A small quadcopter, just like the ones they sell for a few hundred dollars at big-box stores, flies against a cloudless blue sky. On the ground, atop a dune buggy, a glass-paned turret pivots in the drone’s direction.
Inside the vehicle, there’s a motorized whirr. Moments later, flames start to flicker near a microscopic hole in the center of the drone’s wings, and the hard plastic begins to melt. A few seconds later, it crashes to the ground.
This is what it looks like when Raytheon Intelligence & Space, a Raytheon Technologies business, demonstrates the use of lasers to defeat hostile drones. Counter-UAS lasers such as RI&S’ High-Energy Laser Weapons System give military service members and public-safety officials a relatively inexpensive way to defeat swarms of cheap, weaponized drones.
The Raytheon Intelligence & Space High-Energy Laser Weapons System offers a cost-effective counter-UAS solution rather than firing a multi-million dollar missile to disable a $500 commercial quadcopter. Furthermore, commercial, small drones have become much more sophisticated, fly faster and can navigate autonomously without using radio frequencies, making them jam-resistant.
Here’s how they work
Every laser – no matter whether it’s scanning groceries at the supermarket or reading a Blu-Ray DVD – starts with the same idea: converting electricity into light.
“By far and away, semiconductor diode lasers are the most common way to convert energy – electricity – into photons or light,” said Iain McKinnie, Electro-Optical/Infrared and Laser Technologies technical director for RI&S.
But diodes alone can’t take down a drone.
Semiconductor diode lasers spread out and diffuse over distances, which, on their own, makes them ineffective for disabling drones.
“Think of a garden hose nozzle that is set to a wide spray,” McKinnie said. “Only about 50% of the electrical power gets converted into laser light and the other 50% is waste heat. We needed a second stage to convert the semiconductor diode laser light into laser light that we can use in our counter-UAS system. We do that with fiber, turning that wide spray into a concentrated, narrow jet.”
Diode lasers are only step one, serving as a “pump” for a fiber laser
“Diodes are the core building block in a fiber laser amplifier. Within that amplifier, a number of diodes pump their light into a single optical fiber, which produces a very powerful and perfectly formed beam,” said Evan Hunt, director of business development for High Energy Lasers and Counter UAS at RI&S.
Getting enough fiber
The fiber optic cables used in RI&S’ High-Energy Laser Weapons System are very similar to those the telecommunications industry uses – only they can withstand much higher power levels, and the HELWS fiber optic cable is about 10 times wider, at a microscopic level, than the cables used by the telecom industry.
“Fiber-based lasers have become elegant, efficient and pretty robust because of the research, investment and support they’ve received by the very large commercial industry of cutting and welding,” Hunt said. “They are 80% to 90% efficient, generating very little heat. And in addition to the efficiency, the fiber serves to amplify the power of the beam.”
Fiber lasers use a lot of cabling that can run from tens to hundreds of meters long, according to McKinnie, and because of this bulk, the cabling is “spooled up like fishing wire” so it can fit onto a mobile platform and also aids in distributing excess heat.
The fiber laser beam is much more focused than diode lasers. “Instead of a flashlight, you have a laser pointer,” Hunt said. And unlike the red, green or violet beams emitted by common laser pointers, HELWS produces laser light in the infrared spectrum that’s invisible to the naked eye.
Crossing the beams
But a single fiber laser beam does not provide the range and engagement speed to destroy an attacking drone. The third stage is combining multiple fiber laser amplifier beams.
“It’s incredibly difficult to manage such powerful light and the associated heat within such a small system,” said Justin Martin, HELWS chief engineer. “The optics need to be precisely aligned and specially coated so they don’t melt upon contact.”
Once that powerful beam is built, the laser needs a way to find its target.
To accomplish this crucial step, RI&S equipped the system with its Multi-Spectral Targeting System, or MTS, which uses light from many bands of the electromagnetic spectrum to acquire and track targets, and then tell the operator where to fire the laser.
MTS is used on more than 20 rotary-wing, unmanned aerial systems and fixed-wing platforms for long-range surveillance, target acquisition, tracking, range finding and laser designation.