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Radio laser

  1. Jan 19, 2006 #1

    mee

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    Has anyone created a radio laser, if not why not if you know...
     
  2. jcsd
  3. Jan 19, 2006 #2
    the lowest freq. i know of is microwave... its called MASER.
    looked around in the net for RF LASER, havent found anything... maybe it because the energy gaps are too small for such a freq, and its hard to pump such a LASER....
     
  4. Jan 19, 2006 #3
    Yup MASERS are it. Some common ones are Hydrogen which is excited at 1.4 GHz , or Ammonia at 24 GHz. And of course there is Cesium atomic clock which works at about 9.1 GHz.
     
  5. Jan 19, 2006 #4

    mee

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    Are these Masers radio frequency? THought it might be easier to use a radio laser to communicate from space probes and such. a tighter beam aimed at the earth you know rather than all directions.
     
  6. Jan 19, 2006 #5
    From your last post mee, it sounds more like you mean using a laser as a carrier for a radio signal. Is that what you're intending? I'm sorry if I've muddied the waters even more but I'm a little confused as to what you're tryign to convey.
     
  7. Jan 19, 2006 #6

    berkeman

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    Keep in mind that lasers and masers use the phenomena of stimulated emission to acheive the tight, coherent beams. To make a lower-frequency RF maser, you'd need to find an atomic electron level transition that radiated at the lower RF frequency. I don't know if you could find one in the 100s of MHz area. But for mee's idea, a maser in the low GHz region like the hydrogen or ammonia masers might work.

    Masers and Lasers are not very efficient generally, though, so that's probably why it's better to use a parabollic antenna to do the directional gain. It would be interesting to run the numbers though....
     
  8. Jan 19, 2006 #7
    Masers are a source of very precise clock signals which only a few exist like the one's I already mentioned earlier. Few kinds exist because there aren't alot of mediums which absorb radio frequency.

    Because of this, there is a only a limited number of frequencies avialable to communicate with the probe, and I'm sure FCC would not allow transmission at these frequencies anyways.

    Masers are not efficient and in space every circuit is carefully constructed to use as little power as possible. Other electronic circuits like the frequency synthesizer, can be used to synthesize any radio wave at any frequency with accuracy that rivals that of a maser.

    Space probes transmit data back to earth at a power level less that 5 Watts, which means the radio wave signal has power similar to your cell phone or walkie-talkie. It is because of very sensitive dishes on earth that can pick up this signal from a couple billion miles away.
     
  9. Jan 19, 2006 #8

    mee

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    Well, there goes my idea for interstellar probe communication. :)
     
  10. Jan 21, 2006 #9

    vanesch

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    There is in fact no point in develloping, say, a 5 MHz radio-laser. The reason is that with electronic means (locked-in oscillators), we are perfectly capable to generate highly coherent radiation of 5 MHz: a radio transmitter does exactly that. The amplification by stimulated emission of radiation is only interesting if we have no direct means of generating the radiation with the coherent phase relations we desire.
     
  11. Jan 21, 2006 #10

    mee

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    But will it be directional without lasers?
     
  12. Jan 22, 2006 #11

    vanesch

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    The directionality of a laser comes from the construction of the cavity (two slightly focussing mirrors). So if you are able to construct a cavity that would give you high directivity for a laser, then you can also construct the same cavity to guide your generated radiowave from your transmitter. For instance with a parabolic antenna !
     
  13. Jan 22, 2006 #12

    Claude Bile

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    You can generate radio frequencies with a laser by exciting two transitions with very close frequencies. If you then pass this beam through an optically non-linear medium, you will generate sum and difference frequencies. If the original frequencies are close enough, the difference frequency generated by the mixer will be in the RF range.

    Claude.
     
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