Phase-locked random lasing in patterned microstripes of MAPbBr3 porously structured by nanoholes

Abstract

Mode locking is rarely observed in random lasing devices, which is based on the strong optical scattering by random nanostructures and the requirement on the strong nonlinear interactions by conventional mode-locking mechanisms. Our discovery of the cascaded absorption and stimulated emission (CASE) effect solved this challenge, where strong overlap between the absorption and emission spectra in hybrid organic-inorganic perovskites is the responsible physics. Previously, phase-locked random lasing was observed in randomly distributed crystalline nanoparticles, which supply strong optical scattering and facilitate gain mechanisms for random lasing. In this work, we demonstrate phase-locked random lasing in the continuous crystalline microstripes embedded with nanoholes. These nanoholes enable formation of porously structured stripes of the active material, implying a different mechanism for random lasing. Microchannels with different widths were produced by photolithography using mask gratings with different periods and a same duty cycle of 50%. Microstripes were then created by spin-coating the green-emitting MAPbBr3 precursor solution onto the mask gratings. Thus, nanohole-structured MAPbBr3 microstripes formed in the grating grooves. Using femtosecond transient absorption spectroscopy, we were able to resolve the CASE features by the oscillation in the TA dynamics, which has a period less than 400 fs. Phase-locked random lasing modes were identified by the equally distributed spectral lines with a mode separation of 1.26~1.58 nm. Thus, phase-locking mechanisms for random lasers were verified in a nanoporous scheme.