Micro torch assisted nanostructures' formation of nickel during femtosecond laser surface interactions.

In this letter, we perform a comprehensive study of micro torch effect on the formation of femtosecond laser-induced nanostructures on nickel. Under identical experimental conditions, laser induced nanostructures and periodic surface patterns exhibit distinctly different level of morphology with and without the micro torch. In addition, assisted by the micro torch, the ablation threshold is considerably reduced and the content of oxygen in the textured nanostructures keeps a stable low level. It is suggested that the change on the surface directly relates to the status of plasma plume and substrate heating. With the assistance of the micro torch, laser induced plasma plume is confined and its density at center region is raised, which results in the increase of the central plasma's temperature, more energy deposited on the nickel surface, and ultimately leading to the changes in the nanostructures' morphology and ablation threshold. [ABSTRACT FROM AUTHOR]