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Author Topic: Can you diffract other EM waves the same way white light is?  (Read 1879 times)

Offline Kr.I.S

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You can diffract white light into the visual spectrum of different colours, so can you diffract other parts of the EM spectrum in the same way?
e.g can you diffract 'white' radio waves into different 'colours'?
Where 'white' would mean un-polarised, non-coherent and a mixture of wavelengths .
« Last Edit: 13/10/2013 11:19:08 by chris »


 

Offline syhprum

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I remember an old text book with pictures of Hertz doing just this with a large prism made of pitch and a spark generator
 

Offline CliffordK

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Do you mean refraction (bending the light), rather than diffraction (interactions of waves and barriers, or slits).

Any material that is transparent to the target EM wavelength should refract, or bend the waves.  The refraction tends to be less with long wavelength sources, and you need to have a focused source to begin with, so it may be difficult to refract waves much longer than those in the microwave spectrum.

Obviously if the EM you're looking at is invisible to the human eye, you won't see "colors", although there are detectors that could assign false colors to the different wavelengths. 
 

Offline Phractality

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Radio waves, like light, slow down when entering a denser medium. To get diffraction, you just need a block of denser medium which is wider than the wavelength of the radio waves. This is easy with microwaves, but for the AM broadcast frequency, the wavelength is many meters. You would need a huge block of material to diffract the waves in that way.
 

Offline RD

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... but for the AM broadcast frequency, the wavelength is many meters. You would need a huge block of material to diffract the waves in that way.

Like a mountain range ... http://en.wikipedia.org/wiki/Knife-edge_effect
 

Offline Pmb

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Radio waves, like light, slow down when entering a denser medium. To get diffraction, you just need a block of denser medium which is wider than the wavelength of the radio waves. This is easy with microwaves, but for the AM broadcast frequency, the wavelength is many meters. You would need a huge block of material to diffract the waves in that way.
That's not quite right. That gives the impression that it requires a block to be able to diffract radio waves when in fact it could be something as simple as a wall, i.e. a sheet of material rather than a cube.
 

Offline chris

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Yes, you can diffract other EM wavelengths; X-ray diffraction is used routinely to discover the 3D structure of matter, for example.
 

Offline evan_au

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Quote
can you diffract 'white' radio waves into different 'colours'?

This is effectively what every radio does, but using a different technique than diffraction.
  • Traditional AM Radios use a capacitor and inductor, which resonate at a particular frequency to pick out just one station from the many stations in the AM band. By varying the capacitor, it is possible to slowly scan through the AM band to search for particular weak stations.
  • Traditional FM radios use a ceramic electromechanical resonator at around 10MHz to pick out the wide range of frequencies used by a single FM radio broadcast. The frequency of a particular FM radio station is translated down to the 10MHz by nonlinear mixing with the transmitted frequency.
  • Modern Software-Defined Radios use very fast Analogue-to-Digital converters combined with the Fast Fourier Transform to extract the entire spectrum at once, or just desired frequencies from the transmitted radio spectrum.
     
These are different technical implementations of what astronomers do with an optical spectrograph. Astronomers can use an optical prism or a diffraction grating to split the light into a spectrum. This can then be captured all at once, or to scan through the spectrum slowly for a high-resolution search for weak signals from particular chemicals of interest.
 

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