On the fourth-order spatial characterization of laser beams: New invariant parameter through ABCD systems

On the basis of the intensity-moment formalism, commonly used to characterize the spatial profile of laser beams, a new fourth-order parameter is presented that remains invariant after propagation through ABCD optical systems. This parameter is shown to be closely connected with the kurtosis of the beam, providing information about the beam shape (overall flatness) at both the waist plane and the far-field. The lowest limit of this parameter is also determined. (C) 1997 Elsevier Science B.V.