At a distance x laterally from the center 192 of the laser, the boundary 186 extends a distance y from reference plane 190 satisfying the equation ##EQU1## where m is an integer, ??o is the wavelength of the lightwaves in a vacuum, and where yo =??/(n2 n1), ?? being the wavelength of the lightwaves in a lens region 180 or 181 of index n2, and n1 being the index of refraction of the first index reg