The focusing of Gaussian beams by a spherically aberrated bifocal lens and
related focal shift are studied. It is shown that the axial irradiance dist
ribution, maximum irradiance along the axis and its position of focused Gau
ssian beams depend upon the Fresnel number, spherical aberration and Focal
length of the bifocal lens in general. A detailed analysis of the effect of
spherical aberration and bifocal length on focal shift is made. (C) 2001 P
ublished by Elsevier Science B.V.