FOCAL SHIFT OF FOCUSED FLAT-TOPPED BEAMS

The phenomenon of focal shift is studied for the case of focused coher ent beams showing a flat-topped transverse profile. The model describi ng such beams is that of flattened Gaussian beams, which, due to their peculiar analytical expression, are particularly fit for the study of paraxial propagation of flattened beams. Focal shifts for the fundame ntal Gaussian mode and for the field produced by diffraction of a conv erging spherical wave by a circular aperture are shown to be obtainabl e by this model as particular cases. (C) 1998 Elsevier Science B.V. Al l rights reserved.