Green Laser Magic–Of course science is fun and cool
Besides using your laser pointer to entertain your pets (and yourself) or presentations. did you know you could do magic with a laser? Me neither. If you have any doubt about this watch this video:
Was that coolio amazing or what? OMG! Of course you do have to be careful when using lasers.
Little safety lesson here folks, don’t ever, EVER, point a laser at someone’s face (let’s include animals in this okay?). Even the cheapo laser pointers you can get just about anywhere can seriously damage someone’s eyes. Yeah, yeah it’s fun playing laser gun sight with people. Uh huh. Well don’t. ‘Nuff said.
July 2nd, 2007 at 10:19 am
One reason that lasers carry ratings is so you know what safety precautions are needed when using them. Class I lasers are mostly totally enclosed so that the user is not exposed to laser radiation (e.g., CD-ROM reader) (unless the device has been modified, which changes the classification!). Class II lasers my expose the user to weak laser radiation, but the beam is spread enough so that there’s no danger to a user looking at it (e.g., barcode scanner, with an interlock to shut off the beam if the scanning portion fails). A class IIIa laser is what most laser pointers are. These may be dangerous to the eyes, but usually only if the user does something Real Dumb, like intentionally staring into the beam for an extended period of time [1] [2]. Normally, the instability of the person holding the pointer, the small acceptable area of the eye, and the rapid blink response when seeing an intensely bright light will prevent permanent damage (but, may still result in flash blindness, causing a secondary accident). A class IIIb or class IV laser can cause permanent eye damage from even a momentary exposure, so short as to be smaller than the blink response.
[1] Which explains the reason that many laser labs contain the sign “Do not look into the laser with the remaining, good eye!”.[/1]
[2] It’s occasionally easy to do something Real Dumb without meaning to. For example, once, while working with a laser, I wasn’t getting any beam output. I wondered whether there may have been dust or debris blocking the output port. I momentarily considered looking into the output port before realizing that would be a Real Dumb thing to do.[/2]
So, the net result is that you shouldn’t shine any kind of laser, even a laser pointer, into anyone’s (human or animal) eyes. At best, you’ll make them quite angry, and at worst, you may flash blind them, causing them to trip and injure themselves or someone else (etc.), or cause permanent eye damage.
http://www.fda.gov/cdrh/radhealth/products/lpm.html
Part of the reason for concern with laser radiation is that, since it’s monochromatic, and since the beam is mostly parallel, the eye can focus the radiation to a perfect point on the retina of the eye. When you calculate the power density, the result is rather staggering, even for a tiny amount of emitted power.
As an educational exercise, try computing the energy density of a 5 mW laser beam that occupies an area with a diameter of 1/10 inch [3]. For comparison purposes, calculate the energy density of viewing a 60 Watt light bulb from 3 feet. Now calculate the energy density of the sun on a sunny day. Rather surprising isn’t it, that that little thing you can carry around in your pocket can produce light with an energy density comparable to the sun.
[3] Yes, yes, I know English units aren’t favoured for scientific work, but: 1) I’m in the US, and we still use them, and 2) it’s a good exercise for students to become proficient in translating between units.[/3]
Now realize that, when staring at the sun, the light isn’t perfectly focused, due to chromatic abberations in the lens of the eye and the fact that sunlight is composed of the whole spectrum of light. Next, consider that the laser light is monochromatic, and is focused almost perfectly. Finally, compute the energy density when that 5 mW of laser light is focused to a spot with a diameter of about 6600 Angstroms.
Dave