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Also, what happens if you shine a regular consumer laser in space? Would it travel years without dissipating?

Thanks

- Thread starter d3aj1986
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Also, what happens if you shine a regular consumer laser in space? Would it travel years without dissipating?

Thanks

- #2

russ_watters

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Lasers are not faster than the speed of light - they **are** light. You misread whatever link you found.

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- #4

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Yes, the group velocity can formally exceed c_0, and there are also experiments showing that, for example, the leading edge of a pulse can be detected before the pulse was emitted. This is not a conflict with special relativity, because the group and phase velocities are different, and near an absorption line become *very* different.

As for the diffraction of a laser beam, if it is a "normal" (Gaussian) beam, the product w*θ is constant, where w is the beam waist and θ the divergence angle: in order for a Gaussian beam to be collimated, it must be expanded to a large diameter. Non-Gaussian beams (Bessel beams, optical vortices, etc) do not diffract this way and approach a limit of zero diffraction:

http://en.wikipedia.org/wiki/Bessel_beam

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