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The beam propagates along the Z axis. Its intensity distribution in the plane perpendicular to Z is elliptical and the axis of the ellipse are coinciding with X and Y axis. The beam is shaped by an afocal system made of two lenses. The beam propagation is calculated independantly in each XZ and YZ plane with the parameters which are effective in the considered propagation plane. In the present case, the waists in the XZ and YZ planes of the incident beam are considered to have the same position. The page calculates in each propagation plane the half width and the position of the emerging beam waist as functions of the wavelength, the focal lengths of the two lenses, the M2 factor, the half width and the position of the incident beam waist.