Saturation effects in Z-scan measurements

We investigate the behavior of the Z-scan technique in the case where the phase of the electric Geld departs from a Gaussian due to the saturation of the optical nonlinearity. The usual Gaussian decomposition theoretical approach cannot describe experimental results obtained with well-characterized chromium-doped saturable absorbers: ruby and alexandrite. This aim can be accomplished by extending the theory based on the Hankel transformation of the electric field through the inclusion of the phase saturation. As in the case of Kerr media, the nonlinear refractive index can be obtained from the measurement of the transmittance difference between peak and valley.