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How are lasers subject to inverse square law? > Laser light travels as a parallel beam spreading very little, so the inverse square law does not apply. https:
by chime 8y ago
How are lasers subject to inverse square law?
> Laser light travels as a parallel beam spreading very little, so the inverse square law does not apply.
https://www.reed.edu/ehs/laser-safety/1laser_basics.html https://www.reed.edu/ehs/laser-safety/1laser_basics.html
Is the above wrong?
- foldr 8y agoIt seems to be a perennial point of confusion, but as far as I can make out from googling, it's not strictly true that lasers follow the inverse square law. Why is the parent being downvoted? https://groups.google.com/forum/#!topic/sci.optics/P-8VmDlY45g https://groups.google.com/forum/#!topic/sci.optics/P-8VmDlY4...
- chime 8y agoThank you. Not sure why I was downvoted above. I was asking a genuine question politely.
- deepnotderp 8y agoThe point being made there is also incorrect. This is only true for divergence = 0 which doesn't exist. Also, the point made that "if I go 10x further away then my received power won't be 100x less" is misleading since inverse square law is talking about intensity.
- deleted 8y ago[deleted]
- deepnotderp 8y agoIt's an oversimplification. The idea is that laser beams are extremely collimated, with divergences well under 1 degree in many cases, so over 200 meters the beam might only expand a tiny amount. But not to worry, the beam still spreads. Calculate the beam spot size of a laser, where the area increases as the square of the distance. Meanwhile, intensity is the inverse of the area. At sufficiently long distances, this will become apparent.
- foldr 8y agoIsn't that only true of the far field?