White laser pionter?

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zerogx2000

Newly Enlightened
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Jun 21, 2007
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Do you think it possible to have a white laser pointer some day? Also when i shine my high power green laser on the ceiling the light that bounce back is not a solid pattern its more of a wavy texture why is this?
 
Basically no. The long, thin beam characteristic of laser occurs because laser light is coherent (think of a bunch of identical waves marching in neat rows down a channel vs. choppy ocean waves all going which aways...), and coherency requires that the light be monochromatic (only one color). White is not a color, it is all colors mixed, so normal white light is, by definition, not coherent laser light.

It might be possible to combine separate red, green, and blue laser beams into something which might look white to your eye although it wouldn't be truly white in the spectral sense. Not sure about that, though.

Laser light has a funny reflection pattern, called speckling, because it does arrive at an object in an even and coherent wavefront, so the reflections from many points across the object will interfere and cause a spiky diffraction pattern which your eye sees as the wavy, speckle pattern.

You can try checking "speckle" out in wikipedia.

And welcome to CPF!...
 
I'll agree and disagree... There may be a white pointer one day, but you would have to combine R, G, and B lasers to do it. Atleast if you were to try today. I be you could do it if you took a pointer of each color apart and put the guts from all three together with a couple of dichros. I would think you would need an enclosure the size of a big MAG light and probably the 4 D cells to power it (them)...
thinking.gif
 
Re: White laser pOInter?

nerdgineer said:
It might be possible to combine separate red, green, and blue laser beams into something which might look white to your eye although it wouldn't be truly white in the spectral sense. Not sure about that, though.
Click to expand...
The beam might look white but the speckle patterns in the three colours when it hit an object would be different. The dot would look OK from a distance.
 
there was a discussion on this forum a couple of months ago about light and it's particular characteristics with lenses. Someone posted a very interesting post on chromatic wavelengths and how it was very much different than oh I can't remember. Apparently I'm going to have to find the post. Anyway, in it you see that when different colors are shined through the same lens they focus at different distances because of the particular properties of that wavelength of light. It is because of this reason and the wavelength of each color being different that I think it will be impossible for a white laser. Yes all of the colors would be going together in a coherent beam but they... ah nevermind. I'm not knowledgable enough in this field yet to post educated reponses on things I don't know.
 
A "white LED" is not actually emitting white light. They're a combination of 3 colored LEDs...red, green and blue...in a single package. Each LED emits only a single frequency of light. That's how an LED works.

A LASER diode works similarly...they also emit monochromatic light. So, you'd need 3 LASERs. Assuming that you already have 3 collimated beams of equal size, you need only make them overlap to end up with a "white" beam. That can be done with mirrors or optics.

The thing is, though, one of the defining characteristics of a LASER is its spatial and temporal coherence. In other words, all the light waves/photons (I'm not going to get into quantum mechanics on this forum) have to travel in lockstep. That means, all the same size, energy, and color...all traveling in the same way; each precisely mirroring the motion of the photon in front of it, and behind it. There's no internal interference.

3 beams...red, green, and blue, will *never* all travel completely in lockstep. Even if you manage to get them perfectly combined, they will NOT be a single LASER beam, and the waves internal to the combined beam will interfere with each other. Even the output would not be white (though our eyes would probably perceive it as white) because there would be 3 discrete frequencies of light, and truly "white" light is spread across the entire spectrum.

Having said that...that's theory. Practice may be different...but I doubt it. Give it a shot, and let us know the results! You've got me curious.

-- Chuck Knight
 
chuck said:
A "white LED" is not actually emitting white light. They're a combination of 3 colored LEDs...red, green and blue...in a single package. Each LED emits only a single frequency of light. That's how an LED works.
Click to expand...


Not exactly. The current white LEDs are blue LEDs coated with a phosphor to achieve white light. The RGB-LEDs are not typically used for white as the color distribution usually sucks and you get a very uneven "white".

bernhard
 
You *CAN* get a reasonable approximation of white if you drive the red, green, and blue LEDs inside the package of an RGB LED with the correct currents; but repeatibility (getting the exact same tint results from additional RGB LEDs driven from the same sources as the first) would become a rather significant issue.

If the RGB LED is in a milky, diffused case and if the three dice inside are driven correctly, then yes, you can get a pretty decent white out of it.

Since this is about a white light laser though, this technique would not work, as the R, G, and B beams would not have spatial and temporal coherence.

To put this in the shortest terms possible, no, you cannot have a white laser pointer. :shakehead
 
Kiessling said:
Not exactly. The current white LEDs are blue LEDs coated with a phosphor to achieve white light. The RGB-LEDs are not typically used for white as the color distribution usually sucks and you get a very uneven "white".
Click to expand...

NICE! I'm behind the times!

Glad to hear that they're going for a better spectrum in the LEDs. The RGB LEDs definitely left me wanting, even though they did work. I wonder how the efficiency of the LED was affected, by implementing a phosphor based system?

-- Chuck Knight
 
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chuck said:
NICE! I'm behind the times!

Glad to hear that they're going for a better spectrum in the LEDs. The RGB LEDs definitely left me wanting, even though they did work. I wonder how the efficiency of the LED was affected, by implementing a phosphor based system?

-- Chuck Knight
Click to expand...
Some of the best white LEDs are very efficient -- about 100 lumens per watt, compared to more like 30 lm/w for the best RGB LEDs I've seen. The biggest reason for this is that the blue emitters are by far the most efficient ones, as a result, downconverting super-efficient blue chips to other colors is actually substantially more efficient than producing them directly.
 
Hey chuck ... :D ... you might enjoy a visit to the LED forum ... things are evolving faster than the older guys like myself would like them to.
bernhard
 
The white from a white LED is a mix pf a primary color (blue) from the LED, and a secondary color (yellow (mix of red and green)) from the phosphor. so, ideally you could save on complexity (but pay more) by mixing blue and yellow beams to simulate white.

HUH...HUH... sounds good to me.....

Jeff
 
chuck said:
The thing is, though, one of the defining characteristics of a LASER is its spatial and temporal coherence. In other words, all the light waves/photons (I'm not going to get into quantum mechanics on this forum) have to travel in lockstep. That means, all the same size, energy, and color...all traveling in the same way; each precisely mirroring the motion of the photon in front of it, and behind it. There's no internal interference.

3 beams...red, green, and blue, will *never* all travel completely in lockstep. Even if you manage to get them perfectly combined, they will NOT be a single LASER beam, and the waves internal to the combined beam will interfere with each other. Even the output would not be white (though our eyes would probably perceive it as white) because there would be 3 discrete frequencies of light, and truly "white" light is spread across the entire spectrum.
Click to expand...

You can use PWM and alternate red, green and blue laser diode with high frequency 250 Hz or higher, so flickering and colour changing couldn't be seen by human eyes. ONE wavelength is forming the beam at any time. No interference in the beam at all. You can change duty cycles of R, G and B with high resolution of 16 bit or higher and create any colour you want. That's how existing white lasers work.
 
White laser pointer

LightForce said:
You can use PWM and alternate red, green and blue laser diode with high frequency 250 Hz or higher, so flickering and colour changing couldn't be seen by human eyes. ONE wavelength is forming the beam at any time. No interference in the beam at all. You can change duty cycles of R, G and B with high resolution of 16 bit or higher and create any colour you want. That's how existing white lasers work.
Click to expand...
Brilliant, and pretty obvious now that you mention it. But you say existing white lasers. How about a link?
 
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