A technique for measuring the strength of the Kerr nonlinearity of a material, relying on self-focusing.

The z-scan measurement technique is often used for measuring the strength of the Kerr nonlinearity (i.e., the magnitude of the Nonlinear Index n2) of an optical material. Essentially, a plate of the material under investigation is moved through a focus of a Laser beam, and the Beam Radius (or the on-axis intensity) is measured at some point behind the focus as a function of the position. These quantities are affected by the self-focusing effect, which is strongest when the sample is in the focus.