Аннотация:Appreciable enhance of hard x-ray yield from plasma, created onto the surface of melted metal target by sub-relativistic femtosecond laser pulse with a small prepulse, leading the main pulse over few nanoseconds, was observed. Optical shadowgraphy revealed the formation of dense microjets by the action of prepulse, emitted from the surface. Experimental results are discussed using 3D PIC and 1D hydrodynamic widerange EOS simulations.