Deviation from threshold model in ultrafast laser ablation of graphene at sub-micron scale

We investigate a method to measure ultrafast laser ablation threshold with respect to spot size. We use structured complex beams to generate a pattern of craters in CVD graphene with a single laser pulse. A direct comparison between beam profile and SEM characterization allows us to determine the dependence of ablation probability on spot-size, for crater diameters ranging between 700 nm and 2.5 mu m. We report a drastic decrease of ablation probability when the crater diameter is below 1 mu m which we interpret in terms of free-carrier diffusion. (C) 2015 AIP Publishing LLC.