Hot-carrier tunable abnormal nonlinear absorption conversion in quasi-2D perovskite

Controlling the high-power laser transmittance is built on the diverse manipulation of multiple nonlinear absorption processes in the nonlinear optical materials. Here, the authors demonstrate the crucial role of hot-carrier effect to tune the nonlinear absorption response in quasi-2D perovskite films. Controlling the high-power laser transmittance is built on the diverse manipulation of multiple nonlinear absorption (NLA) processes in the nonlinear optical (NLO) materials. According to standard saturable absorption (SA) and reverse saturable absorption (RSA) model adapted for traditional semiconductor materials, the coexistence of SA and RSA will result in SA induced transparency at low laser intensity, yet switch to RSA with pump fluence increasing. Here, we observed, in contrast, an unusual RSA to SA conversion in quasi-two-dimensional (2D) perovskite film with a low threshold around 2.6 GW cm(-2). With ultrafast transient absorption (TA) spectra measurement, such abnormal NLA is attributed to the competition between excitonic absorption enhancement and non-thermalized carrier induced bleaching. TA singularity from non-thermalized Fermi Sea is observed in quasi-2D perovskite film, indicating an ultrafast carrier thermalization within 100 fs. Moreover, the comparative study between the 2D and 3D perovskites uncovers the crucial role of hot-carrier effect to tune the NLA response. The ultrafast carrier cooling of quasi-2D perovskite is pointed out as an important factor to realize such abnormal NLA conversion process. These results provide fresh insights into the NLA mechanisms in low-dimensional perovskites, which may pave a promising way to diversify the NLO material applications.

Automated summary

This study investigates the role of hot-carrier effect in tuning the nonlinear absorption response in quasi-2D perovskite films. By observing the unusual conversion from reverse saturable absorption to saturable absorption, the authors reveal the important role of ultrafast carrier cooling in enabling this abnormal nonlinear absorption conversion process.