Comprehensive evidence of lasing from a 2D material enabled by a dual-resonance metasurface

Semiconducting transition metal dichalcogenides (TMDs) have gained significant attention as a gain medium for nanolasers, owing to their unique ability to be easily placed and stacked on virtually any substrate. However, the atomically thin nature of the active material in existing TMD nanolasers presents a challenge, as their limited output power makes it difficult to distinguish between true laser operation and other "laser-like" phenomena. Here, we present comprehensive evidence of lasing from a CVD-grown tungsten disulphide (WS$_2$) monolayer. The monolayer is placed on a dual-resonance dielectric metasurface with a rectangular lattice designed to enhance both absorption and emission; resulting in an ultralow threshold operation (threshold <1 W/cm$^2$). We provide a thorough study of the laser performance at room temperature, paying special attention to directionality, output power, and spatial coherence. Notably, our lasers demonstrated a coherence length of over 30 $\mu$m, which is several times greater than what has been reported for 2D material lasers so far. Our realisation of a single-mode laser from a wafer-scale CVD-grown monolayer presents exciting opportunities for integration and the development of novel applications.