Nonlinear Two-Photon Absorption in the Near-Infrared Band for Lead Bromide Perovskite Films Using an F-Scan Nonlinear Spectrometer

An F-scan nonlinear spectrometer is used to measure the two-photon absorption coefficient for CH₃NH₃PbBr₃ perovskite films from 690 to 995 nm. This spectrometer uses an electrically focused tunable lens and a tunable femtosecond-pulse laser (Mai Tai-HP) with a resolution of 5 nm. Two-band models and saturation irradiance corrections are used to fit the experimental data. The nonlinear absorption in this wavelength range is of the order of cm/MW. We found that the best agreement between the experimental data, the reported values in the literature, and the theoretical model is obtained for an extended two-band model with irradiance saturation correction.