Single-shot ablation of amorphous silicon films of 50-, 100- and 150-nm thickness by laser pulses of variable (0.2-6 ps) widths demonstrates non-monotonous variation of ablation thresholds and characteristic ablation 1/e-radii with their minima at the 0.6-ps pulse-width and the following increase. For the shorter laser pulses the increased thresholds and enhanced transport can be related to fast ambipolar electron-hole plasma diffusion and other electronic energy losses in dense transient plasma prior its energy transfer to the ionic subsystem (electron-ion thermalization) at 0.6 ps, while for the longer laser pulses slower ambipolar diffusion in moderate-density electron-hole plasma, ionic heat conduction and other thermal losses may predominate. (C) 2017 Elsevier B.V. All rights reserved.