Built on Facts

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.

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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:

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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.

Comments

  1. #1 Hank Roberts
    June 30, 2010

    Thank you.

    What a stupid, crappy, dangerous toy that is.

    How long til some idiot who can’t define “spectral” takes one to a ‘rave’ and waves it around in a dark smoky room packed full of reflective surfaces and people with dilated eyes?

    Retinal damage isn’t _perceived_ as painful:
    “the retina lacks pain sensory nerves.”
    http://www.dermweb.com/laser/eyesafety.html

    By the time the blind spots and streaks are detected, the person who does the damage will be long gone.

  2. #2 Eric Lund
    June 30, 2010

    Plenty of people online have suggested tighter regulation of these things.

    Some have even acted. Several years ago the Town of Hampton, NH, adopted an ordinance restricting the use of laser pointers because there had been problems with teenage kids shining them in the eyes of police officers on the beach (which is the most popular beach in the state). A Class 2 laser may not cause permanent damage, but it can temporarily blind somebody, and there is always the danger that the officer will mistake it for the laser sight on a rifle and open fire.

    Which is why I never transport laser pointers in carry-on baggage, and why I was slightly annoyed that the conference I went to last week passed them out as freebies (I had carried everything aboard for the trip out). Having something like this on the loose makes it all the more likely that TSA will crack down on lasers.

  3. #3 Nemo
    June 30, 2010

    If you think that’s bad, check out this insanity.

    Had I seen that video as a teenager… I would probably have permanent eye damage today.

  4. #4 Comrade PhysioProf
    June 30, 2010

    Safe laboratory practice when infrared lasers are used in an open-path rig requires that the laser never be turned on unless all room occupants are wearing infrared filter eyewear. Infrared lasers are *much* more dangerous than visible light, because you can’t see the beam and by the time you notice something is wrong, you have damaged your retina.

  5. #5 Anonymous
    July 1, 2010

    This is just out of control. The 500 mW is like $3,000 but the 1W is only $200?! How does that work? I just looked around online and had trouble finding any that were stronger than like 150 mW or so, except for at the linked site. People even warn about the dangers of a 55 mW laser!!! These types of lasers are good for astronomy I hear but from what I’m reading with this one I’d be worried about getting blinded from light reflecting back off moisture in the atmosphere lol

  6. #6 CCPhysicist
    July 3, 2010

    I’m surprised that a physicist would include any class 3 laser in a category described as “safe”. The modifier “reasonably” is irrelevant, particularly if it is being used casually as a pointer in a lecture hall.

    Safety is mostly a matter of behavior. Sure, lots of people manage to avoid killing anyone while handling guns in an unsafe manner, but “no one has been injured so far” is the sort of logic that led to Three Mile Island and the Deep Horizon blowout. If you treat a 1 mW laser with care during lectures and lab, you will be less likely to ‘cheat’ a safety when adjusting that class 4 laser in some future laboratory environment.

  7. #7 CommonSense
    May 25, 2011

    If you do not like lasers, do not buy one. Banning them will only increase the interest. You can not make everything illegal just because someone might get hurt. People have always done stupid things and gotten hurt. Let those of us that want to buy lasers, have them.

  8. #8 supratall
    May 26, 2011

    OK, I’ll come clean: this reminds me of an embarrassingly recent conversation with my materials science-trained boyfriend.

  9. #9 BuyLaser
    April 20, 2012

    I totally agree with CommonSense !

    People will be more interested in something banned.

    Anyway if we cannont count on people’s common sense, idk where the world is going…

  10. #10 PeteR
    May 7, 2012

    Of course you should be careful with laser ! Thank you Captain Obvious !

  11. #11 formula 21 formen
    May 15, 2012

    If you do not like lasers, do not buy one. Banning them will only increase the interest. You can not make everything illegal just because someone might get hurt. People have always done stupid things and gotten hurt. Let those of us that want to buy lasers, have them.