Free-electron lasers take aim

30 Apr 2009

Could free-electron lasers provide the cornerstone of the US Navy's directed-energy weapons systems?

Defence contractor Boeing has bagged a US Navy contract that could ultimately be worth as much as $163m (€120m) to develop a directed-energy weapons system based on free-electron-laser (FEL) technology.

The first year of the programme involves a preliminary design review, a project worth $6.9m to Boeing. If successful, that work could lead to the development of a 100 kW lab demonstrator system, followed by field tests in a maritime environment.

"FELs are the only all-electric laser that is capable of achieving the megawatt power the Navy requires for ship defence," the company told optics.org in a statement. "Two unique attributes are the ability to tune the wavelength to maximize transmission of the laser through the marine atmosphere, and being able to precisely target a single small spot on the target. This combination allows the system to destroy the target in the minimum time."

A number of recent breakthroughs in FEL technology have made the new programme possible, according to Boeing. These include the development by Thomas Jefferson National Accelerator Facility (Newport News, VA) of an FEL capable of delivering a record 15 kW continuous laser power, through the use of superconducting particle accelerator technology.

"Following the Jefferson lab success, many US and international laboratories have pursued FELs based on energy recovery linear accelerators (ERLs) for use in next-generation X-ray sources, greatly adding to the ERL and FEL research fields," said the company. "Boeing has researched FELs since the early 1980s, and believes this technology is now ready to move from the laboratory to a prototype suitable for testing."

Free-electron lasers: the basics

FELs operate by passing a beam of high-energy electrons from an accelerator through a series of powerful magnetic fields. The magnets are arranged so that the field strength varies periodically, forcing the electron beam to oscillate and leading ultimately to intense emission of radiation.

Such devices have been demonstrated with emission wavelengths reaching from the terahertz region via the far- and near-infrared, the visible and ultraviolet range to the X-ray region, even though no single device can span this whole wavelength range.

From the US Navy's standpoint, an advantage of FELs for directed-energy weapons is that the laser is all-electric, needing to draw only on the ship's own power to operate without requiring additional explosive or toxic chemicals.