Method for reducing debris and thermal destruction in femtosecond laser processing by applying transparent coating

A cavity processed by a tightly focused femtosecond laser pulse is surrounded by a ring-shaped protrusion, debris, and small droplets. In order to reduce these undesired damages, we propose processing with a coating of transparent material on a target material. PMMA (poly-methyl methacrylate) with the thickness that its surface is not ablated by a single pulse irradiation reduces dissolution and vaporization caused by the interaction between a high-density hot vapor plume and the target material. Furthermore, the material at the target surface does not escape freely due to the coating layer. As a result, a submicrometer-sized cavity is produced with a reduction of debris and a smaller thermal-destruction area.