Microdroplet deposition by laser-induced forward transfer

Abstract

Laser-induced forward transfer was used to deposit aluminum and nickel microdroplets onto a substrate using a Q-switched neodymium:Yttrium-aluminum-garnet laser. The droplets have diameters of a few microns, much smaller than the laser spot diameter, and are transferred at fluences slightly above the melting threshold. Scanning electron microscopy shows that the original donor film is deformed after laser irradiation, such that the film protrudes outward from the center of the laser spot. The film expands during laser heating, but is constrained until the melt interface reaches the free surface. When this occurs, the film is no longer constrained, allowing the melt to rapidly expand, forming the protrusions from which droplets are ejected.