Coherent Random Lasing in Subwavelength Quasi-2D Perovskites

Quasi-2D lead halide perovskites have garnered increasing interest as lasing gain media. Relatively simple fabrication, high refractive index, and unique quantum well structure encourage their use in traditional cavity lasers and cavity-free systems called random lasers (RLs). Despite tremendous advances reported thus far, coherent random lasing in quasi-2D perovskite subwavelength films has not been reported. Consequently, coherent optical feedback mechanisms in quasi-2D perovskite systems are still unexplored. Here, this work reports the observation of coherent random lasing in subwavelength quasi-2D perovskite films. Statistical analysis of spectral measurements reveals Lévy-like intensity fluctuations, replica symmetry breaking confirms random lasing, and the coherent modes are studied with spectral and spatial correlation techniques. The observed coherent lasing modes are found to be extended states that arise from the random crystal grain structure during fabrication and span the entire pump volume. These modes out-compete diffusive lasing due to their coherence.