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http://www.lasereshop.com/green-laserpointer/p-3.html
If the question is meant to be how far the light of a 500mw green laser can propagate, the correct answer is that there is no limit, provided that the light is not absorbed or scattered away in the atmosphere. However, the beam area will eventually become larger due to the beam divergence, so that the intensity e.g. on a screen will be reduced even if the overall power remains constant. Accordingly, an airplane pilot looking down into such a beam from an altitude of 10 km will not be disturbed by the remaining small intensity.
http://www.lasereshop.com/green-laserpointer/p-25.html
20 years, Ultra Powerful Laser Pointer have shrunk from table-size lab equipment to pocket-portable presentation tools (not to mention cat toys). But making laser pointers a household item may have come at a cost. A new study from the National Institute of Standards and Technology reports that some cheap Laser Pointer can emit more than 10 times as much
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