Abstract

We have recently reported a simple experimental technique,¹ Z-scan, for determining nonlinear refraction and nonlinear absorption. By using a Gaussian beam in a tight focusing geometry, the transmittance of a nonlinear medium through an aperture in the far field is measured as a function of the sample position with respect to the focal plane. A typical Z-scan transmittance signal has a maximum before focus and a minimum after focus, or vice versa, depending on the sign of the nonlinearity. In this paper, we explore different geometries of the Z-scan experimental arrangement to further enhance the sensitivity of this technique. Adding an imaging lens in the far field and placing the aperture at the imaging plane of the new system enhances the sensitivity of the Z-scan technique threefold. Moreover, the positions of the peak and valley are reversed with respect to the focal plane.

© 1990 Optical Society of America