You Probably Shouldn't Buy This Laser

The laser pointer, much beloved of PowerPoint lecturers, cat owners, amateur scientists, and middle school boys at movie theaters, is actually a pretty amazing device. There's quite a bit you can do with a relatively cheap laser, and they're just plain fun. They're also relatively safe. The red pointers are usually Class 2 and the green ones are usualy class 3R. Class 2 lasers are very difficult to hurt yourself with, and while Class 3R lasers can cause eye injury, in general brief exposures are unlikely to cause permanant damage.

There's two higher classifications for lasers: 3B and 4. Class 3B lasers are officially in the "not a toy" category, with even very brief direct eye exposure having the potential to do serious and permanant eye damage. For the higher-power end of that class, it's not merely potential but essentially certain. Class 4 lasers cause permanant eye damage on direct exposure, and have the potential to cause burn injuries especially when focused. Because Class 4 is the highest class, there's no labling difference between relatively low-power Class 4 lasers that you barely feel as a tingle even if you stick your hand in them and huge CO2 lasers that can slice through steel.

As an example of the former type of Class 4 laser, one of the lasers in my lab emits a stream of roughly 35 femtosecond long pulses of near-infrared 800nm light. The pulses have an energy of about 1mJ and are emitted at a rate of 1 kHz. As a result, the average power of the laser is 1 watt, which puts it solidly in Class 4 territory. The infrared beam in invisible, so while a green 1 watt laser would be so blazingly bright as to leave no doubt as to its hazard the IR beam doesn't give such an obvious warning. At 1 watt it's just barely intense enough to singe something that's black and flammable, but if it's focused it's considerably nastier. Focused or unfocused, it's instant eye damage and we have to take serious precautions - among many other things, the laser and all the optical components the beam interacts with are bolted to a 1-ton optical table. A permanent blind spot would a rather steep price to pay for shoddy safety, so we practice good laboratory safety standards.

So I'm not so sure I like this: a 1 watt violet diode laser being marketed as a lightsaber.

Now in fairness the actual company selling these isn't marketing along these lines, and they do spend a pretty decent amount of time spelling out the danger of these things. But be assured, this is serious business.

It's not as dramatic as the message board hype; this isn't the Arson-O-Matic and you couldn't blind stadiums of people by waving it around. The beam divergence is listed on their chart:

Extrapolating, the beam is reduced to the same intensity as a 5mW laser at the aperture at a distance of about 22 meters. Outside this range the laser is not exactly safe but it's unlikely to cause instant damage.

But this is sort of faint praise - a 20+ meter danger radius is Bad News for people who're buying this without the intention of being adequately safe. Which I suspect is lots of 'em.

Plenty of people online have suggested tighter regulation of these things. I'm not exactly the government's biggest fan, but I'm not sure this is the sort of thing that ought to be available by mail order on the internet. On the other hand these lasers are integral components of an increasing number of perfectly innocuous devices like Blu-Ray players and projectors. This laser is itself scavenged from a projector, so any person with a screwdriver could get one of these even if they weren't being marketed as lasers.

So I'm not taking sides. I'd just like to advise that if you're interested in one of these, be aware that it's very, very dangerous and if you're a laser hobbyist you ought to treat this in the same way a skydiving hobbyist treats a parachute. I'd really prefer you not touch Class 4 lasers unless you have dedicated safety equipment and training as well as plenty of experience on Class 3R and 3B lasers.