Influence of the focal point position of a focusing lens on a character of an ablative plasma expansion

Abstract

This paper is devoted to explanation, why at a fixed spot diameter of the partly defocused laser beam on the target surface the possibility of creating plasma jets depends strongly on the relative position of the focusing lens focal point to the target surface, i.e. whether it is located inside or in front of the target. We demonstrate how the focal point position can influence properties of the expanding plasma plume and, therefore, substantially change conditions for plasma jet forming. The results of this paper have evidently proved that the plasma strongly modifies the initial distribution of the laser intensity. A change of the laser intensity distribution due to plasma interaction involves also changing the plasma properties, e.g. tendency to the plasma jet forming.