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Green laser appears Yellow, why?
Another question about color reminded me of this.
I developed all my own laser light show hardware and software and I have been doing small light shows for quite some time.
I have a 1mw green HeNe (Helium Neon gas) laser.
I have some red (and green) paper that is very bright in sunlight and really lights up with a good UV light.
When I shine the green HeNe onto the red paper, the dot is yellow.
If a green laser emits ONLY green light (and it does) how can there be any yellow light to reflect?
ADDED:
Other lighting won't do it. This is in a dark room (or not) Try again.
More:
... "refracted..." nope, but a tiny bit closer.
All the clues are there. Re- read them.
BINGO! AL,
The paper "...s very bright in sunlight and really lights up with a good UV light."
It is Fluorescing. Apparently the green HeNe has enough energy to do this. So the paper is actually converting the green incident light (adding energy to electrons) to RED (as the electrons drop back down and emit red photons) and the two now make yellow (additive). I never did understand all that color wheel stuff in grade school, but now...it all makes sense (in the additive case, that is)
More yet:
Xtama Red ,
If I said where's the red coming from, that'd probably give it away.
RE: red laser, green paper> Possibly, but the red may not have enough energy to cause the fluorescence. I do have red lasers and green paper, but it;s more yellow-green and I don't recall if I tried it... Booo on me.
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It's a Mels Griot. Actually it's a .2mw and it has long since stopped lasing.
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Isn't physics (science, electronics, whatever) neat?
*Please note that Xtama Red has the correct answer.* I don't know how to change the ratings.
4 Answers
- 1 decade agoFavorite Answer
Some of the energy is absorbed in the paper so it is refracted at a lower energy(yellow is lower then green). It's either that or you have racist paper. I would have to go with the latter.
- 1 decade ago
The question you should be asking is not necessarily where the "yellow" light comes from, but where the red light comes from, since we know that a combination of green and red light produces yellow. In this case you are supplying the green light, and you would like to know where the other component (the red) is coming from.
Firstly, I am not sure what kind of HeNe laser you are using, because HeNe emits at the 632nm band (red), but I'm gonna assume you know your stuff and you have some pumping going on or whatever, and it is in fact emitting green. The red is coming from the fluorescence of the red dye in the paper when exposed to photons of higher energy. The green photons coming from your laser excite the red dyes in the paper and cause red light to be emitted (in the same way that it would be emitted when exposed to UV).
To test this effect, just try using a red laser on a piece of green fluorescent paper and see if you observe the same effect (a yellow dot). Because the low energy red photons cannot excite the green dyes in the green fluorescent paper, no green light will be emitted and the dot will still be red.
- gintableLv 71 decade ago
You need to do it in a dark room. You are getting interference from other lighting.
