Lasers! Everybody loves them, everybody wants them. But outside a few niche applications they have failed to live up to the destructive potential that Saturday morning cartoons taught us all to expect. In defiance of this failure, a company in China claims to have produced a “laser AK-47” that can burn targets in a fraction of a second from half a mile away. But skepticism is still warranted.
The weapon, dubbed the ZKZM-500, is described by the South China Morning Post as being about the size and weight of an ordinary assault rifle, but capable of firing hundreds of shots, each of which can cause “instant carbonization” of human skin.
“The pain will be beyond endurance,” added one of the researchers.
Now, there are a few red flags here. First is the simple fact that the weapon is only described and not demonstrated. Second is that what is described sounds incompatible with physics.
Laser weaponry capable of real harm has eluded the eager boffins of the world’s militaries for several reasons, none of which sound like they’ve been addressed in this research, which is long on bombast but short, at least in the SCMP article, on substance.
First there is the problem of power. Lasers of relatively low power can damage eyes easily because our eyes are among the most sensitive optical instruments ever developed on Earth. But such a laser may prove incapable of even popping a balloon. That’s because the destruction in the eye is due to an overload of light on a light-sensitive medium, while destruction of a physical body (be it a human body or, say, a missile) is due to heat.
Existing large-scale laser weapons systems powered by parallel arrays of batteries struggle to create meaningful heat damage unless trained on targets for a matter of seconds. And the power required to set a person aflame instantly from half a mile away is truly huge. Let’s just do a little napkin math here.
The article says that the gun is powered by rechargeable lithium-ion batteries, the same in principle as those in your phone (though no doubt bigger). And it is said to be capable of a thousand two-second shots, amounting to two thousand seconds, or about half an hour total. A single laser “shot” of the magnitude tested by airborne and vehicle systems is on the order of tens of kilowatts, and those have trouble causing serious damage, which is why they’ve been all but abandoned by those developing them.
Let’s just pretend they work for a second, at those power levels — they use chemical batteries to power them, since they need to be emptied far faster than lithium ion batteries will safely discharge. But let’s say even then that we could use lithium ion batteries. The Tesla Powerwall is a useful comparator: it provides a few kilowatts of power and stores a few kilowatt-hours. And… it weighs more than 200 pounds.
There’s just no way that a laser powered by a lithium-ion battery that a person could carry would be capable of producing the kind of heat described at point blank range, let alone at 800 meters.
That’s because of attenuation. Lasers, unlike bullets, scatter as they progress, making them weaker and weaker. Attenuation is non-trivial at anything beyond, say, a few dozen meters. By the time you get out to 800, the air and water the beam has traveled through enough to reduce it a fraction of its original power.
Of course there are lasers that can fire from Earth to space and vice versa — but they’re not trying to fry protestors; all that matters is that a few photons arrive at the destination and are intelligible as a signal.
I’m not saying there will never be laser weapons. But I do feel confident in saying that this prototype, ostensibly ready for mass production and deployment among China’s anti-terrorist forces, is bunk. As much as I enjoy the idea of laser rifles, the idea of one that weighs a handful of pounds and fires hundreds of instantly skin-searing shots is just plain infeasible today.
The laser project is supposedly taking place at the Xian Institute of Optics and Precision Mechanics, at the Chinese Academy of Sciences. Hopefully they give a real-world demonstration of the device soon and put me to shame.
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