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Collumating non coherrent light (*topic changed*)

keeperx

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ok my question is this.

concept.. (im sure it wont work for some reason, i want to know why)

lets say i have a prism thru wich i shine a bright white light.
where the prism "outputs" i use a small slit so that only one color (wavelength) can pass thru (is this posible?)
i then capture that color of light (fiber couple maybe) and culminate it into a beam. could i get a similar output as a laser??

OR

could you culminate the light from a single wavelength diode??

im newish (not new wish :)) to lasers (i have built my share of diode lasers) and want to understand a little more..
 

Murudai

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Re: coherent light

That prism idea will get you a single (or close to) wavelength, but it won't be coherent I'm afraid ;)
 

GooeyGus

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Re: coherent light

Wont work. While a prism will separate the light into the different colors of the spectrum, the light still wont be coherent. If the white light coming in was coherent, then it would work. 'Coherent' means that all the photons are 'marching in a line', in time with each other. Light from a conventional light source is just random light, the photons have no set direction.

As far as collimating an LED, yes you can do it but the light still wont be coherent.
 

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Re: coherent light

keeperx said:
ok so culminating an led... can you get a "beam"
Nope, not like a laser.Probably something with huge divergence and diameter by laser standards.

And the prism idea still wont give you monochromatic light, even if take only the green from white light , it's still gonna be more shades of green (like 520nm , 521nm .....).If you were to perfectly filter out a single line it would most likely be something like 0.1% of all the sunlight, or less(just guessing, no exact facts). :-/


And ,btw, it's COLLIMATING."Culminating" means a whole different thing, if it's a word. :p
 

GooeyGus

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Re: coherent light

You can get a beam from collimating an LED, but since the source of light isn't a point source, like a laser diode, you'll never get a small beam. And, as was stated before, it will be highly divergent. I think even the best of the best of the best 'beam' flashlights still have a divergence of something like 6-10mrad, and we're talking highly expensive flashlights.
 
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Re: coherent light

I've heard that LED Lenser flashlights have neat optics to reduce divergence.
 

Zom-B

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Re: coherent light

Not gonna happen. Because the led die is large in size, the spot will always be a factor bigger than that. To be exact the spot will be just as much larger as the ratio between the distance from the lens to the dot and the lens to the die. In other words, to get a dot the same size as the led die, the lens has to be mid-way between the die and the dot (and still capture most of the light, which will make it twenty foot big).

[edit] The color does not have to be monochromatic. Even laser diodes are not monochromatic. It's just that, the wider the band of wavelengths, the shorter the coherence length and the worse the beam quality is. Laser diodes have shorter coherence lengths than gas lasers, which make it a second choice for scientific experiments.

[edit] I could think however of a fiber optic system, that captures all the light (of a single wavelength) with hundreds of fibers, and the end of all fibers are conical in shape, with all points gathered into a single point. Because of internal reflections, the light can only be reflected towards the tips or be absorbed. Wouldn't this make a nice point source? Also, would the tip of each fiber have to be the size of a wavelength to let light pass or can it be several times smaller? This would restrain the size of the point source to the square root of all fibers times the wavelength.
 

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Re: coherent light

[edit] The color does not have to be monochromatic. Even laser diodes are not monochromatic. It's just that, the wider the band of wavelengths, the shorter the coherence length and the worse the beam quality is. Laser diodes have shorter coherence lengths than gas lasers, which make it a second choice for scientific experiments.
So if you shine a laser into a prism ,the beam will eventually split? :-/
 

keeperx

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Re: coherent light

ok what about sticking a crapload of bright ass LEDs in a box and fiber coupling. then trying to collminate the fiber output.

just exploring ideas here...
 

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Re: coherent light

Nope, I'm sorry.the output is still gonna suck.It's gonna be extremely incoherent.
I think it was daguin who said something like

Incoherent light are people dancing at a rave.
Coherent light are soldiers marching in a line.
;D

The only way we know of so far of making incoherent light coherent is to use it to pump an active medium. :-/
 

Foobario

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Re: coherent light

keeperx said:
ok what about sticking a crapload of bright ass LEDs in a box and fiber coupling. then trying to collminate the fiber output.
It depends... metric crapload, or imperial?
 

keeperx

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Re: non coherent beam (*topic changed*)

i changed the topic to be more accurate,

im looking to make a non coherent beam of blue light.

|*\
|* \ < reflective (inside) housing
|* \
|* =============================[O]------------------------------------ <---- non coherent beam
|* / ^----fiber optic ^-- collimating lenses
|* /
|*/
^-------------LEDs
 
L

laserguys

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Re: non coherent beam (*topic changed*)

Get a Blue light bulb or Blue LED and maybe a few Lens ;D ;D ;D ;D ;D ;D
I hear they are very non coherent. ;D
 

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Re: non coherent beam (*topic changed*)

As I just have this free time here and nothing to to with it, I'm gonna make a diagram of what would happen :D

stay tuned ::)

Edit: added picture, well, maybe not the best picture, but that's what would happen.Besides, the reflective surface isn't gonna guide the light into the fiber optic , it's just gonna bounce it back into the LEDs.
 

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