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

Area of Science:

• Nonlinear Optics
• Materials Science
• Condensed Matter Physics

Background:

• Controlling high-power laser transmittance relies on nonlinear absorption processes in NLO materials.
• Traditional models predict SA at low intensity and RSA at high intensity.

Purpose of the Study:

• Investigate the nonlinear absorption mechanisms in quasi-2D perovskite films.
• Understand the unusual nonlinear absorption conversion observed in these materials.

Main Methods:

• Ultrafast transient absorption (TA) spectroscopy.
• Comparative study of 2D and 3D perovskite films.
• Analysis of nonlinear absorption (NLA) processes.

Main Results:

• Observed an unprecedented reverse saturable absorption (RSA) to saturable absorption (SA) conversion in quasi-2D perovskite films at a low threshold (2.6 GW cm⁻²).
• Attributed this abnormal NLA to the interplay between excitonic absorption enhancement and non-thermalized carrier bleaching.
• Detected ultrafast carrier thermalization (<100 fs) and the significant role of the hot-carrier effect.

Conclusions:

• The ultrafast carrier cooling in quasi-2D perovskites is key to the observed abnormal NLA conversion.
• These findings offer new insights into NLA mechanisms in low-dimensional perovskites.
• Potential for novel applications in nonlinear optical materials.