While fashions in high-energy lasers have changed as technology progresses, from gas to diode and now fiber, General Atomics Aeronautical Systems (GA-ASI) has stayed its course over more than a decade and believes its third generation of electric laser weapon is ready for prime time.

The company has responded to an Office of Naval Research (ONR) solicitation for a 150-kw laser weapon suitable for installation on DDG-51-class destroyers to counter unmanned aircraft and small boats using only ship power and cooling.

Under ONR’s Solid-State Laser Technology Maturation program, the weapon is to be demonstrated in 2018 on the USS Paul Foster, a decommissioned Spruance-class destroyer that now serves as the U.S. Navy’s ship-defense test vessel at Port Hueneme in California.

GA-ASI has proposed its Gen 3 High-Energy Laser (HEL) system, which recently completed independent beam-quality and power testing for the U.S. government. The Gen 3 system is the third generation of electrically pumped laser using the architecture developed for Darpa’s Hellads program.

Under development since 2003, the 150-kw Hellads will be tested this summer at White Sands Missile Range in New Mexico. A smaller, lighter and more efficient Gen 2 system was built and tested in 2010-12 for the Pentagon’s HEL Joint Technology Office (JTO), says Jim Davis, director of laser weapons.

Gen 3 has increased electrical-to-optical efficiency, improved beam quality and further reduced size and weight, says GA-ASI. A mockup of the Tactical Laser Weapon Module was displayed for the first time at the Sea-Air-Space show on April 13-15 in Washington.

The module includes high-power-density lithium-ion batteries, liquid cooling for the laser and batteries, one or more laser unit cells and optics to clean up and stabilize the beam before it enters the platform-specific beam-director telescope, says Davis.

The unit cell is a laser oscillator that produces a single 75-kw beam. Modules can be ganged together to produce a 150- or 300-kw beam. There is no beam-combining, Davis says, as there is in systems that use multiple lower-power fiber lasers.

The Pentagon and several other manufacturers have shifted focus to fiber lasers because they are a commercial technology and have higher electrical-to-optical “wallplug” efficiency than diode lasers previously demonstrated at power levels exceeding 100 kw.

But the Gen 3’s efficiency is at the level of fiber lasers, Davis says, adding that the company has worked for several years to improve beam quality and achieved “excellent quality” in the latest tests. Adaptive optics adjust the beam to compensate for atmospheric distortion.

In the independent unit-cell tests, beam quality was measured over a range of operating power and run time, which is limited only by the “magazine depth” of the battery system. “Beam quality was constant throughout the entire run of greater than 30 sec.,” says GA-ASI.

“Fiber lasers are interesting, but it is a matter of maturity,” says Davis. “We are where fiber may be in five years. We have built several versions of this laser over the last 10 years, and we believe [the Gen 3 system] is affordable as is.”

In addition to the ONR program, GA-ASI is eyeing the U.S. Army’s Boeing High Energy Laser Mobile Demonstrator (HEL MD). Live-fire tests of the HEL MD used a 10-kw industrial fiber laser and the Army intends to upgrade the system to a 60-kw Lockheed Martin fiber laser.

The next step is a 120-kw laser, planned for testing in the early 2020s, and for which GA-ASI plans to propose the Gen 3 system. The Air Force Research Laboratory, meanwhile, is interested in a podded laser weapon, although there is no formal program yet.

Davis says the Gen 3’s size enables an airborne laser module in the 150-kw range to be carried by GA-ASI’s Avenger unmanned aircraft. The UAV has sufficient onboard power to recharge the module’s batteries in flight. “That’s the utility; you don’t need to go back to reload,” Davis says.