Laser-beam—material coupling and its influence on the laser-induced formation of crystalline α-Al 2O 3 on an amorphous Al 2O 3 substrate

Abstract

The formation of a plasma during the laser melting of amorphous Al 2O 3 creates a relatively thick crystalline layer. Initially the plasma manifests itself through variations in the thickness of the crystalline layer and in the fineness of its structure. Plasma does not form under protective gas flow at high pressures, and the thickness of the crystalline layer is small. With helium as the protective gas, the vapours arising from the substrate are not completely removed, leading to screening and in consequence to a thinner crystalline layer.