Since pretty much the dawn of history, people have been trying to use beams of energy to burn, melt and blow stuff up. In every film based in the future, lasers tend to play a big  part in how the characters go about mutilating each other; so why don't we seem to be getting any closer to this idyllic lightsaber-filled future?

Archimedes with lasers

Image credit: Wikimedia

The idea of using focused energy as a weapon has been around since the ancient Greeks. Keen students of Archimedes (you'll remember him as the awesome beard-rocking dude behind levers, density-measuring and the screw) will remember that he made a mirror-based contraption to focus the sun's energy on enemy ships, subsequently burning them into sorry ashes. Things went quiet on the laser front after that, until it cropped up again in the early 20th century. Work by British scientists to try and make a "death ray" led to the development of radar (simeltaneously changing the course of WWII), and famed inventor and general eccentric Nikola Tesla went to his deathbed in 1943 swearing he'd made a working version of a death ray, though no one ever saw it.

Death rays really came into the public conciousness in the early 20th century, but through science fiction rather than actual, y'know, science. H.G. Wells described something approximating a ray gun in The War of the Worlds, which used a "beam of heat" to make anything it came into contact with burst into flames; like a Midas touch, just deadlier and more useful for lighting fires. With the invention of lasers in the 1960s, ray-gun type weapons really became immortalised, as anyone who's seen Star Trek or Star Wars can no doubt attest. Compact, accurate and instant, laser weapons were viewed as the next logical step in the arms race in the Cold War era. So, with directed-energy weapons being long perceived as the inevitable next step, why has reality failed to live up to expectations?

The US first started taking laser weapons really seriously in the 1970s and 80s, when nuclear exchanges with inter-continental ballistic missiles started looking increasingly likely. The most famous of these is undoubtedly Ronald Regan's fanciful Star Wars project, which involved satellites using nuclear-powered lasers to shoot down nuclear missiles just after they'd taken off. Although this project was more train-wreck than reality, (probably because it involved frickin' nuclear-powered space lasers!), it did start a series of marginally more successful US defence projects that use lasers to target missiles.

The main reason why laser research has focused on defence (by shooting down missiles) rather than offence (trying to fry actual people) all comes down to one thing: size. Put simply, the amount of energy needed to produce a laser beam capable of blowing stuff up, and the sophisticated optics also needed, means that not even your biggest, butchest soldiers would be capable of wielding the sort of lasers the US was churning out.

Image credit: Missile Defence Agency

Take the example of the now-dead Airborne Laser Testbed. A missile-intercept programme, it consists of a massive chemical-powered laser mounted inside a specially adapted Boeing 747. The idea is to catch missiles in the "launch" phase, when they're moving slowly, and use the megawatt-class laser to zap them into submission. Although it's a sound concept, and has worked a few times in test, it has one pretty gaping flaw: it requires the aircraft to be within a couple hundred kilometres of the missile launch site, with favourable weather, flying in a nice straight line. Since missile launch sites tend to either be submarines in the middle of a barren ocean, or well hidden in supervillain's mountain lairs, the chance of having your fancy zappy plane in the right place at the right time is pretty remote. It's for this reason that the poor Airborne Laser, one of the few working (and pretty damn badass) laser projects got shuttered in 2010, in the face of defence cuts. RIP.

Another project that died an ignominious death was the Tactical High Energy Laser. A slightly smaller-scale weapon, it was designed to shoot down rockets and missiles. (For this reason, it was an Israeli pet project, but eventually fell out of favour after they instituted the Iron Dome missile defence system instead.) Again, though it worked just fine in test conditions, the limited range and relatively long period of time it took to destroy stuff made it far from ideal. Chemical lasers were also falling out of favour around this time, since people were finding out that having to refuel lasers is kind of a shag, and detracts a little bit from the badass death-ray-rocking image.

Current laser development is turning to ships: one of the ongoing projects that shows a lot of promise is the US Navy's Naval Laser Testbed. Generally, ships make good platforms for laser weapons: those handy nuclear generators produce a lot of electricity, boats make excellent targets for lasers (as that crazy Archimedes dude showed), and lastly, they're, well, really big. The Navy, noticing all these things, has made a laser that, when focused on engines, causes them to burst into flames really rather quickly. It only uses around 100kW of energy, a tenth or so of the more powerful airborne laser. Still, being a fibre laser powered by electricity rather than chemicals, it can be fired until it's either too hot or you get bored --  no having to refuel your laser here.

Active Denial System

Image credit: US Department of Defence 

The one other promising avenue of development for directed-energy weapons is for "less than lethal" applications -- think pain ray rather than death ray. Working pain rays are a reality; once again, it's the USA at the front of the research, producing an "Active Denial System" that uses microwave-style emissions to heat up the top layer of your skin, causing a very short, sharp and harmless burst of pain. Given that it works effortlessly over long ranges, it should be a useful bit of kit when you're trying to get rid of someone but don't quite want to shoot them. Only flaw? Doesn't really work if it's snowing. Or raining. Or dusty. Oh.

The future of directed-energy weapons most likely lies in miniaturisation  Though there are some good, working laser weapons around at the moment, they rely on huge power sources and big, complicated optics, which limits them to the biggest of planes and more nuclear-powered ships. Will we ever see Star Wars-style laser weapons? Probably not.

There's an overriding problem with laser weapons; to work, they need to heat something up to a temperature at which it spontaneously combusts (called a flashpoint). The amount of energy required to do that, and also the amount of energy needed to heat the air between you and your target, is insane. It's much easier, if slightly less surgical, to just fire a bullet at the person you don't like any more. Or, just hit him with a hammer. Either way, it takes less energy, and it's a more efficient way of transferring the energy, leaving you more power to watch telly/make tea. Sounds like a no-brainer to me.

Top image credit: Moonraker