Z-scan measurement of nonlinear optical properties of BiOCl nanosheets

Bismuth oxyhalides, such as bismuth oxychlorides (BiOCl), are layered materials with [Bi₂O₂]²⁺ layers sandwiched between two sheets of Cl ions. Much work has focused on the potential for bismuth oxyhalides to be a photocatalyst, but their nonlinear optical properties are rarely studied. In this work, the nonlinear refractive index of BiOCl nanosheets has been characterized with Z-scan measurement under 800 nm femtosecond pulsed laser excitation. A shift from saturable absorption to reverse saturable absorption was observed at higher input pump intensities in the experiments. The transition process was analyzed using a phenomenological model based on saturable absorption and two-photon absorption.