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Thread: New type of mid air laser show

  1. #41
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    I read the posts, but some of it just didn't make sense to me. I understand why it's impossible now. I was just under the impression that the plasma was created and terminated in the same manner as done by a tesla coil. I still don't completely understand why the plasma "hangs" around that extra 1/5th or so of a second. Once the laser turns off, it seems like the plasma would instantly die off, just as it does when the tesla coil is turned off. I'm also unclear on how the laser creates the plasma in mid-air. If it's heating the air to create it, it seems like the plasma would form at the point at which the beam exits the aperture, where it's hottest, rather than several feet from the aperture in the air. Could someone please explain this? Again, sorry if this was covered in the pdf. I read it, but had trouble understanding some of the concepts. I'm a music major, not engineering, electronic, or mechanical.

    Speaking of singing tesla's, I'm building a prototype SG tesla right now, once it's completed I'm going to get some mosFETs and a new capacitor bank, along with a few other materials and build a SST coil so that I can manipulate the pitch. A friend of mine built one in a high school science fair, should be a fun project. If anyone's interested I have pics of my project, videos soon

    Thanks

  2. #42
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    Quote Originally Posted by Pianoman View Post
    I still don't completely understand why the plasma "hangs" around that extra 1/5th or so of a second. Once the laser turns off, it seems like the plasma would instantly die off, just as it does when the tesla coil is turned off.
    The quick explanation is the air surrounding the point of "ignition" is still hot even after the laser has stopped.

    Quote Originally Posted by Pianoman View Post
    I'm also unclear on how the laser creates the plasma in mid-air. If it's heating the air to create it, it seems like the plasma would form at the point at which the beam exits the aperture, where it's hottest, rather than several feet from the aperture in the air. Could someone please explain this?
    The beam is actually being focused to a fine point above the scanner assembly. The focal point can be changed to alter depth of the 3D image.

  3. #43
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    Wink

    But will it pop balloons?
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  4. #44
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    Oh, ok! thanks. That makes sense. This is really fascinating technology. I hope to see it developed to the point of full blown mid air media display before I die ( you know, like in Star Wars ).

  5. #45
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    in the old eximer laser they use for eye surgery they had to cut your cornea . on the new yag system they focus it beyond the corea . been around for a while . only 1 watt though.

  6. #46
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    Quote Originally Posted by buffo View Post
    How is this different than the plasma display, you ask? Because unlike the arc of a tesla coil (which can be extinguished nearly immediately with great precision), the plasma hangs around for around a fifth of a second, and the decay time is random and non-linear
    So you're saying that tesla coils don't generate plasma? Or is it the decay of the plasma generated by a tesla coil dissipates quicker than laser-induced-air-breakdown? If it's the decay that's different, what makes it different? Is it a lower level of ionization?

    Quote Originally Posted by 300EVIL View Post
    The quick explanation is the air surrounding the point of "ignition" is still hot even after the laser has stopped.
    So the air around a tesla coil arc isn't hot? Why not?

    Quote Originally Posted by buffo View Post
    you have between 128 and 200 of these little sound sources all interfering with each other, which is not the case with the tesla coil.
    Why not? I understand the modulation of the continuous plasma stream, but why don't the 120 (or however many) arcs per second in the first type interfere with each other?

  7. #47
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    Some very interesting questions. It made me wonder, does the plasma created by a tesla coil form because of the high energy electrons bumping the air up to the next energy level, or is it created because of the enormous amount of heat generated by an arc of electrons, or a combination? I'm not really sure... going to try to dig up some info on this.

  8. #48
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    Quote Originally Posted by Xytrell View Post
    is it the decay of the plasma generated by a tesla coil dissipates quicker than laser-induced-air-breakdown?
    Bingo. The Tesla coil excites the air with a huge electric discharge (not unlike the arc traveling down the bore of an ion laser, actually), creating the plasma by stripping electrons off atoms in the air. To be sure, there are some thermal effects associated with the arc as well, but the primary mechanism is electrical excitation. There is also some localized heating of the air, but it is insignificant compared to the ionizing power of the arc. So when the discharge ceases, the plasma dissipates almost immediately.

    Contrast that with this 3D display device, which is creating free-air plasma *entirely* through thermal effects. It is literally heating the air (albeit in a microscopic region) to the point where it forms a tiny ball of plasma. Thus, when the heat source goes away (laser switched off), you still have a thermal decay process going on as the air tries to shed this heat, and this allows the plasma to hang around for a few tenths of a second.
    I understand the modulation of the continuous plasma stream, but why don't the 120 (or however many) arcs per second in the first type interfere with each other?
    The arc from the tesla coil is extinguished almost instantly when it's modulated. Not so with the 3D device. As an analogy, the tesla coil is a series of single "snaps" (of which the duration of each can be controlled very precisely) and the 3D plasma ball is a series of roughly .2 second bursts of white noise, each with a more or less random decay time. This is long enough to cause multiple (and chaotic) interferences.

    Adam

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