Parametric characterization of the phase at the far field.
By use of the intensity moment formalism, a new tridimensional beam parameter is defined that is rotationally invariant and remains constant under propagation through certain classes of first-order optical systems. The special case of rotationally symmetric beams is considered in some detail. Also, for coherent beams this parameter is shown to be closely connected to the quadratic form of the phase of the directional power spectrum.
Martínez-Herrero
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Mejías
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Martínez
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