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The waist radius and the divergence of a gaussian beam (or embedded gaussian beam) at a given wavelength are calculated from the angle with the propagation axis corresponding to a given normalized intensity in the far field. Note that, the divergence defines directions with the propagation axis for which the normalized intensity is 1/e² in the far field.

Note that the energy/power contained in the cone defined by the angle to the axis tetaN is "1 - I".