Z-scan with arbitrary aperture transmittance: the strongly nonlinear regime

We consider theoretical models of nonlinear optical propagation suitable for describing optical Z-scan measurements within the strongly nonlinear regime. In particular, we demonstrate the equivalence of two alternative descriptions of beam propagation from a thin nonlinear refractor, in which the transmission measurements are modelled using a receiving aperture of arbitrary size. If nonlinear absorption is the dominant process, then we predict that a localized peak within the normalized transmittance will appear at the waist position and should be observable if the nonlinear interaction is sufficiently strong. (C) 1998 Elsevier Science B.V. All rights reserved.