Please explain this laser phenomena

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So I'm sitting at my dest playing with my greeen laser pointer pointing it at different things. In all cases I see a green dot and its reflection off other objects.

Except when I point it at a pink hilighter standing upright on my desk. Instead of a green dot I see a yellow dot. That dot reflects onto the desk (which is very reflective) and the reflection of the dot off of the hilighter is green.

I see a yellow dot reflected off of the hilighter and a green reflection of the dot on the hilighter that is green.

If I see a yellow dot, which I assume is simply the reflective combining of the pink and green, why do I see a green reflection of THAT???!!! Shouldn't the reflection off the desk be of the yellow dot which should be yellow. I'm seeing a reflection of yellow and a reflection of the yellow reflection which appears green like the original laser.

I may have discovered something strange and I want the effect named after me if it turns out to be special! :smile:

By the way, I have tried this with many other objects of different colors and do not get the same effect. Everything is green.

tex
 

Answers and Replies

  • #2
Delta2
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I don't know what exactly the pink highlighter is but I think the pink component of the reflection is weak (weak but your eye cant see it after the 1st reflection) and is absorbed by the desk during the 2nd reflection and all that survives is the green component.
 
  • #3
Charles Link
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I can take a guess at what it could be=the light reaching your eye from the highlighter is not reflected specularly but scattered upon incidence from the surface. It could be a fluorescence takes place for that material where the wavelength is altered to a longer wavelength. (yellow is around 600 nm, green is 550 nm or thereabouts.)
 
  • #4
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I think it's caused by the body of highlighter, since its translucent (or semi glossy, you can see an image of your surroundings on it) thats cause of green reflection. However what you see as yellow (I call it orange) is mostly a cause of impurity of the ink. Because a red object under green light should be black. If you paint a cardboard or a paper with the marker that would be clearly orange which is between green and pink/magenta.
 
  • #5
davenn
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I don't know what exactly the pink highlighter is
ohhh my !!

35757.jpg
 
  • #6
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It might be interesting to note that LASER's are monochromatic. That means they have "exactly" one color.
The "reflection" can only be green.There could be fluorescence happening which would remit longer wavelengths.
However, that fluorescent light would be diffuse and not like a reflection.

For you to see any other color besides the "one" color of the laser, there would have to be other light besides the light from the laser pointer.
So for example light from the environment wich after being scattered off the object (you are pointing the laser at) lands in your eye and changes the appearance of the text marker.Or the light that is being reemitted by the fluorescent material that has been excited by the green light.

You could test that easily. Just go into a room, close the shutters and extinguish any other light source aside from the laser and test whether the highlighter looks yellow again.My guess is that Charles is right.It is fluorescence and it will look yellow again.
Highlighters are almost always fluorescent...

I assume it happens like this:

Highlighter.jpg

EDIT: I edited it so often that some parts don't make much sense anymore.
 
  • #7
davenn
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Or the light that is being reemitted by the fluorescent material that has been excited by the green light.

that one
 
  • #8
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that one
But maybe the flourescent glow is actually red and just looks yellow with the green laser...
A pink highlighter fluorescing yellow would be very weird :confused:
What do you think about that ?
 
  • #9
davenn
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it would really boil down to the specifics of the chemicals in the plastic as to the final colour emitted

I use UV fluorescence to identify mineral samples.
the white light colour of the minerals can be VERY different to the colour of the emitted light during exposure to
UV light. Whites can be reds or greens under UV light. Similar things may be happening in the OP's case

here's an example of calcite .....

Calcite___UV_fluorescent_by_greenzaku.jpg


I have a pink hilighter, just don't have a green laser to try the experiment


Dave
 
  • #10
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the texan
Could you maybe look at the reflection of the dot through a CD ?
It is pretty much the poor man's spectroscope, but it should be enough to see whether it is red-green or actual yellow.
 
  • #11
Charles Link
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I googled "green laser and fluorescence" and found a lengthy post with a video where someone found fluorescence to occur on a number of plastics using a green laser (dated 2010). I don't know how to "link" it, but apparently this or a similar effect has been previously observed. For the same google, a post from the Physics Stack Exchange also came up and they described it as fluorescence that occurs from the green laser on a number of plastics...
 
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  • #12
Delta2
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ohhh my !!

35757.jpg
What is that??? Alien Technology?? I see it first time in my life...
 
  • #13
Merlin3189
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A photograph of a green laser illuminating rhodamine B and seeming to produce yellow light.
Rhodamine6B.JPG

and graphs of Rhodamine B absorption and emmission
RhodamineBgraphs.gif

These are all in solution, so may not match the solid film effects, but it shows a suitable shift is plausible.
 
  • #14
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... the white light colour of the minerals can be VERY different to the colour of the emitted light during exposure to
UV light. Whites can be reds or greens under UV light
But in those cases, the minimum excitation frequency is usually UV. In our case, green light is able to make the highlighter fluoresce.
So I assume the absorption spectrum for which the highlighter fluoresces is a good part of the optical spectrum.
So you would see it fluoresce under normal white light ...
If it would really emit yellow light then the highlighter would look much more orange than pink when illuminated by white light.Wouldn't it ?
 
  • #15
Charles Link
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But in those cases, the minimum excitation frequency is usually UV. In our case, green light is able to make the highlighter fluoresce.
So I assume the absorption spectrum for which the highlighter fluoresces is a good part of the optical spectrum.
So you would see it fluoresce under normal white light ...
If it would really emit yellow light then the highlighter would look much more orange than pink when illuminated by white light.Wouldn't it ?
With white light there is such a mixture of colors that it would be difficult to recognize any fluorescence. The fluorescence was evident because the incident light is monochromatic and a different color or colors emerged. With white light, any change in color would simply be attributed to selective absorption. e.g. blue appears blue because the reds and greens and yellows are absorbed, etc.
 
  • #16
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With white light there is such a mixture of colors that it would be difficult to recognize any fluorescence. The fluorescence was evident because the incident light is monochromatic and a different color or colors emerged. With white light, any change in color would simply be attributed to selective absorption. e.g. blue appears blue because the reds and greens and yellows are absorbed, etc.
But pink is made by combining blue with a lot of red (in additive mixing). Any green you add in would make it more grey-whitish and unsaturated.
And the highlighter is pretty much as saturated as it gets.(By adding in yellow you would practically add in red and green if you only consider what cones it would stimulate in our eyes or if you think about it in rgb terms)
And the fluorescence under white light is probably not weak. If you assume that a fourth of all the white light is absorbed and stimulates emission at a longer wavelength, that would definitely be a significant effect.
That is what i based my assumption on that it would fluoresce red and not yellow.
And i was right. When I pointed the laser at a sheet of "pink highlighter" colored notepaper it also looked yellow.
But its reflection in a cd had "green-red" diffraction patterns.
I know it looks like a photographed this picture with a potato but the real reason is that the picture did not take the compressing very well.
The colors got all messed up... And photographing it was kind of hard. I only have so many hands.
Green Laser on pink highlighter.JPG
 
  • #17
Charles Link
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But pink is made by combining blue with a lot of red (in additive mixing). Any green you add in would make it more grey-whitish and unsaturated.
And the highlighter is pretty much as saturated as it gets.(By adding in yellow you would practically add in red and green if you only consider what cones it would stimulate in our eyes or if you think about it in rgb terms)
And the fluorescence under white light is probably not weak. If you assume that a fourth of all the white light is absorbed and stimulates emission at a longer wavelength, that would definitely be a significant effect.
That is what i based my assumption on that it would fluoresce red and not yellow.
And i was right. When I pointed the laser at a sheet of "pink highlighter" colored notepaper it also looked yellow.
But its reflection in a cd had "green-red" diffraction patterns.
I know it looks like a photographed this picture with a potato but the real reason is that the picture did not take the compressing very well.
The colors got all messed up... And photographing it was kind of hard. I only have so many hands.View attachment 102771
Very interesting. It could be a good research project for someone who has a spectrometer available. A spectrometer (diffraction grating type) will sort out the colors better than the human eye that can easily misinterpret a color, especially when more than one color is present.
 
  • #18
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I did bounced the laser from the paper I painted it and got similar patterns, in my photo orange is overexposed by the camera.
DSC_0619.JPG
 
  • #19
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I did bounced the laser from the paper I painted it and got similar patterns, in my photo orange is overexposed by the camera.
View attachment 102778
You painted it ??? Why would you do that ?
Oh! I think I get it ... You "applied" some highlighter onto it, right ?
Did you get the same results pointing the laser at the highlighter itself? (not the highlighted paper I mean)
I wonder whether there is the same ingredient in all the same-colored highlighters.There seems to be a lot more yellow and orange in your picture. :confused:
 
  • #20
Charles Link
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The way one of the googled sites=the Physics Stack Exchange explained this flourescence, (and it seems like a good explanation), is the transitions back down to the ground state after absorption of the green photon occurs in a couple of stages rather than a single transition.
 
  • #21
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You painted it ??? Why would you do that ?
Oh! I think I get it ... You "applied" some highlighter onto it, right ?
Did you get the same results pointing the laser at the highlighter itself? (not the

highlighted paper I mean)
I wonder whether there is the same ingredient in all the same-colored
highlighters.There seems to be a lot more
yellow and orange in your picture. :confused:
Yes, exactly I painted a piece of paper just
like highlighting texts.

I got nearly the same results with pointing lazer to body of the marker and even to the cap alone. In these cases I observed a spectrum of red,orange, yellow and green . But most vivid orange I get is by pointing lazer directly to the tip of the marker.
I tried an orange marker and I got greenish yellow and on a green highlighter I didn't see any color change.
However if it's a wavelength shift what are the red and green colors on cd? If it's not a hue shift why it happens on florescents only? Cause I tried a different marker with nearly the same color and also mixed oil paints really close to the pink one but both were failure, only green reflections.
I have other florescent objects, toys and nail polishes maybe I try them later.
 
  • #22
davenn
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A photograph of a green laser illuminating rhodamine B and seeming to produce yellow light.
View attachment 102767
and graphs of Rhodamine B absorption and emmission
View attachment 102769
These are all in solution, so may not match the solid film effects, but it shows a suitable shift is plausible.

great response Merlin :)


Dave
 
  • #23
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Yes, exactly I painted a piece of paper just
like highlighting texts.

I got nearly the same results with pointing lazer to body of the marker and even to the cap alone. In these cases I observed a spectrum of red,orange, yellow and green . But most vivid orange I get is by pointing lazer directly to the tip of the marker.
I tried an orange marker and I got greenish yellow and on a green highlighter I didn't see any color change.
However if it's a wavelength shift what are the red and green colors on cd? If it's not a hue shift why it happens on florescents only? Cause I tried a different marker with nearly the same color and also mixed oil paints really close to the pink one but both were failure, only green reflections.
I have other florescent objects, toys and nail polishes maybe I try them later.
As I explained earlier, lasers are monochromatic.They have exactly one colour.EXACTLY.
Usually materials get their color by absorbing selectively.
So as it was pointed out earlier :
With white light, any change in color would simply be attributed to selective absorption. e.g. blue appears blue because the reds and greens and yellows are absorbed, etc.
That is how normal everyday objects get their color.
Fluorescence is a whole different story.
It absorbs light of one frequency then relaxes part of that energy in some way(either thermally into a vibrational state of some sort or by emission of another photon)
and then reemits light having a lower frequency.
It practically "transforms" light of one color into another color.
It can even transform invisible ultraviolet radiation into visible light like shown in the beautiful picture of calcite under UV.
Usual objects cannot do that. They do not "glow" themselves like fluorescent material does when you shine light on it.
They just throw back some of the light that you shine on them.
And they throw back different colors differently well.If a substance almost doesn't absorb red light it will have a red-ish color.Maybe purple, maybe orange, maybe yellow depending on how well they absorb red and green)
But selective absorption can not make the one color of the laser another color.
The light you get back will only be the color of the laser.Getting back another color through selective absorption is impossible.
That is only possible through fluorescence/or possibly phosphorescence (which is just a special case of fluorescence as far as I know).

You don't seem to know the physics which you need to understand what I mean by "one color"
Light is an electromagnetic wave.The wavelength or frequency of that wave determines how much the cones in your eyes will be stimulated by that light.
And subsequently how you percieve the color.
Shorter wavelengths like 400 to 500 nanometers primarily stimulate the cones that react to blue. 500 to 600 for green and 550 to 650 for red.
This is EXTREMELY CRUDE. Don't ever assume that the numbers above contain any hard facts. They are just there to give you a rough idea.
Light that is monochromatic has exactly one wavelength(exactly one color).For example 532 nm like in most green lasers.
That means this light will stimulate primarily your "green responsive" cone and stimulate the "red responsive" one slightly and pretty much ignore the blue responsive one.
But the human eye cannot tell the wavelength. Light that looks exactly like the green of the laser could be mixed by adding a few red wavelengths at low intensity with some green wavelengths at a much higher intensity. Our eye is not able to tell the difference since they stimulate the cones the same way.
So this one wavelength can not be changed into another wavelength by absorbtion it can only be absorbed.The color of the laser will always stay the same if no fluorescence happens since the wavelength of the laser, no matter the intensity, will always stimulate the cones in the same ratios(Thinking about this in RGB terms really helps).

That is why the paint you mixed did not change the color of the laser but the highlighter did.
 
  • #24
Yeah the colour of the laser you cannot change, but you can fool your eye (or a camera sensor). I specifically shine green and red lasers off reflective points (for visual films), and my camera combines both colours and interprets it as yellow (even though there is no true yellow at all).
 

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