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Beam of 1W blue and 400mW green?

WhyHaveALife

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Hey, trying not to be a noob here :eek: (I've read a lot of stickies), but I have a question.

So I have the Spartan 1W 447nm laser from Dragonlasers and the ZSK 532nm 400mW green laser from Lazerer :D... when I point these into the sky I see the beam "end" at some point.

Can anyone give some insight on like how far up that is where I see the beam end? It's really hard to judge the distance and every night when I use my lasers I dieeeeee to know the answer. All my friends which I show the laser to beg to know too and it's just about the only question I can't answer :p I am a very curious person and posting here just might solve my curiosity :)

So if anyone could reply and give any semi-related info or answers at all that would just make my day, no joke. :thanks:
 

weeba2kv

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The beam stops at exactly 4000 meters cause its 0.4 watt...
 

RA_pierce

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The beam, when viewing from the source, appears to abruptly disappear.
What really happens is that the beam gradually fades away. This is because (1) the beam diverges and less power density makes the beam harder to see, (2) the light is partially absorbed and scattered by the air and the stuff floating around in it and (3) there is less junk in the air at higher altitude so there is less light reflected back to your eye. And I suppose you can also factor in the fact that the brightness of a point of light decreases with distance according to the inverse square law.

*This is based on intuition.

If you shine your lasers straight up into the sky, walk a few meters away and look up at the beam, you will see it get dimmer and fade away as it gets higher.
 
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GeorgeHelio

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The beam appears to fade more abruptly than one might expect because as the illuminated particles are ones further and further away the light intensity you see diminishes much faster than you will expect.

The inverse square law is valid not only for the diverging laser beam outbound but for the light inbound. This now becomes an inverse 4th power law. Double the distance seen for the beam, and the brightness observed by the laser shooter will be seen as 1/16th the brightness level.

Move Jupiter to just within the Oort cloud, say 10,000 AU, and not even the Hubble Space Telescope can't see it, though it has imaged a few exoplanets that are light years away.
 
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