Ultrafast Multi-Shot Ablation and Defect Generation in Monolayer Transition Metal Dichalcogenides

Abstract: Transition metal dichalcogenides are known to possess large optical nonlinearities and driving these materials at high intensities is desirable for many applications. Understanding their optical responses under repetitive intense excitation is essential to improve the performance limit of these strong-field devices and to achieve efficient laser patterning. Here, we report the incubation study of monolayer MoS${}{2}$ and WS${}{2}$ induced by 160 fs, 800 nm pulses in air to examine how their ablation threshold scales with the number of admitted laser pulses. Both materials were shown to outperform graphene and most bulk materials; specifically, MoS${}{2}$ is as resistant to radiation degradation as the best of the bulk thin films with a record fast saturation. Our modeling provides convincing evidence that the small reduction in threshold and fast saturation of MoS${}{2}$ originates in its excellent bonding integrity against radiation-induced softening. Sub-ablation damages, in the forms of vacancies, lattice disorder, and nano-voids, were revealed by transmission electron microscopy, photoluminescence, Raman, and second harmonic generation studies, which were attributed to the observed incubation. For the first time, a sub-ablation damage threshold is identified for monolayer MoS${}{2}$ to be 78% of single-shot ablation threshold, below which MoS${}{2}$ remains intact for many laser pulses. Our results firmly establish MoS${}_{2}$ as a robust material for strong-field devices and for high-throughput laser patterning.