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January 13, 2009

Solid State Laser Programs On Track for 2013 Field Tests


Textron solid state lasers

Aviation Week reports on the status of military solid state lasers.

Hellad [High Energy Liquid Laser Area Defense System] program small [size of a large refrigerator and about 1650 pounds] 150KW lasers are working to ground tests in 2011 and will include a demonstration of the system's ability to shoot down two SA-10-class surface-to-air missiles in flight simultaneously. "We want as realistic a tactical environment as possible," says Woodbury. "The next step is to line up support for an airborne demonstration. The system will be ready in 2012, and we could see a demo in 2012-13."


In 2009, different competing solid-state lasers are expected to run at power levels exceeding 100 kw. Different designs for 150-kw. electric lasers will also be tested in the lab this year as a step toward ground, and later airborne, demonstration of a fieldable laser weapon early next decade.

The military wants speed-of-light weapons with pinpoint accuracy, unlimited magazines and variable effects, but while the megawatt-class Airborne Laser and kilowatt-class Advanced Tactical Laser provide high power levels, their size and logistic issues with the hazardous chemical fuels limit their potential. "Warfighters want an electric laser," says Don Seeley, deputy director of the U.S. Defense Dept.'s High-Energy Laser Joint Technology Office.

Solid-state lasers promise to be much smaller and lighter, easier to integrate on to mobile and airborne platforms, and powered by electricity generated on board. Compared with fuel-hungry chemical lasers, electric weapons offer longer run times and unlimited shots.




Northrop Grumman and Textron Systems are developing competing 100-kw. solid-state lasers under JHPSSL. Textron is also building a more powerful derivative of its JHPSSL laser for Hellads, while General Atomics is developing the unique "liquid laser" that gave the Darpa program its name.

Full-power firings of the Joint High-Power Solid-State Laser (JHPSSL) devices were planned for the end of 2008, but are now expected in February-March for Northrop Grumman and summer 2009 for Textron. Both companies have completed 30-kw. firings as a step toward full power levels. The 100-kw. demos will complete the program, but the solid-state lasers are candidates for the U.S. Army's High-Energy Laser Technology Demonstrator program to test a truck-mounted system in 2013-15 that can counter rocket, artillery and mortar projectiles.

JHPSSL is demonstrating two different approaches to scaling solid-state lasers to high power. Northrop Grumman uses a "master oscillator power amplifier" configuration where the beams from eight lasers are combined optically to get to 100 kw. Textron uses a power oscillator configuration where a single beam goes through a chain of gain modules to produce a 100-kw. laser.

The Hellads program differs from JHPSSL in being the first program to impose size and weight requirements on a complete laser weapon system. The goal is to produce a 150-kw. weapon that fits within 3 cu. meters and weighs no more than 5 kg./kw. - more than 10 times smaller and lighter than any other high-power laser.

"JHPSSL is about scaling to 100 kw. in a laboratory. Hellads has higher power and aggressive targets for weight, size and run time, all within a form factor that fits on a tactical platform," says program manager Don Woodbury. Hellads is small enough to fit inside a bomber, transport or tanker and still allow the aircraft to perform other missions.

The original Hellads was conceived by Michael Perry, president of General Atomics' Photonics division, as a "radically different approach" to making a deployable laser weapon system. Perry says earlier work on ground-based high-energy lasers showed battlefield smoke and dust would degrade the beam. "We had to get the laser off the ground, but the issue was its size, weight and performance." The problem is not the laser head itself, which is "pretty small," he says, but the electrical supply and thermal management systems required to power and cool the weapon.

"The liquid laser design is completely different. It eliminates the thermal gradient and allows it to work a very high power," says Perry. The design is classified, but essentially the beam passes through a series of thin-disk laser amplifiers and the coolant in which they are immersed. The system comprises two 75-kw. modules, but they plug together to produce a single 150-kw. laser resonator, and there is no beam combining.

General Atomics has been working on Hellads since 2003. Textron entered the program only recently, having convinced Darpa it could scale up its ThinZag technology to meet the power and weight requirements. The design has three 50-kw. laser modules - called unit cells - similar to the JHPSSL power oscillator configuration "but with several significant design differences based on lessons learned," a company official says.

"JHPSSL was a great starting point and made it possible for Textron to be a competitor," says Woodbury. "They came in late and had to start from scratch, but they have made great progress in the laboratory and have gone well beyond JHPSSL in power, beam quality, run time and footprint." Darpa plans a shoot-off in the summer, with the winner going on to build the full laser. "All the science is in a unit cell; we simply replicate it to get to 150 kw.," he says.

FURTHER READING
As part of the $612.5 billion 2009 defense appropriations bill signed into law by President George W. Bush in mid-October, Congress fast-tracked Defense Science Board (DSB) recommendations that the military focus on the promise of directed energy weapons such as low-, medium- and high-power lasers, high-power microwaves and millimeter waves.

Textron awarded funding for Hellad lasers

Textron Defense Systems (TDS), an operating unit of Textron Systems, a Textron Inc. (NYSE: TXT) company, announced that it has signed an Other Transaction Agreement (OTA) with the Defense Advanced Research Projects Agency (DARPA) that will provide up to $21 million in government funding to design, fabricate and test a Unit Cell Module for a 150 kilowatt (kW) Laser Weapon System (LWS) and develop a critical design for the 150kW LWS.


Hellads coverage

Textron Defense systems lasers website

Separate from the DARPA Hellad program is the Navy program for megawatt lasers by 2012-2014. The Navy is looking at free electron lasers

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