The US Army is building a laser weapon more than a million times more powerful than any used before – although because it delivers short pulses, the overall energy involved is low.
Existing laser weapons produce a continuous beam that is held on a target, such as a drone or missile, until it melts – the first was deployed by the US Navy in 2014. The new weapon, known as the Tactical Ultrashort Pulsed Laser for Army Platforms, would be more like science-fiction movie lasers, firing bullet-like pulses of light.
Such ultrashort laser pulses carry extreme power over vanishingly short lengths of time: the project is aiming for a terawatt pulse lasting just 200 femtoseconds (2 x 10⁻¹³ s), compared with a maximum of 150 kilowatts for previous systems.
The laser would produce 20 to 50 pulses per second, for an overall power rating of 20 to 50 watts, around 10 times more than an LED light bulb. Ultrashort lasers this powerful are already used in laboratories and factories, but the US Army wants a compact, rugged version that can be aimed at distant targets.
Normal lasers are ineffective over long distances because the beam spreads out, but ultrashort pulses can be shaped into self-focusing light pulses called solitons that turn the air itself into a lens, continually refocusing the pulse.
Such a weapon would produce dramatic effects. The rapid temperature rise from the ultrashort pulse would vaporise the surface of a target rather than melting it, a technique used industrially to drill precise holes through metal. The resulting rapid expansion of gas can also produce a powerful blast wave.
In addition, the US Army hopes to create an electromagnetic pulse (EMP) effect using the laser. On striking a metal target, the laser pulse rapidly accelerates electrons, and the moving charges produce a burst of radio-frequency energy powerful enough to disturb nearby electronics. This is a known problem in laboratory settings where EMPs can affect measuring instruments. A sufficiently powerful EMP could bring down drones or missiles by disrupting their control systems.
Contractor Aqwest in Larkspur, Colorado, is developing a ceramic disk laser for the project. The design is a variation of the thin-disk laser invented in Germany in 1992. The original lasing disc was just 0.1 milimetres thick and was attached to a heat sink to disperse waste heat. Aqwest’s version is thicker and can deliver proportionately more energy in each pulse. The firm declined to comment.
Building this kind of laser weapon is possible with current technology, says Derryck Reid at Heriot-Watt University in Edinburgh, UK. “This is not science fiction.”
Reid sees the self-focusing effect as the key benefit of the new laser. Although the amount of energy is low compared with a continuous beam laser, delivering it rapidly to a small enough area could be effective. “You could certainly do some damage with these power levels,” he says.
Laser weapons are intended for use against small, fast-moving targets like drones or missiles. If used to target a human, it would cause unpleasant burns, but would generally be less harmful than conventional weaponry.
The International Committee of the Red Cross, which has worked to develop international law around laser weapons, declined to comment on the specifics of the weapon, but notes that the only current restriction on such arms is a 1995 treaty prohibiting the use of lasers intended to blind.
Aqwest’s contract states that the prototype ultrashort pulse laser weapon will be demonstrated by August next year, after which the US Army will decide whether to go ahead with further development. This could lead to laser blasters mounted on ground vehicles and helicopters.