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Using lasers to create a luminous spot in transparent medium

  1. Nov 13, 2015 #1
    First allow me to apologize should this thread be in the wrong forum, I am not entirely sure whether Quantum Physics is the right one. I am also unaware of the exact level to which this question belongs, which is why I went for intermediate. Please inform me if this should be changed to advanced.

    For a pet project I'm trying to find a way in which to create simple "holograms". The most feasible way of doing this in a garage seems to be with lasers intersecting to excite a local area within a medium to make it luminescent.

    Now, there are some questions I have regarding this problem but probably the most important is regarding the medium in which this could be most easily achieved. Ideally, I would of course be using simple air, but seeing as I've got no access to very high power lasers this might be out of reach. Since I have been unable to find sufficient articles relating to how one would approach such a problem, I would like some input and possibly discussion concerning the medium.
     
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  3. Nov 13, 2015 #2
    In what stage of hologram production do you need this?
    Do you really mean hologram or you just want to project an image in thin air?
     
  4. Nov 13, 2015 #3

    ZapperZ

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    This is not a "hologram". It is simply illuminating something. Even if the object luminesces, it isn't a hologram.

    I don't quite understand what you are trying to do. Are you simply trying to illuminate something with the hope that you create an excitation of the material in such a way that it it will "glow"? So what's with the crossed laser setup?

    Zz.
     
  5. Nov 13, 2015 #4
    Projecting an image in thin air.

    I want to create an excitation at one point in the transparent medium in such a way that that point will glow. Both of the individual lasers however, have to remain unseen. The assumption I'm making is that in order to do this, you'll need a higher energy area at the spot where you want to excite the material, be that air or something else, than a single laser should provide we don't want stripes after all, we want spots. Which is why I imagine you'd let 2 lasers intersect at a point to get this effect.
     
  6. Nov 13, 2015 #5

    ZapperZ

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    Then this is not "projecting an image in thin air". You are simply trying to make something glow. I can make gas "glow", but you would never call this a hologram.

    Zz.
     
  7. Nov 13, 2015 #6
    You would if you do it with several points at once. But semantics aside, this is still a physics question and has gone unanswered.
     
  8. Nov 13, 2015 #7

    ZapperZ

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    It isn't a semantic question because "holography" is a well-defined physics/optics terminology. When all you want to do is cause something to "glow", then this is a different phenomenon. To be able to answer your question, we simply must understand clearly what you're asking. Having what you say being incompatible with what you are trying to do make it confusing. There's no way one can answer such a question sufficiently.

    The issue here is the medium. I can shine ordinary UV light on many material and it will fluoresces. So if all you care about is to make something glow upon illumination of light, there you have it! There are many photoluminescent material using light sources that are easily available, rather than "laser".

    Zz.
     
  9. Nov 13, 2015 #8
    Which is why I coined the term within quote marks.
    Making something glow upon illumination is exactly what I don't want, so let me paint you a picture.

    Imagine, if you will, a chamber. Within this chamber is a glass floor which easily allows light to pass through. Because you are some form of engineer who originates from somewhere in the vicinity of Betelgeuse, you wish there was a way to visualize your new bathing duck in 3 dimensions. Lucky for you, this room is capable of doing exactly that and after you load in the schematics, the room starts displaying, in it's centre a 3 dimensional image of your bath duck. Of course, like any image, the virtual bath duck will exist entirely out of pixels, be it 3 dimensional pixels.

    I am interested in creating 1 of these pixels.
     
  10. Nov 13, 2015 #9
    Here is something you could try. Just to give you an idea.

     
  11. Nov 13, 2015 #10
    It's a joke, maybe.
    He shows how to make a truncated pyramid not how to project in 3D.
     
  12. Nov 13, 2015 #11
    It not a joke.....its an optical illusion. Its not a projector either, its only reflections off of a transparent surface at an angle. Not a true hologram.
     
  13. Nov 13, 2015 #12
    This is probably closer to what Rataridicta wants to create...but that's not practical. K.I.S.S.


     
  14. Nov 13, 2015 #13
    I mean, the video is a joke. He starts by saying that he will show how to project the image but all he shows is how to make a pyramid.
     
  15. Nov 13, 2015 #14
    Yeah, much closer indeed. But they are ionizing the air, which requires a huge amount of energy as it probably gets heated to somewhere around 5k-10k K
    I'd rather not attempt to toy with such high energy devices; obvious reasons.

    That's why I'm so focussed on finding a medium (maybe some form of crystal) that can re-normalize on its own or maybe even when a current passes through it. That would either become luminescent at the intersection, or opaque. The opaque version would still work, but might be hard to "re-normalize" to a transparent state, if at all possible.
     
  16. Nov 13, 2015 #15
    Very true nasu. The video's creator has only made a pyramid shaped reflector, but that aside its a pretty neat looking visual.
    I've seen so called "ghost" videos that use similar techniques. But crisscrossing 2 lasers in the air I doubt would produce much of any type of visual effect.
     
  17. Nov 14, 2015 #16

    sophiecentaur

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    No. It's not semantics. A hologram is a hologram. A 3D image is a 3D image. The least we can do on PF is to try to use accurate terms.
     
  18. Nov 14, 2015 #17
    Definition of semantics: "The meaning, or an interpretation of the meaning, of a word, sign, sentence, etc." Hologram was in between quote marks suggesting a figurative way of speech as indeed it was as I was not referring to the well defined hologram you find on your currency, but instead the lesser the lesser defined meaning like you find it in books, which is the same word.
    Seeing as both are accepted words, this seems to me like a miscommunication regarding the interpretation of the meaning of a word, which is per definition semantics.

    Now can we stop this discussion going nowhere?
     
  19. Nov 14, 2015 #18

    sophiecentaur

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    If you were to use crossed beams to take a non-linear medium over a threshold, you could produce a coloured spot / pigment where the total energy density is highest. There are a number of photochromic materials which are used in sunglasses and protective goggles. They can be activated by UV, which would be a useful feature. This would not be "thin air" but could be a large volume (depending on cost). One advantage of producing a reflective image would be that you wouldn't necessarily be dealing with high levels of light source.
    I made a brief search but, of course, the majority of hits are either sales orientated or elementary treatments of 'smart materials'. For this to work, you need a threshold or 'knee' in the response of the material so that the indexing beams do not show up except where they cross. There would be other issues such as lag and retention of the image, which could be relevant if you wanted the image to move without streaking.
    Just a suggestion but I guess that's what brainstorming is all about, You may have already been there but rejected it.
    Sorry if my response looked picky but only you know where you were coming from and it can be hard to formulate a question that gets the right idea across. PF does get a lot of daft posts and they tend to spark off equally daft responses.

    PS, would a simple stereoscopic display on a big screen TV not do the job? Solved for a few hundred quid.
     
  20. Nov 14, 2015 #19
    I'm no physicist but I play one on the Internet. Ionization aside, I have noticed that those reflective coatings used on stop signs and license plates (which contain little glass beads) seem to have the strongest reflection in the opposite direction. In other words, the closer to your eye the flashlight is held while pointing it at the reflectively coated object, the brighter the reflection. Fog is made of little "beads" of water and seems to offer a similar effect. I'm assuming that's why fog lights on cars work better than the regular headlights (and the color of the light also matters). So it stands to reason that if you could project the correct two dimensional image from the direction of the observers (if they aren't too close to the intended illusion) into a foggy medium, depending on how many simultaneous projections you can afford to set up, of the same object at different angles - you might get an effect that's not perfect but not entirely lame? :)

    maybe?
     
  21. Nov 14, 2015 #20

    sophiecentaur

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    The result would be a set of lines ('rays') through the medium - a (3 dimensional) cone, if your required image were circular. There is nothing to tell you where the wanted image should be, along each of the rays. You would best observe the effect from near the source of the scanned light beam.
     
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