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psycotica0 t1_j7fm3es wrote

Reply to comment by zerpa in Why are green and red laser pointers so cheap and available, but yellow ones not so much? by SurprisedPotato

True, but the thing that makes lasers lasers and not just tiny flashlights is that they are a single coherent beam of uniform light. This is what allows them to behave reliably for engineering purposes and stay together over long distances, etc.

If I were to build a yellow laser by having a green laser and a red laser, it would be hard to get them to converge on exactly the same point. Or put another way, getting them to converge at a particular distance would be easy, but as soon as you moved slightly closer or further the dots would probably misalign and you'd end up with a red and green dot near each other. Even if the two beams were mirrored into the same trajectory, it's possible they'd refract while traveling due to their different wavelengths and end up as two dots at the end anyway.

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Obsidian_monkey t1_j7g37vl wrote

That lack of mixing is actually a feature for fiber optic communications. There are optics that use four lasers with different wavelengths to send four data streams simultaneously down the same fiber line.

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Octavus t1_j7hb075 wrote

One doesn't need lasers for that, as long as the medium is linear the mixing of light is just superposition. It is no different than transmitting multiple RF signals across multiple different channels at once.

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dramignophyte t1_j7iogxg wrote

I think the staying together property is the important aspect. Light diminishes by 4 times every time you double the distance. Except not really because its just that it disperses at that rate by virtue of spheres. Light itself on an individual scale is as far as I know, infinite. So if you convince them to stay in parallel formation, you can transfer them in a vacuum infinitely.

Lasers don't perfectly align the photons but they do a pretty darn good job. Like take a flashlight and shine it at a wall and step back and the light in the wall keeps getting bigger and bigger. Now I have not verified this next part and I am vaguely remembering what someone else said on reddit so the size probably is a bit different than what I'll say but for the distances its kind of moot. But the lazer on space probes only goes from the base lazer size to about the size of a car going from pluto to earth. So they are shining a little light at earth and it only splits a very small amount. They also mentioned there are designs for perfectly straight lasers but to go from like 99.998% to 99.999% is obnoxiously difficult considering pretty much nothing requires that level and the biggest obnoxious part is it requires a larger and larger lens, eventually reaching infinite size in order to make the perfectly straight lazer. Again, any specifics, take them as a general idea and not a point you want to bring up in casual conversation without adding "I heard it was something along these lines" because this is all "something along these lines" after the point I mentioned that I was parroting off someone from reddit. The points before that I know with much greater confidence.

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Isotope_Soap t1_j7h9ixz wrote

Oddly I’ve experienced this to some degree. I have a scoped air rifle with an illuminated reticle that is capable of red or green crosshair/dot/circle etc. It also has a red laser mounted slightly below the scope. Both are sighted in for 30 yards and when I select the green reticle and turn on the red laser, they do appear almost yellowish when on target at 30 yards. Any closer or father from 30 yards and they diverge, with the red laser dot being above or below the scope reticle. I used to find this frustrating until I realised the amount of divergence actually became a crude range finder of sorts.

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etcpt t1_j7grczf wrote

>Even if the two beams were mirrored into the same trajectory, it's possible they'd refract while traveling due to their different wavelengths and end up as two dots at the end anyway.

Do you mean that they would refract differently passing through an interface, or that the two beams would interfere with each other? It seems like the former should be able to be controlled on the device side as long as you are careful with the optics (though shining the laser through an interface would split the beams, but nothing we can do about that). You could probably cheat your way around inter-beam interference by using a pair of pulse-width modulated lasers set out of phase so that the beams don't overlap and relying on persistence of vision for the laser to be perceived as yellow.

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