Low threshold two-photon-pumped amplified spontaneous emission in thermally nanoimprinted MAPb_0.2Sn_0.8I₃ thin films

Two-photon pumped lasers are pivotal for upconversion devices and nonlinear photonics, yet the realization of stable, high-gain media remains a significant challenge. Here, a thermal nanoimprint strategy to optimize MAPb_0.2Sn_0.8I₃ perovskite films, while achieving simultaneous defect passivation and structural stability, is reported. The resulting films exhibit a two-photon absorption coefficient of 0.098 cm/GW at 1600 nm, enabling low-threshold amplified spontaneous emission of 137.2 μJ/cm² under near-infrared (NIR) excitation at 1600 nm. A high net modal gain of 754 cm^-1 is extracted via variable stripe length measurements. Crucially, suppressed non-radiative recombination leads to markedly improved operational stability beyond 97 minutes. These results demonstrate that thermally nanoimprinted MAPb_0.2Sn_0.8I₃ may work as a promising gain medium for two-photon-pumped upconversion lasers.