If you had a 0mrad laser (yes - i know that doesnt exist), at exactly 100mW.. Could i point it at a laser power checker standing at the moon, and still measure exactly 100mW? Would a laser with 0mrad ever get dimmer/weaker, no matter how long the beam goes?
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Theoretical 0mrad laser questions
- Thread starter kake
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kake said:
you'd still have scattering caused by dust/air/ the atmosphere, but if a 100mw beam was to leave earth's atmosphere then yes you could register 100mw on the moon
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You wouldn't be able to hold it still enough anyway 
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mRad isn't really important. A 100mW laser with 100 mRad divergence would still be 100mW thousands of miles away just so long as nothing got in its way. As said above though, things like atmosphere and all tend to reflect/refract/absorb power little by little.
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pseudonomen137 said:
But you would need a bigass meter to measure that beam ;D
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You would.
Some info on why 0mrad is not possible, and theoretically cannot exist. (Because I like this sort of theoretical physics stuff.)
Chaos theory comes into this too, essentially that if something is perfect, something will interfere with it and destroy the perfection. Something like that, I'm sure someone will correct me.
It is possible, theoretically, with very good optics to achieve very low divergence, <0.001mRad or something. But, if you could get 0mrad, how would you know it was? How would you know it was 0mrad, rather than 0.00000000001mRad or something? You simply cannot measure things carefully enough to know stuff like that.
Also consider this. No optical system is 100% perfect/ loss free. You simply cannot create an optical system to perfection because anything you do has losses in it. This is why perpetual motion is not possible. You simply cannot get 100% of the energy out of something that you put into it. If this was possible, optical trains would almost be like superconductors. (BTW, same thing. They may be very efficient but not 100%. No such thing as 100% efficiency.) And if you could get more energy out of an object than you put in it, well, you can't. There is a set amount of energy in the universe; it just gets converted into different forms.
When you lose photons in an optical system, they most likely hit something and excite its molecules to produce a tiny amount of vibration (heat).
Some info on why 0mrad is not possible, and theoretically cannot exist. (Because I like this sort of theoretical physics stuff.)
Chaos theory comes into this too, essentially that if something is perfect, something will interfere with it and destroy the perfection. Something like that, I'm sure someone will correct me.
It is possible, theoretically, with very good optics to achieve very low divergence, <0.001mRad or something. But, if you could get 0mrad, how would you know it was? How would you know it was 0mrad, rather than 0.00000000001mRad or something? You simply cannot measure things carefully enough to know stuff like that.
Also consider this. No optical system is 100% perfect/ loss free. You simply cannot create an optical system to perfection because anything you do has losses in it. This is why perpetual motion is not possible. You simply cannot get 100% of the energy out of something that you put into it. If this was possible, optical trains would almost be like superconductors. (BTW, same thing. They may be very efficient but not 100%. No such thing as 100% efficiency.) And if you could get more energy out of an object than you put in it, well, you can't. There is a set amount of energy in the universe; it just gets converted into different forms.
When you lose photons in an optical system, they most likely hit something and excite its molecules to produce a tiny amount of vibration (heat).
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It would still be cool to have a laser with divergence that measures in uRad ;D It's divergence would be too low to notice earthbound anyway Not to mention that you could light a match 500 meters away with enough power...Uploading a video of that on youtube would be awesome
Not to mention that you could light a match 500 meters away with enough power...Uploading a video of that on youtube would be awesome - Joined
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Sorry blue, but that's not quite.. accurate. Sure, all processes are inefficient, but that has nothing to do with the divergence of a laser.
What you need to be concerned with is coherence and diffraction - those explain divergence. Also, we need to all remember that with perfect optics, divergence and minimum beam diameter can basically be traded off. So a laser with a minimum 1 mm beam and 2mRad diameter could be optically changed to have a 2mm beam and 1mRad divergence, or a 100mmW beam and .05mRad divergence.
So simply stating a divergence figure alone tells you nothing about the quality of a laser beam. You can always trade it off with diameter. If you need low divergence, you expand the beam or vice versa.
A 0mRad beam is a different story though since trading that off with your diameter would still keep things 0, so you could technically have a beam of infinite intensity regardless of power. That's not the reason why you cannot have a 0mRad beam, but it sure raises the question of how the heck you could have an infinitely intense beam of energy.
What you need to be concerned with is coherence and diffraction - those explain divergence. Also, we need to all remember that with perfect optics, divergence and minimum beam diameter can basically be traded off. So a laser with a minimum 1 mm beam and 2mRad diameter could be optically changed to have a 2mm beam and 1mRad divergence, or a 100mmW beam and .05mRad divergence.
So simply stating a divergence figure alone tells you nothing about the quality of a laser beam. You can always trade it off with diameter. If you need low divergence, you expand the beam or vice versa.
A 0mRad beam is a different story though since trading that off with your diameter would still keep things 0, so you could technically have a beam of infinite intensity regardless of power. That's not the reason why you cannot have a 0mRad beam, but it sure raises the question of how the heck you could have an infinitely intense beam of energy.
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Something that just went through my mind just now: could a single photon be considered as a beam? cause then it would have to have 0 divergence since it can't diverge from anything ;D
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Switch said:
Now this one is gunna blow your mind, but in this wacky world of physics, even that single photon would have diffraction limited divergence! If you were to run one of those double-slit experiments, only using a photon at a time, eventually you'd still see a diffraction pattern after you shot enough single photons at the detector. Crazy stuff eh?
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pseudonomen137 said:
Now this one is gunna blow your mind, but in this wacky world of physics, even that single photon would have diffraction limited divergence! If you were to run one of those double-slit experiments, only using a photon at a time, eventually you'd still see a diffraction pattern after you shot enough single photons at the detector. Crazy stuff eh?
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I have actually thaught of that.That's why I said "one photon" and not "one photon at a time" ;D My one photon could be considered a 0 divergence very short pulse beam that could never be fired again as it would cause it's divergence to change...sorta...(?) :-/
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That is right i guess. Simply by firing another photon you are changing the divergence because that photon would move differently. One single photon could be considered an undivergent beam I guess simply because as you said, the direction of the beam is whichever way that photon goes, and it has nothing to diverge from.
