Mechanisms of formation of sub- and micrometre-scale holes in thin metal films by single nano- and femtosecond laser pulses

Abstract

Mechanisms of formation of sub- and micrometre-scale holes in thin silver and chromium films of variable thickness by tightly-focused single nanosecond IR laser pulses with fluences in the range of are studied by means of optical and scanning electron microscopy. At the minimal fluences above , the micrometre ( in radius) holes are produced in these films, accompanying the lateral heat conduction in the film during the pump laser pulse, cavitation at the metallic/glass interface and subsequent explosive removal of the molten film. At the fluences of much larger ( in radius) holes are formed in the film as a result of its heating by the erosive surface microplasma through the lateral heat conduction in the film during the plasma lifetime of the order of a few microseconds. Finally, at the maximal fluences (well above ), the sub-millimetre holes were produced in these films by intense shock waves, generated in the erosive microplasmas. The comparative analysis of the formation mechanisms for sub- and micrometre-scale holes in the same thin metal films by the single nano- and femtosecond laser pulses is provided.