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Thread: Changing red to green ...

  1. #1
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    Default Changing red to green ...

    This one makes my head hurt.

    It's an article from NEW SCIENTIST that tries to warp the way I thought I understood lightwave physics.

    It appears that a group of MIT scientists will be publishing 'real soon now' in Physical Review Letters a way to shift the frequency of light beams to any desired colour, with near 100 per cent efficiency.

    Ouch! There goes my head again. [img]/ubbthreads/images/graemlins/icon23.gif[/img]

    Go ahead and read the New Scientist article and see if your head hurts, too. *ouch*


  2. #2
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    Default Re: Changing red to green ...

    Cool, controlled Doppler shift. Makes sense, but I wonder what kind of sonic energy and frequencies will be needed to make this work. Could just be trading one kind of hassle for another, from controlling light to controlling sound. And rather than using bullets or directed sound to generate the required shockwave, why aren't they using piezoelectric effects to directly stimulate vibrations in the crystals?

    Hm... 10,000 reflections in .1 nanoseconds. Does that mean the light bounced around 10,000 times at the edge of a single shock wavefront? If you need a sound wave to provide the compression, that kind of limits how much light you can process. There aren't a lot of high energy tweeters out there that can run in the 100khz - 1MHz frequency range, and if you only get 1 .1 nanosecond pulse per compression front, then you're stuck at controlling only 100k to 1M light pulses per second. Far too slow to be practical as optical communication routers. Since it depends on these compression waves, you're going to get discrete pulses out, not a continuous stream of photons...

  3. #3
    Flashaholic* Wits' End's Avatar
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    Default Re: Changing red to green ...

    You beat Canuke by half an hour. I'm amazed at how quickly news breaks here.
    LED Forum--Your DPSS Grenie just became obsolete...

  4. #4
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    Default Re: Changing red to green ...

    This could revolutionise so many things from television to laser surgery!
    Also, imagine a torch which could be tuned to produce any colour monochromatic light including infra red and ultra violet, or a laser which could produce any colour...

    On producing the correct frequency vibrations, I seem to remember a device used in televisions SAWF (Surface Acoustic Wave Filter) which vibrated at video frequencies (a few megahertz). This formed part of the tuner circuit.

  5. #5
    *Flashaholic* James S's Avatar
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    Default Re: Changing red to green ...

    While I can't say for sure about any practical resolutions to the problem of creating the "shock wave" you certainly don't HAVE to use a tweeter. The piezo crystals could be part of the same structure as the light crystal and controlled with regular electrical PWM stuff. The crystal inquestion might exhibit it's own piezo electric properties even...

    The whole idea is indeed VERY fascinating!


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    Default Re: Changing red to green ...

    I noticed canuke posed a link to the article very shortly after I posted mine, Wits' End, but you have to kind of expect something interesting like that to show up quickly and more than once. [img]/ubbthreads/images/graemlins/smile.gif[/img]

    (In fact I responded to your comment over there in canuke's thread. I'm not proud. [img]/ubbthreads/images/graemlins/grin.gif[/img] )


  7. #7
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    Default Re: Changing red to green ...

    OK, never mind that limitation comment.
    http://hyperphysics.phy-astr.gsu.edu...ids/piezo.html

    Piezos are used in ultrasonic medical imaging, running up to 20MHz range. I guess this is a solved problem.

    The next question is, how much energy is needed in the compression wave, and how much of that energy will be leaked outside the system? You can run the sound waves up beyond the range of human hearing, but if they carry so much energy, they will still be deafening...

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