIBRA (Laser Induced Beams of Radiation and their Applications) project aims to produce a single technology that uses interchangeable targets to generate protons, ions, or gamma rays, as required.

"The idea behind the project is to move on from scientific experiments to real applications," said principal investigator Marco Borghesi, from the school of mathematics and physics, Queen's University, Belfast. "To do that, we will need to develop a significant amount of novel technology with regard to the foils or disks onto which we will shine the laser."

Development of the technology will require access to a very high-powered laser with a rapid-fire repetition rate. One such system is the GEMINI laser, due to come on-line at the Rutherford Appleton Laboratory (RAL) near Oxford, UK, later this year. GEMINI is expected to deliver 1 PW (10¹⁵ W) pulses every 20 seconds.

Borghesi added: "At the moment, we are able to produce relatively high-energy ions or gamma rays, but we are only firing maybe one shot every 10 or 20 minutes. Most practical applications would need sources that can emit continuously every second or fraction of a second to produce blasts of radiation."

While solving one problem, the use of such a laser will create other technological challenges. For a start, targets used to generate high-energy ions are destroyed by a single laser blast, which means that researchers will need to find efficient methods to replenish the metal foils in time for the next laser shot. Work is also needed to control interactions between the laser beam and target, specifically to improve the system's overall reliability and accuracy.

Smaller, cheaper

The viability of LIBRA's end-product as a useful technology will rely on high-powered lasers becoming more widely available and affordable. If not, then the benefits of laser-generated radiation over existing synchrotron sources will be far less clear cut. Borghesi is confident, however, that laser technology is advancing so rapidly that sufficiently high-powered table-top lasers will be available by the end of the project.

"A possible additional advantage of these laser-driven sources for cancer therapy will be the ability to produce ions much closer to the patient," he told medicalphysicsweb. "So instead of steering a proton beam around the room using big, expensive, magnetic gantries, it will perhaps be possible to steer the laser beam using mirrors instead."

Other potential applications for laser-generated radiation sources include engineering diagnostics of internal components, quality control of semiconductor electronics, resilience testing of satellites, security screening for explosives, and table-top pump-probe investigations of molecules and nanostructures. Representatives from a variety of relevant industries will be invited to open days as the project progresses, Borghesi said.

He acknowledges that LIBRA is not the only project aiming to exploit the physics of laser-driven ion acceleration for practical use. But most - if not all - competing initiatives are focused on building a technology to fit a specific application. LIBRA will also benefit from the wide range of differing expertise held by researchers at the participating institutions, which are Queen's University Belfast, the Central Laser Facility at RAL, Imperial College London, the National Physical Laboratory, and the universities of Surrey, Birmingham, Paisley, Strathclyde and Southampton.

"A key requirement for the funding of this project was that we would produce a generic technology," he said. "If we can provide the sources as we think we can, then our technology will be of interest for a broad range of applications."