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Effective Distance Question 175-200 mw

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metaman

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Hello, I am a laser newb. I would like to know what the approximate effective distance will be on a 175-200 mw blu ray if pointed into space on a clear night. How far into space will it reach? I do not mean that we can see with human sight, I mean if you had an ultraviolet camera, how far would the effective range be.

IgorT is building me one right now. He is looking for a high wavelength freak diode to use for me. The laser will be used for CSETI work.
 





Hemlock_Mike

Hemlock_Mike

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Uh -- I believe the light goes on until it is absorbed or scattertd into oblivion. A beam of light in a perfect vacuum goes a LLllOoooong ways.

Mike
 
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metaman

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I don't know about that. Scientists have been bouncing lasers off of the moon and back for a few decades now.
 
Glutton

Glutton

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metaman said:
I don't know about that. Scientists have been bouncing lasers off of the moon and back for a few decades now.
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IIRC the beams they use to reflect off the moon are a few meters in diameter and diverge to a few km by the time they get back.

Probably just depends on how good of a UV camera you are using and the divergence of your laser.

You could always use a beam expander to get a better distance. But the atmosphere is probably going to be your biggest enemy.
 
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ElektroFreak

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Once light passes out of the atmosphere, what hasn't been blocked by the impurities in the atmosphere goes on indefinitely until blocked or absorbed by something. To help your perspective, if a laser beam is 3mmx4mm at the aperture and is about 150-200mW, it is several times more intense (it is emitting several times more photons) than the light emitted by a 3mmx4mm section of the sun's surface (editors note: this is taking into account visible light photons only, the sun emits across the entire EM spectrum). There are enough photons present with enough energy to go on a long, long way. As the light beam spreads gradually, the number of photons in a given area of the beam gets smaller and smaller until eventually there are only a few photons in a space the size of the planet earth, so the odds of you sending a message to the other side of the universe with your blu-ray are pretty slim.
 
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Glutton

Glutton

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Also you might have had better luck with a different color if possible.

UV light has a hard time getting through the atmosphere.
 
matrixcs

matrixcs

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well measuring the distance of that kind of blue ray is definitely hard to do.. for that kind of power 170mw hmmm we have to consider a lot of things though...

i guess we better leave this to the experts here...
 
Flaminpyro

Flaminpyro

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I can tell you how far it will reach but first you must tell me how many particles of dust and other matter it will strike in the preposed path :crackup:

Peace All...
 
millirad

millirad

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While that is a nice and powerful B-ray coming from Igor, I have to say sorry but that is miniscule in power in relationship to the effects of particles and ionizing radiation in the upper atmosphere. Remember radiation in space will deflect photons from your beam from the original path(scatter). Probably not a single photon would reach the moon. It is an awesome laser pointer though. After all it is an IGOR build.
 
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ElektroFreak

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millirad said:
While that is a nice and powerful B-ray coming from Igor, I have to say sorry but that is miniscule in power in relationship to the effects of particles and ionizing radiation in the upper atmosphere. Remember radiation in space will deflect photons from your beam from the original path(scatter). Probably not a single photon would reach the moon. It is an awesome laser pointer though. After all it is an IGOR build.
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Photons really don't have all that hard of a time getting out of the atmosphere.. UV might be blocked a little, but 405nm isn't really UV. It's visible spectrum light. I'm not sure how much the upper atmosphere will attenuate the light, but I doubt it would be total. Experiments have been done in the past which involved spacecraft successfully detecting photons from a low-powered HeNe, so generally speaking light doesn't get attenuated by the atmosphere to the point that none gets out.
 
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digital_blue

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Metaman - Lasers that are used to "shoot at the moon" are on the order of several kilowatts(pulsed). Even then, only a few photons make it that far...
 
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ElektroFreak

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^That's correct, but it's not the just power output that determines how many photons make it to the moon and back. Divergence plays a huge role. The photons themselves will continue on infinitely unless they are acted upon by some outside influence.
 
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metaman

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mfo said:
How did you upload a video on youtube that is over an hour long?
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I didn't. That is not my video. I am not officially part of CSETI. However, I just went through the training program and saw first hand that it works. It is not smoke and mirrors or some weird cult. It is instructions for how to vector in UFO's. The laser is for signaling them once they show up and also to show them where on Earth you are. I know, I know I am a crazy nutbag. Its all good I pride myself in being a crazy nutbag. If you watch the video you will find out that this stuff is not very crazy at all. I saw 2 full on UFO's in a one night outing.

I think that you have to have a special account with Youtube, then they will allow large vids like that. Directors account or something like that.
 
mfo

mfo

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metaman said:
I didn't. That is not my video. I am not officially part of CSETI. However, I just went through the training program and saw first hand that it works. It is not smoke and mirrors or some weird cult. It is instructions for how to vector in UFO's. The laser is for signaling them once they show up and also to show them where on Earth you are. I know, I know I am a crazy nutbag. Its all good I pride myself in being a crazy nutbag. If you watch the video you will find out that this stuff is not very crazy at all. I saw 2 full on UFO's in a one night outing.

I think that you have to have a special account with Youtube, then they will allow large vids like that. Directors account or something like that.
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Interesting. Just out of curiosity, how old are you? Also, you do know that you've got to be extremely careful when pointing your laser into the sky, right? Because shining it into the sky is technically breaking the law, due to the fact that you're violating airspace. Also the supposed UFO's that your seeing....well shining your laser at them isn't the best of ideas. What if it turns out to actually be a plane, helicopter or military experiment or something like that?
 
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