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Old Nov 26th 2014, 04:50 AM   #1
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Double slit experiment

Provided that every light source is multiple consists of milions atoms emiting photons,how the unique light source used is considered to be coherent?
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Old Nov 26th 2014, 11:44 AM   #2
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The only thing that needs to be coherent is the combination of the colliding waves of photons moving through both slits.
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Old Nov 30th 2014, 03:31 AM   #3
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Yes.Since the source is multiple (composite) the two separated photonbeams cannot be coherent.
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Old Nov 30th 2014, 04:08 AM   #4
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Two beams can't, but you don't have two beams. There will be a huge number of photons being emitted through what is essentially a diffraction grating with the spacing of an atomic separation. What comes out is a very large (compared to the scale of the atom) central "beam." Coherency is a bit more difficult and depends on how the light is generated. Are you asking about a coherent beam? Or a monochromatic beam with no diffraction pattern?

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Old Nov 30th 2014, 11:03 AM   #5
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Yes,I'm asking about a coherent beam.Is this a laser beam?But this is monochromatic.Are there such beams without patterns?
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Old Dec 1st 2014, 05:44 AM   #6
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Going back to the walking people analogy;
"normal" light could be likened to a crowd of people leaving a stadium,
there is a lot of randomness in the individual photon energies, etc...
Coherent laser light would then be like an army marching out of a barracks,
The individual photons are almost identical, and "marching" in phase.

As you indicate, laser light is monochromatic light,
thus a diffaction grating will not produce a spectrum.
If you were to combine the output of several lasers of different colours into a single beam,
then the difracfraction grating would re-separate the different coloured beams.
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Old Dec 2nd 2014, 09:23 AM   #7
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Has a monochromatic beam no diffraction pattern? Why?
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Old Dec 2nd 2014, 10:57 AM   #8
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Sorry I think I confused the issue unnecessarily,
Monochromatic light will produce a diffration pattern.

Different wavelengths (colours) of light will be diffracted by different amounts by the same diffraction grating.
Monochromatic light will therefore actually give a clearer pattern than multi-chromatic white light.

Coherence is not necessary for diffraction.
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