Ultrafast optical response and ablation mechanisms of molybdenum disulfide under intense femtosecond laser irradiation

Numerous valuable studies on electron dynamics have focussed on the extraordinary properties of molybdenum disulfide (MoS₂); however, most of them were confined to the level below the damage threshold. Here the electron dynamics of MoS₂ under intense ultrafast laser irradiation was investigated by experiments and simulations. Two kinds of ablation mechanisms were revealed, which led to two distinct types of electron dynamics and final ablation morphology. At a higher fluence, the emergence of superheated liquid induced a dramatic change in the transient reflectivity and micro-honeycomb structures. At a lower fluence, the material was just removed by sublimation, and the ablation structure was relatively flat. X-ray photoelectron spectroscopic (XPS) measurements demonstrated that thermal decomposition only occurred at the higher fluence. Furthermore, a theoretical model was developed to deeply reveal the ultrafast dynamics of MoS₂ ablation. The simulation results were in good agreement with the temporal and spatial reflectivity distribution obtained from the experiment. The electron and lattice temperature evolution was also obtained to prove the ablation mechanism. Our results revealed ultrafast dynamics of MoS₂ above the damage threshold and are helpful for understanding the interaction mechanism between MoS₂ and intense ultrafast lasers, as well as for MoS₂ processing applications.