Dark-field Z-scan technique with highly nonlinear absorbing materials: Application to porphyrins

Abstract

The newly introduced imaging Dark-field Z-scan (DFZ-scan) technique is applied here to demonstrate its ability to measure the optical third-order nonlinear (NL) index coefficient in the presence of nonlinear absorption (NLA). We present our experimental results for two compounds of Porphyrin molecules, known to have relatively high NLA in the picosecond regime, at 532[Formula: see text]nm, allowing to test both cases of positive and negative nonlinear refraction (NLR). Moreover, we show that, it is possible to increase the sensitivity of the method by introducing a circular aperture in the image plane. Also, limitations are discussed to process optically a pure NL refractive signal, not subject to the influence of the NLA one, at the output of the imaging setup.