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RGB beam combining with prism?

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Helmholtz Watson

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I am planning on building an RGB laser using a common glass prism to combine the beams.
There doesn't seem to be any information about doing this on the forums, which has made me worry I am missing something since I would have assumed this would be the easiest way to combine multiple wavelengths of light.
Is there any reason this wouldn't work?
Would I be much better of using dichroics and if so, why?
 





mfo

mfo

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I don't believe a prism will work. Search for "RGV laser" in the search box and all of your questions will be answered...
 
H

Helmholtz Watson

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Could you elaborate on your reasoning why slightly?
I've read up a fair bit on using dichroics and will definitely be using them for a future project. Splitting white light into a spectrum with a prism is a fond childhood memory so doing the reverse has a certain appeal to me.
 
FireMyLaser

FireMyLaser

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I've wanted to try this for along time but I haven't gotten a prism. You should try and post your results.
 
mfo

mfo

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Helmholtz Watson said:
Could you elaborate on your reasoning why slightly?
I've read up a fair bit on using dichroics and will definitely be using them for a future project. Splitting white light into a spectrum with a prism is a fond childhood memory so doing the reverse has a certain appeal to me.
Click to expand...

I'm not 100% sure on that exactly, but my guess would be that the laser light is too coherent. Even if it did combine, it would be no where near white (due to the fact that it's not proportionately split). As I said, search for "RGV laser" in the search box and all of your questions will be answered. There are even tutorials in there. Check out jayrob's build when it comes up.

P.S. If you do try the prism, make sure you wear laser safety goggles.
 
pullbangdead

pullbangdead

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A prism should theoretically work, I see no reason it wouldn't work. Easy? Never, alignment is going to be a real PITA, because you add some degrees of freedom when compared to the other multi-colors builds. The other multi-color builds (like sightfx's white fusion kit) have some of those degrees of freedom already fixed by where you attach the lasers.


Big PITA, but possible it seems to me.
 
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mfo

mfo

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pullbangdead said:
A prism should theoretically work, I see no reason it wouldn't work. Easy? Never, alignment is going to be a real PITA, because you add some degrees of freedom when compared to the other multi-colors builds. The other multi-color builds (like sightfx's white fusion kit) have some of those degrees of freedom already fixed by where you attach the lasers.


Big PITA, but possible it seems to me.
Click to expand...

I was also thinking about this today, and I do believe it can work, but as I said I highly doubt it's going to make a pure shade of white. Probably going to make some nasty color because of the coherency of the lasers.
 
diachi

diachi

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mfo said:
I was also thinking about this today, and I do believe it can work, but as I said I highly doubt it's going to make a pure shade of white. Probably going to make some nasty color because of the coherency of the lasers.
Click to expand...


The coherency of the lasers has nothing to do with it. Using a prism would give the same overall effect as using several dichros. Change the power of the lasers to obtain the correct white balance.

I'm interested in the results of this project! Keeps us updated! :D
 
Meatball

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I would also look into the possibility that prisms are not made equally, or of the same materials. More research always helps though!

-Tyler
 
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maxh

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It's certainly possible. I bet you could use a diffraction grating, too. I've thought of trying both, myself. I imagine it's a lot easier to do the alignments using dichros with everything at 45 or 90 degrees, and that's the reason it's the method of choice (and using PBS cubes for up to 2 beams.) Bulk may also be a reason. You'll have to have a high enough index of refraction and/or enough distance from the prism that the width of your input beams wouldn't need to overlap.
 
sightfx

sightfx

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I played around with using prisms to combine lasers and it was just too hard to line everything up. Then I saw Rog8811s tutorial on using a PHR sled and decided that's the way to go.

I am still curious about the prism idea though. I wonder what the power loss through it would be.

Maybe some sort of circular ring can be used to mount the lasers and then some 2 or 3 axis adjustable mounts for finer adjustment.

if you like I will look in my "bone yard" for some mounts that have been tossed aside for cosmetic reasons. It may be a while before I can check though. I'm away from for 2 weeks but I may be home this weekend if I can swing it.

-Ryan
 
Cyparagon

Cyparagon

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Yes, but a diffraction grating would waste most of the beam. The main problem with using a prism is the angle of diffraction. The lasers need to be either very close together or very far away from the prism. I'll try it later and post my results. I'll use BR and Red since they wouldn't need to be as close as say red and green.
 
Cyparagon

Cyparagon

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Wow... Just tried it with my high-tech kitkat and playing card technique. It works, just as I thought, but the angle is a little less than TWO DEGREES. At a distance of ≈3', the beams were ≈¾" apart. And that's with the two wavelengths furthest from each other. In short, its not worth your time unless you have a LOT of space to work with.

Oh, and as for the power losses, I get total of 230mW before, and 190mW after. 17% loss with this particular prism in this particular state of cleanliness with these particular wavelengths. Your results may vary.

PHTO0005.jpg
 
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FireMyLaser

FireMyLaser

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Ha that is cool! Now maybe if the prism was made of diamond it might split a little further. :D
 
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