-
Asked by geantlebu on 30 Dec 2014.
-
Tim Stephens answered on 30 Dec 2014:
The harmfulness of a laser is not based on how many lenses it is shone through. When you’re calculating how to classify a laser hazard, there’s only one lens that matters, and that is the one in your eye. You use information about the laser to work out the maximum amount of energy that can reach the retina at the back of the eye and then check to see whether that amount of light will cause harm.
Laser pointers that you can buy legally in the UK should all be completely safe, and there’s nothing that can be done to make them more dangerous.
-
-
Paul Murcutt answered on 30 Dec 2014:
The trick here is that the light in a laser is all travelling in the exact same direction already.
With lenses you usually focus light that is travelling in different directions onto one point. With a laser that is fairly pointless.
-
Fiona Dickinson answered on 5 Jan 2015:
Laser light is what is called collimated (all going in a straight line), which means if you point it at a wall from up close or far away the dot should be the same size. Due to imperfections this isn’t always perfectly the case but the idea stands. Lenses focus light, and will take a laser beam and focus it onto a point (this is important for my research), but after the focal point it becomes more diffuse.
To me, shining a laser pointer through lenses does make it more dangerous, but not for the reason I think you will be expecting. When light hits an object some of that light is reflected, this reflected light is now my concern, it is still largely collimated, but is now going in another direction. You have to take care not to look directly at this reflected or scattered beam just the same as the original beam.
This scattering of laser light is why I never wear and rings or a watch when I am using the lasers in the lab.
One thing I will say is all lasers are dangerous, never look directly at laser light, always check your laser pointer is Class 2 (especially if using it with pets) and never shine it at people.
Comments
Tim commented on :
The use of a lens doesn’t normally affect a laser’s classification, and the classification is what defines how ‘safe’ it is.
When you’re calculating the classification of a laser (whether it’s class 1 or class 2 or whatever), you work out how much energy can make it to the back of your eye for the way that it could be used and then check to see what that means on the laser classification standard.
I suppose that if you have a very large diameter laser beam, you could make it more dangerous by using a lens to enable more light to get into the eye but this does not apply to laser pointers because they are already smaller than the diameter of the pupil in your eye, so making the spot smaller won’t get more light onto the retina.
(Source: am laser safety officer at work).