Nonlinear optical absorption in thin halide perovskite films under femtosecond excitation at wavelengths of 1064 and 532 nm

The nonlinear optical responses of perovskite films CsPbI₂Br, MAPbI₃ + 1% PVC, MA_0.15FA_0.75Cs_0.1PbI_2.85Br_0.15, and MA_0.15FA_0.75Cs_0.1PbI₃, irradiated by femtosecond laser pulses with wavelengths of 1064 and 532 nm, are investigated using z-scan measurements. Nonlinear absorption is found to occur in perovskite films irradiated at a wavelength of 1064 nm; the nonlinear absorption coefficient in thin films (45 – 65 nm) greatly exceeds that in thick ones (120 – 350 nm): 524 – 928 and 38 – 50 cm GW^-1, respectively. It is shown that the nonlinear absorption saturation intensity for perovskite films depends on the pump pulse duration and increases with pulse shortening. It is also established that the nonlinear absorption coefficient of organometallic perovskite films exceeds that of a film of inorganic perovskite CsPbI₂Br. Bleaching of film samples during z-scanning at a wavelength of 532 nm is related to the irreversible photochemical degradation of films exposed to intense light. The kinetics of photochemical bleaching of the films is detected at a wavelength of 532 nm.