The Science of Beam Weapons

By on April 18, 2013

There are three technologies that collectively line the threshold to The Future: Meal pills, flying cars, and killer laser beams. Two of those are unlikely to happen, one for reasons of taste and the other because who the hell wants their grandma in charge of an aircraft, but that third… Lasers have tantalized everyone from science fiction writers to secretaries of defense, and for a long time there has been a view among many scientists that the pursuit is frivolous.

As we’ll see, there are some fundamental impediments to making lasers into weapons, and some equally fundamental reasons you might not want to succeed, regardless. Still, this month has seen some fundamental steps forward for the technology, including one proof-of-concept in which the US Navy shot down a drone. We finally seem to be on the brink of realizing the dreams of men like Edward Teller and Ronald Reagan, and of the generation they convinced that lasers would keep them safe.

The LASER

LASER is actually an acronym for Light Amplification and Stimulated Emission of Radiation, and it was Albert Einstein who first proposed the mechanism of their creation, what he called stimulated emission. The first realization of his idea created a beam of microwave radiation rather than visible light, making it technically a MASER, but we’ve been using fuzzy definitions of these words for decades; in the eyes of the popular media, everything from a diffuse microwave emitter to a particle beam can be called a laser. The scope of the technologies we will accept in fulfilling the dream may have expanded, but the practical criteria have not: we need a light-quick beam, preferably a solid and unbroken line of fire, one which remains coherent and deadly even at extreme range. We don’t much care if the projectiles are photons or protons, if the projector is hand-held or mounted on a Super Star Destroyer. Just give us our lasers.

From here on we’ll be referring to them as “directed energy weapons,” and we should cut ourselves a little slack — weaponizing this technology is not the entirely the stuff of sci-fi. After all, we can already use lasers to cut diamond, to target aerial strikes, to power small aircraft, and we already use particle beams for everything from destroying tumors to finding the Higgs boson. There’s potential here, even leaving aside the obvious advantages of light-speed projectiles and rechargeable weapon magazines.

Essentially every “advanced” weapons technology in history has just been increasing elaboration on one of two ideas: hit an object with another object, and subject an object to an uncontrolled emission of heat energy (blow it up). Occasionally, we have mixed the two approaches together. Directed energy weapons are one of our few real attempts at pioneering a fundamentally different sort of weapon.

We can break this topic down along two basic axes, each with two states. First, there is weapon type, of which there are two: The too-small weapons, the handheld personal phasers of Star Trek, and the too-far weapons, the great, Hoth-like siege engines floating on battleships or orbital platforms. On the other axis, there’s the technology type, which can also be broken down into two major categories: The lasers, focused emitters of various forms of light energy, and the particle beams, super-rapid-fire miniguns that shoot streams of small, mass-carrying particles. There are a few other weapon types we’ll address at the end, but most real world steps toward the lasers of The Future fall neatly into one of the four quadrants in our matrix.

The X Axis – Using laser weapons

Let’s look first at how these weapons might enter the battlefield, regardless of their engineering. There are two basic approaches to implementation: Hand-held beam weapons like we see in Star Trek, and platform based weapons like those we see in reality. Unfortunately, hand-held beam weapons won’t be happening any time soon.

The reasons for this are numerous, but foremost among them is power. Lasers, particle beams, microwave emitters, all of them require great amounts of power, and even if one was willing to haul around a megawatt battery it would eventually need replacing just like regular ammo. We have an informal threshold of 100 kW to reach, past which point, we’ve pretty much decided, our laser will be a killer battle-laser. Before that threshold, presumably, it’s just a really strong pointer.

So-called “blooming” is also a problem, since powerful lasers tend to turn air to plasma as they move through it, creating refracting conditions that defocus the beam. We must stick with platform-mounted lasers since bulky mirror arrays are currently our best way of overcoming the bloom effect. Additionally, the speed and pinpoint accuracy of lasers are almost totally irrelevant on the human-scale battlefield, since distances are short enough for bullets to be functionally instantaneous already, but long enough to make lasers less useful through errors in aiming. There’s really no hint of progress toward the unbroken laser beam we could sweep over a field of enemies for mass bisection and, as you might imagine, a series of micro-second pulses can be really difficult to aim.

Even in the much more foreseeable future of strategic, platform-mounted lasers, weaponizing light requires the use of pulses. The first reason for this, again, is power, but just as important is the mechanism by which laser damage their targets: when a strong enough laser hits a surface, say the wing of a drone, the surface layer will (should) sublimate — that is, go directly from a solid to a gas — and fill the space around the target with a beam-scattering cloud of vaporized metal. You have to wait a while, maybe ten or fifteen microseconds, for that cloud to disburse, or else waste energy while it scatters your beam all over creation. Once the tiny cloud has puffed away, we can send a second pulse, then a third, and so on.

Particle beams

Different hypothetical laser designs prescribe different numbers of pulses at different energies and spaced with different delays, but they all basically take a burrow-and-clear approach. A fifty-shot burst might unfold over a thousandth of a second, or so. Since the laser has to cluster the pulse impacts very tightly, fast-moving targets require truly incredible aim-and-track technologies, and greater steadiness than any human hand could hope to deliver.

Person-scale combat seems to beg for wider-beam solutions, ones that spread their energy over a more reasonable area. Such diffuse energy projection immediately lends itself to non-lethal applications like controlling a mob or disabling a fleeing target. Energy that might have burned through flesh when concentrated on a square millimeter of space might simply inflame some skin when spread over several square meters. Since this requires large projectors and, again, gobs of general purpose energy storage, this poses most of the same problems for portability as more focused beams.

Particle beams don’t seem much better suited to miniaturization. Rather than imparting heat energy to a target like a laser, particle beams do their damage throughkinetic energy, atomically sand-blasting a target with a stream of atoms or small molecules moving vanishingly close to the speed of light. The problems with portability are easy enough to grasp: we currently use particle accelerators, usually cyclical accelerators like the 17-mile-long Large Hadron Collider, to ramp our ammo up to lethal speeds. As you might imagine, that’s a difficult scale down in size.

As with so many things, graphene offers some hope here, mostly in terms of creating room-temperature super conductors. By reducing waste, basically letting us put the focused power of a liquid helium-cooled MRI machine in a combat backpack, we could realize at least a few of these science fiction dreams. Until then, though, this tech will remain focused on still or smoothly moving far-away targets, like drones seen from the ground or the ground seen from a drone. Again, the 100 kW threshold is critical — it’s seen as the minimum punch needed to shoot missiles out of the sky.

There are problems associated with range, tracking, etc., but these are all ultimately easier to fix than truly insoluble problems like human strength, dexterity, and attention. Even DARPA’s long-in-coming enhanced super-soldier would be hard pressed to carry, aim, and steady such a weapon. A drone with a belly-mounted laser, though, one stabilized with a gimble or similar technology, that might represent the best missile defense system imaginable — one that need not fiddle with the kinetic insanities of hitting a supersonic missile with another supersonic missile. There’s a reason so many presidential administrations have been so eager on Star Wars initiatives; if they worked, boy, they would really work. How worried would we now be if we knew that a drone was circling North Korea, ready and waiting to burn the warhead out of any missile that so much as pokes its head above-ground?

One final note about portability. While I’m usually the last person to doom-say about possible misuse of technology, even I must admit that a long-range, hand-held weapon that hits instantly and with no recoil, disregarding traditional distance issues like wind and the Coreolis Effect, is a truly scary thought. Don’t think the Secret Service could just use their Halo skills to track a telltale laser back to its source — in the real world, a laser attack is totally invisible. If you ask me, this is one tech we should not be in any rush to miniaturize.

http://www.extremetech.com/extreme/153224-the-science-of-beam-weapons

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