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would a standard prism work for rgb?

Merpie101

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hello, so i was seeing all the stuff about rgb lasers using pbs cubes and dichros, but i was thinking why cant you just use a plain old prism?

as in you know how white light will split into the reds, yellows, greens, blues and violets and they all exit the prism at an angle depending on the wavelength

cant you just calculate the angles of the wavelengths and shoot the lasers at the spots on the prism at the angles and get a combined beam?

the picture below describes what i mean






if this doesnt work, why not? im kinda curious because i havent heard of anyone using this so i assume theres a reason. teach me o wise ones
edit: sorry if the picture doesnt work i keep forgetting how to format these things
 
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Encap

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hello, so i was seeing all the stuff about rgb lasers using pbs cubes and dichros, but i was thinking why cant you just use a plain old prism?

as in you know how white light will split into the reds, yellows, greens, blues and violets and they all exit the prism at an angle depending on the wavelength

cant you just calculate the angles of the wavelengths and shoot the lasers at the spots on the prism at the angles and get a combined beam?

if this doesnt work, why not? im kinda curious because i havent heard of anyone using this so i assume theres a reason. teach me o wise ones
edit: sorry if the picture doesnt work i keep forgetting how to format these things
See: https://en.wikipedia.org/wiki/Prism

See: video
 
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Merpie101

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See: https://en.wikipedia.org/wiki/Prism

See: video if too lazy to read.
ok so i watched the video but i still dont get it. really both the article and the video were just explaining how the prism works but i didnt find anything about reversing the process?

im talking about like you have a beam of sunlight and you put a prism, but instead of using an lens and a prism to get white out, cant you just use a mirror perpendicular to the prisms output and get white light down the beam it came from?
 

Alaskan

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I don't see why not, but haven't seen it done. Someone surely has, don't you think? I'd love to see photo's if anyone finds something.
 

Merpie101

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I don't see why not, but haven't seen it done. Someone surely has, don't you think? I'd love to see photo's if anyone finds something.
im gonna try this tomorrow and see how it goes. i just figured i would ask around so i dont end up making something stupid.
 
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Alaskan

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I love the project, more complex than dichros, but cool.
 

Radim

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hello, so i was seeing all the stuff about rgb lasers using pbs cubes and dichros, but i was thinking why cant you just use a plain old prism?

as in you know how white light will split into the reds, yellows, greens, blues and violets and they all exit the prism at an angle depending on the wavelength

cant you just calculate the angles of the wavelengths and shoot the lasers at the spots on the prism at the angles and get a combined beam?

the picture below describes what i mean






if this doesnt work, why not? im kinda curious because i havent heard of anyone using this so i assume theres a reason. teach me o wise ones
edit: sorry if the picture doesnt work i keep forgetting how to format these things

I'm affraid I do not see the pic. However I guess you want to shoot lasers to get white through a prism.

Instead of giving answer to you, I say - why not to get piece of paper, pencil and ruler (and maybe some other stuff) and find out yourself? It will give you even angles with simple calculations. ;)

Check here:
https://en.wikipedia.org/wiki/Refractive_index

BTW I think this joke is appropriate here:



:D :D :D
 

BobMc

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Looking forward to see/read what you find out. Best wishes with your project. Will be interesting. :)
 

Merpie101

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i got it to work... kinda it does work but im having trouble aligning the lasers vertically. im on vacation so i only had the chance to combine 2 beams but i actually managed to keep the beams together for up to 20 feet before you can see they split up and thats just by eyeballing them!





im still not quite sure how to format these things so they show up and everythings slow on mobile.
sorry i cant get a good picture for the distance shot
 
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Encap

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ok so i watched the video but i still dont get it. really both the article and the video were just explaining how the prism works but i didnt find anything about reversing the process?

im talking about like you have a beam of sunlight and you put a prism, but instead of using an lens and a prism to get white out, cant you just use a mirror perpendicular to the prisms output and get white light down the beam it came from?
"RECOMBINING SPECTRUM COLORS"
"Isaac Newton also wondered if the colors of the spectrum could be recombined to again make white light. To do this he used a second prism arranged as shown. He proved that this was possible. What’s interesting is that the light beams exiting the second prism are not on the same line, but they are PARALLEL. And, because the slit is not infinitely narrow, these beams are not infinitely narrow and therefore can mix to create white light."
From: Two Prisms: Four Demos | Educational Innovations --- See for details and graphic representation.

Also see this web site--with interactive graphic representaion : Molecular Expressions: Science, Optics and You - Newton's Prism Experiment - Interactive Tutorial

Hope that helps---good luck.

Red, Green and Blue Lasers to White Light Laser - Reverse Prism
 
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paul1598419

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Better late than never. Of course you can set up three primary colors, red, green and blue, to be combined by a prism, but the angles you need to add the light to the prism will depend on the index of refraction of the glass and the angles of the prism's triangle. Because these angles are usually very small, the distance you will need to get them to the prism correctly becomes quite large and for practical purposes they don't fit into a small enclosure. Good luck with your experiment.
 

Merpie101

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thanks, i will be home tomorrow so i could have a larger area to work with
 

Benm

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The principe of operation works, you can combine lasers with an ordinary prism if you shine them in at the correct angles. Prisms split wavelengths just as well as they can combine them in the reverse direction.

The problem is, as stated, the size of the whole thing, and stability issues that come with that.

You could get something like a large desk, place red, green and blue lasers onto it pointing at a prism. With some adjustment you could get them to come out at the same angle and thus be a combined beam. If that desk warps slightly due to temperature changes or such alignment would be off.

A more practical way of going about this would be using a prism and mirrors so you dont need the units to be so far apart, but this is still much larger to set up compared to a solution with dichros.

So yes, an ordinary prism could be used as a beam combiner, as long as you have plenty of space to build the whole thing (such as inside an entire room) and things do not change position or orientation due to (thermal) fluctuations.

It may be fun to set this up as a proof of concept or science demonstration, but i doubt it would be of much practical application.
 

Light superglue

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Sorry to enter your discussion without much knowledge in this area.

As I see it is possible but the light splitting angle of a single prism is too small so the setup has to be very large.

What if 2 or more prisms are installed in sequence - would it increase the angle?

What if prism material would have higher refraction index than glass - would it increase the angle?
 
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