Pulse duration dependent optical nonlinearities of Bi₂Se₃ thin films

Topological insulators, such as the Bi₂Se₃ material, exhibit significant optical nonlinearities. This work investigates the impact of the pulse duration on the nonlinear optical responses of Bi₂Se₃ layers. Scanning electron microscopy studies have been performed to reveal the crystalline structure of the samples. The nonlinear optical performance has been investigated for a wide range of pulse durations, from 400 fs to 10 ps, using 1030 nm laser excitation. The nonlinear absorption coefficients recorded in this study range from -1.45 x10^-7 m/W to -4.86 x10^-7 m/W. The influence of two different mechanisms on optical nonlinearities was observed and discussed. Identical experimental conditions have been employed throughout the studies allowing a direct comparison of the results.