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Can you change the wavelength of light without disorting its path?

  1. Oct 8, 2011 #1
    If I had a photon with 450nm wavelength, purple. Could I change it to become a radio wave? with out it going in another direction or anything.
  2. jcsd
  3. Oct 8, 2011 #2


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    One of the best ways to do it is to wait for few billions of years. Cosmic microwave background is a visible light emitted long time ago, whose wavelengths got dramatically enlarged by the expansion of Universe.

    You may make it in a shorter time using moving mirrors. Bounce your photon from them, Doppler effect would enlarge its wavelength. If both mirrors are parallel, then after even number of bounces the direction, polarisation, etc won't be affected.

    BTW: there is no such thing as 'photon path'...
  4. Oct 8, 2011 #3
    I believe the answer is, no. A photon is a photon, and what you perceive as it's wavelength depends on the relative velocities of you vs. what emitted it. Over cosmological time and distance scales, I'm no longer certain what exactly that statement means, but otherwise it's straightforward. But it's still the same photon - you can replace it with other photons in various ways, and seemingly "change" it, but you've really just replaced it.
  5. Oct 8, 2011 #4
    The photon will be stretched if...
    -It's source is moving away from you when the photon is emitted
    -You are moving away form the source as you receive the photon
    -the photon is moving upward through a gravitational field
    -The photon is bounced off of a mirror which is moving in the same direction as the photon, I know you said you didn't want to change the direction of the photon but bouncing it off of a second mirror could put it back on its original path.
  6. Oct 8, 2011 #5
    Ok what do you mean by replace? is there no kind of matter that makes photons chenge their wavelength and doesnt really change theyr direction, I know matter can sort out different wavelengths of photons, but there must be a way to make matter where 500nm wavelength hits one side and the other side we get a 1 meter wavelength radio wave. To replace the photon is ok. But now we must be in somekind of electric devices and things are getting complicated. But is there a simple way of doing this?
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