In 1960, when scientists first developed Light Amplification by Stimulated Emission of Radiation, skeptical scientists and engineers joked that this new LASER was a “solution lacking a problem”. But within just a few years, practical uses began to arise for the new technology. Steady advances over the next few decades allowed ever-smaller lasers to produce more powerful and precise beams, and a plethora of new types of lasers were invented that further expanded their application.

Today lasers are ubiquitous and diverse. Several hundred of the smallest lasers can fit on a single microchip, and the largest fills a facility the size of a Wal-Mart. Some generate continuous beams for hours or even days, while others fire a pulse no more than one-millionth of a nanosecond long. In between these extremes lie the everyday lasers inside our CD and DVD players and at the grocery store checkout. But if you’re like me, the first thing you think about when you hear “lasers” is sexy and exotic futuristic weapons, which have been a staple of science fiction since H.G.Wells described a laser-like “heat ray” in his 1898 book The War of the Worlds. Over a century later, though we’re still waiting for our laser guns, some primitive laser-based weapons are finally beginning to appear.

Some of the lasers we use look like those from science fiction, like the one at Lick Observatory atop Mt. Hamilton in southern California. There, astronomers have installed a moderate-sized laser as part of an adaptive optics system. The laser is fired skyward to produce an artificial star within the telescope’s field of view. When the sodium-gas-generated laser beam reaches the mesosphere and thermosphere in the upper atmosphere, it excites sodium atoms causing them to give off an orange glow. This artificial star is then used to calibrate the adaptive optics, resulting in an image almost as clear as one taken with the Hubble Space Telescope.

If we can precisely target and create artificial stars in the upper atmosphere, it would seem a simple matter to use a beefier version of the Lick laser and shoot down incoming missiles, a la Atari’s Missile Command. Early efforts at weaponizing lasers relied on this approach, but they ran into a problem called blooming. At very high power densities, laser beams cause the atmosphere to break down much like lighting does. The plasma then defocuses the laser beam, making it appear to bloom. A blooming beam very rapidly loses the ability to shoot down an insect, much less an incoming hypersonic ICBM. Blooming can be avoided by focusing a very wide laser beam down to a point only at the target, but this requires very large and fragile mirrors not well suited for combat.

The National Ignition Facility (click to enlarge)A laser that just might be powerful enough for planetary defense is under construction at Lawrence Livermore National Laboratories, the site of the National Ignition Facility (NIF). Now only partially complete, the NIF will eventually focus 192 separate laser beams down onto a target the size of a sesame seed. The combined energy output of the beams will be 1.8 megajoules in a single burst, enough energy to instantly vaporize two hundred and fifty gallons of water. This laser is intended to implode a deuterium-tritium target, igniting thermonuclear fusion.

Such a powerful laser, if properly focused, would be formidable defensive weapon. But there have been some major difficulties with the NIF; the government-funded program is seven years behind schedule and ten times over its original budget. Most of the problems stem from the enormous expense of the components of the NIF laser, all requiring extreme tolerances and precision. At an estimated cost of at least $4 billion, not even the Pentagon can afford to build a weapon that could be so easily targeted and destroyed.

Some portable combat lasers have started to appear in modern militaries, including the PHaSR rifle shown here (yes, it’s named after Star Trek). But none of these weapons can deliver enough energy to cause physical damage to personnel or equipment, instead they all rely on the extreme sensitivity of the human eye and electronics to laser light. Most of these weapons are no longer in use due to a 1995 UN protocol outlaws permanent blinding as a combat tactic, with the exception of devices like the PHaSR which supposedly only blind the target temporarily.

Even if hand-held laser weapons were legal under international law, current power storage technology doesn’t allow such small devices to carry nearly enough energy for even a single damaging shot. Pound-for-pound, the destructive power of even the most advanced lasers is far below that of conventional weaponry. Hand-held laser weapons would not suffer from blooming if fired at close range, but until we invent a source of energy able to produce several hundred terawatts at about ten pounds, laser rifles will remain a thing of the future.

Dozens of other active research projects aim to bring actual laser guns into use. The ground-based Tactical High Energy Laser is being studied by the US and Israel as a means of shooting down mortars and shoulder-fired rockets. The Advanced Tactical Laser, a converted 747 equipped with a big laser and focusing mirror, should be capable of destroying ballistic missiles in their “boost phase” as well as unshielded ground-based targets. Various handheld lasers are being studied for crowd-control purposes. And, of course, the “Star Wars” strategic missile defense program under President Reagan would have used space-based lasers and avoided blooming altogether. But none of these weapons is even ready for combat, let alone full-scale war against a technological equal (or superior) society.

Thus, for now, the laser seems destined to remain a tremendous economic and technological boon to the world while resisting its use as a tool of offensive warfare. But military science has proven itself highly adept at weaponizing technology, and coherent-light weapon research is a high priority due to its potential to deliver highly destructive energy at the speed of light. So it may be inevitable that we’ll see ray-gun-toting soldiers and laser gunships well before we get our flying cars.

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