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Laser Beam Diameter

  1. Jan 11, 2015 #1
    Hi Friends,
    I want to know that why one can't achieve diameter of a laser less than the wavelength of the beam in order to get more power through a lens.
    plz explain in simple Physics
     
  2. jcsd
  3. Jan 11, 2015 #2

    mfb

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    Staff: Mentor

    This is given by diffraction.
    There is just no solution for electromagnetic waves that would correspond to a smaller diameter.
     
  4. Jan 12, 2015 #3
    Dear mfb,
    Would you please explain diffraction so that I can comprehend the diffraction?
    Why light does not scatter above the order of its corresponding wavelength?
     
  5. Jan 12, 2015 #4

    mfb

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    There are books about diffraction, I cannot replace books.
    This has nothing to do with scattering.
     
  6. Jan 13, 2015 #5
    Krishnakant,

    check out the section "Diffraction of light" in https://en.m.wikipedia.org/wiki/Diffraction ,
    particularly the animations. The size of the hole in those animations is the laser's aperture, and the "beam" is coming out to the right. You will see that the smaller the aperture, the wider-spread the beam is. The whole article explains why that is.
     
  7. Jan 14, 2015 #6

    Drakkith

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    In simple terms, if the size of the wavefront is much smaller than the wavelength, there will be almost no interference between different parts of the wavefront, which is what keeps a wavefront from immediately expanding outwards in all directions.
     
  8. Jan 14, 2015 #7
    A few weeks back I actually wrote some code as a fun project that simulates the wave equation on a grid, and visualized it (in C#). I futzed around with different aperture sizes and was quite stunned that from >10 wavelengths on of aperture size, the classic "beam" just comes out naturally.
    It made me realize that what we think as the "obvious" behavior of light, I.e. that it will move in a straight line, is really not obvious at all, but rather an outcome of intricate interference patterns.
     
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