Z-scan study of nonlinear optical standards and D-A fluorophores considering fifth-order optical nonlinearities

The third- and fifth-order nonlinear optical components are extracted using z-scan under a series of irradiances for some common reference materials rhodamine B(RhB) and carbon disulfide (CS2) as well as D-A fluorophores triphenylamine-phenylaldehyde (TPA-PA) and 2diphenylamine-tetraphenylethylene-phenylaldehyde (2DPA-TPE-PA). By differentiating the third- order optical nonlinearities from high-order ones, the two-photon absorption (2PA) cross sections of RhB, TPA-PA, and 2DPA-TPE-PA estimated from z-scan are almost all consistent with those estimated from two-photon excited fluorescence, whereas the second-order refractive indices of CS2 and TPA-PA in THF solution agree with reported values in publications as well. If the z-scan curve is captured at only a single irradiance, the 2PA cross sections will probably be overestimated. As for the fifth-order optical nonlinearities, the excited-state absorption cross sections of RhB are reduced with an increase in its concentration in methanol solutions. A more comprehensive photophysical picture of the nonlinear absorption and refraction processes within these samples can be drawn from their z-scan results.