Why can’t we use lasers as ray guns?

January 6, 2012

Dear Cecil:

Now more than ever, the world seems to be in need of ray guns. I’m curious why lasers aren’t used for more of this type of work. Surely the success of such weapons in Flash Gordon, Star Wars, and Star Trek is more than enough justification for their use instead of pesky gunpowder or nuclear weapons. What’s the holdup? Can the problems be solved? Should I be scared of laser pointers?

Cecil replies:

No question, lasers have been one of the great disappointments of our time.

Sure, lasers have had their uses in communication, entertainment, medicine, precision fabrication, scientific measurement, and feline recreation. But what we were really hoping for was ray guns. So much else from science fiction has become reality — pocket communicators, handheld computers. Ray guns, no.

OK, we’re still waiting on transporter beams too. But lasers seemed so close. The requisite technology is there. We know from projects like the Reagan-era Star Wars program, with its proposed laser-based ballistic-missile killers, that the Pentagon has been trying. But the best we’ve been able to come up with is Blu-ray players. It’s as if all we’d done once we invented the wheel was make toys.

At the Straight Dope we knew what we had to do. First, assess the current status of laser technology. Second, see if Straight Dope Labs could, in its humble way, use a homebrew laser ray gun to advance the state of the art.

We note the following facts:

In a 2010 Pentagon test, an aircraft-mounted laser successfully destroyed a just-launched ballistic missile. An impressive feat, but also illustrative of the practical problem with lasers: getting the weapon aloft took a 747. In a test last year, the Navy managed to set fire to a small motorboat with a laser, this one mounted on an 8,000-ton destroyer.

Even small laser weapons aren’t that small. The Defense Department is testing a rifle-sized device it calls a “Personnel Halting and Stimulation Response” (abbreviated PHaSR — get it?) that uses a laser to temporarily blind bad guys. (Permanent blinding is prohibited by the Geneva Convention.) A photo of the prototype shows a guy hoisting what looks like a bison-scale Super Soaker. Is it portable? Yeah, it’s portable. So is a bag of cement.

The issue, as you might surmise, is power. Lasers have great range and accuracy, but doing appreciable damage demands serious juice and bulk. The military’s portable laser research accordingly focuses on nonlethal weapons that briefly blind or sting. How likely are such devices to persuade the recalcitrant? We decided to get a laser and find out.

Most laser pointers are Class IIIA, meaning they put out just 1 to 5 milliwatts and are a hazard only if you stare directly at the beam. Class IIIB lasers, often used by astronomers, can be up to 100 times as powerful and are potentially a serious danger to vision, particularly as sometimes used by jerks who shine them at aircraft. The next step up is a Class IV laser, at least 200 times as powerful as a laser pointer. That’s what my assistants Una and Fierra got, specifically a battery-powered one-watt blue laser bearing a strong resemblance to a light saber. Preliminary conclusion: as a method of crowd control, lasers won’t replace water cannons and tear gas any time soon.

The researchers first set up targets intended to simulate human flesh, namely a pork chop and some strips of bacon, all warmed to room temperature. Then, donning laserproof goggles, they commenced blasting away from various distances. Monitoring the affected areas with an infrared thermometer proved problematic, so instead they timed how long it took the meat to cook, rigging up a second, red laser beam to scintillate off telltale particles of smoke.

Heating the bacon took a lot longer than heating the pork, and the pork took a while — eliciting smoke required 27 seconds of continuous exposure at a range of one foot, 35 seconds at 32 feet. Hoping for more dramatic results, the investigators then substituted matches for the meat. Igniting them with the laser took 11 seconds at one foot, 15 seconds at 32 feet.

Admittedly the coolness factor here was high — nothing like having your own personal laser light show. (Check out the photos on the Straight Dope website.) On the other hand, the likelihood that this laser would actually change somebody’s mind (other than via intimidation alone) is virtually nil. Cooking temperature no doubt is higher than the threshold of pain; the fact remains that no bad guy is going to sit still while you try to fry him. We're guessing you’d need at least a 100-watt laser to get results quick enough to be effective, and good luck dragging around the battery pack for that.

In sum, the near-term prospects for handheld laser ray guns are dim. Despite decades of death-ray hype, the proven uses for this once-promising technology remain depressingly benign.

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References

Austen, Ian. “Laser Pointers Draw Attention (To Themselves)” New York Times 20 January, 2005: G6.

Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May Be Deemed to Be Excessively Injurious or to Have Indiscriminate Effects (with Protocols I, II and III) Geneva, 10 October 1980. Protocol IV, Vienna, 13 October 1995 Protocol II, as amended, Geneva, 3 May 1996.

Gettleman, Jeffrey “F.B.I. to Investigate Reports of Lasers Beamed at Planes” New York Times 31 December, 2004: B6.

Reuters. “Russia: Vision Lost After Laser Show” New York Times 15 July, 2008.

Smothers, Ronald. “New Jersey Man Pleads Guilty in Shining of Laser at Small Jet” New York Times 10 November, 2005: B2.

United States Department of Labor: Weekly Fatality/Catastrophe Report (week ending June 12, 2010): http://www.osha.gov/dep/fatcat/fatca..._06122010.html  

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