Z-scan measurement with a slit instead of a circular aperture is proposed a
nd analyzed for an astigmatic Gaussian beam. This new technique can accurat
ely determine not only the nonlinear refractive index but also the elliptic
ity and positions of x-y foci of the astigmatic beam. (C) 2000 Optical Soci
ety of America [S0740-3224(99)02311-5] OCIS codes: 190.3270, 190.5940, 190.
7110, 120.4570.