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Blue vs. green, how far goes the beam?






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CheeseHasLeafs

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Not just that the beam is worse, but also that blue will be less visible than green.
I would say that even a two or three watt blue will not be as visible at the same distance.
 
C

CheeseHasLeafs

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No idea, tho there was something about a blue laser being seen from the ISS.
Not sure if that's quite the same as 135km through Earth atmosphere though.
 
djQUAN

djQUAN

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Since the high power blues are multimode, poor divergence along with blue easily scattered (Rayleigh scattering?) then I guess it won't go too far.
 
AnselmoFanZero

AnselmoFanZero

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No offense, but GUESSING is what I also do. I am requesting NUMBERS.
Meters or even yards will do. I am more the burning-guy, so I never cared much
about distance/range to be honest.
 
Shakenawake

Shakenawake

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photons travel forever until they strike something. if you mean how far does it still look like a beam, it depends on factors, divergence namely, but also rayleigh scattering. a green and blue laser with identical divergence I believe would perfom very comparably when it comes to distance, though Blue lasers tend to be multi-mode, so in general, green laser beams stay tighter, longer. green lasers can have divergence as good as .5mrad (or better even for a really really nice laser) and worse than 2mrad, so it really all depends. A powerful green laser with good divergence to begin with and equipped with a beam expander will have the farthest reaching beam if I am not incorrect

the light from a 1W 445nm laser was confirmed visible from I.S.S., but they only saw a blue dot on the surface, no beam. I think I remember reading that at that distance the dot of the laser would have been like a kilometer wide or something crazy like that

If you have a specific application in mind, we can better recommend a laser
 
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ZRaffleticket

ZRaffleticket

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Not many of us here have access to a clear stretch of land >100km yet alone >2km. It's not necessarily something many hobbyist people here can test.
 
Shakenawake

Shakenawake

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I'm also willing to bet the distance wicked lasers is talking about for their green is distance the light is visible, not the beam
 
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AnselmoFanZero

AnselmoFanZero

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I live in the city...might be a problem here. Out in the fields, much easier.

Its nothing new you are telling me. No particles in space, so no visible beams.
And I never said I have a use. I just wanna know. Because blue is still more powerful (in mW) then green, beam is much worse. Would just be interesting to know...

Good point shake! Visible beam is indeed what I meant....well dot also...
 
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Shakenawake

Shakenawake

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there are green lasers >1W. the power is not the reason for the bad beam, it's the traverse mode of the diode, though it's true that multi mode diodes are more powerful than single mode diodes. I have also noticed more powerful green lasers tend to have worse divergence than less powerful greens, though there will be exceptions
 
AnselmoFanZero

AnselmoFanZero

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I have seen 50mW green lasers hitting the clowds...so I guess green is the best choice in general.
But a Krypton has 750mW. Found CNI 800mW DPSS for example. They should be visible over miles and miles.
Blue 3W, more power, less visibilty overall...even with beam-shaping.

Wondering that nobody ever tried that. I have seem pics here and on the net:
Green beams over miles. But no numbers :/
 
DJNY

DJNY

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Even if you wish to, there is no definite answer as it depends on too many varying parameters.

Getting us the beam parameters and exact values for your atmospheric conditions, dust, pollen amount, moisture in the air, albedo... we can for sure give you more info.

Of course it also depends one power and the angle you look at the beam / dot.

Even more, with 1 mRad divergence at 2 kilometers you have a dot 2 meters in size. How do you determine how visible the beam would be?

The maximum laser range values all around in the internet are nothing more than jokes trying to impress the casual laser-interested people.
 
Tmack

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You mean my 5mw military 5 miles, laser won't just stop at 5 miles! ! Next thing you'll say is its not military either ;)
 
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