Can We Make a Laser Blaster?

Can We Make a Laser Blaster?
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Like every American kid who grew up with Star Wars, my ears pricked up at recent stories about Chinese laser rifles. Are we going to see wars fought with laser blasters in the near future?

The answer is simple but the explanation and details are not.

There are already plenty of weapons based on lasers as well as laser-like directed energy weapons that focus electromagnetic waves upon a target. The U.S. Military has spent quite a lot of money to design a number of these devices.

All of these are enormous, complex machines that require a ship, airplane or large truck. They are not portable. They are generally focused on either shooting down missiles, melting UAVs or causing skin irritation to disperse crowds.

So, how about the personal arms? To get some idea of their practicality we need to think about what is required of such a weapon.

A true blaster has to be able to hit a person anywhere and hurt them. It must be small enough and light enough for a single soldier to carry it. It can't be a specialized gun that can only target the eyes or a specific weak area like the genitals. That would be impractical in close quarter combat and could be easily blocked by small pieces of shielding or even simple goggles.

A general use sidearm must then knock a target down by heating up and destroying a big chunk of any skin and underlying tissue it hits. NIST research on firefighting says that tissue is completely destroyed when it hits about 75o C (167o F). We'll model tissue as what is basically is: water. A more complex model would look at specific heat transfer and damage properties of skin, but even medical and scientific research in this area is not complete.

Let's guess that we need to heat up 25 cm3 of tissue (about a large finger's worth) to cause massive damage. That's roughly a hole the diameter of a .38 caliber bullet that goes three inches into the body. Heating one cubic centimeter of water by one degree C requires 4.2 Joules of energy. Hence we need to deposit about 105 J on the target. A Joule is a total amount of energy. Lasers are most generally rated in watts: the number of Joules that they can deliver in one second.

Unlike a bullet that delivers all of its impact in a millisecond or two, a laser can deliver more and more damage as it stays on a target. Now we need to guess how long we have to train the laser pistol on the body to dump 105 J into the target. Of course the shorter the time period we can hold the spot on the target, the more watts of power the laser will need to sustain.

In a chaotic combat environment being able to hold the laser trained on a single spot for even one second seems nearly impossible. If we make a very broad estimate that perhaps one tenth of one second might be a reasonable time on target, we can start to estimate the laser power needed. 105 J/.1 s = 1050 W of power.

A 1000 W laser is roughly one million times more powerful than a typical small laser pointer. A laser metal cutter often uses a laser of roughly this strength; more powerful versions pack up to 10000 W. An industrial laser demolition gun (yes, this is extremely cool-here's a video) brings roughly 5000W of power. These devices sure look tough enough to put some damage on some skin.

Considering all of the above, it seems that we need no less than 1000 W and ideally more like 10000 W of power for our blaster.

Current cutting edge handheld laser weapons are puny by comparison with those numbers. A 1990's model had about .015 W. That's not even enough to cause a skin burn. The power of the laser in these new Chinese weapons is unclear, but it's likely no more than 10 W: Short on power by a factor of 100 to 1000. A laser of this strength can light a match or burn a small hole in a sheet of paper, but no way they can blast a hole in a person. Working in laser labs I can say that while a brief exposure to a laser of this power will leave you with a small burn, it's nothing medically serious.

All of the above ideas consider that the laser hits someone directly on bare skin. Of course that's not too realistic.

Bullets are hard to stop because of their incredible kinetic energy transfer, but even they can be blunted by proper body armor. Thermal energy transfer can be stopped as well. Think of a bulletproof vest, but made of asbestos instead of Kevlar. A firefighter's vest might provide some protection.

A quick calculation shows that surrounding the body with a one-inch thick layer of water could absorb enough of a very brief laser blast to reduce the damage to the body to only the level of moderate burns. What's more, a vest that circulates water throughout could easily transfer the heat away so quickly as to possibly prevent all damage. A thick slab of metal could also absorb much of the thermal energy, though it would likely still allow some damage to tissue beneath.

All of these musings lead us to a conclusion that will likely disappoint fans looking to wield Han Solo's blaster pistol: Until the technology of compact laser mechanisms improve by leaps and bounds, we won't have a laser-powered blaster sidearm.

(Image: AP)

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