Time-resolved study of back side ablated molybdenum thin films by ultrashort laser pulses

Ultrashort laser pulses are used to ablate a thin molybdenum layer from glass by irradiating the metal film through the transparent substrate. The trajectories of ablated molybdenum fragments are recorded using a shadowgraphic setup with a time resolution in the nanosecond range. In addition, the shape of collected molybdenum fragments is examined as a function of applied fluence. It is confirmed that in a fluence regime close to the ablation threshold one single disc is ablated as a whole and its velocity is determined in the order of 50 ms-minus1. In a second fluence regime, partial melting at the center of the disc is found and small melt droplets are recorded on their flight. Mo fragments ablated in this regime feature a ring-like structure with a brittle fracture at the outer and a molten appearance at the inner edge.