For a vision of war, it was almost elegant. The smoke and stink and deafening crack of munitions would be replaced by invisible beams of focused light. Modified 747 jets, equipped with laser weapons, would blast ballistic missiles while they were still hundreds of miles from striking our soil. "Directed-energy" cannons would intercept incoming rockets at the speed of light, heating up the explosives inside and causing them to burst apart in midair.
And this wasn't some relic of Reagan-era Star Wars visionaries. These were modern plans, initiated barely a decade ago, that would be realized not in some far-off future, but soon. Out in the New Mexico desert at the White Sands Missile Range, the U.S. Army's Tactical High Energy Laser shot down dozens of Katyusha rockets and mortars. In 2004, Air Force contractors began test-firing the chemically powered beam weapon for a retrofitted 747, the Airborne Laser.
Then reality set in, and these recent efforts to wield battlefield lasers suddenly began looking as doomed as Star Wars. Generating the megawatts of laser power needed to detonate a missile required hundreds of gallons of toxic chemicals—ethylene, nitrogen trifluoride. The weapons grew bulky. Worse, after a few shots, the lasers would have to be resupplied with a fresh batch of reactants. The logistics of hauling those toxins either through the air or across a battlefield made generals shiver. And questions lingered about how effectively the beams would penetrate dust and rain. Last year, the Army canceled its Tactical High Energy Laser project, and some think the wildly overbudget beam-firing 747 may be next to go.
But don't count laser weapons out yet. The ray-gun potential of weapons that fire with precision over tremendous distances is far too militarily appealing, particularly at a time when American soldiers are fighting guerrilla foes who melt quickly into the background. "If I could reach into a crowd and take out one or two targets without a puff of dust or a crack of a rifle—if I could fire for a long time, without ever having to reload," says Marine Corps Major General Bradley Lott, "that's something the United States Marine Corps would be very, very interested in pursuing."
But if chemical lasers can't cut it, what will make beam warfare a reality? The answer is twofold. First, the Pentagon is slowly realizing that if it wants results, it has to lower its expectations. Shoot down mortars first, for example, then missiles. More important, however, is the reemergence of two technologies of the Star Wars past—solid-state and free-electron lasers—in the energized, promise-filled labs of two former colleagues who thought their dreams of laser triumph had died years ago.
Jumping to light speed
Lasers all work in pretty much the same way: Excite certain kinds of atoms, and light particles—photons—radiate out. Reflect that light back into the excited atoms, and more photons appear. But unlike with a lightbulb, which glows in every direction, this second batch of photons travels only in one direction and in lockstep with the first. And instead of shining in every part of the spectrum, laser light is all the same wavelength, which depends on the "gain medium"—the type of atoms—you use to generate the beam. Shine enough of the focused light, and things start to burn.
The first laser experiments in the 1960's used ruby crystals as the gain medium. But solid-state lasers like these originally couldn't produce more than a few hundred watts of power. That's fine for eye surgery. Knocking down a missile—as the military first dreamed of doing—takes millions of watts of power, which is why researchers turned their efforts toward the ultimately failed chemically powered lasers.
There is another kind of laser, however, one that requires no bulky tubs of toxic chemicals, no crystals—no gain medium whatsoever to generate its beam. It's called a free-electron laser (FEL), and it uses a turbocharged stream of electrons to kick-start its reaction. This form of laser dominated the Star Wars national missile-defense program; it was the almost mythical beast that scientists George Neil and Bob Yamamoto toiled on together for defense contractor TRW.
It was hamstrung by high power expections. But both Neil, the project's chief scientist, and Yamamoto, a project engineer, were true believers. They thought that with enough research, a free-electron laser might really be able to stop a rogue missile. And the breakthroughs required in atomic physics, optics and superconductivity would have far-reaching benefits, even if an ICBM never got zapped. But after 10 years and half a billion dollars of investment, the free-electron laser in TRW's lab peaked out at a meager 11 watts—a tenth of what a lightbulb generates.
After several more years of executives continuing to promise 10, 20 megawatts of power, the Pentagon finally pulled the plug in 1989, and Star Wars went down in a flameout of legendary proportions. Neil particularly resented the way the reckless projections had doomed the program and turned his directed-energy ideas into a laughingstock. At scientific conferences for years afterward, Neil would advocate for reviving free-electron research. "People thought we were insane and the technology was unfeasible," he says. "And on the bare evidence, they were right."
Bob Yamamoto, meanwhile, stayed away from military projects for 15 years after the Star Wars fiasco. He went to work for Lawrence Livermore National Laboratory, TRW's partner in the free-electron laser, building magnets for high-energy physics experiments. The lab was close to Berkeley, California, where he had grown up and gone to college, so the shift gave him the chance to keep racing and rebuilding import cars—Toyotas and Datsuns—with his old buddies. In the garage and at the lab, Yamamoto developed a reputation for making things that could be run hard. Because of this and his previous laser experience, he was tapped in 2003 to run Livermore's $50-million Pentagon-funded solid-state laser project. The technology, once deemed so unfeasible, was being resurrected with more measured progress expectations. Yamamoto felt as comfortable with solid-state technology as he did with free-electron lasers, and it proved an intriguing reentry into the field. "Directed-energy weapons, they've been promised for more than 30 years," he says. "I want to be the first on the block to say, 'We took care of it.' "
Under the GUN
The ammunition in Yamamoto's new solid-state laser is a set of four-inch square transparent slabs tinged with the slightest hint of purple. They're exactly what you'd expect to find powering the cannons on board the Enterprise or the Millennium Falcon.
A magazine of these see-through slabs isn't exactly infinite, though; for every 10 seconds they fire, they need at least a minute to cool off. But the slabs—ceramics infused with the element neodymium, the atoms that, when excited, produce the photons that eventually become the laser beam—can never be drained of their potency. And they're a lot less hassle than bulky chemical tubs. They're a big reason why Yamamoto's machine squeezes into a single 30-foot-long lab. It's not hard to imagine the whole thing packed into a small truck, knocking mortars out of the air. "I've been thinking about deployment for a long time," Yamamoto says.
A solid-state laser like his could now make it to a war zone in part because the bar for energy weapons has been lowered. Blasting an ICBM from 100 miles away requires megawatts of light. Solid-state lasers might never get that powerful. But heating up a mortar from a mile away until the explosives inside detonate—that takes only 100 kilowatts.
Yamamoto is getting close. He shows off dozens of blocks of carbon steel and aluminum, each two inches tall and an inch thick. On all of them are burn marks and holes. One block, marked "6-6-05," is almost completely warped by a pair of half-dollar-size depressions. A rope of formerly molten metal sticks out from the bottom. "Can you believe that?" Yamamoto asks, with a booming tenor and a big, boyish grin. He looks much younger than his 50 years. "It's like shining a flashlight, and stuff is melting! It's ridiculous!" The Livermore laser, pushed forward by larger gain-medium slabs and increased pulsing speeds, hit 45 kilowatts of power in March 2005. That's more than triple what the laser could do three years before.
But there's a nervous tension at the lab the day I come to visit. Each of the slabs is surrounded by an array of 2,880 light-emitting diodes, like the ones in a clock radio. When they shine, they excite the atoms in the transluscent ceramic composites and begin the laser chain reaction. The problem is that the more the diodes glow, the more that temperature disparities degrade the quality of the beam. The infrared ray—invisible to the naked eye—starts to lose some of its quality. Which is bad, because the Pentagon wants to see a nice, tight beam, as well as a powerful one. And the Defense Department's team of testers is due here next Tuesday. The visit will largely determine whether the Livermore team will get the cash to make its next laser: a 100-kilowatt, weapons-grade machine.
So Yamamoto's team is making last-minute adjustments to the "adaptive optics"—mirrors fitted with more than 200 actuators that bend them to compensate for distortions in the beam. Yamamoto is politely apologetic. "I'm sorry, but we're under the gun," he says as our meeting draws to a close.
George Neil isn't in such a hurry when I meet him a few days later. The thin, 58-year-old "death race" runner—he recently finished a 78-mile ultramarathon through the Canadian Rockies—has been pushing for a free-electron laser for more than a quarter of a century. It will be another few years before he's got one as strong as Yamamoto's solid-state machine. So he has some time to show me around his lab at the Department of Energy's Thomas Jefferson National Accelerator Facility in Newport News, Virginia.
He opens a pair of magnetically sealed doors. Inside is a 240-foot-long jumble of copper piping, rubber hoses and steel tubes of a dozen different sizes. Almost all of it is designed to do one thing: generate massively powerful pulses of electrons, moving at 99.999 percent the speed of light. The electrons rush through precision-timed micro-wave fields, gathering strength and speed along the way. Then the electron beam is sent through a "wiggler," a series of 29 magnets that bend the electron stream up and down. In the process, the electrons emit photons—and the laser chain reaction begins. This is Neil's gain medium, his answer to Yamamoto's slabs and the chemical laser's toxic gases, and it is by increasing the power and quality of this electron beam that Neil advances his technology.
The FEL's "tunability" is what got the military interested in the first place. Most lasers lose strength as they move through—and get absorbed by—the atmosphere. A little rain only makes things worse. But an FEL could use whatever wavelength flows through the air the best. And there's no emptying the "infinite magazine." No wonder Los Alamos National Laboratory associate director Doug Beason calls it lasers' Holy Grail. But can anyone pull it off?
After Star Wars, ultramarathoner Neil bided his time and paced himself, waiting for the technology to catch up. For five years, he worked here at Jefferson lab on a giant particle accelerator. The lab's director promised that he could build the FEL afterward. Finally, in 1995, when it came time to put the machine together, Neil and his team designed a new FEL that would produce a single kilowatt of light—not the superstrength lasers promised back in the '80s. In 1999 they broke the record power levels of the Star Wars–model FEL by 100-fold. In 2003 the new FEL hit 10 kilowatts, another record. "I always believed the technology would get there," Neil says with a satisfied grin, "if we took manageable steps with reasonable goals."
And now Neil has the military's attention again. The Defense Department is investing $14 million a year in the machine. There's talk of eventually equipping the Navy's next generation of destroyers with free-electron lasers. Today the ships don't have the precision weaponry to stop rocket and small-boat attacks, like the kind Al Qaeda used against the U.S.S. Cole in 2000. A laser might be able to handle the job. And only a free-electron laser could be tuned to cut through the briny ocean air.
In December, Neil gets good news. The Navy has committed to the im-proved FEL in a big way: $180 million for an eight-year, multi-team effort. "There's many a challenge ahead," he writes, "but at least we are started."
Yet Neil's feelings are a little bittersweet. The results have come in for the Pentagon's solid-state laser competition, too—and his old friend and colleague Bob Yamamoto lost out. The money to build a weapons-grade solid-state laser in the lab is going instead to a team at Northrop Grumman.
Northrop's design wasn't all that different from Yamamoto's, but instead of the four big see-through slabs at the core of Yamamoto's machine, Northrop relies on several smaller crystals. Less energy is concentrated on individual crystals, so there are fewer imperfections in the beam. "I'm amazed how much power we're getting out of a piece of glass the size of a stick of gum," says Northrop program manager Jeff Sollee, a 30-year directed-energy veteran, most recently with the defense contractor's last big chemical-laser program, the Tactical High Energy Laser. The Pentagon has given Sollee 33 months to bring his machine to battlefield strength.
Yamamoto, meanwhile, continues to quietly tweak his laser, despite the Pentagon's decision against him. He's learned that, in this business, anything can happen. "For now, we're keeping an extremely low profile," he says. "But we're not done."
Noah Shachtman edits defensetech.org, a military-technology blog.