Coherence time. For an electromagnetic wave, the coherence time is the time over which a propagating wave (especially a laser or maser beam) may be considered coherent. In other words, it is the time interval within which its phase is, on average, predictable.

Coherence length is the space over which a wave is 'nicely' sinusoidal. In other words, it is the space over which we can predict the phase of a wave of beam (if we are speaking of lasers). Coherence time is related to the classical uncertainty principle and is thus a little more complex.

here is a few information about the channel:

FSO transmitter aperture diameter: 5 cm, FSO receiver aperture diameter: 20 cm, Beam divergence: 2 mrad, Index refraction structure (Cn^2): 5e-015 m^(-2/3), Coherence time: 0.5461333333333334e-006 s

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