1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Please explain this laser phenomena

  1. Jul 1, 2016 #1
    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
     
  2. jcsd
  3. Jul 1, 2016 #2

    Delta²

    User Avatar
    Gold Member

    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.
     
  4. Jul 1, 2016 #3

    Charles Link

    User Avatar
    Homework Helper

    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.)
     
  5. Jul 1, 2016 #4
    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.
     
  6. Jul 1, 2016 #5

    davenn

    User Avatar
    Science Advisor
    Gold Member

    ohhh my !!

    35757.jpg
     
  7. Jul 1, 2016 #6
    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.
     
  8. Jul 1, 2016 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member


    that one
     
  9. Jul 1, 2016 #8
    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 ?
     
  10. Jul 1, 2016 #9

    davenn

    User Avatar
    Science Advisor
    Gold Member

    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
     
  11. Jul 1, 2016 #10
    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.
     
  12. Jul 1, 2016 #11

    Charles Link

    User Avatar
    Homework Helper

    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...
     
    Last edited: Jul 1, 2016
  13. Jul 1, 2016 #12

    Delta²

    User Avatar
    Gold Member

    What is that??? Alien Technology?? I see it first time in my life...
     
  14. Jul 2, 2016 #13

    Merlin3189

    User Avatar
    Gold Member

    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.
     
  15. Jul 2, 2016 #14
    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 ?
     
  16. Jul 2, 2016 #15

    Charles Link

    User Avatar
    Homework Helper

    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.
     
  17. Jul 2, 2016 #16
    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
     
  18. Jul 2, 2016 #17

    Charles Link

    User Avatar
    Homework Helper

    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.
     
  19. Jul 2, 2016 #18
    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
     
  20. Jul 2, 2016 #19
    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:
     
  21. Jul 2, 2016 #20

    Charles Link

    User Avatar
    Homework Helper

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Please explain this laser phenomena
  1. Please explain it. (Replies: 1)

  2. Laser/Wave Phenomena (Replies: 2)

Loading...