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      CommentAuthorTrim
    • CommentTimeFeb 10th 2016
     
    NBF

    Do aliens have a beam weapon that could destroy Earth from light years away?

    Or power beamed starships?

    Physics PHD reader of Nextbigfuture proposes megamirror system to explain Star seen dimming for 100 years.

    http://nextbigfuture.com/2016/02/physics-phd-reader-of-nextbigfuture.html
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      CommentAuthorThicket
    • CommentTimeFeb 10th 2016
     
    Nothing of the sort. The dimming is merely a malfunctioning traffic light on the intergalactic highway.
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      CommentAuthorTrim
    • CommentTimeFeb 10th 2016
     
    Bummer.
  1.  
    I don't think that's possible with incoherent light, which is what the star gives you.
    Also, this "dimming over a century" result has been questioned based on properties of older photographic emulsions having been incorrectly calibrated.

    So, no.

    Unless yes. Which is an alternative explanation for climate change.
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      CommentAuthorQuanten
    • CommentTimeFeb 10th 2016 edited
     
    The trick would be to take the incoherent light and massively put it in a pump system (to get a population inversion). You then get coherent light.

    For example , we had as student ruby crystal (which were grown to be cylinder with a certain "direction") we just surrounded them with basic neon light and then got a red light laser. Multiply that with giant ruby crystal and pump sunlight into them ;).
  2.  
    They are called "solar-pumped lasers". The largest one is in Uzbekhistan, believe it or not.
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      CommentAuthorQuanten
    • CommentTimeFeb 10th 2016
     
    Posted By: Andrew PalfreymanThey are called "solar-pumped lasers". The largest one is in Uzbekhistan, believe it or not.


    Well I learned something today. Never knew those really existed.
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      CommentAuthorAngus
    • CommentTimeFeb 10th 2016
     
    Posted By: QuantenThe trick would be to take the incoherent light and massively put it in a pump system (to get a population inversion). You then get coherent light.

    For example , we had as student ruby crystal (which were grown to be cylinder with a certain "direction") we just surrounded them with basic neon light and then got a red light laser. Multiply that with giant ruby crystal and pump sunlight into them ;).


    No. If you amplify incoherent light you get amplified incoherent light. Your ruby crystal also acted as a resonator, so that the light that got amplified started as a single, extremely weak, sine wave. All the amplified light bouncing back and forth in the crystal started from this one random event and is in phase with it - and so it is all coherent.

    Same-same as any other resonant device.
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      CommentAuthorAngus
    • CommentTimeFeb 10th 2016
     
    Posted By: Andrew PalfreymanThey are called "solar-pumped lasers". The largest one is in Uzbekhistan, believe it or not.


    No. The solar pumping provides the energy for the gain. It does not provide the input light.
  3.  
    Really? - thanks. So when the input light is incoherent, is the output light coherent?
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      CommentAuthorAngus
    • CommentTimeFeb 10th 2016 edited
     
    We have to distinguish oscillators from amplifiers here. A laser oscillator produces (usually) intense, coherent narrow spectrum light consisting of oscillations on some of the very closely spaced modes of the cavity, which is very long compared to the wavelength. Optical amplifiers also exist - they are used extensively in the fibre optic telecommunications system. They amplify whatever comes in as long as it is within the fairly broad gain region of the amplifying material. So for example input channels on hundreds of wavelengths, produced by corresponding hundreds of sources, can be amplified by the same amplifier. This is incoherent light.

    So a laser OSCILLATOR produces coherent outputs. A laser AMPLIFIER produces more of whatever you put in.

    Just like electronics.
  4.  
    OK. So needs a seed laser.
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      CommentAuthorAngus
    • CommentTimeFeb 10th 2016
     
    Yes
  5.  
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      CommentAuthorTrim
    • CommentTimeFeb 11th 2016
     
    Anybody who seed a laser risks going blind.
    • CommentAuthortinker
    • CommentTimeFeb 11th 2016
     
    Posted By: TrimAnybody who seed a laser risks going blind.


    +5!
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      CommentAuthorAngus
    • CommentTimeFeb 11th 2016
     
    Posted By: Andrew PalfreymanNo mention of that seed laser in any of these.


    Why would there be? There isn't one. Those are solar powered laser oscillators. An oscillator is a gain mechanism with a feedback mechanism that permits a resonance. The "seed" is a random photon spontaneously emitted within that starts up the oscillation. Same as any oscillator.

    I answered "Yes" to your question because I presumed you wanted to know how you would get coherent light out of a laser amplifier. A laser amplifier, like any amplifier, is a gain mechanism that lacks (if you build it right) any feedback mechanism. Materials with optical gain such as gas clouds with starlight pumping can be found in space. It is a little more difficult to find the carefully aligned mirrors that usually constitute the feedback mechanism.
  6.  
    All clear. I actually re-read your answer and wondered if you were talking about an oscillator or an amplifier.
    • CommentAuthorLakes
    • CommentTimeFeb 12th 2016
     
    An Oscifer, officer, honest.
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      CommentAuthorTrim
    • CommentTimeDec 16th 2019
     
    100 mysterious blinking lights in the night sky could be evidence of alien life.

    https://www.theregister.co.uk/2019/12/13/objects_in_space/